Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/12—Generating the spectrum; Monochromators
  • G01J3/26—Generating the spectrum; Monochromators using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
  • G01J3/433—Modulation spectrometry; Derivative spectrometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/06—Illumination; Optics
  • G01N2201/061—Sources
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/06—Illumination; Optics
  • G01N2201/066—Modifiable path; multiple paths in one sample
  • G01N2201/0662—Comparing measurements on two or more paths in one sample
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/06—Illumination; Optics
  • G01N2201/068—Optics, miscellaneous

Definitions

• the present invention relates to an apparatus for on ⁇ taking an absorption spectrum of a fluid having a first radiation source which emits radiation in a first spectral region along a first beam path, having disposed in said first beam path first measurement path along which the radiation through the fluid enters , having disposed in said first beam path tunable Fabry-Perot interferometer, which can transmit as a displaceable Bandpassfil ⁇ ter radiation in the first spectral range and a first detector for measuring the intensity of the radiation in the first spectral range and a method for receiving a Absorption spectrum of a fluid.
• the concentration of the anesthetic gases used in the breath or in the control of drivers of the alcohol content in the respiratory air is measured, for example, in anesthetized Pati ⁇ often ducks in each breath.
• concentration of the respective components spectrometric methods are used. As a rule, signals are recorded and compared with references using discrete filters in wavelength bands in which the gases exhibit absorptions. From the change of the signals at these wavelengths, which are characterizedis ⁇ table for a particular gas, thus it can be concluded in the breathing air on the concentration of the gas.
• a number of devices are known from the prior art with which the concentration of selected constituents of a fluid or of a fluid can be determined by absorption measurements at selected wavelengths or over a spectral range. of a gas, such as breathing gas.
• Such devices have a radiation source which emits radiation over a selected, continuous spectral range.
• an optical bandpass filter hereinafter referred to as a filter, arranged, which restricts the spectrum of the radiation to a wavelength for a component of the gas whose concentration is to be measured is characteristic.
• the intensity of the radiation after it has passed through the filter and the measurement distance measured by ei ⁇ nem suitable detector From the attenuation of the intensity compared to a reference measurement in a reference fluid in which the concentration of the constituent is known, it is now possible to deduce the concentration of the constituent in the fluid.
• a private geeigne ⁇ tes filter must be used for each component.
• the various filters are arranged on a so-called filter wheel.
• a filter wheel is a rotating ⁇ de disk that moves the filter in quick succession in the beam path between the radiation source and detector.
• a complete absorption spectrum can be recorded using a tunable Fabry-Perot interferometer be as described in DE 10 2006 045 253 B3.
• a tunable Fabry-Perot interferometer is arranged in the beam path between radiation source and detector instead of the filter.
• a Fabry-Perot interferometer is an arrangement that has two partially transparent mirrors arranged parallel to one another, whose reflective coated mirror surfaces are assigned to one another. The distance of the mirror surfaces from one another determines a narrow wavelength range, which is transmitted by the Fabry-Perot interferometer or for which the Fabry-Perot interferometer is permeable.
• the width of the light transmitted by the Fabry-Perot interferometer wavelength range is referred to as spectral on ⁇ solution and is dependent on the wavelength.
• a tunable Fabry-Perot interferometer the distance of the mirror surfaces can be changed and thus the wavelength range that is transmitted can be shifted.
• a Fabry-Perot interferometer therefore represents a sliding band pass filter ⁇ , the width of the spectral resolution of the Fabry-Perot interferometer corresponds. If the absorption spectrum of a fluid over a selected spectral region are fully recorded, the Fabry-Perot interferometer must be tuned le ⁇ diglich over the selected spectral range.
• a Fabry-Perot interferometer can also be permeable simultaneously for two different wavelength ranges. It is thus possible to simultaneously record the absorption spectra of the fluid in the two wavelength ranges.
• a device for recording an absorption spectrum of a fluid using such a Fabry-Perot interferometer is known from DE 10 2009 011 421 B3.
• the spectrum recorded by the detector must be be compared with a reference measurement.
• lock-in amplifiers are used regularly.
• a measured signal is multiplied by a reference signal and the result of the multiplication integrated in a low-pass filter.
