Index


Automation Page

Process automation

    General

    Superior productivity is one of the keys to business success in the manufacturing sector nowadays. The secret to modern manufacturing is flexibility. Factories, such as those assembling automobiles, need integrated production lines that can produce individual items to order, whenever they are needed. To be flexible and efficient, the factory needs to be well automated. This kind of system can bring best productivity ith least costs. In an industrial plant, physical process systems consist of machinesand process equipment. They are individual devices or largersubsystems of their own.

    Manufacturing systems are inherently distributed and heterogeneous. Products are designed and manufactured by a range of people with different skills using a variety of systems specialized for different functions. More recently, significant effort has gone into bridging the islands of automation to a single large systems. In such an environment, system reliability is of utmost importance. One weak link can interrupt the entire chain of events and delay the delivery of the product. Manufacturers have traditionally planned down time for preventive maintenance of machines and had back up machines for those in need of repair.

    There has been many steps in automation systems devellopment. During the 1960s and throughout the 1970s, the machine control industry made the transformation from relay-based logic to programmable logic controllers, commonly referred to as PLC controllers. This transformation let the control engineer create systems with extremely high productivity, flexibility and reliability, and revolutionized the machine control market. PLC controller changed the way standard machine control logic was accomplished.

    Distributed devices interconnected bymeans of a communication network. Earlier generations of digital control systems have beencombinations of existing automationIn an industrial plant, physicalprocess systems consist of machinesand process equipment. They areindividual devices or largersubsystems of their own.

    Most small process autiomation system components are installed to DIN rails and larger systems built to equipment racks (19" rack being the most common). There are few variations of standardized rail types:

    • DIN 15 = EN 50 045 (15 mm wide)
    • DIN 35 = EN 50 022 (35 mm wide)
    The rail types are standardized in Europe and USA. DIN cased devices just snap the cases on to the rail. There are two variations of those rail models. There is assymmetical rail ('G' profile) and symmetrical rail (Top hat profile, sometimes referred as 'T' profile). There are DIN railtelnials and other equipment which plug to those DIN rails. When selecting the rail type, check that the components you plan to instal can plug to that specific rail type. Many components connect only to one rail type, but the ones with "universal mount" mount nicely to more than one rail type. Most common type nowadays seems to be 35 mm top hat profile rail. This DIN rail type is commonly used for example in modern electrical power distribution panels and used there to mount DIN rail mountable electrical wiring components like terminals and miniature circuit breakers.

    Investing in an industrial automation system requires the built-in flexibility that allows your system to cope with your expanding requirements, and with new technologies: the system must grow as you grow. Despite years of activity, truly open and intelligentcontrol systems seem still to be a promise of the future.

    Currently, industry is striving towardsproduct quality, safety and environmental protection. Tight profitmargins and networked manufacturingemphasise the need for integration andglobal optimisation of productionfacilities. The role of informationtechnology in achieving these goals has become critical.

    Safety systems have long been used in the process industries wherever there is a potential threat to life or the environment. Until recently, safety systems have generally been designed according to established practice within each company. Safety standards, such as IEC 61508, are gaining worldwide recognition and providing process plants with more options when choosing a safety system. The international standard IEC 61508 ("Functional Safety of electrical/electronic/ programmable electronic safety-related systems") for safety-related systems defines four Safety Integrity Levels: SIL 1 to 4 each corresponding to a range of target likelihood of failures of a safety function. The standard defines 4 Safety Integrity Levels (SIL), where SIL 4 is the most demanding level. SIL 2 systems are meeting a growing number of safety system requirements in process plants as users are trying to reduce the hazards in their plants to acceptable levels. Higher SIL levels than 2 are not often used, because if an operation requires a SIL 3 rating, then it is often considered too hazardous and needs to be redesigned to on ne that needs SIL 2 or lower. IEC 61508 is a generic standard, and can be applied to any industry that uses electrical systems for safety functions. The SIL levels from IEC 61508 are also used in IEC 61511 for the process industry. A safety-related system can comprise stand-alone equipment dedicated to perform a particular safety function (such as a fire detection system) or can be integrated into other plant or equipment (such as motor speed control in a machine tool). The seven parts of IEC 61508 will be published as EN 61508. Safety design is much more than just looking at standards and SIL ratings. A vital first step in the safety lifecycle is that the necessary safety functions are derived from an analysis of the hazards and risks. It is not only the safety integrity of the safety functions that is important, but also the effective and correct specification of the safety functions themselves. Safety Instrumented System standards (e.g., ANSI/ISA 84, IEC 61508 & 61511) cover a variety of techniques for determining safety integrity levels (i.e., the performance required of safety instrumented functions).

    The term "real-time" is often mentioned when talking about industrial autiomation systems. What exactly is industrial real-time ? The discussion can go forever what it is, because different fields can have different real-time needs. The most stringent requirements for motion control involve cycle times of around 50 microseconds and permissive jitter (deviation from the desired cycle time) of around 10 microseconds. Special applications with requirements tighter than this must be handled with application specific special hardware; normal industrial fieldbus based systems can't handle those applications. Typical cycle times for for position control lie in the 1 to 4 milliseconds range, but have very short jitter times, usually less than 20 microseconds. Pure PLC sequential logic usually doesen't require less than 10 milliseconds cycle times and jitter can be in milliseconds range. Communication with higher level computers will be in the seconds range.

    Automation resources

    Control theory

    • Controllers balance performance with closed-loop stability - If high-speed response is not required, any continuous process can be controlled easily enough. A feedback controller need only measure the process variable, determine if it has deviated too far from the setpoint, apply the necessary corrective effort, wait to see if the error goes away, and repeat as necessary. This closed-loop control procedure will eventually have the desired effect provided the controller is sufficiently patient. A typical controller will apply a whole series of corrective efforts well before its initial efforts have finished affecting the process.    Rate this link
    • Understanding PID Control - Familiar examples show how and why proportional-integral-derivative controllers behave the way they do.    Rate this link

    Programmable Logic Controller (PLC)

    A Programmable Logic Controller (PLC) is a ruggedized special purpose computer that reads input signals, runs control logic, and then writes output signals. They are used in factory production line automation mostly, but can be used in very many other applications also.A PLC (i.e. Programmable Logic Controller) was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at its inputs and depending upon their state, turning on/off its outputs. The user enters a program, usually via software, that gives the desired results. PLCs are used in many "real world" applications, like industrial control. If you are involved in machining, packaging, material handling, automated assembly or countless other industries you are probably already using them. Almost any application that needs some type of electrical control of machine has a need for a PLC.

    A PLC works by continually scanning a program. First the PLC takes a look at each input to determine if it is on or off. Next the PLC executes your program one instruction at a time. Finally the PLC updates the status of the outputs. It updates the outputs based on which inputs were on during the first step and the results of executing your program during the second step. In the beginning all PLC implementations were proprietary, but nowadays there is standardization in this field going on. Nowadays there are still many people relearning different plc systems all because the systems have a different editing suite or lack some instruction or simply MODIFY a timer or counter in some way. Ladder logic is great when it's an efficient medium for solutions, some more advanced solutions are sometimes needed.

    IEC 61131-3 is the first real endeavor to standardize programming languages for industrial automation in Programmable Logic Controllers (PLCs). The standard was IEC 1131 before renumbering. IEC 61131-3 is the global standard for industrial control programming. It harmonizes the way people design and operate industrial controls by standardizing the programming interface. IEC 61131-3 systems are a development that purports to provide a 'suite' of 6 lanquages that are syntactically standard irrespect of specific implementation. A person can learn these six lanquages and write control code that always works if it was written in the correct fashion for the application. With IEC 61131-3 you can write your PLC software using the Standard set of commands and operations. In programming using IEC 61131 standards one is able to mix programming methods [Structured Text, Ladder Diagram, Function Block Diagram and Instruction List] for each program function block. In some cases these may even be mixed within the same function block.There is no doubt that some instructions (for example array handling, complex calculations) are not efficiently handled with conventional ladder instructions, they are better handled using one of the alternate programming tools. This is a definite advantage. However it would seem that this begins to migrate away from a the very advantages that conventional ladder programming offered - namely a language/method that is readily understood and accepted by all parties involved in it implementation and use. This seems to be the ultimate goal of the IEC 61131 standard.

    The standard IEC 61131 is well accepted and being used in Europe. The primary goals are to "standardize" the programming language and provide cross-platform software migration. In practice is apparent that each vendor includes a library of standardized IEC compliant instructions/functions and file tools. However they are free to provide platform/software specific libraries and tools. This means that you get standard 'plus' environment where a product provides the STANDARD plus their optimized extra solutions. The push towards standardized PLC programming was two-fold, it simplifies the I/O interfacing and dare I say it lowered the cost of necessary programming skills. This meant that a wider audience [from programmer to end-user maintenance folks] were able to work with the control devices. On-site changes, program downloads, on-line debugging etc. etc. all became a less painful and simpler process. Programmable logic controllers have been around forever (in technology years).

    Their proven reliability in harsh environments and design to handle many inputs and outputs has made them the foundation of many factory automated systems.PLCs can be combined with most other technologies to provide a sophisticated control and monitoring system.There are a lot of alternatives to the traditional PLC for a control engine. Some of which include Soft PLCs, personal desktop computers running Visual Basic or C, and embedded controllers.

