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Low uncertainties for calibration standards

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

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