GAS ANALYSER APPARATUS AND METHOD

Abstract

A gas analyser apparatus using laser absorption spectroscopy includes at least two lasers, preferably up to five, six or seven lasers, and a laser housing (6). The at least two lasers are mounted in the laser housing. The laser housing (6) includes a monolithic main body defining an interior space for receiving the lasers and a lid for sealingly closing the main body. The laser housing is arranged within an outer housing of the gas analyser apparatus. This gas analyser can be assembled and adjusted in a quite simple way.

Claims

1. A gas analyzer apparatus using laser absorption spectroscopy wherein the gas analyser comprises at least two lasers, and a laser housing, wherein the at least two lasers (66) are mounted in the laser housing and wherein the laser housing comprises a monolithic main body defining an interior space for receiving the lasers and a lid for sealingly closing the main body, wherein the laser housing is arranged within an outer housing of the gas analyser apparatus.

2. The gas analyzer apparatus according to claim 1 wherein the laser housing comprises a side wall with a through opening for each laser and wherein a lens mount with at least one lens is mounted on the laser housing at each of these through openings.

3. The gas analyzer apparatus according to claim 1 wherein the at two lasers are at least one of QCLs (Quantum Cascade Lasers), ICLs (Interband Cascade Lasers), TDLs (Tuneable Diode Lasers), Dual-color QCLs.

4. The gas analyzer apparatus according to claim 1 wherein the laser housing contains at least two slots defined by threaded holes in the bottom of the laser housing, where lasers are placed.

5. The gas analyzer apparatus according to claim 1 wherein the lid is arranged on the top of the main body.

6. The gas analyzer apparatus according to claim 1 wherein the main body is milled from one single block.

7. The gas analyzer apparatus according to claim 1 wherein at least one of the block or the lid is aluminum ace made of aluminium.

8. The gas analyzer apparatus according to claim 1 wherein the main body or the lid comprises a port for filling the interior of the housing with an inert gas.

9. The gas analyzer apparatus according to claim 8 wherein the port is usable for evacuating the interior of the laser housing prior to fill it with the inert gas.

10. The gas analyzer apparatus according to claim 1 wherein the main body comprises windows in the shape of through-openings arranged in one sidewall of the main body, wherein each window is assigned to one laser.

11. The gas analyzer apparatus according to claim wherein collimating or focusing optics are mounted to the main body and are assigned to each through-opening and wherein the optics are adjustable in x-y-z directions.

12. The gas analyzer apparatus according to claim 1 wherein the main body comprises heat-sinks and wherein each laser is placed on one of the heat-sinks.

13. The gas analyzer apparatus according to claim 12 wherein the heat-sinks are temperature controlled.

14. The gas analyzer apparatus according to claim 1 wherein the gas analyser comprises an astigmatic Herriott type multipass cell or a nonastigmatic Herriott type cell.

15. A method for starting-up a gas analyzer apparatus using laser absorption spectroscopy, especially a gas analyser apparatus based on direct laser absorption spectroscopy, the method comprising the following steps calculating a good guess for a bare power laser using set-up parameters, normalizing a detected spectrum, calculating an experimental absorbance, transforming a time based absorbance to a equi spaced, frequency based absorbance, calculating a derivative of frequency equi-spaced absorbance, finding a maximum in cross correlation of experimental data with a HITRAN spectrum or based on a custom made database in order to find the absolute frequencies, preforming a nonlinear regression on the detected spectrum with the found absolute frequencies as the starting parameters, thereby obtaining new start values for subsequent nonlinear regressions.

16. A gas analyzer apparatus using laser absorption spectroscopy wherein the gas analyser comprises a multipass cell with a cell body, a front mirror holder and a back mirror holder, wherein the cell body has a main tube with an interior space for receiving gas to be analysed and wherein the cell body has an gas inlet for leading the gas into this interior space and an gas outlet for leading the gas out of this interior space, wherein the main tube is made of glass, characterized in that the gas inlet and the gas outlet are made of glass.

17. The gas analyzer apparatus according to claim 16 wherein the cell body is completely made of glass.

18. The gas analyzer apparatus according to claim 16 wherein the gas inlet and/or the gas outlet are shaped as tubes.

19. The gas analyzer apparatus according to claim 16 wherein the gas inlet and/or the gas outlet are attached to the main tube by welding.

