Key Technologies Research On Alignment Of Balance Method For Mass Quantum Standard

Research on mass quantum standard was evaluated one of the six hardest projects in the world by Nature magazine in 2012. Nowadays, mass unit is the only one unit which still use material standard to realize basic unit among the SI units. In 2014, the basic physical constant group of CODATA decides that the mass unit will be redefined by basic physical constant in 2018. As we know, quantum mass standard can be derived from the Planck constant h. By tracing to electrical quantum standard, the balance method can realize high precision Planck constant h measurement. The principle of the balance method to realize the quantum mass standard is the balance of the mechanical power/energy and the electrical power/energy. As a key technique in the balance method based mass quantum standard, the alignment in mechanics, optics and electrics decide the accuracy directly. The difficulties among them need to be faced in all the balance experiment devices worldwide.Based on the theory of balance method mass quantum standard, the alignment problems existed in the balance method is throughly studied in the paper. The dynamic alignment parameters in watt balance and static alignment requirements, contents and key technologies on each point along the integral path in joule balance is systematically studied. There proposed new methods on magnet alignment, suspending coil alignment and laser beam alignment in this paper. The main work of this paper is as following:(1) The balance system alignment problems are analyzed and refined, and the alignment effection on the measuring result is modeled in this paper. Based on the theory of watt/joule balance, the alignment theory of the balance m ethod for mass quantum standard is studied, which gives theoretical direction to analyze each alignment item. The influences from magnet alignment, suspending coil alignment and laser beam alignment are simulated and analyzed in details. Accordingly, the theoritical basis of alignment adjustment is established.(2) The problem of current horizontal alignment of magnetic field is the tota l depending on the manufacturing and assembling. Aiming this problem, a vertical standard rotating scanning based magnetic field alignment method is proposed in this paper. The standard vertical axis is provided by a high precision electrical level meter. Measurement results from a gauss meter, which is rotated around the standard vertical axis for one circle, is analyzed to realize the direct measurment of magnetic field levelness. Consequently, the horizontal alignment of the magnetic field can be achieved according to the measured levelness. The mathematical model of this magnetic field alignment method is established. A p ractical model of plane hall effect and vertical component of magnetic field effect is established for the guidance of influence elimination.(3) To eliminate the multi-degree of freedom coupling in current corner cube reflector and PSD based suspending coil levelness measurement, a magnet horizontal standard based suspending coil horizontal attitude adjusting method is proposed. Taking the aligned magnet as reference, three planar capacitance displacement sensors are evenly mounted on the side of suspending coil to measure the relative displacement to outer magnetic yoke. The displacement sensor consist of a pair of capacitor plates on a same plane. The outer magnetic yoke is the shield ground for the planar capacitance. According to the linear relationship between capacitance and the distance, the relative displacement between suspending coil and outer magnetic yoke is measured. The levelness of suspending coil can thus be derived and optimized.(4) Current liquid level reference has the problems of low reflectivity and surface curvature in beam alignment. To solve this problem, a plane mirror horizontal standard based laser beam vertical alignment method is proposed in this paper. In this method, the vertical axis standard is transferred to the levelness adjustment of the plane mirror. Then the alignment of laser beam to vertical direction is realized based on this levelness standard.(5) Experiments are taken to verify the three alignment methods. A direct measuring and evaluating method for magnetic alignment is proposed in watt/joule balance mass quantum standard. Comparing with the indirect measurement scheme, the result of the magnet alignment uncertainty is reduced from 100μrad to 42.3?rad. On the basis of the magnetic field horizontal plane, the uncertainty of suspending coil alignment is controlled to be 71?rad. And there offered a new laser beam alignment method which can easily work in the situation of on-site measuring beam. It has an uncertainty of 41?rad. All the alignment uncertainties above have an effect to the Planck constant measuring of 10-9 level. So it can be said that the alignment methods developed in this paper are effective to the problems of balance mass quantum standard alignment.