Investigation On The Length Determination Of A Fixed Path Cylindrical Resonator

The present definition of the kelvin links the unit of temperature with a material property ,namely the triple point temperature of water.At its 94th meeting in October 2005,the International Committee for Weights and Measures(CIPM) adopted a recommendation on preparative steps towards redefining the kelvin with the exactly defined values of Boltzmann constant. A research project has been conducted in the National Institute of Metrology, China, for the re-determination of the Boltzmann Constant with dual fixed path cylindrical acoustic resonators. The dual wavelength laser interference method was designed for the length determination of a fixed path cylindrical resonator. In this paper,it reports the device of the lengths determination of a fixed path cylindrical resonator with the dual wavelength laser interference method.The resolution of the device of the lengths determination of a fixed path cylindrical resonator is 0.5 nm and the combined uncertainty of the cylinder length determination is 0.03μm.The device consists of hardware and software. The hardware of the device composed of laser, measurement system of the resonator, wavemeter and computer. On basis of the Labview, a program was developed to manage the instrument, analyze and process the images so that the diameter of the interference ring can be accurately obtained. The diameter of the interference ring is related with the inner length of Fabry-Perot cavity, so the length of the resonator can be accurately measured with the interference method.Base on the experimentation, the value of the lengths determination of a fixed path cylindrical resonator is received. The analysis shows that the relative standard deviation is 1.63×10-8and the repeatability of this device is better. The length of the resonator can be measured with pressure at 498.18kpa and temperature at 20.01℃,15.02℃,9.99℃,5.01℃,0.25℃. The measurement data show that length of the resonator will decrease with the decrease of temperature.The length of the resonator will be measured with temperature at 0.01℃and pressure at 498.18kpa,401.58kpa,298.09kpa,101.54kpa,49.27kpa,20.52kpa. The measurement data show that length of the resonator will decrease with the decrease of pressure. Lastly, the uncertainty is particularly analyzed. The result shows that the combined uncertainty of the cylinder length determination is 0.03μm.