Electronics safety pages

    Materials used in electronics

    The materials used in electronics were selected for specific characteristics such as high dielectric strength, good electrical conductivity, poor electrical conductivity, good thermal conductivity, low melting point, etc. Since most electronics manufacturing is performed in industrial environments, it is assumed that dangerous substances will be treated appropriately.An awareness of materials hazards is therefore important to the individual experimenter and people responsible for electronics laboratorios and/or factory safety.Here are some dangrous substanced you might encounter in electronics work:

    • Solders: Solders include nowadays signifcant amount of lead (40-60%, is going to dissapear on some coming years). Lead causes significant health problems, including loss of mental functions. Don't stick the solder in your mouth!
    • Ceramics can be dangerous: One of the favorite ceramics used in electronics is Beryllium Oxide. This substance is a good electrical insulator and a good thermal conductor. It is also one of the most poisonous compounds you will ever encounter!
    • Soldering fume: Fumes from solvents are generally bad for you. The smoke from soldering (vaporized flux) is unpleasant and caustic.
    • Circuit board materials: Dust from filing plastic or glass-epoxy circuit boards is bad for your lungs.
    • Solvents: Most solvents are easily absorbed through the skin, into the blood stream, and on to the liver and/or kidneys. Most of the solvents are poisons.
    • PCB: PCBs were used as dielectric filler liquids in some older types of electrical equipment such as transformers, switchgear, capacitors and motors. You should assume that any capacitor or oil filled transformer manufactured before 1976 may contains PCBs unless you have information to the contrary.
    Be very cautious when you have risk to get into contact with the material listed above. Use necessary safety measures to avoid the dangers.

    Safety information

      Electrical safety

      Different currents and voltage have different effect to human being. Generally the current is what determines the danger to human. The used voltage with some other things (for example skin resistance) generally determines what is dangerous and what not. Generally the AC voltage in 40..50 Hz is very dangerous to human. A current that is less that 10 mA is not dangerous to most people. Alternating current (AC) in range of 70..110 mA and direct current (DC) in the range of 200..250 mA is considered to be very dangerous and lethal if it goes through the chest (where the heart is). The impedance of muman from one hand to hand is generally in the rnage of 600..6000 ohms depending on the skin moisture level and the amount of current flowing. Voltages below 20V can be considered safe to touch (the current does not exceed 10 mA in normal conditions). If the skin is dry, voltages up to aroun 80V do not cause over 30 mA current. There is a popular misconception that steady DC is worst due to its supposed ability to cause muscles to stay contracted. This is largely untrue, and AC actually sometimes causes this. AC of power line frequencies is also more capable of disturbing your heart rhythms than steady DC or AC of higher frequencies.

      Electrical power distribution system design is a compromise between safety and cost. Much of the world considers 220 V (220-240V) to be safe enough for standard residential outlets and lighting.Within the European Community the mains voltage is currently 230V +10/-6% (50Hz) between the LIVE and the NEUTRAL terminals, together with a separate protective EARTH terminal. When this high voltage is developed across the human body it could gives rise to a fatal electric shock. Therefore you MUST NOT under any circumstances simultaneously touch both the LIVE and the NEUTRAL terminals or you are very likely to die. Those countries which use 120V considered that 220V to be to dangerous for most residental uses. For example USA, Canada and many other countris have selected 120V AC. This 120V AC voltage is still high enough to be able to cause fatal electric shock if you touch both live and neutral wires at the same time.

      Remember that electric shocks can be fatal, even for voltages of 50 V, and that most of the resistance of the body is in the skin, so do not handle electrical apparatus with wet or even damp hands. Electricity kills a great many people worldwide every year. A current of 50mA (barely enough to make a low wattage lamp even glow) is sufficient to send your heart into a state called "ventricular fibrillation", where the heart muscles are all working out of synchronisation with each other. Little or no blood is pumped, and you will die within about 3 minutes unless help is immediately at hand. To avoid this kind of things to happen, the electrical installations and devices should be built in such way that people don't come in touch with the dangerous voltages. Different safety measures and standard exist for this. Insulation and grounding are two recognized means of preventing injury during electrical equipment operation. Conductor insulation may be provided by placing nonconductive material such as plastic around the conductor. Grounding may be achieved through the use of a direct connection to a known ground such as a metal cold water pipe.

      The sole purpose of a safety ground in electrical wiring is to protect against hazardous fault currents - if there can be no fault than a ground is never needed. In theory the safest electrical supply is one that is totally isolated fromits environment. In such a case you can safely connect yourself to anypart of the live circuit since there is no return path to carry a currentthrough your body. When you touch that isolated circuit, it is no longer isolated but is tied to ground at the point of contact, with yourbody as the potential fault current path. If a fault has previouslyoccured that caused another part of the circuit to be shorted to groundthen a return path will already exist, you will complete the circuit and acurrent will pass through your body. Whether the effect will be negligible, painful or fatal will depend only upon the fault impedences,potential difference and the current capacity of the supply.

      Floating supplies are permissible in certain circumstances. For example in some places bathroom shaver sockets are isolatedor even use this system - but the supply is provided by a current limiting isolation transformer. Floating supply is also recommended for medical life-support equipment where risks to human life due to an interruption ofthe supply are dominant. Floating supply in form of safety isolation transformer is also used in electronics laboratories to isolate the electronics equipment being tested or repaired from the mains supply. There are totally floating safety isolating transformers that supply 120/230 volts floating with respect to ground. These are intended for use by test/service engineers working on live mains-supplied equipment. The term 'safety' is relative of course - whilst it is perfectly safe to connect yourself to any single point of such a floating circuit it won't give an iota of protection if you were to touch both live and neutral atthe same time! In other words they only give protection against injury to people who know what they are doing - two strikes and you're out! However an isolating transformer should only be used for a single piece of kit. The safety relies on the integrity of the isolation of the entire supply on the secondary side of the transformer. Hence you should always keep power leads as short as possible. Floating the supply doesn't automatically make it safe - it just increases the number of faults necessary to cause anaccident and the greater the size and complexity of the installation the greater the chance of isolation failure. There is one wiring methid that uses ungrounded power supply, it is called TT wiring. In TT wirign system you have to fit analarm that detects the first fault to earth & an RCD system to copewith any further faults to earth. You normally only bother with this system in very special situations.

      Leakage to 'ground' is a very common occurrence and can arise due to insulation failure, cable damage, water ingress, breakdown of capacitorsetc etc, all of which are particularly likely in a mobile, temporary installation with a large amount of equipment and huge quantities of cabling running over metal edges on a truck. It can also occurcapacitively - insulation acts as a dielectric and capacitance increases with area and so may become significant with large cable runs. Because of those risks, the normal electrical distribution safety is generally based on grounding. Most of the time, earthing everything in sight will work. Very occasionally, it doesn't. It depends on the detailed design of the earthing system.

      Sometimes the safety level is expanded with other safety devices. RCDs detect an imbalance in the live and neutral currents. 30mA is usual, asnot being life threatening. This is always indicative of a fault situation, butthe current may be going anywhere. In most cases you puff and bluster to your hearts content about the theoreticalsafety of a totally isolated power installation but the fact remains thatinsulation faults can and do occur and if, as a result, someone were to beinjured or electrocuted then you as the specifier, installer or user wouldbe morally, legally and financially liable.

      Operator Exposure safety details. Operators shall not be exposed to:

      • Energy levels of 240 VA or more.
      • Stored energy levels of 20 J or more.
      • Potentials in excess of 42.4 V peak (30 VRMS) or 60 VDC in dry areas.
      • Potentials in excess of 10 VAC or DC in wet areas.
      The operator(s) shall be protected from electrical and mechanical hazards by one or more of the following:
      • Enclosures, shields, and covers that require a tool to open.
      • Interlock switches on doors, shields, and ovens.
      • Grounded or insulated handles, levers, knobs, shields and covers that are touched held or actuated in normal use.
      Service personnel shall not be exposed to inadvertent contact with hazardous potentials or energy levels. All areas not defined as operator access areas that skilled service personnel must gain access to service or maintain the equipment. Here are some tips for good electrical safety:
      • All systems shall be installed as intended by manufacturer or compentent electrical contractor that knows the device to be installed, and always according local electrical codes.
      • Any electrical installation, materials, equipment or apparatus within a workplace must be so designed, constructed, installed, protected, maintained and tested as to minimise the risk of electrical shock or fire.
      • Electrical wall outlets should be free of cracks, breaks, or other obvious damage. Damaged outlets should be immediatly repaired.
      • Personnel should conduct periodic inspections of all equipment to ensure that all cords are free of wear and splices, and that the casing or insulating covering is free of cracks, holes, or other damage.
      • Any electrical equipment that is damaged, malfunctioning or shows signs of unusual, excessive heating or producing "burning" odors, should be pulled from service and submitted for repair by qualified personnel.
      • If equipment produces shock, no matter how small, it should be removed from service and immediately repaired by a qualified electrician before returning to service.
      • Avoid excess bending, stretching and kinking of electrical supply cords.
      • Overloading electrical circuits is extremely dangerous and should not be permitted at any time. Significant amounts of heat can be generated by electrical leads which may lead to fires; especially if the current rating for the lead is exceeded.
      • Ensure that the wire sizes of extension cords are capable of handling the load without heating. When using extension leads ensure that they are fully extended, not covered by mats, and not placed where they could be a tripping hazard. If extension cord is coiled or covered with mat, it's safe current carrying capacity can be seriously reduced.
      • All electrically operated appliances that are designed to be grounded shall be effectively grounded. Tools or appliances protected by an approved system of double insulation, or its equivalent, need not be grounded
      • All electrical equipment should bear the label of a nationally recognized testing laboratory to guarantee that they are constructed safely.
      • If the competent person decides the equipment is not safe to use, they must attach a durable tag warning not to use the equipment; the equipment must also be immediately withdrawn from use.
      • Properly installed residual current device / earth leakage protection increases safety in dangerous locations. Residual current device should be periodically tested. Correct selection of the type of earth leakage protection is also important to avoid an unacceptable level of circuit tripping by the devices.
      • It is important to ensure that all electrical extension leads are in good condition before they are used.
      • The risk associated with electrical installations in hazardous atmospheres created by flammable gases, vapours from flammable liquids or combustible dusts should be carefully considered. Electrical appliances should either be specially designed equipment or be excluded from hazardous locations.
      • Special circuit protection such as residual current devices (RCDs) or isolation transformers are required for specified electrical equipment in workshops, laboratories, construction sites and other outdoor areas.
      • Patient treatment areas such as medical and dental surgeries have particular requirements on electrical safety.
      • Electrical heating appliances are a common cause of fires. Where possible appliances should have thermostat control and thermal overload protection.
      • Where electrical installations, equipment or extension leads are liable to damage from vehicles, other machinery or heavy people traffic, they should be protected from physical damage by appropriate covers or barriers.
      • The use of multi-outlet power boards or cords can be potentially unsafe because of the potential for overloading, and inadequate protection of circuits. In hazardous or wet areas multi-outlet power boards should be secured in a safe position.
      • All flexible cords will have two layers of insulation throughout their length, and will show no signs of excessive ware or physical damage.
      • Cord sets intended to be permanently attached to an item of equipment will be securely clamped to that equipment (internally or externally).
      European standards are different from US standards because they are intended for use in different overall regimes. Often the concepts forsafety in US standards and European standards are simply different, andrely on differences in the surrounding environments for even similar products. Wiring, earthing, field terminations, power distribution schemes etc. are simply different, and are not under the control of one single organization who writes standards (there are many regional standards organizations, they more or less follow international IEE standards and create their own).

      When working with electronic devices (repairing etc.) switch then off and disconnect from the mains. When you need to test live circuits, use properly sheathed probes and power the device through protection device such as isolation transformer. When working with mains voltage or higher voltage, make sure that there is someone else in the room and that he or she knows what you are doing.

      In normal operation electronics devices are designed such that they are safe to use. The insulation inside electronics devices must be good enough to withstand the mains voltage and overvoltage links. Even though there is insulation, there is always some leakages and potential for failures. There are are different equipment classifications based on their construction:

      • Class I devices are designed to have grounded metal case, which keep the leakage out of reach and burns mains fuse if there is short circuit to case.
      • Class II equipment are designed to work without grounding. They have thicker insulation in wires and components connected to mains. Leakage current from Class II equipment is limited low so that it is safe to touch, and I think we don't have to care of electric shock too much when using correctly designed Class II equipment alone.
      When questioning safety from electrocution the current draw of device in question is typically not an issue. The amount of current through your body depends on Ohm's law.That is, the current in any path is the voltage divided by theresistance of your body along that path. So voltage is the thing here. Any 120 volt appliance can be lethal, regardless of its current draw, sinceyou can possibly be exposed to 120 volts. This applies to 230V equipment also, here the voltage is only higher. Of course, you are exposed tothat current if you stick your finger in an outlet, without any appliance. So the question is, how well is the equipment/installation made to avoid any fault that exposes you to the 120 or 230 volts.

      The severity of an electrical shock depends on both the electrical voltage and current you are subjected to. The probability of getting killed by an electric shock is determined by the current through your body. The level which isconsidered lethal is in the range of about 100 mA to several hundred mA fornormal healthy people with surface skin exposure. The worst range is generally considered to be 100 mA to 1 amp. This is based on guestimates for healthy relatively fit people. Young children, older people or those who are sick can be more susceptible. This is just the worst range, with currents even well outside this range in either direction having a significant chance of causing lethal ventricular fibrillation. The effect of electricity also depends on what route the electricity takes in your body. If it was across the chest or more pointedly, across theheart, then it has a high possibility to cause the heart to go into cardiac arrest. The current through the person is determined by the voltage across the body and the resistance due to body tissue, whether the contact area is wet orsweaty etc. For most people, most of the time simply touching 120 V for a short time is not lethal. So the mains voltage of 120 V in the US is certainly not lethal in most situations. It is possible to be electrocuted by 120v mains, that's for sure. It is possible to be injured severely by mains voltage, but usually 120V mains does not cause severe damages. But for safety reasons it is a very good idea to avoid touching the mains electricity, because there is always the possibity to get killed or get injures. It is better to be safe than "try your luck" of surviving the electrical shock. If one were really afraid of electrocution from any appliance in any setting, then a GFCI device on the circuit containingthe appliance wouldn't be a bad idea. The GFCI would detect a malfunction and shut down the circuit before the person using the appliance got zapped.

