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Temperature measurements

Variable temperature blackbody sources

Range: -40 °C to 1600 °C

Perform high-accuracy calibration of radiation thermometers

Variable temperature blackbody 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.

These sources enable radiation thermometer calibration to be performed at a range of temperatures, whilst maintaining ITS-90 traceability.  NPL can also supply blackbody reference sources which operate over various temperature ranges between – 40 °C and 1600 °C. The calibration is traceable to the ITS-90 via an embedded contact temperature sensor.

A source specifically designed for the calibration and evaluation of tympanic (ear) thermometers is also available.

The blackbody sources which can be purchased from NPL are given with their range (r) and maximum aperture diameter (d):

  • Ammonia heatpipe: r = -40 °C to +50 °C, d = 70 mm 
  • Stirred liquid: r = -15 °C to +80 °C (higher with change of fluid, d = 75 mm 
  • Tympanic (ear) thermometer calibrator: r = +15 °C to +45 °C, d = 10 mm 
  • Water heatpipe: r = +50 °C to +260 °C, d = 40 mm 
  • Caesium heatpipe: r = +300 °C to +600 °C, d = 40 mm 
  • Wide-range calibrator: r = +60 °C to +1000 °C, d = 30 mm 
  • Sodium heatpipe: r = +500 °C to +1000 °C, d = 40 mm 
  • Silicon carbide: r = +600 °C to +1600 °C, d = 15 mm

The emissivity of each source is evaluated using computer programs written at NPL, and is generally at least 0.999. Alternative designs and sizes can be considered to meet customer requirements.

Calibration uncertainties

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. 

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