GB2532088A - Multipoint gas sensing apparatus - Google Patents

Abstract

A modular apparatus provides a multipoint optical gas sensing network. The apparatus comprises a tunable laser diode 220 as optical source, a control unit 210 for generating a control signal for modulating a drive signal for the laser, at least one optical beam splitter 230 for receiving the laser beam and splitting it into a plurality of output beams, a gas sensor interface having a plurality of output ports to direct the beams to a plurality of gas sensor cells 250 via respective waveguides, at least one photo-receiver module 240 with at least one photodetector 241 and a signal processor 245, the gas sensor interface having a plurality of input ports to direct beams from the cells to the corresponding photodetectors, wherein the processor 245 for each receiver module 240 determines the concentration of target gas in each cell from the input beam detected at each photodetector.

Description

MUITIPOINT GAS SENSING APPARATUS

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to the sensing of gas concentrations at a plurality of sites using absorption of incident infrared wavelength electromagnetic waves. In particular, the invention relates to the sensing of gas concentrations in environments where the presence of gas above M certain concentrations may be dangerous or otherwise detrimental.

[0002] Gases have characteristic absorption properties with absorption lines at various wavelengths in the electromagnetic li spectrum. At infrared wavelengths, for example, methane has convenient absorption lines at wavelengths around 1650nm, which lies in the near-infrared (IR): conveniently, some of these lines do not coincide with significant absorption line characteristics of the major constituents of air (i.e. nitrogen, oxygen, water vapour and/or carbon dioxide).

[0003] To detect the presence of a target gas such as methane, it is known to use tunable diode laser spectroscopy (TDLS). The TDLS technique has two main stages: a) a single frequency diode laser is tuned (by varying the diode current) to generate coherent electromagnetic waves at a range of wavelengths that spans one or more of the characteristic absorption lines of a target species; and b) the absorption of the incident electromagnetic waves as their wavelength varies across the target absorption line is detected (for instance by measuring the ratio of power transmitted through a target gas volume to the power generated) and, the gas concentration is thereby deduced.

In the case of methane, it is convenient for the laser to be tunable in a range of infrared wavelengths that span a typical absorption line: this absorption line is up to two orders of magnitude smaller in bandwidth than the effective tunable range of the diode.

[0004] By deploying a plurality of measurement sensors across a physical site at spaced apart locations and supplying each measurement sensor with the laser output via a network of 10 waveguides (typically fibre optical cable), it is possible to detect the gas concentrations at each site using a remotely located optical source. This is intrinsically safer, more convenient to calibrate and simpler to maintain, than alternative sensing technologies, such as pellistors, electrochemical sensors li and locally electrically powered gas analyser systems.

[0005] In the related art, the laser output of the tunable source is directed to a selected gas sensing cell along one of a plurality of optical paths by an optical switch and the laser beam that is transmitted through the cell is detected at a receiver. The laser output may additionally or alternatively be split between optical paths by an optical splitter and directed to a plurality of gas sensing cells, the laser beam transmitted via a given one of those cells being selected by an optical switch and directed to a receiver.

[0006] Other related art makes use of a plurality of photodetectors, the laser output of the tunable source is split between optical paths by an optical splitter and directed to a plurality of gas sensing cells along one of a plurality of optical paths and the laser beam that is transmitted through each respective cell is detected at a corresponding photodetector.

[0007] To compensate for variations in the ambient temperature, it is known to provide a gas reference measurement volume (i.e. a gas reference cell) containing a sample of the 5 gas to be detected, having known gas density, pressure and concentration. By ensuring that the detectors are calibrated against the levels of absorption detected in the gas reference cell and assuming detectors and reference cell are at substantially the same ambient temperature, it is hoped that the effects of ambient temperature can be negated.

[0008] To provide a reference channel in parallel with the detection channels, it is also known to direct at least one laser beam (i.e. split from an incoming beam at an optical splitter or selected by an optical switch) to a photodetector or receiver without traversing a measurement cell. Values from the reference channel may be used to compensate for wavelength dependent attenuation (as the laser beam sweeps across its wavelength range) that is unrelated to the presence of the target gas.

[0009] Existing TDLS systems thus provide sequential updates from each measurement cell in turn, leading to update periods that increase markedly as the sensor network expands.

[0010] There is a requirement for large scale (i.e. greater than 50 detection locations), readily-adapted, multipoint, fast updating (i.e. typically at least an order of magnitude faster than the once every 100 seconds of the related technologies discussed above), intrinsically safe sensing systems for mines, gas distribution, service ducts and similar applications. Ready adaptation conveniently refers to a facility for expansion of a sensor network in the field.

[0011] In such applications there is a need for the sensing systems to be able to adapt and scale as the size of large scale deployment (such as a mine or gas distribution system) evolves.