    A lot of I/O manufacturers are embedding controllers in their I/O. For good programmers, control engines (Soft PLCs) can offer advantages over traditional PLCs. The standard interfaces used in PLCs are most typically digital input (24V binary input), digital output (solid state or relay),analog input (4..20 mA current loop) and analog output (4..20 mA current loop).

    Digital inputs are quite often 24V DC current sinking binary input (IEC 61131-2 type 2):input current is typically 6 mA @ 24V (allowed 4-7 mA). This will mean that the input has around 3.5-6 kohm input impedance. The input current maximum is 30 mA on Type 2 DC input. Logic 0 is 0..+5V and logic 1 is +11..+30V according IEC 61131-2 (in some systems locgic 1 can be +15V or more). IEC 61131-2 type 1 is a lower current input version. Type 1 uses the same voltage levels as type 2, but the input current is typically 3 mA @ 24V. The maximum input current for type 1 input is 15 mA.

    Solid state digital outputs (transistor outputs) are generally current sourcing NPN outputwith 100 mA drive capacity and operation at 24V voltage(those 100 mA digital outputs ae directly compatible with DC inputs).Relay outputs are generally normal relay outputs (typically 1-2A 240V AC, can vary from device to device). (sometimes open collector outputs are used).Analogue inputs are genrally current loop type or voltage type.

    Current loop input generally convert current to voltage through around 100-250 ohm resistor (maximum 300 ohms). Other possible inputs areDC inputs -10V..+10V, 0..+10V and +1..+5V (typically 4..20mA through 250 ohm resistor).Analogue current outputs are typically 4..20 mA current loops(less than 600 ohm output impedance) or DC outputs. IEC 601131-2 standard recommends 4..20 mA range to be used in future designs. Today the 2-wire 4..20 mA solution in sensors/transmitters is much more common than the 3-wire 0..20 mA solution.

    There are also other interface systems in use, for example digital inputs and outputs that can directly interface to mains voltage, to computer 5V logic electronics etc.. For digital interfaces the most commonly used logic voltage are 5V DC, 24V DC, 48V DC, 120V AC/DC and 230V AC. For analogue signals you can see 0..20 mA, 4..20 mA, 0..10V, 0..5V, -10..0..+10V, +-2V etc.

    A typical PLC controlling system is not lighting fast in operation. Pure PLC sequential logic applications usually doesen't require less than 10 milliseconds cycle times and jitter can be in milliseconds range. In many applications much slower controlling cycle times could be used, typically in the range from tens of milliseconds up to 100 milliseconds.

    During the three decades following their introduction, PLCs have evolved to incorporate analog I/O, communication over networks, and new programming standards such as IEC 61131-3. However, engineers create 80 percent of industrial applications with digital I/O, a few analog I/O points, and simple programming techniques. It is estimated that around 80% of PLC application challenges are solved with a set of 20 ladder-logic instructions. Because 80 percent of industrial applications are solved with traditional tools, there is strong demand for simple low-cost PLCs. This has spurred the growth of low-cost micro PLCs with digital I/O that use ladder logic. The rest 20 percent of controlling applications relentlessly try to push the capabilities of traditional control systems. In the 80s and 90s, these "20 percenters" evaluated PCs for industrial control. However, normal PCs were still not ideal for control applications. Many people in this category have cobbled together a system that included a PLC for the control portion of the code and a PC for the more advanced functionality. This is the reason many factory floors today have PLCs used in conjunction with PCs for data logging, connecting to bar code scanners, inserting information into databases, and publishing data to the Web. Building this kind of system is difficult, and typically involves task of incorporating hardware and software from multiple vendors, which poses a challenge because the equipment is not designed to work together. The big problem is the besides that those systems are difficult to construct, they are also difficult troubleshoot and maintain.

    Nowadays PLC functionality is expanding ouside dedicated PLC devices. There are also PC based control systems and so called "Open Control". The purpose of open control is to give the engineer the freedom of choice of the hardware platform, the operating system and the software architecture. Open Control lets you address the problem from your perspective. Instead of fitting your application into a pre-defined architecture, you can design your own, based on hardware and software components, to exactly meet your requirements while drastically reducing costs and time to market. Open Control provides standardization. You can program on Open Control systems using any of the IEC 61131 standard languages. You can use any of the commonly available processors such as the 80X86 family, Motorola processors, Arm or any other one of your choice. You can use commonly available solutions provided by reputable manufacturers or build your own solutions selecting the appropriate component.

    Traditional PLC vendors and PC vendors look at the same problems differently. Traditional PLC software vendors start with a reliable and easy-to-use scanning architecture and work to add new functionality. PLC software follows a general model of scanning inputs, running control code, updating outputs, and performing housekeeping functions. A control engineer is concerned only with the design of the control code because the input cycles, output cycles, and housekeeping cycles are all hidden from the application writer. Most PLC vendors create advanced features by adding into the existing scanner architecture new functionality such as Ethernet communication, motion control, and advanced algorithms. However, they typically maintain the familiar look and feel of PLC programming and the inherent strengths in logic and control.

    PLCs are used mainly in industrial and building automation and process control. They were originally based on microcontrollers with proprietary architectures, but in the last few decades have shifted toward "embedded PC" architectures running "soft PLC" software, such as CoDeSys or ISaGRAF.

    Traditional PC software vendors start with a very flexible general-purpose programming language, which provides in-depth access to the inner workings of the hardware. This software also incorporates reliability, determinism, and default control architectures. Although engineers can create the scanner structure normally provided to the PLC programmer, they are not inherent to PC-based control software. This makes the PC software extremely flexible and well suited for complex applications. The first step when PC is used in controlling applicatio is that vendors is to provide reliability and determinism, which are often not available in a general-purpose operating system such as Windows. This is accomplished through real-time operating systems (RTOS). These RTOSs provide the capability to control all aspects of the control system, from the I/O read and write rates to the priority of individual threads spawned on the controller. These vendors then add abstractions and I/O read/write structures to make it simpler for engineers to build reliable control applications. The result is flexible software suited for custom control, data logging, and communication but lacking the familiar PLC programming approach.

    For the last decade a passionate debate has raged about the advantages and disadvantages of PLCs (programmable logic controllers) compared to PC-based control. As the technological differences between PC and PLC wane, with PLCs using commercial off the shelf (COTS) hardware and PC systems incorporating real-time operating systems, a new class of controllers, the PAC is emerging. PAC, a new acronym created by Automation Research Corporation (ARC), stands for Programmable Automation Controller and is used to describe a new generation of industrial controllers that combine the functionality of a PLC and a PC. The PAC acronym is being used both by traditional PLC vendors to describe their high end systems and by PC control companies to describe their industrial control platforms.

    Programming PLCs

    The configuration of modern PCL systems is usually based on the IEC 61131-3 standard of programming languages for programmable controllers. This standard acknowledges five programming languages, which consist of two textual and three graphical versions. The textual versions are Instruction List (IL) and Structured Text (ST). The graphical versions are Ladder Diagram (LD), Function Block Diagram (FBL) and Sequential Function Chart (SFC). The standard defines a set of operators, functions and function blocks. The user can create new proprietary functions and function blocks with the help of the IEC languages.

      Software projects

      • DCIPLC(free) a virtual PLC - DCIPLC is a ladder logic editor and PLC(Programmable Logic Controller) simulator that incorporates basic functions used in PLC Programming. The program is designed to allow you to easily prepare a PLC program by simply placing blocks. This project has also plans to build 32 channel in and 32 channel output interface module which connects to serial port and is controlled bu DCIPLC software.    Rate this link
      • Linux Programmable Controller (LPC) - A PLC for Linux    Rate this link
      • MatPLC - MatPLC is a PLC-like program for Linux (PLC = Programmable Logic Controller), licensed under the GNU GPL. The project has now mnemonics for logic modules (python or C can also be used), a signal-processing module which includes a PID loop, several I/O modules (including numerous industrial networks and an interface to the comedi project) and some simple HMI modules.    Rate this link
      • ClassicLadder - A project to have a free ladder language in C. Generally, you find this type of language on PLC to make the programs of automation process. It allows to realize little programs or bigger in an electric way. Classic Ladder is coded 100% in C. It can be used for educational purposes or anything you want. The graphical user interface uses GTK. ClassicLadder can run in real-time with RTLinux v3 or very recently with RTAI (optional). ClassicLadder can take advantage of the hardware drivers of the Comedi project.    Rate this link
      • Comedi - The Comedi project develops open-source drivers, tools, and libraries for data acquisition. Comedi is a collection of drivers for a variety of common data acquisition plug-in boards. The drivers are implemented as a core Linux kernel module providing common functionality and individual low-level driver modules.    Rate this link

    Automation buses

    More than any technology on the horizon today, process fieldbus will have the most impact on the way we look at control systems and will forever change the dynamics of the process control and instrumentation marketplace. First conceived as a simple digital replacement for 4-20mA communications (or ven older 0-10V, 0-20mA, 0-5V etc.), the concept of fieldbus was hastened by the introduction of smart field devices in the 1980s.Nowadays information technology (IT) is increasingly determining growth in the world of automation. After it changed hierarchies, structures and flows in the entire office world, it now covers all the sectors from the process and manufacturing industries to logistics and building automation. The communications capability of devices and continuous, transparent information routes are indispensable components of future-oriented automation concepts. The IT revolution in automation technology is opening up new savings potentials in the optimization of system processes. Communication in automation is becoming increasingly direct, horizontally at field level as well as vertically through all hierarchy levels. Depending on the application and the price, graduated, matching industrial communication systems such as the Ethernet-based PROFInet, the fieldbus PROFIBUS, LON, and other systems like the sensor/actuator bus AS-Interface offer the ideal preconditions for transparent networking in all areas and levels of the automation process.

