The oil industry exemplifies mankind's search for resource sin a harsh environment here on the earth. Traditionally, the oil industry has created technological solutions to increasingly difficult exploration, drilling, and production activities as the need has arisen. The depths to which a well must be drilled to produce the finite hydrocarbon resources are increasing and the surface environments during oil and gas activities is the key to success, not information that is hours old or incomplete; but 'real-time' data that responds to the variable environment downhole and allows prediction and prevention. The difference that information makes can be the difference between a successfully drilled well and a blowout that causes permanent damage to the reservoir and may reduce the value of the reserves downhole. The difference that information makes can make the difference between recovering 22 percent of the hydrocarbon reserves in a profitable field and recovering none of the reserves because of an uneconomic bottom line. Sensors of every type are essential in the new oil and gas industry and they must be rugged, accurate, affordable, and long lived. It is not just for the sophisticated majors exploring the very deep waters of the world but for the thousands of independent producers who provide a lion's share of the oil and gas produced in the US domestic market. The Department of Energy has been instrumental in keeping reserves from being lost by funding advancements in sensor technology. Due to sponsorship by the Federal Government, the combined efforts of researchers in the National Laboratories, academic institutions, and industry research centers are producing increasingly accurate tools capable of functioning in extreme conditions with economics acceptable to the accountants of the industry. Three examples of such senors developed with Federal funding are given.

The electric utility industry is reducing operating costs in order to prepare for deregulation. The reduction in operating cost has meant a reduction in manpower. The ability to utilize remaining maintenance staff more effectively and to stay competitive in a deregulated environment has therefore become critical. In recent years, the industry has moved away from routine or periodic maintenance to predictive or condition based maintenance. This requires the assessment of equipment condition by frequent testing and inspection; a requirement that is incompatible with cost reduction. To overcome this dilemma, industry trends are toward condition monitoring, whereby the health of apparatus is monitored continuously. This requires the installation of sensors hr transducers on power equipment and the data taken forwarded to an intelligent device for further processing. These devices then analyze the data and make evaluations based on parameter levels or trends, in an attempt to predict possible deterioration. This continuous monitoring allows the electric utility to schedule maintenance on an as needed basis. The industry has been faced with many challenges in sensor design. The measurement of physical, chemical and electrical parameters under extreme conditions of electric fields, magnetic fields, temperature, corrosion, etc. is extensive. This paper will give an overview of these challenges and the solutions adopted for apparatus such as power transformers, circuit breakers, boilers, cables, batteries, and rotating machinery.

A novel self-calibrated interferometer/industry-based (SCIIB) fiber optic sensor is described in this paper. The novel sensing scheme combines the advantages of both fiber interferometry senors and intensity-based sensors. The sensor operates on a single fiber Fabry-Perot interferometric cavity with a white light source. The interference signal of the sensor is coherent-sliced into two channels. Which allow fully real-time compensation for the source power drifting and fiber los variation. Temperature and pressure sensors with various dynamic ranges were designed and fabricated based on the SCIIB technology. Experimental result show that the SCIIB sensor scheme achieves excellent resolution and accuracy with the self- calibration function.

We report on our irradiation experiments on different types of fiber-optic sensors, including three types of commercially available temperature sensors, a multimode extrinsic Fabry-Perot cavity strain sensor and fiber Bragg- gratings. For the temperature sensors, results show that gamma radiation does not interfere with the basic sensing mechanism and that the most critical component turns out to be the optical fiber itself. Semiconductor absorption temperature sensor showed no degradation up to total doses of 250 kGy, whereas the specifications of Fabry-Perot type sensor and fluorescence temperature sensors were already dramatically influenced below the kGy-level. Replacing the optical fiber by a more radiation resistant version allowed to increase the radiation hardness of the fluorescence sensors system by orders of magnitude. The use of fiber- optic sensors in the presence of neutron radiation remains compromised. Similar conclusions are valid for the Fabry- Perot type fiber-optic strain sensors. We finally show that the Bragg-grating resonance wavelength can shift with radiation dose, but that the temperature sensitivity remains unaltered.

