National Physical Laboratory

Calibration of standard blackbody sources, radiation thermometers and tympanic (ear) thermometers

Blackbody calibration sources for the range from -40 °C to 1000 °C
Blackbody calibration sources for the range from
-40 °C to 1000 °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 for measuring temperatures 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.

In order to provide traceability to the International Temperature Scale of 1990, the ITS-90, through the provision of test and measurement services, NPL maintains a suite of standard blackbody radiation sources which operate over various temperature ranges between -40 °C and 3000 °C. They are used for the calibration and evaluation of:

  • secondary blackbody reference sources
  • infrared radiation thermometers, radiometers, thermal imagers, tympanic ear thermometers and disappearing filament pyrometers

The calibration uncertainties range from 0.05 °C to 0.3 °C over the temperature range from -40 °C to 1000 °C, and from 0.5 °C to 1.5 °C at high temperatures (1000 °C to 3000 °C) (subject to the satisfactory perfomance of the instrument under test).

These services are UKAS accredited (NPL is a UKAS-accredited calibration laboratory number 0478).

A standard blackbody source is a practical means of realising and disseminating the ITS-90. The following table gives the specifications of the NPL blackbody radiation sources. These may be used for the calibration of infrared thermometers and other blackbody sources, offering calibration uncertainties from 0.05 °C to 1 °C depending on the instrument and temperature range. The emissivities have been evaluated using computer programs written by NPL and are generally in excess of 0.999.


Blackbody type Operational
range / °C
diameter / mm
Ammonia heatpipe -40 to +50 70
Tympanic (ear) thermometer calibrator +15 to 45 10
Water heatpipe 50 to 250 40
Caesium heatpipe 275 to 600 40
Sodium heatpipe 500 to 1000 75
Silicon carbide 600 to 1600 15
High temperature graphite 1000 to 3000 25
Calibration of an infrared thermometer at 900 °C using a variable temperature NPL standard blackbody source
Calibration of an infrared thermometer
at 900 °C using a variable temperature
NPL standard blackbody source

Customer blackbody sources may be evaluated by comparison with an NPL standard source using either an infrared radiometer or a suite of transfer standard radiation thermometers operating at wavelengths from 0.65 µm to 14 μm.

In addition, NPL offers:

  • Consultancy and training in non-contact temperature measurement
  • Design and construction of variable temperature blackbody reference sources to meet customer requirements
  • Design and construction of ITS-90 fixed point blackbody sources and high temperature (> 1100 °C) metal carbon eutectic fixed point cells
  • Design, supply and installation of complete radiation thermometry calibration facilities
  • Blackbody emissivity evaluation
  • High temperature materials processing to 3000 °C
  • Supply and calibration of 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

Further information about these services is available by clicking on the links or on request.

Download Reduced uncertainty radiation thermometer calibration service flyer Adobe Acrobat PDF file


Customer Services tel: +44 20 8943 6315

Last Updated: 6 Oct 2014
Created: 11 Sep 2007


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