Research On The Temperature Control And Measurement In The Primary Thermometry From 5K To 25K

Thermodynamic temperature is one of the seven basic units of the international system of units.The high accuracy thermodynamic temperature measurement in the low temperature zone,especially in the5K～25K temperature zone,is of great strategic significance for frontier scientific research,large scientific device operation and national defense security.Temperature measurement value delivery system can be divided into reference device,standard device and industrial application device according to the temperature measurement accuracy from high to low.Only a few developed countries have established reference devices in this temperature region,while China has only established standard devices.However,it is difficult to overcome the bottleneck in the implementation of existing primary thermometry system methods in China,which seriously restricts the development of the above areas.Our group proposed a new primary thermometry system of single-pressure refractive-index gas thermometry,in order to establish primary thermometry system and the source of kelvin value in China’s 5K～25K temperature region,improve the traceability system of measurement value,and realize independent and controllable transmission of measurement value.Theoretically,the uncertainty of the new temperature measurement standard can reach0.25 m K,which expected to hit the world’s highest level.primary thermometry system device is mainly composed of cryogenic thermostatic system,microwave resonance system and pressure control system.Among them,the cryogenic thermostatic system is the basis and important guarantee of the whole device operation.Aiming at the problem of temperature control and measurement,this paper carried out the following research work: Therefore,it is necessary to provide a high stable working environment(temperature control accuracy: <0.2m K,accuracy of pressure control: < 4 ppm)and a high accurate reference point temperature(Realization of fix points of ITS-90.)for microwave measuring device.Aiming to solve the problems of temperature control and measurement,the following research work has been carried out in this paper:1.Designed and built a cryogenic thermostatic system with the pulse tube refrigerator as the cold source.Through the analysis of its performance,explained the transfer rule of the external and internal thermal noise of the system,and established the numerical model of temperature control of the thermostat through the transfer function method;2.A two-stage temperature control strategy is put forward: lowprecision and fast temperature control is adopted in the flange before the core pressure chamber,and slow-speed and high-precision temperature control is adopted in the core pressure chamber.Finally,the ultra-high stability of temperature control within 0.02 m K is achieved in the range of5-25 K,which has reached the international leading level.3.In the temperature range of 5K-25 K,a high precision realization of the fixed point temperature in ITS-90 has been achieved which the uncertainty of the temperature measurement is less than 0.25 m K.and the comparison of several reference grade thermometers is realized in the temperature zone,which provides a reference point of high accuracy for SPRIGT.