• the lock-in amplifier thus forms the cross-correlation between the measured signal and the reference signal.
• the signal outputted from the detector so that the radiation emitted by the radiation source Strah ⁇ radiation must, however, be time-modulated.
• a temporal modulation is to be understood here as a change in the intensity of the radiation with time. In the simplest case, this can be done by switching on and off the radiation source or a downstream chopper, which repeatedly interrupts the beam path between the radiation source and the detector.
• Absorption of selected constituents in the respiratory air is preferably at wavelengths between 2 and 15 ym ym ge ⁇ measure.
• the available broadband radiation sources in this wavelength range are usually thermal radiators. If these electrically modulated in time with a sniff necessary for frequency-resolved measurements of more than 100 Hz, the relative modulation depends In the ⁇ intensity greatly from the considered wavelength from, the modulation of short to long wavelength decreases. In the spectral range between 2 ym and 15 ym, the intensity modulation at frequencies of 100 Hz and more at the longer wavelengths decreases so much that it is no longer sufficient for use with a lock-in amplifier.
• the object is achieved by a device which has a first etalon for the spectral modulation of the radiation, which is arranged in the first beam path and which has a plurality of transmission maxima in the first spectral range.
• the Fabry-Perot is configured such that the formed by the Fabry-Perot interferometer Bandpassfil ⁇ ter can be moved in such a way via the first spectral range, the spectral modulation of the radiation through the first etalon as a temporal modulation of the intensity of the radiation from the first detector can be measured.
• the device initially has a first radiation source which emits radiation in a first spectral range with a preferably continuous spectrum.
• a first radiation source for example membrane ⁇ radiator, which have a continuous spectrum in a wavelength range between 2 ym and 20 ym.
• membrane ⁇ radiator which have a continuous spectrum in a wavelength range between 2 ym and 20 ym.
• powerful helical radiators or other thermal radiators can be used, which also emit in this spectral range.
• the radiation emitted by the radiation source is preferably largely collimated by a lens arrangement or a reflector and guided along a first beam path through the device.
• the first measurement distance, the Fabry-Perot interferometer and the first etalon are arranged in the propagation direction of the radiation prior to the detector, wherein the order in which the radiation, the first measuring ⁇ range, the Fabry-Perot interferometer and the first etalon happens, is arbitrary.
• the first measuring path arranged in the first beam path may, for example, be a cuvette in which the fluid to be examined is arranged.
• An etalon is to be understood here as a Fabry-Perot interferometer in which the distance between the mirror surfaces can not be changed or is not changed during a measurement.
• a blank ⁇ coated, polished thin disk made of silicon or Ger ⁇ Manium or mainly comprises silicon or germanium may be used.
• metallic or dielectric coated discs which are optically transparent or two coated or uncoated parallel spaced plates may be used.
• optical components which have a comb-like transmission or reflection, for example certain plastic components. foils or cuvettes filled with a gas, the gas having a pronounced comb-like absorption.
• the first etalon has a plurality of transmission maxima in the first spectral range.
• a broadband Strah ⁇ development which passes through the first etalon, thus has referred to a spectral modulation, which is characterized by a change from the Etalon specific intensity minima and maxima.
• spectral modulation is meant herein the dependence of the intensity of a radiation on the wavelength or the frequency. For example, in the spectral range between 4 ⁇ m and 5 ⁇ m, a silicon wafer with a thickness of 100 ⁇ m has 35 transmission maxima and just as many transmission minima. In the spectral range between 8 ym and 11 ym, the same disc has 25 transmission maxima.
• the first etalon is formed such that at least some of the transmission maxima of the first etalon comprise wavelengths which are charac teristic ⁇ for the components whose concentration is to be analyzed in the fluid. In this way, the Konzentra ⁇ tion of components of the fluid can be determined optimized, which have only narrow characteristic absorption lines.
• the first etalon is such that the maxima of the transmission rate from ⁇ stand is greater than the spectral resolution of the Fabry-Perot interferometer in the first spectral range ⁇ . If the spectral resolution of the Fabry-Perot interferometer is wider than the distance of the transmission maxima, this leads to an undesired smoothing of the spectrum. In other words, the intensity maxima generated by the first etalon appear broader and shallower when sampled with the Fabry-Perot interferometer.
