How does a digital multimeter judge whether a line is open or short circuit
The use of digital multimeters is very common now, and it plays an important role in line detection and circuit wiring. The most basic and most commonly used measurement of the three physical quantities of the multimeter is voltage, current, and resistance. The title is precisely the measurement of these three basic physical quantities.
voltage measurement
The digital multimeter is used for voltage measurement. At this time, the multimeter is equivalent to a voltmeter, so the multimeter is connected in parallel to the power-consuming components or both ends of the power supply on the line. Before measurement, find out whether the measured voltage is AC or DC, and estimate the highest voltage value, and then select the corresponding AC voltage range or DC voltage range. If the voltage is unknown, it is safer to use the maximum range of voltage.
current measurement
When a digital multimeter measures current, it is equivalent to an ammeter. So connect the multimeter in series with the circuit under test. Before measuring the current, it is also necessary to distinguish whether it is DC current or AC current. After estimating the maximum value of the current, select the corresponding AC current range or DC current range. If the current value is unknown, it is safer to use the maximum range.
Determine if the line is open or short circuited?
Make sure that the line is not charged before testing and judging. Short circuit means that the line from the power supply is directly connected without passing through the load, which is equivalent to connecting the two ends of the power supply directly with wires. If it is alternating current, that is, the live wire and the neutral wire are put together. At this time, as long as the power is turned off, when measuring with the resistance gear of the digital multimeter, the resistance is very small or zero, which means that there is a short circuit in the circuit. You can also use the buzzer position of the multimeter, if there is a short circuit, the buzzer of the multimeter will beep.
Circuit break judgment
The three elements of a circuit are power supply, load, and intermediate links. As long as one of the elements does not conform to the circuit, the circuit cannot be formed. If the power supply is normal, then the disconnected part may be in the load or intermediate link. The premise is that the line is charged when there is no short circuit in the line. If there is a voltage at both ends of the measured load, it means that there is no open circuit in the line, but the load is damaged. If there is no voltage at both ends of the measured load, it means that there is an open circuit in the intermediate link, which may be an open circuit of the wire or an open circuit of the auxiliary equipment.
