Power Frequency Magnetic Field Test (PFMF)

A power frequency magnetic field test is performed to measure the magnetic field generated by electrical systems operating at power-line frequencies (typically 50 Hz or 60 Hz). This test ensures compliance with safety standards and electromagnetic compatibility (EMC) regulations.

​Purpose of the Test

  1. Health and Safety: Assess magnetic field exposure to ensure it is within acceptable limits set by regulatory bodies such as ICNIRP or IEEE.

  2. Electromagnetic Compatibility (EMC): Evaluate the impact of magnetic fields on nearby sensitive equipment.

  3. Equipment Performance: Confirm that devices function correctly when subjected to magnetic fields.

Test Standards

Some commonly followed standards for power frequency magnetic field testing include:

  • IEC/EN 61000-4-8: Immunity to power frequency magnetic fields.

  • ICNIRP Guidelines: For exposure limits to magnetic fields.

  • IEEE C95.6: Safety levels for electromagnetic fields (0 Hz to 3 kHz).

Test Procedure

1. Test Setup

  • Equipment Under Test (EUT): Place the device or system in a controlled test environment.

  • Magnetic Field Generator: Use a Helmholtz coil or a magnetic loop to generate a uniform magnetic field at the desired frequency (50 Hz or 60 Hz).

  • Test Environment:

    • Shielded room to prevent external interference.

    • Ambient magnetic field should be minimal and measured before starting.

  • Field Measurement Devices: Use a calibrated magnetic field meter (e.g., fluxgate magnetometer).

 

2. Test Equipment

  1. Magnetic Field Generator

    • Helmholtz coil or current loops for producing uniform fields.

  2. Field Strength Meter

    • Devices like Hall effect sensors or fluxgate magnetometers.

  3. Oscilloscope/Analyzer

    • For monitoring the response of the EUT during testing.

  4. Power Supply

    • Stable AC source to generate consistent fields at 50/60 Hz.

3. Test Parameters

  • Frequency: 50 Hz or 60 Hz.

  • Field Strength: Varies based on standards:

    • Typical ranges: 1 A/m to 1000 A/m.

    • Specific applications (like medical or industrial equipment) may demand higher or lower values.

  • Duration: Field exposure duration per standard (often 1–5 minutes).

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4. Test Levels

IEC/EN 61000-4-8 defines levels for magnetic field immunity testing:

  • Level 1: 1 A/m

  • Level 2: 3 A/m

  • Level 3: 10 A/m

  • Level 4: 30 A/m

  • Custom levels based on the operational environment of the EUT.

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5. Test Process

  1. Pre-Test Calibration:

    • Verify the magnetic field strength and uniformity using a measurement device.

  2. Apply Magnetic Field:

    • Subject the EUT to a magnetic field perpendicular to its surface.

    • Rotate the field (if required) to test different orientations.

  3. Monitor the EUT:

    • Check for disruptions, malfunctions, or degradation in performance.

  4. Record Results:

    • Measure the magnetic field at different distances and angles.

    • Log any operational abnormalities in the EUT.

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6. Post-Test Evaluation

  • Inspect the EUT for permanent damage or residual effects after exposure.

  • Compare results to allowable thresholds in applicable standards.​​

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