    Field bus technology Standards General information
    Foundation Fieldbus (FF) IEC/EN 61784-1 CPF 1, IEC61158 Type 1 Process bus, up to 32 devices, speed 31,25 kbit/s, 2.5 Mbit/s or 10 Mbit/s, up to 1900 range at lowest speed
    ControlNet IEC/EN 61784-1 CPF 2, IEC61158 Type 2 Universal Ethernet/IP bus, up to 99 nodes, 5Mb/s, 1000/3000 meters
    Profibus IEC/EN 61784-1 CPF 3, IEC61158 Type 3 Universal bus, up to 32 nodes per segment and up to 125 nodes in network, electrically RS-485, speeds from 9.6 kbit/s to 12 Mbit/s, up to 1200 meters at low speeds
    P-Net IEC/EN 61784-1 CPF 4, IEC61158 Type 4 Two wire circular network, up to 32 hosts / 125 devices, electrically RS-485, sped 78.6 kbit/s
    FP High Speed Ethernet (HSE) IEC/EN 61158 Type 5 Adaptation of Foundation Fieldbus to Ethernet, uses 100 Mbit/s Ethernet media
    WorldFIP IEC/EN 61784-1 CPF 5, IEC61158 Type 7 Universal bus, up to 256 nodes per bus, speeds 31.25 kbit/s, 1 Mbit/s and 2.5 Mbit/s, up to 2000 meters
    Interbus-S IEC/EN 61784-1 CPF 6, IEC61158 Type 8 Sensor bus, master-slave data transfer and common frame protocol, supports up to 4096 I/O points, speed 500 kbit/s, up to 400 meters
    Fieldbus Messaging Specification (FMS) IEC/EN 61158 Type 9 This is OSI layer 7 command set (Fieldbus Messaging Specification), does not specify any physical bus
    Profinet IEC/EN 61158 Type 10 Ethernet based Profibus protocol
    Acutuator Sensor Interface (ASI) IEC 62026-2:2000, EN 50295:1999 Binary sensor bus, up to 31 slaves, up to 124 binary operations, 5 ms, 100 meters
    DeviceNet ISO 11898, IEC 62026-3:2000, EN 50325-2:2000 Sensor bus, transport layer is based on CAN technology, 125-500 kbit/s, 500-100 meters
    SDS ISO 11898, IEC 62026-5:2000, EN 50325-3:2001 Sensor bus, transport layer is based on CAN technology, 125 kbit/s - 1 Mbit/s
    CANopen ISO 11898, EN 50325-4:2002 Up to 2032 objects, 125 kbit/s - 1 Mbit/s, up to 40 meters at full speed
    LON-Works Manufacturer specific system Used mostly in building autiomation, 255 segments, 127 nodes per segment, maximum 32385 nodes in system
    Modbus MODBUS Protocol is a messaging structure that is widely used to establish master-slave communication between intelligent devices. The MODBUS protocol comes in 2 flavours: ASCII transmission mode and RTU transmission mode. MODBUS is traditionally implemented using RS232, RS422, or RS485 over a variety of media (e.g. fiber, radio, cellular, etc.).
    Modbus TCP/IP MODBUS Protocol is a messaging structure that is widely used to establish master-slave communication between intelligent devices. MODBUS TCP/IP uses TCP/IP and Ethernet to carry the MODBUS messaging structure.
    Modbus RTPS IEC PAS 62030:2004 On-going MODBUS standardizing work

    At sensor/actuator level the signals of the binary sensors and actuators are transmitted via a sensor/actuator bus. Sensor/actuator level interfaces use simple, low-cost installation technique, through which data and a 24-volt power supply for the end devices are transmitted using a common medium using cyclical communications. At field level the distributed peripherals, such as I/O modules, measuring transducers, drive units, valves and operator terminals communicate with the automation systems via an efficient, real-time communication system cyclically (with option for acyclical alarms). At cell level, the programmable controllers such as PLC and IPC communicate with each other using large information packets. Network infrastructures for industrial communications are complex. The importance of a high-performance plant network is growing dramatically.

      BACnet

      on BACnet - A Data Communication Protocol for Building Automation and Control Networks is a communications network developed under the auspices of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). BACnet is an American national standard, a European pre-standard, and an ISO global standard. BACnet is "a data communication protocol for building automation and control networks." A data communication protocol is a set of rules governing the exchange of data over a computer network. The rules take the form of a written specification (in BACnet's case they are also on compact disk) that spells out what is required to conform to the protocol. Everything from what kind of cable to use to how to form a particular request or command in a standard way. What makes BACnet special is that the rules relate specifically to the needs of building automation and control equipment, i.e., they cover things like how to ask for the value of a temperature, define a fan operating schedule, or send a pump status alarm. The trick is that BACnet provides a standard way of representing the functions of any device, as long as it has these functions. Examples are analog and binary inputs and outputs, schedules, control loops, and alarms. This standardized model of a device represents these common functions as collections of related information called "objects," each of which has a set of "properties" that further describe it. Each analog input, for instance, is represented by a BACnet "analog input object" which has a set of standard properties like present value, sensor type, location, alarm limits, and so on. Some of these properties are required while others are optional.

      CAN

      CAN (Controller Area Network) is a serial bus system, which was originally developed for automotive applications in the early 1980's. The CAN protocol was internationally standardized in 1993 as ISO 11898-1 and comprises the data link layer of the seven layer ISO/OSI reference model. CAN (Controller Area Network) is an automation bus unowadays sed in automotive applications and in industrial automation. The CAN standard, popular in automotive applications, defines a simple broadcast serial network that works well for real-time short range communications. Controller Area Network (CAN) is a fast serial bus that is designed to provide an efficient, reliable and very economical link between sensors and actuators. CAN uses a twisted pair cable to communicate at speeds up to 1Mbit/s with up to 40 devices.

      CAN bus was originally developed to simplify the wiring in automobiles. Bosch developed the "Controller Area Network" (CAN), which has since been standardized internationally (ISO11898) and has been "implemented in silicon" by several semiconductor manufacturers. Using CAN, peer stations (controllers, sensors and actuators) are connected via a serial bus. The bus itself is a symmetric or asymmetric two wire circuit, which can be either screened or unscreened.

      CAN supports operation up to 40m at 1 Mbps speed without repeaters, and up to 1 km at 20 kbps speed. Can uses twisted pair wiring. The CAN bus cable is typically 4-wire unshielded cable (carrying two signal wires, ground and power). The CAN Nodes are usually powered via the 4-wire CAN bus cable (typically 12-24V power). The length of wiring depends on the baud rate used (up to 3 km at 20 kbps, up to 270 meters at 250 kbit/s). The electrical parameters of the physical transmission are specified in ISO 11898. Suitable bus driver chips are available from a number of manufacturers.

      Can uses CSMA bus arbitration. CAN data packets are 8 bytes long and use 11-bit packet identifier. provides two communication services: the sending of a message (data frame transmission) and the requesting of a message (remote transmission request, RTR). All other services such as error signaling, automatic re-transmission of erroneous frames are user-transparent, which means the CAN chip automatically performs these services. The CAN protocol, which corresponds to the data link layer in the ISO/OSI reference model, meets the real-time requirements of automotive applications.

      CAN provides:

      • A multi-master hierarchy: This allows building intelligent and redundant systems. If one network node is defect the network is still able to operate.
      • Broadcast communication: A sender of information transmits to all devices on the bus. All receiving devices read the message and then decide if it is relevant to them. This guarantees data integrity as all devices in the system use the same information.
      • Aophisticated error detecting mechanisms and re-transmission of faulty messages. This also guarantees data integrity.

      CAN specifies well the low layers, but there are few rules at the upper layers. Although CAN provides a reliable communication channel, the application developer still must perform a substantial network design to make a CAN application work. CAN users still have to define the language/grammar and the words/vocabulary to communicate. CAN is the basis of several sensor buses such as Device-NET of Allen Bradley, CAN Application Layer (CAL) from CAN in Automation, or Honeywell SDS.

      Several standardized higher-layer CAN protocols are available, such as CANKingdom, CANopen, DeviceNet, J1939, and Smart Distributed System. Most of these protocols were designed for specific applications, including use in trucks or industrial automation. When implementing a CAN-based application, developers have to make a choice to either use an existing, standardized higher-layer CAN protocol or invent a proprietary protocol. Developers working on systems consisting of only a few nodes and a few network variables fear that a higher-layer CAN protocol is overkill and has a large learning curve. On the other hand, developing and maintaining an inhouse standard can be expensive, especially considering the lack of development tools. Many monitors, analyzers, configurators, and other tools available support the standardized higher-layer protocols.

