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EMF Measurement Sensitivity & Accuracy Problems & Solutions
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
EMF measurement instrument sensitivity & accuracy: this article explains the sensitivity and accuracy of EMF or ELF measuring instruments used for performing electromagnetic field (EMF) or
electro-magnetic radiation EMR measurements to 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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Sensitivity & Accuracy of EMF Measuring Instruments
 Because RF and EMF measurement tools need to be properly chosen to measure the particular type and frequency of RF or EMF signal that is of interest, be sure to also see EMF RF FIELD & FREQUENCY DEFINITIONS for a simple explanation of different types of radio frequency (RF) and electromagnetic frequency (EMF) types and where they are found. Also see Definitions of Gauss vs Milligauss for details about gauss and milligauss and definitions of these terms
See ENVIRO-SCARE, EMF & Property Values if you don't know what EMF, ELF, or electromagnetic fields are or if you want a summary of the possible health effects of EMF exposure and the more likely effect on the property value of homes located very close to power transmission lines. Readers who intend to make their own EMF measurements should be sure to also see EMF MEASUREMENT WORKSHEET and also WORKSHEET for EMF MEASUREMENTS - Example.
Most hand-held low-cost EMF measuring instruments (see our list at Evaluation of Low-Cost EMF Instruments) can make measurements down to 1 milligauss. Because it is common for us to find background EMF levels of 1-3 milligauss in residential neighborhoods where local electrical power distribution lines and transformers are present, and because some studies examined EMF field strengths down to this low level, a do-it-yourself EMF measurement project should probably avoid using instruments that lack that level of sensitivity.
But as we explain next, an accurate, sensitive EMF instrument is insufficient for making accurate and repeatable EMF measurements.
- Some instruments obtain EMF measurements that are sensitive to the orientation or position in which the instrument is held. Be sure to check that your instrument's readings are consistent regardless of instrument position, use a Tri-field instrument to avoid this source of inaccuracy, or if you prefer, as we do, to be able to see the field shape and source, be sure that your measurement procedure copes with this variation.
We describe the position sensitivity problem in more detail at EMF Polarity & Shape Affect Measurements. We describe how to do so at Recommended EMF Measurement Procedure. We illustrate the EMF field shape at EMF/EMR Measurement Procedure Overview.
- EMF measurements are sensitive to distance from the source of the EMF. See Distance from the EMF Source Affects Strength.
- EMF measurements are sensitive to interference from local EMF sources that may swamp or distort EMF from a power transmission line. See Local EMF Sources May Exceed Power Line Strength for details.
- EMF measurements are highly sensitive to hourly and seasonal variations in the load on power transmission lines; See Time of day & Season Affect EMF Strength for details.
- EMF measurements of local EMF sources such as appliances are entirely sensitive to whether or not the appliance is turned on and in-use as well as to variations in electrical current depending on appliance settings.
- Because RF and EMF measurement tools need to be properly chosen to measure the particular type and frequency of RF or EMF signal that is of interest, be sure to also see EMF RF FIELD & FREQUENCY DEFINITIONS for a simple explanation of different types of radio frequency (RF) and electromagnetic frequency (EMF) types and where they are found.
- See Definitions of Gauss vs Milligauss for details about gauss and milligauss and definitions of these terms
Inconsistency in EMF measurement methods is a problem: In order to permit comparison of measurements (and studies) it is important not only to have line load data
available (for researchers) but also that site measurements are made in a very consistent manner from building to
building.
To do otherwise would make it impossible to compare conditions at one property with those at another, even if
both properties are equidistant from the same power line and even if both measurements were made at the same moment.
Position-insensitive EMF Measurement Instruments - best for the amateur
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Some EMF measuring instruments, typically called "tri-field" or tri-position instruments, will give a consistent EMF strength reading in a given location regardless of how you are holding the instrument or where you are pointing it - providing the field strength has not changed between measurements.
We recommend this type of instrument for home use by "do it yourself" emf measurers.
See EMF Polarity & Shape Affect Measurements for further explanation. |
Position-sensitive EMF Measuring Instruments - Why and How They are Used
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Other EMF measuring instruments such as our Safeco (Photo at left) are very position-sensitive. The spreadsheets we provide allow for collecting EMF measurements
on three axes when using an instrument such as this one.
The disadvantage of the instrument is the requirement to make multiple measurements at each location during an EMF survey.
But the advantage of the instrument is that it allows us to see the shape, source, and even orientation of an electromagnetic field at a given location.
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 EMF MEASUREMENT WORKSHEET you'll see that provision is made for recording raw data points
as well as the individual mG readings.
See EMF Polarity & Shape Affect Measurements (just below) for further explanation, and see EMF MEASUREMENT WORKSHEET for the proper calculation method used to combine multiple position-sensitive EMF measurements into a single field strength number for a location.
Readers should also see Comparing Gauss versus Milligauss Field Strength Measurements where we explain the greater accuracy of low-level EMF readings when using the milligauss scale on an ELF EMF meter. |
EMF Polarity and Shape, not just Distance, Affect some EMF Measurements
 Electromagnetic fields are created around power transmission lines by the passage of high levels
of current through the transmission line wires themselves. A power-line generated
electromagnetic field has polarity and shape, roughly
spherical around a power line.
The problem of the electromagnetic field having polarity and shape means that some early or low-cost
EMF measuring devices will give widely varying field strength measurements depending simply on the
physical orientation of the device when the measurement is made - that is, what direction you point the
instrument affects its reading.
But don't think that pointing directly towards the power line wires overhead
gives the maximum reading.
It may not, due to field polarity. More costly EMF meters have multiple sensors to
overcome this defect.
We discuss the problem of electromagnetic field shape, polarity, and instrument testing sensitivity to instrument orientation or position at Sensitivity & Accuracy of EMF Measuring Instruments.
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.
Frequently Asked Questions (FAQs)
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Questions & answers or comments about how to hold, position, & use EMF field strength measurement instruments to account for variations in sensitivity and accuracy of Instruments for EMF power line and other source surveys.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Electric Power Lines, Electromagnetic Fields, Cancer Risk,
& "Enviro-Scare" - The Normal Curve Cycle of Public Fear About Environmental Issues - online document by DF
- A Procedure for Measuring EMF electromagnetic fields online document by DF
- "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).
- EMF RF FIELD & FREQUENCY DEFINITIONS RF and EMF measurement tools need to be properly chosen to measure the particular type and frequency of RF or EMF signal that is of interest. See EMF RF FIELD & FREQUENCY DEFINITIONS for a simple explanation of different types of radio frequency (RF) and electromagnetic frequency (EMF) types and where they are found.
- Definitions of Gauss vs Milligauss for details about gauss and milligauss and definitions of these terms.
- Consumer Product Safety Commission, 800-638-CPSC.
- US Environmental Protection Agency, Office of Pesticides
and Toxic Substances, TSCA Assistance Office (TS-799), 800-424-9065
or 202-554-1404.
- "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
15213
- "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
2, 1991
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
- Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
- Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear of Environmental Issues
- Electromagnetic Fields in the Workplace sample very good NIOSH document online, links to other NIOSH docs.
- Electromagnetic Field Surveys & Hazards full list of our links to services and technical article
- Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear About Environmental Issues - online document by DF
- A Procedure for Measuring EMF electromagnetic fields online document by DF
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