Electrical Engineering ⇒ Topic : Electromechanical Counter

Electromechanical Counter

Perhaps the most simple and direct method of measuring slip (i e, difference between synchronous speed and rotor speed) is to compare the speed of induction motor with a small synchronous motor's speed as shown in Fig.(a).The synchronous motor employed must have the same number of poles as the induction motor.At the end of each shaft is a cylinder of phenolic or other suitable insulating material into which has been fitted a circular slip ring to which a small motor contactor is connected as shown in Fig. 12.9. The slip rings are connectd to a voltage source in series with an electric pulse counter, either of the electrochemical relay type or an electronic digital pulse counter. The synchronous motor always runs at synchronous speed, which is the speed of the rotating field of the induction motor. Each time the indication motor slips, a revolution, the synchronous, and induction motor contactors close the circuit and register a pulse. The number of pusles registered per minute is the slip in r.p.m.

                                                           Fig.(a) Electromechanical counter