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An EMF meter is a scientific instrument for measuring electromagnetic fields (abbreviated as EMF). Most meters measure the electromagnetic radiation flux density (DC fields) or the change in an electromagnetic field over time (AC fields), essentially the same as a radio antenna, but with quite different detection characteristics.
The two largest categories are single axis and tri-axis. Single axis meters are cheaper than a tri-axis meters, but take longer to complete a survey because the meter only measures one dimension of the field. Single axis instruments have to be tilted and turned on all three axes to obtain a full measurement. A tri-axis meter measures all three axes simultaneously, but these models tend to be more expensive.
Electromagnetic fields can be generated by AC or DC currents. An EMF meter can measure AC electromagnetic fields, which are usually emitted from man-made sources such as electrical wiring, while gaussmeters or magnetometers measure DC fields, which occur naturally in Earth's geomagnetic field and are emitted from other sources where direct current is present.
An example of an EMF meter.
[edit]Sensitivity
As most electromagnetic fields encountered in everyday situation are those generated by household or industrial appliances, the majority of EMF meters available are calibrated to measure 50 and 60 Hz alternating fields (the frequency of US and European mains electricity). There are other meters which can measure fields alternating at as low as 20 Hz, however these tend to be much more expensive and are only used for specific research purposes.
B12. Are there different kinds of EMFs?
Yes, there are three basic kinds of EMF. Magnetic fields are the EMF component most often linked to serious health effects in the scientific research literature (e.g., between power lines and childhood leukemia). They are emitted from power lines, building wiring, lights, appliances, and virtually everything that runs on regular electricity.
Electric fields make up the other half of the "electro"magnetic fields emitted from power lines, wiring, lights and appliances. They are also related to certain biological effects, and anecdotally, electric fields are often involved when people knowingly feel discomfort or “symptoms” from electrical sources.
Finally, Radio frequency or “RF” includes the higher frequency fields and microwaves emitted by cell towers and cell phones, cordless phones, TV/radio broadcast towers, Wi-Fi and other wireless computer devices, microwave ovens, and various electronics. (The electric and magnetic parts of RF fields are not separated, so you only need one meter to detect the RF field.)
B13. How are the different kinds of EMFs measured?
Each of the three kinds of EMFs requires a different type of test meter. Magnetic fields are usually measured in units called milligauss (mG) with special instruments called "gaussmeters." Electric fields are detected by either measuring the volts (V) on a person's skin with a "body voltage tester" or the volts per meter (V/M) with a standard "electric field tester." RF/microwave fields require a special test meter that can detect a wide range of RF frequencies, especially the digital microwaves, in units of microwatts per centimeter squared (?W/cm²).
B14. What levels are considered safe?
There is great controversy about what levels are safe, so you will have to make your own decision. For magnetic fields, the lowest level linked to childhood cancer in the power line studies is 2.0 milligauss (mG). The average in homes around the country is probably around 0.5 mG, with dense urban areas like San Francisco probably averaging closer to 1.0 mG. In our consulting work, we try to reduce long-term exposures to well below the levels linked with disease in the research studies, so we generally try to reduce magnetic field exposures to 0.5 mG or less.
Electric fields in homes are typically around 0.5 to 2.0 volts (V) using a body voltage meter. We usually use a cautionary level of 1.0 V for living areas, and 0.5 V for sleeping locations. Anecdotally, very sensitive individuals usually need to reduce electric fields below 0.1 V to feel relief of symptoms. RF/microwaves in the home vary greatly, usually depending on the use of cell phones, cordless phones, wireless and Wi-Fi. Average levels vary from 0.01 to 0.5 microwatts per centimeter squared (?W/cm²). We generally use a precautionary level of 0.1 ?W/cm² as suggested by the Bioinitiative Report, and 0.001 or less for sensitive individuals.
B15. Are all test meters the same?
No. A triple-axis meter allows you to simply hold the test meter in any orientation, and get a full, accurate three-dimensional reading. A single-axis meter requires you to move the meter around in all possible directions to find the highest field strength, or take three readings in orthogonal directions and do a math calculation. In practice, most people will get much more accurate readings with a triple-axis meter, because it is so easy to miss the strongest direction with a single-axis meter and underestimate the true field strength.
For magnetic fields, we usually recommend a gaussmeter that can detect both ELF and VLF frequency ranges. ELF includes the 60 Hz frequency from power lines, wiring, refrigerators, transformers, lights, appliances and everything that runs on regular electrical power. VLF includes higher frequencies in the range of 10,000 Hz and more that often come from televisions, computers, fluorescent lights, compact fluorescent bulbs, and other electronics. For RF/microwaves, it is also important to use a meter which can measure a wide range of frequencies. For example, the 5.8 GHz frequency of some cordless phones is not detected by many RF meters.