20. The gas analyzer apparatus according to claim 16 wherein the gas inlet and/or the gas outlet are arranged at a distance to the front mirror holder and the back mirror holder.

21. The gas analyzer apparatus according to claim 16 wherein the back mirror holder comprises a back mirror and adjustment means for adjusting the back mirror wherein the adjustment means comprises a lever arm which is rotatable around a longitudinal middle axis of the multipass cell by movement of a micro-screw which can be moved in a direction perpendicular to the longitudinal middle axis of the multipass cell.

22. The gas analyzer apparatus according to claim 21 wherein the lever arm is arranged on a lever arm body which lever arm body is translatable in a direction parallel to the longitudinal middle axis of the multipass cell independently of the rotatable movement by movement of a further micro-screw which can be moved in a direction parallel to the longitudinal middle axis of the multipass cell.

23. The gas analyzer apparatus according to claim 21 wherein the back mirror holder comprises a mounting ring, a guiding element (43), a stem attached to the back mirror, a lever arm body with a lever arm extending radially from the lever arm body, first micro-screws, a second micro-screw and a third micro-screw, wherein the mounting ring receives the guiding element, wherein the guiding element receives the stem, the guiding element having a flange comprising indentations for being contacted by one of the first micro-screws each, wherein the lever arm body has a blind hole receiving the stem of the mirror, wherein the second micro-screw acts on the lever arm to rotate the lever arm around the longitudinal middle axis and wherein the third micro-screw acts on a front face of the lever arm body in order to move the stem of the mirror along the longitudinal middle axis.

24. The gas analyzer apparatus according to claim 23 wherein the back mirror holder comprises a micro-screw holder for holding the second and the third micro-screw, for receiving the lever arm body and for being attached together with the lever arm body to the mounting ring, wherein the micro-screw holder has a recess for allowing rotational movement of the lever arm.

25. The gas analyzer apparatus according to claim 1 wherein the gas analyser apparatus comprises at least two lasers, and a laser housing, wherein the at least two lasers are mounted in the housing and wherein the housing comprises a monolithic main body defining an interior space for receiving the lasers and a lid for sealingly closing the main body.

26. The gas analyzer apparatus according to claim 25 wherein the laser housing comprises a side wall with a through opening for each laser and wherein a lens mount with at least one lens is mounted on the laser housing at each of these through openings.

27. The gas analyzer apparatus according to claim 16 wherein the gas analyser comprises an astigmatic Herriott type multipass cell or a nonastigmatic Herriott type cell.

28. A gas analyzer apparatus using laser absorption spectroscopy wherein the gas analyser comprises an optical sample cell with a cell body, a front mirror holder and a back mirror holder, wherein the back mirror holder comprises a back mirror and adjustment means for adjusting the back mirror, characterized in that the adjustment means comprises a lever arm which is rotatable around a longitudinal middle axis of the optical sample cell by movement of a micro-screw which can be moved in a direction perpendicular to the longitudinal middle axis of the optical sample cell.

29. The gas analyzer apparatus according to claim 1 wherein the gas analyser comprises five or six or seven lasers.

30. The gas analyzer apparatus according to claim 25 wherein the gas analyser comprises five or six or seven lasers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] A preferred embodiment of the invention is described in the following with reference to the drawings, which are for the purpose of illustrating a present preferred embodiment of the invention and not for the purpose of limiting the same. In the drawings,

[0089] FIG. 1 shows a schematic view of a gas analyser apparatus according to the invention;

[0090] FIG. 2 shows a schematic view of a gas analyser system with the inner elements of gas analyser according to FIG. 1;

[0091] FIG. 3 shows perspective view of a multipass cell according to the invention;

[0092] FIG. 4 shows a side view of the multipass cell according to FIG. 3;

[0093] FIG. 5 shows an exploded view of a part of the multipass cell according to FIG. 3;

[0094] FIG. 6 shows another exploded view of a part of the multipass cell according to FIG. 3;

[0095] FIG. 7 shows a part of the multipass cell according to FIG. 3;

[0096] FIG. 8 shows a longitudinal sectional view of a part of the multipass cell according to FIG. 3, the section being taken aseptically;

