Guide to Using Electromagnetic EMF Measurement Instruments
EMF MEASUREMENT INSTRUMENT USE TIPS - CONTENTS: These tips on how to use EMF measurement instruments to make an electromagnetic field survey can help avoid several pitfalls and will increase the accuracy of your EMF readings. We also provide definitions of Gauss vs Milligauss. We explain how to cope with position-sensitive EMF Instrument Reading
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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.
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.
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.
Definition of Gauss versus Milligauss Field Strength Measurements
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,
SI Derived unit: Wb/m2
Magnetic Fluxe is measured in
SI Derived Unit: V·s
SI Base Units:
For Position-sensitive EMF measurement instruments, three readings are necessary.
Horizontal (spin through 360 degrees and record highest reading)
Vertical (same as above)
Pointed towards suspected source (e.g. distant power line
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.
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.
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.
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"Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields", Federal Communications Commission, Office of Engineering and Technology, US FCC, OET Bulleting 56, 4th Edition, August 1999
" Many consumer and industrial products and applications make use of some form of
electromagnetic energy. One type of electromagnetic energy that is of increasing importance
worldwide is radiofrequency (or "RF") energy, including radio waves and microwaves, which
is used for providing telecommunications, broadcast and other services. In the United States
the Federal Communications Commission (FCC) authorizes or licenses most RF
telecommunications services, facilities, and devices used by the public, industry and state and
local governmental organizations. Because of its regulatory responsibilities in this area the
FCC often receives inquiries concerning whether there are potential safety hazards due to
human exposure to RF energy emitted by FCC-regulated transmitters. Heightened awareness
of the expanding use of RF technology has led some people to speculate that "electromagnetic
pollution" is causing significant risks to human health from environmental RF electromagnetic
fields. This document is designed to provide factual information and to answer some of the
most commonly asked questions related to this topic." - original source: U.S. Federal Communications Commission Office of Engineering and Technology, http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf
"Magnetic Field Exposure and Cancer: Questions and Answers [ copy on file as /emf/EMF_Fact_Sheet_NCI_NIH.pdf ] - ," National Cancer Institute, U.S. National Institutes of Health, web search September 2010, original source: http://www.cancer.gov/cancertopics/factsheet/Risk/magnetic-fields
makes these five key points about EMF
Electric and magnetic fields (EMF) are areas of energy that surround any electrical device. EMFs are produced by power lines, electrical wiring, and appliances (see Question 1).
Electric fields are easily shielded or weakened by walls and other objects, whereas magnetic fields are not. Since magnetic fields are more likely to penetrate the body, they are the component of EMFs that are usually studied in relation to cancer (see Question 1).
Overall, there is limited evidence that magnetic fields cause childhood leukemia, and there is inadequate evidence that these magnetic fields cause other cancers in children (see Question 2).
Studies of magnetic field exposure from power lines and electric blankets in adults show little evidence of an association with leukemia, brain tumors, or breast cancer (see Question 3).
Past studies of occupational magnetic field exposure in adults showed very small increases in leukemia and brain tumors. However, more recent, well-conducted studies have shown inconsistent associations with leukemia, brain tumors, and breast cancer (see Question 4).
US Environmental Protection Agency, Office of Pesticides
and Toxic Substances, TSCA Assistance Office (TS-799), 800-424-9065
"Evaluation of Potential Carcinogenicity of Electromagnetic Fields,"
EPA Report #EPA/600/6-90/005B October 1990. EPA: 513/569-7562.
"Biological Effects of Power Frequency Electric and Magnetic Fields"
background paper, prepared as part of OTA's assessment of "Electric Power
Wheeling and Dealing: Technological Considerations for Increasing Competition,"
prepared for OTA by Indira Nair, M. Granger Morgan, H. Keith Florig, Department
of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA
"Biological Effects of Power Line Fields," New York State Powerline
Project. Scientific Advisory Board Final Report, July 1, 1987.
"Extremely Low Frequency (ELF) Fields," Environmental Health
Criteria 35. World Health Organization, Geneva, 1984.
"Electric and Magnetic Fields at Extremely Low Frequencies:
Interactions with Biological Systems. In: Non ionizing Radiation Protection,
World Health Organization, Regional Office for Europe, Copenhagen, 1987.
"Electric and Magnetic Fields from 60 Hertz Electric Power: What do
we know about possible health risks?," Department of Engineering and Public
Policy, Carnegie Mellon University, Pittsburgh, PA 15213 1989.
"Electromagnetic Fields Are Being Scrutinized for Linkage to
Cancer," Sandra Blakeslee, New York Times, Medical Science section, April
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