Digital multimeter screen has a digital display function can not be used, how can it be used?
Ordinary three-phase squirrel cage motor has two speeds: one is the synchronous speed N1, the so-called synchronous speed is the speed of the motor rotating magnetic field, this speed has a strict relationship with the number of magnetic poles of the motor, that is, n1 = 60f/p
Where n1 - synchronous rotational speed, rev / min;; and
J - frequency of the current, weeks/second; and
P - the number of magnetic pole pairs of the motor.
The second is the asynchronous speed, i.e. the speed of the motor shaft. When the motor drives the production machinery, the speed of the motor shaft is slightly lower than the speed of the rotating magnetic field, but the difference is not much. For example, the speed of the motor wheel is 2950 rpm for a one-pole motor, 1430 rpm for a two-pole motor, and 920 rpm for a three-pole motor. On the basis of the above principle, a multimeter can be used to determine the number of poles in a motor and thus the speed of the motor.
Steps for determining the number of magnetic poles of a motor using a multimeter
1. Fold the six wires of the motor; 2.
2. Use the ohm stop of the multimeter to find out any phase of the three-phase winding, such as the end of l ~ 2 in the figure.
3. dial the milliamperage of the multimeter to the smallest block, and its two wires across the l ~ 2 end;
4. Slowly rotate the motor shaft, observe the change of the multimeter pointer. If the rotor shaft rotates a circle, the pointer swings once, indicating that the current changes a cycle, for a pair of magnetic poles; if the swing twice, then two pairs of magnetic poles; swing three times, for three pairs of magnetic poles.
