Comparison of Transfer Standard Industrial Lamps against PTB-assigned Radiance Temperature of Vacuum and Gas Filled Tungsten Strip Lamps

Abstract

Accurate determination of temperature is one of the prime requirements in almost all the areas of physical metrology as it affects the process of any of the industrial manufacturing products. Planck’s equation serves the best approximation for determining temperature of a thermal radiating source. The ratio of pyrometric output signal due to intensities of two radiating sources can be utilized to measure temperature of an unknown source in terms of the temperature of reference metal freezing point source or a high stability tungsten strip lamp. The present paper provides an assessment of a set of tungsten lamps having strip or ribbon filament when compared against the emission of high stability standard lamps. The temperature measured in terms of electrical current across the lamp terminals has been estimated with an uncertainty reasonably acceptable for accurate determination of radiance temperature by these lamps. The uncertainty of temperature at each comparison point for lamps under assessment has been evaluated and reported. The best uncertainty of temperature was estimated to be ±1.7 K at 1073 K, ±1.5 K at 1273 K and ±3.7 K at 2473 K. The uncertainty at 1,073 K is higher as compared to at 1,273 K, is because of very low value of photocurrent signal produced due to low intensity observed at this temperature. The industrial strip lamps, compared against reference standard lamps serve as accurate sources of radiance temperature for comparing the disappearing filament Opto-spectral pyrometers used as direct temperature measuring instruments in the laboratories and in industries in the range above 1,073 K to as high as 2,500 K.