Temperature calibration for distributed temperature sensing of printed circuit boards using optical fiber sensors

Abstract

The work investigates the procedures for temperature calibration of optical fiber sensors (OFSs), implemented on printed circuit boards (PCBs), aiming to accomplish accurate distributed temperature measurements, during temperature cycles. The OFSs are interrogated by optical frequency-domain reflectometry, OFDR, which provides plenty of sensing points using a single OF. For temperature measurements, it was used a polyimide-coated optical fiber within a PTFE sleeve and conventional type-K thermocouples, as a temperature reference. Samples with different OFS dispositions were placed in a static oven under distinct programmed temperature profiles. The temperature calibration correlates the OFS signal frequency shift to the temperature profile registered by reference thermocouples. The proposed calibration methodology results in temperature measurement with low error (±1 °C/3%). Different calibration fittings were obtained depending upon the type of OF configuration and temperature profile used (temperature ranges and rates) since some calibration curves showed an undesired 'bow effect' (hysteresis), which appears to be dependent on the heating/cooling rates. The results of OF within PTFE sleeve, bonded to a PCB and covered with aluminum tape, present smaller deviations and a more stable signal. Nevertheless, the calibration of OFS for distributed temperature measurements is still dependent on application-oriented calibration adjustment.