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72.检定动圈仪表能否单用直流电位差计的标准毫伏值输入给动圈仪表? 答:不能单用直流电位差计毫伏值输入给动圈仪表。根据JJG-187-78检定规程规定:检定动圈仪表一定要采用标准仪器——直流电位差计,以及辅助设备——直流毫伏发生器。二者不可缺一。虽直流电位差计可输出标准毫伏值,但由于被输入回路(动圈仪表)的分流,影响输出值,给检定带来一定的误差,分析如下: 直流电位差计是用补偿法将被测电势与标准电势相比较,直接测量电势或电压的基本原理如图39所示。从图可以看出,用电位差计测量未知电势E_x时,调补偿电阻R为R′,使检流计G无电流通过,I_2=0。这时,I_1=I,E_x=I_1R′=IR′。只要保证I恒定不变,触头X的位置若直接刻成mv值,就可测定E_x的大小。当直流电位差计标准毫伏值直接输入动圈仪表时,(将
72. Check dynamic instrument can single DC millivoltmeter standard millivolt input to the dynamic instrument? A: You can not only use the DC potentiometer millivolt input to the moving coil instrument. Accordance with the JJG-187-78 test procedures: test dynamic instrument must be used standard instruments - DC potentiometer, and auxiliary equipment - DC millivolt generator. One of the two indispensable. Although the DC potentiometer can output the standard millivolt value, but because of the input circuit (moving coil meter) shunt, affecting the output value to the test to bring some error, as follows: DC potentiometer is to use compensation method will be Measured potentials compared with the standard potential, the direct measurement of potential or voltage of the basic principles shown in Figure 39. It can be seen from the figure, when measuring potentiometer unknown potential E_x, the compensation resistor R is R ’, galvanometer G no current through, I_2 = 0. At this time, I_1 = I, E_x = I_1R ’= IR’. As long as the guarantee I constant, if the location of the contact X engraved directly mv value, you can determine the size of E_x. When the DC potentiometer standard millivolt value directly into the dynamic instrument, (will