[0097] FIG. 9 shows an exploded view of a laser housing according to the invention;

[0098] FIG. 10 shows a partial longitudinal sectional view of the laser housing according to FIG. 9;

[0099] FIG. 11 shows a cross sectional view of the laser housing according to FIG. 9;

[0100] FIG. 12a to FIG. 12f graphs showing the steps in the start-up algorithm and

[0101] FIG. 13 a flow chart of the start-up algorithm.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0102] FIG. 1 shows a schematic view of a gas analyser apparatus according to the invention. Preferably it is based on the apparatus of the applicant which is already on the market, preferably comprising the components of this apparatus where applicable and where not replaced by the inventive parts and methods.

[0103] The apparatus comprises an outer housing 1 with at least one fan 11 and a display 10. Depending on the embodiment, the display 10 can be a touch screen as well and act as a machine user interface. On the rear side, which cannot be seen in FIG. 1 but in FIG. 2, there is an electronic interface 13 with plug connections and a power switch, a first coolant port 140, a second coolant port 141, a first port 150, a second port 151 and a third port 152.

[0104] As can be seen in FIG. 2, the inventive gas analyser preferably comprises two sections in one single housing 1, wherein these two sections are preferably divided by a dividing wall 12 or an internal enclosure.

[0105] The first section forms the optical part, the second section forms the electronics part.

[0106] The optical part comprises a multipass cell with a cell body 2, a front mirror holder 3 and a back mirror holder 4, a photodetector 5, a laser housing 6 and deflection mirrors 7. The light path is marked in FIG. 2 with the reference sign L. These optical elements are preferably mounted on one single base plate, which is preferably fixed to the bottom of the housing in a shock absorbing way. The single base plate is preferably made of carbon-fibre or aluminum. It is not shown in the figures.

[0107] This optical part of the gas analyser apparatus is connectable to an outside suction pump 90, preferably a membrane vacuum pump, and a cooling device 91, preferably a water chiller. The gas analyser apparatus, the pump 90 and the cooling device 91 form a gas analyser system. Additional parts can be present in this system as well.

[0108] A first external coolant line 910 leads a cooled or warmed fluid, preferably water or another liquid cooling agent, to the first coolant port 140. A first internal coolant line 912 guides the cooled fluid to the laser housing 6, a second coolant line 913 leads from the laser housing 6 to the second coolant port 141 and through a second external coolant line 911 to the cooling device 91. The fluid is usually lead through the base of the monolithic laser housing by dedicated tunnels. The cooling device 91 is preferably used to cool other parts and elements of the gas analyser apparatus as well.

[0109] The multipass cell is preferably an astigmatic multipass cell of the Herriott type, preferably with a range of several meters to several tens or even hundreds of meters absorption path.

[0110] The cell body 2 of the multipass cell comprises a gas inlet 21 and a gas outlet 22. The gas inlet 21 is connected by an inlet line 902 to a valve 903. The valve 903 is preferably a three-way valve, for example a solenoid valve. The valve 903 can switch between a first gas line 904 and a flushing line 905, the two lines being connected to the second port 151 and the first port 150 respectively.

[0111] The gas outlet 22 of the cell body 2 is connected by a second gas line 906 to the third port 152, which lead through an external suction line 901 to the suction pump 90.

[0112] A gas sample to be analysed enters the apparatus through the second port 151 and is sucked by the suction pump 90 through the multipass cell. Preferably, the measuring rate is chosen such that it is either comparable or greater than the multipass cell gas exchange rate.

[0113] The gas can be a mixed gas and several components of the mixed gas can be measured.

[0114] By switching the valve 903, the cell body can be filled with a reference gas with known concentrations or a non-absorbing zero-gas (e.g. nitrogen) for automatic calibration and offset corrections.

[0115] The laser housing 6 comprises at least one, preferably at least two lasers. Laser light emitted from the lasers are guided by the deflection mirrors 7 through a hole in the front mirror arranged in the front mirror holder 3 into the cell body 2. The laser light is multi-passing the cell body 2 a multiple of times before it leaves the multipass cell through the hole of the front mirror again. It is then detected by the photodetector 5. The detector is preferably a photovoltaic MCT-based or InAsSb-based infrared detector.

