Electromagnetic Measurements and the Tri-Field Meter

Electromagnetic Measurements and the Tri Field EMF Meter Direct and indirect evidence suggests that AC electric and magnetic fields increase the risk of certain cancers and other physiological and psychological abnormalities. Although how this happens is not fully understood, both magnetic and electric AC fields that surround the body can produce AC electric current inside the body. The best available theory is that this current interferes with the normal transport of ions across cell membranes. (1)

At a continuous exposure of about one billionth of an amp of AC current per square centimeter (give or take a factor of three), biological effects begin to be observed. Very preliminary results show that at five times that level, for example, an increase in protein production in cancer cells is seen; but when the field is increased 1000 times further, the increase in protein production is only three times greater (not 1000 times greater). These changes are seen for AC current at several different frequencies, including 60 Hz (60 oscillations per second). (2)
If the cell-membrane-interference theory is correct, the body should be sensitive to current at any frequency up to about 1000 Hz (the exact upper limit frequency is not known and experimental measurement of it has not been attempted).

Based on the above evidence and some epidemiological studies, (3) it would be prudent to avoid continuous exposure to any electromagnetic pollution that produces AC current inside the body higher than one billionth amp per square centimeter, at frequencies of 1000 Hz or below. (No absolute hazard threshold has been established yet, but the lower limit for biological effects is probably between one-third and three times that level). Preliminary results suggest also that it's better to spend a short time well above this threshold than a long time just above it.) At frequencies above 1000Hz, the body is likely also to be sensitive, but not as sensitive as it is to lower-frequency currents.

An external magnetic field of 3 milligauss or an electric field of 2.5 kilovolts/meter at 60 Hz will produce approximately one billionth amp per square centimeter. The current produced inside the body is proportional to field strength times frequency, so at 120 Hz (twice the frequency), only half as much field (i.e., 1.5 milligauss and 1.25 kilo-volts/meter respectively) is required to produce the same current inside the body. Interestingly, a fairly strong magnetic field (500 milligauss) and electric field (about 2 kilovolts/meter) exist in nature, but these fields are static, and thus have a frequency of zero - they produce no current inside the body.

Therefore, an electromagnetic pollution meter should be frequency weighted, meaning that it reads the product of magnetic field strength times frequency and/or electric field strength times frequency, if it is to gauge whether the electric current inside the body exceeds a threshold level. This frequency-weighting should extend up to about 1000 Hz and then the meter sensitivity should decrease at higher frequencies.

Magnetic and electric fields are vector quantities. This means they are specified as having a magnitude (or field strength, measured in milligauss or kilovolts/meter respectively) as well as a direction (an "arrow" showing which way they are pointing). The effect on the body is more or less independent of the direction of the field; only the magnitude is important. Virtually all field meters read the field strength in one direction only. The sensor of these meters must be pointed in the same direction as the field happens to be pointing; otherwise the meter will read less than the true magnitude of the field strength. If the sensor is pointed perpendicular to the local field direction, the meter will read zero, no matter how strong the field is. Then it will completely miss the field. To avoid this inaccuracy, a meter should read the true magnitude of the field, so a user could walk through a room with a meter and get an accurate, immediate reading of the field magnitude at every point along the path, regardless of which way the meter is oriented.

This TriField meter combines all the features needed for fast, accurate screening of electromagnetic pollution. It independently measures electric field and magnetic field and is properly scaled for both, to indicate the full magnitude of currents produced by each type of field inside the body. As a result, it "sees" much more than any other electromagnetic pollution meter. Depending on where the knob is set, it detects either frequency-weighted magnetic fields (two separate scales) or frequency-weighted electric fields in the ELF and VLF range (it has significant sensitivity at 100,000 Hz, well past the 17,000 Hz horizontal scan of video displays). It also has a setting which lets you gauge radio wave power all the way up to three billion Hz (3 GHz), which includes home microwaves (2 GHz), CB and cellular phone equipment, and many radars.

This TriField meter is also the only one which combines magnetic, electric, and radio/microwave detectors in one package, so the entire non-ionizing* electromagnetic pollution spectrum is covered. In addition, the magnetic setting and the electric setting measure true magnitude, a feature found elsewhere only in very expensive meters. If you hold the meter in the center of a room and tip it to various angles, the magnetic reading will stay approximately the same (+/- 15% typical) regardless of which way you tip or rotate it. The electric reading is similar, although the presence of your body alters the actual electric field, so readings will vary more. The radio/microwave setting reads full power radiated into the front of the meter.

Surprisingly, the TriField meter is one of the least expensive meters available. The few other meters below $200 read only low-frequency magnetic fields and only one direction (not true magnitude). The magnetic section of the TriField meter has three field-detecting coils pointing in the X, Y, and Z directions. A circuit amplifies these signals and gives them the proper frequency-weighting (sensitivity increases linearly from 30 Hz to 500 Hz, it stays level to 2000 Hz, then it falls off slowly to near zero at 100,000 Hz, but with some residual sensitivity up to 100 MHz). A unique network combines the three coil outputs non-linearly to approximate a true magnitude. The meter is sensitive from .2 to 100 milligauss full scale at 60 Hz (or .1 to 50 milligauss full scale at 120 Hz, etc.) with a resolution of .2 milligauss in the sensitive range. Accuracy is +/-20% at mid-range.

