How to master the basic functions and characteristics of pointer multimeter?

There are many varieties and models of pointer multimeters, but their working principles are basically the same or similar. Its biggest display feature is that the measured value is indicated by the pointer on the meter.

(1) Voltage measurement accuracy. A multimeter can generally measure DC and AC voltages ranging from a few hundred millivolts to a few hundred volts or even a few thousand volts. Its measurement accuracy is ±2.5% for DC and ±4.0% for AC. Its frequency range is usually 40 to 1000 Hz. If the accuracy requirement is not high, it can also be used to test sine and non-sine wave signals up to 10 kHz. Since the AC scale of the multimeter is set based on the effective value of the sine wave, its indication value for square wave voltage is too large, while its indication value for sawtooth wave and pulse wave is too small.

(2) Input impedance. The input impedance of each voltage level of the multimeter is different. Its resistance value is equal to the product of the voltage full-scale value Uo (i.e., range) of the corresponding level and the multimeter sensitivity S (Ω/v), that is, Ri=UoS

Therefore, the low-range input impedance of the multimeter is small, while the high-range input impedance is large. Because the input end of the instrument is connected in parallel with the circuit being measured when measuring voltage, its input impedance will play a shunt role. In order to minimize the measurement error, it is usually required that the input impedance of the corresponding voltage level of the multimeter should be more than 10 times the resistance of the circuit being measured, so a multimeter with a larger sensitivity value must be used to measure voltage. Generally, the sensitivity of the multimeter should not be less than 2kQ/V.