抄録
A fixed point blackbody furnace is an effective means for Calibrating radiation thermometers. It is not commonly used because of its complicate structure and troublesome operation. This paper deals with a set of fixed point blackbody furnaces which are simple in design and easy to operate. Metals for the fixed points are Cu, Ag, Al, Sb, and Zn. Their temperatures range from 1085°C to 420°C.
The graphite crucible in a stainless steel capsule contains about 26cm3 metal of 0.99999 nominal purity and has a cylindrical cavity of 10mm diameter and about 46mm length. The emissivity of the cavity is calculated to be 0.999±0.0005 assuming that the surface of the graphite is diffuse and its intrinsic emissivity is 0.85 at 900nm, and considering that the aperture made of stainless steel is 6mm in diameter.
Twelve trenches, cut in the length direction on the outer surface of the stainless steel capsule in an alumina tube, hold a nichrome heater winding. The furnace is a cylinder of 10cm diameter, 25cm length and 3kg weight, and consumes so little energy that input electric power of 400W raises the temperature of the capsule up to 1100°C in about an hour and a half, and that of 240W keeps the capsule at this temperature. Argon gas is blown into the capsule so as the crucible is not oxidized.
Freezing curves are measured by a 900nm silicon narrow band radiation thermometer. Plateau durations are longer than 10 minutes. The errors of the temperatures of the cavities in the realization of the fixed points are estimated to be -0.1±0.1K, and the accuracies of the fixed points for the calibration of the silicon radiation thermometer to be 0.3K.
