Some applications of infrared optical sensing

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Sensors and Actuators B, 11 (1993) 185-193

Some applications of infrared optical sensing* Alan D. Stuart BHP Research -Newcastle Laboratories, P.O. Box 188, Wallsend, NSW 2287 (Australia)

Abstract Infrared optical chemical sensing has been a significant program of research at the BHP Research Laboratories over the past 10 years . Major developments within the program are described in this paper . The program commenced with the development of FT-IR/software techniques for rapid characterization of mineral species in the laboratory . This work, which saw the development and licensing of CIRCOM software, subsequently led to field trials of on-line FT-IR spectroscopy for minerals characterization and was then extended to the characterization of used lubricating oils . A major activity within the program has been the investigation of methods for the measurement of methane and other gases in an underground coal mine using optical fibres, and the development and testing of a multipoint infrared-based system for coal-mine methane monitoring . Details of the system and its performance are described . Other activities within the program have included laboratory investigations of pulsed laser remote spectroscopy techniques for detection and ranging of methane gas leaks at LNG installations, and the measurement of the composition of liquid hydrocarbon mixtures by optical fibre-based spectroscopy . More recently, the application of IR spectroscopy for characterization of wastewaters containing cyanide species has been investigated within the program. I R spectroscopy is also being used as part of a preliminary screening protocol for waste products that require characterization and then development of appropriate treatment procedures .

Introduction The BHP Company has major interests in iron and steel making, mining and minerals processing, oil and gas, and shipping . In support of the requirement for better process monitoring and control in relation to those interests, a major research and development activity in sensing, including optical sensing, has been underway for over 10 years . Optical sensing in general has many attractions for use as a tool for industrial process monitoring . These potential advantages include : • it is a non-invasive method that does not distort the process while making the measurement ; • only line-of-sight access is required ; • major components of the overall system can be located away from the process in an area where maintenance demands are lowered and maintenance access is easier. The most useful optical techniques for the BHP program have proved to be time-of-flight laser ranging and infrared (IR) sensing. I R sensing in particular is a powerful tool for measurement of chemical parameters because of the specificity and sensitivity that can be obtained from the technique . IR methods can potentially be applied to the characterization of materials or to the detection and measurement of specific parameters.

'Keynote address.

0925-4005193J$6 .00

In this paper, some of the progress in IR sensing research and development is described . Activities have focused on three approaches : full spectral acquisition and interpretation, fibre optic systems, and laser-based systems.

Full spectral acquisition and interpretation Initial work within the program concerned the IR spectra of raw materials such as iron ores, coals, manganese ores and many other minerals . It was soon found that many of the chemical and physical properties of these materials could be correlated with parts of their mid-IR or near-IR spectra [1-4] . A factorial analysis software program called CIRCOM (computerized IR characterization of materials), for use with an FT-IR spectrometer, was developed to implement the spectral examination . Properties of an unknown sample could be predicted after establishment of the general relationship of those properties to the IR spectrum using a calibration suite of fully characterized materials . The range of properties amenable to the factorial analysis approach was impressive : chemical analysis characteristics, specific energy content, relative density, coke strength, battery activity . The CIRCOM package was subsequently licensed to PerkinElmer as part of their QUANT + software package . Coal blend ratios could also be measured successfully [5] ; this was further developed into an on-line monitoring version of the process and tested at a coal washery.

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Elsevier Sequoia. All rights reserved



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The trial met with mixed success, and would probably have benefitted from using the more robust industrialgrade FT-IR spectrometers now available . Lubricating oil quality is an important issue for a large industrial company, where the consequences of a lubricant failure in heavy-duty equipment can be severe . Companies generally operate a routine analytical screening of oil quality, but this is an expensive and time-consuming exercise . The IR characterization approach was found to be applicable to used lubricating oils [61 ; factors such as fuel and water contamination could be measured directly, whilst other parameters, including viscosity and total base number (TBN), could be extracted using the CIRCOM approach derived from a calibration suite of oils . The procedure was amenable to automation, and a 40-sample analyser was developed for use at a company operation . The analyser (Fig . 1) could produce the analytical information indicated in Table I in an operational time of 10 min per sample [7] . Similar IR analysis packages for used oils are now commercially available [8] . The use of IR methods for minerals characterization has since been extended in two directions within the program . An airborne spectrometer has been used as a tool for minerals exploration [9], and a field spectrometer for use by geologists for minerals identification in the field has been developed [101 . Several field spectrometers are now in use within the company .