• the surfaces of the first etalon are not aligned pa rallel ⁇ to the surfaces of the elements in the propagation direction of the radiation immediately before and arranged behind the first etalon in order to prevent additional undesirable Etaionef ⁇ fect.
• a Fabry-Perot interferometer is arranged in the first beam path, in which the distance between the mirror surfaces can be adjusted so that the Fabry-Perot interferometer represents a displaceable bandpass filter in the first spectral range.
• the bandpass filter formed by the Fabry-Perot interferometer can be displaced over the first spectral range, preferably continuously, such that the spectral modulation by the first etalon is measured as a temporal modulation of the intensity of the radiation from the first detector.
• the spectral modulation of the radiation through the first etalon with the tuning of the Fabry-Perot interferometer and the associated displacement of the band-pass filter in a zeitli ⁇ che intensity modulation of the radiation is transmitted.
• the spectral modulation of the radiation through the first etalon with the tuning of the Fabry-Perot interferometer and the associated displacement of the band-pass filter in a zeitli ⁇ che intensity modulation of the radiation is transmitted.
• due to the known width of the Fabry-Perot interferometer at any time on the transmitted wavelength and da ⁇ be concluded with the wavelength of the radiation.
• the Fabry-Perot interferometer travels five times per second over the spectral range of the smallest to the largest wavelength and then tuned back ent ⁇ this indicates an intensity modulation of the radiation at a frequency of 350 Hz.
• a spectral region that includes the wavelengths between 8 ym and 11 ym has the sliding ⁇ che silicon wafer, for example, 25 Transmissionsmaxima- and minima.
• the device has a first detector which is arranged so that it can measure the intensity of the radiation after it has passed the first etalon, the Fabry-Perot interferometer and the first measuring path.
• the first detector may, for example, be a semiconductor sensor, a thermopile, a thermoresistor, a pyroelectric sensor or a photoacoustic gas sensor. The latter is preferably arranged in the first measuring section.
• Such a device is advantageous because it has no macro-mechanical elements and it is nevertheless possible to modulate the intensity of the radiation with a sufficiently high frequency for a breath-resolved measurement over a broad spectral range.
• the apparatus operates almost ver ⁇ from wear, making the maintenance compared to known prior art devices can be reduced and the service life is increased.
• a first lock-in amplifier In a preferred embodiment for the determination of the absorption spectrum of the fluid from the measured with the first Detek ⁇ tor intensities of the radiation a first lock-in amplifier is provided.
• the lock-in amplifier forms the cross-correlation function between the output from the first sensor measurement signal and a reference signal and represents a particularly narrow band-pass filter, which allows even with strongly noisy signals, already minor Ab ⁇ deviations between the measurement signal and the reference signal. Therefore, the lock-in amplifier allows you to particularly advantageous way to record an absorption spectrum of the fluid.
• the device comprises a second radiation source having a radiation in a second areas of the spectrum ⁇ rich emitted along a two ⁇ th ray path, a second measuring path along which the light emitted from the second radiation source passes through the fluid, and a second Detector for measuring the intensity of the radiation in the second spectral range.
• the first and the second beam path are such forms ⁇ out that the Fabry-Perot interferometer is disposed in the first and the second beam path.
• the Fabry-Perot interferometers In ⁇ can transmit band-pass filter as a moveable radiation in the second spectral range.
• the device has a second etalon for the spectral modulation of the radiation, which is arranged in the second beam path and which has a plurality of transmission maxima in the second spectral range.
• the Fabry-Perot is adapted to that the of the Fabry-Perot interferometer ge ⁇ formed band-pass filter can be shifted such via the second spectral range, the spectral modulation of the radiation through the second etalon as a temporal Modulati ⁇ on the intensity of the radiation can be measured by the second detector.
• This preferred embodiment has a second radiation ⁇ source, emits radiation in a second spectral range, wherein the second spectral range, preferably re walls ⁇ includes wavelengths than the first spectral range.
