Ten Practical Tips for Using a Multimeter
① Before use, verify that the function selector switch is set to the position corresponding to the quantity to be measured and that the test leads are inserted into the correct jacks.
② Place the multimeter vertically or horizontally as required by the "ground" or arrow symbol on the meter face. If the pointer does not rest at the start of the scale, perform mechanical zero adjustment first.
③ Select an appropriate range according to the magnitude of the measured quantity. When measuring voltage or current, try to make the pointer deflect to more than half of full scale to reduce measurement error. If the magnitude of the measured value is unknown, start with the maximum range and gradually switch to lower ranges until the pointer shows a substantial deflection. Do not change ranges under power when measuring high voltage (above 100 V) or large current (above 0.5 A); otherwise, arcing and burning of the selector switch contacts may occur.
④ Observe the polarity when measuring DC voltage or DC current. If the potential level of the two measured points is unknown, briefly touch the two test leads to these points. Judge the potential polarity by the direction of the pointer's kick before formal measurement.
⑤ When measuring AC voltage, confirm that the AC frequency falls within the operating frequency range of the multimeter. The typical operating frequency range for ordinary multimeters is 45–1500 Hz. Readings will drop sharply above 1500 Hz. The AC voltage scale is calibrated for the RMS value of sine waves, so multimeters cannot accurately measure triangular waves, square waves, sawtooth waves and other non‑sinusoidal waveforms. When DC voltage is superimposed on an AC voltage, connect a blocking capacitor with sufficient withstand voltage in series before measurement.
⑥ When measuring voltage across a load, check whether the internal resistance of the multimeter is much higher than the load resistance. If not, the shunting effect of the multimeter will make the reading far lower than the true value; direct measurement with a multimeter is not feasible and alternative methods should be adopted. The internal resistance of the voltage range equals voltage sensitivity multiplied by full‑scale voltage. For example, the MF‑30 multimeter has a DC voltage sensitivity of 5 kΩ/V on the 100 V DC range, giving an internal resistance of 500 kΩ for this range. Generally, low ranges have lower internal resistance while high ranges have higher internal resistance. If the shunting effect is significant when measuring voltage with a low-voltage range due to low internal resistance, switch to a higher range instead. Although the pointer deflection angle will be smaller, the weaker shunting effect may yield higher accuracy. Similar rules apply to current measurement. When a multimeter functions as an ammeter, higher current ranges have lower internal resistance than low current ranges.
⑦ Perform zero adjustment every time the resistance range is changed. The mid-scale resistance of a resistance range is the value at the geometric center of the resistance dial multiplied by the range multiplier, which equals the internal resistance of the multimeter at this range. Common center scale values include 8, 10, 12, 13, 16, 20, 24, 25, 30, 60, 75 and so on. The resistance scale is non-linear. Select a proper range so that the pointer falls near the center as much as possible. Readings within the range of 0.1Ro to 10Ro (Ro - mid-scale resistance) are relatively accurate; errors will increase outside this interval. For example, the MF10 multimeter has a center scale value of 13. At the R×10kΩ range where Ro = 130 kΩ, this range is suitable for measuring resistors from 13 kΩ to 1.3 MΩ.
⑧ When measuring resistance with a multimeter, the red test lead connects to the negative terminal of the internal battery, and the black test lead connects to the positive terminal of the internal battery. This design ensures that current always flows into the red lead and out of the black lead for voltage, current and resistance measurements, enabling normal forward deflection of the pointer without reverse kick. Remembering this polarity rule is helpful for testing polarized components such as transistors, diodes and electrolytic capacitors.
⑨ When checking large-capacity capacitors with the resistance range, discharge the capacitor first to prevent residual voltage from damaging the multimeter. To measure a resistor on a circuit board, disconnect one end of the resistor to avoid interference from other resistors in the circuit. Never measure resistors on energized circuits with the resistance range.
⑩ After measurement, turn the range selector switch to the highest voltage range to prevent accidental damage to the meter in the next use. If there is a black dot or "OFF" mark, turn the switch to this position to short the measuring movement.
