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AC Milligauss Meter
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AC Milligauss Meter
This meter is designed to do precise measurements of AC magnetic field in a wide frequency range of 13 Hz to 75 kHz (75,000 Hz). The frequencies include most ELF (that is, frequencies below 1 kHz) and VLF (above 1 kHz) magnetic fields. The meter measures the true 3-axis magnitude of the AC field. Two other more specialized measurements can also be performed: 3-axis VLF-only (1kHz – 75 kHz) to measure the strength of higher-frequency fields, and 1-axis full bandwidth (13 Hz – 75 kHz) to determine the principal direction of the AC magnetic field. These specialized measurements are selected by the knob labeled "TYPE OF MEASUREMENT". A "RANGE" knob allows a wide range of field strengths to be measured—from .01 to 1999 milligauss.

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Most measurements will be performed with both knobs turned to the left-most position. This setting is for measurement of true magnitude of magnetic field at the widest range of frequencies (ELF + VLF) up to a strength of 19.99 milligauss. If the field becomes stronger than 19.99, most of the display will go blank except for a "1" at the extreme left. This indicates over-range. Then switch the left-side switch to 199.9 (or 1999 if the 199.9 setting still shows over-range).

To use the meter, slide the power switch (on right edge) upward. With both knobs at their left-most position, the display can read up to 19.99 milligauss. You’ll notice that if you suddenly rotate the meter or tap it, the display will read higher for a fraction of a second. This is caused by the Earth magnetic field, which is about 500 milligauss DC. Normally a DC (non-oscillating) field will not be detected by this meter; however, any motion (tipping the meter or tapping it) will modulate this DC field, creating a temporarily-changing field, which will be detected. The effect is especially noticeable in this very sensitive 19.99 range. To avoid this false signal, keep the meter body stable and always oriented the same way in space as you walk along making measurements. For example, if the meter is vertical and the slide switch on the side is pointing, let’s say, northwest, then you should keep the meter always vertical with the power switch side pointing northwest, as you walk along. While rotating or changing orientation of the meter, the reading will usually be higher than it should be, but the reading will return to the correct value as soon as you stop rotating it. The meter will also read a higher level if it's being moved near magnetized metal.

If the "TYPE OF MEASUREMENT" switch is set to its center position, the meter will read 3-axis VLF fields (at frequencies of 1 kHz and higher). Generally in video displays and fluorescent lights a large percentage of the fields are at these higher frequencies. Please note three factors when measuring these higher frequencies: 1) These VLF measurements should be less than (or at most the same as) the measurement obtained when the knob is set on its left-most position of "3-AXIS ELF + VLF". In most areas, the VLF (with knob set in center) will be very low or zero; at most it will never be more than the reading obtained when the RANGE knob is switched to "3-AXIS ELF + VLF". In other words, VLF alone is never more than ELF + VLF. 2) The center position of that knob is slightly sensitive to 60 Hz fields, even though it is supposed to reject frequencies below 1 kHz. The rejection is 400:1. That is, if there is a field of 400 milligauss that is exclusively at 60 Hz, the VLF (center) position of the knob will yield a (false) reading of 1.0 milligauss. Similarly a 200 milligauss field at 60 Hz will yield a false VLF field of 0.5 milligauss. 3) If the reading on ELF + VLF (left position of knob) is too high, the VLF reading may not be correct when the RANGE knob is set at a lower number for the VLF reading. Specifically, if the ELF + VLF (left side) reading is more than 40 milligauss, do not do a reading of the VLF-only (center position) with the RANGE switched back to 19.99. Instead, use the 199.9 RANGE. Similarly, if the ELF + VLF is higher than 400 milligauss, continue to use the 1999 RANGE when you switch to VLF. Otherwise, the VLF reading may be falsely low.

When the "TYPE OF MEASUREMENT" switch is set to the 1-AXIS position (right side), the meter reads ELF + VLF but in only one axis. The direction of this 1-AXIS is the same as the "thickness" dimension of the meter (as opposed to the left-right "width" or up-down "height" that are the conventional definitions of width and height, with respect to the writing on the front label). This 1-axis sensor is just behind the center of the black panel that’s on the top surface, or "roof" of the meter. The 1-AXIS measurement can be used to determine the direction in which the field is strongest; unfortunately, this does not exactly correspond to the direction (or the position relative to the meter) of the field source. The direction of strongest field can give you some information about the direction of the field source, as per the convention developed by Edward Leeper (see

For your reference, the other two magnetic sensors are 1) on the extreme right side of the meter’s "roof" (This is the position of the sensor in the up-down direction.), and 2) the extreme left side under the "roof" (The position of the left-right sensor). Generally, if you are very close to a field source, these three sensors will be at three different distances from the field source, and as a result, the reading will be strongly dependent on the angle at which you hold the meter. For field measurements more than about two feet from the source, this angle dependence is minimal.

Warranty for this meter is one year.
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