EMF meter GM3120

Have you ever wondered about how safe your place or position is regarding electromagnetic and magnetic fields? Then here is your chance to find out. Everyone is exposed to a complex mix of weak electric and magnetic fields, both at home and at work, from the generation and transmission of electricity, domestic appliances and industrial equipment, to telecommunications and broadcasting.

There are different views how those field can affect you. There are established biological effects from acute exposure at high levels (well above 100 µT) that are explained by recognized biophysical mechanisms. But foe low level field there is no one universal truth. Some members of the public have attributed a diffuse collection of symptoms to low levels of exposure to electromagnetic fields at home, but there is no solid evidence on those. To date, scientific evidence does not support a link between various symptoms and exposure to electromagnetic fields. IARC published a monograph classifying ELF magnetic fields as “possibly carcinogenic to humans”. According to IARC there has been found increase in childhood leukaemia associated with average exposure to residential power-frequency magnetic field above 0.3 to 0.4 µT. But there are no accepted biophysical mechanisms that would suggest that low-level exposures are involved in cancer development.

The Shady Science of Ghost Hunting often makes use of different kind of detectors, including EMF meters. EMF meter is among the most common devices used by ghost hunters today. The association between EMF meters and ghosts is frequently made, but there is no firm evidence connecting the two. I don’t believe in ghosts, bit I thought this should be mentioned here.

Electromagnetic fields can also affect electronics. Electromagnetic interference (EMI) is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. Both man-made and natural sources generate changing electrical currents and voltages that can cause EMI. In case electrical circuit receives unwanted EMI, a meter that can give idea of EMI around the circuit can be helpful in fault finding.

An EMF meter is a scientific instrument for measuring electromagnetic fields (abbreviated as EMF).EMF meters measure fluctuations in electromagnet fields. Measurements of the EMF are obtained using an E-field (electrical field) sensor or H-field sensor (magnetic field). I have earlier tested Velleman VTEMF meter for measuring alternating magnetic fields (calibrated to measure 50 and 60 Hz alternating fields ). I have also tested DT-1180 Electrical field and RF meter for measuring electrical fields. This time I am testing GM3120 Electric Magnetic Radiation Detector Tester Phone PC Home Equitment Radiation Monitoring with Lcd Display product that promises to measure both magnetic field and electrical field at the same time. It’s interesting to see how much electromagnetic radiation around us at home!


GM3120 features:

- can test the electric field and the magnetic field radiation at the same time

- Unit: V/m (Electric Field); μT(Magnetic Field)

- Measurement range: Electric: 1-1999V/m; Magnetic: 0.01-19.99μT

- sound-light alarm, when the test result exceeds the safe value, the instrument will alarm automatically. 

- Alarm Threshold: Electric: 40V/m; Magnetic: 0.4μT

- data locking key

- LCD display (3-1/2 LCD Display)

- processing by control micro-chip

- Test Bandwidth: 5Hz-3500MHz

- Sampling Time: Approx. 0.4 Seconds

- Power Supply: 1 x 6F22 9V Battery

- Size: 12.5 x 6 x 3cm / 4.92 x 2.36 x 1.18in (L x W x H)

- Weight: 109g / 3.84oz

Data on back

I am still testing this EMF n detector but it already comes out with some interesting results. Item performance are quite satisfactory, considering its cheapy price. It is easy to use. It detect well mains frequency fields. The alarm levels are so low that the meter alarms very often in very many locations at a normal house. That’s a bit annoying and make you want to turn off the alarm beep (that can be done with button). With alarm turned of it can be used as quite nice EMF field surveying instrument.

Device performance are quite satisfactory, considering its cheapy price. It detects the 50 Hz or 60 Hz of main power and electrostatic charges well. At those measurements the performance was pretty much in line the separate instruments I had, meaning that they gave somewhat similar looking results (I did not have any tightly controlled lab to test the actual accuracy). This device can detect mains power cables in walls. In addition the device seems to detect also radio frequency signals (Wifi at 2.4GHz, PMR at 446 MHz, cellular phone). The meter seems to pick up electrical fields towards top end best. For magnetic fields it seems to pick strongest the fields from the side of the meter. In real world field testing you should try neter in different directions ti get reading from strongest electrical and magnetic fields.

The plastic case of this device is very cheap looking and has cheap feeling. Otherwise the construction seems to be OK. The measurement works OK, but sometimes the response to the changing fields seems to be somewhat slow.

Here are some measurement results with PRM446 (446 MHz radio with maximum power of 500 mW ):

Magnetic field next to big utility transformer that powers several buildings:

A look at the electrical and magnetic fields near 110 kV power line:

Some useful conversions between units are:

1 uT = 0.7958 A/m

1 A/m = 1.257 uT

1 T = 10,000 gauss

Here is a look inside the EMF meter:

The piece of bare circuit board on the front of the device acts like capacitive sensor for electrical field. The red component that looks like big resistor is a coil used for picking up magnetic field.

Her you can see the circuit more closely. It looks like the signal from electrical field sensor is amplified with FET and the signal from coil goes pretty directly to the rest of the circuitry.

GM3120 Electric Magnetic Radiation Detector Tester seems to work and do measurements. With my short testing it is hard to say how accurate this device really is on different situations and at different frequencies. The manufacturer has web page for GM3120.


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