How Do AC Magnetic Field Meters Measure?

If you're wondering how AC magnetic field meters work, this guide explains the basic methods they use to detect magnetic fields and how to get more reliable readings.

Key Things To Know Before You Measure:

AC magnetic field meters detect magnetic fields produced by alternating electrical currents. Different meters use different types of sensors depending on their intended frequency and measurement range.

Induction-coil sensors detect changing magnetic fields by measuring the voltage produced in a coil. This is a common method for measuring AC magnetic fields.

Hall-effect sensors detect magnetic fields electronically and can be used for AC or DC measurements, depending on the meter.

Three-axis meters measure the field in three directions—X, Y, and Z—and combine them to provide an overall field-strength reading.

Meters commonly display magnetic fields in microtesla (µT) or milligauss (mG).

1 µT = 10 mG

The meter's frequency range is also important. A meter designed for 50/60 Hz measurements may not accurately measure higher-frequency fields.

Measurement Methods:

Induction-Coil Measurement

A changing magnetic field passing through a coil creates a small electrical signal. The meter processes this signal and converts it into a magnetic-field reading.

Hall-Effect Measurement

A Hall-effect sensor produces a voltage when exposed to a magnetic field. The meter uses this response to determine the field strength.

Three-Axis Measurement

Three-axis meters measure the magnetic field from multiple directions, making them useful when you don't know which direction the field is coming from.

How To Use an AC Magnetic Field Meter:

1. Check the specifications.
Make sure the meter covers the frequency range you're measuring.

2. Select AC mode.
Choose the AC magnetic-field setting if your meter has separate AC and DC modes.

3. Take a background reading.
Measure the area before approaching the suspected source so you have something to compare against.

4. Keep your distance consistent.
Magnetic fields can change significantly with distance, so use the same distance when comparing readings.

5. Rotate the meter.
With a single-axis meter, changing the sensor's orientation can change the reading. Rotate it slowly to check different directions.

6. Record your results.
Note the reading, units, location, distance, and frequency setting if available.

Practical Tips:

For more consistent measurements:

  • Move the meter slowly when searching for a source.
  • Take several readings rather than relying on one measurement.
  • Check the meter's frequency range and accuracy.
  • Use a three-axis meter when the field's direction is unknown.
  • Compare readings at different distances to see how the field changes.

Understanding the Reading

An AC magnetic field meter measures the magnetic field detected by its sensor under the conditions of the measurement. The displayed number doesn't identify the source by itself, so taking measurements at different locations and distances can help determine where the field is coming from.