To apply optical fiber image guide (IG) to harsh radiation environments, we have developed two new techniques. One technique is a visible type IG with a color correcting system and the other technique is an IR type IG. We irradiated the IGs utilizing a ⁶⁰Co gamma source. Measured Images with the visible type IG became dark and yellowish because of radiation induced loss. By using a color correction system, the original color of the images can be obtained. In the case of IR type IG, because of low radiation induced loss in the IR region, the degree of darkening was less than half of that for the visible type of IG. For a fixed irradiated length of 2.5m, the dose limit for using IG was estimated to be 4.6 X 10⁸ with the visible type IG and 1.2 X 10⁹ with the IR type IG. These radiation resistivities were more than 10³ times of that for usual CCD cameras. With these techniques, IG can be applied to harsh radiation environment.

A fiber optic monitoring technique for the thickness of furnace wall is demonstrated where conventional monitoring techniques failed because of harsh environments. Based upon OTDR technique, its working principle, structure, and installing manner are introduced. This technique can monitor the thickness wall continuously with an accuracy of 5mm which is enough for the management of operating the furnace.

Optical fiber sensors have numerous advantages over conventional sensing technologies. One such advantage is that optical fiber sensors can operate in high temperature environments. While most conventional electrical-based sensors do not operate reliably over 300 degrees C, fused silica based optical fiber sensors can survive up to 900 degrees C, and sapphire based optical fiber sensors can survive up to 2000 degrees C. Using both fused silica and sapphire technologies, we present result for high temperature strain, pressure, and temperature sensors using Extrinsic Fabry-Perot INterferometric-based and Bragg grating sensors. High temperature strain and temperature sensors were used to conduct fatigue testing of composite coupons at 600 degrees C. The results from these specific high temperature applications are presented along with future applications and directions for these sensors.

In this paper we report of experimental studies on strain monitoring by using fiber Bragg grating sensors in concrete structures. The strain variation of the specimen under different loading conditions were monitored by the Fiber- optic Bragg grating (FBG) sensors. The FBG sensors have been pre-installed in the structure by embedding either inside the concrete specimen or at the interface between the concrete and the composites. The strain reading from the fiber grating sensor compares favorably with that obtained from the conventional strain gauge in uni-axial compression testing. The test result generally indicated that the concrete structures can be strengthened significantly by wrapping with glassfiber composites. The sensor embedded at the notch tip provides a very good indication of the health condition of the strengthened structure, especially in high stress concentration area. The strain sensitivity by using FBG sensor is 67 (mu) (epsilon) .

3D mapping has many applications including robot navigation, medical diagnosis and industrial inspection. However, many applications remain unfilled due to the large size and complex nature of typical 3D mapping systems. This paper describes a 3D mapping system being developed by the Photonics Laboratory at Virginia Polytechnic Institute which uses a fiber optic coupler as a fringe generator or grid projector-in essence forming a Young's Double Pinhole interferometer. Two significant benefits are derived from this arrangement. First, the fringe projector is much smaller than what is currently used allowing this system to be used where others cannot. Second, the laser source can be remotely located from the fringe generator, hence further reducing the size of the sensor head without loss of optical power. The system design, mathematical model, calibration procedures and initial results are presented.