[0012] It is an aim of certain embodiments of the present disclosure to solve, mitigate or obviate, at least partly, at least one of the problems and/or disadvantages associated with the related art. Certain embodiments aim to provide at least one of the advantages described below.

SUMMARY OF THE INVENTION

[0013] In one aspect of the present disclosure, there is provided an apparatus for sensing a target gas species, the apparatus comprising: an optical source including a tunable laser diode which is configured to generate a laser beam in accordance with a driving signal; a control unit for generating a control signal for modulating the driving signal applied to the tunable laser diode; at least one optical beam splitter for receiving the laser beam from the optical source and for splitting the laser beam into a plurality of output beams; a gas sensor interface having a plurality of output ports, each port being adapted to direct output beams from the at least one optical beam splitter to a respective one of a plurality of gas sensors via a respective optical waveguide; and at least one photoreceiver module, each photoreceiver module having at least one photodetector and a signal processor, wherein the gas sensor interface further includes a plurality of input ports, each input port being adapted to direct input beams from respective ones of the plurality of gas sensors to a corresponding one of the photodetectors, each input beam corresponding to a portion of a respective output beam after having traversed the respective gas sensor and the attenuation of the input beams having a predetermined correlation to the concentration of the target gas species in the gas sensor, and wherein the signal processor for each photoreceiver module operates to determine the concentration of the target gas species from the characteristics of the input beam detected at each photodetector in the photoreceiver module.

[0014] The apparatus facilitates the provision of a gas-species-specific sensing system using TDLS techniques deployed 10 over a large scale fibre optic sensor network; a deployment being considered 'large scale" where it has in excess of 50 points. The system returns optical signals dependent on gas concentrations from multiple sensing elements to a central location remote from the sensing area. As a consequence of the 75 above, the present disclosure provides a convenient, field-expandable, inherently safe, optical gas sensing system. The apparatus facilitates ease of expansion by virtue of the modularity of the components of the apparatus: the fact that each photoreceiver module has a respective signal processor distributes the burden of processing at a rate that follows the increase in number of sensing points.

[0015] Certain embodiments of the present disclosure have typical update times of around 2 seconds, even when serving a 25 large scale network.

[0016] In yet another aspect of the present disclosure, there is provided a method for sensing a target gas species comprising: generating, at an optical source including a tunable laser diode, a laser beam in accordance with a driving signal; generating a control signal for modulating the driving signal applied to the tunable laser diode; splitting the laser beam into a plurality of output beams; directing each of said output beams via respective output ports to a respective one of a plurality of gas sensors; receiving input beams from respective ones of the plurality of gas sensors, each input beam corresponding to a portion of a 5 respective output beam after having traversed the respective gas sensor, the attenuation of the input beams having a predetermined correlation to the concentration of the target gas species in the gas sensor; directing each of said input beams to a corresponding one of a plurality of photodetectors; and determining the 70 concentration of the target gas species from the characteristics of the input beam detected at each photodetector.

[0017] Another aspect of the present disclosure provides a computer program comprising instructions arranged, when executed, 15 to implement a method in accordance with any one of the above-described aspects. A further aspect provides machine-readable storage storing such a program.

[0018] Various further aspects and embodiments of the present disclosure are provided in the accompanying independent and dependent claims.

[0019] It will be appreciated that features and aspects of the present disclosure described above in relation to the first and other aspects of the invention are equally applicable to, and may be combined with, embodiments of the invention according to the different aspects of the invention as appropriate, and not just in the specific combinations described above. Furthermore features of the dependent claims may be combined with features of the independent claims in combinations other than those explicitly set out in the claims.

DESCRIPTION OF THE DRAWINGS

[0020] The invention, together with objects and advantages thereof, may best be understood by reference to the following description of exemplary embodiments together with the 5 accompanying drawings in which: [0021] Figure 1 illustrates a gas sensor network in accordance with the related art; [0022] Figure 2 illustrates a gas sensor networks in accordance with an aspect of the present disclosure; [0023] Figure 3 illustrate a gas sensor networks in accordance

with a further aspect of the present disclosure;

[0024] Figure 4 illustrates a small scale (three point) sensor system in accordance with certain embodiments of the present disclosure; [0025] Figure 5 shows a schematic diagram of a large-scale (>50 point) sensor system in accordance with certain embodiments of the present disclosure; and [0026] Figure 6 shows a schematic diagram of a typical master control unit in accordance with an aspect of the present 20 disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0027] The detailed description set forth below in connection with the appended drawings is intended as a description of certain exemplary embodiments of the invention, and is not intended to represent the only forms in which the present invention may be practised. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the scope of the invention. In the drawings, like numerals are used to indicate like elements throughout. Furthermore, terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that module, circuit, device components, structures and method steps that comprises a list of elements or steps does not include only those elements but may include other elements or steps not expressly listed or inherent to such module, circuit, device components or steps. An element or step proceeded by "comprises does not, without more constraints, preclude the existence of additional identical elements or steps that comprises the element or step.

