Digital Design And Research Of Low Temperature Current Comparator

Precision measurement and testing play an important role in our daily production and experiments of the scientific research.The detection and transmission of small electric currents have been a hot topic in the field of electromagnetic measurement long time,especially when establishing quantum current to redefine "ampere" that the base units of SI,the strongly demand and challenge are put with device of the detection and transmission in small current.In this paper,a series of discussion and design are carried out on the precision measuring instrument--Cryogenic Circuit Comparator.Cryogenic Current Comparator is the most accurate instrument to detect small current.It is the best instrument for measuring and transmitting quantum Current.Because of the highly precision,which has been widely used in national metrology experiments.In order to further improve the performance of cryogenic current comparator,the paper conducted a series of improvement and to its design,mainly embodied in the traditional analog control improvement for the digital control circuit,the digital design of cryogenic current comparator.The structure of the paper is introducing the background and development status of the research in the first chapter,and the main contents of the paper are summarized.In the second chapter,the principle of cryogenic current comparator and the related measurement circuit was introduced in detail.Then,the design of hardware circuit and software design are expounding respectively in later chapters.Finally,the experiments verify the design is feasible and the article is summarized.Design of the digital control design of CCC is mainly divided into two aspects,one hand is using the digital design to current source;on the other hand,take the digital design to the voltage compensation module of Cryogenic Current Comparator.Digital design of current source is mainly reflected in that adding the highly precision DA unit to produce the voltage and adding offset DA module to adjust the voltage.In this way,the current source module of Cryogenic Current Comparator is adjusted by digital control circuit instead of the analog circuit of traditionally,it can guarantee the good stability and operability of the Cryogenic Current Comparator.A trapezoidal binary voltage compensation module with R-2R is designed to replace the winding resistance of traditional voltage compensation module,the design can improve the resolution of the voltage compensation and reduce the pressure of the experiment of calibration circuit.Because the resistance value of the R-2R trapezoidal binary voltage compensation module used in the circuit is always using the ratio of two,so the resistance of the reading compensation module of CCC does not need to be calibrated one by one,and you just need to calibrate it according to a certain percentage.In addition,16 bits DA are added in the compensation circuit to improve the resolving of the reading compensation circuit further.All digital control in this design is completed by the computer,it through LabVIEW to configuration parameter information and sent it to DSP to carry out.There are experiment on the current source module and reading compensation module,further affirmed the stability and the accuracy of the design of the digital control of the CCC,achieving the desired designed goal.