A MULTICHANNEL FIBRE OPTIC TEMPERATURE MEASUREMENT SYSTEM

A novel approach to monitoring and control temperature in processes where conventional electrical methods are difficult or ineffective, such as in extremely hostile environments, in biological applications, or in presence of strong electromagnetic interference, is based on the use of fibre optics. The intrinsic characteristics of the optical fibres give to fibre optic sensors several unique features. In food processing applications, such as in microwave or in radiofrequency heating, there is a need of very localised measurements of both surface and bulk temperatures of the foodstuff, which is immersed in an intense electromagnetic field. While for surface temperatures IR thermometry, or thermography, are possible, the inner temperature can be measured only with the insertion of small probes, immune from electrical disturbances, into the bulk. In this situations, fibre optic sensors are often the only viable alternative for temperature measurement A multi-channel optical fibre temperature system based on fluorescence thermometry was developed as part of a project aimed at identifying unsatisfactory temperature distributions in food heated in a microwave oven. The system consists of a digital fluorescence lifetime thermometer, a 12-channel optical fibre multiplexer and a set of fully dielectric optical fibre probes. A custom analog-to-digital signal processing (A-DSP) circuit for fluorescence lifetime detection was developed and special probes, suitable for microwave oven applications, were constructed