by Richard Conrad, Ph.D., 6/19/10
Most gaussmeters (magnetic field meters) are designed primarily to measure 60 cycle magnetic fields from house wiring. They usually are not accurate at frequencies much higher than 60 cycles, and are largely insensitive to frequencies in the Megahertz and Gigahertz range, where most monitors and computers have much of their emissions. A useful, inexpensive ($99. from Frys Electronics on line, the last I looked) milligauss meter for measuring magnetic fields from house wiring and power lines is the standard analog TRIFIELD meter by AlphaLab (their least expensive model: Trifield Meter 100XE). It is very helpful that a gaussmeter measure all three field directions simultaneously, as the Trifield does.
EXPLANATION OF TERMS:
Gauss = a unit of magnetic field strength, magnetic field intensity. This is different from frequency (see below) and can be for either DC or AC current. Any flow of electric current in a wire generates/has associated with it a magnetic field.
Milligauss = one-thousandth of a gauss.
Three field directions: every magnetic field has a directionality associated with it. The intensity of a magnetic field is usually different in different directions (for example, vertical axis, vs front-to-back horizontal axis, vs left-right horizontal axis). If one uses a meter that measures only one direction/axis at a time, it is easy to miss an even greater intensity along another axis.
Frequency. A flow of electric current is either: all in one direction (DC, or Direct Current, frequency = 0); or oscillating back and forth at a particular rate or frequency (AC, or alternating current). Frequency is expressed in number of alternations/reversals/cycles per second, or cps, but more commonly today in Hertz.
Hertz or Hz = cps (cycles per second);
KiloHertz or KHz = thousands of cps;
MegaHertz or MHZ = millions of cps;
GigaHertz or GHz = billions of cps.
Low frequencies are for example, 60 Hertz AC house current and higher harmonics on dirty house current such as 180 Hertz. Radio frequencies are in the KiloHertz and MegaHertz range (for example, the AC noise on top of DC power from switching power supplies and the EMF RF emissions from computers and computer screens).
Microwave frequencies are in the GigaHertz range, such as from microwave ovens, cell phones and cordless phones, Wi-Fi and also from computers and computer screens.
Frequency measurements, magnetic field measurements, and electric field (=Voltage) measurements are all separate things. A gaussmeter measures not frequency, but magnetic field intensity, and it is sensitive to magnetic fields only over a certain frequency range. (Some meters, like the Trifield, have a knob that can be turned to change it into an electric field strength meter.) The frequency sensitivity of a meter can be expressed as a graph or curve that usually looks like a mountain. For example for the Trifield meter begins to sense magnetic field strength at about 40 Hz, its sensitivity rises to a maximum at 500 Hz, and then falls off above 10 KHz.
The Trifield Meter 100 XE has a meter with a needle readout, which gives faster readings and is easier to use to scan an enviroment, see trends, changes, etc, than a meter with a digital readout. (Also, meters with digital readouts generate their own EMF, which can affect persons with EHS - Electrical hypersensitivity). Trifield also has a "Trifield BroadBand Meter 100XE Meter", which costs more but is not really any more useful, since its increased sensitivity in the electric field radio frequency range does not make it even near as sensitive as most people with EHS are. The frequency response specifications of the Trifield meters are given at: www.trifield.com/content/trifield-meter/
For using a gaussmeter to measure the magnetic fields in your home, see the excellent, easily understandable book by Karl Riley: "Tracing EMF's in Building Wiring and Grounding" which is available from:
The Trifield meters are useful as gaussmeters to measure magnetic fields from 40 Hz to about 10 KHz. Their greatest sensitivity is at 500 Hz. House current and power line frequency is 60 Hz, with harmonics from dirty power possible at 180 Hz and higher. The Trifield meter displays readings from about 0.1 milligauss up to 100 milligauss. In Europe, they recommend environments to be below 3.0 milligauss. Anything above 3 milligauss has the potential to induce EHS in susceptible persons who live within it for any length of time. Most persons with EHS should keep their environment below 0.3 milligauss, and for some, below 0.1 milligauss is necessary to not have symptoms. Most of the emissions from computers are above 100 KHz, in the Megahertz range, and go all the way up into the Gigahertz range, which is the microwave range where cell phones, Wi-Fi and microwave ovens emit. For detecting these high frequencies, there are many different meters available from $300. to $3,000. and up, but you can get good idea of high frequency emissions by using a simple portable AM radio as described in the article: AM RADIO AS INEXPENSIVE HIGH FREQUENCY SENSOR.