      For embedded applications that don't require all the functionality of a "full-grown" higher-layer CAN protocol, CANopen is a popular choice, because with it you can implement only the functionality required by your particular application. MicroCANopen is an "entry-level" alternative to CANopen that works well in systems with embedded applications with limited resources.

      CAN bus is also pushing to safety related application. Conventional fieldbus technology is generally prohibited for safety-related use, unless the bus system is designed to meet the requirements of a safety system. Using a fieldbus to carry safety-related data is a major development, replacing traditional parallel hardwiring used in many existing safety systems. With the introduction of IEC 61508 (Functional safety of electrical/electronic/programmable electronic safety-related systems) new safety-related technologies are no longer held back, allowing the utilisation of machine safety fieldbus, such as SafetyBUS p from Pilz, which already has a proven installed base. Pilz has led the market with the introduction of SafetyBUS in 1998, which now has a significant installed base and has achieved market acceptance of safety fieldbus in an understandably cautious market sector.

      • Controller-area network - Controller-area network (CAN or CAN-bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer.    Rate this link
      • Approximating CANopen - The CAN standard, popular in automotive applications, defines a simple broadcast serial network that works well for real-time short range communications. But there are few rules at the upper layers. Here's an easy way to keep proprietary application-layer CAN protocols compatible with an open standard.    Rate this link
      • A short trip on the CAN bus - How do we reduce the amount of cabling in cars as we install more complex embedded systems? A bus architecture is the answer.    Rate this link
      • CANbus networks break into mainstream use - It takes years for some technologies to reach commodity status. CAN is one that's now enjoying acceptance. Cost-effective development kits and test equipment ease your entry into this robust networking environment.    Rate this link
      • SafetyBUS p Club International e.V. - This site is about safety-related CAN. With the introduction of IEC 61508 (Functional safety of electrical/electronic/programmable electronic safety-related systems) new safety-related technologies are no longer held back, allowing the utilisation of machine safety fieldbus, such as SafetyBUS p from Pilz, which already has a proven installed base.    Rate this link
      • CAN in Automation (CiA) - international users and manufacturers group    Rate this link
      • Controller Area Network (CAN) Protocol - The CAN protocol is an international standard defined in the ISO 11898. Beside the CAN protocol itself the conformance test for the CAN protocol is defined in the ISO 16845, which guarantees the interchangeability of the CAN chips.    Rate this link
      • Controller Area Network (CAN) - CAN (Controller Area Network) is a serial bus system, which was originally developed for automotive applications in the early 1980's. The CAN protocol was internationally standardized in 1993 as ISO 11898-1 and comprises the data link layer of the seven layer ISO/OSI reference model.    Rate this link

      MAP

      Manufacturing Automation Protocol (MAP) is a communication bus standardised in Standard 802.4. IEEE 802.4 defines a token-passing bus running at either 5 or 10 Mbps. The network is a classic broadband using frequency shift keying as the modulation method.

      MODBUS

      Modbus is a communications protocol positioned at the level 7 of the OSI Model, based on master/slave or client/server architecture, designed by Modicon for use with its programmable logic controllers (PLCs). It is has become a de facto standard communications protocol in industry, and is now the most commonly available means of connecting industrial electronic devices.

      MODBUS Protocol is a messaging structure, widely used to establish master-slave communication between intelligent devices. Modbus devices communicate over a serial network in a master/slave(request/response) type relationship using one of two transmission modes: ASCII (American Standard Code for Information Interchange) mode or RTU( Remote Terminal Unit) mode.

      A MODBUS message sent from a master to a slave contains the address of the slave, the "command" (e.g. "read register" or "write register"), the data, and a check sum (LRC or CRC). MODBUS is traditionally implemented using RS232, RS422, or RS485 over a variety of media (e.g. fiber, radio, cellular, etc.). MODBUS TCP/IP uses TCP/IP and Ethernet to carry the MODBUS messaging structure.

      Each device that intends to communicate using Modbus has a unique address. Any device can send out a Modbus command, although usually only one master device does so. A Modbus command contains the Modbus address of the device it is intended for. Only the intended device will act on the command, even though other devices might receive it. All Modbus commands contain checking information, ensuring that a command arrives undamaged. The basic Modbus commands can instruct a RTU to change a value in one of its registers, as well as commanding the device to send back one or more values contained in its registers.

      The MODBUS protocol comes in 2 flavours: ASCII transmission mode and RTU transmission mode. The higher layers are the same (Though you won't find any description of layers in the protocol specification, it can be implemented as a layered protocol).

      In ASCII mode, eight-bit bytes of information are sent as two ASCIIcharacters. The primary advantage of ASCII mode is the flexibility of thetiming sequence. Up to a one second interval can occur between charactertransmissions without causing communication errors. ASCII mode uses only ASCII character for datacoding and can be used with any dummy modem like communicationinterface, even ones with with 7bit communication channel.

      In RTU mode, data is sent as two four-bit, hexadecimal characters,providing for higher throughput than in ASCII mode for the same baudrate. Modbus RTU is a binary protocol and more time delay critical than the ASCII protocol. This means that RTU protocol does not always transfer well over modemsthat tend to buffer and error correct data. The RTU format follows the commands/data with a cyclic redundancy check checksum. ASCII format uses a longitudinal redundancy check checksum.

      Both ASCII and RTU work nicely with direct wire connection and with 2-/4-wire short haul modems.

      ASCII is more verbose, human readable and easier to implement, but RTU is about twice as efficient. As a result most low bandwidth applications use the RTU protocol.

      If you are building system that needs to use Modbus protocok, I'd recommend implementing both to your system. If you have to choose, generally it is the best idea for local communications needs is to pick the RTU protocol.

      For long distance connections where there are lots of communication devices in the communication route,the ASCII protocol is preferred, because it is less sensitive to delays and can be transported also over 7-bit communication channels.

      Modbus/TCP is very similar to Modbus RTU, but is transmitted within TCP/IP data packets.

      Information is stored in the Slave device in four different tables. Two tables store on/off discrete values (coils) and two store numerical values (registers). The coils and registers each have a read-only table and read-write table. Each table has 9999 values. Each discrete coil or contact is assigned a one bit data address from 0000 to 270E. The registers are each 16 bits = 2 bytes = 1 word and also have a data address from 0000 to 270E. Coil and Register Numbers are just location names and do not appear in the actual messages. The Data Addresses are used in the messages. For example, the first Register Number is 40001 has Data Address 0000. Each table has a different offset. 1, 10001, 30001 and 40001.

      Each slave in a network is assigned a unique address from 1 to 247. The first byte it sends is the Slave address. The second byte sent by the Master is called the Function code. This is number telling the slave which table to access and whether read from or write to the table.

      Please note that almost all modbus implementations have variations from the official standard (for example more data bytes, longer addresses support etc.).

      Profibus

      PROFIBUS is an international, vendor-independent, open fieldbus standard, under the European fieldbus standard EN 50170 and EN 50254. In manufacturing, industrial process and building automation applications, serial fieldbuses can act as the communication system, exchanging information between automation systems and distributed field devices. Both high-speed time critical data transmission and complex communication tasks can utilize PROFIBUS. The standard also allows devices from multiple vendors to communicate without special interface adjustments. Development and administration of PROFIBUS technology is handled by the User Organization known as the PTO in North America.

      PROFIBUS is an open standard. It was originally standardised in Germany in 1989 as DIN 19245 and in July 1996 as EN 50 170. The EN 50 170 specification is available through any of the national standards bodies of CENELEC / IEC and the PROFIBUS Specification can be supplied by any of the Regional PROFIBUS Associations. PROFIBUS is a polled protocol, with a layered architecture designed specifically for industrial control networks. Operations specific to industrial controls (such as Fail-Safe operation and globally coordinated Device Updates) are included in the protocol specification. Reliable operation is augmented by powerful error detection algorithms (CRC or Cyclic Redundancy Checking) and Watchdog timers.

      PROFIBUS uses a twisted-pair transmission medium and industry standard RS-485 in manufacturing applications or IEC 1158-2 in process control. Profibus can also use Ethernet/TCP-IP. Profibus DP is the Profibus running on standard RS-485 interface. Profibus PA (Process Automation) was developed by the Profibus User Organization (PNO) as a lower-speed intrinsically safe counterpart to Profibus DP for applications in process environments. Profibus PA is essentially Profibus DP technology superimposed on the standard IEC 1158-2 standard fieldbus physical layer. Several extensions were added to Profibus DP to make it appropriate for process applications in the form of Profibus PA (extensions include acyclic read or write of process data, confirmation of diagnostic and alarm messages, transmission of device status, bus power and intrinsic safety).