[0028] Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as li contemplating plurality as well as singularity, unless the context requires otherwise.

[0029] Figure 1 illustrates a gas sensor network 100 in accordance with the related art.

[0030] Here, under the control of a control unit 110, a laser source module 120 launches a laser beam into an optical splitter 130. The optical splitter 130 splits the laser beam into a plurality of beams (here, four beams). Three of these beams are 25 directed to respective sensing points (150a,150b,150c) along respective optical waveguides.

[0031] The level of absorption of light from the incident beam is related to the concentration of the target gas present in each sensor. The portion of each laser beam transmitted through the sensing points (150a,150b,150c), and not absorbed, is directed along further corresponding optical waveguides to respective photodetectors (141a,141b,141c) in a photoreceiver module 140. A further one of the split laser beams is directed along a reference optical fibre 152 to a further photodetector 141r to provide a reference channel. Values from the reference channel may be used to compensate for wavelength dependent 5 attenuation (as the laser beam sweeps across its wavelength range) that is unrelated to the presence of the target gas: the reference channel is not to be confused with a calibration channel where a gas reference cell is used to obtain sample values associated with the presence of a known concentration of 70 the target gas in a cell of known dimensions.

[0032] The photoreceiver module 140 includes four photodetectors (where the transmitted beams are sampled). The samples measured by the respective photodetectors are streamed to the control unit 110. The control unit 110 then processes the respective streams of data to determine the concentration of the target gas at each sensing point.

[0033] Figure 2 illustrates a gas sensor network in accordance

with an aspect of the present disclosure.

[0034] In Figure 2, a laser source module 220, controlled by a master control unit (MCU) 210, launches a laser beam into an optical splitter 230. The optical splitter 230 splits the laser 25 beam into a plurality of beams (here, as for Figure 1, illustrated as four beams). Three of these beams are directed to respective sensing points (250a,250b,250c) along respective optical fibres.

[0035] The level of absorption of light from the incident beam is related to the concentration of the target gas present in each sensing cell. The portion of each laser beam transmitted through the sensing points (250a,250b,250c), and not absorbed, is directed along further corresponding optical fibres to respective photodetectors (241a,241b,241c) in a photoreceiver module 240. A further one of the split laser beams is directed along a reference optical fibre 252 to a further photodetector 241r to provide a reference channel. Again, values from this reference channel may be used to compensate for wavelength dependent attenuation and again the reference channel is not to be confused with a calibration channel where a gas reference cell is used to obtain sample values associated with the presence of a known concentration of the target gas in a cell of known dimensions.

[0036] The photoreceiver module 240 of Figure 2 includes four photodetectors (where the transmitted beams are sampled) and a 75 signal processor unit 245 (where the level of absorption in the sampled beam is determined). The signal processor unit 245 processes the determined values for the levels of absorption from each associated photodetector, calculates a corresponding target gas concentration from said determined values relative to the reference channel values and generates data packets including the calculated gas concentration levels to the master control unit 210. The master control unit 210 then collates the respective data packets to provide reports (and/or alarms) concerning the concentration of the target gas at each sensing point.

[0037] The architecture of Figure 2 thus includes a system management layer that overlays the basic TDLS sensing technique. As the architecture is modular, multiple sensing points may be 30 addressed and managed from a single laser source and master controller unit (MCU) pairing. Each of the sensing points (potentially >200 points) is served by a fibre optic network, returning transmitted beams to one or more photoreceiver modules, each with dedicated signal processing capabilities.

[0038] Figure 3 illustrates an expanded gas sensor network in accordance with a further aspect of the present disclosure.

[0039] As was the case in Figure 2, the gas sensor network 300 of Figure 3 includes a laser source module, controlled by an MCU, that launches a laser beam into an optical splitter. Each M of these components corresponds to components of the network in Figure 2 and the same reference numbers are used as a result.

[0040] The optical splitter 230 in Figure 3 splits the laser beam into a plurality of beams (here, three groups of beams 250, 15 254, 256, are shown for illustration, each group representing a plurality of beams). The three transmitted beams and the reference channel of Figure 2 are represented in Figure 3 as a single group of beams 250. Sensing points such as points 250a, 250b, and 250c in Figure 2 are present in each of the groups of beams but not shown for the sake of simplicity.

