Abstract
As a substitute for the common method of calibration of radiation pyrometers, which requires either a blackbody furnace provided with a standard thermocouple or a blackbody cavity immersed in a freezing metal of high purity, a simple method having a practically sufficient accuracy is reported.
A small sheet of pure metal, the melting point of which is known, is set in a refractory cavity in a furnace, and the pyrometer to be calibrated, connected with a recorder, is aimed at the metal sheet. The furnace is heated up and, in due course of time, an abrupt increase of the pyrometer indication is observed on the record. The terminal point of this increase corresponds to the temperature of a blackbody kept at the melting point of the metal, as, at the moment of the melting doum of the metal sheet, the condition of radiation in the cavity turns from an incomplete equilibrium to the complete one, because of the disappearance of the specularly reflecting surface of the metal sheet and the consequent disclosure of the roughly reflecting surface of the refractory cavity wall. The departure from the expected correspondence gives the amount of error of the pyrometer indication at the melting point of the metal.
The reproducibility of calibration by this method, estimated from the results of application to three different models of infrared radiation pyrometer, was within ±2K at the melting points of gold and of silver. This method is also applicable to the melting point of copper and to that of palladium, if proper care is taken.
