Multimeter voltage and current range selection and measurement error
The accuracy level of the multimeter is generally divided into several levels such as 0.1, 0.5, 1.5, 2.5, and 5. For DC voltage, current, AC voltage, current and other gears, the calibration of the accuracy (accuracy) grade is expressed by the percentage of the maximum absolute allowable error △X and the full scale value of the selected range. Expressed by the formula: A%=(△X/full scale value)×100%...... 1
(1) The error caused by measuring the same voltage with multimeters with different accuracy
For example: There is a 10V standard voltage, which is measured with two multimeters at 100V, 0.5 and 15V, and 2.5. Which meter has the smallest measurement error?
Solution: Obtained from formula 1: The first meter is measured: the maximum absolute allowable error
△X1=±0.5%×100V=±0.50V.
The second meter is measured: the maximum absolute allowable error
△X2=±2.5%×l5V=±0.375V.
Comparing △X1 and △X2, it can be seen that although the accuracy of the first meter is higher than that of the second meter, the error produced by the measurement of the first meter is larger than that of the second meter. Therefore, it can be seen that when choosing a multimeter, the higher the accuracy, the better. With a multimeter with high accuracy, it is necessary to select the appropriate range. Only by selecting the correct range can the potential accuracy of the multimeter be brought into play.
(2) The error caused by measuring the same voltage with different ranges of a multimeter
For example: MF-30 type multimeter, its accuracy is 2.5, choose 100V gear and 25V gear to measure a 23V standard voltage, which gear has the smallest error?
Solution: The maximum absolute allowable error of 100V block is:
X(100)=±2.5%×100V=±2.5V.
The maximum absolute allowable error of 25V block: △X(25)=±2.5%×25V=±0.625V. From the above solution it can be seen that:
Use the 100V block to measure the 23V standard voltage, and the indicated value on the multimeter is between 20.5V and 25.5V. Use the 25V gear to measure the 23V standard voltage, and the indication value on the multimeter is between 22.375V and 23.625V. From the above results, △X (100) is greater than △X (25), that is, the error of the 100V measurement is much larger than that of the 25V measurement. Therefore, when a multimeter measures different voltages, the errors produced by different ranges are different. In the case of satisfying the value of the measured signal, the small range should be selected as much as possible. This improves the accuracy of the measurement.
(3) The error caused by measuring two different voltages with the same range of a multimeter
For example: MF-30 type multimeter, its accuracy is 2.5, use 100V gear to measure a standard voltage of 20V and 80V, which gear has the smallest error?
Solution: Maximum relative error: △A%=maximum absolute error △X/measured standard voltage adjustment × 100%, the maximum absolute error of 100V block △X(100)=±2.5%×100V=±2.5V.
For 20V, its indication value is between 17.5V-22.5V. The maximum relative error is: A(20)%=(±2.5V/20V)×100%=±12.5%.
For 80V, its indication value is between 77.5V-82.5V. Its maximum relative error is:
A(80)%=±(2.5V/80V)×100%=±3.1%.
Comparing the maximum relative error of the measured voltage of 20V and 80V, it can be seen that the error of the former is much larger than that of the latter. Therefore, when using the same range of a multimeter to measure two different voltages, whoever is closer to the full range value has higher accuracy. so