[0041] The level of absorption of light from the incident beam is related to the concentration of the target gas present at each sensing point. The portion of each laser beam transmitted through the sensing points (250a,250b,250c,etc.), and not absorbed, is directed along further corresponding optical fibres to respective photodetectors in a respective one of a plurality of photoreceiver modules 240, 244,246.

[0042] The photoreceiver modules of Figure 3 are illustrated as having four photodetectors (where the transmitted beams are sampled) and a signal processor unit (where the level of absorption in the sampled beam is determined). Certain embodiments have a single photodetector while others have a larger number of photodetectors per photoreceiver module that is essentially arbitrary. The number of photodetectors would conveniently be eight or sixteen, for example.

[0043] As for Figure 3, the signal processor unit in each photoreceiver module processes the determined values for the levels of absorption from each associated photodetector, calculates a corresponding target gas concentration from said determined values relative to the reference channel values and generates data packets including the calculated gas concentration levels to the master control unit 210. The master control unit 210 then collates the respective data packets to provide reports (and/or alarms) concerning the concentration of the target gas at each sensing point.

[0044] In certain embodiments, the laser source/MCU combination (pairing) is configured to target a selected absorption line of at least one gas species of interest. A 20 system calibration is derived from the paired source/MCU configuration. This calibration is specific to each laser source as each diode laser has a different response to the driving signal (i.e. current or voltage modulation) applied to the diode; the calibration is also specific to the capabilities of the MCU.

[0045] The master control unit 210 includes one or more processor, a communication unit, a memory and a bus. The operation of the MCU is described further below.

[0046] As the correct interpretation of the absorption data from the photodetectors requires information about the laser source, the MCU and/or the pairing between source and MCU, the MCU broadcasts reference channel and system calibration information to each of the photoreceiver modules. The photoreceiver modules each include a respective signal processing unit which uses the reference channel and calibration information (in the form of a lookup table, or equation variables, for example) to interpret the output from the respective photodetectors. The reference channel referred to here is used to compensate for wavelength dependent attenuation as might be experienced by the light beam as its wavelength is varied across its range (and over the target absorption line). The reference channel should not to be confused with a calibration channel where a gas reference cell is used to obtain the calibration information associated with the presence of a known concentration of the target gas in a cell of known dimensions. A plurality of these gas reference cells having different target gas concentrations would be used to generate the calibration information.

[0047] In certain embodiments, the MCU may then receive and collate data packets containing the gas concentration information.

[0048] As can be seen from a comparison of Figures 2 and 3, when the system requires expansion, additional sensing points 25 can be incorporated into the optical network and further photoreceiver modules added to receive the transmitted signal from the respective additional sensing points. The initial splitting of the laser beam from source may require one or more than one optical splitter (the splitters being used in series in the latter case): the optical splitters used may be conventional, "off the shelf" components and availability and/or monetary cost may determine the selection of optical splitter components.

[0049] Figures 2 and 3 thus illustrate how the present architecture may be expanded. In addition to a core set of components (i.e. an MCP, a tunable diode laser source, an optical beam splitter and a single photoreceiver module), expansion of the system requires only additional photoreceiver module(s) and the associated sensor network deployment and control and data connections. Optionally, or conveniently further optical splitters may be deployed.

[0050] In the case where a new photoreceiver module is added, that photoreceiver module receives the system calibration and 15 control signals that are broadcast from the MCP. As a result, the new photoreceiver is configured to detect characteristics of the beam transmitted through an associated sensing point. The photoreceiver is further configured to generate a dataset from the detected characteristics of the transmitted beam and to 20 transfer the data set to the MCU in the payload of one or more data packages. The MCP in turn recognizes and collates the datasets from the associated sensing point (or points) as they become available.

[0051] This system management protocol aims to optimize the capabilities of the MCP processor (or processors), to reduce overheads and to facilitate expansions with little or no loss in processing time.

[0052] The management system comprises dedicated hardware modules and custom firmware, which govern system communications, signal generation and processing measurement collation and data output. A local area network, LAN, communication protocol, such as Ethernet protocol, is preferably used to provide the communication backbone between the MCU and the photoreceiver modules.

[0053] Certain embodiments are "self-referencing", by which is meant they employ mechanisms to compensate for changes in optical losses in the plurality of optical waveguiding paths.

[0054] After an initial factory setting using gas reference M cells at different known target gas concentrations, no re-calibration is required. In essence the source is paired to the MCU. This results in a reduction in maintenance and installation costs.

[0055] As previously noted, a system where the sensing points are addressed only using low-power infrared laser light is intrinsically safe.

[0056] Conveniently, the sensing points do not have a point of saturation; when configured to sense the presence of methane, for example, these sensing points are typically capable of operating at concentrations from <500ppm to 100.