The development of a fiber optic dual use sensor for embedding in concrete structure or buildings are described. The sensing system could monitor the state of a structure during construction and throughout its working life. The embedded optical fiber sensor, at first, can be employed as a transducer for measurement the temperature of fresh concrete at early age. Then, the embedded fibers do not degrade during curing, and they bond strongly to the matrix. The permanently embedded fiber optic sensors offers the opportunity to monitor the strain or displacements associated with the opening of the micro-cracks of the concrete structures in its whole life. In our experiments, a white light fiber optic interferometer is used to sense and measurement the temperature in a specimen concrete beam. A direct relationship between the fiber deformation and the optical path variation of the fiber sensor is obtained. A calibration procedure is developed by which the optical signal is converted to displacements. The temperature test result are compared with a convenience thermal couple. Experiments involved embedment of the optical fiber in concrete beams. In order to investigate micro-crack opening displacement characteristics, the sensor was employed in a series of fracture test. Specimens were center-edge-notched and the fiber optic sensor with the gauge length L were embedded at the tip of the notch. This arrangement allowed for direct measurement of displacements associated with the opening of microcracks at the crack tip. Experimental results are presented and crack-tip opening displacement results are compared with crack-opening displacements measured by conventional transducers at the crack mouth.

Deregulation of the power industry and increasingly tight emission controls are pushing gas turbine manufacturers to develop engines operating at high pressure for efficiency and lean fuel mixtures to control NO_x. This combination also gives rise to combustion instabilities which threaten engine integrity through acoustic pressure oscillations and flashback. High speed imaging and OH emission sensors have been demonstrated to be invaluable tools in characterizing and monitoring unstable combustion processes. Asynchronous imaging technique permit detailed viewing of cyclic flame structure in an acoustic environment which may be modeled or utilized in burner design . The response of the flame front to the acoustic pressure cycle may be tracked with an OH emission monitor using a sapphire light pipe for optical access. The OH optical emission can be correlated to pressure sensor data for better understanding of the acoustical coupling of the flame. Active control f the combustion cycle can be implemented using an OH emission sensor for feedback.

The environment of the gas turbine engine is one of the harshest environments that require sensors for control and monitoring. The combination of extreme temperatures and vibration levels poses a difficult problem for even the most robust electrical sensor. Optical sensors are becoming an attractive alternative to electrical sensors for this application because of their higher temperature operation and remote sensing capability. In this paper, we present an overview of some of the senor being developed and/or offered by BF Goodrich for turbine engine applications. The issues involved in designing a sensor for this environment and some of the packaging issues will also be discussed.

A newly developed fiber optic pressure sensor for gas turbine applications is described in this paper. The sensor is based on Self-Calibrated Interferometric/Intensity-Based fiber optic sensor technologies. In addition to the generic fiber sensor advantages, the new sensor was also shown to have all the distinct advantages of interferometric and intensity-based sensors while their disadvantages are significantly reduced. The sensor has a frequency response of approximately 100 kHz, and can be operate at temperatures up to 700 degrees C. The sensor was tested in simulated flow conditions similar to that found in a gas turbine engine. Excellent agreement was obtained in the measured pressure comparing the fiber-optic sensor to a conventional high frequency, semiconductor based pressure transducer.

Sapphire optical fiber sensor are greatly promising for high temperature sensing applications because of their high melting point, which exceeds 2000 degrees C. The extrinsic Fabry-Perot interferometric (EFPI) sapphire fiber sensors, based on absolute white light spectrum scanning signal processing, are extremely attractive in engineering applications because they do not require initialization and/or calibration when the system is turned on. Furthermore, it is not necessary to operate them in linear regions to avoid nonlinear effects, a significant problem in other EFPI sensor. In this paper, we use a single-crystal sapphire fiber for making an EFPI sensor. Interference fringes were observed by using both laser and light emitting diode sources. The effect of the lead-in fiber diameter on fringe visibility is also discussed.

A fiber-optic bragg grating sensor for flow-induced vibration measurement is described. The sensor is based on monitoring shift in the Bragg wavelength of a fiber Bragg grating. the fiber Bragg grating, when bonded onto a structure, can measure local axial strain variation of the structure. The strain can be related to the structural bending displacement. Experiments were conducted to measure the flow-induced vibration of a cylinder in a crossflow. The measurement results in terms of then natural frequency of the fluid-structure system and the vortex shedding frequency are consistent with the result obtained from a laser vibrometer. Fiber Bragg grating sensors have potential applications in the study of fluid-structure interactions of cylinder arrays in a crossflow.