      PROFIBUS is a Fieldbus network designed for deterministic communication between computers and PLCs. Based on a real-time capable asynchronous token bus principle, PROFIBUS defines multi-master and master-slave communication relations, with cyclic or acyclic access, allowing transfer rates of up to 500 kbit/s (or 1.5 Mbps or up to 12 Mbps in some application). The maximum bus distance without repeaters is 200 m and if repeaters are used the maximum distance is 800m.Maximum number of nodes is 32 witout repeters and 127 if repeaters are used. PROFIBUS-DP is designed for high-speed data communication at the device level. In this case, central controllers (e.g., PLCs/PCs) communicate with their distributed field devices (I/O, drives, valves, etc.) via a high-speed serial link. Most of the data communication with these distributed devices is done in a cyclic manner. The functions required for these communications are specified by the basic PROFIBUS-DP functions in accordance with EN 50 170.

      PROFIBUS DP uses RS-485 on twisted pair or fiber. The communication speed can be 9.6 Kb-12 Mbit/s. The number of devices is max 125 slaves (according the PROFIBUS). The PROFIBUS standard specifies that twisted pair implementations use 9 pin D-SUB connector (female on the device, male on the cable). The PROFIBUS Standard does not specify an alternative to the 9 pin D-SUB connectors. Alternative connectors may be used.

      PROFIBUS-DP bus should be properly installed, terminated and shielded to work reliably in process automation environment, The right cable type to use is shielded twisted pair cable with impedance of around 120 ohms. The RS485-line must be terminated to get rid of reflections and define state of lines when no device is transmitting. Termination of a bus line is done to prevent signal reflections on the PROFIBUS-DP cable. Wrong or missing termination of the line results in lower efficiency due to transmission errors or in worst case that the communication link does not work at all. In addition to to traditional termination at right cable impedance (to avoid signal reflections), PROFIBUS-DP termination also provides a defined idle level on the cable. Ideally, termination is only implemented in the two devices by the twoends of the line. Typical applications use 390 ohm for biasing resistors (one from line to ground and other from +5V to another signal wire) and 150..220 ohm for line terminating resistor (value depends on cable impedance used).

      It is recommended to connect the shield of communications cable on both sides low inductively with the protective ground in order to achieve optimal electromagnetic compatibility. In case of separate potentials the shield should be connected only at one side of the bus cable to the protective ground. Preferably the connection between shield and protective ground is made via the metal cases and the screw top of D-sub connector. If this is not possible the connection can be made via pin 1 of the D-sub connector (9-pin connector). Is is also possible to bare the cable shield at an appropriate point and to ground with a cable as short as possible to the metallic structure of the cabinet. To ensure easy handling an additional signal ground/reference wire is not used by PROFIBUS. It is recommended to isolate the interface circuit from the local ground (e.g. by opto couplers). This reduces a possible common mode voltage between transceivers to a minimum.

      Profibus DP has been designed for fast data exchange at field level. Data exchange with the distributed devices is primarily cyclic. The communication functions required for this are specified through the DP basic functions (version DP-V0). DP supports implementation of both mono-master (only one master is active on the bus during operation of the bus system) and multi-master systems (several masters are connected to one bus). Basic DP functions have been expanded step-by-step with special functions. Nowadays several different versions called DP-V0, DP-V1 and DP-V2 are available. All versions of DP are specified in detail in the IEC 61158. Here are some general details of those different versions:

      • DP-V0 provides the basic functionality of DP, including cyclic data exchange, station, module and channel-specific diagnostics and four different interrupt types (diagnostics, process interrupts, pulling of stations, plugging of stations)
      • DP-V1 contains enhancements geared towards process automation, in particular acyclic data communication for parameter assignment, operation, visualization and interrupt control of intelligent field devices, parallel to cyclic user data communication. Acyclic data communication allows online access to stations using engineering tools (parameterization and calibration of the field devices over the bus during runtime, confirmed alarm messages). Transmission of acyclic data is executed parallel to cyclic data communication, but with lower priority. Three additional interrupt types: status interrupt, update interrupt and a manufacturer-specific interrupt.
      • DP-V2 contains further enhancements and is geared primarily towards the demands of drive technology. Additional functionalities include isochronous slave mode and lateral slave communication (DXB). DP-V2 can also be implemented as a drive bus for controlling fast movement sequences in drive axes. Slave-to-Slave Communications (DP-V2) enables direct and thus time-saving communication between slaves using broadcast communication without the detour over a master (slaves act as publisher). Isochronous mode (DPV-2) enables clock (deviations of less than a microsecond) synchronous control in masters and slaves, irrespective of the bus load. Upload and download (DP-V2) allows the loading of any size of data area in a field device with a single command (for example software update).

      There are two master classes:

      • DP master class 1 (DPM1) is a central controller that cyclically exchanges information with the distributed stations (slaves) at a specified message cycle. Typical DPM1 devices are programmable logic controllers (PLCs) or PCs. A DPM1 has active bus access with which it can read measurement data (inputs) of the field devices and write the setpoint values (outputs) of the actuators at fixed times. This continuously repeating cycle is the basis of the automation function.
      • DP master class 2 (DPM2) are engineering, configuration or operating devices. They are implemented during commissioning and for maintenance and diagnostics in order to configure connected devices, evaluate measured values and parameters and request the device status. A DPM2 does not have to be permanently connected to the bus system.

      Slaves are peripherals (I/O devices, drives, HMIs, valves, transducers, analyzers), which reads in process information and/or uses output information to intervene in the process. There are also devices that solely process input information or output information. As far as communication is concerned, slaves are passive devices, they only respond to direct queries. DP-V0 suppport is already completely included in the profibus interfacing hardware (special profibus intrface ICs).

      PROFIBUS-PA is a PROFIBUS version specially designed for process automation. It permits sensors and actuators, which can be connected through one common bus line even in intrinsically-safe areas. PROFIBUS-PA allows data communication and power transmission across a bus using 2-wire technology in accordance with the international standard IEC 1158-2. The physical media is IEC 1158-2 twisted pair or fiber. Baud rate is 9.6 Kb-12 Mbit/s. There can be max 31 devices/PROFIBUS-PA segment. PROFIBUS-PA uses the same communications protocol as PROFIBUS-DP; therefore their communication services and telegrams are identical. The difference is that in the PROFIBUS-PA, the RS 485 transmission system used for PROFIBUS-DP has been replaced with a transmission system based on the IEC 1158- 2. This system is internationally standardized to be used for intrinsically-safe applications. PROFIBUS-PA = PROFIBUS-DP communications protocol + IEC 1158-2 transmission system. PROFIBUS-PA's information and the power supply are transmitted along two-wire cable. When used in explosive surroundings, the PA bus and all connected devices must be designed with the "Intrinsically safe" type of protection. Up to 31 field devices in the nonhazardous area and up to 10 field devices in hazardous zone 1 can be connected to a PROFIBUS-PA segment.

      Profiles are the specifications defined by manufacturers and users regarding specific properties, performance features and behavior of devices and systems. Profile specifications define the parameters and behavior of devices and systems that belong to a profile family. Standardized profiles facilitating device interoperability and in some cases device interchangeability on a bus. The term profile ranges from just a few specifications for a specific device class through to comprehensive specifications for applications in a specific industry. The generic term for all profiles is application profiles. A distinction is drawn between general application profiles with implementation options for different applications (this includes, for example, the profiles PROFIsafe, Redundancy and Time stamp), specific application profiles (developed especially for a specific application, such as PROFIdrive, SEMI or PA Devices), and system and master profiles (describe specific system performances that are available to field devices). PROFIBUS offers a wide range application profiles.

      Profinet

      PROFInet is a cross-vendor communications, automation and engineering model, optimized for automation systems with distributed intelligence. PROFInet incorporates the current PROFIBUS solution.PROFInet uses DCOM for basic communication between components. PROFInet defines a runtime object model which must be implemented in every PROFInet device. The runtime software was developed to be strictly independent of operating systems. PROFInet also defines an engineering model on which configuration tools will be based using components from different vendors.

      Fieldbus

      Fieldbus is a "New Language" for digital process control instrumentation in the 21st Century.Fieldbus is a generic-term which describes a new digital communications network which will be used in industry to replace the existing 4 - 20mA analogue signal. The network is a digital, bi-directional, multidrop, serial-bus, communications network used to link isolated field devices, such as controllers, transducers, actuators and sensors. Fieldbus is much more than a replacement for the 4 - 20mA analogue standard.The fieldbus technology promises to improve quality, reduce costs and boost efficiency.

      AS-i

      AS-Interface is a highly efficient networking alternative to the hard wiring of field devices. It is an excellent partner for fieldbus networks such as PROFIBUS, DeviceNet, Interbus and Industrial Ethernet, for whom it offers a low-cost remote I/O solution.

      Functional Safety too! AS-i provides the ideal basis for Functional Safety in machinery safety/emergency stop applications. A special profile called Safety as Work (sometimes called ASi-Safe) is used. Safety devices are connected on the same cable as the control system and can provide Safety support up to SIL (Safety Integrity Level) 3 according to IEC 61508.

      AS-Interface (AS-i) is the a simple networking solution for actuators and sensors in manufacturing systems. Using the now-famous yellow cable, it is an 'open' technology supported by over 100 vendors worldwide. AS-i is a low-cost electromechanical connection system designed to operate over a two-wire cable carrying data and power over a distance of up to 100m (longer distances can be accommodated if repeaters).