[0057] The architecture described facilitates the self-checking of the integrity of the transmission path through the entire system, since it will be readily apparent when a given sensing point is providing anomalous results or a link in the connecting fibre optical network has been severed (for example). Furthermore, certain embodiments may be configured to generate alarms to indicate failures, such as failure of a cell specific section or indeed of the system as a whole.

[0058] Certain embodiments may be extended, after initial deployment, to incorporate 240 or more sensors and/or to reach distances of 20km or more from the MCU depending on the system application requirements and the limitations of safe operation.

[0059] The combination of the use of TDLS, an optical fibre network and an overlaying systems management allows the present architecture to address the problems identified above and consequently provide a conveniently field-expandable, optical 10 gas sensing system.

[0060] Certain embodiments implement two sensing techniques: direct absorption measurement and wavelength modulation spectroscopy (WMS). Used in tandem, absorption measurement and WMS effectively detect a target gas at a large dynamic range of gas concentrations (for instance from as little as 100ppm to 100% methane).

[0061] Fibre optic networks provide a low loss transmission medium that allows long sensor deployment distances (with the off-the-shelf fibre optic cabling familiar to telecommunications engineers this can extend as far as 20km). Certain implementations take advantage of the fibre's inherent low loss to provide a large number of points (currently up to 240).

[0062] The systems management architecture of the present disclosure achieves convenient expansion of the number of sensing points, such that a field deployment can be expanded as required without further calibration. The architecture (with associated communications protocol, firmware and hardware support) provides an electronic backbone that ensures the continued operation of the existing deployed sensor network while facilitating the addition of new sensing points.

[0063] The system management architecture is implemented in electronics as separable modules for installation in a housing. The housing may conveniently provide suitable electrical and optical shielding and a power supply. The separable modules include a laser source module, a master control unit, at least one optical beam splitter and at least one photoreceiver module.

In certain embodiments, the modules have a form factor and connector profile which affords insertion into the housing and electrical and optical connection between modules. As a result, these embodiments allow easy system expansion should the scope of the sensing deployment increase in scale.

[0064] A typical initial installation begins with the physical insertion of the respective modules in the housing and the laying out of a suitable network of optical waveguides with gas sensors placed at a plurality of sensing points. The laser source module is then optically connected to a first beam splitter; further beam splitters may be connected in series. The plurality of ports of the first beam splitter are then optically connected to the sensor network. With the requisite sensor network in place, the sensing capabilities of the system are completed with insertion and optical connection of the photoreceiver modules to the sensor network (so that light transmitted across the respective sensor is received at a respective photoreceiver module). Once connected in this manner the system is powered to allow the master control unit to establish electrical communication with each of the connected modules.

[0065] Figure 4 illustrates a small scale (three point) sensor system in accordance with certain embodiments of the present disclosure.

[0066] Figure 4 shows an embodiment of the present disclosure having three sensing points. Here a laser source module 410 launches a laser beam of known properties (e.g. scanning a known range of frequencies that span a given absorption line for a target gas species at a known power, with a known modulation).

The laser beam propagates along a launch optical waveguide 415 to an optical splitter 420. The optical splitter 420 splits the laser beam into a plurality of beams (here, three beams) and these beams are directed to respective sensing points (not shown) along corresponding optical waveguides 425a.

[0067] The level of absorption of light from the incident beam is related to the concentration of the target gas present in each sensor. The portion of each laser beam transmitted through the sensing points, and not absorbed, is directed along further corresponding optical waveguides 425b to a photoreceiver module 430. The photoreceiver module 430 includes at least one photodetector 432 (where the transmitted beam is sampled) and a signal processor unit 434 (where the level of absorption in the sampled beam is determined and a resulting data set is generated).

[0068] The operation of the source module 410 and the photoreceiver module 430 is controlled by a master control unit, MCU, 440. Power is supplied by a power supply unit 450.

[0069] Figure 4 illustrates a typical deployment of the small scale (three point) sensor system used to implement a network as illustrated in Figure 2.

[0070] Figure 5 illustrates a larger scale sensor system in accordance with certain embodiments of the present disclosure.

[0071] Figure 5 shows an embodiment of the present disclosure having a plurality of sensing points. Here a laser source module 510 launches a laser beam of known properties. The laser beam propagates along a launch optical waveguide 515 to a first optical splitter 520. Optionally the output of the first optical splitter 520 is itself applied to at least one further optical splitter 522. The first optical splitter 520 (or the series of optical splitters 520, 522, etc.) splits the laser beam into a plurality of beams (in certain exemplary embodiments, eight or sixteen beams) and these beams are directed to respective sensing points (not shown) along corresponding optical waveguides 525a.

