National Physical Laboratory

Voltage Calibrations

NPL provides calibration services for standard cells and electronic reference standards at 1.0 V, 1.018 V and 10 V.

Measurements of voltage at NPL are referred to the Josephson effect using the conventional value of the Josephson constant KJ-90 = 483 597.9 GHz/V exactly. The uncertainty of the value of KJ-90 in the SI system is not included in the uncertainty assessment.

By using an automated measurement system including automated low thermal switches, we are able to calibrate all customer standards directly against our primary standard (Josephson array).  This eliminates the use of a transfer standard as an intermediate step and the associated additional uncertainty.  The following table specifies the uncertainty for the calibrations we offer.

Voltage Level Uncertainty
(95 % confidence level)
1.0 V Electronic 0.14 ppm
1.018 V Electronic 0.14 ppm
1.018 V Standard Cell 0.09 ppm
10 V Electronic 0.02 ppm

Electronic Voltage Reference
Electronic voltage reference
Standard Cell Voltage Transfer Standard
Standard cell voltage transfer standard

Booking a calibration

Standard cells and electronic reference standards are calibrated according to an annual timetable, in a batch process three times a year.  It may be possible for us to carry out calibrations out-of–cycle, but this may incur an extra charge.


Customer Service tel: +44 20 8943 7166

Last Updated: 25 Mar 2010
Created: 8 Jun 2007


Please note that the information will not be divulged to third parties, or used without your permission