Metglas based extrinsic miniaturized fiber optic magnetic field sensor system has been designed and fabricated for measuring DC magnetic fields. A simple geometry and modification of sensor gage show 98 percent suppression of thermally induced output variation and 92 percent of fringe visibility. A single-board microcomputer is used for accurate signal demodulation and calibration. The system has demonstrated a resolution of better than 100 nT over a range of 100 nT to 40,000 nT.

A fiber optic sensor for measuring the diameter and from errors of very small hole or blind hoe. with diameter down to 0.2 mm and depth to diameter ratio up to 20 was developed. Since optical non-contact methods are difficult to use for measuring the diameter and from errors of small hole at any cross section, a fiber optic sensor, which combines the advantages of optical non-contact method and mechanical contact one, was proposed. The principle is based on the evaluation of a central position of stylus ball by an optical system. Experiments show that the accuracy of the system is better than 1 micrometers and the measuring force is less than 10 (mu) N.

This paper describes the optical fiber sensor based on modulated fiber grating model filter according to the principles of gas molecule's absorption spectra. This sensor system is important in real-time monitoring of the fault gases dissolved in transformer oil to ensure that transformer runs safely. Firstly this paper theoretically analyzes the optical quality of each component, including the wide band LED source, the modulated reflection fiber grating and gas molecules' absorption line, then gives their mathematical models. Some parameters in relation to these models are presented. In order to find out how the intensity of modulated light signal changes after the light passes the gas cell, a set of equations are given according to these models. These equations show that the variation of harmonic light intensity is determined by some factors such as modulation range and the wavelength difference between bias level of modulated fiber grating and peak of absorption line. A measurement system is built up, then detecting sensitivity is analyzed. Effects of temperature and noises are also analyzed. Some methods are presented to decrease their influences.

We have used fiber optic remote process to monitor processes at Kodak in the lab, in development or pilot, and in production. This talk will examine the use of near IR (NIR) diffuse reflectance spectroscopy as a process technology. Diffuse reflectance spectroscopy offers the capability of looking at powders, slurries, emulsions, and dispersions. Unlike attenuated total internal reflectance spectroscopy, diffuse reflectance offers the capability of interrogating both the liquid and solid phases of the material. This provides the ability to examine the physical state of the solid, such as particle size and morphology, even in a slurry, or in the presence of large amounts of solvent, in addition to the chemical quality of the solution. The use of the NIR spectral region provides the advantages of high signal-to-noise ratio, impressive photometric stability, and commercially available instrumentation, probes and optical fiber cable. Some representative examples will be presented to demonstrate the capabilities of diffuse reflectance spectroscopy for process monitoring with fiber optics.

In pharmaceutical manufacturing, it is critical to determine the cleanliness of the reactor walls prior to the blending/formulation process. A remote non-contact, real- time reflectance probe was developed to monitor these cleaning procedures. It utilizes the principals of IR spectroscopy and it works in the mid-IR region, as the ability to obtain spectral information in the mid-IR region not only enables this probe to monitor processes like reactor cleaning, but also to identify contaminants based on their spectral fingerprints. The spectral data can then be compared against-pre-existing calibrations or spectral libraries to determine surface cleanliness or to identify contaminants. This manuscript will discuss the design principles of the probe and present data obtained in actual tests. The non-contact reflectance probe is certainly not limited to its application for determining the cleanliness of reactor walls. Such a probe would find numerous applications in process monitoring and as a research tool for surface analysis and characterization.

