When the capacitance is calibrated, it still moves downward when touching the metal plate.

Cause analysis: ① Slag on the nozzle and other reasons make the amplifier unable to detect the collision plate. ② The metal plate has poor contact with the machine tool, so the amplifier cannot detect the collision plate. ③ The metal plate has a plastic protective film. Solution: ① Clean the nozzle and keep it clean. ② Ensure good contact between metal plate and machine tool. ③ Remove the plastic protective film.