Selecting the Multimeter Range and Details of Measuring Errors
Making measurements with a multimeter introduces certain errors. Some of these errors are the maximum absolute error allowed by the accuracy level of the meter itself. Some of them are human errors brought about by improper adjustment and use. Correctly understand the characteristics of the multimeter and the causes of measurement error, master the correct measurement techniques and methods, you can reduce the measurement error.
Human reading error is one of the reasons affecting the measurement accuracy. It is unavoidable, but can be minimized. Therefore, the use of special attention to the following points: 1, the measurement should be placed horizontally before the multimeter, mechanical zero; 2, read the eyes and pointer to maintain vertical; 3, resistance measurement, every change in the block should be adjusted to zero. When the zero is not adjusted, new batteries should be replaced; 4, when measuring resistance or high voltage, the metal part of the pen should not be pinched with the hand, so as not to shunt the human body resistance and increase the measurement error or electric shock; 5, when measuring the resistance of the RC circuit, cut off the power supply in the circuit and drain the capacitor stored electricity, and then measure again. After excluding the human reading error, we analyze some of the other errors.
1. Multimeter voltage, current block range selection and measurement errors
Multimeter accuracy level is generally divided into 0.1, 0.5, 1.5, 2.5, 5 and other levels. DC voltage, current, AC voltage, current and other blocks, accuracy (precision) level of calibration by its maximum absolute allowable error △ X and the percentage of the full-scale value of the selected range. Expressed by the formula: A% = (△ X / full-scale value) × 100% ...... 1
(1) the use of different accuracy of the multimeter to measure the same voltage error
(2) The error generated by measuring the same voltage with different ranges of a multimeter
(3) The error generated by measuring two different voltages with the same range of a multimeter
2. Resistor range selection and measurement error
Each range of the resistor can measure the resistance value of 0 to ∞. The scale of the ohmmeter is a nonlinear, uneven inverted scale. It is expressed as a percentage of the arc length of the scale. And the internal resistance of each range is equal to the scale arc length of the center of the number of scales multiplied by the multiplier, called the "center resistance". In other words, 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. The accuracy is expressed by the following formula:
R% = (△R/center resistance) × 100% ......2
(1) When measuring the same resistance with a multimeter, the error generated by choosing different ranges
