How to use a multimeter to determine the speed of the motor
A regular three-phase squirrel cage motor has two speeds: one is the synchronous speed N1, which is the speed of the motor's rotating magnetic field. This speed is strictly related to the number of magnetic poles of the motor, that is, n1=60f/p
Among them, n1- synchronous speed, revolutions per minute;
J - frequency of current, cycles per second;
P - the number of magnetic poles of the electric motor.
The second is asynchronous speed, which refers to the speed of the motor shaft. When an electric motor drives production machinery, the speed of the motor shaft is slightly lower than the speed of the rotating magnetic field, but the difference is not significant. For example, for a pair of pole motors, the speed of the motor wheel is 2950 revolutions per minute, for two pole motors it is 1430 revolutions per minute, and for three pole motors it is 920 revolutions per minute. According to the above principle, a multimeter can be used to determine the number of magnetic poles of the motor, and then determine the speed of the motor;
Steps to determine the number of magnetic poles of an electric motor using a multimeter
1. Fold open the six wire ends of the electric motor;
2. Use the ohm range of the multimeter to find any phase of the three-phase winding, as shown at terminals 1-2 in the diagram;
3. Set the milliampere range of the multimeter to the minimum setting and connect its two wires across terminals 1 to 2;
4. Slowly rotate the motor shaft and observe the changes in the multimeter pointer. If the shaft rotates once and the pointer swings once, it indicates that the current changes by one cycle, which is a pair of magnetic poles; If it swings twice, it is two pairs of magnetic poles; Swing three times to form three pairs of magnetic poles.
