I wrote about EMF measurements and told that for magnetic field measurements I have used Velleman Magnetic Field Detector VTEMF. Velleman describes the product uses: “Detects the harmful electromagnetic fields generated by high voltage cables, computer and television screens, microwave ovens, waterbeds, electric blankets, etc.”.
That sounds reasonable. The description continues “Scientists believe that electromagnetic fields of 2-3mG and above, increase the risks of cancer and other dangerous disorders”, which is gives some numbers but it is hard to say based on recent research if those levels cause any problems or not.
Anyways being able to measure varying magnetic fields is useful, and this meter is much more more sensitive in that than my DIY magnetic field measurement adapter.
Here is the picture of the product:
VTEMF Magnetic Field Detector User Manual says that VTEMF detects well the low-frequency fields (like caused by 50-60 Hz currents). The device had LED indication: 1, 3, 6 and 10mG (milliGauss) magnetic field strengths. In addition the meter has a beeper that makes sound when highest level LEDs are on. (If you want results in other units then think that 1 mG = 0.1 uT and 1 A/m = 12.6 mG).
When searching for information on VTEMF meter on Internet (I was looking for the manual and comments on meter), I found an interesting note on VTEMF: some ghost hunters use this meter and have rated it as good tool, although there is no evidence connects the use of EMF meters for ghost detection.
A look inside VTEMF meter:
As you can see in the picture there is a large air cored coil that acts as the magnetic field detector (you need to aim it to point to the source to get best reading). Signal from coil is fed to amplifier, rectifier and display control circuitry. I have not reverse-engineered the measuring circuit inside meter, but I think it would resemble pretty much LED VU meter or similar device.
When I tested the meter with different magnetic fields, it seemed that it gave somewhat sensible measurement results (although without any accurately calibrated magnetic field or instrument to compare is hard to say anything on the absolute accuracy). I found some sources of EMI easily with it. I get the device beeping near wall-warts. I found magnetic field near mains distribution panel and some equipment. VMEMF also detects bass beats when put near bass speaker (light ups to few milliGauss flashing). I have also used VTEMF as a debug tools when trying to figure out why noise gets to some audio/video systems.
Besides detecting mains frequency fields, I have found that VTEMF also detects higher frequency fields up to few kHz with somewhat reduced sensitivity. I did tests with a coil connected to a signal generator to get idea of the frequency response. It also seemed detect (reduced sensitivity) also electronics tooth-bush chargers (operating at 10-22 kHz frequencies).
This VTEMF seems to be OK meter for measuring magnetic fields. The list prices I found this meter seems to be around 35-60 Euros depending where to buy it. I got mine years ago at much cheaper price.