Precision Measurement Of The Rmal Expansion Coefficient For Cavity Based On Microwave Resonance

Temperature is one of the seven basic units of international unit system,which plays an important and fundamental role in scientific research,industrial production and daily life.Thermodynamic temperature is the real temperature of the physical system,but because of the difficulty in measuring results,according to the thermodynamic temperature measurement of the international temperature organizations to develop a practical protocol scale,also known as the international scale,at present we are using the ITS90 international temperature scale.The international temperature scale is approaching to the thermodynamic temperature.But with the development of scientific research,new research shows that the current international temperature scale and precision measurement of thermodynamic temperature the latest results showed the system deviation,in some temperature range,the deviation is close to the international scale of uncertainty,so we need to accurately measure the thermodynamic temperature,provide the basis for the revision of the next stage of the scale.At present,acoustic resonance method is one of the most accurate methods to measure the thermodynamic temperature.The thermal expansion of acoustic resonance cavity is one of the main sources of the measurement of thermodynamic temperature uncertainty.The accurate measurement of the thermal expansion coefficient is the necessary precondition for the accurate measurement of thermodynamic temperature.Thisarticle based on microwave resonance,using the principle of obtaining cylindrical cavity size and the thermal expansion coefficient by microwave resonant frequency,Based the experimental platform of high temperature acoustic thermometer of Chinese Institute of Metrology,wedesigned and processed of microwave resonantcavity,including high temperature microwave electric cable and antenna,established the high temperature pressure vessel system,seted up precision temperature and temperature control system,improved the automatic control and data acquisition system.The temperature stability of the new system has been measured.The results show that the temperature stability of resonance cavity in an acoustic resonance frequency measurement period(about 30 min)can reach ± 0.002?,which meets the demand of acoustic thermometer measurement.We studied on the thermal expansion coefficient of cylindrical cavity with temperature from 50 ?~230?.we obtained four transverse magnetic(TM)microwave resonant frequency of microwave mode,using TM001 model to obtain the cavity radius and radial thermal expansion coefficient,using TM101,TM201 and TM301 three TM model to obtain the cylindrical cavity length and axial thermal expansion coefficient.we analyzed consistency of the thermal expansion coefficient obtained by three axial microwave resonant frequencies,and the relative standard deviation is-71×10.The results can meet the uncertainty requirements of high temperature acoustic thermometer measurement.The research of this article lays an important foundation for the future measurement of high temperature thermodynamic temperature by using cylindrical acoustic and microwave resonance methods.