An extrinsic optical fibre temperature sensor has been investigated and preliminary results are presented. An active coating is used which consists of a mixture of two phosphor powders. Thermal quenching dominates the luminescent characteristics of one phosphor at temperatures in the range of interest while the other more stable phosphor is used as a reference. Ratios of their emission intensities are calculated and analysed. Preliminary results show a decreasing ratio for increasing temperature. This paper describes initial testing of the coating and its application, as part of a temperature sensor, for monitoring surface temperatures in electromagnetically harsh industrial environments.