[0072] The level of absorption of light from the incident beam is related to the concentration of the target gas present in each sensor. The portion of each laser beam transmitted through the sensing points, and not absorbed, is directed along further corresponding optical waveguides 525b to a plurality of photoreceiver modules 530a-530d. Each of the photoreceiver modules 530a-530d includes at least one photodetector 532 (where the transmitted beam is sampled) and a signal processor unit 534 (where the level of absorption in the sampled beam is determined and a resulting data set is generated).

[0073] The operation of the source module 510 and the 30 photoreceiver module 530 is controlled by a master control unit, MCU, 540. Power is supplied by a power supply unit 550.

[0074] Figure 6 shows a schematic diagram of a typical master control unit in accordance with an aspect of the present disclosure. Here, apparatus suitable for use as a master control unit 600 includes one or more processor 610, a communication unit 630, a memory 620 and a bus 605. An Input/Output (I/O) module 640 may be provided to allow user interaction with the MCU and the display of data received from respective photoreceiver modules.

[0075] The processor 610 is configured to implement an operating system 614. Further applications including a sensor system management application 612 are stored in memory 620 and when required, retrieved via the bus 605. The processor is further configured to execute the system management application 612. The system management application 612 includes procedures for: system supervision; distribution of calibration tables/values; generating reference signals and synchronisation signals; and collection, collation and reporting of data streams.

[0076] As noted above, optical network deployment and testing are conveniently undertaken prior to system commissioning. Certain embodiments make use of conventional telecommunications optical fibres and cables, so that installers local to the deployment location can be used without additional specialist training. Optical sensor and electronic installation can then be undertaken in a shorter period than would be expected for a conventional gas-measurement optical network: the time scale for trained personnel to fully commission the system on-site is thereby substantially reduced.

[0077] Certain embodiments of the present disclosure use sensor designs that have been tested to ensure their inherent safety in explosive environments, by using only ATEX and/or IECEx compliant materials for example, and verified optical powers 5 several orders of magnitude below ignition risk levels. ATEX is a set of legal requirements set by the European Commission for controlling explosive atmospheres and the suitability of equipment and protective systems used in them; whereas IECEx refers to compliance with the International Electrotechnical 10 Commission Scheme for Certification to Standards Relating to Equipment for use in Explosive Atmospheres and is an internationally recognized certification.

[0078] The sensors (the physical components housing each sensing element) exhibit several features to withstand potentially hazardous and inhospitable environments. These features may include drip shields, fine mesh and sturdy housings which prevent water damage, dust ingress and physical damage to the sensing element while allowing air circulation to facilitate gas detection.

[0079] It will be appreciated that embodiments of the sensor system can be realized in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage, for example a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory, for example RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium, for example a CD, DVD, magnetic disk or magnetic tape or the like. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement embodiments of the present invention.

[0080] Accordingly, embodiments provide a program comprising code for implementing apparatus or a method as claimed in any one of the claims of this specification and a machine-readable storage storing such a program. Still further, such programs may be conveyed electronically via any medium, for example a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

[0081] Features, integers or characteristics described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other 15 aspect, embodiment or example described herein unless incompatible therewith.

[0082] It will be also be appreciated that, throughout the description and claims of this specification, language in the general form of "X for Y" (where Y is some action, activity or step and X is some means for carrying out that action, activity or step) encompasses means X adapted or arranged specifically, but not exclusively, to do Y. [0083] The description of the preferred embodiments of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or to limit the invention to the forms disclosed. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiment disclosed, but covers modifications within the scope of the present invention as defined by the appended claims.

Claims (15)

