Patent Description:
In a wide variety of systems, it is necessary to align a transmitter and receiver with respect to one another such that the output of the transmitter is successfully detected at the receiver. As an example of this, a mechanism or device may be provided for the alignment of system components along a line of sight. The alignment device may be coupled to the transmitter or to the receiver, or in some cases multiple co-operating alignment devices are provided, one for each transmitter and receiver. An alignment device associated with a transmitter aligns the line of sight through the alignment device and onto a given target point, area or aperture for receipt by a receiver. The receiver may be located at a fixed distance from the origin, this being defined as the starting viewpoint along the line of sight; i.e. the point of emission of the transmitter. The transmitter emits one or more of material, electromagnetic waves and acoustic waves towards the receiver. The receiver includes a detector that is capable of detecting the emitted material, electromagnetic waves and/or acoustic waves. The detector generates a signal that is proportional to at least one property of the incident emission, such as intensity. However, many detectors have a limited field of view and any material, electromagnetic waves and/or acoustic waves that fall outside the field of view will not be detected. Such emissions represent a loss of signal. Loss of signal is undesirable and so in many systems it is desirable to maximise the amount of emission that falls within the field of view of the detector. The region within the detector's field of view may be referred to as a 'target' or 'target region'.

One example of a system requiring precise alignment is an industrial gas analyser system for performing laser absorption spectroscopy. In such a system, a laser beam source (transmitter) can be mounted onto one side of an industrial process gas pipe or duct or chamber to point towards a receiver aperture (target) on another part of the pipe, duct or chamber, such that the laser beam travels across the process pipe, duct or chamber (and hence through the process gas) and enters the aperture. The receiver, which incorporates a light detector, generates a signal that is usable for analysis purposes of the contents of the process gas. Gas measurements using tunable lasers, which are scanned across gas absorption lines in order to obtain useful parameter information such as the fractional component of the gas of interest or process temperature information, may typically be used to optimise and control production processes, combustion processes or monitor pollutants for continuous emission monitoring systems (CEMS) and hence are important for minimising pollution from industrial processes and optimal usage of finite natural resources.

In this exemplary context, an alignment device may alternatively or additionally be used at a receiver end of the line of sight, to align the receiver and detection means with the laser light source. In addition, one or more alignment devices could also be used to align a laser light source and/or receiver, or light source and detector combined unit with a retro-reflector located at another location within the duct.

A number of alignment devices already exist that allow adjustment of the pointing direction of a line of sight. For discussion of these devices, it is convenient to visualise a line of sight as the direction of a unit vector n that is normal to a given plane of reference of the alignment device. <FIG> illustrates the principle: as the reference plane <NUM> is rotated in space about either of the two orthogonal axes x, y contained within the reference plane <NUM>, the line of sight will alter its pointing direction in space in either azimuth or elevation. The third rotational degree of freedom is given by rotating the reference plane <NUM> about the line of sight itself. This does not result in the line of sight changing its pointing direction in space, unless the line of sight is not normal to the plane of rotation in the first instance. In practice, however, this idealisation does not hold for existing alignment devices as adjustment of the pointing direction causes some translation of the line of sight with respect to the centre of rotation, in which case the line of sight will describe a cone as the plane is rotated, which is undesirable. This is inevitable in any real world system due to mechanical tolerances.

In the field of optics, kinematic mounts are often used for altering the angle of beam steering mirrors or other optical components. These mounts have two rotational degrees of freedom and the kinematic design means that they are not over or under constrained, giving a highly deterministic and repeatable movement. However, this kinematic design requires that the optical component cannot be rotated about its centre meaning that any adjustment in rotation also gives a translation, effectively moving the apparent origin of the beam. In fact, kinematic mounts are generally used in pairs to give both angular and translational control of optical beams.

Another problem with kinematic mounts is that they are difficult to lock into position due to their precise nature. For the applications for which they are designed, predominantly laboratory conditions, this is acceptable, but they are not suitable for industrial applications where high levels of vibration and large temperature changes are often present.

Some industrial gas analysers use a large cross-section elastomeric component such as an o-ring <NUM> to provide both a spring and a seal, as shown in <FIG>. O-ring <NUM> is differentially compressed using an adjustment means which may be, for example, four nuts and bolts <NUM> between a mounting flange <NUM> and a fixed base flange <NUM>, such that the angle of the plane of mounting flange <NUM> can be altered relative to the plane of the fixed base flange <NUM>. The apparatus can be locked in a desired configuration using, for example, a further four screws (not shown) driven against base flange <NUM>, giving one advantage for industrial use. Other suitable configurations for the adjustment means will be readily apparent to a skilled person having the benefit of the present disclosure.

A drawback of the alignment device of <FIG> is that the point of rotation of mounting flange <NUM> is indeterminate. When the adjustment means is adjusted, there is no guarantee that the centre of rotation will lie on the axis of the alignment device due to many variable mechanical stresses and frictions between parts. Also, if all four nuts and bolts <NUM> are driven equally in the same direction, no rotation occurs and o-ring <NUM> is simply compressed or relaxed uniformly. This changes how the alignment device of <FIG> subsequently responds to any given adjustment. This change of response according to the current state of compression of the o-ring makes it difficult to consistently achieve a reliable alignment using an alignment device such as shown in <FIG>.