[0116] At least the photodetector 5 and the lasers of the laser housing 6 are connected with the electronic part of the apparatus. This electronic part preferably comprises a data acquisition device (DAQ) 80, a data processing device 81 and driving electronics 82. Preferably, the suction pump 90 and the cooling device 91 are also controlled by the electronic part of the apparatus or they receive and/or send at least data from respectively to each other. The electronic part preferably comprises active temperature control elements for each of the lasers. The DAQ is preferably a FPGA based data-acquisition system to record the absorption signals detected by the detector 5. The data processing device 81 processes, controls, stores and displays data.

[0117] In general and with some exceptions, these main parts of the gas analyser system are known in the state of the art.

[0118] However, the cell body 2 according to the inventive apparatus comprises a main tube 20 made of glass and the gas inlet 21 and gas outlet 22 are made of glass as well (see FIG. 3). The main glass tube 20 defines an interior space for receiving gas to be analysed. Preferably, it has the shape of an elongate circular cylinder. The gas inlet 21 and the gas outlet 22 have the shape of tubes, preferably also in the form of circular cylinders. Preferably, they are arranged on the lateral surface of the main glass tube 20 near the front and the back mirrors of the cell. Preferably, they extend perpendicular to the longitudinal axis of the main glass tube 20. Preferably, the inlet and the outlet both extend in the same direction. In other embodiments, they extend perpendicular to each other or at an angel to each other.

[0119] As can be seen in FIG. 8, the gas outlet 22 is directly fixed to the main glass tube 20 so that this part of the cell body 2 only comprises glass and no other material, even not some adhesive. The same applies for the gas inlet 21 and the region of the main glass tube 20 around the gas outlet 22. Preferably, the main glass tube 20, the gas inlet 21 and the gas outlet 22 are produced of glass as single tools and then gas inlet 21 and the gas outlet 22 is fixed to the main glass tube 20 by glass blowing.

[0120] The front face and the back face 23 of the main glass tube 20 is preferably plane and comprises not threads or anything else, as can be seen in FIGS. 5 and 8.

[0121] The gas inlet 21 and the gas outlet 22 are preferably arranged at a distance to the front face and the back face 23 of the main glass tube.

[0122] The inventive multipath cell comprises a minimum of metal. Preferably, only the mirrors are coated with metal and the mirror holders are at least partially made of metal. Preferably, the metal surface of the holders are located on the rear side of the mirrors, so that sampling effect is improved in case of a constant flush through the cell.

[0123] The front mirror holder 3 is not shown in detail. It comprises at least one mounting ring, preferably made of aluminium with a window, and a front mirror, which has a hole for the laser beams to enter and exit the cell. The front mirror holder 3 is preferably shaped as known in the state of the art and does therefore not have to be described in detail. Preferably, for the sake of simplicity the front mirror is preferably fixed and not adjustable.

[0124] FIGS. 5 to 8 show the special back mirror holder 4 of the inventive gas analyser apparatus. FIG. 5 shows on its left hand side the rear end part of the main glass tube 20 with the back face 23 and the gas outlet 22. A first mounting ring 40 is next to the back face 23. The first mounting ring 40 comprises a central through-opening 401 with a diameter, which is almost the same as or which is larger than the outside diameter of the main glass tube 20. As can be seen in FIG. 8, the first mounting ring 40 encompasses the rear end of the main glass tube 20.

[0125] The first mounting ring 40 comprises fixation openings 400 for fixing to first mounting ring to a second mounting ring 41. A third mounting ring 44 is screwed to the other side of the second mounting ring 41. An endpiece 49 ist screwed to the third mounting ring 44.

[0126] The second mounting ring 41 follows the first mounting ring 40, the second mounting ring 41 preferably being thicker than the first mounting ring 40. It comprises a central through-opening 411 and fixation openings on both sides. The fixation openings 410 fixation of the third mounting ring 44 are shown in FIG. 5.

[0127] As can be seen in FIG. 8, the second mounting ring 41 comprises a circumferential inner step 412, which is abutted by the rear end face 23 of the main glass tube 20. A sealing ring 413 is arranged between the first and the second mounting ring 40, 41. The glass tube is sealed by these O-rings when the ring 40 presses the ring 41. In order to fix the rings to glass tube edges, the glass tube is evacuated. In other embodiments, bars are used extending along the glass tube and fixing the front and the back mirror holder.

