Range Selection and Measurement Error of Digital Universal Electric Barrier
Each range of electrical barrier can measure the resistance value from 0 to ∞. The scale of the ohmmeter is a non-linear, uneven inverse scale.
Expressed as a percentage of the ruler's arc length. And the internal resistance of each range is equal to the center scale of the arc length of the scale multiplied by the multiplying factor, which is called "center resistance".
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 points in the center of the scale. Its accuracy is expressed as:
R%=(△R/center resistance)×100%……2
(1) When measuring the same resistance with a multimeter, the error caused by selecting different ranges. Electrician: www.dgjs123.com
For example: MF-30 type multimeter, the central resistance of the Rxl0 block is 250Ω; the central resistance of the R×l00 block is 2.5kΩ.
The accuracy rating is 2.5. Use it to measure a standard resistance of 500Ω, and ask the R×10 block and the R×100 block to measure, which has the largest error? Solution: From formula 2, we get:
The maximum absolute allowable error of R×l0 block △R(10)=center resistance×R%=250Ω×(±2.5)%=±6.25Ω.
Use it to measure 500Ω standard resistance, the indication 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)=center resistance×R%2.5kΩ×(±2.5)%=±62.5Ω.
Use it to measure 500Ω standard resistance, the indication 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 errors generated by the measurement are very different 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.
