https://www.bkneddy.com/eddy-current-testing-equipment/pre-multi-frequency-eddy-hardness-separator.html Eddy Current Brake for Sale Stimulating the coil makes a magnetic induction to the tested material. The induced electromotive force received by the testing coil is related to the shape and size of the material hysteresis loop. When the low-frequency sinusoidal wave excitation voltage is magnetically induced, the induced electromotive force obtained is also a sinusoidal waveform, usually including a fundamental wave. By measuring the fundamental wave component of the inductive potential of the testing coil, the measured alloy composition and heat treatment status can be obtained, thereby achieving material hardness sorting.