What is Magnetic Field Testing?

Magnetic field testing determines whether a system is immune and able to operate as intended when subjected to a magnetic field. All electric currents have magnetic fields. In AC, when the magnitude or direction of the current changes (both likely to happen every time), its magnetic field also changes, and a changing magnetic field can induce unwanted currents in nearby conductors (PCB traces, wires, or part of another component). Excessive current can lead to the burning of insulation causing a short-circuit.

For example, medical devices such as MRIs emit very strong magnetic fields which can greatly affect the operation of other nearby devices if they are not immune to these magnetic fields. Stray magnetic fields often cause disturbance and lead to weakness of operating magnetic fields.

Which EMC Standards are used for Magnetic Field Testing?

The IEC 61000-4-8 is an EMC standard by the International Electrotechnical Commission for immunity requirements of the equipment to magnetic disturbances. The equipment covered in this standard operates at power frequencies of 50 Hz and 60 Hz and is used in the following environments:

• residential and commercial locations;
• industrial installations and power plants;
• medium voltage and high voltage sub-stations.

This standard does not cover the capacitive or inductive coupling disturbances in cables or other parts of the field installation.

The preferred ranges of test levels for continuous and short duration application of magnetic field, applicable to distribution networks at 50 Hz and 60 Hz, are given below:

For continuous field

For short duration: 1 to 3 secs

"X" is an open level. This level needs to be given in the product specification.

Which Equipment is Required for Magnetic Field Testing?

• Equipment under test (EUT)
• Induction coil
• Test Generator
• Ground Reference Plane

What is the Test Method for Magnetic Field Testing?

Precautions are needed to be taken to avoid the interference of the test magnetic field with the test instrumentation and other sensitive equipment in the test set-up.

The EUT is subjected to a continuous magnetic field of 3 A/m or 10 A/m or/and short pulses for 1 s to 3 s with the help of an induction coil of standard dimensions 1m x 1m. The induction coil is rotated by 90° in order to expose the EUT to the test field from all directions.