Another drawback of the alignment device of <FIG> is that, over time, the adjustment device can become solid or slack at the extremes of o-ring compression. Where the alignment device is deployed as part of a process gas analyser, a slack o-ring can cause a gas leak. In addition, elastomeric components are subject to creep over time, which can lead to a gradual change in the line of sight and hence cause the system to become misaligned.

Moreover, several factors in the design of the alignment device of <FIG> inherently limit the range of adjustment. The use of an elastomeric component (o-ring <NUM>) tends to give a restricted amount of travel, even in the case of o-rings having large cross sections. Also, the nut and bolt adjuster arrangement becomes unusable as the angle between mounting flange <NUM> and base flange <NUM> increases. In practice, these factors limit the angular adjustment of the line of sight to within a cone with a half angle of approximately <NUM> degree when using an alignment device such as shown in <FIG>. It is also necessary to use a large cross-section elastomeric component to give an acceptable range of adjustment and this exacerbates the problem of creep associated with elastomers mentioned above, potentially causing drift in stability in the long term.

Another known alignment device that is used on industrial gas analysers is the bellows arrangement shown in <FIG>. This arrangement includes bellows <NUM>, adjustment and locking nuts <NUM>, mounting flange <NUM> and base flange <NUM>. A standard flange seal <NUM> is provided to seal the interface between mounting flange <NUM> and base flange <NUM>. Flange seal <NUM> may be, for example, an o-ring or gasket.

<CIT> discloses a lens mounting unit for a camera or enlarger, the unit comprising a lens system mounted in a lens carrier member for universal movement at one end of a casing by means of a ball and socket connection said casing being rigid and capable of being fixed at its other end to a camera or enlarger, the arrangement enabling the lens system to be tilted about an axis at right angles to the longitudinal axis of the unit and swung about an axis at right angles to the tilt axis.

<CIT> discloses a mount for an optical device having <NUM> degrees of freedom; three translations along the x, y and z axes and three pivotal or rotational movements about each of the axes. A semi-spherical drive means which is rotatably journaled in a complimentary semi-spherical fixed mount. The drive means defines an optical axis within having interior threads. A first carrier is threaded into the drive means and translated along the z axis by rotation of the spherical drive means. A second carrier is mounted for x, y translation within the first carrier. Pivotal or rotational movement about the x and y axes may occur between the first carrier of the drive hemisphere, or between the drive hemisphere and the fixed mount. Roll movement about the z axis occurs between the first carrier and the fixed mount.

<CIT> discloses a plate positioning mechanism wherein the air wedge angle between the specimen and an optically flat plate is adjusted by pivoting one of the plates about the centricity of its surface facing the other plate.

<CIT> discloses lens mountings for optical projects such as photogrammetric stereo plotters and similar devices and it relates more particularly to improvements in the mechanism for tilting the optical axis of the lens held therein.

<CIT> discloses the technical scheme which is capable of realizing aiming, positioning and installing of an infrared thermometric optical probe on a small furnace cover of a coke oven flue. The technical scheme comprises a set of installing device and a set of aiming lever, wherein the integrated installing device is of a centripetal ball joint structure, and is capable of causing the infrared thermometric optical probe to aim and position a nose brick center for thermometry, and the aiming lever is an auxiliary aiming tool, and is capable of causing the measuring pointing direction of the installing device to aim the nose brick center in advance before the infrared thermometric optical probe is arranged; a heat insulation cooling measure is carried out on the small furnace cover, and thus installation personnel can perform aiming adjustment and locking operation by hand; the infrared thermometer arranged on the small furnace cover is facilitated to be influenced less by the heat conduction from the bottom up.

<CIT> discloses an across-the-stack gas analyzing spectrometer having a radiation source assembly including a cylindrical tube having, in succession from its outer end toward the stack end a radiation emission assembly, a first lens assembly, and an AOTF assembly, all in optically aligned arrangement because of the circular perimeter of the elements in the circular tube, the arrangement also including a projecting second lens nozzle received in an air window assembly which forms a venturi with the second lens, the air window having a ball joint arrangement for easy alignment of the directed beam, and also including a small diameter air window tube through which clean air is directed into the stack through a larger diameter stack opening.

<CIT> discloses a compact and lockable ball joint mechanism. Optical mounts are presented. Both stationary plate and movable plate have a partial-spherical hole or conical hole. Facing spacing aligns the bases of the partial-spherical holes or conical holes; a space adjustable cavity is formed. An external-spherical circumference shape optical element carrier plate fits and mates in the space adjustable combined cavity, forming a ball joint mechanism, or an external-column circumference and edges chamfered optical element carrier plate fits and mates in the space adjustable combined internal-spherical shaped cavity forming a tiltable and swivellable joint pair mechanism. A removable tooling for exporting a tilting and rotating movement to the optical element carrier plate are presented. ; Locking ring pushes the movable plate to adjust the combined cavity and locking the optical element carrier plate and to lock optical element that is carried thereby.

<CIT> discloses an electron microscope adapted to enable spectroscopic analysis of a sample. A parabolic mirror having a central aperture through which the electron beam can pass. The mirror focuses laser illumination from a transverse optical path onto the sample, and collects Raman and/or other scattered light, passing it back to an optical system. The mirror is retractable (within the vacuum of the electron microscope) by a sliding arm assembly.

