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.