How to use a multimeter to detect short and open circuits
A multimeter is a necessary "hard core" tool for friends engaged in electronics, electricians, and maintenance. It has very powerful functions and can be used to measure AC voltage, DC voltage, AC current, DC current, resistance, capacitance, diode, transistor, temperature, etc. For example, when testing and debugging products, we need to use a multimeter to assist in finding problems.
When a product malfunctions, I usually use a voltage range to measure whether the input and output voltages are normal, in order to determine whether the circuit of the power supply is normal. The voltage is abnormal, and often there is a short circuit or open circuit.
Short circuit or open circuit detected by buzzer gear
A digital multimeter usually has a buzzer, and when connected, it will sound "BI", which is very intuitive and does not require staring at the multimeter.
When measuring two positions that should not be connected, if a "BI" or "BI" sound is emitted, it indicates a short circuit; When measuring two positions that should be connected, but no "BI" or "BI" sound is emitted, it indicates that there is an open circuit;
If your multimeter does not have a buzzer range, you can also use a resistance range to determine whether there is a short circuit or open circuit by measuring the resistance value. If the resistance becomes very small, only a few ohms, or even a few tenths of an ohm, it indicates a short circuit; If the resistance value cannot be measured or is quite large, it indicates an open circuit.
When using the buzzer or resistance range for measurement, remember to disconnect the power supply first!
Leakage measurement
Leakage is divided into strong current leakage and weak current leakage. Strong current leakage refers to the leakage of AC high voltage, which can cause electricity to a person or cause the leakage switch to trip. The multimeter can be set to the AC range to measure the presence of a certain AC voltage. Another method is to cut off the power supply and measure the resistance value between the leakage point and the live wire (L) or zero wire (N) using the maximum resistance range. If there is no leakage, the resistance value is extremely high, equivalent to insulation. If the resistance value to the ground is not large enough and a resistance value of several hundred K is measured, then there may be leakage.
If you want to measure the weak leakage of a weak current circuit, you can use the current range of a multimeter to connect the multimeter in series to the circuit and measure whether the working current has increased. For example, when the product is in normal standby mode, the current is several tens of microamps, but the measured current is several hundred microamps, or even a few milliamps, which indicates that there are leakage components in the circuit. If you are not clear about the magnitude of the working current when measuring the current, you can start with a gear with a larger range first, and then slowly reduce the range to test. Overrange can easily burn out the fuse of the multimeter.
What other functions does a multimeter have?
A multimeter has many functions, such as measuring capacitance, diodes, LEDs, transistors, and even connecting thermocouples to measure temperature. Of course, not all multimeters have such powerful functions, and it depends on the specific model