      This same safety basics apply to 230V AC also. This higher voltage is even more dangerous than 120V AC because of higher currents involved if you touch the wire. Touching an exposed 230V AC wire here is much more dangerous than touching 120V AC wire.

      Generally the leakage current below 0.5 mA is not considered dangerous. And the isolation from the mains wiring to equipment case should be at least few kilovolts. Here are some general values for maximum allowed leakage current and insulation specifications of some power supply types / devices:

      • Office devices (EN60950): Maximum leakage 250 microamperes, 3000V insulation rating on test (60 seconds)
      • Medical types B and BF (EN60601): Maximum leakage 100 microamperes, 4000V voltage rating with 60 second test
      • Medical type CF (EN60601): Maximum leakage 10 microamperes, 4000V voltage rating with 60 second test
      Here are some general definitions considering electrical safety (from IEC 60950 / EN 60950 glossary):
      • Basic Insulation: Insulation to provide basic protection against electric shock. The standard defines levels of insulation required in terms of constructional requirements (creepage and clearance distances) and electrical requirements (compliance with electric strength tests) . Basic insulation is considered to be shorted under single fault conditions. The actual values required depend on the working voltage to which the insulation is subjected, as well as other factors.
      • Bounding Surface: The outer surface of the electrical enclosure, considered as though metal foil were pressed into contact with accessible surfaces of insulating equipment.
      • Class I: Equipment where protection against electric shock is achieved by using basic insulation, and also providing a means of connecting to the protective earthing conductor in the building wiring those conductive parts that are otherwise capable of assuming hazardous voltages if the Basic Insulation fails.
      • Class II: Equipment in which protection against electric shock does not rely on basic insulation only, but in which additional safety precautions, such as double insulation or reinforced insulation, are provided, there being no reliance on either protective earthing or installation conditions.
      • Clearance: The shortest distance between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured through air.
      • Creepage Distance: The shortest path between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured along the surface of the insulation.
      • Double Insulation: Insulation comprising both basic insulation and supplementary insulation.
      • Functional Insulation: Insulation needed for the correct operation of the equipment.
      • Hazardous Energy Level: A stored energy level of 20J or more, or an available continuous power level of 240 VA or more, at a potential of 2V or more.
      • Hazardous Voltage: A voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.
      • Limited Current Circuit: A circuit which is so designed and protected that , under both normal conditions and a likely fault condition, the current which can be drawn is not hazardous.
      • Primary Circuit: An internal circuit which is directly connected to the external supply mains or other equivalent source (such as motor-generator set) which supplies electric power.
      • Reinforced Insulation: A single insulation system which provides a degree of protection against electric shock equivalent to double insulation under the conditions specified in this standard.
      • Safety Critical: A component which affects the safety of the equipment. All components in primary circuitry are safety critical. Other components which protect the equipment under normal and fault conditions, such as thermal switches, optocouplers, etc. are also safety critical.
      • Secondary Circuit: A circuit which has no direct connection to primary power and derives its power from a transformer, converter or equivalent isolation device, or from a battery.
      • SELV Circuit (Safety Extra Low Voltage): A secondary circuit which is so designed and protected that, under normal and single fault conditions, its voltages do not exceed a safe value (definatley lower than 42.4V peak or 60V d.c).
      • Supplementary Insulation: Independent insulation applied in addition to basic insulation in order to ensure protection against electric shock in the event of failure of the basic insulation.
      • Telecommunication Network: A metallically terminated transmission medium intended for communication between equipments that may be located in separate buildings, excluding mains electrical network, TV distribution systems using cable and SELV circuits connecting units of data processing equipment.
      • TNV Circuit: A circuit in the equipment to which the accessible area of contact is limited and that is so designed and protected that, under normal operating and single fault conditions, the voltages do not exceed specifying limiting values.
      • TNV-1 Circuit: A TNV circuit whose normal operating voltages do not exceed the limits for a SELV circuit under normal operating conditions and on which overvoltages from telecommunication networks are possible.
      • TNV-2 Circuit: This is a TNV circuit whose normal operating voltages exceed the limits for a SELV circuit under normal operating conditions. These circuits are not subject to overvoltages from telecommunication networks.
      • TNV-3 Circuit: This is a TNV circuit whose normal operating voltages exceed the limits for a SELV circuit under normal operating conditions. Overvoltages from telecommunication networks are possible for TNV-3 circuits.
      • Touch Current: Electric current through a human body when it touches one or more accessible parts. (Touch current was previously included in the term 'leakage current')
      Some other related terms from other standards:
      • Insulation resistance: Electrical resistance measured by applying a DC voltage of 500 V between two elements of a relay that are insulated from one another.
      • Creepage distance: Shortest distance on the surface of an insulating material between two conductive elements. [Source: IEC 664-1]
      • Tracking resistance Evaluation of insulating materials by determinating their creepage distance formation (by dripping a watery solution onto a horizontal surface so that it leads to electrolytic conducting), specified by the so-called "comparative number of creepage formation" (CTI) according to IEC 112. [Source: IEC 664-1, mod.]
      • Clearance distance: Shortest distance in air between two conductive elements. [Source: IEC 664-1]
      • Impulse form: The impulse form is characterized by the following values: voltage amplitude (e.g. 1.5 kV), rise time T1 (e.g. 1.2 ?s) and fall time T2 (e.g. 50 ?s
      • Insulation according to IEC 664 / VDE 0110 (1/89): Data for insulation coordination requires values for rated voltage, pollution degree and overvoltage category.
      • Insulation distance: The distance that needs to be insulated between two conductors.
      • Insulation group: Insulation group is the classification of equipment according to environmental and operating conditions and takes into account the reduction of insulation of equipment due to environmental effects at the site, increases in voltage that result from activities in the plant or in the atmosphere and direct results of insulation malfunction depending on short-circuit power.
      • Insulation distance: The distance that needs to be insulated between two conductors.
      • Overvoltage category: Classification of electrical equipment to the overvoltage to be expected.
      • Pollution degree: Classification of the pollution from external materials that affect the insulation.
      • Rated voltage: The voltage value above which the creepage distance is measured.
      • Surge voltage: Amplitude of a voltage impulse of short duration with a specified impulse form and polarity that is applied to test insulation paths in device/component. This proves that the device/component (for example relay) will withstand very high overvoltages for very short periods.
      • Test voltage (Dielectric test voltage AC): Voltage (effective value in AC voltage) that is applied between elements that are insulated from one another in the voltage test.
      • Voltage withstand test: A short-circuit fault in a circuit breaker creates an electrical arc in the device and subsequently results in high temperature and pressure. This test measures the insulating capability of a circuit breaker's components when twice the rated voltage plus 1,000 V is applied.
      Internaltiona Electrotechnical Commission (IEC) specified overvoltage categories:
      • Cat I: Electric devices (electric equipment, low energy equipment with transient limiting protection) (test for 600V working voltage: 2500V peak impulse, 30 ohms source, 20 repetitions)
      • Cat II: Appliances, PCs, TVs (outlets and long branch circuits, all outlets more than 10 meters from Category III source, all outlets at more than 20 meters from category IV source) (test for 600V working voltage: 4000V peak impulse, 12 ohms source, 20 repetitions)
      • Cat III: MC panels etc. (feeders and short branch circuits, distribution panel devices, heavy appliance outlets with "short" connection to service entrance) (test for 600V working voltage: 6000V peak impulse, 2 ohms source, 20 repetitions)
      • Cat IV: (outside and service entrance, service drop from pole to building, run between meter and panel, overhead line to detached building, underground line to well pump) (test for 600V working voltage: 8000V peak impulse, 2 ohms source, 20 repetitions)
      In those overvoltage categories the idea is the following: As you move close to the power source (higher category number), a higher level of protection is required. Demarcation between Installation Categories III and IV is arbitarily taken to be at the meter or at the mains disconnect (according ANSI/NNPA 10-1990, article 230-70) for low voltage service. If service is provided to user at high voltage, the demarcation between Installation Categories III and IV is at the secondary of the service transformer. Within each category you will also find a voltage rating. The higher the voltage rating, the higher the transient withstand rating. However, it is wrong to use voltage rating as the only criterion, and assume that a CAT II-1000V rated meter is superior to a CAT III-600V meter.

      Electrical safety cannot be over emphasised. When working with electricity, make sure that you find out the legal requirements in your country, and don't do anything that places you at risk - either from electrocution or legal liability. Neither is likely to be a pleasant experience. When working with eldctrical wiring or electronics circuits with dangerous voltages in them, working with them sould be done with them when the power on those devices is disconnected (exception to this are some special operations tha can only be done when those are powered up, and a special precautions and care shpuld be taken when performing those).

      When working with electrical wiring, the power should be cut out by removing a fuse and/or turning of electrical palel main switch off. When you turn th epower of for someone to work with electrical wiring, the switches/breakers should be locked out and marked that there is work in progress. Lock out devices are made for pretty much every breaker made to physically lock it out. In addition to this in some application the wires that needs to be worked with are grounded (especially in application where high voltages are present). There is no guessing when it comes to your life or others that may come in contact. If you are working on the wiring of a circuit (not just connecting alantern or adjusting one), in repairing it, you should use a lock-out/tag-out system. Turn off the breaker(s) that affect the circuit and using aproper lock device with a key that only you have, lock it and tag it withyour name, date and reason why it is locked out. This guarantees that ne can randomly turn it back on without your knowledge since they would have to get the keyfrom you. I which case, YOU are the only one that should be the one to re-energize that circuit. You are then the one responsible for whether or not the circuit is safe to reenergize.

      When working with electrical system you should consider doing risk assessment (in many countries there are legal requirements for this to guarantee workplace safety). The accepted best practice is for people with relevant experience andtraining in risk assessment to carry them out. Risk assessments are generally used to justify the safety related decision. There are many situations in the workplace that are perfectly 'legal' but might still need attention from a health and safety viewpoint.

      When voltages get higher than normal mains voltages, new extra safety things needs to be considered. Alternating current with a voltage potential greater than 550 volts can puncture the skin and result in immediate contact with the inner body resistance. A shock from greater than 600 volts almost always will result in very dangerous current levels. The most severe result of an electric shock is death. When voltages go even higher, new dangers enter to the picture. Electrical equipment operated over 10 kV in a vacuum may produce x rays that can penetrate the vacuum enclosure.

      The frequency of voltage has some effect how it affect human. At 60 Hertz, humans are more than six times as sensitive to alternating current than at 5000 Hertz. This sensitivity decreases further still as frequency increases. Above 100 to 200 KHz, sensations change from tingling to warmth, although serious burns can occur from higher radio-frequency energy. At much higher frequencies (e.g., above 1 MHz), the body again becomes sensitive to the effects of an alternating electric current, contact with a conductor is no longer necessary and energy is transferred to the body by means of electromagnetic radiation (EMR).

      Be careful whatever you do with electricity. 'Carelessness' is a the majority cause of accidents. Since electrocution is permanent it only takes one unlucky instance of carelessness in an entire career to terminate your contract!

    Electrostatic Discharge (ESD) information

    Static electricity is defined as an electrical charge caused by an imbalance of electrons on the surface of a material. To many people, static electricity is little more than the shock experienced when touching a metal doorknob after walking across a carpeted room or sliding across a car seat. In ordinary circumstances, static electricity and ESD are little more than an annoyance. However, in an increasingly technological age, the familiar static shock we receive when walking across a carpet can be costly or dangerous.his same static discharge can ignite flammable mixtures and damage electronic components. Static electricity can attract contaminants in clean environments or cause products to stick together.

    Environmental conditions have some effect on ESD problems. The lower the humidity, the higher the likelihood for ESD problems. Humidity helps because the moisture reduces the surface impedances, allowing charges to recombine at a faster rate. As a result, it's more difficult to develop the high voltage necessary for an ESD breakdown. In fact, studies have shown that at greater than 50% humidity, it's difficult for humans to exceed about 2000V. At 5% humidity, that level can reach 15,000V or more. Anything less than 20% humidity should cause you to suspect ESD. The high voltages are also felt by the people when they touch something grounded (the threshold of human feeling is about 2000 to 3000V). Humidity doesn't really control ESD, it just prevents high-voltage levels from occurring in the first place. Even with high humidity, though, you can still have problems.

    Static dissipative materials also provide a low surface impedance on materials such as countertops or packing material. This avoids high voltages to build up.

    Static electricity has been a serious industrial problem for centuries. The age of electronics brought with it new problems associated with static electricity and electrostatic discharge. And, as electronic devices became faster and smaller, their sensitivity to ESD increased. Today, ESD impacts productivity and product reliability in virtually every aspect of today's electronics environment. The cost of ESD-damaged electronic devices is usually very high. The cost of damaged devices themselves ranges from only a few cents for a simple diode to several hundred dollars for complex hybrids. When associated costs of repair and rework, shipping, labor, and overhead are included, clearly the opportunities exist for significant improvements.

    An ESD event is characterized by a very slow buildup of energy (often in the tens of seconds), followed by a very rapid breakdown (typically in the nanoseconds or even picoseconds). This fast breakdown causes many EMI problems in modern electronic equipment. ESD is a very fast transient. Two parameters are important: peak level and rate of change (dI/dt). Peak currents can exceed tens of amps, and rise times are in the nanosecond range. Due to this high speed/high frequency, ESD energy can damage circuits, bounce grounds, and even cause upsets through electromagnetic coupling. In the EMI world, you often convert rise times to an equivalent EMI frequency, where F=1/(p tr), where tr=rise time. With a typical 1-nsec rise time, the equivalent ESD frequency is more than 300 MHz. This is no longer static electricity, and VHF (not DC) design techniques it requires. The typical circuit for ESD (electrostatic discharge) testing is a 150 pF capacitor charged to test voltage (several kilovolts) and discharged to the tested device through 330 ohm resistor.

    You have two choices when dealing with ESD: prevent it or deal with it. Prevention is the primary strategy in manufacturing. Controlling electrostatic discharge begins with understanding how electrostatic charge occurs in the first place. Static electricity is measured in coulombs. Commonly, however, we speak of the electrostatic potential on an object, which is expressed as voltage (usually in the range from few hundred volts to 30 kV).

