National Physical Laboratory

Supply of variable temperature blackbody sources (-40 °C to 1600 °C)

Blackbody Source
Blackbody source for the
range -15 °C to 180 °C

Radiation thermometry is a vital technique in industry, offering non-intrusive temperature measurement with a rapid response time for process control. It may be used in situations where traditional contact thermometry may be inappropriate or impractical, for example when an object is very hot, moving, in a hostile environment or where contamination must be avoided.

NPL can supply blackbody reference sources which operate over various temperature ranges between – 40 °C and 1600 °C with calibrations traceable to the International Temperature Scale of 1990 (ITS-90). These sources are constructed to an NPL design which can usually be modified to meet specific customer requirements. They may be used for the calibration and evaluation of radiation thermometers, radiometers thermal imagers and other blackbody sources. A source specifically designed for the calibration and evaluation of tympanic (ear) thermometers is also available.

In addition, NPL offers calibration of customer supplied blackbody sources, the design and supply of ITS-90 fixed-point blackbody sources, blackbody emissivity evaluation, consultancy and training in non-contact temperature measurement, and the design, supply and installation of complete radiation thermometry calibration facilities.

Technical information

A blackbody reference source is a practical means of realising and disseminating the ITS-90. It consists of a blackbody cavity, generally cylindrical in shape, which has a high emissivity. This is immersed in either a bath or furnace, depending on the temperature range, to maintain it at a steady and uniform temperature. The radiance temperature is indicated by a contact probe inserted in the rear of the cavity.

Blackbody sources may be made with apertures of various sizes depending on the application. However, a high emissivity is only achieved if the ratio of the cavity size to aperture diameter is sufficiently large.

The following table outlines the specifications of the blackbody sources which can be purchased from NPL. The emissivity of each source is evaluated using computer programs written at NPL, and is generally at least 0.999. The sources are evaluated and calibrated by comparison with an NPL primary standard blackbody reference source. They are supplied with a calibration certificate and instructions for use. Calibration uncertainties typically range from 0.2 °C to about 0.8 °C at 1600 °C.

Blackbody type Operational temperature
range / °C
Maximum aperture
diameter / mm
Ammonia heatpipe -40 to 50 70
Stirred liquid -15 to 180 75
Tympanic (ear) thermometer calibrator +15 to 45 10
Water heatpipe 50 to 260 40
Caesium heatpipe 275 to 600 40
Wide range 60 to 1000 30
Sodium heatpipe 500 to 1000 75
Silicon carbide 600 to 1600 15


Supply of fixed-point blackbody sources and pyrometric lamps

NPL also supplies the following calibrated artefacts for non-contact radiation thermometry applications:

  • Certified fixed-point blackbody cavities (emissivity >0.9999) for In (156.5985 °C), Sn (231.928 °C), Zn (419.527 °C), Al (660.323 °C), Ag (961.78 °C), Au (1064.18 °C), Cu (1084.62 °C) and metal-carbon eutectic fixed-point blackbody cells from 1324 °C to 2750 °C.
  • Pyrometric tungsten ribbon lamps to cover the range 700 °C to 2600 °C, with calibration uncertainties as low as 0.5 °C at 1000 °C for the high-stability type.

Radiation thermometry facilities

NPL has a wide range of radiation thermometry facilities and expertise which can be made available to customers for research investigations, and applications such as high temperature materials processing to 2800 °C. More information on these facilities and capabilities is available on request.


Customer Services tel: +44 20 8943 6315

Last Updated: 1 Mar 2012
Created: 11 Sep 2007


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