ELF AC Milligauss Meter

Overview

The simple circuit is used to illustrate the method of measuring the amount of AC magnetic and electric fields or the extremely low frequency fields in a workplace or home environment.

Terminology

• Extremely Low Frequency (ELF) – a radio frequency band that ranges from 3 Hz to 300 Hz
• Gauss – a unit of measurement pertaining to magnetic induction, magnetic flux or magnetic field
• 1N1418 – a small-signal silicon epitaxial planar diode used for fast switching applications with a reverse voltage of 100 V and forward current of 150 mA

Circuit Explanation

Magnetic and ELF fields are produced not only by artificial means, but also by natural sources. The human body is absorbing electromagnetic energy as well as the home appliances are emitting electromagnetic radiation. These can be measured using the milligauss meter which can give an output range of 0.01 to 1999 milligauss. The meter is powered by the eddy current that is created upon exposing a conductor to a changing magnetic field which is produced by the variation of the field in reference to time or the motion of conductor and the field source. The human body is normally producing this eddy current via alternating current fields. The voltmeter recognizes the energy stored by capacitor C1 as it instantly charges virtually.

A conversion exists in changing the value from volts to gauss, wherein the millivolts is divided by 4 to attain a value in milligauss. Extremely low frequency fields at 60 Hz are produced from electrical wiring, power lines or electrical equipment. Being exposed to ELF or magnetic field exposure from power lines can increase the risk of having a cancer, according to some epidemiological studies. The range of milligauss value refers to certain levels of radiation like the range from 1 to 3 milligauss which is a low electromagnetic radiation but according to Denver studies, can double the leukemia rate for children; the range of 20 to 25 milligauss which is a significant electromagnetic radiation can be obtained by keeping the meter against the television; 100 milligauss are high electromagnetic radiation; and 250 milligauss are maximum risk exposure that can be found on substations. There are already studies showing the ELF fields have negative and harmful effects on humans especially those exposed for longer period of time. Aside from cancer, the exposure can also lead to miscarriage or premature births.

Those home appliances using AC have possibly high magnetic fields that reduce quickly with distance. Normally, magnetic fields in appliances are stronger than those found in power lines in which the intensity is dependent on the nature and purpose of the design. Some examples of appliances with average magnetic levels on a 6-inch distance include microwave oven (200 milligauss), coffee maker (7 milligauss), can opener (600 milligauss), hair dryer (300 milligauss), and electric shaver (100 milligauss).

The sensor at the tip could be made at the end of an 8-wire cable having a length of 4 feet or a variety of distances. Since the cable points in the same direction as the component of the field that is being detected, the sensor can be termed as axial. It can be made of high sensitivity material for high precision magnetic field measurement, a copper piping cut in short stub, or a piece of wire used for fencing. Any material can be utilized for as long as it can make good hand contact.

Application

ELF AC gaussmeter have a wide range of applications for mechanical, material, electrical, laboratory field to check the magnetic value of a material. Likewise, it is used for checking the magnetic fields and frequencies created by equipments like induction heaters, computer monitors, scientific, medical and industrial equipment; and for surveying the office, home and schoolyard for any existing magnetic field radiation. Some people would tend to use it in a different manner like the paranormal hobbyist, ghost hunters, UFO hunters and government conspiracy people for their own purpose. Other form of meter like the DC gaussmeter can be used to measure solenoids, magnets, and other strong sources of magnetic field.

The eddy current used in the circuit to provide power for the meter can be used in other applications like structural testing which includes aircraft fuselage, heat exchanger tubes and aircraft structural components; in identification of metals used in vending machines for detecting slugs or counterfeit coins; in electromagnetic braking like those used in roller coasters; and repulsive effects and levitation where it can induce magnetic field in aluminum cans to be separated from other recyclables. One disadvantage of eddy current is in conductors possessing AC current since it is the main cause of skin effect.

Extremely low frequencies can also bring benefits as they are being used in some 20 Hz transmitters which are coupled in pipeline inspection gauges. It is essential to some radio hams as it pick-up ELF from homemade antennas then play them back at higher speeds so that it can take hold of the natural fluctuations in the electromagnetic field of the Earth.

Source:www.zen22142.zen.co.uk/Circuits/Testgear/mgausmeter.htm