A ${-}30\,^{\circ }\hbox {C}$ to $80\,^{\circ }\hbox {C}$ Stirred-Liquid-Bath-Based Blackbody Source

Abstract

At the national facility for blackbody source radiance temperature calibration of the National Institute of Metrology, China, a stirred liquid bath blackbody was developed for use as a radiance temperature reference source, which has a temperature range from $-30\,^{\circ }\hbox {C}$ to $80\,^{\circ }\hbox {C}$. This blackbody source consists of a stirred liquid bath, a blackbody cavity, a standard capsule platinum resistance thermometer, and a dry-air purging system. The cavity is cylindrical with $31^{\circ }\,\hbox {V}$ grooves on the inner wall. The cavity is 80 mm in diameter, with a depth of 520 mm, and is immersed in a bath filled with a water–ethylene glycol mixture. The average normal emissivity of the cavity is calculated to be better than 0.9999 with V grooves and when painted with Nextel 811-21 coating. The temperature stability of the blackbody source is $0.005\,^{\circ }\hbox {C}$ over a period of 20 min, and the temperature uniformity of the cavity bottom is $0.02\,^{\circ }\hbox {C}$. The standard uncertainty of the radiance temperature of the stirred liquid bath blackbody source is estimated to be $0.013\,^{\circ }\hbox {C}$.