<CIT> discloses a sleeve having an eyepiece side portion rested against the outer wall of an eyepiece tube. The housing side portion of the sleeve fits around the inner wall of an opening in the tube housing of the eyepiece tube.

<CIT> discloses a tilting standard lamp having a telescopic column outside tube connected to a lighting head. The inner fixed tube is connected to the ball joint within the base. The electric cable to the illuminating head is a removable helical coil with the column and it is taken outside via a tension compensator and through the ball joint. The telescopic column on the base can be fixed into vertical position and it can be readily rotates about its axis by a simple handle even if the lighting fitting is hot. It can be extended and rotated into any required direction or angular position without moving the base.

<CIT> discloses a device for interconnecting optical units includes three elements, namely a pair of carriers and an intermediate body having passages defining an optical path in the device. At least two of the three elements contains an optical unit. A hinge connects one of the carriers to the other carrier and/or the intermediate body for changing the shape and possibly the length of the optical path through the device. One of the carriers of the intermediate body is slidable transversely of the other elements for also changing alignment of the elements and consequently of optical units mounted therein.

Bellows <NUM> can be used to account for misalignment in couplings between rotating shafts and the bellows concept has been adapted for use to adjust the line of sight of optical devices. The bellows <NUM> has no elastomeric, or indeed any, spring and so once the adjustment and locking nuts <NUM> are slackened, the system is unconstrained until re-locked into a given position. This means that locking it without at the same time changing its position is difficult. The bellows arrangement of <FIG> suffers from the same indeterminacy of the centre of rotation as the elastomeric spring design shown in <FIG>, for the same reasons as outlined above. Again, if all adjustment and locking nuts <NUM> are moved in one direction equally, the bellows <NUM> simply compresses or extends without rotation, changing its response characteristics. The bellows <NUM> inherently gives a greater range of adjustment than an elastomeric spring like o-ring <NUM>, but this is limited by the fact that the studding on which it is supported can only work with a limited angle between mounting flange <NUM> and base flange <NUM>.

Another drawback of the bellows concept is that the studding which carries the adjusting and locking nuts <NUM> must also be a strong enough cantilever to carry the weight of anything attached to the alignment device because the bellows itself is not a structural element. This tends to make the entire device relatively large and bulky.

In view of this, it is clear that there remains a need for an alignment device that can predictably and repeatably align a transmitter and receiver system.

Aspects of the invention are set out in the accompanying claims.

A first aspect provides an alignment device according to claim <NUM>.

A second aspect of the invention provides a system according to claim <NUM>.

A third aspect of the invention provides a method of aligning a first apparatus with respect to a second apparatus according to claim <NUM>.

Embodiments of the present invention are described below, by way of example only, with reference to the following drawings in which:.

Alignment devices <NUM>, <NUM>' and <NUM>" according to certain embodiments are shown in <FIG>, <FIG> and <FIG>. <FIG> shows a first embodiment and <FIG> and <FIG> show cross sectional schematics of second and third embodiments <NUM>' and <NUM>", respectively. Common features in all three embodiments are given like reference numerals and, in the interests of brevity, are described in detail only once in the following detailed description. References in the following detailed description to 'alignment device <NUM>' are understood to apply equally to alignment devices <NUM>' and <NUM>" unless otherwise expressly indicated.

Alignment device <NUM> is discussed in the following generic description in the context of optical alignment of a transmitter and a receiver. In some embodiments, this is a direct "line of sight" optical alignment, but it will be appreciated that an optical path may include reflective surfaces, so it is not essential for a direct line of sight. The alignment device has a number of applications in systems where alignment control can help to achieve accurate measurement of transmission through a medium, such as for use in laser spectroscopy in an industrial gas analyser system. However, it will be appreciated that alignment device <NUM> is not limited to use with a laser spectroscopy gas analysis system. In particular, alignment device <NUM> will find utility in any system in which it is desirable to align one apparatus with respect to another in order to enable transmission between the two apparatuses. Moreover, the transmission is not limited to optical radiation; electromagnetic radiation, acoustic and matter transmissions are also contemplated. The transmitter may be configured to emit one or more of optical radiation, electromagnetic radiation, acoustic transmissions and matter transmissions and the receiver may be configured to detect one or more of optical radiation, electromagnetic radiation, acoustic transmissions and matter transmissions. Typically the transmitter and receiver are arranged substantially in opposition to one another, although reflected signals (such as electromagnetic radiation or audio transmissions) are also envisioned.

Alignment device <NUM> includes a mount <NUM> that sits within a housing <NUM>. In the illustrated embodiments, mount <NUM> comprises a hollow body having a central through bore whose longitudinal axis defines a "line of sight" for an optical transmitter or receiver when connected to the mount. In the illustrated embodiments, a tubular first part of the mount <NUM> that includes a connection point for a transmitter or receiver has a circular cross-section, but this is not essential, and tubes and non-tubular mounting portions having any other cross sectional shape are also contemplated for mount <NUM>. In some embodiments, the cross-sectional shape of a central through bore of mount <NUM> is chosen such that it co-operates with a device (e.g. a tunable diode laser) that is to be held in mount <NUM>. However, the mount <NUM> may have a threaded end connection or another interconnection or coupling means <NUM> on an interior or exterior surface for connecting devices or device holders. The coupling means <NUM> for connecting to devices may also be separate to mount <NUM> and integrated onto mount <NUM> by suitable coupling means and sealed to mount <NUM> if required by sealing means <NUM> such as at least one o-ring. The coupling means may also include sealing means <NUM> such as an o-ring or gasket for sealing to the connecting device.

