DC CurrentSP provides calibration services for current shunts and various types of current measuring and generating instruments.
The current unit
At SP the unit of current, the ampere (A), is realised at dc with the use of Ohms law with traceability to the units of voltage and resistance. The measurement uncertainty is on the order of 25 nA/A for the realisation at the 100 µA level.
At levels below 100 pA an alternative realisation method is used. A well defined generated voltage ramp is applied to a capacitor. The lowest measurement uncertainty is on the order of 30 µA/A. Traceability is from the units of voltage, frequency and capacitance.
In order to further secure traceability, SP also participates regularly in international comparisons.
SP offers calibration of dc current in the range 10 fA - 6000 A. Other types of measurements are also performed, for example, determination of temperature coefficient. See also ac current.
The final uncertainty given at calibration depends not only on the uncertainty contribution from the calibration equipment but also from the device under test contribution (stability, temperature coefficient, voltage dependence, etc.). A preliminary measurement uncertainty can often be estimated from experience prior to calibration.