Characteristics of several kinds of I.R.P. using optical fiber were investigated. The fundamental structure of these pyrometers is that the infrared flux radiated from an object is accepted and transmitted to an infrared detector by an optical fiber, and converted into electric signals by a detector. Therefore, this type of pyrometer is suitable for measuring the temperature of a very small object whose temperature changes rapidly. Besides, the flexibility of optical fiber makes it possible to measure the inner temperature of the object by drilling a microscopically fine hole in it and inserting the fiber. In the present study, SiO2 and fluoride fibers were used as optical fibers and Ge, PbS, InAs and InSb cells were used as IR-detectors. The results are as follows. These two kinds of optical fiber had the upper limit wavelength of light transmission depending on their core materials, so that this type of I.R.P. had the lower limit of measurable temperature. By using SiO2 fiber, PbS-I.R.P, was useful for the temperature above 300°C, and InAs and InSb-I.R.P. which have a high speed response were suitable above 400°C with a good degree of accuracy. Ge-I.R.P. had a high speed response but was inferior in sensitivity. InSb-I.R.P. using a fluoride fiber whose spectral transmission loss is much smaller in the range of 2-4μm than that of SiO2 fiber was useful for the temperature range above 150°C. The optical fiber with a core of larger diameter was effective for improving the sensitivity of I.R.P., but had a little effect on the lower limit of measurable temperature.
