4.2.8 Appendix 2 Calibration and rating of the ref...
Although the refitted meter is completed,its accuracy(or measurement error)is not determined,so it cannot be directly used.And it must be calibrated and rated with a standard meter.According to the national standard of China(GB),the accuracy of the meter is divided into 7 rates:0.1,0.2,0.5,1,1.5,2.5,and 5.The smaller the rate,the higher the accuracy of the meter(same as that the smaller the measurement error).UseΔto represent the limit error of the meter during its measurement,then:
The following takes the refitted 5 mA ammeter as an example to introduce the calibration and rating method of the meter.
1)Calibration
The calibration circuit is shown in Figure 4.2.3.
(1)Adjust the sliding rheostat RW to increase the current I of the refitted meter from 0 to 0.5,1.0,1.5,2.0,2.5,3.0,3.5,4.0,4.5,5.0 mA and then respectively record the corresponding value of the standard meter as I′.
(2)Adjust the sliding rheostat R to reduce the current I of the refitted meter from 5.0 mA to 4.5,4.0,3.5,3.0,2.5,2.0,1.5,1.0,0.5 mA and respectively record the corresponding value of the standard meter as I″.(https://www.daowen.com)
(3)Calculate Istandard=(I′+I″)/2 andΔI=Istandard-I.ΔI is the calibration value of each corresponding reading of the refitted meter.Make the calibration curve of the calibration value table using I as the abscissa and Istandard as the ordinate.
2)Rating
(1)Calculate the maximum error of the readings of each gear between the refitted meter and the standard meterΔmax(the one with the largest absolute value among the calibration valuesΔI).Calculate the limit error(accuracy)Δstandard in the range of the standard meter.Use the“root-sumsquare”method to calculate the limit errorΔ′of the refitted meter:
(2)According to the limit error Equation(4.2.6),calculate the rate of the refitted meter:
(3)Compare α′with the accuracy rates(seven rates)of the national standard of China and take the proximate lower rate as the accuracy rate α of the refitted meter.
