EXTENDING THE RANGE OF A FIBEROPTIC RELATIVE-HUMIDITY SENSOR

A new signal-processing method to extend the linear operational range of an optical-fibre humidity sensor is presented in this study. The se nsor is based on a Nafion-crystal violet complex immobilized on a glas s substrate. Low-cost plastic optical fibres are employed as light gui des to direct light from a tungsten halogen source to the sensor and f rom the sensor to a CCD-based spectrometer. Generated spectra for vary ing relative-humidity levels are analysed using artificial neural netw orks. Sensor measurements at wavelengths corresponding to the red, ora nge, yellow and NIR LEDs are used for the artificial neural network in put. This study has shown that the artificial neural networks successf ully extend the linear response range of the fibre-optic relative-humi dity sensor from the 40-55% humidity range previously recorded to a no minal range of 40-82%. The use of LED-compatible wavelengths shows tha t the sensor can be readily adapted for use with low-cost solid-state instrumentation.