TABLE l . Output from automated IR used-oil analyser Measured directly from IR spectrum

Measured indirectly using a calibration suite

Fuel contamination Water contamination Oxidation factor

Viscosity Suspended solids Total base number

Fibre optic systems An interest in developing safer systems for gas monitoring in underground coal mines, prompted by disastrous explosions at Australian mines in 1979 (Appin) and 1986 (Moura), led to an investigation of the possibilities of an optical fibre-based approach . Optical fibre sensing has several potential advantages over conventional approaches to coal-mine gas sensing, including : (a) potentially intrinsically safe monitoring system ; (b) measurements can be made over long distances ; (c) readily extendable to multipoint systems . The main gases to be measured in coal-mining applications are methane (CH4), carbon monoxide (CO) and carbon dioxide (CO,) ; there would be advantages for any systems which could also measure other gases, such as oxygen, hydrogen and nitrogen . An initial analysis [111 suggested that three approaches to an optical fibre-based system warranted further investigation : (1) use of 'optrode' sensors, in which a chemical indicator reagent is immobilized at the end of an optical fibre ; (2) Raman spectroscopy ; (3) IR spectroscopy . The preferred approach was not clear ; each sensing method had apparent advantages and disadvantages (see Table 2) . Consequently, further assessment of the potential of each of the three approaches was undertaken .

Optrodes

Fig . 1 . Automated infrared used-oil analyser.

Most effort in this area was directed to the identification of a suitable reagent for the detection of CO . This gas is often present at 0-10ppm background concentrations in a mine . An increase in concentration above background is an indicator of a heating ; rapid reliable detection of such an event is essential for mine safety. The low detection levels required preclude the use of Raman or IR methods (pathlengths of around 100 m would be required in an IR cell ; the approach of using a White cell was considered to be impractical) . Because of the continuous background levels, an optrode for CO in this application would require a reversible indicator reagent . Traditionally, non-reversible indicators such as palladium black [12] or molyb-



187

TABLE 2 . Relative merits of three approaches to an optical fibre-based system Method

Advantages

Disadvantages

Optrodes

High sensitivity possible Broad spectral changes occur

Potential cross-sensitivity to other parameters Reagent lifetime may be limited

Raman

All polyatomic gases and other chemicals are Raman active

Sensitivity is relatively low Signal can be masked by fluoroescence from other materials

Infrared

Reasonable sensitivity High specificity possible

Symmetrical diatomic gases not IR active Strong absorption bands for some gases (e .g ., CO) do not lie in optimum fibre transmission window

denum blue [ 13] have been employed for low-level CO detection ; these materials would be unsuitable for the coal-mining application. To date, no satisfactory optrode reagent for CO has been identified. A product established to be sensitive to ppm levels of CO [ 14] was found to be cross-sensitive to humidity and temperature variations, while more stable reagents, such as the osmium species H 20s3 (CO) 10 [15], were found to require percent concentrations of CO to produce significant spectral changes and worked only in solution. A number of optrodes for CO 2 have been described [16] ; these typically take advantage of the pH change caused by adding CO2 to an aqueous solution . The drying conditions of a coal mine would therefore make these optrodes inappropriate for long-term use .

