Multimeter resistance range selection method and measurement error
Each range of the resistance stopper measures resistance values from 0 to ∞. The scale of an ohmmeter has 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%.
Use A Uni-Tech (UNI-T) digital multimeter UT33B measurement of the same resistance, the choice of different ranges of the error generated by the
For example: MF-30 type multimeter, the Rxl0 block of the center resistance of 250Ω; R × l00 block of the center resistance of 2.5kΩ. accuracy level of 2.5. Using it to measure a standard resistance of 500 Ω, which error is greater when measured with the R x l0 block and the R x 100 block?
The maximum absolute permissible error of the R×l0 block is △R(10)=center resistance×R%=250Ω×(±2.5)%=±6.25Ω. If it is used to measure a 500Ω standard resistor, the value of the 500Ω standard resistor will be between 493.75Ω and 506.25Ω. The maximum relative error is: ±6.25÷500Ω×100%=±1.25%.
The maximum absolute allowable error △R(100)=center resistance×R%2.5kΩ×(±2.5)%=±62.5Ω. If it is used to measure the 500Ω standard resistor, the value of the 500Ω standard resistor ranges from 437.5Ω to 562.5Ω. The maximum relative error is: ±6.25÷500Ω×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 ranges, the measurement produces a large difference in error. Therefore, when selecting 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.