[0128] The next part comprises several items, which are shown in more detail in FIG. 6. It forms a basic mirror holder with the adjustment means, especially some micro-screws 470, 471, 472 and a lever arm 460, and the mounting ring 44, which basic mirror holder mounts the back mirror 42 to the cell body 2.

[0129] In FIG. 6, the direction of view is changed. This means that elements being on the left side in FIG. 5 are now arranged on the right side in FIG. 6.

[0130] This part comprises a back mirror 42, which is preferably highly reflective for the wavelengths provided by the lasers. The mirror 42 is fixed to a stem 420 having a central opening 421. A lever arm body 46, which will be described later in the text, is screwed to this stem 420 by using this opening 421. The opening for receiving the fixation screw needed for fixing the lever arm body 46 to the stem 420 has the reference number 463.

[0131] The stem 420 penetrates a guiding element 43, which holds and guides the stem 420. The guiding element 43 comprises a main body 431 with a central through-opening 432 for receiving the stem 420 and with a flange 430 directed to the stem 420. The flange 430 has some fixation openings 433 arranged on its circumference. The flange 430 comprises three arms extending radially outside. Each arm comprises an indentation 434 for receiving the free ends of a first micro-screw 470. Preferably, there are three first micro-screws 470.

[0132] Individual pressure can be applied on each arm of the flange 430, which then can tilt the stem 420 and which can therefore tilt the mirror 42 along the X and Y axes.

[0133] The main body 431 of the guiding element 43 penetrates a central through-opening 445 of a middle ring 440 being arranged in a third mounting ring 44. The middle ring 440 and the third mounting ring 44 are made of one single piece. The circumferential rim seen in FIG. 6 is used for holding a seal ring 446 i.e. an O-ring, as can be seen in FIG. 8. On the other side of the third mounting ring 44, a further sealing ring 447

[0134] The third mounting ring 44 comprises outer fixation through-openings 441 matching with the fixation openings 410 of the second ring 41 so that the third mounting ring 44 can be fixed with screws to the second mounting ring 41 and to the main glass tube 20. The third mounting ring 44 also comprises outer fixation openings 444 in the form of threaded holes for fixing a cap 49 described later in the text. The middle ring 440 comprises inner fixation openings 442 and micro-screw openings 443 for fixing the microscrew holder 48.

[0135] An inner ring 451 is arranged within the central through-opening 445 of the middle ring 443. It is fixed to the main body 431 of the guiding element 43. There are fixation through-openings 454 which corresponds to the fixation openings 433 of the guiding element 43. The screws needed for these fixations are not shown in the figures, as they are not shown for all the other fixations openings mentioned in this text. The inner ring 451 comprises a central through-opening 453 as well. This opening is penetrated by the stem of the back mirror 42, as can be seen in FIG. 8.

[0136] A first spring 450 is arranged between the inner ring 451 and an inner flange 448 of the middle ring 440 being part of third mounting ring 44. The first spring 450 is arranged around the main body 431 of the guiding element 43, as can be seen in FIGS. 6 and 8. The first micro-screws 470 extend through the body of the middle ring 440, which cannot be seen in the sectional view of FIG. 8. The first spring 450 pushes the guiding element 43 towards the first micro-screws 470.

[0137] On the opposite side of the inner ring 451, a lever arm body 46 with a protruding lever arm 460 is arranged. The lever arm body 46 has a cylindrical shape and comprises a blind hole into which the stem 420 extends. This can be seen in FIGS. 6 and 8. Within the blind hole of the lever arm body 46, the stem 420 is surrounded by a second spring 452. The second spring 452 has two functions. It pushes the mirror assembly towards the third micro-screw 472 and it provides a rotational force such that the lever arm pushes the second micro-screw 471.

[0138] As can be seen in FIG. 6, the inner ring 451 comprises a slit 455 for fixing the second spring 452 preventing it from free rotation. A rotational movement of the lever arm body 46 around the longitudinal axis of the sample cell leads to a rotational movement of the stem 420 of the mirror 42. The rotational movement of the lever arm body 46 is caused by a second micro-screw 471 pushing on the lever arm 460 in a direction perpendicular to the longitudinal axis of the cell body 2. It is used for the z-axis rotation adjustment of the back mirror 42.