5% CH, in N 2

LABORATORY AIR

Raman spectrometry

Raman spectroscopy has previously been reported for the detection of gases including CH 4 by optical fibre [17]. Typically, Raman measurements are made using high-powered UV laser sources, since Raman cross sections are higher in the UV region and decrease in proportion to .14. However, fibre transmission is poor in the UV. Our analysis [ 18] showed that, for a fibre length of I km, the optimum Raman excitation wavelength for measurement sensitivity was in the region 600-700 nm . Interference from fluorescence is also lower in this region than in the UV . A system based around a He-Ne laser (633 nm) was assembled, and percent levels of various gases were found to be detectable ; some responses are shown in Fig. 2 . However, the sensitivity was poor and several minutes' acquisition time was required in each case . Also, the cell alignment was an intricate operation and did not augur well for a rugged final system . IR spectroscopy (a) First prototype system

Several authors have reported investigations into the detection of methane and other hydrocarbons by optical fibre-based methods [19-24]. We assembled a sys-

0 640

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800

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WAVELENGTH, nm Fig . 2 . Responses from Raman gas-detection system .

tem based upon a white light source and interference filters, since this allowed for greater potential versatility in its applications [25]. The system design involved the use of pairs of optical fibres for each sensor cell ; one fibre to transmit light from the source to the cell and the second fibre to return it to the detector . The system, called FORGAS (fibre optic rapid gas analysis system), was tested at the Teralba Colliery, near Newcastle, Australia, in late 1988, with sensors located underground adjacent to a sampling point for the existing mine gas-monitoring system . The existing system was a mechanical one (known as the `tube bundle' system) in which gases were drawn to the surface for analysis; therefore, it offered intrinsic safety but at a cost of long delays (10-30 min) while the gas sample was pumped to the surface .



188

150m

VERTICAL SHAFT /

8 FIBRE CABLE

/ /

CELLS

DISTRIBUTION BOX

300m

JUNCTION BOX F J

Fig . 3. Schematic of installation of first prototype IR gas-detection system at coall mine .

The main part of the optical fibre system was located in the mine control room, and connected by two lengths of multimode optical fibre cable to the sensing point, which was 300 m below ground and a total distance of 1 .5 km by cable from the control room . Six-fibre cables were installed to the single sensing point, to allow up to three cell configurations to be tested . The prototype system had no optical switching facility, and hence only one cell could be operated at any given time . Cable installation at the mine (see schematic, Fig . 3) was readily accomplished. The cable was laid in standard ducting to the main mine shaft, where it was loosely supported in a 300m drop . The cable terminated a further 200 m into the mine, and was connected by standard optical fibre connectors to the second cable . Some effort was required to achieve low-loss connections in the dusty environment . The cabling underground was kept away from traffic and potential damage by tying it to the tunnel roof . After installation, and also several months later, fibre transmission performance was checked by OTDR and found to be unchanged from the performance prior to installation . The sensor cells used had an optical pathlength of 50 cm. Two cell designs were investigated, a single-pass cell and a mirrored double-pass (i.e ., single reflection) cell . Because of concerns about cell ruggedness, and limitations on the metals approved for use in collieries, the cells were manufactured from stainless steel . The single-pass cell proved to be superior to the double-pass cell for several reasons, including: (a) the sub-components were more easily constructed and assembled;

(b) the optical system was more easily aligned ; (c) better initial optical performance (typical insertion losses for the single-pass cells were around 0 .5 dB lower than for the double-pass cell) ; (d) better long-term optical performance (the mirror in the double-pass cell was difficult to keep clean) ; (e) the weight balance, with optics at either end of the cell, made the cells less awkward and cumbersome to carry about; (f) the installation of cells at the mine was easier . An unprotected cell in the mine quickly became unusable due to high light losses from internal dust accumulation; however, a simple membrane was found to be sufficient to prevent dust problems while retaining the required rapid responses to changing gas concentrations . The short-term performance of the prototype FORGAS system was very good . Using the response from the tube bundle sensor or from a hand-held methanometer at the monitoring point as a calibration mark, excellent correlations over periods of many hours or days with the tube bundle results were obtained . An example is shown in Fig. 4. When methane was deliberately released at the sensing point, the optical fibre system responded instantly, whereas it required 9 min for the tube bundle system to respond. This interval reflects the time delay to draw a sample from the sensing point to the above-ground analyser . Although the short-term performance was very good, the FORGAS system response was prone to drift over the longer term, primarily because of thermal fluctuations at the (uncooled) detector photodiode and other



1 89 1 .50

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FORGOS (charnel - 2)

