Abstract: A resistance temperature detector measures the temperature of fluid flowing through a pipe at a given point in the pipe. In the temperature detector, normal and backup temperature sensing resistance elements are secured with inorganic adhesive onto an inner wall surface of a thin-walled tubular sheath having its tip end closed. These temperature sensing resistance elements are disposed in spaced parallel relationship and are respectively connected to insulated lead wires separately disposed within the resistance temperature detector. The resistance temperature detector also includes a sheath cable assembly having sheathed cables, each of which is electrically connected to a respective one of the insulated lead wires and secured to the other end of the tubular sheath. Thereby a sealed vacant space is defined within the temperature sensing assembly.