Power Frequency Magnetic Field (PFMF) test
Details
The Power Frequency Magnetic Field (PFMF) immunity test mainly assesses the anti-interference ability of electronic equipment in the 50Hz/60Hz power frequency magnetic field environment, and is applicable to equipment that may be exposed to strong magnetic field environments such as power transformers and large current busbars. The following is the globally recognized testing standard system and implementation norms:
1. Core international standards:
IEC/EN 61000-4-8 (Basic Standard)
- Test the magnetic field intensity:
| Grade | Magnetic field strength (A/m) | Corresponding magnetic flux density (μT) | Typical application scenarios |
| 1 | 1 | 1.26 | Electronic office equipment (keep away from strong magnetic fields) |
| 2 | 3 | 3.78 | Commercial equipment (close to the distribution cabinet) |
| 3 | 10 | 12.6 | Industrial environment (near substation) |
| 4 | 30 | 37.8 | Harsh environment (beside electric furnaces/welding equipment) |
| 5 | 100 | 126 | Special Industry (High Current Test Station) |
- Test waveform:
Pure sine wave (50Hz or 60Hz)
Optional 1Hz to 1000Hz modulated magnetic field (simulating harmonic interference)
- Test duration:
- Continuous magnetic field: at least 3 minutes
- Short-term magnetic field (1s to 3s) : Simulating fault conditions
Derivative standard
- GB/T 17626.8 (Chinese National Standard, equivalent to IEC 61000-4-8)
- JIS C 61000-4-8 (Japanese Industrial Standard)
2. Industry-specific standards:
Medical equipment
- IEC 60601-1-2:
Life support equipment must pass the level 3 (10A/m) test
The performance criterion requires that no dangerous conditions occur during the test
Power monitoring equipment
- IEC 60255-26:
The relay protection device needs to withstand a short-term magnetic field of 100A/m
Automotive electronics
- ISO 11452-8:
Simulate the low-frequency magnetic field interference during vehicle charging (50Hz to 150kHz)
3. Test Equipment and configuration:
- Key equipment:
Power frequency magnetic field generator (such as EMTEST MAG61000)
Induction coil (Standard size: 1m×1m or 0.6m×0.6m)
- Current transformer (calibrated magnetic field intensity)
4. Test Procedure (Taking IEC 61000-4-8 as an example)
1). Equipment positioning:
Place the EUT at the center of the coil, at least 1 meter away from the coil boundary
Test three orthogonal directions (X/Y/Z axes)
2). Magnetic field calibration
When there is no EUT, calibrate the target magnetic field intensity with a Hall probe
3). Formal testing:
Apply a continuous magnetic field (for 3 minutes) and a short-term magnetic field (1 second to 3 seconds)
Monitor the functional status of the equipment (communication bit error rate, display anomalies, etc.)
4. Criteria:
Grade A: Fully functional
Class B: Temporary performance degradation with automatic recovery
Grade C: Manual intervention is required for recovery
5. Global Certification differences
- EU (CE) : EN 61000-4-8 is the harmonized standard, and industrial equipment usually needs to meet grade 3 (10A/m).
- China (GB) : GB/T 17626.8 mandatorily requires smart meters to pass the 100A/m test
- North America: IEEE C37.90.1 sets similar requirements for power equipment
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