I I I 9 : 00a" noon 3 : 00P"

B :OOpn

+ TUBE BUIOLE

Fig. 4 . Comparison of performances of optical fibre and 'tube bundle' gas-detection systems .

electronic components . Nevertheless, the practicality of a fibre-based system for coal-mine gas detection had been established . (b) Second prototype system System description . The first prototype system demonstrated many of the potential advantages of using optical fibres for mine gas monitoring . However, it was far from being a complete mine monitoring system which could be used in place of existing systems ; a significant developmental program was now undertaken [26, 271 . Several key performance requirements were identified through discussions with underground coal-mining personnel. These were : (a) multiple point operation, with rapid data measurement ;

Operator's Console

FORGAS

Control Unit

(b) general system operation and maintenance able to be handled by mine personnel with minimum of necessary training; (c) user-friendly software and ability to change aspects of system operation using software ; (d) ability to recalibrate ; (e) ability to measure samples collected from other locations (e.g., from places having no sensor cell) ; (f) easy to relocate sensors underground ; (g) minimal restrictions on location of above-ground instrumentation . Based on these performance requirements and the general opto-electronic requirements of the fibre-based method, a basic system concept was developed in concert with mining personnel . The general outline of the system is shown in Fig. 5 . The three units which

Calibration Unit

Computer

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Detector

Junction

Junction Box

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Underground

Fig. 5 . General outline for the FORGAS multiple-point system .

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Junction Box

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comprise the FORGAS above-ground instrumentation are functionally separate, and need not be in the same room. Each unit remains functional if communication links to other units are broken, resuming full system performance on repair . The Control Unit is the main unit for system operation, and would typically be located near to the mine shaft for greatest convenience, since the optical fibre cables connect to the unit . The Calibration Unit permits both the ability to recalibrate the system and to measure samples collected from other locations . Because of the flammable gases that could be present during these operations, the unit might, for example, need to be located in a shed some distance from the control room. The Operator's Console is the main interface with the overall system and typically would be located in the mine's control room so that an operator could readily access previously measured data and change the system operation through this unit . The Control Unit incorporates a 3 x 13 optical fibre switch and, in the design of the current prototype, is able to operate 12 sensor cells with another fibre loop dedicated to source monitoring . The Calibration Unit contains a cell with similar path length to the cells used underground, but totally enclosed and isolated from the outside air . The Unit contains two fittings, one suitable for attaching a gas bottle containing a calibration gas and the other a bag sample which may have been obtained underground . A series of electrically operated pumps, valves and filters allows the cell to be flushed and filled with the sample. The cell holds approximately 80 ml of gas. It is connected optically to the Control Unit and hence the gas concentration in the cell can be measured in exactly the same ma^ner as for any underground cell . A standard weather station, measuring temperature, pressure and relative humidity, was included into the Calibration Unit, logging data to the system . The design of the underground sensor cells was further refined after the trials of the first prototype system . The outer diameter for the single-pass cells was reduced to 50 mm by careful optical design, and optical fibre connectors were embedded into the cell so that there were no exposed fibres (identified as a weak point in the first system) . Figure 6 is a photograph of a typical cell for use underground . Fibre connections within the fibre network were a mixture of mechanical splices and expanded beam connectors . Mechanical splices were used at all points underground involving a semipermanent connection of fibres, while the expanded beam connectors were used at points above and below ground where colliery personnel might be expected to make and break fibre links (e.g., to relocate sensor cells) . The optical performance of the'expanded beam connectors was generally much

Fig. 6. FORGAS underground sensor cell .

poorer than from the mechanical splices (losses around 1-2 dB compared with 0 .2-0 .4 dB) and added significantly to the overall system loss budget . However, they did provide a much more consistent connection performance .

System performance . An initial calibration for methane was carried out in the laboratory, with a standard sensor cell placed within a gas box alongside a methanometer. Figure 7 shows the correlation that was obtained . Work with higher CH4 concentrations was carried out using the Calibration Unit . Because of the small volumes required and as the gas mixtures were kept fully enclosed, the entire 0-100% methane range could be covered . At higher concentrations, the response departed from the Beer-Lambert law, but a reproducible calibration curve could be generated . As can be seen from Fig . 8, the FORGAS system can be used across the entire concentration range. The system has been installed at the Tower Colliery, near Wollongong, Australia, which operates a coal seam 500 m below ground level . Cable has been laid for 10 sensing points around the mine, although at this stage of the trials only three points are being operated .