Housing <NUM> is secured to base flange <NUM> by a securing means, such as by using nuts and bolts. Housing <NUM> may have different dimensions and securing means to suit various base flange <NUM> attachment arrangements. Additionally, housing <NUM> may comprise more than one component to facilitate the integration onto base flange <NUM>. A suitable securing means such as secured bolts or a threaded engagement means will readily be chosen by the skilled person. Optionally, a conventional flange seal <NUM> may be provided between housing <NUM> and base flange <NUM> if required. It will be readily apparent to a skilled person having the benefit of the present disclosure that some of the features described here could be integrated into fewer or more components for convenience or for varying end user requirements, whilst still fulfilling the same essential functions described. For example, housing <NUM> and collar <NUM> could be integrated into a single component and a suitable constraining means such as a circlip or attachment ring (not shown) could be used to stop translational movement along the Z-axis.

As illustrated in <FIG>, the end of the mount <NUM> that is proximate to the base flange <NUM> is fashioned such that it contains a set of curved bearing surfaces. The curved bearing surfaces of the mount <NUM> are preferably shaped such that they act to centre the longitudinal axis of the mount within housing <NUM>. In one embodiment, each of the curved bearing surfaces is part of a spherical surface having its centre of curvature at the centre of rotation of the mount. In the illustrated embodiment, each of these bearing surfaces is defined by a spherical sector centred at the same point on the longitudinal axis of the alignment device, but other suitable smooth, continuous, curves (such as parabolic) may be used instead. Various, appropriate materials may be used for the mount <NUM>, housing <NUM>, bearing <NUM>, collar <NUM> or other components for optimal application suitability. The criteria for choosing appropriate materials may include one or more of the following: thermal expansion coefficient, chemical resistance, mechanical strength, wear resistance, coefficient of friction, material compatability, optical properties (such as emissivity and/or reflectivity) and achievable surface finish.

Typically, a ferrous alloy such as stainless steel of varying composition may be chosen for mechanical strength and/or corrosion resistance for any surfaces exposed to the process fluid or ambient conditions. Low thermal expansion coefficient stainless steel alloys may be chosen for applications where large temperature changes are seen. Ideally, low friction contact (due to material and surface finish) with high wear resistance should be present at any sliding surfaces such as at the interface of the bearing <NUM> and mount <NUM> and the housing <NUM> and mount <NUM>. Optical properties influenced by material and surface finish may be important due to the generation of background radiation and stray reflections, which may cause interference in an optical measurement.

Various, appropriate surface coatings may be used for the mount <NUM>, housing <NUM>, bearing <NUM>, collar <NUM> or other components for optimal application suitability. The criteria for choosing appropriate surface coatings may include one or more of the following: thermal expansion coefficient, chemical resistance, mechanical strength, wear resistance, coefficient of friction, material compatability, optical properties (such as emissivity and/or reflectivity) and achievable surface finish. Examples of these are polytetrafluoroethylene (PTFE) for reduced friction, PTFE or tantalum for increased chemical resistance and titanium nitride TiN for increased wear resistance. The coatings are ideally expansion coefficient matched to the substrate to minimise internal tension and risk of delamination. In addition, specular reflectivity may be reduced by increasing the surface roughness and/or decreasing the intrinsic reflectivity of the coating material at the wavelength range of interest.

The curved end of the mount is secured within housing <NUM> such that it cannot translate in any of the x, y or z directions. The curved end of the mount is secured by translation restraining means <NUM>, which in one particular embodiment comprises as a spring and bearing. However, translation restraining means <NUM> is not limited to this, and any suitable means known to the skilled person that removes any free play of mount <NUM> can be used for translation restraining means <NUM>. For example, the translation restraining means may alternatively comprise a set of bearing surfaces arranged to cooperate with the curved bearing surfaces of the body portion of the mount. The curved bearing surfaces bear against the translation restraining means <NUM>. This arrangement allows the necessary rotation of mount <NUM> to facilitate beam alignment whilst simultaneously preventing translation of mount <NUM> with respect to housing <NUM>.

