How to Measure Circuit Faults with a Multimeter
How to use a multimeter to measure short circuits, open circuits, and short circuits in a circuit
Using ohm x1 scale, measure the two ends of the circuit. If the resistance value is close to zero, it is a short circuit. If there is a certain amount of resistance value (depending on the load in the circuit), it is not a short circuit. When the voltage is constant, the smaller the resistance value, the greater the current flowing through the circuit. Use Ohm 1k or 10k to measure the two ends of the circuit. If the resistance value is infinite, it is an open circuit
The basic principle of a multimeter is to use a sensitive magnetoelectric direct current meter (microampere meter) as the meter head.
When a small current passes through the meter head, there will be a current indication. But the meter head cannot pass through large currents, so it is necessary to shunt or reduce voltage by connecting some resistors in parallel or series on the meter head, in order to measure the current, voltage, and resistance in the circuit.
The measurement process of a digital multimeter is converted into a DC voltage signal by a conversion circuit. Then, the analog to digital (A/D) converter converts the voltage into a digital quantity, which is counted by an electronic counter. Finally, the measurement results are directly displayed in digital on the display screen.
The function of measuring voltage, current, and resistance with a multimeter is achieved through the conversion circuit, and the measurement of current and resistance is based on voltage measurement. This means that a digital multimeter is an extension of a digital DC voltmeter.
The A/D converter of a digital DC voltmeter converts the analog voltage that continuously changes over time into a digital quantity. The digital quantity is then counted by an electronic counter to obtain the measurement result, which is then displayed by a decoding display circuit. The coordination work of the logic control circuit controls the entire measurement process in sequence under the action of the clock.
Principle:
1. The reading accuracy of the pointer meter is poor, but the process of pointer oscillation is relatively intuitive, and the amplitude of its oscillation speed can sometimes objectively reflect the measured size (such as the slight jitter of the TV data bus (SDL) during data transmission); The reading on the digital meter is intuitive, but the process of changing the numbers looks messy and not easy to watch.
2. There are usually two batteries in a pointer meter, one with a low voltage of 1.5V and the other with a high voltage of 9V or 15V. The black pen is relatively positive compared to the red pen. A digital meter usually uses a 6V or 9V battery. In the resistance range, the output current of the pointer meter is much larger than that of a digital meter, using R × 1 Ω gear can make the speaker emit a loud "click" sound, using R × 10k Ω gear can even light up light-emitting diodes (LEDs).
3. In the voltage range, the internal resistance of a pointer meter is relatively small compared to a digital meter, and the measurement accuracy is relatively poor. In some situations where high voltage and micro current are present, it is even impossible to accurately measure them because their internal resistance can affect the circuit being tested (for example, when measuring the acceleration stage voltage of a television picture tube, the measured value may be much lower than the actual value). The internal resistance of the voltage range of the digital meter is very high, at least at the megaohm level, and has little impact on the circuit being tested. But the extremely high output impedance makes it susceptible to the influence of induced voltage, and the data measured in some places with strong electromagnetic interference may be false.
4. In short, pointer meters are suitable for measuring analog circuits with relatively high currents and voltages, such as television sets and audio amplifiers. Digital meters are suitable for low voltage and low current digital circuit measurements, such as BP machines, mobile phones, etc. Not absolute, you can choose a pointer table and a digital table according to the situation.