1

2

3

4

Methane Concentration (by metnenometer) Fig . 7 . Methane concentrations measured by FORGAS compared with those measured by a methanometer over the 0-5% range .

1 91 100

80

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20

40

60

80

100

Methane (by FORGAS)

Fig. 8 . Methane concentration measured by FORGAS compared

to the concentration added to the calibration cell .

The system has been operating for several months . Two main problems encountered have been temperaturedependent wavelength transmission performance of certain expanded beam connectors (now replaced), and repeatable coupling between fibres within the optical fibre switch . This latter problem is being dealt with by the use of index-matching gel, but is currently a regular maintenance requirement and needs improvement . In general operation, though, the multi-point system is performing well and measuring concentrations of CH4 to ±0 .2% over distances of 1-3 km . Underground cells have been operated maintenance-free to data, in-

eluding a cell located at the mine upcast shaft, which is the area of greatest dust and humidity levels . Figure 9 shows a performance comparison for a sensor in the mine upcast shaft . Due to a temporary ventilation fault, methane concentrations rose to over 2 .5% for a brief period . This change could be detected immediately with the optical fibre system. The mechanical tube bundle system detected the same gas surge, but with a considerable delay (accentuated by the cycle time for the system) and did not record the peak concentration (due to cycle-time effects and some broadening of the gas pocket in transit through the tubing) . Further system development is in progress, as is research aimed at the expansion of the system to measure additional parameters . These further developments will be reported in due course . Commercialization options for the FORGAS system are presently being investigated .

Laser-based systems In some applications, a point sensor such as that provided from the fibre optic system is insufficient because of the localized variations in concentrations that can occur . A system that can detect the parameter of interest anywhere within a large area is preferable in these applications . A relevant example is found in the handling of liquefied methane or natural gas (LNG) . The thermal

FORGAS

2.5 -

2 -

-a- TUBE BUNDLE

POWER FAILURE

I

FAN FAILURE

0 12:00 PM 4 :00 PM 8 :00 PM 12 :00 AM 4:00 AM 8 :00 AM 12 :00 PM Fig . 9. Comparison of performances of FORGAS and `tube bundle' systems in mine upcast shaft .

19 2

shock experienced by components in contact with the cold liquid can be sufficient to produce high stresses and sometimes leaks . Such damage could occur almost anywhere within a plant or LNG tanker where cold liquid is present . There is a need for a system that can measure the presence of methane in the atmosphere at percentage levels and which is capable of monitoring large areas in a short time. A system currently being investigated uses a Nd :YAG laser coupled with a tuned etalon to generate a single alternately overlapping and then adjacent to a methane absorption line in the 1 .34 µm region [28] . This could form the basis of a laser radar (LIDAR) system which would be used to scan an area looking for any cloud of methane gas that is present, as the indicator of a leak and potential hazard . System development is continuing on this important IR sensing application .

Future directions Infrared sensing has been recognized as a useful approach for several industrial applications to date with the sensing research program at BHP ;. these applications will continue to progress . Many additional opportunities for 1R-based sensing to contribute to the aims of the program would seem to exist . It has been shown that useful spectral information from the nearinfrared region can be obtained from liquefied hydrocarbon gases by use of a fibre optic probe connected to an FT-IR spectrometer [29], and similarly from the gases [7] . This raises the possibility of using a fibre-based system to determine the composition of a mixture such as natural gas, including its liquefied and compressed forms . Applications could include compositional analysis, blend control and calorific value determination. Other applications for IR monitoring are arising through an increasing interest in environmental matters . We have shown that cyanide and metallo-cyanide species in solution can be detected and speciated by IR spectrometry to sensitivities in the 10-100 ppm range [30] . IR spectrometry has also proved to be a useful non-invasive tool in the characterization of samples of unknown origin or composition. It is often instructive to examine the IR spectra of such materials first, at the very least to be able to understand potential matrix effects during conventional analytical procedures . For example, we have been able to identify the iron cyanide species Prussian Blue as a major component of certain sludges from IR analysis; chemical analysis showed the presence of cyanides with no indication that they were present in an essentially inert form . In a related exercise, cyanide balances could only be closed after discovery by IR spectrometry of the presence in sludges of the

species K 2 Zn[Fe(CN)6 ], which is stable to the conventional digestion for cyanide analysis,