[0139] The translation adjustment of the back mirror 42 along the longitudinal axis of the cell body 2, i.e. the z-axis, is performed by movement of a third micro-screw 472 which acts on a front face 461 of the lever arm body 46. Like this, the back mirror 43 can be adjusted by translation and rotational movement with independent adjustment means, i.e. the micro-screws 470, 471, 472. Especially the z-rotational adjustment and the translation along the z-axis can be made independently of the x,y rotational adjustment.

[0140] Going back to FIG. 5, the assembled part forming the basic mirror holder shown in FIG. 6 in an explosive view can now be better understood. This assembled basic mirror holder can be attached and fixed as one single piece to the second mounting ring 41 and therefore to the cell body 2. As can be seen in FIGS. 5 and 8, the lever arm body 46 is encompassed by a micro-screw holder 48. The micro-screw holder 48 comprises a main body 480 with a cylindrical shape and having a hole. A flange 481 with fixation through openings 482 surrounds the hole.

[0141] A central micro-screw opening 483 extends along the longitudinal axis into the blind hole and a lateral micro-screw opening 484 extends in radial direction into the main body 480 of the micro-screw holder. The micro-screw holder 48 holds the second and the third micro-screw 471, 472.

[0142] The three first micro-screws 470 are located within some indentations 485 of the flange 481 of the micro-screw holder 48 and are independent of this holder 48.

[0143] A recess 486 in the main body 480 of the micro-screw holder 48 enables the lever arm 460 to be moved.

[0144] The invented back mirror holder 4 comprises an end piece 49. It has a main body 492 with a cylindrical shape and a blind hole. A sensor port 493 in the form of an electrical feedthrough allows measurement of the temperature inside the cell.

[0145] A flange 490 comprising fixation through openings 491 is directed towards the cell body 2. The flange 490 can be fixed to the third mounting ring 44, since the fixation through openings 491 correspond to the outer fixation openings 444 of the third mounting ring 44. The blind hole has a step. The part with the greater inner diameter encompasses the micro-screw holder 48, the part with the smaller inner diameter accommodates the central micro-screw 483. This arrangement allows to reduce the dead volume where gas could be trapped.

[0146] As can be seen in FIG. 5, the back mirror holder 4 can be easily mounted and disassembled for cleaning. Re-adjustment is quite easy to handle. In case a readjustment is necessary before or during operation, the end piece 49 can easily be removed and all the micro-screws 470, 471, 472 necessary for the adjustment are readily accessible. FIG. 7 shows the situation when the end piece 49 is removed.

[0147] FIGS. 9 to 11 show the laser housing 6 of the inventive gas analyser apparatus. The housing comprises a main body 61 and a lid 60. The main body 61 has preferably the shape of a square-like box or a similar box with a similar shape which is open at the top. It is preferably milled or cut from one single block. The main body 61 and/or the lid 60 are preferably made of aluminium. The housing 6 is preferably hermetically sealed using a sealing element, such as a circumferential O-ring, between lid 60 and main body 61. The sealing element is not shown in the figures. The lid 60 is preferably removably fixed to the main body 61.

[0148] The main body 61 comprises cooling ports 67 for connection with the coolant lines 912, 913. The bottom of the main body 61 as shaped to circulate a cooling fluid flowing through these ports 67.

[0149] On long side wall of the main body 61 comprises windows 610 in the form of through-holes. A lens mount 62 is fixed to the main body 61 in front of each window 610. Preferably it is screwed or otherwise removably mounted to the main body 61. Each lens mount 62 holds at least one lens 63 within an own hole 620, the lens being preferably adjustable with some screws or with any other kinds of known adjustment means.

[0150] In the interior of the main body 61, there are at least two slots or places, here five slots, to receive laser. There can also be another number of slots. On each slot or place, a temperature control element 64, preferably a Peltier element, is arranged on the bottom of the main body 61.

[0151] On each temperature control element 64, a heat sink 65, such as a copper plate, is arranged. The heat sink 65 carries the laser 66, preferably a QCL (Quantum Cascade Laser), an ICL (Interband Cascade Laser) or TDLs (tuneable diode lasers).

