The voltage and current units in a.c. are related to d.c. units by means of thermal converters.
In the past BCR programme an intercomparison was made of the calibration of high frequency voltage by means of ac-dc thermal converters. This involved seven metrology laboratories in the Member States. The main reason for this is the considerable requirements of industry for a wide variety of applications where instruments of very high accuracy are used (current sources, multimeters,etc). A large number of industry laboratories are also accredited for carrying out such measurements. The field of electric current was not covered by this intercomparison and it is felt by the metrology laboratories of the Member States that there is a need to ensure that there is sufficient agreement among themselves. This is of particular importance for the future to facilitate mutual acceptance of calibration laboratories.
The project consists of an intercomparison of the calibrations of thermal ac-dc current transfer devices for currents ranging from 10 mA to 20 A. The measurements are done on a set of five single junction thermal convectors with appropriate shunts for the different current ranges. Each device is to be calibrated at 10 or 20 Hz, 1 kHz, 20 kHz, 50 kHz and 100 kHz. In the case of 20 A the maximum frequency is limited to 5 kHz.
The project established a very good agreement among the participating metrology laboratories in the two 10 mA to 20 A and 10 Hz to 100 kHz ranges: at low current level (10 mA and 100 mA) the standard deviation was found between 15 to 30 1E-6, then it was observed to progressive degrees to 100 1E-6 over the full ranges of currents to 20 A and above.
Funding SchemeCSC - Cost-sharing contracts