Acknowledgements The contributions of many colleagues within BHP to the work described in this report are gratefully acknowledged . The contributions of Dr Peter Samson to the fibre optic research program are particularly notable . Part of the work described was supported by National Energy Research & Development Board Grants 85/5069 and 88/1211 . I thank the BHP Co Ltd for permission to publish .

References I P . M . Fredericks, J . B. Lee, P. R . Osborn and D . A . J. Swinkels, Materials characterization using factor analysis of FT-IR spectra . Part 1 : Results, Appl. Spectrosc ., 39 (1985)303-310 . 2 P . M . Fredericks, P . R . Osborn and D . A . J . Swinkels, Rapid coal characterization by FT-i .r. spectroscopy, Fuel, 63 (1984) 139-141 . 3 P. M . Fredericks, P . R . Osborn and D . A . J . Swinkels, Rapid characterization of iron ore by Fourier transform infrared spectrometry, Anal . Chem ., 57 (1985) 1947-1950 . 4 D. A. J . Swinkels and P . R . Osborn, Infrared spectroscopy of manganese dioxide, in Prog. Batteries Solar Cells,, 7 (1988) 20-30 . 5 P . M . Fredericks, R . Kobayashi and P . R . Osborn, Rapid analysis of coal blends by diffuse reflectance FT-i.r . spectrometry, Fuel, 66 (1987) 1603-1608 . 6 A. D. Stuart, S. M. Trotman, K . J . Doolan and P . M. Fredericks, Spectroscopic measurement of used lubricating oils, Appl. Spectrosc ., 43 (1989) 55-60 . 7 A. D. Stuart and G . W . Bryant, unpublished results . 8 R . Lardner, Trend analysis of oils with FTIR, Lab . News, (Sept.) (1990) 26-27 . 9 J. B . Lee, A . S. Woodyatt and M . Berman, Enhancement of high spectral resolution remote-sensing data by a noise-adjusted principal components transform, IEEE Trans . Geosci . Remote Sensing, 28 (1990) 295-304 . 10 J . B . Lee, P. R . Osborn and A . B . Duval, unpublished results . 11 A . D. Stuart and P . J . Samson, Optical fibre based gas sensing in coal mines, Aust . Dept . of Primary Industries and Energy, NERDDP Report 85(5069, Oct . 1988 . 12 C . L . Walters, Determination of carbon monoxide with palladium chloride, Microchem . J., 27 (1982) 116-123 . 13 M . Shepherd, S . Shiford and M . V . Kilday, Determination of carbon monoxide in air pollution studies, Anal. Chem ., 27 (1955) 380-383 . 14 A . D . Stuart and P. J. Samson, Optrode sensors for carbon monoxide and relative humidity, Proc. 13th Aust . Conf. Optical Fibre Technol ., Hobart, Australia, Dec . 4-7, 1988, pp. 117-120. 15 A . J . Deeming and S . Hasso, Isolation of intermediates in metal carbonyl substitution: adducts of H2Os,(CO),,,, J. Organomet . Chem., 88 (1975) C21-C23 . 16 See, for example : G . G . Vurek, P . J . Feustel and J . W . Severinghaus, A fibre optic pCO 2 sensor, Ann . Biomed. Eng., 11 (1983) 499-510 .