In some embodiments, an optional flexible sealing means is provided. This could be located anywhere within housing <NUM>. For example, alignment device <NUM> has a flexible sealing means <NUM> located at the curved end of mount <NUM> that is proximate to base flange <NUM>, and alignment devices <NUM>' and <NUM>" both have a flexible sealing means <NUM> located at the curved end of mount <NUM> that is distal from base flange <NUM>. Flexible sealing means <NUM> may be, for example, an elastomeric seal or metal seal. Embodiments having multiple seals are also contemplated. These embodiments may have multiple elastomeric seals, multiple metal seals or a combination of at least one elastomeric seal and at least one metal seal. Flexible sealing means <NUM> is placed within a suitable feature within housing <NUM> and/or collar <NUM> and/or mount <NUM>. A suitable feature may be a recess. Wherever it is located, flexible sealing means <NUM> is placed such that translation restraining means <NUM> acts to push the mount <NUM> against the flexible sealing means <NUM>, and preferably to push the spherical base portion of the mount <NUM> against the flexible sealing means <NUM>. This provides a gas tight seal between mount <NUM> and housing <NUM> and/or collar <NUM>. This is desirable where alignment device <NUM> is deployed in an industrial gas analyser system, since it is desirable to prevent process gas from escaping the process stack and it is desirable to know which gas is being analysed. Specifically, flexible sealing means <NUM> prevents fluid leaking either into or out of the process stack whilst alignment device <NUM> is in use. As noted above, in some embodiments, the device includes multiple flexible sealing means such as one or more elastomeric seals and/or one or more metal seals or combinations thereof, in order to increase sealing efficiency and/or to allow a seal to be maintained in case of an individual seal failure. Such multiple sealing is not usefully employable in the case of the discussed prior art.

In some embodiments, such as the embodiment illustrated in <FIG>, alignment device <NUM>" includes an optional purging means such as a purge fluid inlet <NUM> or <NUM> and outlet <NUM> or <NUM> to allow the internal volume of alignment device <NUM> to be flushed by a purge fluid, such as nitrogen or air. Alternatively, the inlet or outlet may be either end of the mount <NUM>. One or more of inlet <NUM>, <NUM> or either end of mount <NUM> may be blanked off as required. As a further alternative, the internal volume may be sealed and/or the internal volume may be scrubbed (chemically filtered) using a scrubber rather than purged to eliminate any unwanted compounds. Although no purging means is shown in either of <FIG> or <FIG>, it will be appreciated that alignment device <NUM> and/or alignment device <NUM>' may include purging means as described above.

As shown in <FIG> and <FIG>, alignment device <NUM>' and alignment device <NUM>" additionally incorporate at least one optical element <NUM>. Optical element <NUM> is optional and alternative non-illustrated embodiments of alignment device <NUM>' and/or <NUM>" that do not include any optical element(s) are also contemplated. In addition, although optical element <NUM> is not shown in <FIG>, it will be appreciated that alignment device <NUM> of <FIG> may include at least one optical element as described in the following.

Optical element <NUM> may typically be composed of any combination of at least one of a window, diffuser, lens and reflective element, any of which may be used to re-direct and/or re-shape the beam. The reflective element may be a reflective surface. The lens may be a refractive lens. Any window used may have a wedge shaped cross section. Any of the aforementioned optical elements may have an anti-reflective coating to minimise reflective losses and also to minimise the interference effects from etalons (optical fringes) in laser based measurement systems. This at least one optical element may be positioned anywhere within the alignment device including, for example, within mount <NUM> and/or housing <NUM> and/or connecting means <NUM>. Due to the presence of particulates and potential contaminants, as well as thermal issues, any optical element in contact with the gas may need to be purged. Alignment device <NUM> may also incorporate suitable purging means for the at least one optical element including inlet and outlet purge means or may be inserted within a larger, separate purged feature. In some embodiments, the optical element purge means may be the same as the internal volume purge means (for example <NUM>, <NUM>, or either end of the mount <NUM>).

The purge fluid may be monitored using a fluid flow device and/or a flow alarm and/or a pressure alarm to indicate cessation or fluctuation of purge. The flow alarm may be a pressure monitoring system. In the case of spectroscopic absorption measurements, such purge fluid or scrubbed atmosphere will be optimally chosen so as not to absorb electromagnetic radiation in the wavelength band of interest.

In some embodiments, alignment device <NUM> also includes a rotational restraining means <NUM> which prevents rotation of the tube about its own axis. This only leaves two rotational degrees of freedom, giving azimuth and elevation adjustment for the line of sight which is, nominally, along the tube axis. In the illustrated embodiments, rotation restraining means <NUM> comprises a protrusion or pin that engages within an indentation or narrow slot near or at the curved end of the mount <NUM> (alignment device <NUM>, <FIG>) or it may comprise a protrusion in the mount <NUM> engaging in a slot in the housing <NUM> or collar <NUM> (alignment devices <NUM>' and <NUM>", <FIG> and <FIG>). However, other rotational restraining means known to the skilled person may be used instead of or in addition to a pin/slot configuration.