    The first Principle is to design products and assemblies to be as immune as reasonable from the effects of ESD. This involves such steps as using less static sensitive devices or providing appropriate input protection on devices, boards, assemblies, and equipment. IEC-801 standard covers protection of electronic device against ESD. Then define the level of control needed in your environment. Identify and define the electrostatic protected areas (EPA). These are the areas in which you will be handling sensitive parts and the areas in which you will need to bond or electrically connect all conductive and dissipative materials, including personnel, to a known ground. Also eliminate or reduce the generation and accumulation of electrostatic charge in the first place and safely dissipate or neutralize those electrostatic charges that do occur. Proper grounding and the use of conductive or dissipative materials play major roles.

    In electronics workshops when people are working with electronics devices special antistatic straps (grounding straps) and mats are used to control then environment so that no considerable electrostic charges can build up. Grounding straps, either of the sort included with such amat or sold separately (the sort that have a wrist band andthen connecto somehow to a ground point) SHOULD have a fairly high resistance in series with the ground connection - about 1Mohms is common. The idea is to drain off static chargefrom the wearer WITHOUT adding a safety hazard - so you put a high enough resistance in the path such that no appreciable current would flow if you contact, say, the AC line. Always place a current limiting resistor in series with you ground wire to limite the current passing through your body if you accidently touch a hot wire. Always connect it to your wrist, and never to you ankle. Many electronics laboratories have testers to test the effectiveness of the grounding practices used. The testing range is ypically so that around 500 kohms to 10 Mohms is considered as working ESD protection. Anything less than 500 kohms is a safety hazard and anythign more than 10 Mohms is considered as not adequate grounding to avoid ESD problems.

    You are not the only thing that needs to be discharged. It's also equally important to discharge any static charges from the circuit that you're working on, so its also a good idea to have a second grounding strap, or grounded anti-static mat, in contact withthe circuit assembly you're working on. Never handle a PCB assembly without grounding off any charge that one may have accumulated. Always touch the bench first, even if strapped up. The skin on the wrist is a lot drier than the hand. Wrist straps do not always make as good a connection to the body as they need to. A good rule of thumb is to ALWAYS touch the antistatic mat (or other similar connected grounding point) when you walk to to an ESD workstation. In that way, you, the mat, and anything on the mat (PCBassemblies)are at equipotential. It's important to elmininate ESD, but more important to avoid becoming electrocuted in the process. Always be sure that there is a current limiting resistor in your grounding path for ESD. It's also an important safety precaution to NEVER connect any ground strap to your ankle, becuase it's your hands that generally run the risk of contacting a dangerous voltage level. Under no circum stance do youwant any current path to run through your body trunk for obviousreasons.

    A proper "ESD workstation" would be comprised of many or even all of the following:

    • A grounded ESD work surface where said ground line contains the proper 1M ohm dropping resistor.
    • Your PCB assembly can be considered safe while on this mat.
    • A grounding strap for your wrist to make a constant contact with the ground mat or other grounded element on the bench will keep you balanced. This strap should also have a 1M Ohm resistor in series with it to the ground point.
    • You should also have either only cotton clothes on, or you should wear an ESD vest, or smock. Never wear poly fabrics when working on electronic assemblies.
    • Heal straps are a good thing, but are not required, provided you remember to constantly ground yourself at the mat. You should also never pick up an assembly from the bench without the wrist strap in your grasp or on your wrist.
    • The ground should be earth via nearby ground rod, but electrical ground is also suitable, though not ideal.
    You can buy the necessary parts to build such "ESD workstation" from many companies whick sell tools for electronics work.

    ESD is a major issue with elecronics device interface design and can be difficult to handle well. The important thing to remember is that ESD currentscan be very high at the instant of discharge, and can disrupt signals and grounds throughout a circuit if they are allowed to pass through (or near)the circuit. Many people try to use brute-force methods to channel the currents to ground, and assign all sorts of mystery to the ESD problem - and usually fail to resolve it. It is better to stop and consider the situationin a logical fashion, and then allow the usual rules of circuit design todictate the methods to use. A human being crossing a floor accumulates a charge. The human appears as acapacitor in series with a resistor, one end of which is connected to thefloor/building/earth. With the capacitor charged to tens of thousands of volts. When this human being touches the electronics device interface, the energy in the capacitor will discharge through the ground contacts, data contact, and whatever circuitry is connected to them, in an attempt to reach ground. Analyze what what happens on the route to ground.

    There are several standards that define human body model ESD protection and test methods, such as IEC 61000-4-2 (EN61000-4-2), EN50022, MIL-STD-883 Method 3015.7 etc., each with a different emphasis.

    For example, IEC 61000-4-2 requires the use of an ESD "gun," which allows testing with either contact discharge or air discharge. Contact discharge requires physical contact between the gun and the I/O pin before test voltage is applied by a switch internal to the gun. Air discharge requires the gun to be charged with test voltage before it contacts the I/O pin (produces a spark at some critical distance from the test unit). ESD produced by air discharge resembles real ESD events, but However, like real ESD, the air-discharge variety is not readily duplicated. Therefore, attesting to the general importance of repeatability in testing, contact discharge of IEC 61000-4-2 is recommended. The standards call for at least 10 discharges at each test level. According to IEC 61000-4-2, the severity levels range from 2kV to 15kV (air discharge), depending on the environment. For contact discharge the highest level is 8kV.

    Electromagnetic Compatibility (EMC)

      General EMC introduction

      EMC is the ability of an electric device to functionsatisfactory in its electromagnetic environment (immunity)without introducing intolerable electromagnetic disturbancesto that environment (emissions) or to other devices there in.Most products today have microprocessors used to control its functions and to enable data to be sent to associated peripheral devices and beyond, by, for example, connections to local area networks and telecommunications lines. These products generally fall into a class of products called information technology equipment (ITE) and are subject to mandatory RF emission limits in most countries, and to mandatory immunity requirements for specific regions of the world such as the European Union.There are many both regional and international standards related to EMC. Here are some commonly seen:

      • CISPR Publication 22 (Emission limits and measurement methods)
      • CISPR 24 (Immunity limits and measurement methods)
      Historically, definitions of environments with "abnormally high ambient electromagnetic interference" have been vague. The field strength guideline most commonly accepted as the threshold for high EMI environments is 3 Volts/meter4 (V/m). Usually interference levels greater than 3 V/m typically exceed the noise immunity levels of digital devices and are above the sensitivities of analog devices. Measured Field Strength of some devices (as example only,data from Siemeon UTP Cabling and the Effects of EMI paper):
      • Electric hand drill 1-2 V/m
      • Radio transceiver set 3-18 V/m ("walkie-talkie" radio 154 MHz)
      • Fluorescent light 1-3 V/m
      • Microwave oven 1-3 V/m
      Those are just examples of interference that can be present near those specified equipment.

      Designing for EMC in mind and solving problems

      There are three essential elements to any EMC problem. There must be a source of an electromagnetic phenomenon, a receptor (or victim) that cannot function properly due to the electromagnetic phenomenon, and a path between them that allows the source to interfere with the receptor. Each of these three elements must be present although they may not be readily identified in every situation. Electromagnetic compatibility problems are generally solved by identifying at least two of these elements and eliminating (or attenuating) one of them. Electromagnetic interference may be produced from a number of sources within electrical and electronic equipment, including components on PCBs such as microprocessor clocks or relays, or by the equipment's power supply. Other potential sources of electromagnetic compatibility problems include radio transmitters, power lines, electronic circuits, lightning, lamp dimmers, electric motors, arc welders, solar flares and just about anything that utilizes or creates electromagnetic energy. Potential receptors include radio receivers, electronic circuits, appliances, people, and just about anything that utilizes or can detect electromagnetic energy. Methods of coupling electromagnetic energy from a source to a receptor fall into one of four categories.

      • 1. Conducted (electric current)
      • 2. Inductively coupled (magnetic field)
      • 3. Capacitively coupled (electric field)
      • 4. Radiated (electromagnetic field)
      Coupling paths often utilize a complex combination of these methods making the path difficult to identify even when the source and receptor are known. There may be multiple coupling paths and steps taken to attenuate one path may enhance another. The interference may then be radiated from the equipment via a number of different paths, depending on the frequency of that interference. At high frequencies tracks on PCBs may well radiate directly. At lower frequencies interference may well be coupled from the equipment via connecting leads, such as signal or mains cables, as conducted emissions.These conducted emissions may well be radiated at a different location as further radiated emissions. The transition between radiated and conducted emissions is generally assumed to be around 30 MHz - conducted emissions dominating below this figure, and radiated emissions above. One very large source of EMC problems are related to the cabling. The signals entering the cablings should be properlyfiltered and cabling should be suitable for the application(quite often shielded). Even with quality cable installed EMC may be a problem if interfering circuits are not properly enclosed. The design of enclosures and subsequent testing is usually a costly iterative process. The reason for iterative testing usually comes from the fact that the enclosure needs to be such that it shields well enough, but is not too expensive.For shielding to be effective it is essential that all apertures and holes are designed to minimise electromagnetic radiation. A good rule of thumb is to keep holes apertures and seams less than 1/20th of a wavelength in size. For example to mitigate up to 100MHz (wavelength of 3m) openings must be less than 150mm and this includes the front door of the cabinet. Non-removable joints and seams may be coated with conductive paint. Close spacing of bolts with metal to metal contact is advised and doors may be fitted with EMC gaskets (contact fingers).Cables are a common source of noise exiting from the devices. A proper shielding of cables and filtering of signals getting to those cables help to avoid EMC problem. Usually when the devices operate at the high frequencies, suitable EMI/RFI filters ar needed to stop the high frequencies inside the equipment to get out of it through the cables. Passive EMI/RFI Filters consist of inductors, capacitors and in some cases resistors in selected combinations, designed to pass or reject selected frequencies. In some cases ferrite beads are needed in the cables.The function of a ferrite bead on a cable is to help ensurethat there is no "common mode" current flow (i.e., a netcurrent in one direction only) along that cable. Cableradiation is primarily due to such currents, as they createfields which are not cancelled by opposing fields from acurrent in the opposite direction. Ideally, cables carryinghigh-frequency signals would be perfectly "balanced" -any "outward" flow of current is exactly matched by a"return" current following the same physical path, resultingin completely cancelled fields. A ferrite bead increasesthe impedance seen by unbalanced or "common mode"currents (by adding inductance to that path); balancedcurrents see nothing at all, since both the "outbound" and"return" currents pass through the ferrite. (And if thecurrents are already perfectly balanced, the addition ofa ferrite "bead" or "core" will have absolutely no effectbeyond making the cable assembly heavier...:-)) In short,the ferrite does not usually act by "shielding" or absorbing theradiation. In fact there are some bead materials are specifically designed to be lossy and these types are quite often used for common mode supression purposes. In practice, depending upon frequency ranges, power levels, etc... thelossy beads will outperform the "lossless" ones. However, it's still not working just by "absorbing" any RF noise in the vicinity.Placing a ferrite on a cable will reduceRF pick-up by the cable only to the degree to which theRF generates common-mode noise. The common mode signals on the cable generallyresult from the "return" current finding another path back tothe source. For example, a common source of RFI inPC systems is the video cable - when a part of the videoreturn current makes it back to the PC over the safetyground path or some other cable's shield, rather than viathe video cable's intended return path. In this case, addinga ferrite reduces the "attractiveness" of that path for thecurrents in question, as it appears as a series impedancein any such path.In the case of RF being induced on a cable, common-modeinduced current results from both the "outbound" and "return"conductors seeing identical ambient fields. Differential currents, though, can also be induced in cablesvia fields coupling in through any open "loop area" betweenthe two conductors, and again ferrites around BOTHconductors will have no effect on these. (And it is oftenthe case that the equipment in question will be far moresensitive to differential-mode noise vs. common-mode.)Ferrite beads are usually a good quick radiated-noise fix, but it is not generally considered ferrites to be a particularlyworthwhile cure for many RF-susceptibility problems.

      EMC testing information

      EMC testing can be made in many ways. Techniques are available to enable both conducted and radiated emissions measurements to be made. Those both types of emissions need to be tested in EMC testing.

      For radiated emissions the most commonly used measurement techniques are antenna-based measurements in screened rooms, anechoic chambers, open area test sites and GTEM cells. Conducted emissions are measured via a line impedance stabilising network or using a ferrite (absorption) current clamp.

      Open field measurements involve placing EUTs on a non-metallic turntable in the calibrated green field test site and measuring the electric field for various orientations to the antenna, and with vertical and horizontal wave polarisations over the frequency range of perhaps 30 MHz - 1 GHz. The EUT to antenna distance is set to 3, 10 or 30 metres to place the receiving antenna well into the far field for the emissions. An open area test site (OATS), as its name suggests, is a large, flat, outdoor open area, free from overhead wires, and sufficiently large to allow adequate separation between antenna, test unit, and nearby reflecting structures - including the test equipment housing. Open area or open field test sites are specified by most regulatory authorities, such as CISPR (CISPR 16), for radiated emissions testing of domestic and commercial electronic equipment. They can, however, only be used for emission testing. The major disadvantage of open-field test sites is their lack of isolation from the electromagnetic ambient, which can on some sites preclude the use of some frequencies (usually at broadcast bands). For this reason OATS must be calibrated before testing in order to account for the site's electromagnetic ambient. The major advantage of an open-field test site is its accuracy and repeatability when compared to an unlined or even semi-anechoic screened chamber due to its complete absence of reflections (except from the ground plane).

      Unlined screened rooms can be, and certainly are, used for radiated emissions measurements, although such tests would comply with no standards because a multitude of reflection paths via the floor, walls and ceiling can effect the measurement results considerably. The test cases where equipment are passing or failing by a wide margin can usually made quite well with this kind of room. You can for example use this type of room for your pre-compliance testing before sending your equipment to a test facility for the final tests.

      A very popular alternative to open area test sites radiated emissions measurements is the anechoic chamber. The big advantages of anechoic chambers for emissions measurements are that the facility is indoors and shielded from external noises. But the the anechoic chambers have their limitations: size constraints and limits of RF performance. At UHF frequencies and above a chamber can be made anechoic - the depth of the absorber on the walls limits the lowest anechoic frequency and few chambers can be considered anechoic below 100 MHz. The lack of anechoic performance below 100 MHz results in resonances within the chambers and leads to measurement uncertainties, negating the chamber's advantage of negligible electromagnetic ambient. The absorptive material (expensive stuff) is strictly to reduce(hopefully eliminate) reflections within the chamber. External RF is kept out simply by making the chamber asealed conductive enclosure - which is done easily enoughvia sheet metal, wire mesh/screen, and gasketing.

