Multimeter to determine the motor speed method and steps
Ordinary three-phase squirrel cage motors have two speeds: one is the synchronous speed N1, the so-called synchronous speed is the speed of the rotating magnetic field of the motor, this speed has a strict relationship with the number of magnetic poles of the motor, i.e., 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 rotational speed of the motor shaft is slightly lower than the rotational 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. Based on the above principle, a multimeter can be used to determine the number of poles of a motor and thus the speed of the motor.
Steps to determine 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.
3. dial the milliamps 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.
How to use a multimeter to measure the motor speed and the number of poles
If the motor does not have a nameplate, there is no tachometer, in the case of not disassembling the motor, the multimeter can be used to determine the speed of the motor.
With a multimeter of the smallest milliamperes file were connected to the above has been judged out of a winding of the first and last, the rotor slowly and uniformly rotate a circle, look at the multimeter pointer swing a few times, if swinging once, indicating that the current is positive, negative changes in a cycle, you can judge that it is a 2-pole motor. For the same reason, it is a 4-pole motor by swinging 2 times, and a 6-pole motor by swinging 3 times, and so on.
Judging the number of poles of the motor, you can know its approximate speed (slightly lower than the synchronous speed). Synchronous speed of the motor and the number of poles of the relationship between the power supply frequency of 50Hz can be projected in this way: two extremely 3000r/min, four extremely 1500r/min, six extremely 1000r/min.
In operation, the multimeter pen and the terminal to maintain good contact. Otherwise, the process of rotating the rotor needle will swing, judgment is not the result.
