Low-temperature Current Comparator Automatic Resistance Bridge Feedforward System Design

The cryogenic current comparator designed by the article does not use dc superconducting quantum interference device as a feedback loop, so it is an open loop cryogenic current comparator.The system mainly consists of four parts.The four parts is the PC configuration program,the digital controller of optical isolation, the current source circuit of current comparator and loop. The cryogenic current comparator automatic resistance bridge uses the DC superconducting quantum interference device(DC-SQUID)as a feedback loop,to detect the magnetic flux balance,to to adjust ratio accuracy of the current source. Because the linear working range of the device is smaller,the stability of the system is vulnerable easily. The open loop system designed by this paper through setting the parameters of the DA PC program can adjust the output of the current comparator, and through the adjust of the offset DA, it can significantly improve the the ratio precision of current output.In addition,the paper puts forward a kind of open loop test plan for the system,to test the ratio of the system can achieve the biggest output precision. The paper mainly tested the current comparator when the output is 1:100 and 1:1, we can get ratio accuracy and stability of the current by data. Through the experiment and data analysis, current ratio being 1:1, The voltage difference in the resistance bridge is less 3μv, also the precision of the current ratio can reach 3×10-5 and the value of the standard deviation after calculating is 1×10-6.When the current ratio is 1:100, the voltage difference in the resistance bridge is less 5μv, also the precision of the current ratio can reach 5×10-5 and the value of the standard deviation after calculating is 3×10-6.