1. CLAIMS1. Apparatus for sensing a target gas species, the apparatus comprising: an optical source including a tunable laser diode which is configured to generate a laser beam in accordance with a driving signal; a control unit for generating a control signal for 10 modulating the driving signal applied to the tunable laser diode; at least one optical beam splitter for receiving the laser beam from the optical source and for splitting the laser beam into a plurality of output beams; a gas sensor interface having a plurality of output ports, 15 each port being adapted to direct output beams from the at least one optical beam splitter to a respective one of a plurality of gas sensor cells via a respective optical waveguide; and at least one photoreceiver module, each photoreceiver module having at least one photodetector and a signal processor, wherein the gas sensor interface further includes a plurality of input ports, each input port being adapted to direct input beams from respective ones of the plurality of gas sensor cells to a corresponding one of the photodetectors, each input beam corresponding to a portion of a respective output beam after having traversed the respective gas sensor cell and the attenuation of the input beams having a predetermined correlation to the concentration of the target gas species in the gas sensor cells, and wherein the signal processor for each photoreceiver module 30 operates to determine the concentration of the target gas species from the characteristics of the input beam detected at each photodetector in the photoreceiver module.
2. 2. The apparatus of claim 1, wherein the control unit is further configured to store data for a given control unit and optical source pairing.
3. 3. The apparatus of claim 2, wherein the stored data is stored as a lookup table and/or equation variables.
4. 4. The apparatus of any one of claims 1 to 3, wherein a given M pairing of the optical source and the control unit is configured with a predetermined calibration profile that corresponds to a characteristic response of the apparatus to the presence of the target gas at a plurality of known different concentrations.
5. 5. The apparatus of claim 4, wherein the control unit includes a memory and wherein the calibration profile is stored in the memory as a calibration table or equation variables.
6. 6. The apparatus of claim 4 or claim 5, wherein the control unit is in communicative connection with the optical source and with the at least one photoreceiver module, and wherein the control unit is further configured to transmit calibration profile information to the at least one photoreceiver module.
7. 7. The apparatus of claim 6, wherein the control unit is further configured to transmit at least one of reference signals and/or synchronization pulses to the at least one photoreceiver module.
8. 8. The apparatus of claim 6 or claim 7, wherein the signal processor for each photoreceiver module further operates to generate sensor data corresponding to the determined concentration of the target gas species, and wherein the control unit is further configured to receive said sensor data.
9. 9. The apparatus of any one of claims 6, 7 or 8, wherein a local area network, LAN, communication protocol is used to encapsulate data transferred between the control unit and at least one photoreceiver module.
10. 10. The apparatus of claim 9, wherein the LAN communication 10 protocol is an Ethernet protocol.
11. 11. The apparatus of any one of the preceding claims, wherein the optical beam splitter receives the laser beam via a launch optical waveguide.
12. 12. The apparatus of any one of the preceding claims, wherein the tunable laser diode generates a laser beam having a characteristic wavelength in the infrared.
13. 13. A method for sensing a target gas species comprising: generating, at an optical source including a tunable laser diode, a laser beam in accordance with a driving signal; generating a control signal for modulating the driving signal applied to the tunable laser diode; splitting the laser beam into a plurality of output beams; directing each of said output beams via respective output ports to a respective one of a plurality of gas sensors; receiving input beams from respective ones of the plurality of gas sensors, each input beam corresponding to a portion of a 30 respective output beam after having traversed the respective gas sensor, the attenuation of the input beams having a predetermined correlation to the concentration of the target gas species in the gas sensor; directing each of said input beams to a corresponding one of a plurality of photodetectors; and determining the concentration of the target gas species from the characteristics of the input beam detected at each 5 photodetector.
14. 14. The method of claim 13 further comprising: configuring a given pairing of the optical source and the control unit with a predetermined calibration profile that corresponds to a characteristic response of the apparatus to the presence of the target gas at a plurality of known different concentrations.
15. 15. The method of claim 13 or claim 14 further comprising: establishing a communicative connection with the at least one photodetector, and transmitting calibration profile information to the at least one photodetector.Amendments to the claims have been filed as followsCLAIMS1. Apparatus for sensing a target gas species, the apparatus comprising: an optical source including a tunable laser diode which is configured to generate a laser beam in accordance with a driving signal; a control unit for generating a control signal for 10 modulating the driving signal applied to the tunable laser diode; at least one optical beam splitter for receiving the laser beam from the optical source and for splitting the laser beam into a plurality of output beams; a gas sensor interface having a plurality of output ports, In 15 each port being adapted to direct output beams from the at least one optical beam splitter to a respective one of a plurality of CD gas sensor cells via a respective optical waveguide; and (:) a plurality of photoreceiver modules, each photoreceiver 1-- module having at least one photodetector and a signal processor, wherein the gas sensor interface further includes a plurality of input ports, each input port being adapted to direct input beams from respective ones of the plurality of gas sensor cells to a corresponding one of the photodetectors, each input beam corresponding to a portion of a respective output beam after having traversed the respective gas sensor cell and the attenuation of the input beams having a predetermined correlation to the concentration of the target gas species in the gas sensor cells, wherein the control unit is in communicative connection with 30 the optical source and the photoreceiver modules and is further configured to broadcast reference channel and system calibration information to each of the photoreceiver modules, wherein the signal processor for each photoreceiver module operates to determine the concentration of the target gas species from: the characteristics of the input beam detected at each photodetector in the photoreceiver module; the reference channel information; and the system calibration information