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Temperature and humidity measurements

Relative humidity

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. 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.

Relative humidity calibrations against an NPL primary standard

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

Find out about calibration in terms of dew-point in air

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