National Physical Laboratory

Temperature & Humidity Research

Our experienced team provides world-leading research into the development of innovative sensors, standards and measurement solutions.

Temperature Measurement

NPL carries out world-leading research into temperature standards, calibration and measurement methods using a wide variety of techniques.

For more details, please choose an area below.


Contact Thermometry

NPL carries out research into developing new temperature reference points and improving the uncertainties on those already in use for contact thermometer calibrations. NPL also carries out research into and development of new measurement techniques - to enable reliable contact temperature measurements in, for example, harsh environments.

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Acoustic Thermometry

In acoustic thermometry, the temperature is determined from measurements of the speed of sound in a gas. NPL uses acoustic thermometry in three distinct applications: ultra-precision primary measurements using a resonator; more practical measurements using tubes; and free-space measurements for meteorological applications.

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Non-contact Thermometry

NPL carries out research into high temperature fixed points (HTFPs), together with developing radiation thermometers able to make best use of them, with a view to having the HTFPs incorporated into the S.I. through the mise en pratique for the definition of the kelvin (MeP-K). The ultimate aim is to provide wide access to low uncertainty thermodynamic temperature, to at least 3300 K, that is even simpler to establish than ITS-90. In the meantime, the developments allow in-situ pyrometer calibration checking and facilitate corrections in situations for varying window transmission.

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Thermal Imaging Metrology

Thermal imaging (TI) metrology is a growth area due to the affordability, practicality and functionality of modern thermal imaging systems. These systems provide non-contact, full field thermal measurement which are now being investigated, implemented and exploited across many sectors to provide rapid, in situ, vision based measurement systems. NPL collaborates widely across all sectors in the development of state-of-the-art thermal imaging measurement solutions.

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Other Techniques

Several additional techniques/facilities are currently under investigation:

  • Flame thermometry - the development of a standard flame with a known and reproducible temperature. The temperature of the flame is determined with laser Rayleigh scattering. Once calibrated, the flame can be used to calibrate other optical diagnostic techniques used in industry.
  • Emissivity free radiation thermometry - novel methods that can determine the temperature of a hot surface without knowledge of the surface emissivity are currently under investigation.

These are being developed with a view of providing new techniques/facilities to address future industrial needs.

Humidity Measurement

NPL carries out research into standards, calibration and measurement methods for humidity and related properties.

Our work comprises the following projects:

  • Provision of humidity standards
  • Development of humidity standards and traceability for industrial conditions
  • Development of capability for measurement of moisture in materials

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