The Alignment Technologies For The Characteristic Vectors In The Project Of The Quantum Mass Metrological Standard Based On The Joule Balance Method

Research on the mass quantum standard was evaluated one of the hardest projects in the world by Nature magazine in 2012,and this research is hot in the international metrology research field.In 2006,the National institution of Metrology of China has proposed their project for kilogram traceability based on joule balance method.The purpose of this project is to establish the relationship between the kilogram and the Planck constant by the balance of the mechanical energy and the electromagnetic energy.There are four vectors to describe the state of the coil in joule balance,which are the ampere force,the gravity,the moving direction of the coil and the direction of the laser beam for measuring the movement.These vectors are called the “characteristic vector” of the coil.And there will be alignment error when these vectors are not aligned to one line.The measurement uncertainty of the alignment error determines the measurement accuracy of the Planck constant.Therefore,how to measure and compensate the alignment error has become the core problem of the joule balance project.Based on the principle of the joule balance project,this subject is to conduct a throughly study on the alignment error,and analyze the alignment-error source and uncertainty influence,then building a mathematic model for the alignment error.And this subject developed the new alignment method for the vertical movement and laser direction.The main research works are as follows:A model of the alignment error of the characteristic vectors is established in joule balance project.Based on the virtual work principle,this model represent the energy convertion in the way of the working of the horizontal ampere force and magnetic torque in four degrees of freedom.The accuracy of the model is verified by the silmulation and experiment results.According to the model,the measurement error of the vertical-moving straightness and the angle between the vertical-moving-measurement laser and the vertical direction,has been the major alignment errors for the measurement of the Planck constant.Therefore,these errors needs to be compensated.A measurement method for vertical-moving straightness is proposed based on a vertical filament direction reference.This method combines the filament reference and a cylindrical electrode to a filament-cylinder capacitive sensor.This method transforms the vertical-moving straightness to the capacitance change of a capacitive sensor.The influence of the edge effect of the cylinder electrode is analyzed,and we evaluates the measurement error caused by this edge effect by the finite element simulation.The result of the similation showes this error can be ignored.Experimental results show that the measurement uncertainty of the capacitive sensor with a vertical direction reference of the brittle filament is decreased from 2.5?m to 1.7?m.A measurement method for the decline angle between the laser beam and the vertical direction is proposed based on the liquid mirror normal reference.This method estabished a silicone oil liquid mirror normal vertical reference,and combines the normal reference and a laser beam parallelism measurement method to measure the decline angle from the vertical.The change of the mirror surface curvature is measured to obtain the uncertainty of the mirror normal in 40×40mm2 area around the mirror centre.The measurement result showes that the uncertainty of the mirror normal is approximately 3.2?rad.Experimental results show that the measurement uncertainty of the decline angle between the laser and the vertical direction is decreased from 25?rad to 11?rad.Finally,the accuracy of the model of the alignment error is verified by comparing the results of the model simulation and the experiment.And the measurement uncertainty of the vertical-moving straightness and the angle between the laser and the vertical direction is also verified by the experiments.These two measurement methods both meet the uncertainty requirements of the joule balance project for the final uncertainty by the experimental results.