FIBRE OPTIC COUPLED, INFRARED THERMOMETERS FOR PROCESSES INCURRING HARSH CONDITIONS

This study undertook the development and testing of fibre optic coupled infrared thermometers (IRTs) that could substitute for thermocouples in harsh conditions that would affect contact temperature measurements deleteriously. The IRTs have been configured without photodiode cooling and signal chopping but achieved low minimum measurable temperatures, fast responses and good sensitivities. IRTs were configured with mid-wave infrared (MWIR) and short-wave infrared (SWIR) photodiodes, to measure over different temperature ranges. The thermometers had small footprints, therefore could be installed into constrained spaces and not cause interference with the process. The MWIR thermometers were substituted for thermocouples in high temperature conditions in end milling tool temperature measurements and reactive electrochemical conditions in Lithium-ion cell temperature measurements. The conditions into which the fibre optics were embedded would lead to inaccurate measurements from thermocouples, whereas the fibre optic and remotely positioned IRT offered immunity against these errors.
Calibration drift is a major problem that afflicts thermocouple temperature measurements. There has been progress towards addressing this weakness with improved thermocouples. The SWIR thermometer used a zero drift operational amplifier to minimise offset voltage, drift and noise. The IRT was coupled to a sapphire fibre optic probe that had tin deposited onto the core to form an integral fixed point temperature calibration cell. This low drift IRT provided an increment towards creating a drift-free, self-calibrating IRT that would substitute for thermocouples with integral calibration capabilities.
The feasibility of substituting thermocouples with embedded fibre optics coupled to IRTs has been demonstrated and potential improvements of these thermometers have been identified.