How to measure the short circuit, open circuit and short circuit of the line with multimeter
Measure the two ends of the line with ohm x1. If the resistance is close to zero, it is a short circuit. If there is a certain amount of resistance (depending on the load in the line), it is not a short circuit. When the voltage is constant, the smaller the resistance, the greater the current flowing through the line. Use ohm 1k or 10k to measure both ends of the line. If the resistance is infinite, it is an open circuit.
Extended data:
The basic principle of multimeter is to use a sensitive magnetoelectric DC ammeter (microammeter) as the meter head.
When a small current passes through the meter, there will be a current indication. But the meter can't pass large current, so it is necessary to shunt or step down some resistors in parallel and series on the meter to measure the current, voltage and resistance in the circuit.
In the measuring process of digital multimeter, the measured signal is converted into a DC voltage signal by a conversion circuit, and then the voltage analog signal is converted into a digital signal by an analog-to-digital (A/D) converter, and then counted by an electronic counter. Finally, the measurement result is directly displayed on the display screen in digital form.
The function of multimeter to measure voltage, current and resistance is realized through the conversion circuit, and the measurement of current and resistance is based on the measurement of voltage, which means that digital multimeter is extended on the basis of digital DC voltmeter.
A/D converter of digital DC voltmeter converts the analog voltage that changes continuously with time into digital value, and then the digital value is counted by electronic counter to get the measurement result, and then the measurement result is displayed by decoding display circuit. The logic control circuit controls the coordinated work of the circuits, and the whole measurement process is completed in sequence under the action of the clock.
Principle:
1. The reading accuracy of the pointer meter is poor, but the process of pointer swing is intuitive, and its swing speed and amplitude can sometimes objectively reflect the measured size (such as the slight jitter of the data bus (SDL) of the TV set when transmitting data); The reading of digital meter is intuitive, but the process of digital change looks messy and not easy to watch.
2. Generally, there are two batteries in the pointer meter, one with low voltage of 1.5V and the other with high voltage of 9V or 15V, and its black stylus is the positive terminal relative to the red stylus. Digital meters often use a 6V or 9V battery. In the resistance range, the output current of the stylus of the pointer meter is much larger than that of the digital meter. Using R×1Ω range can make the speaker make a loud "beep" sound, and using R×10kΩ range can even light up the light emitting diode (LED).
3. In the voltage range, the internal resistance of the pointer meter is relatively small compared with the digital meter, and the measurement accuracy is relatively poor. It is even impossible to measure the high-voltage micro-current in some occasions, because its internal resistance will affect the circuit to be measured (for example, the measured value will be much lower than the actual value when measuring the voltage of the acceleration stage of the TV picture tube). The internal resistance of digital meter voltage file is very large, at least in the order of megaohms, which has little influence on the circuit under test. However, the extremely high output impedance makes it vulnerable to the induced voltage, and the measured data may be false in some occasions with strong electromagnetic interference.
4. In short, the pointer meter is suitable for the measurement of analog circuits with relatively high current and high voltage, such as TV sets and audio amplifiers. It is suitable for digital circuit measurement of low voltage and small current, such as BP machine and mobile phone. Not absolute, you can choose a pointer table and a number table according to the situation.
