Method of selecting the electrical blocking range of a multimeter and measuring error
Each range of electrical resistance can measure resistance values from 0 to ∞. The scale of the ohmmeter is a non-linear, uneven inverted scale. It is expressed as a percentage of the arc length of the ruler. Moreover, the internal resistance of each range is equal to the central scale number multiplied by the arc length of the ruler, which is called the "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 is in 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 choosing different ranges
For example: MF-30 multimeter, the center resistance of Rxl0 block is 250Ω; the center resistance of R×l00 block is 2.5kΩ. The accuracy level is level 2.5. Use it to measure a standard resistance of 500Ω, and ask if you use R×l0 block or R×100 block to measure, which one has the larger error?
Then the maximum absolute allowable error of R×l0 block is △R(10)=center resistance×R%=250Ω×(±2.5)%=±6.25Ω. Use it to measure the 500Ω standard resistance, and the indication value of the 500Ω standard resistance is between 493.75Ω and 506.25Ω. The maximum relative error is: ±6.25÷500Ω×100%=±1.25%.
The maximum absolute allowable error of R×l00 block is △R(100)=center resistance×R%2.5kΩ×(±2.5)%=±62.5Ω. Use it to measure the 500Ω standard resistance, and the indication value of the 500Ω standard resistance is between 437.5Ω and 562.5Ω. The maximum relative error is: ±62.5÷500Ω×100%=±10.5%.
Comparison of the calculation results shows that the measurement errors vary greatly when different resistance ranges are selected. Therefore, when selecting the gear range, try to keep the measured resistance value at the center of the arc length of the range scale. The measurement accuracy will be higher.