      GTEM cells are special devices that can be used for radiated susceptibility measurements and for radiated emissions measurements. GTEM cell is a specially designed screened measurement enclosure with HF absorber and special signal feeding/receiving wire. The susceptibility measurements are made by feeding radio frequency signals (from some form of radio transmitter) to the GTEM sell feeding point. Emissions are measured at the feeding point of the GTEM cell, at each frequency in the range, and for orthogonal arrangements of the EUT. The measurements are then converted by means of a "GTEM antenna factor" into a field intensity value. GTEM cells can be generally used for the frequency range 30 MHz to 1 GHz.

      An absorbing ferrite clamp consists of a current transformer and a further series of ferrite rings which act as a power absorber and impedance stabiliser. The ferrite clamp is intended to allow the measurement of the interference power present on the mains cable of equipment. Again, in a similar way to RF current probes, ferrite clamps can be hinged open to allow insertion of the mains cable. The ferrite absorbers behind the current transformer attenuate reflections, and absorb interference, isolating the measurement from noise on the mains supply itself. The construction and use of a ferrite clamp is specified in the standard CISPR 16.

      A LISN, or line impedance stabilising network, also known as an artificial mains network, allows conducted voltage emissions tests to be made on the mains connections of an EUT. Such a device isolates the EUT from interference on the mains supply and provides a known RF impedance for coupling to a measuring instrument. CISPR 16 includes a design of LISN intended primarily for use up to 30 MHz, although other designs do exist (also for higer frequencies).

      EMC is a hard topic to cover well. However, almost the whole EMC business is on a very shaky base, due topractical limitations and complexities that are inherent in the subject.

      Examples of tests to current standards

      • EN 55011 Interference emission from industrial, scientific and medical devices (ISM appliances)
      • EN 55013 Interference emission from radio receivers and consumer electronic appliances
      • EN 55020 Interference immunity of radio receivers and consumer electronic appliances
      • EN 55014-1 Interference emission from household appliances
      • EN 55014-2 Interference immunity of household appliances
      • EN 55015 Interference emission from electric lighting equipment
      • EN 61547 Interference immunity of electric lighting equipment
      • EN 55022 Interference emission from information technology equipment (IT appliances)
      • EN 55024 Interference immunity of information technology equipment (IT appliances)
      • EN 61000-4-2 Interference immunity to electrostatic discharge (ESD)
      • EN 61000-4-3 Interference immunity to electromagnetic fields
      • EN 61000-4-4 Interference immunity to fast transient orders of interference (burst)
      • EN 61000-4-5 Interference immunity to surge voltage
      • EN 61000-4-6 Interference immunity to conducted orders of interference induced by high frequency fields
      • EN 61000-4-8 Interference immunity to magnetic fields with energy technology frequencies
      • EN 61000-4-11 Interference immunity to voltage drops, short-time interruptions and voltage fluctuations
      • EN 50081-1 Interference emission from appliances in the household area
      • EN 50081-2 Interference emission from appliances in the industrial area
      • EN 50082-1 Interference immunity of appliances in the household area
      • EN 50082-2 Interference immunity of appliances in the industrial area
      • EN 61000-6-2 Interference immunity of appliances in the industrial area
      • EN 61000-3-2 Reactions in electricity supply systems - harmonic oscillations
      • EN 61000-3-3 Reactions in electricity supply systems - voltage fluctuations
      • EN 60601-1-2 EMC medical electric appliances

      There is trend that the electrical noise is increasing in our environment and electronics needs to ne designed in such way that it work is noisy environment. ADSL and VDSL (broadband internet over ordinary telephone wires), low voltage lighting using "transformerless" power supplies, plug-top switch-mode power supplies, variable-speed motor drives used in domestic appliances to save energy, power line telecommunications (PLT), ultra-wideband (UWB) radar and radiocommunications are examples of the kinds of "noisy" low-cost electronic devices and systems likely to enjoy wide adoption over the next few years. There is a huge RFI noise caused by "ensembles" of many thousands of such cheap and cheerful interference sources, even if they all actually complied with the relevant emissions standards prevailing at the time they were taken into service and none were faulty.


      • Understanding EMC Standards and specifications - Document collection introduces the standards and regulations associated with EMC protection, and provides detailed information to help you understand filter design and specifications. It will help you identify for your application the right specifications and type of filter.    Rate this link


      • Dealing with Computer generated RFI/EMI - One of the most frustrating problems about using computers with radios, whether it be for controlling purposes or for decoding, is the amount of RFI generated by these machines. Most of the time, the RFI generated is enough to render certain bands useless and on other bands, it may drown out any weak signals and distort or interfere with signals that you want. The bad news is that, there is no way that I know of to completely remove the computer generated RFI in most situations. The good news is that there are definite steps that we can take to reduce the RFI to a very acceptable level and in some cases, it will almost disappear altogether. This document is a compilation of suggestions from various persons and some of the things I have tried with my own system when dealing with this problem. Many of the documents I have seen relate to situations involving transmitters and how not to generate them (RFI). This document is written from a receiving point of view.    Rate this link
      • Reducing Emissions - Many hardware-design engineers use signal-integrity-analysis software to check every trace on their boards for acceptable ringing, crosstalk, and delay. Often during this process, the termination resistors are changed to ensure that the proper voltage waveforms arrive at every receiver. Once the voltage waveforms are acceptable, the design process is complete. This process is good enough for signal integrity, but it's not good enough for EMI because most radiated-emissions problems depend more on signal currents than on signal voltages.    Rate this link

      Conducted emissions measuring

      Power Line Impedance Stabilization Networks (LISN) and absorbing clamps are intended for electromagnetic interference testing and certification of electronic products at an EMC test laboratory. Line Impedance Stabilization Networks (LISN) are specialized low pass filter networks used to measure common mode conducted emissions from power lines. Used to test for compliance testing requirements. During the conducted emissions tests, the LISN isolate the electrically powered equipment under test from the external power source, stabilize the line impedance and provide a 50 Ohm RF connection to measure EMI voltage generated by the equipment under test. The absorbing clamps also known as ferrite clamps are used for measuring radio noise power in lieu of radiated emissions measurements for certain restricted frequencies and for certain types of products.

      • EMI Testing Fundamentals: Radiated & Conducted EMI - The FCC regulations that outline the legal requirements relevant to permissible radiated and conducted EMI from electronic products are contained in Part 15, Subpart J of the Article 47 of the Code of Federal Regulations (CFR). These rules define the types of electronics products that are explicitly regulated, the maximum permitted EMI signal limits, the formal FCC product approval process, and legal penalties for noncompliance.    Rate this link
      • EMI Testing Fundamentals    Rate this link

    EU regulations and CE marking

    The CE Mark is a product certification mark that is placed on products compliant to the New Approach Directives of the European Union. The CE Mark is required for manufacturers (from anywhere in the world) wishing to sell their products into the European Union. The CE Mark proves to buyers that the product fulfills all the essential safety and environmental requirements as defined in the European Directives.

    The CE Marking Directive (93/68/EEC) was adopted on 07-22-1993. From the 1st January, 1996, all equipment containing electrical components or electronics need to be 'CE' labelled if they are for sale within the European Community or EFTA. A product should not be in the EU market unless it complies with whatever Directives are applicable. The 'CE' mark tells that the product fullfills the applicable directives (whatever they might be for a particular product). The CE Marking Directive marking directive defines the use of CE mark. Very many products must have CE mark to be legally sold within EU, but not all (and there are some products you are not allowed to put CE mark to). The CE Marking Directive gives a detailed description of the initials CE and any other marks specific to a particular directive and the ways conformity may be acquired. In return for fulfilling the CE Marking requirements, the manufacturer (or its agents) is able to market the product across the entire European market with only one approval procedure.

    For equipment manufactured in the EC, the manufacturers are responsible. For equipment imported into the EC, the importers are responsible.First you need to understand what 'CE marking' means. isn't, in itself, something you can 'meet'. Products marketed in Europe are subject to the requirements of certain European Directives, the Low Voltage Directive (on electrical safety),the EMC Directive, the Medical Devices Directive, the Machinery Directive and several others. Some of these invoke the CE Marking Directive, which requires the CE mark to be applied to the product, showing to Customs officers and regulatory authorities that the product may cross national boundaries and be legally offered for sale. CE mark was created to to ease restrictions oncommerce between EU member states by "leveling the playing field. "That is ALL that the CE mark is for.

    Labeling on products that bear the CE Mark or documentation accompanying such products should indicate the year in which the manufacturer affixed the CE Mark. If this date is absent, customs inspectors can assume that the importer or manufacturer represents the product as complying with all directives that apply to products of the appropriate class on the date of the customs inspection. The inspection can occur long after application of the CE Mark. So, manufacturers and importers of products whose documentation or labeling fails to indicate when the CE Mark was affixed might be responsible for some expensive retrofits or upgrades.

    The CE Mark means that an importer or a manufacturer declares that its products comply with the portions of the EU's Marking Directive that apply to products in a particular class. Ir says "Trust me." It also says "I (manufacturer or importer) promise I did adiligent effort ensure compliance, or you can legally beat me up." The responsibility for placing a CE mark on a product is that of the manufacturer, in case the product is manufactured in EEU. As soon as something is imported from outside of the EEU, only the "importer" (inside the EEU, naturally) is responsible for CE certification. His name and address have to be given on the CE certificate. After all, CE is only a self-certification, but it provides enough information to start legal action in case something goes wrong.

    Many products are "Self compliant", which simply means that any company can put apply the CE mark, if they're willing and able to support the claim. That's why most companies prefer to pay Notified or Competent Bodies to check their products that they are according the standards. In all cases, the company bears responsibility for applying the mark. The responsibility cannot be delegated to a third party. Reports from a third party can only support the company's Declaration of Conformity.

    In the case of RF equipment like radios, transceivers, etc. some of it is not "self compliant" and must be submitted to a Notified Body, who will ensure that the EUT complies. RTTE Directive applies only to products which communicate using radiated RF.If, per se, a unit falls into a category where by the same standard applies to all countries, testing to a "harmonised" standard could be sufficient.

    So in practice CE Mark indicates neither that any government or private body has tested the product nor that the product is designed or manufactured in accordance with any standards. For example, the CE mark can appear on products manufactured in facilities that do not comply with ISO 9000-series documents. Low voltage directive says that the manufacturer must have some sort of quality control system that makes sure that every manufactured device meets the directive and the technical specifications the product is claimed to have.

    There are no 'listing authorities' in Europe. There are independent test-houses that conduct their tests according to international standards are subject to strict by national accreditation services.

    Authorities in any European country who determine that a CE-marked product fails to comply with applicable directives can halt the sale or distribution of the product throughout the EEA. Moreover, if the authorities determine that willful mismarking took place, they can prosecute the manufacturer, or, in the case of products manufactured by companies outside Europe, the importer. Many observers describe this arrangement as "self-policing." Unless they have something to hide themselves, many companies are only too happy to inform the authorities of their competitors' violations. Actually, a Declaration of Conformity (of CE marking) and labelling product with CE put the manufacturer in position to be sue if it is not true, thus manufacturer don't have the advantage to claim what is false.

    You need to determine which Directives apply to your product and how youcan show that your product is satisfactory. In most cases, you can use European Standards (ENs); you show that your product conforms to all applicable ENs, and those ENs give a presumption of conformity with the relevant Directives. Here are few tips to recognize what could be relevant to yout products:

    • Electronic products fall under the EMC and Low-Voltage (LV) directives. The LV Directive covers electrical safety.
    • Electromechanical products, such as printers and copiers, fall under the LV and Machinery directives as well as the EMC directive.
    The EMC, LV, and Machinery directives exemplify "'horizontal" directives, because they are not application-specific. Other directives, such as the Medical Device Directive, apply to products for vertical markets. The EC-directives which apply to most products are:
    • 73/23/EEC - Low voltage directive: Electrical equipment for use within certain voltage limits (electrical equipment if used for applications at nominalvoltages between 50 V and 1000 V for alternating current and between 75 V and 1500 V for direct current)
    • 89/336/EEC - EMC-directive: Electromagnetic compatibility (applies to any apparatuses, equipment and systems containingelectric or electronic components)
    • 89/392/EEC - Machine directive: Safety of machines (The manufacturers of machines orequipment are obliged to use components which meet the corresponding EC directives, for example the low voltage or EMC directives.)
    • 88/378/EWG Toy Directive for the equipment that can be considered as toys ment for children to use

    Often seen product groups and related standard:

    • Electrical domestic appliances: These include electrically powered appliances such as vacuum cleaners, cookers, microwaves, hair dryers, toasters, mixers, and lots more. This product group is covered by such important test standards as EN 60335, EN 60730.
    • Lighting, furniture with electric connections: Standard lamps, wall and ceiling lights, strings of lights and storage units with lighting belong to this product group. One important test standard for this group is EN 60598.
    • Information Technology, office equipment, multimedia equipment: Information Technology (PCs, office equipment...) EN 60950
    • Multimedia equipment, consumer electronics: Consumer electronics (stereo equipment, TV sets...) EN 60065
    • Tools / Powertools: These include handyman tools, hand circular saw, hand drill, grinder, planers, glue guns e.g. Important test standards for the following appliances are: EN 50144, EN 61029.

    The conformity with these directives is the precondition of the free exchange of goods in Europe. One method - often the least painful one - of demonstrating compliance is via an "EU Declaration of Conformity. This document, a copy of which usually appears in the product manual, lists the EU directives and ENs with which, according to the manufacturer, the product conforms. The document also indicates where and under whose custody the manufacturer maintains the files of supporting documentation. As a notified body for the above directives, we can help you to implement these requirements at all stages of product design and production.

    A manufacturer can also meet the requirements of the EMC Directive by having a "competent body" (CB) or a "notified body" (NB) conduct product tests. The final route for demonstrating conformance is the Technical Construction File (TCF). The EMC Directive sets forth conditions under which a manufacturer might choose to satisfy EMC requirements via a TCF. A CB must certify a TCF or must produce a report that supports the TCF. Even so, the TCF need not contain test data (but it may in some cases).

