Multimeter range selection and detailed explanation of measurement error
There will be some errors when measuring with a multimeter. Some of these errors are the maximum absolute errors allowed by the accuracy class of the meter itself. Some are human errors caused by adjustment and improper use. Correctly understand the characteristics of the multimeter and the causes of measurement errors, and master the correct measurement techniques and methods, you can reduce the measurement errors.
Human reading error is one of the reasons that affect the measurement accuracy. It is unavoidable but can be minimized. Therefore, special attention should be paid to the following points during use:
1. Before measurement, place the multimeter horizontally and perform mechanical zero adjustment;
2. Keep your eyes perpendicular to the pointer when reading;
3. When measuring resistance, zero adjustment is required every time a gear is changed. Replace the battery with a new one when the adjustment is less than zero;
4. When measuring resistance or high voltage, do not pinch the metal part of the test lead with your hands, so as to avoid shunting of human body resistance, increasing measurement error or electric shock;
5. When measuring the resistance in the RC circuit, cut off the power supply in the circuit, discharge the electricity stored in the capacitor, and then measure. After excluding the human-made reading errors, we conduct some analysis on other errors.
1. Multimeter Voltage, 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) level is expressed by the percentage of the maximum absolute allowable error △X and the full scale value of the selected range. Expressed by formula: A%=(△X/full scale value)×100%... 1
(1) Using a multimeter with different accuracy to measure the error generated by the same voltage
For example: There is a 10V standard voltage, and it is measured with two multimeters with 100V gear, 0.5 level and 15V level, 2.5 level. Which meter has the smallest measurement error?
Solution: From formula 1: the first piece of meter measurement: the maximum absolute allowable error
△X1=±0.5%×100V=±0.50V.
The second meter test: 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 watch is higher than that of the second watch, the error produced by the measurement of the first watch is larger than the error produced by the measurement of the second watch. 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 choose an appropriate range. Only by choosing 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
Use the 100V block to measure the 23V standard voltage, and the indication on the multimeter is between 20.5V-25.5V. Use the 25V block to measure the 23V standard voltage, and the indication value on the multimeter is between 22.375V-23.625V. From the above results, △X (100) is greater than △X (25), that is, the error of 100V block measurement is much larger than that of 25V block measurement. Therefore, when a multimeter measures different voltages, the errors generated by different ranges are different. In the case of meeting the value of the signal to be measured, the gear with the smallest measuring range should be selected as much as possible. This increases the accuracy of the measurement.
(3) The error caused by measuring two different voltages with the same range of a multimeter
Comparing the maximum relative error of the measured voltage 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 scale value will have higher accuracy. Therefore, when measuring voltage, the measured voltage should be indicated above 2/3 of the multimeter's range. Only in this way can the measurement error be reduced.
2. Range selection and measurement error of electrical barrier
Each range of electrical resistance can measure the resistance value from 0 to ∞. The scale scale of an ohmmeter is a non-linear, uneven, inverted scale. It is expressed as a percentage of the arc length of the scale. Moreover, the internal resistance of each range is equal to the multiplier of the central scale number of the arc length of the scale, which is called "central resistance". That is to say, when the measured resistance is equal to the center resistance of the selected range, the current flowing in the circuit is half of the full scale current. The pointer indicates the center of the scale. Its accuracy is expressed by the following formula:
R%=(△R/center resistance)×100%……2
(1) When using a multimeter to measure the same resistance, the error caused by selecting different ranges
