How do you test for short circuits and open circuits with a multimeter?
A multimeter is an essential "hardcore" tool for those engaged in electronics, electrical engineering, and maintenance. It boasts powerful functions and can be used to measure AC voltage, DC voltage, AC current, DC current, resistance, capacitance, diodes, transistors, temperature, and more. For instance, when we test and debug products, we need to use a multimeter to assist in identifying issues.
When a product malfunctions, I usually first use a voltmeter to measure whether the input and output voltages are normal, in order to determine whether the power supply circuit is functioning properly. When the voltage is abnormal, it often indicates a short circuit or an open circuit.
Buzzer gear test for short circuit and open circuit
Digital multimeters typically have a buzzer setting. When a connection is detected, it will emit a "BI" sound, which is very intuitive and eliminates the need to constantly monitor the multimeter.
When measuring two positions that should not be connected, if a "BI" sound is emitted, it indicates a short circuit; when measuring two positions that should be connected, if no "BI" sound is emitted, it indicates an open circuit;
If your multimeter does not have a buzzer setting, you can still use the resistance setting to determine whether there is a short circuit or an open circuit by following the method for measuring resistance. If the resistance becomes very low, only a few ohms, or even a few tenths of an ohm, it indicates a short circuit; if no resistance value can be measured or the resistance value is quite high, it indicates an open circuit.
Leakage measurement
Electric leakage is divided into strong electric leakage and weak electric leakage. Strong electric leakage refers to the leakage of high-voltage alternating current (AC), which can electrocute people or cause the leakage switch to trip. You can use a multimeter set to AC mode to measure whether there is a certain AC voltage present. Another method is to disconnect the power supply and use the resistance setting at the maximum range to measure the resistance between the leakage point and the live wire (L) or neutral wire (N). If there is no leakage, the resistance value will be extremely high, equivalent to insulation. If the resistance to ground is not high enough, and the measured resistance is in the hundreds of kilohms, then there may be leakage.
If you want to detect the slight leakage in a weak current circuit, you can use the current range of a multimeter and connect it in series to the circuit to measure whether the operating current increases. For example, if the current of a product in normal standby mode is tens of microamps, but it measures hundreds of microamps or even several milliamps, it indicates that there is a leaking component in the circuit. When measuring current, if you are not sure about the magnitude of the operating current, you can start with a larger range and gradually reduce it to test. Exceeding the range can easily burn out the fuse of the multimeter.