    Some products use 'Technical Construction File' method to prove that they meet the technical specifications set by the directives and standards instead of testing every product version. Technical Construction File have to be at one place in the EEA (Europeean Economic Area), and will be used to claim that the product has been verified to comply by a third party. And those laboratories (third-party) are everywhere.

    Manufacturers of highly configurable products often choose the TCF route, because testing of all possible product configurations is impractical. The TCF must explain the rationale for the protocol the manufacturer uses to assure conformance. If testing is part of the protocol, the TCF must explain to the CB's satisfaction why the protocol's limited tests are adequate to assure the conformance of all configurations.

    In order to meet the necessary legal requirements, tests need to be performed relating to Electro-Magnetic Compatibility and a certificate of compliance needs to be generated and signed by an authorised representative of the company. There are several ways in which to obtain a certificate of compliance, and the most cost-effective of these is to do'self-certification', whereby the appropriate measurements are done in-house using the appropriate equipments.

    Putting an approval mark of some testing laboratory in equipment indicates that the type-approval sample conformed to the standard when it was tested and that the factory was capable of makingproducts that were sufficiently similar to the sample to satisfy the inspector. Putting CE mark to the equipment means that the manufacturer indicates that the equipment meets the type-approval requirements (needs not to be tested by third party, but must be proven, for this reason this is tested by testing companies for liability reason).

    Which steps are necessary do to receive the CE labe? Do we need some special documents? To get a CE mark to a product you need to fullfill following needs: You or your representative in the EU must sign a Declaration of Conformity. Legally you do not have to do any testing to get a CE mark. However that will leave you vulnerable to law suites and fines etc. The CE mark is a label that the manufacturer places on equipment that certifies that the product meets various standards such as safety and EMC amongst others.

    The CE mark is a self declaration process where no testing is legally required. With all this being said one should be able to back up their self declaration with tests to prove that the product is safe as the companies representative in the EC that must sign the DOC is the one that may go to jail if there is problems. The amount of testing one should do depends onthe complexity of the equipment and the gambling nature of the manufacturer.

    Recommended procedure for getting a CE mark is the following: First, establish which standards for EMC and safety apply to your product (if your competitor has similar products, it is a good idea to check what Directives they are claiming compliance with in thei DoC). Buy those relevant standards and study them. Assess your product interms of their requirements. Modify as necessary. Carry out your selves the tests that you can carry out. Compile your technical files, describing the product and how it conforms to the requirements. After you understand in depth what the EMC and safety requirements are, and why you need to design conformity in (not impose it after the design is finished) approach test-houses, to do the tests you cannot do in your laboratory. Approach more than one. Choose the one that you relate to best, not the cheapest. This will cost you less than going to test laboratory just before product is ready, take less time and you can carry the knowledgethat you have gained, forward to the next product. If you just go directly without knowledge to a "notified body" to scope the tests and analysis, this will easily cost lots of money (easily 10 kiloeuros or more). Hiring a contract licensing engineer usually helps you with the "notified body" interface. Please note that there are also some special products or product groups which need tests performed by "notified body". Only a few types of equipment need a "notified body" most are self certifiedby the manufacturer ( EU based, ) or the importer / agent in the EU.

    Make a note that not everyhting needs to be CE market (and some things are not be even allowed to be CE marked). There are many cases where an ignorant customer mught be requiring everything to be CE Marked regardless of whether or not it's needed. Please note that a product may not be CE marked, unless it is covered by a directive providing for its affixing.

    The Restriction of Hazardous Substances Directive (RoHS) 2002/95/EC [1] was adopted in February 2003 by the European Union. The RoHS directive took effect on July 1, 2006. his directive restricts the use of six hazardous materials in the manufacture of various types of electronic and electrical equipment. It is closely linked with the Waste Electrical and Electronic Equipment Directive (WEEE) 2002/96/EC which sets collection, recycling and recovery targets for electrical goods and is part of a legislative initiative to solve the problem of huge amounts of toxic e-waste. RoHS is often referred to as the "lead-free" directive, but it restricts the use of the following 6 substances: Lead, Mercury, Cadmium, Hexavalent chromium (Chromium VI or Cr6+), Polybrominated biphenyls (PBB)and PBDE (polybrominated diphenyl ether). PBB and PBDE are flame retardants used in some plastics.

    The maximum concentrations are 0.1% or 1000ppm (except for Cadmium which is limited to 0.01% or 100ppm) by weight of homogeneous material. This means that the limits do not apply to the weight of the finished product, or even to a component, but to any single substance that could (theoretically) be separated mechanically ? for example, the sheath on a cable or the tinning on a component lead. Everything that can be identified as a homogeneous material must meet the limit.

    Most electronics products fall within the RoHS directive. Practically all consumer electronics are within RoHS. The directive applies to equipment as defined by a section of the WEEE directive. These are:

    • Large and small household appliances.
    • IT equipment.
    • Telecommunications equipment (although infrastructure equipment is exempt in some countries)
    • Consumer equipment.
    • Lighting equipment ? including light bulbs.
    • Electronic and electrical tools.
    • Toys, leisure and sports equipment.
    • Automatic dispensers.
    RoHS applies to these products in the EU whether made within the EU or imported. Certain exemptions apply, and these are updated on occasion by the EU. For example monitoring and control equipment are outside RoHS. Also some parts of car electronics are outside RoHS. Some countries have exempted medical and telecommunication infrastructure products from the legislation.

    Batteries are not included within the scope of RoHS, but are under the European Commission's 1991 Battery Directive (91/157/EEC).

    RoHS directive is expected to cause negative impacts on product quality and reliability, plus high cost of compliance (especially to small business: some small businesses have been forced to close down, citing the cost of compliance). Restricting lead content in solders for electronics requires expensive retooling of assembly lines and different coatings for the leads of the electronic parts. Low-lead solders have a higher melting point (up to 260 ?C, instead of just 180 ?C), requiring different materials for chip packagings and for some circuitboards. Admission of reliability problems is found in Annex, item #7, of the RoHS directive itself, granting servers exemption from regulation until 2010.

      CE mark

      The CE marking symbolises the conformity of the product with the applicable Community requirements imposed on the manufacturer. The CE marking affixed to products is a declaration by the person responsible that: the product conforms to all applicable Community provisions, and the appropriate conformity assessment procedures have been completed. The CE marking is mandatory and must be affixed before any product subject to it is placed on the market and put into service, save where specific directives require otherwise. Where products are subject to several directives, which all provide for the affixing of the CE marking, the marking indicates that the products are presumed to conform to the provisions of all these directives. A product may not be CE marked, unless it is covered by a directive providing for its affixing.

      All apparatus covered by the Directive 89/336/EECin accordance with the protection requirements and accompanied by one of the means of certification provided for in Article 10 must bear the CE marking. CE marking informs the authorities that the requirements of the applicable directives have been met, but is not intended to inform the purchaser and makes no statement about quality. The CE mark is an indication that a company has met the essential heath, safety and environmental requirements detailed in 22 European Union directives covering an array of products, including electronics, machinery, simple pressure vessels, telecommunications, medical devices, toys and others. Once a company has met these requirements, it can affix the CE mark to its products and sell them throughout the European Union without having to make separate product modifications in each EU country to which it is selling. The purpose of rile CE mark is to harmonize health, safety and environmental regulations in order to facilitate trade and ensure a baseline level of consumer safety among EU member states. If a company fails to meet CE mark requirements, its product can be held up by European customs at the point of entry. If the non-CE marked product makes it through customs, CE mark enforcement officials in each member state could discover the violation while making routine checks at manufacturing centers or in stores. Initial CE mark violators are usually penalized by fines. Repeated violations can lead to a product being banished from the European market. Legally the CE mark must be applied if there is any directive to do so.

      There are strict guidelines regarding the size and placing of the CE Marking. Placement of CE markings is regulated by 93/68/EEC. It is a pretty detailed description. Each Directive specifies where the marking may be placed and whether additional marks are required. The CE marking is affixed by the manufacturer or his authorised representative established within the EEA to the apparatus or, if this is not possible, to the packaging, instructions for use or guarantee certificate, in that order of priority. It would be sensible, but it is not mandatory, to more readily facilitate free movement to affix the CE marking to more than one place, for example, marking the outer packaging, as well as the apparatus inside can be ascertained without opening the package. There is nothing in the Directive 89/336/EEC to prevent this.

      Manufacturers or their representatives in Europe must show compliance with the relevant Directives. This is sometimes, but not always, possible by testing against the appropriate standards. This testing can be carried out in the manufacturers in-house lab or can be carried out by a third party test laboratory. For self certification you require a detailed design file or testing records (both to be kept for the next 10 years). Based on either of these, you write and sign a 'declaration of conformality' (DoC) and based on this declaration, you are allowed to use the CE mark. Many manufacturers include a copy of the DoC with the product. DoC does not have to travel with your product but must be 'producable' (available on request). Design files would typically exist as part of the normal design process. CE marking (after self certification) has two distict routes:

      • You can build your design fully on existing norms. The so called 'paper route'. Keep a record of the design process and comply. (Basically even without testing)
      • You can build your design and test it toward the different requirements. If the test results match all specifications your product complies. (And you keep a record of the testing process.)
      In general, even if you keep good design records normaly not qualify as to prove that your design will meet all requirements for CE marking. For products that are clearly conforming, without the need for testing, a set of manufacturing drawings (kept up to date) is sufficient for the technical file for both EMC and safety. If a few components have been added for safety reasons or EMC reasons (usually immunity), the a brief statement about them is sufficient.

      Defining to which standards the product must comply can sometimes be somewhat hard to define. There are gereric standards, product family standards and pdoduct standard. A Product Family Standard takes precedence over a generic standard. If a Product Standard exists for the particular product, then it will take precedence over the Product Family Standard. You need to comply with the standard as defined earlier and all the standard referenced by it. But there are few exceptions to this general rule: 61000-3-2 and -3 standards (Harmonics & Flicker) apply even if product standard or product family standard do not mention them. They are 'Product Family Standards' but the 'family' is everything rated less than 16 A that is connected to the 230 V 50 Hz public mains supply.

      Please note that placing the CE mark on a product that does not require it would be a violation of the use of the mark. The CE mark implies compliance with Directive(s), not compliance with nothing (due to lack of a Directive). This use of the mark would seem to imply that you are claiming compliance with your imagination. In practice there are so many marginal cases and grey areas that it simply isn't practicable to maintain a stringent ban on unnecessary marking. Mis-applied mark is an indication of sloppy process, and lessens my confidence in the rest of the products claims. Legally the CE mark must be applied if there is any directive to do so. Certain Directives, notably the EMCD, require SOME products within their scope to be marked, but some do not need to be marked. This is not described in the Directive but in the official (but legally non- definitive) Guidelines. The case that produced this thread is that of a product which, in itself, does not in fact give rise to either EMC or safety issues, but which some significant people (customs offices and potential buyers) might expect to be CE-marked. A product may not be CE marked, unless it is covered by a directive providing for its affixing.

      Electromagnetic compatibility (EMC)

      Most products today have microprocessors used to control its functions and to enable data to be sent to associated peripheral devices and beyond, by, for example, connections to local area networks and telecommunications lines. These products generally fall into a class of products called information technology equipment (ITE) and are subject to mandatory RF emission limits in most countries, and to mandatory immunity requirements for specific regions of the world such as the European Union. The stated motivation for the EMC Directive and related EU directives (formerly European Commission (EC) directives) is reasonable: When a user employs products in a way a seller describes as appropriate, products should be able to safely perform their intended functions. EU directives indirectly establish performance standards and require that manufacturers be able to demonstrate that products conform to those standards.

      • EN 300 386 - "Electromagnetic Compatibility and Radio Spectrum Matters (ERM); Telecommunication Network Equipment; ElectroMagnetic Compatibility (EMC) Requirements"
      • EN 50022:1998 - "EMI emissions in electronic equipment" (based on CISPR222:1997, limits conducted emissions in 150 kHz - 30 MHz range)
      • EN61000 (here are for example many ESD tests, radiated immunity test, cinducted immunity)
      • ENV 50121 - "European railway specific EMC standards"
      • EN 50081-1 - "Emissions - Residential, Commercial, and Light Industrial"
      • EN 50082-1 - "Generic limit, residential"
      • EN 50082-2 - "Generic limit, industrial"
      • EN 55013 - "Broadcast Sound, Television Receivers, and Associated Equipment"
      • EN 55014-2 - "Appliances and power tools"
      • EN 60601-2 - "Medical devices"
      • EN 55011 - "Emissions - Industrial, Scientific, and Medical (ISM) Equipment"
      • EN 50013
      • EN 50014

      Where there is a relevant dedicated EMC standard for a product or product-family, then it should take precedence over the generic standard. Indeed, much effort is presently being expended in preparing product related standards, especially in areas where the generic standards are not very satisfactory. A case in point is the audio electronics, where the industry has great difficulty in econciling some aspects of the generic standards, for instance in the design of suitable low level microphone pre amplifiers. There are also other product groups that have their specific limitations and demands.

      EU directives and the specifications usually specify the limits and methods to measure the EMC properties. EU does not mandate any specific testing before the prduct can be shipped. EU EMC Directive effectively mandates compliance with several EMC specifications. Manufacturers often choose to submit products for testing by EU-accredited bodies as a way of demonstrating compliance with EU directives. The EMC Directive requires that commercial products comply with conducted- and radiated-emissions standards. In addition to this EMC Directive covers products' susceptibility to several types of EMI phenomena. EMI can enter a product through the air, via power or signal lines, or - in the case of ESD - through operator contact. Before the EMC Directive, most companies that concerned themselves with their products' EMI immunity or susceptibility were in avionics or military electronics. The EMC Directive targets immunity from ESD; RF-radiated interference (RFRI); RF-conducted interference (RFCI), which enters products via power and signal lines; electrical surges, usually resulting from lightning strikes to power or telephone lines; and electrical fast transients (EFTs), or bursts, which usually result from arcing of switch contacts that open while current is flowing.

