Principles and operating procedures for selecting a multimeter
1. The reading accuracy of the pointer meter is poor, but the process of pointer oscillation is more 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) when transmitting data); The reading on the digital meter is intuitive, but the process of number changes looks messy and not easy to observe.
2. A pointer usually has two batteries inside, one with a low voltage of 1.5V and the other with a high voltage of 9V or 15V. The black probe is relatively positive compared to the red probe. A digital meter often uses a 6V or 9V battery. In the resistance range, the output current of the pointer meter is much larger than that of the digital meter. Using the R × 1 Ω range can make the speaker emit a loud "click" sound, and using the R × 10k Ω range can even light up the light-emitting diode (LED).
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 high voltage and low current situations, it is even impossible to accurately measure because its internal resistance can affect the tested circuit (for example, when measuring the acceleration stage voltage of a television tube, the measured value will be much lower than the actual value). The internal resistance of the voltage range of the digital meter is very high, at least in the megaohm level, and has little impact on the tested circuit. But the extremely high output impedance makes it susceptible to the influence of induced voltage, and the data measured in some situations with strong electromagnetic interference may be false.
4. In summary, pointer meters are suitable for analog circuit measurements with relatively high current and voltage, such as television and audio amplifiers. Digital meters are suitable for low voltage and low current digital circuit measurements, such as BP machines, mobile phones, etc. It is not immutable, and pointer and number tables can be selected according to the situation.
Operating procedures
1. Before use, one should be familiar with the various functions of the multimeter, and correctly select the gear, range, and probe socket based on the measured object.
2. When the size of the measured data is unknown, the range switch should be set to the * maximum value first, and then switch from a large range to a small range, so that the instrument pointer indicates more than half of the full scale.
3. When measuring resistance, after selecting the appropriate magnification range, touch the two probes to make the pointer point at zero. If the pointer deviates from the zero position, adjust the "zero adjustment" knob to reset the pointer to zero to ensure accurate measurement results. If it cannot be zeroed or the digital display meter emits a low voltage alarm, it should be checked in a timely manner.
4. When measuring the resistance of a certain circuit, the power supply of the tested circuit must be cut off and live measurement is not allowed.
5. When using a multimeter for measurement, attention should be paid to the safety of personnel and instrument equipment. During the test, it is not allowed to touch the metal part of the probe with your hands, and it is not allowed to switch gears with electricity to ensure accurate measurement and avoid accidents such as electric shock and burning of the instrument.
