ResistanceSP provides calibration services for electrical resistance standards and various types of instruments, such as calibrators, multimeters, LCR meters and some temperature measuring instruments.
The resistance unit
At SP the unit of resistance, the ohm (Ω), is realised at direct current (dc) and the levels 6.45 kΩ and 12.9 kΩ with traceability to the numerical value of the ratio of Planck's constant and the square of the elementary charge known as the von Klitzing constant R K-90. The realisation is performed with a "quantized Hall resistance standard" based on the quantized Hall effect. The measurement uncertainty is on the order of 0.013 μΩ/Ω for the realisation of the ohm.
The realised resistance unit is transferred to groups of 1 Ω, 100 Ω and 10 kΩ primary and secondary standards maintaining the resistance unit. Between realisations, the primary and secondary standards are compared regularly to secure the maintenance of the resistance unit.
At alternating current (ac) the resistance is frequency dependent and deviates individually from the dc-value for all types of resistance standards. Resistance standards at 1 kΩ and 10 kΩ, calibrated at dc, with a calculable ac-dc difference are used for realisation of traceability for ac-resistance. The uncertainty in the calculation of the ac-dc difference at 1 kHz is less than 0.1 μΩ/Ω.
In order to further secure traceability, SP also participates regularly in international comparisons.
SP offers calibration of resistance standards and different types of instruments such as resistance bridges, multimeters, calibrators and LCR-meters in the range 1 μΩ - 10 PΩ.
Resistance standards are calibrated with resistance bridges or TΩ-meters. Several types of instruments are calibrated by measuring secondary resistance standards. The best measurement capability is 0.25 μΩ/Ω.
Calibration of resistance standards in the range 1 Ω - 10 kΩ can be offered using a so-called cryogenic current comparator (CCC). The best measurement capability is 0.05 μΩ/Ω.
Calibration of ac-resistance can be offered in the range 1 Ω - 100 MΩ for frequencies up to 10 kHz. An ac-resistance bridge or LCR-meter for so-called substitution measurement is used for ac-resistance standard calibrations. LCR-meters are calibrated by measuring secondary ac-resistance standards. The best measurement capability is 5 μΩ/Ω.
Other types of measurements are also performed, for example, determination of temperature coefficients and resistivity.
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.