      Immunity testing is unusual in that, in many cases, it permits the product manufacturer to select the failure criteria. Sometimes, the manufacturer can even say that a product has passed if it becomes inoperable and the purchaser must return it to an authorized facility for repair. Such behavior might be acceptable in a small appliance subjected to a line-voltage-surge test. A product that becomes hazardous to touch after a surge test definitely fails the test, however. The limits used in the immunity tests vary in the used signal strengths. In most cases, testing has found that the EMC environmental directives are more severe than most actual industrial or other environments. A good example of this is in the radiated immunity category. 10 V/meter is a common test level for radiated immunity verification of industrial products. However, to produce a 10 V/meter level, it requires roughly 39.6 watts of power from a transmitter located two feet away from the equipment. As demonstrated in this simple relationship, the power of the transmitter is relatively large compared to hand-held cellular telephones at 0.6 watts or most two-way radios at 3 watts (ERP) effective radiated power. A poorly designed product will experience problems even with low power transmitters such as cellular phones when in close proximity to the equipment.

      Thanks to the EMC Directive and related EU directives, many design and quality-assurance engineers have begun to become familiar with a bewildering array of acronyms and document numbers. Many of these documents are European Norms (ENs). Others are specifications of the International Electrotechnical Commission (IEC). Many ENs reference IEC specs. Most manufacturers of electrical products have little to fear from the EMC Directive and compliance will be straightforward so long as they take a logical approach to the requirements and maintain accurate records. Manufacturers of more complex electronic products may have to spend some time and money testing equipment. It's vital to understand that the EMC Directive does not actually require you to perform testing, it simply requires you to comply with the protection requirements outlined above. For simple electrical apparatus containing only electromechanical controls and induction motors, one can have a reasonable level of certainty that equipment will comply with these requirements (i.e. will meet the levels defined in the standards) without ever actually needing to do any testing. Even where testing is required, it may be that only partial testing is needed to determine performance in one particular aspect (e.g. performance under flickering mains conditions).

      The bulk of the EMC standards are to do with setting up and performing tests in such a way as to be able to get reasonably meaningful and repeatable results. What the test labs don't tend to admit is that this doesn't always work.There is a 6dB margin of error permitted in the measurements under most standards and the same product tested to the same standard in different labs quite often gives results which vary by 10dB or more.

      For radiated emission tests the right method is Open Area Test Site (OATS). It's the ONLY method. Yes, you might try semi-anechoic rooms or even TEM or GTEM cells, but you need to validate the performance of the room or cell with comparative OATS data. The OATS method is an "open-field" method, where you put the equipment to open field where you do the measurements. Theoretically easy, but in practice gives some problems. The real fun comes in locating a big plot of ground for the OATS, then leveling it and carpeting it with a good ground screen. If you live in any metro area, the whole effort is futile; you really need to think very rural area, no nearby powerlines, and very nice weather.

      For conducted emissions the emissions on the wires are typically measured with aid of a gadget in the metal box is called a Line Impedance Stabilization Network (LISN).

      Calibration of signal path equipment isn't optional. There are no generic correction factors. You need to traceably calibrate antennas, pre-amplifiers, cables, LISN's (characteristic impedance & port loss), analyzers, attenuators, filters and limiters. And you need to periodically re-calibrate these items. If you are gathering data for your own products, then you must exercise "due diligence" in performing the testing. If you are not an expert in this type of testing, then you are on shaky legal ground declaring compliance. There's big-time legal exposure for the willfully negligent or inadequate.

      Sometimes doing your own tests with some of your own equipment might make sense. If you just want to see a quick picture of how bad your product may be, you can do your own "pre-compliance" testing. To do this you need to buy for example an old HP-141 analyzer (peak detection is worst-case anyway) (you can get this equipment maybe from eBay or used equipment company), buy a biconical and maybe a log-periodic antenna, and go out in the parking lot during third shift (fewest cars & quietest ambient). Some people do pre-compliance testing in their basement or in hallways; not recommended, but better than no testing at all. Radiated emission testing is a real gamble; without comparative OATS data, you are really in the dark as to how weird your site is. For radiated emission FCC or EN work, a good rule of thumb is that if you can see an emission above ambient with cruddy equipment, you probably have a problem. When you are in control of your measurement uncertainty and quite familiar with your EUTs, a simple set consisting of a turntable, a wire mesh for the ground plane, enough place for the CISPR ellipse free of any other metal objects, a test receiver, an antenna plus motorized antenna pole will do.

      Conducted emission testing is easier can could be done quite reasonably on laboratory environent. Conducted Emissions will need a shielded room and an AMN/LISN, a pulse limiter at the input of your test receiver will prevent the input stage from frequent damage through transients present during this test. With a quiet powerline, and a little attention to grounding, and somewhat shielded room, you can do reasonably accurate conducted emission testing.

      Putting together an OATS & a decent test lab is capital intensive and time consuming. Most testingh laboratories are put together by one or two experts. The magic is in the hard-learned details. If you want to spend a lot of time setting up a decent lab, you can do do it. But you will have to be your own controller of everything. And you will have to develop a tolerance for reading (and a decent budget for buying) such inspiring documents as the 47CFR, flocks of EN documents and ISO guides. If you are basically the only person running the lab - build it up gradually. It takes time to learn the correct use of your equipment and even more time to use it efficiently. There is no use having a bunch of fancy equipment when you don't know how to use it the right way. At least by the time you surmount all the challenges, you'll be a fairly decent test lab guy. If you are planning to sell testing services, you might find that potential customers don't want to risk dealing with you unless you have a third-party accreditation. Accreditation and testing according to the standards means to invest a lot more time and money. A few words: CISPR 16-1 compliance for the measuring equipment for EN testing for ITE equipment (automotive wants CISPR 25, depends all on your EUTs). You must control the field attenuation of your OATS, etc.

      Decide for yourself if you only want precompliance or more and what are the important aspects of your tests. If precompliance is the answer and your EUTs are small, a GTEM cell is also worth to be considered. Be very aware of what you intend to do before spending your first buck! Most companies do their compliance testing at an external lab. Only large companies are in a situation that they can justify the cost of a fully accreditated lab as the reduced external costs are (usually) larger than the required budget for the lab. A precompliance lab makes sense when products often failed during compliance testing. In this case - start where it hurts most, start to test in-house, learn from it and establish a set of recommendations to follow for the design engineers. It takes a while to get it running and you really have to insist, but after a while it pays off well.

      One can adopt a number of strategies to deal with the Directive. One is to bite the bullet and test every piece of apparatus comprehensively. This is expensive and it doesn't really guarantee compliance since it's possible that the standards are not appropriate for the actual application that the equipment is being sold for. Another strategy is to ignore the EMC issue completely, or at least to assume that the products will comply and that testing will only be an expensive way to prove this. The dangers in this approach are obvious and it cannot be recommended to any reputable manufacturer. The best strategy is to learn enough about EMC and the requirements of the Directive that you can spend a reasonable testing budget in a way that actually gives you both useful design information and some confidence that your products comply.

      • The Electromagnetic Compatibility Directive - The Electromagnetic Compatibility (EMC) Directive 89/336/EEC is one a series of measures introduced under article 100a of the Treaty of Rome. Article 100a directives all have the primary objective of creating a single European market in goods and services. The directive was originally enacted in 1989 but was modified in 1993 by directive 93/68/EEC to modify the marking requirements of the original directive and bring them into line with the other CE mark directives.    Rate this link

      Low voltage directive (LVD) information

      The Low Voltage Directive (73/23/EEC) states that electrical and electronic equipment placed on the market in the European Union (EU) must be safe. It applies to almost all electrical equipment, designed to operate in the voltage range 50-1000 V ac or 75-1500 V dc. "Low Voltage Directive" that unified theproduct safety standards for electronic products throughout the 12 member EC (Great Britain, France, West Germany,Belgium, Netherlands, Luxembourg, Spain, Portugal, Italy,Greece, Denmark and Ireland). The Low Voltage Directive, designated 73/23/EEC, acknowledged that the product safety requirements of some governments of the EC had become"repressive" and had to be eliminated. The original directive became law in Europe in 1973 by Publication in the Official Journal of the European Communities. This was long before the CE mark was a requirement in Europe. In 1993, the LVD was amended to bring it into compliance with the requirements for using a CE mark. As of January 1st 1997, the Low Voltage Directive 73/23/EEC came into effect (mandatory compliance). Equipment that comes under this directive may no longer be sold without the CE mark.

      Most electronic equipment in Europe will be tested and approved to the Lov Voltage Directive (LVD). This ensures that the unit is safe and allows the manufacturer to fix a CE mark on the product. The LVD is Europe's oldest Directive, it was introduced in 1974 and was upgraded on January 1st 1997. LVD applies to all electrical products with an intristic function and with an input or output voltage of 50-1000V AC or 75-1500V DC.

      Electrical safety is implemented using the concept of double safety layers:

      • 1. Isolation + Grounding
      • 2. Insulation + Extra Insulation (double or re-enforced insulation)
      Any part at hazardous voltage should be separated from the operator by 2 layers of safety like specified under 1. or 2. In addition to this both layers are not to be affected in their efficacy in the case of single fault (oose wire, defective component, loss of earth etc.). Foreseeable abuse of an equipment is considered as a single fault.

      The testing is carried out against Product or Industry Specific Standards; there are no Generic Standards. There are two types of test.

      • Type testing proves the safety pf the product design.
      • Production testing proves that the product is built correctly.
      Those tests are done to ensure that the product is safe and that there is no risk of electrocution. Testing confirms that the insulation is good enough to prevent contact with voltage and tests that the earth path is good enough in order to enable safety devices to operate and cut power. There are four main tests:
      • Protective Wire (Earth Bond): Typical testing arrangement is that 25A current goes down to the earth lead from 'furthest away' part of cover and tests that circuit reistance is less than 0.1 ohms.
      • High Voltage (Dielectric Strength Test): This tests the isolation of electrical equipment. The test voltage (usually 2.5 kV) is applied between shorted power lines and the protective earth. No measurable current is allowed to flow between those two points. This testi is carried out with a DC source. This test can be destructive in a failure mode.
      • Insulation Resistance: This test is very similar to high voltage test but the voltage applied is lower, usually 500V DC at low power. This test is designed to be only a measurement test and not a destructive test. This test is usually performed on output lines with reference to earth and the resistance is measured. In order to pass the test the resistance must be at least 1 Mohm.
      • Earth Leakage Current: The earth leakage current test is performed to ensure that the current flowing back down the earth wire is within acceptable limits and not likely to cause injury to personnel. This test is only requited by some specific standards (eg EN61010 and EN60950). The test is performed by applying mains power to the equipment under test (EUT) and measuring the leakage current. Different standards dictate different pass criteria (for exmaple medical equipmen can han limit of fe micropamperes while IT equipment pass limit could be up to 3.5 mA).
      The LVD states that all equipment supplied must conform to the type test documentation and the only way to conform this is to perform production line testing. A lot of confusion exists LVD area. Products that use an internal voltage between the ranges given by this directive are also part of this directive. There is also a number of products are excluded from this directive.Among the repressive requirements was the need forequipment to receive the national mark of each country to besold. The standards would be chosen by the Common Market itself.This resulted in one common safety document and all members of the EC must accept each other's safety marks. Nowadays the national marks are pretty much replaced with common CE mark.

      In order to prove compliance to the essential requirements of the LVD one has to make up a Technical Construction File. This includes all safety related topics, such as precautions, instructions, test reports and everything necessary to identify the apparatus, such as circuit diagrams, mechanical drawings and detailed part lists. The LVD is not about electrical safety only. Once an apparatus falls into the scope of it, many other aspects of safety like fire hazards, mechanical hazards, radiation and chemical hazards are part of the approval procedure.

      Manufacturers or their representatives in Europe must show compliance with the relevant Directives. Some examples of Harmonised Safety Standards are:

      • EN 60950 Information Technology, Business and Communication Equipment
      • EN 50091 Uninterruptible Power Supplies (UPS)
      • EN 60065 Audio, video and similar electronic apparatus - Safety requirements (e.g. TV, Hi-Fi, Alarms)
      • EN 61010 Safety requirements for electrical equipment for measurement, control and laboratory use (Measurement, Control and Laboratory Equipment)
      • EN 60335 Domestic Appliances
      • EN 60601 Medical Devices
      Both EN61010-1 and EN60950 are listed in the Official Journal (OJ) of the European Community as suitable standards for claiming compliance with the Low Voltage Directive (LVD) 73/23EEC. EN60950 is also listed as a suitable safety standard for claiming compliance with the R&TTE Directive 91/263EEC. Some other related standards:
      • EN 41003 Particular safety requirements for equipment to be connected to telecommunication networks
      • EN 50083-1 Cabled distribution systems for television, sound and interactive multimedia signals (Safety requirements)
      • EN 60127 Miniature fuses
      • EN 60215 Safety requirements for radio transmitting equipment
      • EN 60238 Edison screw lampholders
      • EN 60269 Low-voltage fuses
      • EN 60309 Plugs, socket-outlets and couplers for industrial purposes
      • EN 60320 Appliance couplers for household and similar general purposes
      • EN 60335 Safety of household and similar electrical appliances
      • EN 60357 Tungsten halogen lamps (non-vehicle)
      • EN 60432 Safety specifications for incandescent lamps
      • EN 60491 Safety requirements for electronic flash apparatus for photographic purposes
      • EN 60570 Electrical supply track systems for luminaires
      • EN 60669 Switches for household and similar fixed electrical installations
      • EN 60742 Isolating transformers and safety isolating transformers - Requirements
      • EN 60799 Electrical accessories - Cord sets and interconnection cord sets
      • EN 60838 Miscellaneous lampholders
      • EN 60898 Circuit-breakers for overcurrent protection for household and similar installations
      • EN 60934 Circuit-breakers for equipment (CBE)
      • EN 60998 Connecting devices for low-voltage circuits for household and similar purposes
      • EN 61008-1 Electrical accessories - Residual current operated circuit-breakers without integral overcurrent protection for household and similar uses (RCCB's)
      • EN 61009-1 Electrical accessories - Residual current operated circuit-breakers with integral overcurrent protection for household and similar uses (RCBO's)
      • EN 61050 Transformers for tubular discharge lamps having a no-load output voltage exceeding 1 kV (generally called neon-transformers) - General and safety requirements
      • EN 61058 Switches for appliances
      • EN 61071 Power electronic capacitors
      • EN 61093 Electromechanical contactors for household and similar purposes
      • EN 61143 Electrical measuring instruments
      • EN 61184 Bayonet lampholders
      • EN 61187 Electrical and electronic measuring equipment - Documentation
      • EN 61195 Double-capped fluorescent lamps - Safety specifications
      • EN 61199 Single-capped fluorescent lamps - Safety specifications
      • EN 61204 Low-voltage power supply devices, d.c. output - Performance characteristics and safety requirements
      • EN 61230 Live working - Portable equipment for earthing or earthing and short-circuiting
      • EN 61243 Live working - Voltage detectors
      • EN 61242 Electrical accessories - Cable reels for household and similar purposes
      • EN 61293 Marking of electrical equipment with ratings related to electrical supply - Safety requirements
      • EN 61549 Miscellaneous lamps
      • EN 61558 Safety of power transformers, power supply units and similar
      • HD 21 Polyvinyl chloride insulated cables of rated voltages up to and including 450/750 V
      • HD 22 Rubber insulated cables of rated voltages up to and including 450/750 V
      • HD 27 Colours of the cores of flexible cables and cords
      • HD 289 S1 Safety of household and similar electrical appliances - Particular rules for routine tests referring to appliances under the scope of EN 60335-1
      • HD 516 S2 Guide to use of low voltage harmonized cables
      • HD 630.2.1 Low-voltage fuses - Supplementary requirements for fuses for use by authorized persons (fuses mainly for industrial application)
      • HD 630.3.1 Low-voltage fuses - Supplementary requirements for fuses for use by unskilled persons (fuses mainly for household and similar applications

      Manufacturers use various levels or types of insulation to obtain isolation. They base insulation on spacing, or separation, distances and dielectric-withstand, or isolation, tests. The standards list the required spacings, creepage, and clearance. Creepage is a spacing distance measured over a surface, such as between two traces on a printed-wiring board or across the surface of an optoisolator. Clearance is the shortest distance through air, such as from the pin-to-pin of a connector. For example, a 250V-rated product with a peak working voltage of 300V requires 3 to 4 mm of creepage on the printed-wiring board and 6 mm of creepage on other parts between hazardous and nonhazardous voltages. Dielectric-withstand testing measures the amount of voltage the insulation can withstand for a specified period of time, such as 2300V rms for one minute across the isolation barrier.

