If the measured voltage is commercial power, that is, 50Hz alternating current, and both meters are qualified, it can only mean that the internal resistance of the measured voltage is too large. The biggest factor affecting the measured voltage results between analog multimeters and digital multimeters at the same frequency is the difference in internal resistance, which is very different and not of 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 significantly different.
In this case, it is possible that the measured voltage is not the actual 220V live wire power line, or it is the voltage measured after the live wire passes through a certain electrical appliance, or it is the voltage of the leaky shell of the electrical appliance.
The manuals of various multimeters currently on the market are marked with the frequency response range and AC waveform of the meter when measuring AC voltage. For all kinds of ordinary digital multimeters, the frequency response is generally 40-1000Hz, and it is required to be a sine wave (distortion Less than or equal to 1%). Measurement accuracy is not guaranteed for measured AC voltages beyond the above range. This is because the AC/DC (alternating current/direct current) conversion circuits in most digital multimeters are basically designed using the low-power dual operational amplifier TL062. This operational amplifier has limited GBW (gain bandwidth product), so the digital multimeter cannot measure High-frequency AC voltage (of course, it also depends on whether the voltage dividing resistor of the multimeter is compensated).
As for the general analog multimeter (it was first invented by the Americans, it has been 100 years ago), its internal structure is quite simple, with a high-sensitivity meter + diode rectifier + voltage dividing resistor (a few analog multimeters In order to improve the sensitivity of the multimeter, an operational amplifier (AC amplifier) is added between the meter head and the voltage-dividing resistor), so the measurement accuracy of this old, cheap multimeter cannot be compared with that of a digital multimeter. The voltage-dividing resistor of this kind of meter Generally, capacitance compensation is not performed, so the frequency response is generally 40-400Hz.
The AC/DC conversion circuit in this portable true RMS multimeter is generally designed using dedicated TRMS integrated circuits AD736 and AD737 (produced by Analog Devices, USA), so it can measure AC voltages of arbitrary waveforms.
