The selection method and measurement error of multimeter electric barrier range
Each range of electrical resistance can measure the resistance value from 0 to ∞. The scale scale of an ohmmeter is a non-linear, uneven, inverted scale. It is expressed as a percentage of the arc length of the scale. Moreover, the internal resistance of each range is equal to the multiplier of the central scale number of the arc length of the scale, which is called "central resistance". That is to say, 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. Its accuracy is expressed by the following formula: R%=(△R/center resistance)×100%
When using a UNI-T digital multimeter UT33B to measure the same resistance, the error caused by selecting different ranges
For example: MF-30 multimeter, the central resistance of the Rxl0 block is 250Ω; the central resistance of the Rxl00 block is 2.5kΩ. The accuracy level is 2.5. Use it to measure a 500Ω standard resistance, and ask whether to measure it with R×l0 gear or R×100 gear, which one has the larger error?
Then the maximum absolute allowable error of R×l0 gear △R(10)=central resistance×R%=250Ω×(±2.5)%=±6.25Ω. Use it to measure 500Ω standard resistance, then the indicated value of 500Ω standard resistance is between 493.75Ω～506.25Ω. The maximum relative error is: ±6.25÷500Ω×100%=±1.25%.
The maximum absolute allowable error of R×l00 block △R(100)=central resistance×R%2.5kΩ×(±2.5)%=±62.5Ω. Use it to measure 500Ω standard resistance, then the indicated value of 500Ω standard resistance is between 437.5Ω～562.5Ω. The maximum relative error is: ±62.5÷500Ω×100%=±10.5%.
The comparison of the calculation results shows that the measurement error varies greatly when different resistance ranges are selected. Therefore, when selecting the gear range, try to make the measured resistance value in the center of the arc length of the range scale. The measurement accuracy will be higher.