• the first spectral range could comprise the wavelengths between 2 ym and 6 ym - preferably between 4 ym and 5 ym - and the second spectral range the wavelengths between 7 ym and 15 ym - preferably between 8 ym and 11 ym. It is also conceivable that the first radiation source and the second radiation source to emit radiation over the same spectral region, and are used by respective band-pass filter to the respective spectral ranges turned ⁇ limits.
• the apparatus further comprises a second etalon which is arranged in the second beam path and modulates the radiation in the second spectral range in a similar manner as the ers ⁇ te etalon radiation in the first spectral range.
• the second etalon in the second spectral range comprises a plurality of transmission maxima whose distance preference ⁇ example is greater than the bandwidth or spectral resolu ⁇ solution of the Fabry-Perot interferometer in the second areas of the spectrum ⁇ rich.
• the second etalon is configured in such a way that at least some of the transmission maxima of the second etalon comprise wavelengths that are characteristic of the constituents whose concentration in the fluid is to be investigated.
• the surfaces of the second etalon are also not aligned parallel to the surfaces of the elements arranged in the propagation direction of the radiation directly in front of and behind the second etalon, in order to avoid additional undesirable etalon effects.
• This preferred embodiment further includes a second measurement path along which the light emitted from the second radiation source ⁇ radiation passes through the fluid. It is conceivable that the first and the second measurement path have the same length, of the length of a Messstre ⁇ blocks the route is to be understood that traverses the radiation along the measurement path through the fluid.
• the first measurement section is integrally formed with the second measurement path, ie the first and the second measuring section coincide or extend on the same Way through the fluid.
• the first and the second measuring section have different lengths. Last ⁇ res is particularly advantageous when the fluid in the ers ⁇ th and in the second spectral range absorbed to different extents. So it is for example conceivable that a Be ⁇ standing part of the fluid whose concentration is to be determined, absorbs only very weak in the first spectral range. Nevertheless, in order to achieve measurable changes in the absorption for the first detector, a longer first measuring section is used. Conversely, it is also conceivable that, for example, the concentration of a constituent of the fluid determines who should ⁇ , the strongly absorbed already in low concentrations in the second spectral range. In this case, the second measuring section could be selected to be correspondingly short, so that measurable changes in the absorption occur even at high concentrations of the second detector.
• the Fabry-Perot interferometer is arranged in the first and the second beam path.
• both the radiation emitted by the first radiation source and the radiation emitted by the second radiation source passes through the Fabry-Perot interferometer, wherein the first and the second optical path extend parallel, approximately parallel or one above the other through the Fabry-Perot interferometer.
• the beam splitter is arranged, for example, such that the portion of the radiation emitted by the first radiation source in the Fabry-Perot interferometer transmits the first beam path while the portion of the radiation emitted by the second radiation source is reflected there by the beam splitter forms the second beam path.
• the device further comprises a second detector adapted to measure the intensity of the radiation in the second spectral region after passing through the second etalon, the second measurement path and the Fabry-Perot interferometer.
• the Fabry-Perot interferometer is purchasedbil ⁇ det, that the distance of the mirror surfaces can be adjusted so that the Fabry-Perot interferometer is a displaceable bandpass filter in the second spectral range.
• the band-pass filter formed by the Fabry-Perot interferometer can such via the second spectral region - are shifted, that the spectral modulation is measured by the second etalon as a temporal Mo ⁇ dulation the intensity of the radiation from the second detector - preferably continuously.
• the spectral Modulati ⁇ on the radiation through the second etalon with the tuning of the Fabry-Perot interferometer and the associated displacement of the band-pass filter is transmitted to a temporal intensity ⁇ modulation of the radiation.
• the Fabry-Perot interferometer is designed such that it can transmit radiation in the first and in the second spectral range at the same time and that the light emitted by the Fabry-Perot interferometer can be transmitted.
• bandpass filter can be shifted over the first and the second spectral range at the same time that the spectral modulation of the radiation by the first and the second etalon can be measured as a temporal modulation of the intensity of the radiation from the first and the second detector.
• the distance of the mirror surfaces of the Fabry-Perot interferometer can be adjusted so that it simultaneously forms a band pass in the first and the second spectral range.
