Range Selection and Measurement Error Analysis for Multimeter Gears
(1) Errors produced when measuring the same voltage with multimeters of different accuracy grades
Example: A standard voltage of 10 V is measured by two multimeters: one is 0.5 grade with a 100 V range, and the other is 2.5 grade with a 15 V range. Which multimeter has a smaller measurement error?
Solution: According to Formula (1): Maximum allowable absolute error of the first multimeter: \(\Delta X_1=\pm0.5\% \times 100\,\text{V}=\pm0.50\,\text{V}\)
Maximum allowable absolute error of the second multimeter: \(\Delta X_2=\pm2.5\% \times 15\,\text{V}=\pm0.375\,\text{V}\)
By comparing \(\Delta X_1\) and \(\Delta X_2\), we can see that although the first multimeter has a higher accuracy grade, its measurement error is larger than that of the second one. Therefore, a higher accuracy grade does not always mean better when selecting a multimeter. Even with a high-precision multimeter, an appropriate range must be chosen. Only by selecting the correct range can the inherent accuracy of the multimeter be achieved.
(2) Errors produced when measuring the same voltage with different ranges of one multimeter
Example: An MF‑30 multimeter has an accuracy grade of 2.5. Use the 100 V range and the 25 V range to measure a standard voltage of 23 V. Which range gives a smaller error?
Solution: Maximum allowable absolute error for the 100 V range: \(\Delta X(100)=\pm2.5\% \times 100\,\text{V}=\pm2.5\,\text{V}\)
Maximum allowable absolute error for the 25 V range: \(\Delta X(25)=\pm2.5\% \times 25\,\text{V}=\pm0.625\,\text{V}\)
It can be seen from the above calculation: When measuring the 23 V standard voltage with the 100 V range, the reading of the multimeter is between 20.5 V and 25.5 V. When measured with the 25 V range, the reading is between 22.375 V and 23.625 V. The result shows that \(|\Delta X(100)|>|\Delta X(25)|\), which means the error of the 100 V range is much larger than that of the 25 V range. Therefore, one multimeter will produce different errors when measuring different voltages with different ranges. Where the measured signal value permits, use the smallest possible range to improve measurement precision.
