Development Of A Precision Current Measurement System

In daily measurement and testing work,Current is a measure that often requires accurate measurements.The traditional test current meter is realized by the voltage drop generated by the sampling resistor,but the current will be heated and the resistance value will be changed.Aiming at the problem that the stability of the current measuring equipment in the test current is not high,it can not accurately reflect the current value,Based on the traditional current measurement theory and the "very low load factor sampling resistor" designed by the Chinese Institute of metrology,this paper designed and built the precision current testing system so that we can realize the precision measurement of the current.This system mainly includes the current transformation、voltage sampling、A/D conversion、micro controller unit and its peripheral components.This paper mainly introduces the hardware and software realization of the precision current testing system,as well as the performance of the system,the specific research as follows:1.This paper presents the principle of "small current direct measurement,high current measurement" split test principle.The current of 1A following directs sampling resistance for follow-up testing,1-30 A and 30A-600 A current through the current transformer to transform into small current for sampling measurement.2.According to the DC current transformer developed by National Institute of Metrology,this paper designed the comparsion experiment of the stability of the transformer.According to the experimental results,the short-term stability index of the current transformer is better than 0.2ppm.3.Completed the process of the whole sample resistance.On commercial resistance temperature coefficient of screening,making resistance 1ohm sampling resistance,and the load coefficient and stability are studied,the actual measured can reach the order of 10-7.4.Designed hardware circuit of measurement system.Completed The selection of high precision conversion chip AD7190 、 STM32 micro controller and touch screen,The writing of PC software to achieve the test system’s display、control and communication function.5.Experimental test of whole current measuremental system.First,the sampling control module is studied and the error value of the system is corrected.Then the zero stability and repeatability of the machine was studied.The N6970 A and the 10 A constant current source were tested.The actual measured 0-30 A short-term stability at 0.8ppm~76ppm.The precision current measuring system developed in this paper is not only a wide range,but also the stability of the measurement,which meets the current scientific research and industrial production in the demand for precision current measurement.