The alignment of mount <NUM> relative to housing <NUM> of alignment device <NUM> is adjusted and locked by adjustment means <NUM>. In the illustrated embodiments, adjustment means <NUM> comprises four screws or bolts that are equally spaced around the circumference of the tubular mounting portion seated in a collar <NUM> that extends for some length parallel to the longitudinal axis. The collar <NUM> may be secured to the housing <NUM> by appropriate securing means such as by using bolts into threaded holes in the housing <NUM> or vice versa. In some embodiments, the collar <NUM> may be sealed by suitable sealing means <NUM> to the housing <NUM>, such as by using an elastomeric or metal o-ring or gasket. In one embodiment collar <NUM> includes connection means for releasably connecting a transmitting or receiving apparatus to mount <NUM>. The four adjustment screws <NUM> in the collar <NUM> include a first pair of opposed screws and a second pair of opposed screws, where the second pair is arranged at <NUM> degrees to the first pair around the circumference of the tubular mounting portion. Other adjustment means known to the skilled person can be used instead of or in addition to screws or bolts. In addition, in some embodiments, at least one goniometric scale may be added so that the angle of mount <NUM> may be indicated for at least one of the azimuth and elevation. This may take the form of graduated marks on the adjustment screws with a spacing that corresponds to a given angular increment at a given position, for instance. The adjustment screws act in a line perpendicular to the longitudinal axis Z of alignment device <NUM> when the device is centralized. Flat surfaces may be provided on the tube for the screws to act upon, meaning that adjustment in one angle does not alter that set in the other. The screws can only push, meaning that the opposite screw must be wound clear when its counterpart is pushing mount <NUM>. When the desired position is reached, the unwound screw is wound back, locking the device without altering its position. It will be appreciated that more or fewer than four screws can be provided, and at least two adjustment screws are used in an arrangement that allows both push and pull via the same adjustment means.

Optionally, the screws may be chosen to have a point contact with a domed end or to have a gimble mounted, pivoted flat end in order to increase the contact surface area. This reduces the risk of a high stress point of contact and hence reduces the risk of damage to the contact surface or mechanical creep.

Optionally, the screws may also constrain springs onto a fixed flat surface on the tube. Initially, all the screws are loosened and then the orientation of the tube is adjusted to the optimum position using two of the screws in orthogonal directions and then locked by securing with the other two screws. The locking of the screws into position or other suitable alignment means may optionally be reinforced by suitable adhesive means to minimise any loosening due to mechanical creep or vibrational effects.

In some embodiments, a flexible, protective sheath <NUM> may be used to cover the gap between the mount <NUM> and collar <NUM>, so as to prevent ingress of environmental contamination such as particulates or fluids. In some embodiments, such as those shown in <FIG> the protective sheath may also cover the adjustment means <NUM>.

In some embodiments, the alignment device <NUM> may incorporate or allow to be temporarily or permanently attached, an alignment verification means (not shown). This alignment verification means serves to verify that the origin and target are correctly aligned before securing into position. The alignment verification means may be optical or acoustic or other suitable means; for example, it could take the form of an optical scope temporarily inserted into the mount aligned along or parallel to the central axis of the mount focusing on an appropriate feature on the target. In addition, the target may also incorporate an enhanced feature, such as an optical or acoustic source or reflector to facilitate the alignment of the origin and target. This can involve a secondary optical source of divergent light built into a transmitter's alignment device, and a secondary detector built into a receiver's alignment device for receiving a part of the divergent beam. The intensity of the received beam can be measured during adjustment to identify the alignment that achieves optimal measured intensity, for an initial manual or automatic detection of approximate alignment. Fine adjustment can then be carried out using the primary optical source, such as a laser in the case of a laser spectroscopy system. A feedback signal from the receiver can be used to identify optimal alignment, and can be used for automated control of alignment and/or automated determination of optical alignment.

Alignment device <NUM> provides a very intuitive process to adjusting the azimuth and elevation angles of the line of sight. Specifically, adjustment in only two orthogonal angular degrees of freedom, e.g. azimuth and elevation, is permitted, where the adjustment of one angle neither causes a change in the other nor gives any significant translation of mount <NUM>. This makes it possible to set each angle independently of the other, greatly simplifying the alignment process. Furthermore, a set alignment position is not altered when adjustment means <NUM> are used to lock mount <NUM> in position, meaning that the process of locking mount <NUM> in the desired position does not affect alignment. Mount <NUM> is then securely fixed in the aligned position for as long as desired.

In contrast to prior art alignment devices, alignment device <NUM> also gives a rotation about a single known point. This facilitates easy alignment and also ensures reliable, repeatable alignment. This is because the line of sight of alignment device <NUM> always passes through the centre of rotation, meaning that adjustment of pointing direction in azimuth or elevation does not produce any translation of the origin of the line of sight.

Additionally, the adjustment mechanism itself is not limited by the angle of the tube and so large angular adjustment ranges can be achieved. The device may be compact and the tube gives a highly rigid mechanical mounting that is resistant to mechanical disturbance, e.g. due to vibrations. This makes alignment device <NUM> highly suited to use in a rugged environment such as is found around a process stack.

With reference to <FIG>, use of an alignment device according to embodiments described herein will now be illustrated in the exemplary context of a cross stack gas measurement, for example, for carbon monoxide (CO) monitoring for a combustion system. Combustion systems typically will burn carbon (coal) or hydrocarbon (natural gas and oil) based fuel using air (oxygen) as the oxidant. The heat produced by the reaction may be used to create steam to drive turbines for electricity generation or for process heating. In either case, the desire for minimal environmental pollution and wastage of natural resources and for economical operation require close control of the efficiency of the combustion process. If the combustion mixture has too much excess oxygen (O<NUM>), all of the fuel will be burnt, but some heat will be wasted by heating up excess, unreacted air. This condition may be monitored by using oxygen monitoring equipment such as a laser gas analyser or alternative technology such as in-situ or extractive zirconia or extractive paramagnetic technology. The alternative condition that may be present is too little excess oxygen. In this case, not all of the fuel is completely burnt and therefore, not all of the potential heat is generated. The early symptom of incomplete combustion will be CO generation, which may be measured by an in-situ tunable laser cross stack system or other extractive means such as by using a catalytic sensor or infrared based absorption system. For a controlled combustion process therefore, ideally, both the O<NUM> and CO levels should be monitored and manual or automatic feed-back systems used to control the amount of fuel and air supplied to the process. The following description will now concentrate on illustrating the device for use on a CO cross stack measurement using a tunable laser diode system. It will be readily understood by the skilled reader that this example application of the invention is purely exemplary, and that other uses of alignment devices according to embodiments described herein are possible.

