Use the DC voltage range of a multimeter to measure AC current
If you use a digital multimeter to measure AC voltage with the DC voltage block, it will definitely damage the thermistor, voltage divider resistor, limiting protection diode inside the multimeter, and in severe cases, the A/D converter. If you use a digital multimeter When measuring DC voltage at the AC voltage level, 000 will be displayed. General digital multimeters also use half-wave rectification. However, after half-wave rectification, the voltage must be amplified by an operational amplifier and then sent to the A/D converter, so even if you use a digital multimeter If the AC voltage is blocked to measure the DC voltage, the measured signal is 000
If you use the DC voltage block of a pointer multimeter to measure AC voltage, it will definitely damage the voltage dividing resistor with the lowest range in the DC voltage block, the fuse, the meter head limiting protection diode, and in serious cases, the mechanical meter head. If you If you use a pointer multimeter AC voltage switch to measure DC voltage, the measured value will be twice as high as the actual value. For example, if you use an AC voltage switch to measure a 5V voltage, the displayed voltage will generally be about 10V-11V. Since the AC voltage block has a half-wave rectification circuit, the measured DC voltage reaches the meter after half-wave rectification. Ue reflects 0.44 times the average value of the AC current. Therefore, the voltage value measured by using the AC voltage block to measure the DC voltage must be It is twice as high as the actual value, which means it is equivalent to the voltage signal coming out of the half-wave rectifier circuit.
There is a problem in estimating the readings of the voltage and current ranges of the multimeter.
When using a multimeter to measure unknown voltage or current, first use the highest setting to measure, and then gradually reduce it to the appropriate setting. The so-called appropriate setting is to try to keep the meter pointer near one-third of the dial.
When measuring, try to use high-end settings (especially the current setting, which has the greatest impact when the internal resistance is connected in series to the circuit), so as to reduce the error. When choosing a multimeter, you should try to choose one with a DC internal resistance of more than 20,000 ohms/volt. Of course a digital meter is more accurate.
