How to use a multimeter to measure short circuits, open circuits and short circuits in a line
With ohm x1 gear, measure the line two, such as resistance is close to zero is a short circuit, such as a certain amount of resistance (depending on the load in the line), it is not a short circuit, in a certain voltage, the smaller the resistance, the greater the current flowing through the line. With ohm 1k file or 10k file, measure the line two ends, if the resistance value is infinite is open circuit
Extended information:
The basic principle of a multimeter is to use a sensitive magneto-electric DC ammeter (microammeter) as a meter head.
When a small current passes through the head, there will be a current indication. However, the head cannot pass large currents, so some resistors must be connected in parallel and in series to shunt or step down the current, voltage and resistance in the circuit.
Digital multimeter measurement process by the conversion circuit will be measured into a DC voltage signal, and then by the analogue / digital (A/D) converter will be the voltage analogue into digital quantities, and then through the electronic counter counting, and finally the results of the measurements with a digital direct display on the display.
Multimeter measurement of voltage, current and resistance function is achieved through the conversion circuit part of the current, resistance measurements are based on the measurement of voltage, that is to say, the digital multimeter is in the digital DC voltmeter on the basis of the expansion into.
The digital DC voltmeter A/D converter will change the analogue voltage quantity that changes continuously with time into digital quantity, and then the digital quantity is counted by the electronic counter to get the measurement result, and then the measurement result is displayed by the decoder display circuit. The logic control circuit controls the coordinated work of the circuit and completes the whole measurement process in sequence under the action of the clock.
Principle:
1, pointer table reading accuracy is poor, but the process of pointer swing is more intuitive, and the amplitude of its swing speed can sometimes be more objectively reflect the size of the measured (such as measuring the TV data bus (SDL) in the transmission of data when the slight jitter); digital table readings are intuitive, but the process of digital change looks very messy, not very easy to watch.
2, pointer table generally have two batteries, a low-voltage 1.5V, a high-voltage 9V or 15V, the black pen is positive relative to the red pen. Digital meter is commonly used a 6V or 9V battery. In the resistance file, the pointer meter pen output current relative to the digital table is much larger, with R × 1Ω file can make the speaker emit a loud "da" sound, with R × 10kΩ file can even light up the light-emitting diode (LED).
3, in the voltage file, the pointer table internal resistance is relatively small compared to the digital table, the measurement accuracy is poorer. Some high-voltage micro-current occasions can not even be measured accurately, because of its internal resistance will affect the measured circuit (for example, in the measurement of the accelerated stage voltage of the TV tube when the measured value will be much lower than the actual value). The internal resistance of the digital meter voltage is very high, at least in megohm level, which has little effect on the circuit under test. But the very high output impedance makes it susceptible to the influence of induced voltage, in some electromagnetic interference is relatively strong occasions measured data may be false.
4, in short, in relatively high-current, high-voltage analogue circuit measurements in the application of pointer gauge, such as televisions, audio amplifiers. In the low-voltage small-current digital circuit measurements for digital meters, such as beepers, mobile phones and so on. Not absolute, according to the situation can be selected pointer meter and digital meter.
