What is a Magnetic Field Generator?

Magnetic fields caused by power/frequency are being generated all around us by means of AC (Alternating Current) flowing in conductors. A good example is a magnetic field due to the 50/60 Hz in the main power cord of a laptop. If unchecked this magnetic field can cause interference for electronic devices and other electronic components in its vicinity.

The power-frequency magnetic fields may be present continuously or for a short duration. The continuous or steady power line frequency magnetic field is generated during normal operating conditions (i.e., due to the normal AC flow through the conductors). Magnetic field present for a short duration is due to fault occurrence or initial power turn-on of electronic equipment. Hence, it is necessary to test the immunity of the electronics products against this power-frequency magnetic field.

The IEC 61000-4-8 standard is the international EMC standard to conduct the power frequency magnetic field immunity test on equipment to check the ability of the equipment against these magnetic fields. 

In EMC testing, a magnetic field generator is used to generate/simulate the power-frequency (60/50 Hz) magnetic field (A/m) as per international EMC standards such as IEC/EN 61000 4-8 to test the immunity of the electrical and electronic equipment against these magnetic fields. These generators usually simulate the magnetic environment in residence, commercial and industrial areas, power stations, and low & high substations.

Fig. 1 Magnetic field generator

The magnetic field generator also called the current generator consists of a power supply unit, a 50/60 Hz sine wave generator to generate the sine wave, a power amplifier, and a potentiometer to control the output current range. The main function of the generator is to provide/control the current flow through a loop antenna to establish the required power-frequency magnetic field for conducting both continuous and short-duration magnetic field immunity EMC tests. The output current control may be manual or remote control (software control). In addition, these generators can be used for both vertical and horizontal plane testing by simply rotating the coil antenna through its mounting on the included stand.

These generators comply with international EMC standards such as IEC/EN 61000 4-8 and can be used as a stand-alone instrument. 

How does a magnetic field generator work to test a EUT?

The power-frequency magnetic field is generated/simulated by using a magnetic field generator (current generator) and a magnetic field loop or loop antenna (i.e., coil) set up. The loop antenna may have a circular or rectangular shape with the coil factor Cf. The magnetic field strength (A/m), which is generated at the center of the loop antenna is given by the following formula.

H = Cf × I (A/m)

Here, H is the generated field, Cf is the coil factor, I is the current flowing through the loop.

Thus, in a magnetic field immunity test, the equipment under test (EUT) is placed at the center of the loop antenna, and the magnetic field generator provides/controls the current flow through the coil to establish the required power frequency magnetic field.

Key features of magnetic field generator:

        1. Compatible to IEC 61000-4-8 test

        2.  User-selectable Frequency: 50/60 Hz

        3. Temperature protection

Key specs of a magnetic field generator:

Field strength: Represents the minimum & maximum level of magnetic field strength that can be provided by the magnetic field generator. It is expressed in Ampere/meter (A/m). The magnetic field generator can produce both continuous and short-duration magnetic fields.

Frequency: Represents the frequency of the output current in Hertz (Hz). It can be 50/60 Hz. 

EMC Standard: Represents the EMC standard to which the magnetic field generator complies.

Output current range: Represents the output current range that can be provided by the magnetic field generator. It is represented in Ampere (A). 

Harmonic distortion rate: Represents how much percentage of harmonics present in the output current waveform. The harmonic distortion rate is the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. It is expressed in % or a number (for example, 8% or 0.08) 

Power consumption: Represents the power consumption of the magnetic field generator in Watts (W). 

Test duration: It means that the duration of the test that can be supported by the generator. It may vary from 1 minute to few hours for the continuous tests and from 1 to 3 sec for short duration tests. 

Supply voltage: Represents the input AC supply voltage in Volts (V). 

Operating modes: It may be manual or remote control.

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