This project aims to deal with the development of international system of units. A quantum mass s...

Start Date

2006

End Date

2010

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Quantum Mass Standard of Joule Balance

 

This project aims to deal with the development of international system of units. A quantum mass standard with higher accuracy whose value will not change over time or location is to be established. Through this project, value-tracing ability of mass unit (mechanical) to quantum standards will be established.

 

The research work of national mass natural standard is still in progress. It is the first time in the world a scheme developing from Watt balance to Joule balance is adopted in mass standard. Through communication with domestic experts and foreign colleagues, Joule balance project becomes a well-known one. During a four-year study, the first stage plan of Joule balance project has been completed. Joule balance apparatus has been built and the Planck constant h was measured with a relative uncertainty of 2.5×10-5. Three technical difficulties have been solved as follows:

 

1. A kind of special sampling resistance with a minimum load coefficient was developed. For 50 mW power consuming. The resistance change caused by current heating is in an order of 10-9.

 

2. The uncertainty of mutual inductance measurement, which is  a crucial part in this project, is only 1×10-7, better than published result (uncertainty 3×10-6, NPL).

 

3. A constant current source of 250 mA was designed for necessary magnetic field with a stability of 3×10-7( 30 min).