Fiber optic sensors have very attractive features for industrial applications. Because they use nonconducting glass instead of wires they can operate in high electromagnetic field environments and explosion hazard areas. The expectations of the 1980s were that fiber optic sensor usage would be over $100 M per year in 1993; actual sales were under $20 M. The order-of-magnitude error was in part due to forecasting methodology and in part due to users not accepting the new sensor technology to replace traditional sensors. To understand the difference between predicted and actual sales, 15 studies generated in the mid 1980s were examined and compared with actual industry revenues in 1993. General trends in sensor development were examined by looking at published papers. Fiber optic sensor papers now account for about 30% of all fiber optic papers published with the fraction growing. Industry needs were examined by surveying sensor applications engineers in chemical process control, industrial companies, and electric power. A 55% reply rate was achieved. Sensor characteristics most desired were reliability and stability; cost and size were not considered as important.
The development of fiber optic cheraical sensors over the last decade2 has involved a number of conflicting priorities. Some of the most interesting are perhaps associated with the individual disciplines involved in the development process.
Sensors for oxygen in liquids have been commonly used for clinical chemistry applications. Optical approaches to blood gas applications have been known for some time2. The opportunity for fiber sensor applications in this area is created by familiar fiber sensor advantages: small size, dielectric isolation, and the availability of a number of sensor chemistry systems3' 4. The overall sensor system is based on a viologen compound that changes absorbance as oxidation (or reduction) occurs. This compound responds to short wavelength light by darkening; the time for a return to the clear state depends on the amount of oxygen present.
A fiber-optic temperature sensor of the type described by Saaski et al. (1986) was modified to allow current measurements. The current sensor is constructed by bonding a thin (about 1 micron) layer of silicon by a protective Pyrex layer on the bottom and a thin-film temperature sensor on the top. Current flowing through the resistor heats the temperature sensor. With a 1-ohm resistance, the (I-sq R) heating required for a 20-dB signal-to-noise ratio is 100 microW. Sensor parameters were demonstrated to frequencies of 3 GHz for currents in the 10 to 300 mA range. The sensor response time is 10 millisec for an in-circuit sensor and 65 millisec for a noncontacting sensor configuration.
Course Instructor
SC287: Intensity Based Fiber Optic Sensors and the Fabry-Perot Fiber Sensor
The emphasis in this video segment is on practical sensor configurations. Drawings, sensor samples, and experiences with product development will be used to illustrate concepts.
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