The multianalyzer is a powerful amplitude modulated fiber optic sensor which is perhaps quite typical of so many sensor innovations in that it is a technology looking for an application. Consequently, a series of collaborations with fruit juice, brewing, distilling, biotechnology and polymer industries were made with the objective of identifying potential applications of the multianalyzer. An assessment of these interactions is made for each of the industrial fields explored, by giving for each, just one positive result from the work. The results are then critically assessed. While these studies have illustrated the universal nature of the technology, in every case, lessons have been drawn of a general nature. This experience in particular underlined the difficulty in acceptance of a fiber based technology in industrial process monitoring, against the backdrop of the conservative practice of industry with long established instrumentation. The hard won experience of this product development has shown the vital important of technologists understanding the difference between the marketing concepts of features, benefits and advantages. Three categories of conclusions are drawn, the technical, the commercial, and finally, conclusions drawn from generalizations of the project by the Kingston partners based on their own independent experience in sensor development involving industrial and medical collaborations.

Some aspects concerning a methodology for the measurement of thickness of dry and wet coatings which is based on a fiber optic probe are discussed in order to verify the feasibility of this approach and the capability of such a probe of on- line measuring. In this preliminary step of the research some problems discussed mainly concerning the methodology which has been proposed and which is based on the measuring of the reflectance of the coating plated on thin steel sheets for use in the food industry. Furthermore the effect of the main interfering and modifying quantities is discussed both theoretically and experimentally when the measurement has to be carried out in order to allow on-line coating thickness measurements with satisfactory accuracy.

This paper describes the development and evaluation of an automated measurement system for assessing at-line and on- line polyester thickness uniformity. The instrument is based on non-coherent light interferometry and includes a dual- interferometer, single mode optical fibers, sample coupling optics, custom electronics, data acquisition system, transport mechanism, data outputs, and computer. The principles of operation and measurement system performance are discussed. The use of the measurement data for measuring machine parameters in addition to thickness uniformity will be shown. Experiments were performed on an extruder machine to determine the suitability of the instrument and the optical probe design for on-line measurements. An automated measurement system was also developed for assessing at-line web thickness uniformity. The instrumentation for the at- line measurements was the same as the on-line system except a sample transport system was added.

During the assembly of high-end digital cameras, it is necessary to determine the location and orientation of the imager plane in order to assess the camera's focusing capability. An apparatus based on non-coherent light interferometry has been developed, which performs these test immediately after the digital imager is installed into the camera body. The instrument includes a camera lens flange- mountable multipoint fiber optic probe, an optical multiplexer and a non-coherent light interferometer measurement system with LabWindows CVI software specifically developed for this purpose. This talk describes the principle of the measurement, the fiber optic probe design, and presents results demonstrating the performance capability of the apparatus.

Introduced in this paper is a fiber optic gauging technique with millimeter accuracy for river level measurement. It plays an important part in flood-control season. The principle of operation and structure are illustrated. In order to ensure the reliability and to keep the millimeter accuracy in 16-meter range of fluctuation, some key techniques in optic, mechanism and electronics of this gauge are discussed in detail in this paper.

The dynamic response characters of the wavelength scanning fiber-optic interferometry for distance measurement have been studied. When the measurand moves, the output signals are analyzed in the time-domain and frequency-domain. Then the measurement errors are obtained with the numerical simulation methods. It is important for the deformation process measurement.

By writing one or more fiber gratings onto birefringent optical fiber a multi-axis fiber grating is created that is capable of measuring transverse as well as axial strain. In addition to the measurement of transverse gradients it is possible to identify the axis and magnitude of transverse strain gradients. This allows detailed diagnostic of the interior of parts as they are being cured and after fabrication health monitoring systems capable of supporting the measurement of multidimensional strain fields.

This talk describes the development and evaluation of bi- directional fiber-optic based low airflow sensors for use in solvent containing elevated temperature manufacturing process environments. The sensors developed are based on Measureand Inc. cantilever beam optical fiber bend sensors. Customized paddles are added to match sensor output to the range of airflows under investigation. This talk discuses the sensor requirements, sensors' design, calibration, manufacturing process installation and testing process worthy prototypes in an elevated temperature solvent containing environment.

