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This article explains how to use EMF or ELF measuring instruments when performing electromagnetic field (EMF) or electro-magnetic radiation EMR measurements either by engaging a professional or by consumers using low-cost instruments which measure EMF exposure levels in gauss or milligauss. We discusses sources of error and variation in EMF measurements and we review and make suggestions for using several low-cost EMF measurement devices to determine the instantaneous electromagnetic field exposure.
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The information provided here is for research and study purposes. The author makes no representation of unique expertise on this topic, other than having field experience in EMF measurement, having studied technical literature and having conversed with other experts and authors in the field for a number of years.
For position-insensitive equipment, a single reading is usually provided, directly in mG.
For position sensitive equipment you'll find an enormous range of response depending on the angle and direction in which you hold the measurement device.
While this type of instrument is more work to use (see calculations below and in spread sheet) it provides more clear indication of when you're approaching a field. Some instruments do not provide a reading directly in mG and you'll have to simply record the "raw" measurements and to convert them later.
Some readers may be confused between two common terms used to describe the strength of an electromagnetic field: Gauss and Milligauss. Both of these terms measure the same effect, but at different ranges of strength level. It's simply a matter of moving the decimal point, as we demonstrate in our photographs above.
In our first photo (above left) the ELF EMF meter has been set to the Gauss range and we are measuring a field strength of 0.03 Gauss with our meter touching a small power transformer.
In our second photo (above right) the same ELF EMF meter has been set to its more-sensitive Milligauss range and we are measuring 25 milligauss.
Because usually the electromagnetic field strength around residential properties is very weak, most measurements will probably be made in the milligauss range. 0.03 Gauss is the same as 30 Milligauss. Our instrument, more accurate in the lower milligauss range, shows that we are actually measuring 25 milligauss, a number which was rounded up to 0.03 Gauss when the scale was shifted.
Definitions of Gauss and Milligauss for Measuring Electromagnetic Fields - EMF
Gauss is a measurement scale used to measure the strength of an electromagnetic field (EMF). The gauss level measured in a given location depends on the strength of the source of the EMF and the distance from the source. The measured field strength of an EMF falls off quite rapidly with distance (field strength declines as the square of the distance from the source).
When electrical current flows through a wire (such as in an electrical distribution wire or inside of an electric motor) an electromagnetic field is produced. Power lines, local electrical wires, air conditioning motors, computers, TVs, hair dryers, toasters, all devices that use or transport electricity will produce an electromagnetic field. Usually the strength of these fields is low (Electric fan 1 mG, TV 1mG, chain saw 2.5 mg(?) at chest height, electric stove 6 mG, older electric blankets before circuit redesign 20 mG, and under a distribution line for electrical power transmission, 2-20 mg depending on the line height, KVA rating, and actual level of usage at the time of measurement.
If there is a concern for measuring exposure or possible exposure to electromagnetic fields, it's critical that we have a correct understanding of the levels of exposure that are being examined. For example, one of our readers informs us that that manufacturer of his pacemaker recommends avoiding exposure to electromagnetic fields stronger than 5 gauss. (EMF generated from small electric motors (such as a chain saw) measured with the saw held in normal operating position may be as much as 2.6 Gauss at the user's chest.)
When recording EMF measurements be certain that you've got the right order of magnitude.
1 Milligauss (mG) = 10-3 Gauss, or 0.001 Gauss
Published sources provide lots of examples of producing and measuring electromagnetic fields at a known gauss level. For example, using a 1.5V battery and a 150 Ohm resistor to make a long straight wire circuit, the EMF field strength when measured at 0.1m (about 4") from the wire will be about 0.2 milligauss (mG).
NIST, focused on SI units, measures electromagnetic fields in Tesla units of magnetic flux density: magnetic flux density Tesla,
To compute the actual point measurement, each of these numbers, once converted to mG, must be squared, the three squares added, and the square root taken of the sum. This is because the measurement scale is not linear, so a direct raw average would be incorrect.
In the EXCEL worksheet which we provide (at WORKSHEET for EMF MEASUREMENTS) you will observe that provision is made for recording raw data points as well as the individual mG readings. Formulas embedded in the worksheet compute the mean square average in order to obtain a valid point measurement of emf strength by this method.
Please do not contact us with a request buy EMF or RF measuring equipment. We do not sell anything. To do so would be a conflict of interest for this website. These devices are readily available from many electrical equipment and home inspection equipment suppliers. See Evaluation of Low-Cost EMF Instruments This article describes several low-cost and reasonably accurate EMF measurement devices that are readily available. See Radio Frequency RF Detection Meters This article describes several low-cost and accurate radio frequency or RF detection and measurement devices suitable for radio, TV, cellphone, microwave, and similar signals.
Instead of contacting us with a request to perform EMF Electromagnetic or RF Radio Frequency Field Strength measurements, in most cases it is more economical and convenient for a property owner to purchase their own instrument, making measurements under varying conditions. In this series of articles we describe how to make measurements using a consistent approach and using good documentation. See Recommended EMF Measurement Procedure for details of how to collect EMF measurement data.
Following good procedure and using instruments properly are two steps towards making accurate, repeatable EMF measurements. But because the signal transmission for RF sources such as radio, TV, or cell towers, the load on a power transmission line is not under control of an individual property owner, and because the EMF strength varies as the power transmission line load varies, it is important to have an idea of that condition as well when attempting to characterize EMF exposure at a specific location. In contrast, EMF measurements are quite accurate and repeatable at other EMF sources such as close to electrical appliances and service entry cables.
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