According to the law of electromagnetism, when the magnetic field changes, an induced electromotive force will be generated in the nearby conductor, and its direction conforms to Faraday's law and Lenz's law, which is exactly opposite to the voltage originally applied to both ends of the coil. This voltage is the back EMF.

Back EMF refers to the electromotive force in the opposite direction to the electromotive force of the power supply. Back EMF can occur when multiple power sources are present in a circuit. For example, two metal rods on the same rail loop cut the magnetic field at different speeds, and back EMF may appear; when both emotional and induced EMFs exist simultaneously, back EMF may appear. For coils, when the energized current changes, a back electromotive force is generated at both ends of the coil. For example, the change of the voltage across the inductor coil in the LC oscillator circuit is closely related to the back electromotive force; when the motor coil rotates, the back electromotive force is also generated.

The test of back electromotive force can judge the rotor and performance of a permanent magnet synchronous motor. Therefore, in the production of permanent magnet synchronous motors, the back electromotive force test is widely used, and how is back electromotive force tested? The brushless DC motor tester produced by AIP can meet the AC Hi-pot, surge, insulation resistance, coil resistance, coil inductance, rotation, back EMF, phase sequence, and Hall characteristics of permanent magnet synchronous motors. , barcode entry, inductance, and other items of testing.