The primary volt is derived at present from Josephson Junctions and maintained in the metrology laboratories with Weston Cells.
The transfer of the volt eg to industrial calibration laboratories is done by means of digital voltmeters which provide an accuracy of about 10 ppm. Recent solid state voltage standards using Zener diodes appeared to be able to transfer and maintain the volt with an accuracy of the order of 1 ppm or better over one year.
The objective of the project was to investigate how such a solid state standard would behave when transported from one metrology laboratory to another for an intercomparison.
Three instruments are being circulated amongst the metrology laboratories for calibration at 1 V and at 10 V.
For intercomparison measurements three sources of two different types have been circulated:
1. Fluke model 732 with the output of 10 V, 1.018 V and 1 V.
2. Cropico VSIO, with the output of 10 V.
3. Cropico ECSI, with the output of 1.018 V and 1 V.
The laboratories agreed in their measurements to within +/- 1 x 1E-6. The long term stability analysis performed by the pilot laboratory (PTB) over a longer period (5 years) has shown for all sources a linear drift with time of a few parts in 1E-6.
Funding SchemeCSC - Cost-sharing contracts
TW11 0LW Teddington