How to use a multimeter to measure the motor speed and number of poles
If the motor has no nameplate and tachometer, you can use a multimeter to judge the speed of the motor without disassembling the motor.
Use the minimum milliampere range of the multimeter to connect the head end and tail end of a certain winding that has been judged above, turn the rotor slowly and uniformly, and watch the pointer of the multimeter swing several times. If it swings once, it means that the current changes positively and negatively. One cycle, it can be judged that it is a 2-pole motor. For the same reason, it is judged to be a 4-pole motor by swinging twice, and it is judged to be a 6-pole motor by swinging three times, and so on.
By judging the number of poles of the motor, you can know its approximate speed (slightly lower than the synchronous speed). The relationship between the synchronous speed of the motor and the number of magnetic poles can basically be calculated as follows when the power frequency is 50Hz: the two poles are 3000r/min, the four poles are 1500r/min, and the six poles are 1000r/min.
During operation, the multimeter pen and the terminal should be kept in good contact. Otherwise, the hands of the watch will swing during the process of turning the rotor, and the result cannot be judged.
Multimeter Circuit Board DC Resistance Detection Method
This is a method to use the ohm block of a multimeter to directly measure the positive and negative DC resistance values of each pin of the IC and peripheral components on the circuit board, and compare it with the normal data to find and determine the fault. Pay attention to the following three points when measuring:
(1) Disconnect the power supply before measurement, so as not to damage the meter and components during the test.
(2) The internal voltage of the electric block of the multimeter shall not be greater than 6V, and the range is preferably R×100 or R×1k.
(3) When measuring IC pin parameters, pay attention to the measurement conditions, such as the model under test, the position of the sliding arm of the potentiometer related to the IC, etc., and also consider the quality of the peripheral circuit components.
