Abstract: A temperature measuring device for measuring temperatures at axially spaced positions along the bore of a tube comprises a sensor in the form of a central rigid wire of constantan base alloy on to which thermocouple foils are spot welded at prescribed locations. The foils are silver plated over half their length thus forming a silver/constantan thermojunction; the constantan end of the junction only being welded to the rigid wire. A copper wire is crimped to the silver plated end of each foil. The detector may be supported coaxially within a resistance heated tube and in use the temperatures sensed by the thermocouples are continuously monitored.