Development Of The Low Thermal EMF Multi-channel Scanner

According to the overall planning of the national key scientific instrument and equipment development project "Ultra-high Precision Current Measuring Instrument with Wide Measuration Range",achieving the application of the multi-channel scanner in the "Precision Resistor Load Coefficient Calibration System" must ensure that the typical thermal electromotive force(EMF)of the scanner is better than 50 nV with a measuring repeatability better than 10 nV.Up to now,the commercial scanners can match the requirement of the project are monopolized by a few foreign companies.In order to nationalize the low thermal EMF multi-channel scanner,the following will be studied tersely in this dissertation.Firstly,the theoretical channel model of the relay-based scanner is established and the ideal formula to calculate the channel thermal EMF is deduced based on the theory of Seebeck effect,which provides the theoretical basis for the analysis of the channel thermal EMF sources.Secondly,the effects of some specific factors—such as the temperature,device properties,terminal connection method—on the thermal EMF of the scanner are analyzed respectively,and then four feasible solutions are proposed to improve the key technical indicators of the scanner.Thirdly,a low thermal EMF multi-channel scanner prototype is developed and an array-type control and detection method is applied to realize the closed-loop control of the 128 relays,which improves the reliability of the channel switching.In the meanwhile,the prototype is compatible with the programmed commands of the existing commercial scanners,which improves the system suitability of the homemade scanner.Fourthly,four kinds of thermal EMF measurement methods are summarized to satisfy the different demands of the test occasions,which laies a theoretical foundation for the domestic low thermal EMF scanner verification regulation.The low thermal EMF multi-channel scanner mentioned in this paper has been realized the small batch trial production,moreover,the self-test results and the third-party testing results indicate that the typical and maximum thermal EMF of the homemade scanner can,respectively,reach 20 nV and 50 nV with a measuring repeatability better than 10 nV,which achieves or exceeds the related technical indicators of the commercial equipment.Part of the prototypes have been applied in the "Precision Resistor Load Coefficient Calibration System" and other high precision test systems,which attains the anticipative goals.