• the first and second spectral regions can be scanned simultaneously, and the absorption spectrum of the fluid can be recorded in both spectral regions in a particularly short time, making it possible to measure the concentration of constituents in a fluid whose composition changes in very short periods of time ,
• a second lock-in amplifier is provided.
• first etalon integrally with the second etalon.
• first and the second etalon only one etalon is provided which has a plurality of transmission maxima both in the first and in the second spectral range.
• a 100 ym thick slice of silicon could be used which has 35 transmission maxima in the spectral range between 4 ym and 5 ym and 25 transmission maxima in the spectral range between 8 ym and 11 ym.
• the size of the device can be significantly reduced.
• the first etalon is arranged in such a way in the first and in the second beam path as a beam splitter, that the first beam path and the second beam path. lengang run parallel in the propagation direction of the radiation behind the first etalon.
• the first etalon and the second etalon to be replaced by a common Eta ⁇ lon, which is also designed as a beam splitter and the first and the second beam path brings together such that the Fabry-Perot interferometer in Ausbrei ⁇ power direction of the radiation behind the etalon, is passed in parallel by the radiation emitted by the first and the second radiation source.
• Such a device is also particularly advantageous, since in this way a particularly compact design can be realized.
• first detector integrally with the second detector.
• first and a second detector only one detector is provided, which measures the intensity of the radiation in both the first and in the second spectral range, whereby a particularly compact design of the device is possible.
• the first radiation source is identical to the second radiation source.
• only one radiation source is provided, which emits radiation in the first and in the second spectral range. This also makes it possible to realize a particularly compact design.
• the first radiation source is a thermal radiator whose intensity can be modulated in time so rapidly that the relative change in the intensity of the radiation is more pronounced in one of the two spectral ranges than in the other spectral range. If only one radiation source is present and that formed as a ther ⁇ mixer radiator, so it is advantageous to the intensity ⁇ In the radiation source to modulate in time quickly. If the modulation frequency is sufficiently high, then the intensity modulation affects only the shorter wavelength spectral range, while the longer wavelength one of the two spectral ranges is essentially not modulated. Significant net ⁇ a detector an overlay of the absorption spectra in the first and second spectral range, this additional modulation of shorter wavelength spectral range can be used in a particularly advantageous manner, to separate the first and second absorption spectrum from one another.
• the device can also be configured such that the absorption of the fluid in further spectral ranges can be determined.
• a radiation source that emits in the Spekt ⁇ ral Scheme radiation along a beam path.
• a measurement path, an etalon and a detector are arranged, the radiation passing through the fluid along the measurement path, the etalon for modulating the radiation in the spectral range having a plurality of transmission maxima and the detector for measuring the intensity of the radiation is set up in the spectral range.
• the beam paths are designed such that the Fabry-Perot interferometer is arranged in each beam path.
• the Fabry-Perot interferometer is adapted to transmit radiation in each of the spectral regions as a displaceable bandpass filter, wherein the bandpass filter can be shifted over the spectral regions such that the spectral modulation of the radiation through the etalons as a temporal modulation of the intensity of the radiation from the Detectors can be measured.
• the bandpass filter can be shifted over the spectral regions such that the spectral modulation of the radiation through the etalons as a temporal modulation of the intensity of the radiation from the Detectors can be measured.
• all the radiation sources, all etalons, all measuring sections and / or all detectors are integrally formed with each other, whereby a broadband device for recording absorption spectra can be realized in a particularly compact construction.
• the object is further achieved by a method for using a device according to the invention, in which the Fabry-Perot interferometer is tuned so that the bandpass filter formed by the Fabry-Perot interferometer is shifted over the first spectral range such that the spectral modulation of the radiation the first etalon is measured as a temporal modulation of the intensity of the radiation from the first detector.
• a measurement signal output by the second detector is compared with the first lock-in amplifier with a reference signal.
• the reference signal required for this purpose can be determined in a variety of ways.
• the intensity maxima of the radiation produced by the first etalon and the Fabry-Perot interferometer usually do not occur at a constant time interval. Therefore, an external reference signal with a constant frequency can not be used as a rule. It is conceivable, however, such a match, the control of the Fabry-Perot interferometer to ⁇ that the maxima of intensity-modulated radiation in a temporally equidistant occur. In this case, it would be possible to use a constant frequency reference signal.