In most homes and offices, a large fraction of the total magnetic field is at frequencies above 60 Hz. A TriField meter, when exposed to a 3 milligauss field, will read "3" if the frequency of the field is 60 Hz, but it will read "6" if the 3 milligauss field is at 120 Hz. In contrast, a non-frequency-weighted meter will read "3" in both cases, and a 60 Hz-only meter will read "3" and "0" respectively (even though in the 120 Hz case, the current induced in the body is twice as much.) This underscores a problem with present epidemiological studies of magnetic field health effects: generally, non-frequency-weighted meters (or even 60 Hz-only meters) were used. Indications are that in homes where these meters read consistently above 3 milligauss, the chance of developing certain cancers is increased. Depending on the distribution of frequencies (which was not recorded in the studies), a TriField meter would generally read between "3" and "9" if the other meters read "3". Consequently, the threshold for the TriField might be more appropriately placed as high as "9" milligauss, with the uncertainty arising because previous studies did not measure frequencies above 60 Hz in a standard or uniform way.

The electric section consists of four metal plates under the meter face. Because the meter housing is plastic, the electric fields can go through to the plates, which are also arranged to detect AC electric fields in the X, Y, and Z directions. Circuitry similar to the magnetic section converts the signals into an electric field signal which is frequency-weighted. Sensitivity is .5-100 kilovolts per meter at 60 Hz, with resolution of .5 kilovolt/meter. Accuracy at mid-range is +/-30%.

Radio and microwaves are composed of a particular combination of electric fields and magnetic fields that is self-sustaining. For frequencies below about 100 MHz (100 million Hz) the principle effect on the human body is from the magnetic field part only. This is because the electric field component of radio waves produces much weaker currents in the body than does the magnetic field unless the wavelength of the waves is smaller than the height of the body. Low-frequency electric fields by themselves can be strong enough to create significant current, but only if they are from sources other than radio waves.

The radio/microwave section has a small L-shaped antenna in the front. The signal is amplified and converted to a power density magnitude, calibrated at typical home microwave oven frequency (2 GHz). It reads 0 to 1 milliwatt/square centimeter. The resolution in the low range is .01 mW/cm2, which is the Russian standard for maximum safe microwave exposure to avoid changes in brain activity, (4) and is the most conservative standard of any country. (The new OSHA safety threshold, as of 1-1-93 is 1 mW/cm2, down from the previous 10 mW/cm2). Typical accuracy is within a factor of two. Variations are caused by reflections off the user's hand and body.
A knob on the front has six positions: OFF, BATTERY TEST, two MAGNETIC field sensitivities (.5-100 milligauss at 60 Hz, and .2-3 milligauss at 60 Hz, to measure low fields more accurately), ELECTRIC field and RADIO/MICROWAVE power density. The meter face is analog (needle type). A needle reading of one-third of full scale corresponds to either .6 milligauss or 3 milligauss @ 60 Hz, 3 kilovolts/meter @ 60 Hz, or .04 mW/cm2 respectively in the magnetic, electric, or radio/microwave field settings. Long-term personal exposure to levels higher than these should be avoided, so the meter is labeled "HIGH", above these levels. Unfortunately, because of uncertainty of population studies, the true health-effect threshold may be as low as 1 milligauss or as high as 10 milligauss.

In most homes or offices, some areas are "hot" spots with readings in the HIGH range. Most often, this is caused by magnetic fields, which come largely from unpaired internal wiring. (Contrary to popular belief, outside power transmission lines and transformers do not generally contribute as much magnetic field as does internal wiring.) Other magnetic sources include video displays, motorized clocks and other equipment, electric blankets and heaters, fluorescent lights and light dimmers, and the transformers that are inside consumer devices. Many of the effects are from frequencies that are harmonics or multiples of 60 Hz (120 Hz, 180 Hz, etc.) and 17,000 Hz of video displays. Magnetic fields are difficult to shield, and either sheets made of specialized metal, or electronic instruments which actively produce magnetic fields to counter ambient fields, are required.

A few areas in most homes read HIGH in the electric field setting. These include areas near improperly grounded equipment, the front of video screens, and fluorescent lights. Most of these fields are at 60 Hz. Unlike magnetic fields, electric fields can be easily shielded using a grounded metal screen or foil; VDT screens of this type are readily available. You can greatly reduce the strength of an electric field just by placing your hand in front of the source. This effect can be seen using a TriField meter.

Occasionally, certain areas read HIGH in the radio/microwave setting. These include door seals around microwave ovens, and cellular phones (but not regular radio phones, which are very low-power). Radio/microwaves can be shielded in the same way as electric fields, although the lower frequency radio waves are not shielded by your hand as easily as microwaves are. (Metal screens will shield both.) In the U.S., radars and FM transmitters can legally expose residents to moderately high power levels, but such exposure is not common.

By seeing "hot" spots in your home or office, you can move furniture, cribs, or beds to reduce exposure. You can also take corrective action to avoid long term exposure to appliances that emit high electromagnetic pollution levels. If you have unusual sensitivity to a particular type of field, you can identify where problems exist (e.g., wearers of pacemakers should avoid even brief exposure to high radio/microwave power levels. Some anecdotal evidence indicates that brief exposure to very high AC electric or magnetic fields may cause nervousness or seizures in some people.)

The TriField meter comes with a one-year limited warranty and a 9-volt transistor battery included. This type of battery lasts about 10 hours (total measurement time). When the BATTERY TEST reads low, it can be replaced with any rectangular 9 volt transistor or alkaline (which lasts about 50 hours) type.