How to use a multimeter to measure the break point of a cable
Bila a wire break occurs within a cable or cable, the exact location of the wire break is difficult to determine due to the wrapping of the outer insulation. This problem can be solved easily with a digital multimeter.
Spesifik kaedah: Connect one end of the wire (kabel) dengan a breakpoint to the live line of the 220V mains power, and leave the other end floating. Pull the digital multimeter to AC2V, start from the live wire access end of the wire (cable), hold the tip of the black test lead with one hand, and slowly move the red test lead along the insulation of the wire with the other hand. At this time, the display The voltage value displayed on the screen is approximately 0.445V. When the red test lead moves somewhere, the voltage displayed on the display suddenly drops to 0.0 volts (about one-tenth of the original voltage). About 15cm from this position forward (the live wire access end) is the wire ( Cable) break point.
Bila menggunakan this method to check the shielded wire, if only the core wire is broken but the shielding layer is not broken, this method is powerless.
How to use a multimeter to measure motor speed and pole number
If the motor has no nameplate and no tachometer, you can use a multimeter to determine the motor's speed without disassembling the motor.
Use the minimum mA setting of the multimeter to connect the head end and tail end of a certain winding that has been judged above, slowly rotate the rotor in a circle at a constant speed, and see how many times the multimeter pointer swings. If it swings once, it means that the current changes positively or negatively. One cycle, it can be judged that it is a {{0}% 7dpole motor. For the same reason, if it swings twice, it is judged to be a 4-pole motor, if it swings three times, it is judged to be a 6-pole motor, and so on.
By determining the number of poles of the motor, you can know its approximate speed (sedikit lower than the synchronous speed). The relationship between the synchronous speed of the motor and the number of magnetic poles can be basically calculated as follows when the power supply frequency is 50Hz: the second pole is 3000r/min, the fourth pole is 1500r/min, and the sixth pole is 1000r/min.
During operation, the multimeter probes and terminals must be in good contact. Otherwise, the hands of the watch will swing during the rotation of the rotor, and the result cannot be judged.
