Multimeter Range Selection and Measurement Error Explanation
When measuring with a multimeter, there may be some errors. Some of these errors are the maximum absolute errors allowed by the accuracy level of the instrument itself. Some are Personal equation caused by improper adjustment and use. By correctly understanding the characteristics of a multimeter and the reasons for measurement errors, mastering the correct measurement techniques and methods, measurement errors can be reduced.
Human reading error is one of the reasons that affects measurement accuracy. It is inevitable, but it can be minimized as much as possible. Therefore, special attention should be paid to the following points during use: 1. Before measuring, the multimeter should be placed horizontally and mechanically zeroed;
2. Keep your eyes perpendicular to the pointer when reading;
3. When measuring resistance, zero should be adjusted every time the gear is changed. Replace the battery with a new one if it cannot be adjusted to zero;
4. When measuring resistance or high voltage, it is not allowed to hold the metal part of the meter pen with your hand to prevent the human body's resistance from diverging, increasing measurement error or electric shock;
5. When measuring the resistance in the RC circuit, cut off the power supply in the circuit and discharge the electricity stored in the capacitor before measuring. After excluding human reading errors, we conducted some analysis on other errors.
Voltage and current range selection and measurement error of a multimeter
The accuracy level of a multimeter is generally divided into several levels, such as 0.1, 0.5, 1.5, 2.5, and 5. The calibration of accuracy level for various gears such as DC voltage, current, AC voltage, and current is represented by the maximum absolute allowable error △ X and the percentage of the selected full scale value. Expressed by the formula: A%=(△ X/full scale value) × 100%... 1
(1) The error caused by measuring the same voltage using a multimeter with different accuracies
For example, there is a 10V standard voltage that is measured using two multimeters at 100V, 0.5 level, 15V, and 2.5 level. Which meter has the smallest measurement error?
Solution: According to equation 1, the first surface measurement: maximum absolute allowable error
△ X1=± 0.5% × 100V=± 0.50V.
Second meter measurement: maximum absolute allowable error
Δ 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 generated by measuring with the first meter is greater than that generated by measuring with the second meter. Therefore, it can be seen that when selecting a multimeter, the higher the accuracy, the better. With a multimeter with high accuracy, it is necessary to choose a suitable range. Only by selecting the correct range can the potential accuracy of a multimeter be fully realized.
(2) The error caused by measuring the same voltage using different ranges of a multimeter
For example, the MF-30 multimeter has an accuracy level of 2.5. When measuring a 23V standard voltage in the 100V and 25V gears, which gear has the smallest error?
Solution: Maximum absolute allowable error in 100V gear:
X (100)=± 2.5% × 100V=± 2.5V.
Maximum absolute allowable error in 25V gear: △ X (25)=± 2.5% × 25V=± 0.625V. From the above solution, it can be seen that
