Research On The Superposition Noise Thermometer System

Accurate measurement of thermodynamic temperature is the basis for defining an international temperature scale,and a noise thermometer is a thermometer that can measure thermodynamic temperatures.In China,the China Institute of Metrology has realized a laboratory-level quantum voltage calibration noise thermometer system and a four-channel noise thermometer design in 2012,which can achieve higher precision thermodynamic temperature measurement in the laboratory.This paper will propose a superposition thermometer structure to eliminate the switch in the traditional system structure.On the one hand,this scheme does not need to match the transmission line,and on the other hand,it can increase the resistance of the sensor and the measurement bandwidth to improve the signal-to-noise ratio of the measurement and reduce the measurement time.Finally,within a short time measurement,low measurement uncertainty is guaranteed.The main research work is as follows:(1)Using the pulse-driven quantum voltage standard system to synthesize the equal-amplitude and equidistant odd-distribution AC reference voltage noise source signals required in the superimposed noise thermometer system,and develop the compensation current source by itself;(2)Constructing a hardware part of the superimposed noise thermometer system using a quantum voltage standard system,a compensation current source module,a low noise amplification filter circuit,and a data acquisition circuit;(3)Write the FPGA control program that controls DAC5791,the FPGA control program of the data acquisition circuit,the LabVIEW data processing program,and the matlab data processing program to complete the software design of the superimposed noise thermometer system;(4)The feasibility of verifying the superimposed noise thermometer under the thermodynamic temperature environment of the triple point of water.The transmission line model is established,the parameters of the low-pass filter circuit are adjusted,and the fourth-order fitting is extrapolated to DC(0 Hz)to eliminate the influence of the transmission line effect,thereby obtaining the correct thermodynamic temperature value.Finally,the measurement uncertainty of the superimposed noise thermometer system is analyzed.