One of the inherent problems with the processing of composites is the development of internal stresses and the resulting warpage, which results in out-of-tolerance components. This investigation examines possible fiber-optic sensor methods, which can be applied to measure internal strain and thus residual stress during production. Extrinsic Fabry-Perot Interferometers (EFPI) and Bragg gratings are utilizes to monitor the strain behavior during manufacturing of large-scale composite parts. Initially, a 24 in X 18 in X 1 in thick part was manufactured using the vacuum- assisted resin transfer molding (VARTM) technique. In this part, one Bragg grating, multiple thermocouples and a resin flow sensor (SMARTweave) were integrate to measure the flow and cure behavior during production. An AGEMA thermal image camera verified the temperature history on the part surface. In addition, several EFPI's and Bragg gratings were implemented into three temperature history on the part surface. In addition, several EFPI's and Bragg gratings were implemented into three 13 ft X 32 ft X 20.3 in civilian bridge deck test specimens manufactured with the VARTM process. The Bragg gratings showed great promise to capture the changes in strain due to the residual stress during cure. The actual implementation of fiber optics into large composite parts is a challenge and the problems of sensor survivability in these parts are addressed in this study. The fiber optic measurements in combination with SMARTweave's ability to monitor flow could lead to a sensor system, which allows feedback for process control of the VARTM technique. In addition, the optical fibers will be used for health monitoring during the lifetime of the part.

In a robust, durable, and low-cost design Optrand pressure sensors utilize the principle of light intensity changes, transmitted by two optical fibers, upon reflection from a specially shaped, metal diaphragm deflecting under the effect of pressure. The non-contact detection principle combined with the diaphragm design optimized for infinite fatigue life translates into a sensor with extraordinary lifetime. The sensor's signal conditioner contains one LED and one photodiode and is permanently attached to the fibers. The electronic circuitry provides the auto- referencing function compensating for the effects of fiber bending, fiber-to-optoelectronics coupling changes, sensor thermal drift, as well as temperature and aging effects of the LED and the photodiode. The results of several along- term test in two key gas machinery applications are reported here: continuous and intermittent monitoring of power and compressor cylinders. In the longest application to date, hundreds of combustion pressure sensors have demonstrated over 12,000 hours or 500-million pressure-cycle lifetime. Dynamic pressure sensors for compressor monitoring have already demonstrated the lifetime of 1 billion cycles and target 5 billions. In compressor applications the sensor demonstrate typical +/- 0.25 percent accuracy while combustion pressure sensor accuracy is typically +/- 1 percent. For almost two years tens of indicator valve- mounted combustion sensor have been monitored for calibration stability demonstrating better than +/- 0.1 percent performance over a 6-month period.

On-fiber optical sensors, designed with chromogenic materials used as the fiber modified cladding, were developed for sensing environmental conditions. The design was based on the previously developed on-fiber devices. It is known that the light propagation characteristics in optical fibers are strongly influenced by the refractive index of the cladding materials. Thus, the idea of the on- fiber devices is based on replacing the passive optical fiber cladding with active or sensitive materials. For example, temperature sensors can be developed by replacing the fiber clad material with thermochromic materials. In this paper, segmented polyurethane-diacetylene copolymer (SPU), was selected as the thermochromic material for temperature sensors applications. This material has unique chromogenic properties as well as the required mechanical behaviors. During UV exposure and heat treatment, the color of the SPU copolymer varies with its refractive index. The boundary condition between core and cladding changes due to the change of the refractive index of the modified cladding material. The method used for the sensor development presented involves three steps: (a) removing the fiber jacket and cladding from a small region, (b) coating the chromogenic materials onto the modified region, and (c) integrating the optical fiber sensor components. The experimental set-up was established to detect the changes of the output signal based on the temperature variations. For the sensor evaluation, real-time measurements were performed under different heating-cooling cycles. Abrupt irreversible changes of the sensor output power were detected during the first heating-cooling cycle. At the same time, color changes of the SPU copolymer were observed in the modified region of the optical fiber. For the next heating-cooling cycles, however, the observed changes were almost completely reversible. This result demonstrates that a low-temperature sensor can be built by utilizing the chromogenic SPU copolymer as the modified cladding material.