obtained from the control unit, wherein the signal processor further operates to generate sensor data corresponding to the determined concentration of the target gas species, and wherein the control unit is further configured to receive said sensor data from each photoreceiver module and to collate the sensor data into one or more reports concerning the concentration of the target gas at respective gas sensor cells.V)15 2. The apparatus of claim 1, wherein the control unit is further configured to store data for a given control unit and optical source pairing.C1- 3. The apparatus of claim 2, wherein the stored data is stored as a lookup table and/or equation variables.4. The apparatus of any one of claims 1 to 3, wherein the system calibration information broadcast by the control unit is a predetermined calibration profile that corresponds to a characteristic response of the apparatus to the presence of the target gas at a plurality of known different concentrations for a given pairing of the optical source and the control unit.5. The apparatus of claim 4, wherein the control unit includes a memory and wherein the calibration profile is stored in the memory as a calibration table or equation variables.6. The apparatus of claim 5, wherein the control unit is further configured to transmit at least one of reference signals and/or synchronization pulses to the photoreceiver modules.7. The apparatus of any one of the preceding claims, wherein a local area network, LAN, communication protocol is used to encapsulate data transferred between the control unit and the 10 photoreceiver modules.8. The apparatus of claim 7, wherein the LAN communication protocol is an Ethernet protocol.9. The apparatus of any one of the preceding claims, wherein LC) the optical beam splitter receives the laser beam via a launch 1-- optical waveguide.CD 10. The apparatus of any one of the preceding claims, wherein the tunable laser diode generates a laser beam having a 1-- characteristic wavelength in the infrared.11. The apparatus of any one of the preceding claims, wherein the gas sensor interface is further adapted to direct output 25 beams from the at least one optical beam splitter to at least one further gas sensor cell via a respective further optical waveguide, the apparatus further comprising: a further photoreceiver module, said further photoreceiver module having at least one further photodetector and a further 30 signal processor, the input beams from the at least one further gas sensor cell being directed to a corresponding one of the at least one further photodetectors, wherein the control unit is further configured to establish communicative connection with the further photoreceiver module and to broadcast the reference channel and the system calibration information to the further photoreceiver module; wherein the further signal processor operates to determine the concentration of the target gas species from: the characteristics of the input beam detected at each photodetector in the photoreceiver module; the reference channel information; and the system calibration information obtained from the control unit, wherein the further signal processor further operates to 10 generate further sensor data corresponding to the determined concentration of the target gas species, and wherein the control unit is further configured to receive said further sensor data from the further photoreceiver module and to collate the further sensor data into one or more reports In 15 concerning the concentration of the target gas at respective further gas sensor cells.CD 12. A method for sensing a target gas species comprising: CD generating, at an optical source including a tunable laser 1- diode, a laser beam in accordance with a driving signal; generating, at a control unit, a control signal for modulating the driving signal applied to the tunable laser diode; splitting the laser beam into a plurality of output beams; directing each of said output beams via respective output ports to a respective one of a plurality of gas sensors; receiving input beams from respective ones of the plurality of gas sensors, each input beam corresponding to a portion of a respective output beam after having traversed the respective gas sensor, the attenuation of the input beams having a predetermined correlation to the concentration of the target gas species in the gas sensor; directing each of said input beams to a corresponding one of a plurality of photodetectors, each photodetector being provided in a respective one of a plurality of photoreceiver modules, each photoreceiver module having a signal processor; establishing a communicative connection between the control unit and each of the photoreceiver modules; broadcasting, from the control unit, reference channel and system calibration information to each of the photoreceiver modules; determining the concentration of the target gas species from the characteristics of the input beam detected at each 10 photodetector, the reference channel information and the system calibration information obtained from the control unit and generating sensor data corresponding to the determined concentration of the target gas species, said determination and generation operations being performed at the signal processor of n 15 the photoreceiver module in which said photodetector is provided; and CD at the control unit, receiving said sensor data from each CD photoreceiver module and collating the sensor data into one or 1- more reports concerning the concentration of the target gas at respective gas sensor cells.13. The method of claim 12, wherein the system calibration information broadcast by the control unit is a predetermined calibration profile that corresponds to a characteristic response of a given pairing of the optical source and the control unit to the presence of the target gas at a plurality of known different concentrations.14. The method of claim 12 or claim 13 further comprising: providing at least one further gas sensor cell; providing a further photoreceiver module, said further photoreceiver module having at least one further photodetector and a further signal processor, the input beams from the at least one further gas sensor cell being directed to a corresponding one of the at least one further photodetectors, establishing communicative connection between the control 5 unit and the further photoreceiver module; from the control unit, broadcasting the reference channel and the system calibration information to the further photoreceiver module; determining the concentration of the target gas species 10 from: the characteristics of the input beam detected at each photodetector in the photoreceiver module; the reference channel information; and the system calibration information obtained from the control unit and generating further sensor data corresponding to the determined concentration of the target gas species, said In 15 further determination and generation operations being performed by the further signal processor; and CD at the control unit, receiving said further sensor data from CD the further photoreceiver module and collating the further sensor 1- data into one or more reports concerning the concentration of the target gas at respective further gas sensor cells.