In order to shift some of our human resources to other essential activities, such as establishing the calculable capacitor and collaborating on the BIPM watt balance project, while at the same time continuing our support for the CCEM and our programme of comparisons and calibrations, the CCEM (2007) agreed the following guidelines for the calibration of electrical standards at the BIPM:

• NMIs are asked to limit the frequency of their BIPM calibrations of resistors, capacitors and electronic voltage standards (Zeners) to once every two years for the same type of standard.


• Users of the BIPM electrical calibration services should please limit the number of standards of a given type to no more than three standards of the same nominal value.


• The calibrations will be carried out at the BIPM in two or three batches during the year.

In addition to calibrations, a bilateral comparison scheme using conventional standards is offered to those laboratories that desire well-documented traceability to the BIPM voltage, resistance, and capacitance standards. This uses methods and procedures similar to those used in the former large-scale international comparisons and the results are proposed to the CCEM for inclusion in the CIPM MRA database.

Further information on the calibrations available for electrical standards of national laboratories is provided in the "Voltage", "Resistance" and "Capacitance" pages above.

Technical description of the service

Electronic voltage standards referenced to Zener diodes are now widely used, creating the need to carry out calibrations at 10 V as well as 1.018 V. The BIPM uses 10 V arrays of Josephson junctions as the reference voltage standard and all votages are defined with respect to K_J-90.

Calibrations at 10 V are carried out either by comparison with a Zener working standard that is calibrated with a 10 V array or by direct comparison with an array. Calibrations at 1.018 V are carried out either by comparison with a calibrated standard cell or by direct comparison with an array. The combined standard uncertainty (relative to the nominal output voltage) assigned to the calibration of a 1.018 V or 10 V Zener voltage standard is typically 1.4 parts in 10⁸ (excluding uncertainty components associated with transportation).

BIPM Zener diode calibration request form

In the area of resistance calibrations, the BIPM was the first laboratory to use a cryogenic current comparator for routine resistance calibrations. This provides a significant increase in the precision of the comparisons and makes it possible to obtain, for example, precise estimates for the pressure coefficients of travelling standards received for calibration by measuring variations in resistance caused by natural changes in atmospheric pressure.

Routine calibrations are carried out at 1 , 100 and 10 k. With respect to R_K-90, the combined standard uncertainty assigned to the calibration of a 1 resistance standard is typically 1.7 parts in 10⁸ relative to the nominal value; that assigned to the calibration of a 100 or 10 k resistance standard is typically 1.8 parts in 10⁸ (excluding uncertainty components associated with transportation).

The link between 1 pF, 10 pF and 100 pF capacitance standards and the quantized Hall resistance has been established at the BIPM.

With respect to R_K-90, the combined relative standard uncertainty assigned to the calibration of a 1 pF, 10 pF or 100 pF capacitance standard is typically 5 parts in 10⁸ at 1000 Hz and 4 parts in 10⁸ at 1592 Hz (excluding uncertainty components associated with transportation). These uncertainties have been confirmed by several international comparisons.

The BIPM offers a calibration service for 1 kg national prototypes in Pt-Ir. This service is available free of charge to Member States. The Physical Metrology Department maintains a number of prototypes and other standards in Pt-Ir. A subset of these are used as working standards to calibrate national prototypes upon request. The remainder are used for quality control. The standard uncertainty currently assigned to the calibration of a national prototype depends on the time since the last use of the IPK. The last use of the IPK was in 2014 and the combined standard uncertainty of the calibration of national prototypes is currently 0.0045 mg.

The BIPM also fabricates Pt-Ir prototypes for Member States upon request.

• Request the calibration of a national prototype

The BIPM offers a calibration service for 1 kg standards in stainless steel. This service is available free of charge to NMIs of Member States. The volume of the standard will be determined by hydrostatic weighing at the BIPM if this parameter is unknown (typical combined standard uncertainty obtained at the BIPM is 0.44 mm³ at the reference temperature of 20.0 °C). However, the volumetric thermal expansion near room temperature must be supplied by the NMI or the manufacturer of the standard. If not already in our database, the BIPM will determine the location of the centre of gravity of the standard. The combined standard uncertainty currently assigned to the calibration of a 1 kg standard in stainless steel is typically 0.010 mg.

• Request the calibration of a 1 kg standard in stainless steel