Analysis of the Impact of Multimeter Errors on Measurement Results
The larger the internal resistance Rv of the voltmeter, the closer the measured value is to the actual value that is less than the measured voltage, the smaller the error, and the higher the sensitivity. Therefore, the resistance range of the multimeter is a parameter of the multimeter. This article draws the following conclusions through analysis:
1. If two multimeters with different voltage sensitivities are used to measure the same object, the measurement error of the multimeter with higher voltage sensitivity will be smaller than that of the multimeter with lower voltage sensitivity.
2. For different ranges of the same multimeter, the larger the voltage range, the higher the internal resistance, and the smaller the impact of errors on the measurement results.
Here is an example to illustrate the impact of errors on measurement results. The error analysis during voltage measurement is shown in the figure.
In the figure, the DC power supply U=10v, with an internal resistance r=200K Ω. A multimeter with a voltage sensitivity of 20K Ω/V is selected to measure this voltage. How much does the error affect the measurement results? If we choose 50V instead of 10V, with an internal resistance of 1M Ω, how much impact does the error have on the measurement results?
Solution:
When measuring for the first time, select the 10V voltage range and the internal resistance Rv=200k Ω, then:
The relative error is:
When measuring for the second time, select the 50V voltage range and the internal resistance Rv=1M Ω, then:
The relative error is:
It can be seen that the relative error has a smaller impact on the measurement results during the second measurement. That is to say, in the measurement process, in order to ensure its sensitivity and reduce measurement errors, sometimes a larger voltage range can also be selected. This is because the larger the voltage range, the greater the internal resistance and the higher the voltage sensitivity. Of course, the voltage range cannot be selected too large, otherwise the pointer deflection angle will be too small and the reading will be inaccurate. The internal resistance of AC power supply is usually low, and a multimeter with low voltage sensitivity can be used to measure AC voltage.
From the above analysis, it can be concluded that when measuring voltage with a multimeter, it is preferable to have a higher internal resistance in the voltage range of the multimeter, as the meter head of the multimeter is connected in parallel with the circuit being measured. The larger the internal resistance of the meter, the smaller the impact of errors on the measurement results, and the higher the sensitivity.