      Understanding safety-isolation rules and testing requirements enables you to address potential safety-isolation vulnerabilities. Safety isolation protects information-technology and measurement products and users from electrical hazards. Information-technology and measurement instruments operate as intended and are considered safe when you design them following all isolation and applicable safety rules. Once the spacings and components of a product are in order, you can perform isolation tests to verify the design and production of the product and to ensure conformity with the standards. You use dielectric-withstand testing, also known as electric strength and high potential, to verify isolation. The product must pass a one-minute V rms or V dc test. The tester performs a one-minute test on a representative test sample for design verification, and a one- to two-second routine test on 100% of production before shipping. Dielectric-withstand test values can vary somewhat between the standards, such as basic insulation of 1350V rms for test-and-measurement instruments or 1500V rms for information-technology products rated at 250V. Preparation for testing:

      • Connect all the mains power carrying input wires toghether
      • Connect the input signals together (if you have many groups of signal isolated from each other you coudl need to group them to several groups)
      • Establish a connection point on the metal enclosure
      • Set the V rms or V dc value current (V rms/120 k?), 10-sec or less ramp, and one-minute dwell time
      Test for doulble insulation (between two signal groups):
      • Connect one lead of the test instrument to two points where you have grouped the signals of two insulated signal interfaces
      • Perform one-minute 2300V rms or 3250V dc dielectric-withstand test
      • Record the pass/fail result
      Test for basic insulation (signal to case):
      • Connect one lead of the test instrument to common point where interface wires are wired and other to equipment metal case
      • Perform a one-minute, 1350V rms or 1900V dc dielectric test for basic insulation (substitute double insulation of 2300V rms or 3250V dc if the metal enclosure is not reliably grounded)
      • Record the pass/fail result
      If you lack the expertise to assess isolation or perform the tests, you can send the product to a qualified safety lab for evaluation and certification. Manufacturers can use certification and marks to limit their risks and demonstrate safety compliance. The best route to ensuring that a product meets isolation and other safety requirements is to purchase certified products that bear a safety mark. Safety marks are evidence of isolation and safety conformity. Look for them on products with ratings greater than 42.4V peak or when isolation claims are greater than 400V rms.

      The present practice is to choose an appropriate standard, such as IEC 60950 (used for IT equipment). It is assumed that if the product meets all of the requirements in the standard that it is in compliance with the directive.

      Many makers of small electronics device use an external "wall wart" power supply to power them. The reason for this is that when use a readily approved power supply it is pretty much easier to be sure that the product meets the necessary LVD regulations related to mains power connection. Generally ou can't assume that you cna pick up any "wall wart" with CE mark and expect that it will always make your product to comply with LVD. The standards required for wall-wart (plug-top) power supplies depend on what they are being used with and in what environment. You need to consider the end-product requirements, and then see what's suggested for power supplies/transformers. Audio equipment is for eample evaluated to EN 60065. The EN60950 stndard applies to information technology and similar equipment. EN60335-1 applies to Household and similar electrical appliances. The genenic European standard for safety extra low voltage transformers is EN 60742.

      The original Low Voltage Directive (LVD) was published in 1973 and further amended in 1993 to transform it into a new approach directive. One of the long-standing problems with the LVD is the voltage range specified (from 50 to 1000 V ac and from 75 to 1500 V dc). Most of the present standards use 30 V ac or 60 V dc as the lower limit to determine whether a voltage might present a shock hazard. Both the standards and the LVD have ignored the potential fire hazard at lower voltages, particularly from batteries. The Radio and Telecommunications Terminal Equipment Directive (R&TTE) published in 1999 recognized the voltage-limit problem, and lowered the low-voltage limit to zero for the LVD when the R&TTE Directive is being used. A point of confusion with the existing LVD is the CE marking of components. Official interpretations have indicated that components should not be marked, but common industry practice has been to CE mark components.

      The Declaration of Conformity is most often based on a one sample of a "type tested product" that ideally should be identically reproduced in series. In order to maintain safety in real life production, some quality control is imperative. Therefore each and every produced apparatus must be numbered and verified for a list of essential parameters -composed by your test house- such as functionality, dielectric strength , the grounding qualities and potential pitfalls created by foreseeable mistakes in production. This focuses the attention on those faults that are easily made without being detected in functionality tests, and that may create a potential hazard to the operator. Examples are grounding clips, insulation barriers, warning labels, insulation (rubber) rings below ring core transformers etc. Routine test must be logged, therefore serial numbering your equipment is required. Standards exist for setting up these so-called routine tests:

      • House hold appliances EN 50106
      • Hand held motor operated tools EN 50144-1
      • Luminaries ENEC 303
      • ITE equipment EN 50116
      There are many reasons why an equipment can fail on LV-Directive (73/23/EEC). The most common failure reasons are:
      • Insufficient insulation distances in connectors and printed circuit boards: Although exceptions exist, the insulation between metal parts and hazardous voltages (mains) must be no less of 4 mm and up to 8 mm in medical equipment.
      • Unknown safety status of safety critical components: Also components must be tested for safety. Most components comply to international IEC or EN standards. You definitely have to make sure that your components are suitable for European voltages and make sure they are sold to you with written proof of compliance (in many cases approval by UL is for 115 Volts only instead of 230 Vac for Europe). Component manufacturers in generally are not very cooperative in producing accurate declarations, as a ce-declaration of conformity involves direct liability of the manufacturer for the safety of it's components
      • Compliant with standard: Correct part number and applied standard are best be mentioned on a signed document.
      • Undefined parts: Make sure you know who's manufacturing the building blocks of your equipment, and on which components the safety of your equipment and reputation of your brand relies.
      • Incomplete manuals

      All equipment should ideally be accompanied by the following documents:

      • Compliance declaration
      • Statement of origin
      • Safety manual
      • Installation Manual
      • Operators manual
      • Service manual
      Of all these parts the safety part MUST be translated in the language of the country you are selling to. Many countries require other parts to be translated too. It is a good idea to put a separate sheet for those safety aspects that require immediate attention when opening the box.

      LVD is now being reinvented to far exceed the requirements covered by the current harmonized electrical safety standards that are used to show compliance for placing the CE mark on products. The expected release date is 2004 under the proposed name "Electrical Product Safety Directive" (EPSD). The major changes are: lowering the lower limit of the voltage range to 0 V (presently 50 V ac or 75 V dc), adding very specific safety-related items that must be considered for every piece of equipment and additional marking/identification requirements (for example on marking of electrical/electronics components). The existing LVD harmonized standards will need to be extensively revised to address all of the stated risks, or the manufacturer will need to do a risk assessment. This means that most manufacturers will need to do a risk assessment, something that is not required for the present LVD. The new directive expands the marking and documentation requirements, but the impact is likely to be insignificant because these requirements are essentially the same as those being required by most agencies. Equipment must be identified either by means of type, batch, serial number, or any other information allowing for the identification of the product and for the traceability of the manufacturer. The name and address of the manufacturer (and, if the manufacturer is not established in the European Community, the name and address of the person established in the community responsible for placing the equipment on the market) must be included along with instructions for safe installation, maintenance, cleaning, operation, and storage. Where risks remain despite all the measures adopted or in the case of potential risks that are not evident, appropriate warnings must be provided. The changes being proposed are major. Of primary importance is the number of additional products that will be brought under the umbrella of the new directive simply because the lower voltage limit is 0 V! Battery-powered products, including such items as handheld calculators, will be required to comply, and they will potentially need a risk assessment or compliance to a harmonized standard. In addition, significant changes to the safety standards will be required to harmonize them to this new directive. It is important to remember that this directive is still in the proposal stage and is subject to lots of change before becoming law. The direction is very clear: compliance with the requirements is going to be a greater challenge in the future.

      Environmental compliance

      Nowadays environmental concerns are beginning to play an important role in electronic-circuit design. Over the last few years, momentum has rapidly accelerated behind the adoption of "green" manufacturing requirements designed to protect the environment from dangerous marerials. For many electronics manufacturers today, no development can proceed without closely examining compliance with global environmental regulations. Almost all products using integrated circuits will be affected by RoHS, although there are some exceptions.

      Driving this concern is a growing recognition of the dangers of heavy metals, particularly lead (Pb), to the environment. There is scientific evidence that Pb, absorbed into the body through water or food, becomes a cumulative poison, which can lead to a variety of health problems. Green manufacturing requirements designed to protect the environment from further Pb contamination. Today, green product development is only at the early stages of the adoption curve.

      Protecting the environment is considered essential for the quality of life of current and future generations in EU. The most aggressive environmental regulations are being enacted in Europe via Waste Electrical and Electronic Equipment (WEEE) and The Restriction of the Use of Hazardous Substances (RoHS) Directives. The European Union (EU) is about to restrict the use of environmentally hazardous materials in electronic components and systems. European Union environment policy is based on the belief that high environmental standards stimulate innovation and business opportunities. Recent environmental initiatives like RoHS, WEEE, and Pb-free are creating new challenges for electronics engineers and companies in electronics component business.

      WEEE Directive, effective in the European Union in early 2005, will hold manufacturers financially responsible for the collection and recycling of used electronics and applies to virtually all electronics products.

      The Restriction of the Use of Hazardous Substances (RoHS) Directive, scheduled to become effective in July 2006. The RoHS Directive refers to an earlier regulation, the Waste Electrical and Electronic Equipment (WEEE) Directive. RoHS restricts the use of Pb, mercury (Hg), cadmium (Cd) and hexavalent chromium (Cr+6), as well as two brominated flame-retardants, in most electrical and electronic equipment sold in the European market. The substances covered by the RoHS Directive are scientifically well researched and evaluated and have been subject to different measures both at community and at national level. Member States shall ensure that, from 1 July 2006, new electrical and electronic equipment put on the market does not contain lead ("lead free"), mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE).

      WEEE Directive lists 10 product categories defining the types of products covered (from Annex). Those same categories are also referenced in RoHS directive.

      • 1. Large household appliances (for example, washing machines, microwaves, air conditioners)
      • 2. Small household appliances (for example, vacuum cleaners, toasters, coffee machines)
      • 3. IT and Telecoms equipment (for example, PCs, printers, cellular phones)
      • 4. Consumer equipment (for example, radios, TV, VCRs, DVD players)
      • 5. Lighting equipment
      • 6. Electrical and electronic tools (for example, saws, drills, sewing machines)
      • 7. Toys, leisure and sports equipment (for example, electric trains, video games)
      • 8. Medical equipment (for example, cardiology equipment, dialysis machines) (NOTE: not currently covered by the RoHS Directive)
      • 9. Monitoring and control instruments (for example, smoke detectors, heating regulators) (NOTE: not currently covered by the RoHS Directive)
      • 10. Automatic dispensers (for example, vending machines)

      There are some exemptions to the RoHS Directive. Exemption status has been granted to servers, storage and storage array systems (until 2010), as well as network infrastructure, and military equipment.

      Exemption to RoHS has also been granted to spare parts that are used for the repair or reuse of equipment put on the market before July 2006. Evalution boards are also not subjected to the RoHS directives.

      Batteries are also not covered in RoHS the directive, but disposal of used batteries is covered in the WEEE Directive.

      For electronics manufacturers RoHS compliance is about so much more than confirming whether a device is free from lead or any of the six restricted hazardous substances. It's about the way you design products, buy products and do business in an increasingly green world. Under the EU's Restrictions on Hazardous Substances (RoHS) directive, literally hundreds of thousands of products currently produced and marketed by industry companies could become obsolete, forcing semiconductor and other electronics manufacturers to determine what products they will have to re-design to remove certain toxic materials. Companies not in compliance would not be able to sell their products into EU countries. Ther regulation can also have effect for companies that don't make products for EU markets. Even if your product doesn't have to meet RoHS specifications (either not sold to EU or belongs to those extempted from RoHS group), you're still going to be confronted with modified materials in almost every component.

      Today, green product development is only at the early stages of the adoption curve. Many manufacturers are just beginning to understand the implications of the transition and explore the changes they will have to make to modify their manufacturing processes. Thing should be ready in the middle of year 2006 for those companies that make products for EU markets. Lead free solders are nowadays available, but they are generally more expensive and/or harder to work on than tradional solders that have lead in then. For example modern SnAgCu lead free solders have a melting temperature of around 220 degrees celsius, which is somewhat higher than what traditional solders used to have (usually below 200 degrees celsius) and quite close to maximum rating of components (most lead free SMD components are rated for maximum 260 degrees celsius soldering temperature).

