Range selection and measurement error of resistance gear
Each range of the resistance range can measure resistance values ranging from 0 to ∞. The scale of an ohmmeter is a non-linear and uneven reverse scale.
Expressed as a percentage of the arc length of the ruler. And the internal resistance of each range is equal to the center graduation of the scale arc length multiplied by the multiplier, known as the "center resistance".
When the measured resistance is equal to the center resistance of the selected gear range, the current flowing through the circuit is half of the full scale current.
The pointer indicates at the center of the scale. Its accuracy is represented by the following equation:
R%=(△ R/center resistance) × 100%... 2
(1) The error caused by selecting different ranges when measuring the same resistance with a multimeter. Electrician: www.dgjs123.com
For example, the center resistance of the MF-30 multimeter in Rxl0 gear is 250 Ω; R × The center resistance of the l00 gear is 2.5k Ω.
The accuracy level is 2.5. Use it to measure a standard resistance of 500 Ω and ask for R × L0 gear and R × Which error is greater when measuring at 100 gears? Solution: Derived from equation 2:
R × Maximum absolute allowable error in l0 gear △ R (10)=center resistance × R%=250 Ω × (± 2.5)%=± 6.25 Ω.
Using it to measure a 500 Ω standard resistance, the indicated value of the 500 Ω standard resistance is between 493.75 Ω and 506.25 Ω. The maximum relative error is ± 6.25 ÷ 500 Ω × 100%=± 1.25%.
R × Maximum absolute allowable error in l00 gear △ R (100)=center resistance × R% 2.5k Ω × (± 2.5)%=± 62.5 Ω.
Using it to measure a 500 Ω standard resistance, the indicated value of the 500 Ω standard resistance is between 437.5 Ω and 562.5 Ω. The maximum relative error is ± 62.5 ÷ 500 Ω × 100%=± 10.5%.
The comparison of calculation results shows that selecting different resistance ranges results in significant differences in measurement errors.
Therefore, when selecting the gear range, it is necessary to try to keep the measured resistance value at the center of the arc length of the range scale. The measurement accuracy will be higher.
