Multimeter range selection and measurement error details
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, special attention should be paid to the following points in use:
1、Place the multimeter horizontally before measurement and make mechanical zeroing;
2, the eyes should be kept perpendicular to the pointer when reading;
3, when measuring resistance, every time you change the block should be zeroed. Replace the battery with a new one when it cannot be adjusted to zero;
4, when measuring resistance or high voltage, can not pinch the metal part of the pen with your hand, so as not to shunt the human body resistance, increasing the measurement error or electric shock;
5, in the measurement of resistance in the RC circuit, to cut off the power supply in the circuit, and drain the capacitor stored electricity, and then measure. 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 error generated by using multimeters with different degrees of accuracy to measure the same voltage
(2) with a multimeter of different ranges to measure the same voltage of the error generated
(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) with a multimeter to measure the same resistance, the selection of different ranges of the error produced
For example: MF-30 multimeter, its Rxl0 block of the center resistance of 250Ω; R × l00 block of the center resistance of 2.5kΩ. accuracy level of 2.5. It is used to measure a standard resistance of 500 Ω. Which error is greater if it is measured with the R x l0 block or the R x 100 block? SOLUTION: From equation 2:
R × l0 block maximum absolute permissible error △ R (10) = center resistance × R% = 250 Ω × (± 2.5) % = ± 6.25 Ω. With it to measure a 500 Ω standard resistance, the 500 Ω standard resistance value between 493.75 Ω ~ 506.25 Ω. The maximum relative error is: ±6.25÷500Ω×100%=±1.25%.
R × l00 block maximum absolute allowable error △ R (100) = center resistance × R% 2.5 kΩ × (± 2.5)% = ± 62.5 Ω. With it to measure the 500 Ω standard resistor, the 500 Ω standard resistor between 437.5 Ω ~ 562.5 Ω. The maximum relative error is: ± 6.25 ÷ 500 Ω × 100% = ± 1.25%. The maximum relative error is: ±62.5 ÷ 500Ω × 100% = ±10.5%.
Comparison of the results from the calculation shows that the choice of different resistance range, the measurement of the error generated by the difference is very large. Therefore, in the selection of the range of stops, try to make the measured resistance value in the center of the arc length of the range scale. Measurement accuracy will be higher.
