Temperature and humidity measurements

Relative humidity calibrations

Range: 0.5%rh to 98%rh

Relative humidity calibrations over a wide range of temperatures

Relative humidity calibrations are offered at primary level, directly against an NPL primary standard humidity generator.

  • Range: 0.5 %rh to 98 %rh, at temperatures from -40 °C to +100 °C.
  • Best uncertainty ±(0.6 % of reading + 0.1 %rh)

Calibration against a transfer standard is also available (against a traceably calibrated transfer standard hygrometer).

NPL can advise on selecting the range and number of calibration values appropriate for a particular instrument and application.

A recommended general calibration could consist of 5 relative humidities in the range 10 %rh to 90 %rh at 20 °C and two additional temperatures (such as 15 °C and 25 °C) at 50 %rh. This combination would give some indication of the linearity and temperature dependence of the instrument under test.

Air temperature is closely controlled, monitored and reported as part of the relative humidity calibration, since relative humidity is strongly dependent on temperature. As an additional service, temperature sensors can be calibrated in air.

Find out more about Calibration of hygrometers

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