<FIG> illustrates a typical cross stack arrangement <NUM>, whereby the tunable laser diode source <NUM> is positioned on one side of a stack <NUM> having process gas <NUM> flowing through it. A combined laser light receiver and detector <NUM> is situated on the opposite side of stack <NUM>. A first alignment device <NUM> according to embodiments described herein is used to align source <NUM> and a second alignment device <NUM> according to embodiments described herein is used to align detector <NUM>. Other embodiments in which only one alignment device is used, either to align source <NUM> or detector <NUM>, are also contemplated. Detector <NUM> is communicatively coupled to signal processing electronics <NUM> which are configured to process the output signal from detector <NUM> in order to determine e.g. a concentration of a particular measurand in the process gas. Suitable processing electronics are well known in the art and will not be described in further detail here.

Processing electronics <NUM> are also communicatively coupled to laser drive electronics <NUM>, which are in turn communicatively coupled to tunable laser diode source <NUM>. Laser drive electronics <NUM> are configured to operate tunable laser diode source <NUM> in the following manner.

Laser drive electronics <NUM> operate the tunable laser diode at a particular wavelength. The tunable laser diode line width is much less than the width of the absorption line that it is measuring. The tunable laser diode is typically maintained at a fixed, controlled temperature and the laser output wavelength is tuned or scanned across the wavelength range of interest by varying the current applied to the laser diode. As the laser light beam passes through the process gas, some of the beam will be attenuated at the absorption wavelengths corresponding to CO if any CO is present, as described by the Beer Lambert law. The amount of absorption will depend on ambient process conditions (pressure and temperature), path length, fractional concentration of CO and the extinction coefficient (fundamental absorption strength of the absorption line). From the amount of light absorbed, for a calibrated system, the fractional quantity of CO in the process gas may be deduced. The absorption profile may typically be measured by using a direct absorption system or wavelength modulated system, both of which are known to those skilled in the art and will not be described further here. Typical cross stack path length measurements may vary from about one metre to several tens of metres. Appropriate laser diode sources and light detectors may be chosen with regard to the desired working range and ambient conditions for the analyser and path length. As previously described, due to the presence of particulates and potential contaminants, as well as thermal issues, any optical element in contact with the gas may need to be purged. This purge gas will typically be nitrogen or air, but could also be any other suitable (preferentially non-CO containing) purge gas. In this case, the purge gas will typically be input into mount <NUM> via inlet <NUM>, sweep past optical element <NUM> and exit into the process stack (<NUM> being blanked off).

Alignment of a light source such as a tunable laser diode source <NUM> (origin) and light detector <NUM> (target) may not be a trivial task if the stack is several tens of metres wide and the respective base flanges that source <NUM> and detector <NUM> are attached to are not perfectly aligned either in angle or height, as is normally the case. This may necessitate the use of an alignment verification means as discussed earlier and also, in some cases, may alternatively or additionally require the incorporation of a diffusive element (diffuser) into the optics of the device. This is particularly the case for large path lengths (tens of meters). A diffuser will normalise the laser beam intensity over a larger area, such that it will be less critical to exactly align laser source <NUM> with detector <NUM>. The diffuser will also enhance immunity to vibrational effects, where a narrower beam might become misaligned with the target for the same angular displacement. The use of diffusers in cross stack measurements is known to those skilled in the art and will not be discussed further here. In one embodiment, a diffuser can be used during a preliminary alignment step to achieve an approximate alignment using a wider beam, and then removed for final adjustment and use in laser measurements.

Alignment device <NUM> will typically be fixed onto a base flange on the process stack wall. In some embodiments bolts are used to secure alignment device <NUM> to the process stack wall, although other securing means can be used instead. Alignment device is then adjusted and aligned with the target. This may involve the use or insertion of an alignment verification means as discussed earlier. The following will give an illustration of the alignment procedure, but is intended merely as an illustration of one potential alignment method and not intended as a limiting case.

With reference to <FIG>, in step <NUM> an alignment device according to embodiments described herein is fixed to the wall of a process stack. In some embodiments bolts are used to fix the alignment device to the wall of the process stack. However, any fixing means capable of reliably fixing the alignment device to the wall of the process stack can be used. By avoiding the need for precise alignment during this initial step, the initial fitting of the alignment device is relatively fast.

Once alignment device is secured in place, in step <NUM> an alignment verification means is used to check the alignment of the transmitter with respect to the receiver and in particular the alignment of the origin of the transmitter (i.e. the point of emission) with respect to a target region of the receiver. In the illustrated embodiment, the transmitter is a tunable diode laser and the receiver is a photodiode, but this is not essential and other transmitter and receiver means can be used instead.

