PURPOSE: To simply check the operating time of a moving coil magnet by observing a reversed voltage generated by movement of moving coil.

CONSTITUTION: A drive pulse is applied to a moving coil 3 and a voltage across terminals of coil 3 is measured. At this time, movement of coil 3 stops at the point B where a wire 4 hits the platen and a coil voltage becomes zero. When the wire 4 returns to the initial position owing to a restoration spring 9, the coil voltage also becomes zero. Here, the time taken until a voltage becomes zero at first (point P) is considered as the collision time C of magnet and the time taken until a voltage becomes zero next (point Q) is considered as the forward and backward movement time D. As described above, an operating time of moving coil magnet can be checked easily.