What are the differences between electromagnetic attraction relay and electromagnetic induction relay?

Answer 1

Electromagnetic attraction relays have a fixed contact and a moving contact, attached normally to either a hinged plate, or the moving piston of a solenoid. The contacts are brought together by the magnetic attraction of an energized coil attached to one of the contact supports, or in the case of the solenoid, the coil which surrounds the moving piston. These relays can operate on either ac or dc inputs, and have virtually no time delay. This makes them ideal for instantaneous operations.

Electromagnetic induction relays operate on the principle of the induction motor - that is, magnetic flux applied to a rotor will develop torque in that rotor, and cause it to rotate. However, instead of spinning like a motor, the rotor in this type of relay has a mechanical stop or reset point, and a contact fixed to it that will eventually touch the stationary contact, when the input quantity meets or exceeds the predetermined setpoint. Relays of this type only operate with ac quantities, and, in many or most cases, can be adjusted to provide a time delay (which in reality simply moves the reset point farther away from the contact point, so that the rotor must rotate farther to pick up the contacts).