      With the increasing global demand to eliminate all lead from the electronics industry, electronics repairing inductry will soon also be also faced with the challenge of Lead-Free Rework on all the new circuit boards. The new Lead-Free alloys that are being used in manufacturing have a higher melting temperature and do not wet as well as the tin lead alloy that we have been used to. For hand soldering this will require us to make major changes in our methods of rework and in many cases new tools with more accurate temprature control.

    IEC 950 (EN60950) information

    IEC 950 (EN60950) document is very important. It consolidates the requirements in the former IEC 380 (Safety of Electrically Energized Office Machines) and the former IEC 435 (Safety Data Processing Equipment). IEC 950 is embodied in several other national and regional standards, including UL 1950 (U.S.), EN 60950 (European Community), VDE 0805, Part 100 (Germany), BS 16204 (U.K.) and CSA C22.2950 (Canada). In general, the major portions of these individual standards are the same as IEC 950. Some IEC 60950 terminology:

    • Bonding Surface: The outer surface of the electrical enclosure.
    • Class I: Equipment where protection against electric shock is achieved by: using basic insulation, and also providing a means of connecting to the protective earthing conductor to those conductive parts that can otherwise have hazardous voltage if the Basic Insulation fails. Class I equipment use protective earthing.
    • Class II: Equipment in which protection against electric shock does not rely on basic insulation only, but in which additional safety precautions, such as double insulation or reinforced insulation. There is no reliance on either protective earthing.
    • Clearance: The shortest distance between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured through air.
    • Creepage Distance: The shortest path between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured along the surface of the insulation.
    • Detachable Power Supply Cord: A flexible cord, for supply purposes, intended to be connected to the equipment by means of a suitable appliance coupler.
    • Direct Plug-In Equipment: Equipment that is intended to be used without a power supply cord; the mains plug forms an integral part of the equipment enclosure so that the weight of the equipment is taken by the socket-outlet.
    • Double Insulation: Insulation comprising both basic insulation and supplementary insulation.
    • Functional Insulation: Insulation needed for the correct operation of the equipment.
    • Hazardous Energy Level: A stored energy level of 20J or more, or an available continuous power level of 240 VA or more, at a potential of 2V or more.
    • Hazardous Voltage: A voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.
    • Leakage current: Leakage currents (touch currents in EN60950 3rd edition) are those currents originating from a hazardous voltage circuit which flow to earth, either via the earthing conductor in class I products, or via the body from any connection or accessible part of the enclosure for class II products.
    • Limited Current Circuit: A circuit which is so designed and protected that , under both normal conditions and a likely fault condition, the current which can be drawn is not hazardous. These are accessible circuits derived from hazardous voltage sources (above SELV) where some form of limiting protective series impedance reduces the available current to a safe value. The current limits are 0.5mA RMS, 0.7mA peak (at 50 Hz) and 2mA DC; higher values are allowed where frequencies are 1kHz and above, subject to a maximum of 70mA.
    • Non-Detachable Power Supply Cord: A flexible cord, for supply purposes, fixed to or assembled with the equipment.
    • Rated Current: The input current of the equipment as declared by the manufacturer.
    • Rated Frequency: The primary power frequency as declared by the manufacturer.
    • Rated Voltage: The primary power voltage (for three-phase supply, the phase-to-phase voltage) as declared by the manufacturer.
    • Reinforced Insulation: A single insulation system which provides a degree of protection against electric shock equivalent to double insulation under the conditions specified in this standard.
    • Reinforced Insulation: A single insulation system which provides a degree of protection against electric shock equivalent to double insulation under the conditions specified in this standard.
    • Secondary Circuit: A circuit which has no direct connection to primary power and derives its power from a transformer, converter or equivalent isolation device, or from a battery.
    • SELV Circuit (Safety Extra Low Voltage): A secondary circuit which is so designed and protected that, under normal and single fault conditions, its voltages do not exceed a safe value.
    • Supplementary Insulation: Independent insulation applied in addition to basic insulation in order to ensure protection against electric shock in the event of failure of the basic insulation.
    • Telecommunication Network: A metallically terminated transmission medium intended for communication between equipments that may be located in separate buildings, excluding: mains system for supply of electrical power, TV distribution systems using cable an SELV circuits connecting units of data processing equipment
    • TNV Circuit: A circuit in the equipment to which the accessible area of contact is limited and that is so designed and protected that, under normal operating and single fault conditions, the voltages do not exceed specifying limiting values.
    • Touch Current: Electric current through a human body when it touches one or more accessible parts. (Touch current was previously included in the term 'leakage current').
    • Working Voltage: The highest voltage to which the insulation under consideration is, or can be, subjected when the equipment is operating
    Please note that Class I products may also contain class II situations from parts of the enclosure not protectively earthed or made from/covered in insulating material, and it may therefore be necessary to consider both class I and class II leakage current limits for such a product. If you are designing products to meet EN 60950, you must have access toa copy of the standard. You cannot produce safe designs, except by chance, without reading andunderstanding the standard. The same thing applies to other safety standards.There is no simple answers to questions on those standards, becausethere are many factors involved. Remote power supplies (external to device) may represent the survival of thesmall entrepreneurial electronics company in America and elsewhere.By using approved remote power supplies, and sizing themcorrectly, all products powered by them become as exempt aspossible from safety agency compliance. Remeber that even if something runsoff a 9 V battery, they can argue it could be a fire hazard anddemand compliance. But the use of approved remotepower supplies makes compliance usually simple, fast and economical.

    Medical Electronics Safety

    Any electricla device that is in direct contact with a human needs to be carefully designed to be safe to use. The reason for this that even very low voltages and currents can kill a human in certain conditions. The following information is just a collection of general safety notices and warnings. This is in not in any way trying to be be any design advice on this kind of devices.It is quite nuts to make medical electronics that connect to a human being yourself unless you have anelectronics engineer and a medical doctor on your development team. Naivety may well get you and others hurt or killed.

    The basic idea of preserving patient safety is to analyse your system and the other systems it interfaces with to try and discover if there is a single fault that would presenta risk. Remember that even a single fault can and most likely will lead to a cascade of secondary failures. In practice this means thattwo safety "isolation barriers" are necessary the second to protectagains the failure of the first. If it can happen it will happen and usually at the worst possible moment imaginable. Even assuming that you do get the isolation and sigle fault analys is right there is more (as ever)to bear in mind.

    A couple of millamps applied directly to someone's heart can kill them. Even very small currents (as low as a few uA) can be fatal under certain circumstances. Your skin usually has a fairly high resistance which is what protects usfrom heart stoppage due to static shock etc. However, that resistance isquite variable - is your skin dry or moist? Are you sweating, or, theworst, have you just taken a bath and you're fingers are all crinkly?Add in pace-makers, hearth conditions and wounds (apply current directly toan iron-laden blood supply). Broken skin has a resistance of a few tens of ohmscompared with many Kohms for unbroken skin and this will dramatically affect the injected current from any voltage source. Even a 9v battery can kill - takes a freak accident but, those freak accidents happen. There is a good reason that all "consumer" electronics come with adisclaimer saying they cannot be used for life-safety devices or where failure (for whatever reason) may pose a risk of injury to anyone.

    Here are some general safety notices:

    • Under no circumstances connect your self to a mains powered device or to a phone line. A wall brick PSU or battery eliminator is absolutely not safe to use in this kind of application.
    • If you need to build your own in this field, it it must be purely battery powered.
    • To stay safe, even a battery powered device must never be connected to another mains powered device like a PC or a phone line.
    • The device you make must be current limited, even a small current applied through a small electrode may generate sufficent current ensity to cause burns and permanent nerve damage.
    If you are stimulating something electronically the stimulus must bebiphasic with respect to the return electrode, ie the positive andnegative charge injected per cycle must average out at zero. If notthe end result is electrolysis at the electrode sites and we aretalking about painful burns and tissue damage. These burns break downthe high resistance of healthy skin and the lowered resistance may cause a rapid and exponential rise in damage.

    The purpose of safety testing medical electronic equipment is to be sure that a device is safe from electrical hazards to the patient and caregivers. There are a number of UL, European and Canadian standards that serve as the ruling body on how medical products will be tested, one in particular, IEC60601-1 (the International Electrical Safety Standard for medical electronic equipment) is experiencing ?global harmonization,? meaning it is being accepted and implemented around the world. The IEC60601-1 standard is mainly intended for product development where safety considerations must be taken into account early in the design phase of a product. Medical device standard IEC60601-1 is the most widely recognized standard with detail regulations for the design of safe medical electronic equipment.

    There is many tests that are made to medical electronics at the factory. The ground bond or continuity test should be the first electrical safety test on a product following visual inspection and is performed on many electrical products, including consumer appliances as well as medical products. The test checks the connection from any user exposed or user accessible metal parts to the earth reference on the product?s line cord. Many product standards require that the presence of this continuity connection be verified during production testing. IEC60601-1 specifically says that user accessible conductive parts connected to the safety ground be tested with a current of 25 Amps or 1.5 times the product?s current consumption, whichever is greater. This current shall be from a source with a maximum no load voltage of 6 volts AC. Other medical standards allow variations where the maximum voltage can be up to 12 volts, AC or DC. The 12V, or less value, is used to limit the test operator to hazardous voltage levels. The resistance of this ground path is the important parameter calculated from the test current and voltage drop and it should be less than 0.1 ohms on equipment using a detachable power cord, or 0.2 ohms when using a permanently attached power cord.

    The Hipot test, often called the voltage breakdown or dielectric withstand test, is intended to electrically stress a product?s insulation beyond what it might encounter in normal use. The end goal being assurance that the product will function as designed and not cause any harm to the product?s user. The rule of thumb, in most standard requirements, is to apply a test voltage two times the normal operating voltage plus 1000V, this being 1250 or 1500 VAC depending if the product is to be operated at 115 or 240 VAC. This is usually a sinusoidal AC voltage, but in some cases a DC voltage typically higher by a factor of 1.414 can be substituted. For hard-wired corded product, the test voltage is applied between the high (hot) and neutral conductors shorted together, and power ground or exposed metal parts. During this test the product?s power switch should be in the "on" position. The test voltage is raised from zero to the predetermined test voltage and typically held for 1 minute. No breakdown should occur during this test, a breakdown being defined as a rapid increase in current across the tested insulation. The hipot test detects excessive leakage current through a product?s insulation system as the result of a deliberate over voltage condition. Hipot tests are usually required for 100% of electrical products in a production line.

    The line leakage test detects leakage current at normal operating voltage, not at over voltage. It measures the current through a simulated human body impedance while the product is turned on and powered up at normal operating conditions. The leakage test is intended to measure current flow through various parts of the product, one being through the ground system, another from the product enclosure to ground and the last being in, out, or between patient accessible parts. If these currents are excessive it can result in an electrical shock to the user or patient. Because of this potential hazard, safety agencies have set standards for the maximum amount of current that may leak from a non defective product. Line leakage tests are typically required on medical products as a production test, the purpose being to ensure that a device is safe for the patient and caregiver. Just by their very nature, health reasons alone can place a medical patient at higher risks from electrical shocks, thus the reason for the added caution. Leakage current specifications for all IEC601-approved power supplies are more stringent than for non-medical units. The specifications define several different kinds of leakage current, but the most important with respect to power supply design are: earth leakage current, that is the current flowing along the earth conductor; enclosure leakage current, that is the current flowing from the enclosure to earth via the patient. Maximum leakage current is defined for three main types of application with respect to IEC601-1 approved power supplies:

    • Type B: equipment where there is no physical contact with the patient e.g, laser treatment systems.
    • Type BF: equipment where there is intentional physical contact with the patient e.g. ultrasound, monitors of various kinds including ECG equipment, and operating tables.
    • Type CF: equipment where there is intentional cardiac physical contact with the patient e.g. invasive heart monitors
    Reducing leakage current within a power supply usually means eliminating or limiting the value of Class Y filter capacitors from live-to-earth and neutral-to-earth. It also demands that stray capacitance to earth is minimised through careful design. Unfortunately, the overall effect of these measures tends to compromise EMC performance, although minimising stray capacitance can reduce common mode noise. As a result, IEC601-1 approved power supplies often m meet EN55022/11 Class A instead of the more demanding Class B EMC specifications

    • Controlling Cardiac Probe Leakage Current - Medical procedures sometimes require direct connection of electronic instrument probes to the heart. Examples are direct EKG electrodes and thermocouples. The probe wires usually pass through a catheter to some external measurement equipment that sits beside the patient. When this equipment must be operated from the AC mains, a major design problem is leakage current at the mains frequencies of 50 Hz and 60 Hz. Currents of only a few tens of microamps through the heart can be fatal. Since leakage current is normally limited by small capacitances in isolating components; the challenge is to choose the isolating components, arrange the board layout, and separate components for minimum capacitance. This article shows you how to design for minimum leakage and pass IEC-601 leakage tests.    Rate this link
    • Medical Electronics: Ensuring Compliance with Product Safety Tests - Performing the required safety tests for medical electronics is complex, but the process can be simplified with automatic testing.    Rate this link
    • Ensuring the Safety of Medical Electronics - Safety standards in themselves cannot ensure that a medical electronic device is safe to use. The device manufacturer's testing program should do that.    Rate this link
    • Ensuring the Safety of Medical Electronics - The purpose of safety testing medical electronic equipment is to be sure that a device is safe from electrical hazards to the patient and caregivers. There are a number of UL, European and Canadian standards that serve as the ruling body on how medical products will be tested, one in particular, IEC60601-1 (the International Electrical Safety Standard for medical electronic equipment) is experiencing ?global harmonization,? meaning it is being accepted and implemented around the world. The IEC60601-1 standard is mainly intended for product development where safety considerations must be taken into account early in the design phase of a product, however much of it is applied to production line testing since it is the only way for a manufacturer to be sure they are shipping safe product.    Rate this link
    • Power Supplies In Medical Electronics - There can be few more critical applications for power supplies in electronic equipment than in the field of medical electronics. Medical equipment will often have lives dependent upon its reliable operation. This article looks at the safety standards and how they translate into power supply design.    Rate this link


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