Calibration of humidity instruments against primary standards
Calibration against an NPL primary standard
+95 °C to +75 °C, best uncertainty ±0.12 °C to ±0.05 °C
+75 °C to +60 °C, best uncertainty ±0.05 °C to ±0.033 °C
+60 °C to -60 °C, best uncertainty ±0.033 °C
-60 °C to -75 °C, best uncertainty ±0.033 °C to ±0.10 °C
-75 °C to -90 °C, best uncertainty ±0.10 °C to ±0.50 °C
Calibrations are directly in terms of dew point in air (including frost point) or given in terms of related humidity quantities such as amount fraction, vapour pressure, vapour density and others.
Depending on the instrument type and the dew-point range, calibration is made by supplying a flow of gas to the instrument, or by locating the instrument in a humidity-controlled chamber or housing. Instruments with separate measuring head can be accommodated in a temperature-controlled chamber at above the dew-point temperature.
In addition, we offer calibration with larger uncertainty against a traceable reference, typically a condensation-principle hygrometer.
Calibration against a transfer standard
+95 °C to +82 °C, best uncertainty ±0.15 °C to ±0.1 °C
+82 °C to -50 °C, best uncertainty ±0.1 °C
-50 °C to -90 °C, best uncertainty ±0.1 °C to ±0.8 °C
Humidity calibrations are also available in non-air gases and at a range of pressures.
We can also carry out calibrations below -90 °C, and for other special requirements, please enquire.
Find out more about Relative humidity calibration