Accuracy and Calibration Considerations for Fiber Optic Temperature Sensors

In the present work, the performance characteristics of a set of six fiber optic temperature sensors based on the fluorescence lifetime of neodymium-doped glass have been investigated. The experiment is aimed at verifying whether a satisfactory probe-to-probe repeatability and sensor accuracy can be obtained with minimum calibration effort. To accomplish this task the fiber-optic probes were calibrated, in the temperature range 0 degrees Celsius to 250 degrees Celsius, by comparison against a platinum resistance thermometer in a metal block furnace. The experimental set- up consisted of an electro-optical unit for fluorescence excitation and detection and an analog-to-digital signal processing circuit for lifetime measurements. The temperature probes were assembled by placing the Nd-doped glass at the distal end of a silica optical fiber and by splicing the other fiber end to a 1 by 2 wavelength- independent coupler. The calibration results and the temperature repeatability of the Nd:glass probes are reported. The reproducibility of the measurement method, with an optimum calibration function, and the resulting accuracy are discussed.