Working principle
The measurement is based on coil sense impedance. A magnet and an electromagnet in the detector vibrate the plate. The current flowing through the electromagnetism is reduced when the detector is covered by the measured solid. The sensor detects this change to determine the presence of solid and gives an output. When the detector is not covered by the material, the electromagnet vibrates at the operating frequency when an alternating current is applied. The back electromotive force on the electromagnet becomes the largest, depending on the change in magnetic field in the magnetic field.
The sensor determines that the detector is not covered by the material. Applying an alternating current when the detector is covered with material does not cause the electromagnet to vibrate at the operating frequency. The back electromotive force is absent when the magnet is stationary.