A method of assembling a fiber optic sensor in a protective tube, and fiber optical sensor with a thermowell

The invention relates to a method of assembling a fiber optic sensor (2, 32, 42) in a protective tube (1, 30, 41), wherein in the protective tube (1, 30, 41) a shape-variable filling body (4, 31, 43) axis substantially parallel to the optical fiber sensor (2, 32, 42) is introduced. By change of shape of the filling body (4, 31, 43), the storage of the fiber optic sensor (2, 32, 42) remaining free inner cross-section of the protective tube (1, 30, 41) so reduced that the sensor is pressed against the tube wall. Thereby, the thermal transition between the protective tube (1, 30, 41) and sensor (2, 32, 42) is improved and reduces the response time for temperature measurements. Preferably, as packing elements (4, 31, 43) is a wire made of spring steel is used, which assumes a substantially helical shape in twisting.