 The temperature measuring system consists of a controller (laser source, pulse generator for OTDR or code generator for Code Correlation or modulator and HF mixer for OFDR, optical module, receiver and micro-processor unit) and a quartz glass fibre as line-shaped temperature sensor.The fibre optic cable (can be 30 km+ in length) is passive in nature and has no individual sensing points and therefore can be manufactured based on standard telecoms fibres.This offers excellent economies of scale.