193 17 R . K. Chang and R . E . Benner, Laser Raman point monitoring of CH4 vapour in the LNG storage field, Gas Research Institute Report GRI-79/0050, Dec . 1979. 18 P. J . Samson, A . D . Stuart and H . Inglis, Fibre optic gas sensing using Raman spectrometry, Proc. 14th Aust . Conf. Optical Fibre Technol., Brisbane, Australia, Dec . 5-8, 1989, pp . 145-148 . 19 A . Hordvik, A . Berg and D . Thingbo, A fibre optic gas detection system, Proc . Eur . Conf. Opt . Commun . (ECOC), Geneva, Switzerland, Oct . 1983, pp . 317-320 . 20 S . Stueflotten, T . Christensen, S. Inversen, J . 0. Hellvik, K . Almas, T . Wien and A . Graav, Infrared fibre optic gas detection system, Proc . 4th Conf. Optical Fibre Sensors (OFS), Stuttgart, Germany, Sept . 1984, pp . 87-90 . 21 K . Chan, H . Ito and H . Inaba, Optical remote sensing of CH 4 gas using low loss optical fibre link and InGaAsP light-emitting diode in 1 .33 micron region . Appl . Phys . Lett ., 43 (1983) 634-636 . 22 J . P. Dakin, C . A. Wade, D . Pinchbeck and J . S . Wykes . A novel optical fibre methane sensor . Int. J. Opt . Sensors, 2 (1987) 261-267 . 23 M. Aizawa, T . Okamoto and H . Nagai, Remote detection of methane gas with a wavelength tunable DFB LD in 1 .65 µm wavelength region, Proc . 7th Conf. Optical Fibre Sensors (OFS), Sydney, Australia, Dec . 1990, pp. 47-50 . 24 H . Tai, K . Yamamoto, S . Osawa and K . Uehara, Remote detection of methane using a 1 .66 µm diode laser in combination with optical fibers, Proc . 7th Conf. Optical Fibre Sensors (OFS), Sydney, Australia, Dec . 1990, pp. 51-54 . 25 P. J . Samson and A . D . Stuart, Coal mine methane sensing by optical fibre, Proc. 13th Aust. Conf. Optical Fibre Technol., Hobart, Australia, Dec . 4-7, 1988, pp . 113-116 . 26 J . C . Hopkins, P . J . Samson and A . D . Stuart, Multipoint optical fibre gas sensing in coal mines, Aust . Dept. of Primary Industries and Energy, NERDDP Report 88(1211, Dec . 1990 . 27 J . C. Hopkins, P. J. Samson and A . D. Stuart, A fibre optic based continuous mine monitoring system . Proc . 7th Conf. Optical Fibre Sensors (OFS), Sydney, Australia, Dec . 1990, pp . 207-210 . . 28 J . C . Scott, R . A . M . Maddever and A . T. Paton, Spec troscopy of methane using Nd :YAG laser at 1 .34 microns, Appl. Opt., 31 (1992) 815 .

29 G . W . Bryant and A. D. Stuart, Feasibility of a fibre optic probe for measuring liquefied hydrocarbon gases, Proc . 7th Conf. Optical Fibre Sensors (OFS), Sydney, Australia, Dec . 1990, pp. 215-218 . 30 A . D. Stuart and R . van den Heuvel, Assessment of infrared spectroscopy for detecting cyanide species in aqueous solutions. Int . J. Env . Anal. Chem., in press .

Biography

Alan Stuart is a graduate in chemistry from the University of Western Australia (B .Sc. 1974, Ph .D. 1979) . After post-doctoral terms at the University of Sussex (1979-81) and the Australian National University (1981-83), he joined the research division of BHP at their laboratories in Newcastle, Australia . He was initially involved in process development research, particularly for new uses for manganese dioxide . An interest in spectroscopy and chemical characterization led to his involvement in the development of the sensing research program at BHP. He was group leader for the optical fibre sensing part of the program, and pursued the development of extrinsic and intrinsic fibre sensors and sensing systems for use in Company applications . More recently, he has become involved in waste management and pollution control research for his Company. His present interests are in waste-management strategies, in particular the integration of technologies to develop the most appropriate solutions to problems . Sensing is still an important component of the overall research thrust; the major emphasis in this area now is the development of systems rather than sensing techniques . He is the manager of a project to develop on-line monitors for total P and total N in effluents .