A novel SOA-based, dual-wavelength, FBG laser sensor system for simultaneously measuring vibration, temperature
and humidity is demonstrated. The sensor interrogations are completed with a wavelength matching
method by adjusting temperatures of two TECs to control wavelengths of two reference FBGs matching with
those of two sensor FBGs. Two corresponding TEC control signals are used as detection outputs for temperature
and humidity measurements. Some experimental results on simultaneous measurements of vibration, temperature
of the sensor system with a FBG vibration/temperature senor and a 10-layer polyimide coating FBG
humidity sensor are presented. The fundamental system performances in respects of the frequency response
of system in vibration measurements and the tracing of the Bragg wavelength of sensor FBG through a TEC
temperature control method were also demonstrated. The experimental results verified that the proposed FBG
laser sensor system has a desired detection performance. This sensor system can be used in many industrial
measurement fields, particularly in the electrical power industry for condition monitoring of power generators as
well as high-voltage power transformers.
Experimental studies on humidity measurements by using a FBG-based humidity sensor with multi-layer polyimide
coating are demonstrated. As an important sensing application, the FBG humidity sensors have many
unique advantages, such as immunity to electromagnetic interference and compact size, over the conventional
electrical humidity sensor. In the detection principle, The Bragg wavelength of the FBG sensor shifts with the
volume of the moisture absorbed by the polyimide film coated on the FBG. Experimental results show a good
linear relationship between the shifts of the Bragg wavelength of FBG sensor and the changes in the relative
humidity level. The preliminary experiments for investigating the performances of this polyimide-coating FBG
humidity sensor were carried out and several experimental results in measurements of the relative humidity in
air and moisture in oil are presented.
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