Correct Operation Methods and Precautions for Analog Multimeters
During operation, never use the ohm range to measure a resistor while it is live, otherwise the applied voltage will easily damage the multimeter or cause unexpected faults in the circuit.
Make correct connections. Since the DC meter movement inside a multimeter only allows current to flow in from the "+" terminal and out from the "–" terminal, the jacks and terminals on the multimeter panel are marked with polarity. During use, connect the red test lead to the "+" jack and the black test lead to the "–" jack. When measuring DC voltage or DC current, ensure the polarity of the positive and negative leads is not reversed, as this will cause the pointer to deflect backward. If reverse deflection occurs, switch the leads immediately. When measuring current, the meter must be connected in series in the circuit under test; when measuring voltage, the meter must be connected in parallel across the circuit. When testing transistors with a multimeter, remember that the red lead connects to the negative pole of the internal battery, and the black lead connects to the positive pole.
Select the correct measurement range, including both the measurement function and full-scale value. For example, set the selector switch to the corresponding voltage range for voltage measurement, or the current range for current measurement. Using the current range to measure voltage will damage the meter. When selecting a current or voltage range, aim to have the pointer move to at least two-thirds of full scale. For resistance measurement, position the pointer near the center of the scale to minimize measurement error. If the approximate value of current or voltage is unknown, first set the switch to its maximum range, then gradually reduce to an appropriate range based on pointer deflection.
Read the meter correctly. The multimeter dial has multiple scales for different measurement quantities, so readings must be taken from the corresponding scale. Pay attention to matching the scale reading with the selected range. Do not confuse the "scale reading" (the value directly read from the scale) with the "actual measured value", which is often obtained by calculation. Although they are sometimes numerically equal, they often differ. In addition, to avoid parallax error, align the pointer with its reflection in the mirror while taking readings.