• the measuring signal produced in this manner can also be compared with an ex ⁇ tern generated reference signal. It is also conceivable first to record an absorption spectrum in which the first or second measurement path is filled or evacuated with a reference fluid of known composition, and to use the measurement signal output by the detector for further measurements as a reference signal.
• the Fabry-Perot interferometer is tuned in such a way that the bandpass filter formed by the Fabry-Perot interferometer is shifted over the second spectral range such that the spectral modulation of the radiation by the second etalon is a temporal modulation of the intensity the radiation is measured by the second detector.
• a measurement signal output by the second detector is compared with the second lock-in amplifier with a reference signal.
• the Fabry-Perot interferometer is tuned in such a way that time ⁇ equal to the absorption spectrum of the fluid in the first and in the second frequency range can be determined.
• This embodiment is particularly advantageous because it allows to record an absorption spectrum of the fluid in the first and in the second spectral range in a particularly short time.
• the frequency modulation can also be used for a Fourier analysis of the signal sequence.
• FIG. 1 shows a first embodiment of an inventive device Shen ⁇ Fig. 2 shows a second embodiment of an inventive device ⁇ SEN,
• Fig. 3 shows a third embodiment of an inventive ⁇ Shen device.
• Fig. 4 shows a fourth embodiment of an inventive device ⁇ SEN
• Fig. 5 shows a fifth embodiment of an inventive device ⁇ SEN
• FIG. 6 shows a method for determining an absorption spectrum from a measuring signal output by a detector
• the first radiation source 1 is a thermal radiator (eg membrane radiator, helical radiator or Nernst pin) which extends over a spectral range from 2 ⁇ m to .mu.m 20 ym has a continuous spectrum whose maximum is about 5 ym.
• a thermal radiator eg membrane radiator, helical radiator or Nernst pin
• the etalon 3 arranged in the direction of propagation of the radiation behind the radiation source 1 consists of a silicon wafer having a thickness of 100 ⁇ m, which transmits radiation in a first spectral range and in a second spectral range and has a plurality of transmission maxima in both spectral ranges.
• the calculated transmission of the etalon 3 in the first spectral region ym wavelengths of 4 comprises up to 5 ym, is shown in Figure 7, wherein on the Radofs ⁇ senachse 13, the wavelength is shown in m and the relative transmission on the ordinate axis 15 °.
• the etalon transmission maxima at 3 35 17 and as many transmission minima 19th 8 shows the calculated transmission of the etalon 3 in the second areas of the spectrum is rich ⁇ comprising wavelengths between 8 and 11 ym ym, shown, wherein for identical elements of all Zeichnun ⁇ gene, the same reference numerals have been used.
• the wavelength in m represents ⁇ Darge and on the ordinate axis 15, the relative transmission of the etalon 3.
• the etalon 25 transmission peaks 17 3 and as many transmission minima 19.
• a first measuring section 5 is referred to ⁇ sorted, which is, for example, is a column filled with a respiratory gas cuvette.
• the etalon 3 is such to ⁇ arranged that the top surface 21 does not extend ⁇ facing the surface of the cuvette parallel to this, unwanted Etaion bine between the cuvette and the etalon 3 to vermei ⁇ .
• the Fabry-Perot interferometer 7 is arranged, which has a first and a second mirror surface 23, 25, wherein the first mirror ⁇ surface 23 parallel to the second mirror surface 25 ver ⁇ runs and assigns to them.
• the spacing of the Spiegeloberflä ⁇ surfaces 23, 25 of the Fabry-Perot interferometer 7 can be turned so ⁇ assumed that the band-pass filter formed by the Fabry-Perot interferometer 7 transmits radiation in the first and second spectral range simultaneously.
• a detector 9 is arranged, which measures the intensity of the radiation after it has crossed the etalon 3, the first measuring section 5 and the Fabry-Perot interferometer 7.
• the De ⁇ Tektor 9 may be for example, a quantum detector or a thermal detector such as a py roelektrischen sensor.