The alignment verification means will be chosen by the skilled person according to the specifics of the system that is being aligned, but will in general comprise some means that is readily detectable by the person or automated system that is performing the alignment. In the illustrated case of an industrial process gas analyser, the alignment verification means can be a visible laser light source or other suitable visible feature. The output of the transmitter itself may be used as the alignment verification means in which case no ancillary alignment verification means is required.

The alignment verification means may be located within the target, along the main axis of the target and is used to check the alignment of the origin and target. In some embodiments, at least one of the transmitter and receiver includes attachment features to allow the attachment of the alignment verification means. The attachment features may comprise any suitable means known to the skilled person such as attachment bolts or screws. Where alignment verification means is a visible laser light source, it is preferable that the laser light source is attached to the transmitter and/or receiver in a manner such that the main optical axis of the transmitter and/or receiver is aligned with the main optical axis of the laser light source. This common main optical axis is preferably orthogonal to the attachment face.

In this illustrated example in which the alignment verification means emits visible laser light, checking may comprise inspection by eye to determine if the light is visible at the origin (appropriate eye protection must be used when performing a determination by eye using laser light). Alternatively, detection means such as a photodiode may be used to determine if the light is visible at the origin.

To assist the alignment process, a second, complimentary alignment verification means can be used. In the illustrated embodiment the second alignment verification means may comprise an optical scope with cross hairs that is inserted within the origin and along the main axis of the origin. Other suitable secondary alignment verification means will be apparent to the skilled person.

After checking the current alignment with the alignment verification means, in step <NUM> a determination is made as to whether the current alignment is satisfactory. A satisfactory alignment may be defined as an alignment that is within a tolerance of the system that is being aligned. In the illustrated embodiment, a satisfactory alignment may be defined as an alignment in which the laser light outputted by the alignment verification means is visible at the origin. In embodiments in which an optical scope is being used, a satisfactory alignment may be defined as an alignment where the cross hairs of the optical scope are aligned with the light output from the target light source. A satisfactory alignment may alternatively be defined by the intensity of the laser light incident on the origin being greater than a threshold intensity, which threshold intensity is defined with respect to the output intensity of the laser light of the alignment verification means. Laser gas analysers typically have a facility to indicate the intensity level of radiation received due to the laser beam at the detector and so a satisfactory alignment may be indicted by means of increased or maximal laser light intensity at the detector when aligned. Other ways of defining a satisfactory alignment will be apparent to the skilled person.

If it is determined in step <NUM> that the current alignment is not satisfactory then in step <NUM> the alignment is adjusted. This is achieved by adjusting attachment device <NUM> in the manner described earlier. Specifically, in the embodiment of <FIG> the orientation of the origin is adjusted using adjustment means <NUM>. In embodiments where adjustment means <NUM> comprises two pairs of orthogonally orientated adjustment screws, these are tightened and loosened in small increments as required in the manner discussed earlier to adjust the alignment. Steps <NUM> and <NUM> are repeated after each small adjustment until a satisfactory alignment is achieved. At this point, the alignment is complete and in step <NUM> the position of adjustment device <NUM> is locked using the adjustment screws.

Following locking, in step <NUM> all alignment verification means are removed from the system and in step <NUM> the alignment process is ended. The system is now aligned and ready for use. It will be appreciated that, in embodiments where the output of the transmitter is used as the alignment verification means, step <NUM> is omitted.

In some embodiments more than one alignment device is provided. For example, an embodiment in which both the transmitter and receiver have respective alignment devices is contemplated. In these embodiments, step <NUM> of <FIG> is modified such that adjustment comprises adjustment of at least one of the alignment devices.

Whilst the alignment device described herein has been primarily illustrated for laser beam alignment in a laser gas analyser, it will be obvious to one skilled in the art that the alignment device may also be employed to align alternative arrangements such as non-laser light sources and detectors, acoustic sources and detectors and/or other suitable transmitters and receivers (origins and targets). In addition, since the orientation of the origin is unaffected by the alignment procedure, embodiments described herein can also be for used for image projection and/or collection.

Claim 1:
An alignment device (<NUM>, <NUM>', <NUM>"), comprising:
a mount (<NUM>) comprising:
a body portion with at least one external curved bearing surface and a tubular mounting portion that includes a connection point for an optical or acoustic transmitter or receiver; and
an attachment collar (<NUM>) projecting from the body portion and secured to the housing;
a housing (<NUM>) for the mount that is arranged to allow rotation of the mount within the housing, wherein the housing comprises translation restraining means (<NUM>), the at least one external curved bearing surface for bearing against the translation restraining means during rotation of the mount within the housing for preventing translation of the mount during rotation;
adjustment means (<NUM>) for adjusting the alignment of the mount within the housing, for alignment of a received source or detector with a desired transmission direction, wherein the adjustment means (<NUM>) comprises one or more pairs of opposed screws or bolts that are equally spaced around the circumference of the tubular mounting portion seated in the attachment collar (<NUM>); and
rotation restraining means (<NUM>) for preventing rotation of the mount about an axis corresponding to the transmission direction, wherein the rotation restraining means (<NUM>) comprises a protrusion in the body portion that engages with a slot in the attachment collar.