Calibration Services
Electrical: Standard Resistor
General
The Direct Current Laboratory of SCL can provide calibration services for resistance standards ranging from 0.1 mΩ to 10 TΩ.
Measurement of resistance at SCL are referred to the quantised Hall effect using the following value of the von-Klitzing constant RK = 25 812.807 459 3045 Ω exactly.
The calibration system comprises of the Quantised Hall Resistance Standard (QHRS), Ratio Bridge, Direct Current Comparator (DCC) resistance bridge/range extender, Kelvin Ratio resistance bridge, modified Wheatstone bridge and a series of decade standard resistors.
Quantised Hall Resistance Standard
Quantised Hall Resistance Standard
For oil-immersed standard resistors, the stated Calibration and Measurement Capability (CMC) will be assigned only to 4-terminal decade-valued standard resistors of high quality, and for measurements being made with the resistors immersed in a constant temperature oil bath at 23°C. Measurement at oil temperatures other than 23°C and in the temperature range of 18 to 25°C can also be made with additional uncertainties.
Resistors not suitable for oil immersion or of values above 10 MΩ will normally be measured in air at nominal temperature of 23°C with increased measurement uncertainty.
Resistors of non-decade value are measured with additional uncertainties.
High-value Resistors
High-value Resistor
The Laboratory offers calibration for high-value DC resistors and resistance boxes in the range 10 MΩ to 10 TΩ (1×1013 Ω). In general, measurements will be made in air at nominal ambient temperature of 23°C and relative humidity of 45%. Customers may specify their required test voltage between 100 V and 1 kV.
Measurement uncertainties will vary with test voltages and resistances.
Current-Carrying Resistors (Current Shunts)
Current-carrying Resistor
Four-terminal current-carrying standard resistors in the range 0.1 mΩ to 1 Ω can be calibrated. The maximum test current is 100 A at 0.1 mΩ but becomes smaller at higher resistance values. At 1 Ω, it is limited to 1 A.
Resistors suitable for oil immersion will normally be measured in a constant temperature oil bath at 23°C. Air-cooled resistors will be measured in air at an ambient temperature of 23°C.
Resistors are usually measured at rated currents. If other current levels are required, customers should specify their particular requirements.
Temperature coefficient of resistance
Calibration of temperature coefficients for oil-immersed standard resistors is also available. Normally, 23°C is taken as the reference temperature and the temperature coefficients are determined from results of our resistance measurements made at the reference temperature and at three other temperatures over the temperature range of 18 to 25°C, using appropriate curve fitting techniques. The resistance value at the reference temperature will also be reported.