[0152] Each laser 66 is driven separately. The wires connecting the lasers 66 with electronic elements and the power supply and therefore leaving the laser housing 6, are not shown. They preferably pass either through the lid 60 or the back wall of the main body 61. The corresponding holes are preferably sealed, for example, the connectors are glued to the housing.

[0153] The inventive gas analyser apparatus preferably uses a startup-algorithm with pre-defined temperatures for the laser, where the lasers are preferably known to be close to the exact operating wavelength. Once the lasers reach that temperature, they are turned on and the spectrum is recorded.

[0154] If the laser emission frequency drifts away from the one in the last run it might also change the laser emission intensity (baseline). As the newly recorded spectrum contains some absorption lines it hinders from measuring the baseline directly. Within the typical laser drifts though the shape of the emission intensity stays almost the same. This helps to find the new baseline by scaling the baseline from the previous run such that it touches the new measured spectrum from above. This allows to recalculate the experimental spectrum into absorbance. Then a cross correlation of the derivative of the found absorbance with the derivative of the HITRAN-simulated absorbance determines the frequency shift between the previously stored absorption line position (fitting parameter) and the new line position. The absorption line position of the fitting function is adjusted to start fitting the absorption line. The new starting fitting parameters are therefore found and the line of interest is successfully fitted.

[0155] Once the absorption line is fitted, the software gives a feedback to regulate the laser heatsink temperature to move the absorption line position to the original.

[0156] This procedure allows a robust automatic startup and a reproducible (and therefore accurate) fitting result. It also allows to automatically find absorption lines after a fit was lost, e.g. due to a too low/high signal or instrument drifts.

[0157] The procedure is performed sequentially (within seconds) for all lasers in the instrument.

[0158] FIG. 13 shows a flow diagram of the inventive start-algorithm, which is explained in more detail in the summary part of this text. FIGS. 12a to 12f illustrate graphs showing the steps in the start-up algorithm, which steps are mentioned in more detail in the summary part of this text.

[0159] This inventive gas analyser can be assembled and adjusted in a quite simple way. This gas analyser further enables a compact device which provides accurate and precise measurements of a multiple of gases and which is quite easy to handle. The inventive start-up method is one element, which improves handling and accuracy.

TABLE-US-00001 LIST OF REFERENCE SIGNS 1 analyser housing 431 main body 10 display 432 central through-opening 11 fan 433 fixation opening 12 dividing wall 434 indentation 13 electronic interface 44 third mounting ring 140 first coolant port 440 middle ring 141 second coolant port 441 outer fixation through 150 first port opening 151 second port 442 inner fixation opening 152 third port 443 micro-screw through- opening 444 outer fixation opening 2 multipass cell 445 central through-opening 20 main tube 446 sealing ring 21 gas inlet 447 sealing ring 22 gas outlet 448 inner flansch 23 back face 450 first spring 3 front mirror holder 451 inner ring 452 second spring 4 back mirror holder 453 central through-opening 40 first mounting ring 454 fixation through-opening 400 fixation opening ??? 455 slit 401 central through-opening 41 second mounting ring 46 lever arm body 410 fixation through-opening 460 lever arm 411 central through-opening 461 front face 412 step 463 fixation hole 413 sealing ring 470 first micro-screw 42 back mirror 471 second micro-screw 420 stem 472 third micro-screw 421 central opening 43 guiding element 48 micro-screw holder 430 flange 480 main body 481 flange 67 cooling port 482 fixation through-opening 483 central micro-screw opening 7 deflection mirror 484 lateral micro-screw opening 485 indentation 80 data acquisition device 486 recess (DAQ) 81 data processing device 49 end piece 82 driving electronics 490 flange 491 fixation through-opening 90 suction pump 492 main body 901 external suction line 493 sensor port 902 inlet line 903 valve 5 photodetector 904 first gas line 905 flushing line 6 laser housing 906 second gas line 60 lid 61 main body 91 cooling device 610 window 910 first external coolant line 62 lens mount 911 second external coolant line 620 hole 912 first internal coolant line 63 lens 913 second internal coolant line 64 temperatur control element 65 heat sink L light path 66 laser