ABSTRACT
One design of two color pyrometer uses a rotating disk containing two filters which alternately exposes a solid state detector to one of two wavelengths. The device works on a similar principle of null balance as the Cahn micro balance (section 5.1): A filter, partially blocking the incoming radiation, is moved via a servo mechanism until it attenuates the intensity of one of the wavelengths5 (the other unaffected) until the two wavelengths are equal. The position of the filter is then graduated in units of temperature. A more contemporary device is depicted in Figure 8.10. In this device, an indium phosphide filter acts to transmit radiation over 1 J.Lm and reflects radiation of narrower wavelength. Superposition of the band gap of the silicon detectors with the InP filter results in effective wavelengths of 0.888 J.Lm and 1.034 J.Lm at the reflected and transmitted detectors, respectively. The current required to equate the output of the
twodetectorsmimicstheequalizationofintensities,andthe temperatureisexponentiallyrelatedtotheintensityratio:
W-'1=¢CIEA)..15exp(~)=(A2) 5exp[C2(_!___!_)] w,\2¢C2t,\2A25exp(~~)AITA2A!