A reliable and high performance novel method of flame and gas optical spectral analysis was developed to meet the specific flame and gas detection of the petrochemical industry. Petrochemical industries, especially the offshore and unmanned areas in onshore refineries, pose a major safety hazard with respect to potential explosions and fire events. Unwanted fuel spills or fugitive flammable vapor clouds, migrating along congested pipe lines and hot production areas may cause upon ignition significant loss or damage. To help prevents events like the catastrophic fire that destroyed the offshore oil platform Piper Alpha in July 1988, a reliable and fast gas and flame detection system can be used to trigger effective risk management actions. The present paper describes a patented method of Triple Optical Spectral Analysis employed for the detection of various gases in the air according to their unique 'spectral finger print' absorption characteristics of radiation, as well as for analysis of emission and absorption radiation from combustion processes for flame detection purpose. The method has been applied in the development of unique gas and flame monitoring system designed for 'high risk - harsh/extreme weather conditions continuous operation'. These systems have been recently installed on several offshore platforms and oil rigs as well as on 'floating production Storage and Offloading' - FPSO vessels. The systems advantages and limitations as well as several installations and test data are presented. Various atmospheric conditions as well as false alarm stimulus are discussed.

This paper describes a method and instrumentation for electrical pH control in aqueous solutions. It is targeted to environmental and industrial on-line chemical and optic fiber sensors measurement, calibration and process control. The method is an alternative to the existing automatic pH controllers based on correction chemical addition. The on- line measurement of dissolved gaseous species which produce acidic and basic waters is of great concern for environmental monitoring applications. Such measurements are maintained by using preconditioned water samples and ion- selective electrodes or absorption spectrometry. A gas- permeable membrane can be used to allow only the transport of the molecular form of the measured species where the solution pH is controlled to ensure the reversible transition of the species of interest from ionic to molecular form and to allow their permeation through the membrane. An electrochemical instrument for electrolysis- based feedback controlled pH regulation has been attempted. The choice of galvanostatic, potentiostatic and combined methods of modulation electrodes biasing with their speed, settling time and accuracy are discussed. Different feedback control approaches, involving electrochemical and optical sensors, are compared.

FIber optic sensors have repeatedly been shown to provide measurement capabilities of parameters within such reinforced concrete structures. Development of a fiber optic chloride sensor capable of being embedded within a roadway or bridge deck is reported. Once the specific chemistry of the fiber optic sensor was developed and tested, multiple iterations occurred in order to result in a sensor system capable of being embedded into roadway bridges. During the summer and fall of 1997, a total of 64 fiber optic sensors were then embedded into 3 roadway bridges which spanned rivers in northern Vermont. Installation details as well as results are presented.

We report a fast response and inexpensive optical sensor capable of measuring pH in the range of 0.5 to 13.5 units with good resolution. Three indicator dyes viz. Bromocresol Green, Bromothymol Blue and Nile Blue were used to fabricate the sensor head. ion-exchange resin, Amberlite IRA 400, was powdered and immobilized by these dye solutions. In order to prepare sensing membranes, Polyvinyl chloride was dissolved in Tetrahydrofuran and the solution was poured on to a glass plate. Before the membrane was completely dry, the immobilized resin powder was uniformly sprinkled so that the granules are properly glued to it. A bundle of fibers was attached to the membrane mechanically to carry the light from the source to the membrane and collect the reflected optical signal. He-He laser was used as a light source. The experimental results show a linear dependence of pH value on reflected optical signal for the pH range of 0.5 to 13.5 with the resolution of 0.02 unit. The optrode was also characterized by studying the effect of ionic strength and temperature of the solution on the probe response.