High-quality blackbody sources for infrared thermometry and thermography between -40 and 1000 °C

The National Physical Laboratory (NPL) has designed and constructed four high-quality infrared (IR) blackbody sources to provide standards for the calibration of IR thermometers and thermal imaging systems. These are based around heat-pipe technology and are delineated by the working fluid of the cavity; ammonia (from -40 to +50 degreesC), water (from +50 to +275 degreesC), caesium (from +280 to +600 degreesC) and sodium (from +500 to +1000 degreesC). The emissivities of these cavities are in excess of 0.999 and the expanded radiance temperature uncertainties [U(k = 2)] range from less than 0.1 degreesC at lower temperatures to about 0.2 degreesC at 1000 degreesC. The sources are used to provide traceability to the International Temperature Scale of 1990 via a calibration service, accredited by the UR Accreditation Service (UKAS) (Calibration Laboratory 0478). This paper describes the general design of the NPL blackbody cavities and their performance. It then describes the use of the blackbody cavities for testing two different commercial thermal imagers. Imager 1 is based on scanning technology; imager 2 has a focal plane array detector package; both systems operate within the 3-5 mum atmospheric transmission band. The parameters tested are the temperature accuracy, uniformity across the image plane, effect of range setting on output and sensitivity to atmospheric carbon dioxide.