How to use a multimeter_ Tips on how to use a multimeter

　　A multimeter is also called a multimeter, a three-function meter, or a multiplexer. It is a multifunctional, multi-range measuring instrument. Generally, a multimeter can measure DC current, DC voltage, AC voltage, resistance, and audio level, etc. Some multimeters can also measure AC current, capacitance, inductance, and some parameters of semiconductors. It is a simple and practical measuring instrument.

　　Nowadays, the most common multimeters are digital multimeters, and pointer multimeters are rarely used. Digital multimeters are relatively simple measuring instruments. As a multi-purpose electronic measuring instrument, it generally includes functions such as ammeter, voltmeter, ohmmeter, etc., and is sometimes also called a multimeter, multimeter, multimeter, or three-meter. Multimeters are widely used. Here are the basic usage methods and tips for multimeters.

　　How to use a multimeter

　　(1) Before using the multimeter, you should first perform "mechanical zero adjustment", that is, when there is no electrical quantity to be measured, make the multimeter pointer point to the position of zero voltage or zero current.

　　(2) When using a multimeter, do not touch the metal part of the test leads with your hands. This can ensure accurate measurement and personal safety.

　　(3) When measuring a certain amount of electricity, you cannot change gears while measuring, especially when measuring high voltage or high current. Otherwise, the multimeter will be damaged. If you need to change gears, you should disconnect the test leads first and then measure after changing gears.

　　(4) When using the multimeter, it must be placed horizontally to avoid errors. At the same time, attention should also be paid to avoiding the influence of external magnetic fields on the multimeter.

　　(5) After using the multimeter, the conversion switch should be set to the maximum AC voltage. If the multimeter is not used for a long time, the battery inside the multimeter should be removed to prevent the battery from corroding other components in the meter.

　　When using an analog multimeter, insert one end of the two measuring probes into the measuring end according to the requirements of red to positive (+) and black to negative (-), and then confirm whether the pointer is at the "0" position. The pointer should be aligned with the end line on the left side of the dial. If it is not consistent, zero adjustment should be performed. Before measuring current and voltage, estimate the range of the current and voltage to be measured, set it to a larger gear first, and then adjust it to a suitable gear to avoid excessive current burning the multimeter.

　　When measuring, the influence of the multimeter's internal resistance must be considered. For example, to measure voltage, the test lead must be connected to the circuit being measured. At this time, current also flows through the resistance inside the multimeter, which has a certain influence on the measured value. When measuring the voltage at the same point, if different gears are used, the internal resistance of the multimeter is different, and the degree of influence is also different.

　　When measuring transistor electronic circuits, it is better to select an internal resistance of 20kΩ/V in the DC range. This value is usually marked on the multimeter dial. In addition, transistor circuits often need to measure low-value voltages, such as 0.1V. In this case, the selected multimeter should have a measurement range of 1V.

　　Instructions for use of multimeter

　　The following uses the MF30 multimeter as an example to explain the readings of the multimeter. The first scale line indicates the resistance value, with infinity at the far left and zero at the right, and the scale in the middle is uneven. The resistance ranges are R×1, R×10, R×100, R×1K, and R×10K, which respectively indicate the multiples that need to be multiplied to get the actual resistance value (in ohms).

　　For example, if you use the R×100 range to measure a resistor and the pointer indicates "10", then its resistance value is 10×100=1000, that is, 1K. The second scale line is shared by the 500V range and the 500mA range. It should be noted that the indication principle of the voltage range and the current range is different from that of the resistance range. For example, the 5V range means that the range can only measure voltages below 5V, and the 500mA range can only measure currents below 500mA. If the range is exceeded, the multimeter will be damaged.

　　Note: The multimeter should be placed horizontally when in use. Insert the red test lead into the + hole and the black test lead into the - hole. Use the current range to test the current, and do not use the voltage range or resistance range by mistake. The same applies to other ranges. Otherwise, the fuse in the multimeter may burn or the meter head may be damaged. If you do not know the range in advance, try to measure with the maximum range, then disconnect the measuring circuit and change the range. Do not change the range while online. If the needle quickly deflects to the bottom, you should immediately disconnect the circuit and check.

　　Finally, there is one more rule, which is that after use, the range switch of the multimeter should be turned to the highest AC voltage level to prevent others from accidentally measuring 220V AC voltage and causing damage.

　　Tips for using a multimeter

　　1. Check the block before measuring, do not measure without checking

　　Every time you pick up the test lead to prepare for measurement, be sure to check whether the measurement category and range selection switch are in the correct position. For safety reasons, you must develop this habit.

　　2. Do not shift gears during measurement, shift to neutral gear after measurement

　　Do not turn the selection knob arbitrarily during measurement, especially when measuring high voltage (such as 220V) or large current (such as 0.5A), so as to avoid arcing and burning the switch contacts. After the measurement is completed, the range selection switch should be turned to the "?" position.

　　3. The dial should be level and the reading should be correct.

　　When using a multimeter, it should be rotated horizontally and your line of sight should be facing the needle when reading.

　　4. The measuring range should be appropriate, and the needle should be more than half

　　When selecting a range, if you cannot estimate the size of the measurement in advance, you should try to choose a larger range, and then gradually switch to a smaller range based on the deflection angle, until the pointer deflects to about 2/3 of the full scale.

　　5. Measure R without charge, and measure C with discharge first.

　　It is strictly forbidden to measure resistance when the circuit under test is connected. When checking large-capacity capacitors on electrical equipment, the capacitors should be short-circuited and discharged before measurement.

　　6. Adjust to zero before measuring R, and adjust to zero when shifting gears

　　When measuring resistance, you should first turn the conversion switch to the resistance block, short-circuit the two test leads, turn the "Ω" zero adjustment potentiometer, and make the pointer point to zero ohms before measuring. Every time you change the resistance block, you should readjust the ohm zero point.

　　7. Black must be negative, remember that the black in the table is connected to "+"

　　The red test lead is the positive pole and the black test lead is the negative pole, but on the resistance block, the black test lead is connected to the positive pole of the internal battery.

　　8. When measuring I, connect them in series, and when measuring U, connect them in parallel.

　　When measuring current, the multimeter should be connected in series with the circuit being measured; when measuring voltage, the multimeter should be connected in parallel across the circuit being measured.

　　9. Do not connect the polarity in reverse, and use it with one hand

　　When measuring current and voltage, special attention should be paid to ensure that the polarity of the red and black test leads are not reversed, and one-handed operation must be developed to ensure safety.