Ac milligauss meter - model UHS

 

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 - 75kHz) to determine the principal direction of the AC magnetic field. These specialized measurements are selected by the knob labelled "TYPE OF MEASUREMENT". A "RANGE" knob allows a wide range of field strengths to be measured - from .01 to 1999 milligauss. Most measurements will be performed with both knobs turned to the leftmost 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 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 some information about the direction of the field source, as per the convention developed by Edward Leeper (see www.silencingthefields.com). 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 at which you hold the meter. For field measurements more than about two feet from the source, this angle dependence is minimal.

Accuracy: This meter has a typical error of +/-3% of the reading in the frequency range 45 Hz to 5kHz. At certain measurement angles and certain frequencies in the 3-AXIS modes, the error may be as high as +/-7%. That is, a reading of 10.00 milligauss means the field is as high as 10.70 or as low as 9.30, but most of the time the actual field will be between 10.30 and 9.0 (this is in RMS units). Note that this accuracy specification is for sine waves in the very wide frequency range of 45 Hz to 5 kHz. Other manufacturers of digital 3-axis meters only specify the accuracy for 60 Hz sine waves. (Those types of meter will generally have significant additional error above 100 Hz. Because of advanced high frequency detection circuitry, the model UHS does not have this problem). The meter works by measuring the absolute value of the AC field strength in 3 axes (or 1 axis), and then finding the time-average of that absolute value. That time average is then scaled so that a sine wave reads in RMS units. Sensitivity is down to ½ at the frequency limits 13 Hz and 75 kHz. In the 3-AXIS 1 kHz - 75 multiplier in the lower right of the table) if the wave is actually 50 kHz. Also, if you're measuring pure 60 Hz, and it reads 13.62 milligauss on the ELF + VLF, then it will only read .0025 x 13.62 = .03 milligauss on the VLF only setting. These calculations require that you know the frequency. The alkaline 9v battery lasts about 20 hours. "LOW BATTERY" will appear on the display when approximately one hour of battery life remains. To replace the battery, press down on the back door (near the centre of the back of the meter) and slide this door outward (downward) to separate it from the meter body. Then change the battery. Warranty for this meter is one year.