Methods for Using a Multimeter to Find Faults in Electrical Control Circuits
Generally, there are two methods for finding circuit faults: the voltage method and the resistance method. The voltage method is to use voltage measurement to detect the fault point, while the resistance method is to use resistance measurement to find the fault. Each method has its own advantages. If you are not familiar with the circuit, we recommend using the resistance method to judge the fault, which is relatively safer. Before measuring the control circuit, first disconnect the power supply/fuse of the control circuit to separate the control circuit from the main circuit. The purpose of doing this is to avoid interference from the main circuit when measuring the control circuit.
Then, place one probe on the odd starting number (such as 101) of the control loop, and the other probe on the even starting number (such as 102) of the control loop. The resistance between them should be infinite. Then press the pushbutton switch SB2. At this time, there should be a certain resistance value (the resistance value is equal to the resistance of the coil). If the resistance value is still infinite, it means that the circuit between the two probes is not connected and there is a break somewhere, and then continue to search further.
Then, press the button again and measure the resistance between the next terminal (103) of the starting terminal and the even starting number (102). If there is a certain resistance value, it indicates that there is an open circuit between 101 and 103. If the resistance value is still infinite, it means that there is still an open circuit somewhere between 103 and 102, and then continue to search further.
Since the numbering rule determines that the terminals with odd and even tail numbers belong to two circuits of different polarities, when we measure the terminals ending with odd numbers and those ending with even numbers, there should normally be a certain resistance between them. (Of course, this is based on the premise that they are in the same power supply loop.)