      An AS-Interface network offers a cost-efficient alternative to conventional cabling at the lowest level of the automation heirarchy simple - often binary - field devices such as switches need to interoperate in a stand-alone local area automation network controlled by PLC or PC. AS-Interface is tailored to the needs of devices such as sensors and actuators where low connection cost per node is critical and simplicity is paramount. Each AS-Interface network needs a 'master', which can be a local controller box having limited functionality. However, most masters are built into a separate controller - often a PLC - using either built-in or plug-in modules. PC interface cards are also available. The host PLC or PC runs the automation program via the master, which polls the network issuing commands and receiving and processing replies from connected devices in the usual way. A gateway to a higher level fieldbus or Ethernet can also be an AS-Interface master. Vendor software can normally configure, control and monitor the AS-Interface remotely, in which case the AS-Interface network is usually seen as remote transparent I/O - a highly cost-effective and simple approach to field or machine wiring.

      Any kind of conventional two-state I/O device can be connected using a 'User Module' - which is actually an intelligent slave with a built-in interface chip. Many vendors have also launched stand alone 'intelligent' slaves which use the AS-Interface protocol for more than simple switching, e.g. parameterising a proximity switch on-the-fly. The original AS-Interface specification (V1) allowed for 31 slaves ('User Modules' count as one slave) to be connected and if you choose to use only intellligent devices such as a re-rangebale proximity sensor, then this is the maximum capacity of a network. However, User Modules can accommodate up to 4 inputs and outputs each. Thus, if 31 User Modules are connected a total of 124 Inputs and 124 Outputs are feasible, giving a maximum capacity of 248 I/O per network. The recently announced V2.1 Specification virtually doubles the capacity of a network (number of I/O increases to 186 + 248 = 434).

      Connected slaves are polled in turn by the master. A fully loaded V1 network offers a maximum response time of 5mS per I/O. Fewer connected devices means that cycle times are faster. AS-Interface telegrams (the data messages exchanged by master and slaves) have four useable output bits, and these are used to control connected devices - e.g. to open a valve, or close a switch. A slave answers immediately, returning four bits related to the control function, e.g. confirming the closure of a valve. The four input and output bits can be used for other functions, in particular the analog signalling possible with V2.1 devices. Each slave has a unique address which can either be programmed manually using a simple 'hand-held' or set automatically by the master.

      The AS-i bus provides both power and the data signal on the same wire pair. Power typically comes from a 24V floating DC supply which is fully isolated from the data signals on the devices. An AS-Interface network is typically rated up to 8A though the cable itself can handle more and sensible design allows currents higher than 8A to be drawn provided voltage drops in the network are as prescribed by the AS-Interface specification.

      International Standards to which AS-Interface complies include IEC62026 and EN50295. The AS-Interface specification is available free of charge to all members and no license fees are required to use AS-Interface devices (except Safety at Work Profile).

      AS-Interface Safety at Work Profile is an enhancement to the capabilities of AS-Interface, developed by a consortium of companies interested in machine safety and having the objective of introducing the benefits of networking to safety systems in European markets. A special slave, called a Safety Monitor, has the single job of monitoring the activity of Safety Slaves on the network. Typically, a Safety Sensor or Emergency Stop Button is connected to a Safety Slave and the AS-Interface network is responsible for transmitting safety signals to the Monitor, which contains relays to initiate the safety procedures. The profile can meet the requirements of international standards such as IEC 61508. The Safety Monitor and the Safety Slaves can co-exist with conventional AS-Interface devices in a normal network.

    Ethernet in industrial automation

    Ethernet is the most popular and widely accepted communications network, and it works at all enterprise levels. Use of Ethernet communcations is entering to industrial automation.Ethernet is entering to factories to the human-machine interface (HMI)/SCADA automation applications.The addition of industrial grade components as well as the availability of several media types, including fiber optics, gives Ethernet unmatched momentum. As a result, the Internet is now a part of human-machine interface (HMI)/SCADA automation applications. Combining Ethernet and TCP/IP allows users to control and monitor their industrial systems from anywhere in the world. Using HMI/SCADA and other software that has Web interface, one can monitor statistical process control and other process information. When applying Ethernet technology to process industry, the devices used in the plant needs to be somewhat differently built than their office environment counterparts. Industrial Ethernet products generally have more rugged heavy-duty design, can use redundant voltage supply, feature reliable no-fan operation, offer flexible topology structures (line-ring-star), can be easiily installed on a standard DIN rail, have signaling contacts for function control, operate from from O degree C to +60 degree C, operate from 24V DC industrial power supply, operate at 10% to 95% non condensing humidity and had good enough protection level in case (for example IP30).

    Here are some considerations on Industrial Ethernet network

    • When installing twisted pair cabling use at least CAT5 cable, preferably CAT5e or CAT6 cable
    • Install twisted pair cable enough far away from power carrying wires (at least 15 cm from 230 VAC and at least 20 cm from 400 VAC cables).
    • Use shielded cable on all noisy places (for example near welding machines and variable speed motor controls). The shielded cable should be grounded only from one end (cable with telescopic shielding ie even better). On very noisy places use fiber optics because it is immune to EMI.
    • You must take environment in consideration when selecting the connectors. In some places you need protection classes IP56 or IP67. Most RJ45 connectors on the market do no meet the needs of industrial Ethernet on reliabity on hard conditions.
    • When you are in very hard enviroments with lots of electrical noise or high voltages nearby, seriously consider using fibre optic connections instead of copper.
    • The cables and connectors in industrial environment need often withstand the following conditions: dirt, mechanical stress, oil, moisture/water, varuing temperatures (-20..+60 typical, can be harder)
    • Some plastics such as PVC become brittle at low temperatures, so be certain about temperature ratings. At low temperatures the insulation in most normal office Ethernet cables breaks.
    • Industrial Ethernet switches need typically to be able to operate in temperature range 0..60 C and run on 24V DC power. (Typical office switches use fans and are designed to operate at +10..+50 C and run from 110-120V or 220-240V AC power).
    • For twisted-pair cable, the RJ-45 remains the most popular connector although it is frequently criticised for its lack of robustness. There has been a movement to use IP67-rated micro-connectors for data rates up to 100Mbps. As a compromise, bulkhead-mounted boot-covered adapters exist allowing RJ-45 connectors to survive an IP67 environment.
    • Do not use copper cables to link buildings! The ground potential between the two buildings may be different. This can introduce transient voltages and any number of dangerous problems. Copper cable attracts lightning strike damages to the system. Use fibre to connect buildings instead.
    • If equipment is subject to washdown, or exposure to corrosive chemicals, be sure to select cables with insulation rated to withstand exposure to those chemicals such as PUR (polyurethane). Otherwise acids, fertilisers, and petroleum can be absorbed by the cable jacket and degrade the electrical characteristics of the conductors.
    • Are the cables to be subjected to flexing? Be absolutely certain that the cable is designed for this purpose.

    Industrial Ethernet systems are wired using different kind of connectors. In locations where environmental conditions are easy (control rooms, inside equipment racks etc.) typically normal RJ-45 connector without extra protection is enough. When you need a connector that can withstand moisture and dirt, you will need to look for better shielded connector. There are two groups of industrial Ethernet connector for hard enviroments: RJ-45 based connector based design and special industrial connectors. There is a selection of connectors that basically consist of normal RJ-45 connector that is surrounded by extra protective casing that protects it. There are various design and many protective case designs, typically incompatible with each other (I have seen round M connector sheels, XLR connector shell, push-pull type sheels, various industrial connector sheels etc.. adapted to take RJ-45 plug in). Some RJ-45 protective shell designa can be even put to a ready made normal Ethernet cable without need to remove and reconnect the RJ-45 plug from the cable. Other group of connector are made by taking exiting other industrial connectors (originally desinged for industry use in mind) and adapt the suitable models to carru Ethernet signals (100 ohm twisted pair). One polular type of connector is to use 4 pin M12 connector (M12 is widely used in instrumentation already) and use it to carry Ethernet signals. Four wires is enough to carry 10Base-T and 100Base-TX signals (but not Gigabit Ethernet that needs all four wire pairs available on RJ-45 connector). There are also other connector models in use.

    Most control system providers steer away from from discussions about Ethernet at the I/O bus level, because of its perceived speed and determinism. Ethernet can, on its own, provide very high speed, microsecond-level communication interchanges. The communication in full-duplex switched networks can be made also very deterministic with a well working Ethernet switch. The real-time problem is not with Ethernet, but with higher level protocols like TCP/IP and UDP/IP. When they are layered on top of Ethernet, the overall communications speed goes down into the millisecond range. From those protocols TCP was never designed to be very fast real-time protocol, but meterly a protocol that works well in congested networks to carry large amounts of data, so is not ideal for rela-time. The UDP protocol pretty simple protocol for simply sending and receiving packets over different networks. This protocol itself does not limit the real-time or speed in any way, but how it is implemented in many operating systems can have it's limitations. For those reasons the Ethernet's high-speed and real-time potential has gone unnoticed by many control systems vendors.

