How to Select Multimeter Ranges and Avoid Measurement Errors
Each range of the resistance gear can measure resistance values from 0 to ∞. The scale of an ohmmeter has a non-linear and uneven inverted 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 arc length of the scale multiplied by the multiplier, called the "center resistance". That is to say, when the measured resistance is equal to the center resistance of the selected range, the current flowing through the circuit is half of the full scale current. The pointer indicates in the center of the scale. Its accuracy is expressed as follows: R%=(△ R/center resistance) × 100% .....2
(1) The error caused by selecting different ranges when measuring the same resistance with a multimeter
For example, the MF-30 multimeter has a center resistance of 250 Ω in the Rxl0 range; The center resistance of the R × l00 gear is 2.5k Ω. The accuracy level is 2.5. Use it to measure a standard resistance of 500 Ω. Which one has the largest error between measuring with R × l0 gear and R × 100 gear? Solution: From equation 2: R × l0 gear * large * * allowable error △ R (10)=center resistance × R%=250 Ω× (± 2.5)%=± 6.25 Ω. Using it to measure a 500 Ω standard resistance, the displayed value of the 500 Ω standard resistance is between 493.75 Ω and 506.25 Ω. *The large relative error is: ± 6.25 ÷ 500 Ω× 100%=± 1.25%.
R × l00 gear * large * * allowable error △ R (100)=center resistance × R% 2.5k Ω× (± 2.5)%=± 62.5 Ω. Using it to measure a 500 Ω standard resistance, the displayed value of the 500 Ω standard resistance is between 437.5 Ω and 562.5 Ω. *The large relative error is: ± 62.5 ÷ 500 Ω× 100%=± 10.5%.
The comparison of calculation results shows that there is a significant difference in measurement errors when different resistance ranges are selected. Therefore, when selecting the gear range, it is important to try to place the measured resistance value at the center of the arc length of the range scale. The measurement accuracy will be higher.
