Analysis of Voltage Errors Measured by Digital Multimeter and Pointer Multimeter
If the measured voltage is mains electricity, that is, 50Hz alternating current, and both meters are qualified, it only means that the internal resistance of the measured voltage is too large. Under the same frequency, the biggest factor affecting the measurement voltage results of the pointer multimeter and the digital multimeter is that the internal resistance is different, and the difference is very large, not in the same order of magnitude. When the internal resistance of the measured voltage is small, the difference is not obvious. When the internal resistance of the measured voltage is large, the measurement results will be quite different.
In this case, it is possible that the measured voltage is not the actual 220V live wire power line, or the voltage measured after the live wire passes through some kind of electrical appliance, or the voltage of the leakage shell of the electrical appliance.
Excluding the above possibilities, it can only mean that one of the two watches is inaccurate and needs to be repaired and adjusted.
There is an error in the measured voltage. First of all, you have to figure out, what is the frequency of the measured AC voltage in Hz? Is this voltage a pure sine wave?
All kinds of multimeters on the market are marked with their frequency response range and AC waveform when measuring AC voltage. For all kinds of ordinary digital multimeters, the frequency response is generally 40-1000Hz, and the requirement is a sine wave (distortion ≤ 1%). The measured AC voltage beyond the above range does not guarantee the measurement accuracy. This is because the AC/DC (alternating current/direct current) conversion circuit in most digital multimeters is basically designed with a low-power dual op amp TL062. The op amp GBW (gain-bandwidth product) is limited, so the digital multimeter cannot measure High-frequency AC voltage (of course, it is also related to whether the voltage dividing resistor of the multimeter is compensated).
As for the general pointer multimeter (it was first invented by the Americans, it has been 100 years ago), its internal structure is quite simple, and there is a high-sensitivity meter + diode rectifier + voltage divider resistor (a few pointer type multimeters) inside. In order to improve the sensitivity of the multimeter, an AC amplifier composed of an operational amplifier is added between the meter head and the voltage dividing resistor), so the measurement accuracy of this old and cheap multimeter cannot be compared with the digital multimeter at all. Generally, there is no capacitance compensation, so the frequency response is generally 40-400Hz.
The two meters measure the same AC voltage with a difference of tens of V. First, you need to check their voltage divider resistor network. Does one of the resistors change value? If everything is normal, for the pointer multimeter, you can also check whether the pointer of the meter head can point to zero? For the digital multimeter, you can check if the calibration potentiometer of the AC voltage block is loose?
By the way, if you want to accurately measure the AC voltage of arbitrary waveforms, it is recommended to purchase a true effective value (TRMS) multimeter, which can accurately measure AC voltages of various waveforms such as sine waves, triangle waves, and rectangular waves. irrelevant.