    Using an instrument as a Web server is a new aspect in industrial automation. Web-server technology is particularly well-suited to instruments that connect to Ethernet networks and that use TCP/IP (Transfer Control Protocol/Internet Protocol). It's true that Web-server technology has become so compact and inexpensive that individual sensors costing no more than a few hundred dollars each can transmit Web pages that users can view via the browser software of any Web-enabled PC. This works well on small systems, but can have it's downsides on large systems. Web server on each sensor approach quickly becomes unmanageable in applications that involve more than a few sensors. Applications involving hundreds and even thousands of sensors are common. To aggregate the multiple device outputs into a Web page that portrays the data in a form that users can understand, these applications need software that can't reside within individual sensors. Ethernet TCP/IP web servers are finding use at all system levels from field device to supervisory roles.

    Then configuring the devices, programmable logic devices and such generally support BootP service to se their IP address, network mask and default gateway. DHCP is a newer version of this protocol, but it is not yet widely supported. Some traditional Internet protocols that might be found on industrial devices are DNS (Domain Name Service), SMTP (Simple Mail Transfer Protocol) and SNMP (Simple Network Manegement Protocol).

    Typical use of TCP/IP and UPD/IP in automation is the following: TCP/IP is used for communication between the controllers and the controlling room. This communication is typically not time critical. UPD/IP is used for time-critical data, because it is light and simple. Because UDP/IP does not provide reliable transport, the errors in data transfer needs to be handler on application layer (different manufacturers have developed different protocols for this). UDP/IP is suitable for example for transporting cyclic control state data that is transmitter from tranmitter to receiver often and same data is repeated. In this case some packets lost due noise or network error does not cause considerable problems because same information is sent over again soon. There are also some low level I/O controlling protocols that run directly on top of Ethernet without IP.

    Ethernet and TCP/IP alone does make a device open, also higher level protocols needs to be open. Most Ethernet based automation devices in use nowadays are more or less proprietary. Industrial Automation for open Networking Allance (IAONA) is working on to advance the use of Ethernet in automation. Modbus originator Schneider Electric predicts that standards-based Industrial Ethernet will enter just about just about every area of industrial network communications - including even those areas which are presently and comfortably occupied by fieldbus and similar. Ethernet is expected to substitute most proprietary network technologies.

    Here is overview of serveral networking protocols that are used on Ethernet based industrial networks:

    • Profinet: Profiner is an integrated and open Industrial Ethernet standard for automation. Automation with Real-Time Ethernet. Uses TCP/IP and IT standards. PROFIBUS International supports the dissemination of PROFINET.
    • Modbus TCP: Modbus protocol (originator Schneider Electric) isa dapted to be carried over TCP/IP. Modbus TCP is based on Modbus-RTU protocol adapted to be carried over TCP/IP. Standard is controlled by Modbus-IDA. Modbus TCP does not have hard realtime support built in. Large market share.
    • EtherNet/IP: EtherNet/IP extends commercial off-the-shelf Ethernet to the Common Industrial Protocol (CIP?) ? the same upper-layer protocol and object model found in DeviceNet. CIP allows EtherNet/IP and DeviceNet? product developers, system integrators and users to apply the same objects and profiles for plug-and-play interoperability among devices from multiple vendors and in multiple sub-nets. Ethernet/IP uses all of the protocols of traditional Ethernet including the Transport Control Protocol (TCP), the Internet Protocol (IP) and the media access and signalling technologies found in all Ethernet network interface cards (NICs). Large market share.
    • Foundation Fieldbus High Speed Ethernet (HSE): Foundation Fieldbus H1 adapted to Ethernet
    • Ethernet POWERLINK: Ethernet for high performance Real-Time networking systems (microsecond timing) based on the ETHERNET Powerlink Real-Time protocol, introduced by B&R end of 2001. Powerlink manages this process by breaking the communication cycle into time slots, each of which usually relates to a particular device. These time slots can also be shared among a group of 'less critical' devices in a manner similar to time division multiplex, providing a means of bandwidth optimisation. Standard Ethernet frames are used, ensuring compatibility with the IEEE 802.3 standard for Fast Ethernet. In this way, all IP based protocols (TCP, UDP) can be transferred at the same time as isochronous time-critical data, providing seamless integration from higher order IT systems down to the drives and sensors on the shop floor, and Internet access for remote control and diagnostics. Developed by EPSG (ETHERNET Powerlink Standardization Group) that works in co-operation with CAN in Automation Group, the IAONA, the IEC and the ISO. Supported by Lenze, Hirschmann and Kuka Robots, B&R.
    • EtherCAT: EtherCAT is an Ethernet-based fieldbus system. EtherCAT is the new open real-time Ethernet network developed by Beckhoff. EtherCAT sets new standards for real-time performance since it processes 1000 distributed I/O in 30 ?s or 100 axis in 100 ?s using twisted pair or fiber optic cable. The EtherCAT protocol is optimised for process data and is transported directly within the Ethernet frame thanks to a special Ethertype. It may consist of several sub-telegrams, each serving a particular memory area of the logical process images. EtherCAT UDP protocol version packages the EtherCAT protocol into UDP/IP datagrams. EtherCAT is an open technology for which IEC standardization is in progress.

    One of the most notable trends in manufacturing today is the desire to integrate real-time operating and equipment status data from field devices and measurement and control systems with enterprise-wide systems controlling overall plant production and asset management. End-users want a seamless exchange of production and equipment status information across the plant floor with production management and business systems. One of the biggest barriers to achieving this goal is the inability to easily integrate information from plant-floor measurement and control systems with production and maintenance management systems. There is a great deal of momentum in the plant automation and condition monitoring industries to provide integrated solutions based on open industry standards that leverage off-the-shelf, commercial computer hardware and software technology such as Ethernet networks, XML (eXtensible Markup Language), and the Internet to provide access to information. OPC has emerged as the worldwide industry standard, enabling connectivity and interoperability of plant-floor information between disparate fieldbus networks, programmable controllers, distributed control systems, condition monitoring, plant asset management, and production management systems. OPC has emerged as the worldwide industry standard, enabling connectivity and interoperability of plant-floor information between disparate fieldbus networks, programmable controllers, distributed control systems, condition monitoring, plant asset management, and production management systems. HMI, DCS, SCADA, modeling, simulation, advanced control, CMMS, EAM, scheduling, and other applications can act as OPC clients and servers to permit data exchange between cooperating applications. Any application software that supports the OPC client interface can exchange information with any device, control system, or industrial network that provides an OPC server interface.

    The OPC DA specification defines a set of standard COM objects, methods, and properties that specifically address interoperability requirements for factory automation, process control, and machine condition monitoring applications. OPC DA leverages DCOM, allowing client/ server applications to access plant-floor data via an Ethernet network distributed across the manufacturing enterprise. Many suppliers ship products with built-in OPC support. OPC DA based on COM/DCOM is primarily used to provide horizontal data integration and interoperability between measurement and automation systems on the manufacturing floor and plant applications performing monitoring, alarming, historical data collection, and supervisory control. The current OPC DA 3.0 specification primarily deals with scalar data that represents 90 percent of typical plant floor data. Scalar data might represent machine operating parameters from analog measurements such as pressure, temperature, flow, level, and vibration, or discrete signals used to represent on/off state or abnormal alarm conditions.

    XML-DA technical working group is creating a new standard with more features. OPC XML-DA provides vertical integration between the plant floor and condition monitoring, maintenance, production management, and enterprise applications using XML, HTTP, and SOAP industry standards. The OPC Foundation selected XML as an alternative to the existing OPC DA COM-based specification for moving plant floor.

    • An Ethernet World Bus Tour - Explore real-world industrial applications to see how Ethernet has become a true world bus    Rate this link
    • Ethernet/IP Overview - The Industrial Ethernet Protocol (Ethernet/IP) has been developed by ODVA with strong support from Rockwell Automation. It uses the Control & Information Protocol (CIP) which is already well known from ControlNet and DeviceNet. CIP provides a wide range of standard services for access to data and for control of network devices via so-called "implicit" and "explicit" messages.    Rate this link
    • A revolution in industrial networking? - Ethernet-based communication TCP/IP protocols are starting to invade all levels of the mass communication market but, as Mark Jackson of Pulse points out, Power over Ethernet (POE) is set to revolutionise industrial-based networking systems    Rate this link
    • EtherMATE - Industrial Ethernet connector model for hard environment.    Rate this link
    • Ethernet rules closed-loop system - Traditional process control systems have used programmable logic controller (PLC)-based centralized control techniques to implement closed-loop control applications. Packet-based networks with collisions, such as Ethernet, are generally considered too slow and unreliable to safely handle closed-loop control. Use of synchronized clocks in data-driven closed-loop control systems using Ethernet as the field bus is a viable solution.    Rate this link

    Communication interfaces

    Instrumentation interfaces

      General information

      Voltage interfaces

      Industrial control systems continue to employ standard analog signals for transmitting data between the process and the control equipment. For example ?5 and ?10V signals are also very common in industrial systems, where signals do not be transported for long distances. A typical voltage interface used in 0-10V interface. This is widely used in many measuring and controlling applications. In some special apllications you can also find -10V to +10V interface. In some case you might also encounter 0-5V or 1-5V interfaces.

      Nowadays current loops interfaces are favoured in many applications, because robust 4-to-20mA or 0-20mA current-loop signals can be easily transmitted over several thousand feet.