• the distance between the mirror surfaces 23, 25 is continuously changed so that the bandpass filter formed by the Fabry-Perot interferometer 7 simultaneously scans the first and second spectral ranges.
• the detector 9 records a Intensi ⁇ ty of the radiation at this time, the wavelength can be assigned to the distance of the mirror surfaces 23, 25 of the Fabry-Perot interferometer 7, the band-pass filter formed by the Fabry-Perot interferometer 7 transmits or passes at this distance.
• the detector 9 consequently measures a superposition of the radiation transmitted in the first and the second spectral range.
• the first embodiment of the invention is particularly advantageous since it provides a particularly compact apparatus ⁇ which allows to record the absorbance spectrum of a fluid simultaneously with intensity modulated radiation in two spectral regions without the macro mechanical components must be used. Such devices are low maintenance, durable and inexpensive to manufacture.
• the measurement signal 33 output by the detector 9 has to be separated.
• the difference ⁇ Liche frequency of the transmission maxima can be 17 used in the first and second spectral range, the position of which also is known.
• the device may have a first and a second lock-in amplifier (not shown) with which the measuring signal 33 is compared with a reference signal suitable for the spectral range.
• the measurement signal 33 of a reference measurement in the respective spectral range can be used as the reference signal.
• the detector 35 is at a broadband photoacoustic sensor (eg microphone, cantilever, tuning fork-shaped oscillating quartz or the like), which is arranged in the first measuring path 5 forming cuvette 37.
• a broadband photoacoustic sensor eg microphone, cantilever, tuning fork-shaped oscillating quartz or the like.
• a third embodiment is shown in Figure 3, wherein a second Strah ⁇ radiation source 39 is provided adjacent to the first radiation source. 1
• the first and second Strah ⁇ radiation source 1, 39 are both wide-band thermal emitter, the radiation of which are restricted by suitable bandpass filters 41, 43 on the first and the second spectral range.
• the radiation emitted by the second radiation source 39 radiation is guided along a second beam path 45 through the Vorrich ⁇ processing.
• first and second beam path 11 45 is a first etalon 3, and a second etalon 47 are arranged in the propagation direction behind the band-pass filter having a multi ⁇ plurality of transmission peaks in the first and second spectral range.
• the embodiment illustrated in Figure 3 is advantageous ⁇ way, since the first and the second radiation source 1, 39 inde pendent ⁇ can be switched from each other and it is thus possible in a simple manner to record absorption spectra in only one of the two spectral ranges.
• different thickness etalon 3 and 47 can be used, which allows to adapt the modulations in the first and the second spectral range separately to the absorption ⁇ spectrum of the fluid.
• FIG. 4 shows a fourth exemplary embodiment, which is a modification of the third exemplary embodiment shown in FIG.
• a first etalon 3 is merely used, which also serves as a beam splitter and as an etalon in the first and second spectral range.
• the device according to the invention shown in FIG. 4 is particularly advantageous since it has two independent radiation sources and nevertheless a particularly compact construction.
• FIG. 5 shows a fifth exemplary embodiment, which shows the use of a first and a second etalon 3, 47 in front of a cuvette 37 through which a gas flows, in which the radiation passes through the gas along a first and a second measuring section 5, 5 ' , wherein the first and the second measuring section 5, 5 'have different lengths.
• These con ⁇ figuration has the advantage that on the longer path gases with low absorption cross-section, on the shorter route but gases with a high absorption cross section can be detected gleichzei ⁇ tig over a wide concentration range.
• Darge ⁇ represents in Fig. 6. In the upper diagram in FIG.
• the abscissa 51 represents the wavelength and the ordinate axis 53 the transmission of the etalon and the Fabry-Perot interferometer, the dashed curve 55 representing the transmission of the etalon and the solid curve 57 representing the Transmission of the Fabry-Perot interferometer, which is shifted from small to large wavelengths.
• the absorption spectrum of Messsig ⁇ Nalles on the intensity maxima and minima is integrated during recording. This is schematically shown in the lower diagram in Fig. 6, in which on the abscissa axis 51 is also the wavelength and the ordinate axis 59, the integrated measuring signal 61 is Darge ⁇ represents.

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• 2012
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