Selection of Ranges for Multimeters and Analysis of Measurement Errors
There may be some errors when using a multimeter for measurement. Some of these errors are the maximum errors allowed by the accuracy level of the instrument itself. Some are human errors 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 measurement, the multimeter should be placed horizontally and mechanically zeroed; When reading, keep your eyes perpendicular to the pointer; When measuring resistance, zero adjustment should be performed every time the gear is changed. Replace the battery with a new one if it cannot be adjusted to zero; When measuring resistance or high voltage, do not hold the metal part of the meter probe with your hands to avoid human resistance diversion, increase measurement errors, or electric shock; When measuring the resistance in an RC circuit, cut off the power supply in the circuit and discharge the stored electricity in the capacitor before proceeding with the measurement. After excluding human reading errors, we conducted some analysis on other errors.
1. Selection and measurement error of voltage and current range for 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, current, etc. is represented by the maximum allowable error △ X and the percentage of the selected range full scale value. Expressed by formula: A%=(△ X/full scale value) x 100%... 1
(1) The error caused by measuring the same voltage using a multimeter with different accuracies
(2) The error caused by measuring the same voltage with different ranges of a multimeter
(3) The error caused by measuring two different voltages using the same range of a multimeter
2. Range selection and measurement error of resistance gear
Each range of the resistance gear can measure resistance values ranging from 0 to ∞. The scale of an ohmmeter is a non-linear and uneven reverse scale. It is expressed as a percentage of the arc length of the ruler. And the internal resistance of each range is equal to the center degree of the scale arc length multiplied by a multiplier, known as the "center resistance". That is to say, when the measured resistance is equal to the center resistance of the selected gear range, the current flowing through the circuit is half of the full scale current. The pointer indicates at the center of the scale. Its accuracy is expressed as follows:
R%=(△ R/center resistance) x 100%... 2
(1) The error caused by selecting different ranges when measuring the same resistance with a multimeter