      4-20 mA Current loop interface

      4-20mA is an analog current loop protocol which has become the defacto U.S. standard for supplying DC power to a field transducer, and receiving a scaled return signal. DC power is typically supplied via an unregulated +10 to +30Vdc supply. Many industrial current-loop data acquisition systems operate on a 24V or 28V single supply. The field transducer controls the current flow, and is often referred to as a 2-wire "transmitter". You can easily receive 4-20 mA signals by passing the current through 100 ohm resistor, so you get 0.4-2V voltage over the resistor. 4-20mA current signals can be also quite easily opto-isolated using optocouplers. There are many reasons why current loop was chosen in automation instrumentation applications. Current-based signal systems are much more stable and resistant to outside influences than voltage based. For transmitting low-amplitude low-frequency signals over several hundred yards in a noisy industrial-control environment, current is preferred over voltage, because the current at any instant is constant over the entire length of the cable. Voltage transmission is not recommended, because the voltage at any point depends on line resistance and capacitance, which change with the cable's length. Current transmission also allows a single 2-wire cable to carry power and signals at the same time. Also it is actually fairly difficult to create unwanted CURRENT flows in a signal wire due to crosstalk or other induced voltages. Typical induced voltages are small, and easily swamped out by the loop driving voltage. At the end of the transmission line, a precise termination resistor converts the loop current to an accurate voltage. This resistor (typically 50 to 750) establishes the current-loop receiver's input impedance. A high signal-source impedance minimizes voltage fluctuations across the termination resistor caused by variations in line resistance, but it also picks up more EMI and other industrial interference. Large-valued bypass capacitors reduce EMI pickup by helping to lower the signal-source impedance. To summarize, current loops offer four major advantages:

      • Long-distance transmission without amplitude loss
      • Detection of offline sensors, broken transmission lines, and other failures
      • Inexpensive 2-wire cables
      • Low EMI sensitivity
      In fact, the driving voltage of a typical 4-20mA system can vary from about 10Vdc to 35Vdc with the current signal still under control. Thus the poor electrical connection which would ruin a voltage signal might work fine with a current signal. There is one truly remarkable thing about 4-20mA communication: the ability of the sensor transmitter to be powered by the same two wires that carry the loop signal! Lowered wiring cost may be the single biggest reason for the dominance of 4-20mA. No separate viring is need to supply power to the transducer! You can feed a 4 to 20 mA signal to an a channel in two separate modules signal processing, connected in a series loop in some special cases. First the oputs of those modules need to be "floating" (isolated from ground) in at least one of the modules receiving the signal. Also the transmitter will have to be capable of driving the 4 to 20mA signal into the total resistance of the two modules. When receiving the 4-20 mA signal, there are different possible circuits. One of the simplest approach to convert 4-20 mA current to voltage signal is the following: feed the current through a known resistor and measure the voltage over the resistor. For example a 250 ohms resistor will nicely convert 4-20 mA current loop signal to 1-5V voltage range (you can feed this nicely to 0-5V ADC input). Many current loop sensors/transmitters are configurable to send currents out of allowed 4-20 mA range in case of sensor failure. In those applications the current ie either considerably more than 20 mA (typically 22-23 mA) or considerably less than 4 mA (3 mA or less). The 4-20 mA current loop was not the only system proposed. A 10-50mA standard was around before 4-20mA, but lost the long-term battle for dominance. Also 0-20 mA has been used in some applications, but it lacks the ability to supply power to the sensor through the same wire. 4-20mA has won the battle, andit is predicted that 4-20mA will be around for a long, long time.

      HART

      HART? is a digital communications protocol using a 1200 baud Frequency Shift Keying (FSK) digital signal which is superimposed over a conventional 4-20mA analog signal. HART is the de-facto digital communications standard for the process industries using conventional 4-20mA analog loops. With HART system a single twisted pair of wire (plus shield), can supply power to the transducer, carry the output signal, and with HART? also carry setup, calibration and transducer integrity information between the transducer and the control system.HART? is an industry standard with over 5 million HART? field instruments installed in more than 100,000 plants worldwide, it is the most widely used digital communications protocol in the process industry.

    Real-world controlling

    Automation software information

    Design guides

    PID controlling

    PID (Proportional-Integral-Derivative) control action allow the process control to accurately maintain setpoint by adjusting the control outputs. Proportioning control continuously adjusts the output dependent on the relative positions of the process temperature and the setpoint. PID (Proportioning/Integral/Derivative) are control functions commonly used together in today's controls. These functions when used properly allow for the precise control of difficult processes. Please note that there is no single PID algorithm. Different fields using feedback control have probably used different algorithms ever since math was introduced to feedback control. Also there is no standard terminology.

    Presently there are three basic forms of the PID algorithm. Expressed by their Laplace transforms the three forms are:

    First form: Kc(1 + 1/Tis)(1 + Tds)/(1 + Tds/Kd)
    Second form: Kc'(1 + 1/Ti's + Td's)
    Third form: Kc" + 1/Ti"s+Td"s

    where

    • Kc, Kc' and Kc" relate to the P part of PID
    • Ti, Ti' and Ti" relate to the I part of PID
    • Td, Td' and Td" relate to the D part of PID
    • s is the Laplace notation for derivative with respect to time
    • Kd is the derivative gain

    The first form is called "series" or "interacting" or "analog" or "classical". The variables are:

    • Kc = controller gain = 100/proportional band
    • Ti = Integral or reset time = 1/reset rate in repeats/time
    • Td = derivative time
    • Kd = derivative gain

    Early pneumatic controllers were probably designed more to meet mechanical and patent constraints than by a zeal to achieve a certain algorithm. Later pneumatic controllers tended to have an algorithm close to this first form. Electronic controllers of major vendors tended to use this algorithm. It is what process industry control users were used to at the time. Most major vendors of digital controllers provide first algorithm as basic, and many provide also provide the second form as well. Also, many provide several variations.If you are unsure what algorithm is being used for the controller you are tuning, find out what it is before you start to tune. Different algorithms behave differently.

    Industrial Control Programming

      IEC 61131-3

      IEC 1131-3 was the first real endeavor to standardize programming languages for industrial automation. It is independent of the efforts of any single company. IEC 1131-3 work is now known as IEC 61131-3 standard.IEC 61131-3 is the only global standard for industrial control programming. It harmonizes the way people design and operate industrial controls by standardizing the programming interface. The standard includes the definition of the Sequential Function Chart (SFC) language, used to structure the internal organization of a program, and four inter-operable languages: Instruction List (IL), Ladder Diagram (LD), Function Block Diagram (FBD) and Structured Text (ST). IEC 61131-3 provides a standard definition for their software development environments. Basically, IEC 61131-3 consists of two parts, i.e. Common Elements and Programming Languages. The structuring tools within IEC 1131-3 are focused on the common elements, although, clearly, links to the programming languages are needed.

Home automation

Modern homes with an emphasis on comfort and convenience are being increasingly equipped with programmable installation technology that has already become a matter of course in functional buildings.

    General information and resource pages

    Standards

      X10

      X10 is a communications protocol for remote control of electrical devices. It is designed for communications between X10 transmitters and X10 receivers which communicate on standard household wiring. Transmitters and receivers generally plug into standard electrical outlets. X10 signaling adds few bursts of around 121 KHz signal to the mains power near the mains zero crossings. Those bursts contains the data sent.

      Lonworks

      LonWorks technology allows you to build a network of intelligent devices from different manufacturers for many applications including home, building, and factory automation. You can monitor and control these networks remotely. Lonworks networks can can range in size from two to 32,000 devices. Devices in a LonWorks network communicate using LonTalk, the standardized language of the network. LonTalk consists of a series of underlying protocols that allow intelligent communication among various devices on a network. The protocol provides a set of services that allow the application program in a device to send and receive messages from other devices over the network without needing to know the topology of the network or the names, addresses, or functions of other devices. LonTalk uses per to peer (P2P) network architechture. LonTalk protocol is defined in ANSI approved standard EIA/CEA-709.1-A-1999. LonTalk and thus LonWorks networks can be implemented over basically any medium, including power lines, twisted pair, radio frequency (RF), infrared (IR), coaxial cable and fiber optics.

      EIB

      The EIB is an intelligent building control system which is able to control, regulate, measure, switch, service and monitor. Its basis is a communications bus which lies in parallel with the 230V mains network. Intelligent system components, operating by distributed control, are coupled to this communications bus. Connection of the bus can be in linear, star or tree configurations which allows flexibility in the applications in all forms of modern electrical installation. EIB signals can be transmitted through twisted pair wiring and also through mains power network.Each system component can be programmed to perform prescribed functions in combination with other system components, either from controlling elements within the system or via PC control. Together, these form the infrastructure of the basic functional level of the system. Two types of system component are used: Sensors (Transmitters) and Actuators (receivers).

      The EIB installation consists mainly of sensors (senders) e.g. light barriers, switches, thermostats, infrared, timers and actuators (=receivers) controlling engines, heaters, ventilators, lights and blinds. A tpyical EIB cable is screened installation cable based on type J-Y(ST)Y according to DIN VDE 0815, conductor single-wired, bare copper, diameter 0.8mm, measurements 2 x 2 x 0.8 diameter, 4 single-wired cores twisted to a star quad.

    Project pages and software

    Related pages


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