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ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY
ENVIRO-SCARE, EMF & Property Values
ENVIRO-SCARE Defined, Effects
ENVIRO-SCARE Effects on Property Values
EMF MEASUREMENT PROCEDURES
EMF SURVEY PROCEDURE - Details
  Introduction to EMF Measurement
  EMF/EMR Measurement Procedure Overview
    EMF Variability
    Electrical Utility Workers & EMF Exposure
    EMF Instrument Sensitivity & Accuracy
    EMF Polarity & Shape Affect Measurements
    Distance from the EMF Source Affects Strength
    Time of day & Season Affect EMF Strength
  Local EMF Sources May Exceed Power Line Strength
  Recommended EMF Measurement Procedure
    Outside EMF Measurements
    Outside EMF Measurement Documentation
    Indoor EMF Measurements
    Other Indoor EMF Measurement Targets
    Workplace EMF Measurements
  EMF Measurement Documentation Details
  EMF Measurement Instrument Use
    Definitions of Gauss vs Milligauss
    Position-sensitive EMF Instrument Readings
  Interpreting Electromagnetic Field Strength EMF Survey
  Evaluation of Low-Cost EMF Instruments
    Accuracy & Calibration of EMF Instruments
    Calibration of EMF Instruments in the Field
    Calibration of EMF Instruments by Electric Company
    Descriptions of Low-Cost EMF Instruments
    F.W. Bell Model 4060 ELF Meter
    Safeco™ analog EMF ELF EMR meter
    Walker Scientific ELF-50D™ Digital EMF Meter
References for Electromagnetic Fields and Cancer
WORKSHEET for EMF MEASUREMENTS
WORKSHEET for EMF MEASUREMENTS - Example
WORKPLACE EXPOSURE to Electromagnetic Fields

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EMF meter (C) Daniel Friedman EMF Measurement Sensitivity & Accuracy Problems & Solutions
InspectAPedia®  -    

  • Sources of error and variability in electromagnetic field strength measurement surveys
  • How to select & use low cost EMF measurement instruments
  • Sensitivity and accuracy of Instruments for EMF power line and other source surveys
Our site offers impartial, unbiased advice without conflicts of interest. We will block advertisements which we discover or readers inform us are associated with bad business practices, false-advertising, or junk science. Our contact info is at InspectAPedia.com/appointment.htm.

Here we discuss 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.

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 WORKSHEET for EMF MEASUREMENTS and also WORKSHEET for EMF MEASUREMENTS - Example.

Also see Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear of Environmental Issues which discusses the impact of EMF and other environmental concerns on property values. And see ELECTROMAGNETIC FIELDS & HUMAN EXPOSURE which discusses EMF exposure in the workplace.

© Copyright 2010 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

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.

Sensitivity & Accuracy of EMF Measuring Instruments

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.
  • 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

EMF meter (C) Daniel Friedman

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

Safeco EMF meter  (C) Daniel Friedman

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 WORKSHEET for EMF MEASUREMENTS 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 WORKSHEET for EMF MEASUREMENTS 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

bar magnet shows the typical shape of an electromagnetic fieldElectromagnetic 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.

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Technical Reviewers & References

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

ENVIRO-SCARE, EMF & Property Values
ENVIRO-SCARE Defined, Effects
ENVIRO-SCARE Effects on Property Values
EMF MEASUREMENT PROCEDURES
EMF SURVEY PROCEDURE - Details
  Introduction to EMF Measurement
  EMF/EMR Measurement Procedure Overview
    EMF Variability
    Electrical Utility Workers & EMF Exposure
    EMF Instrument Sensitivity & Accuracy
    EMF Polarity & Shape Affect Measurements
    Distance from the EMF Source Affects Strength
    Time of day & Season Affect EMF Strength
  Local EMF Sources May Exceed Power Line Strength
  Recommended EMF Measurement Procedure
    Outside EMF Measurements
    Outside EMF Measurement Documentation
    Indoor EMF Measurements
    Other Indoor EMF Measurement Targets
    Workplace EMF Measurements
  EMF Measurement Documentation Details
  EMF Measurement Instrument Use
    Definitions of Gauss vs Milligauss
    Position-sensitive EMF Instrument Readings
  Interpreting Electromagnetic Field Strength EMF Survey
  Evaluation of Low-Cost EMF Instruments
    Accuracy & Calibration of EMF Instruments
    Calibration of EMF Instruments in the Field
    Calibration of EMF Instruments by Electric Company
    Descriptions of Low-Cost EMF Instruments
    F.W. Bell Model 4060 ELF Meter
    Safeco™ analog EMF ELF EMR meter
    Walker Scientific ELF-50D™ Digital EMF Meter
References for Electromagnetic Fields and Cancer
WORKSHEET for EMF MEASUREMENTS
WORKSHEET for EMF MEASUREMENTS - Example
WORKPLACE EXPOSURE to Electromagnetic Fields

References for Electromagnetic Fields and Cancer Risk/Carcinogenicity

  • 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
  • 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 design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
  • ...
ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY
ENVIRO-SCARE, EMF & Property Values
ENVIRO-SCARE Defined, Effects
ENVIRO-SCARE Effects on Property Values
EMF MEASUREMENT PROCEDURES
EMF SURVEY PROCEDURE - Details
WORKSHEET for EMF MEASUREMENTS

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