Temperature measurement apparatus

Abstract

A light source for forming an optical path extending across a closed vessel and a light receiving unit for receiving light from the light source are disposed outside the closed vessel. A portion to have its temperature measured as lies in the closed vessel is provided with a temperature detecting device which consists of a temperature sensor and a light interceptive plate. The temperature sensor is formed to be downwardly convex by sticking two members of different coefficients of thermal expansion one over the other (the member of the larger coefficient of thermal expansion being arranged over the member of the smaller coefficient of thermal expansion). The light interceptive plate is arranged over the member of the larger coefficient of thermal expansion. When the portion to have its temperature measured has reached a predetermined temperature, the temperature sensor inverts the downwardly convex state into an upwardly convex state. Owing to the inversion of the state of the temperature sensor, the light interceptive plate is turned into the optical path extending across the closed vessel, from outside the same and intercepts part of the light from the light source. Thus, the quantity of the light to be received by the light receiving unit changes, and the temperature of the portion is measured through a light quantity--temperature conversion.