CU3 is a control unit which detects stopped motion and is ideal for use with guard locking interlock switches. The CU3 detects motion of single or three-phase induction motors by measuring the back electro magnetic field (e.m.f) of the motor. When the supply to a motor is disconnected, motor speed will reduce to zero. During the run down period the back e.m.f generated is monitored by the CU3. When the level of e.m.f reaches the level preset at the CU3, the safety outputs of the CU3 close. This enables the output device (e.g., solenoid locking or unlocking switch) to be activated. The CU3’s e.m.f sensitivity level can be adjusted to alter the speed at which the safety contacts close. Features * 2 N.O. safety outputs * 1 N.C. auxilliary output