a slight tube assembly , in combination with a sensing instrument , such as an optical pyrometer , for use in continuously monitoring the temperature of the first row of rotating blades in large gas turbines , particularly the type used in industry . temperature data received by the pyrometer unit is fed to a control circuit , which regulates fuel input to the tubine to control the firing temperature . the key to obtaining reliable blade temperature data in the practice of this invention is the position of the sight tube in the turbine , which enables the pyrometer to &# 34 ; view &# 34 ; the rotating blades along a direct line of sight that penetrates a hot gas duct , but not the turbine section of the engine .