WO1997049984A1 - Syntonisation et etalonnage d'un dispositif photothermique de detection de gaz - Google Patents

Syntonisation et etalonnage d'un dispositif photothermique de detection de gaz Download PDF

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Publication number
WO1997049984A1
WO1997049984A1 PCT/CH1997/000244 CH9700244W WO9749984A1 WO 1997049984 A1 WO1997049984 A1 WO 1997049984A1 CH 9700244 W CH9700244 W CH 9700244W WO 9749984 A1 WO9749984 A1 WO 9749984A1
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WO
WIPO (PCT)
Prior art keywords
photothermal
speed
measurement
resonator
heat source
Prior art date
Application number
PCT/CH1997/000244
Other languages
German (de)
English (en)
Inventor
Oscar Oehler
Original Assignee
Oscar Oehler
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Oscar Oehler filed Critical Oscar Oehler
Priority to EP97925808A priority Critical patent/EP0846261A1/fr
Publication of WO1997049984A1 publication Critical patent/WO1997049984A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
    • G01N27/74—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables of fluids
    • 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
    • G01N21/37—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using pneumatic detection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/024—Analysing fluids by measuring propagation velocity or propagation time of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/32—Arrangements for suppressing undesired influences, e.g. temperature or pressure variations, compensating for signal noise
    • G01N29/326—Arrangements for suppressing undesired influences, e.g. temperature or pressure variations, compensating for signal noise compensating for temperature variations
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0006—Calibrating gas analysers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/01—Indexing codes associated with the measuring variable
    • G01N2291/014—Resonance or resonant frequency
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/02863—Electric or magnetic parameters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/02881—Temperature

Definitions

  • the invention lies in the fields of gas sensors, ultrasound technology, photothermal spectroscopy and paramagnetic gas detection. It relates to a method and a device for calibrating and monitoring the tuning of a gas sensor based on an ultrasonic resonator.
  • gases can be selectively detected using an ultrasound resonator.
  • the changes in the speed of sound, which occur during the absorption of IR radiation by the gas in the resonator cavity, respectively. occur in the inhomogeneous magnetic field are small. They are in the range of mm / sec. Such Small deviations can be measured very reliably and exactly at the resonance operating point via the phase difference between the excitation signal at the ultrasound transmitter and the signal at the opposite receiver, since the phase steepness is greatest at the resonance maximum. As such, the resonator detuning can also be detected on the basis of an amplitude change in a resonance flank. However, it has been shown that the phase measurement results in a higher measuring accuracy for changes in sound speed.
  • This operating point can be checked by changing the frequency.
  • this tuning method can create problems - in particular if the tuning range is large (for example with a 300 kHz resonator exceeds 5 kHz) - because the ultrasonic transducers themselves have resonator properties.
  • Another control method is that the resonance is mechanically maintained by regulating the distance between the ultrasound transducers, for example by means of a piezo actuator.
  • the high price for the piezo actuator should be considered.
  • the long re-tuning time plays an important role.
  • the resonator cavity always has the highest sensitivity to sound velocity at the resonance operating point if the latter is determined on the basis of a phase measurement.
  • Sound transmission from the transducers to the gas column in the resonator is consistently low due to the poor acoustic adaptability and, moreover, direct transmission of structure-borne noise from the transmitter to the receiver cannot be completely prevented. It is therefore quite possible that the measured resonance maximum does not correspond to that of the pure gas column, but is overlaid or even dominated by the resonances of the transducers. The maximum amplitude is therefore not necessarily a reliable measure of optimal sensitivity to sound velocity. It is an object of the invention to demonstrate a method and to provide a device which allows constant optimization and monitoring of the resonator tuning in relation to the speed of sound sensitivity of the ultrasound resonator and additionally allows constant calibration of the device.
  • the method for checking and calibrating the speed of sound sensitivity of the ultrasonic resonator consists in that a modulatable heat source is attached in the resonator cavity.
  • a modulatable heat source is attached in the resonator cavity.
  • the same can consist of an electro-thermal element, for example a heating wire, or an opto-thermal element, for example a light guide with an end absorber.
  • 1 shows an example of a photothermal device with a modulatable heat source in the form of a heated wire coil.
  • 2 shows a possible embodiment of a paramagnetic oxygen measuring device in front and side view with an ultrasonic resonator and a modulatable heat source in the form of a light guide with end absorber.
  • Fig. 3 shows the course of the photothermal signal as a function of the ultrasound frequency without and taking thermal calibration into account.
  • Fig. 4 shows the course of the photothermal signal as a function of
  • FIG. 1 shows an example of a photothermal device which is based on an ultrasonic resonator.
  • the latter consists of two ultrasonic transducers arranged opposite one another in a tube 12, one of which is operated as a transmitter 13, the other as a receiver 14.
  • the use of a single ultrasonic transducer 13 is also conceivable if an acoustic reflector is used at the same time to maintain a resonance.
  • the ultrasonic transmitter is operated from the high-frequency oscillator 15.
  • the high-frequency demodulator 16 which preferably compares the phase of the signal at the ultrasound transmitter 13 with that at the ultrasound receiver 14, is used to detect the resonator tuning.
  • the resonator can be tuned electrically via the ultrasound frequency by means of the controllable oscillator 15. There is also the possibility of controlling the resonance via the distance between the ultrasound transducers 13, 14 with the aid of a mechanical displacement unit, for example a piezo actuator.
  • a mechanical displacement unit for example a piezo actuator.
  • One more way is based on the thermal control of the resonator tuning with a Peltier element 18 and a thermal mass 19 or by means of a heating element 35 (as shown in FIG. 2).
  • Temperature changes or larger changes in the speed of sound can occur when the gas composition in the resonator cavity changes.
  • thermal light source 1 - in this case consisting of a radiator 2, an elliptical reflector 3 and a counter reflector 4 - reaches the cavity 11 of the ultrasonic resonator. If necessary, there is an optical filter 5 in the beam path for generating monochromatic radiation.
  • thermal radiation source a laser or an LED element is also conceivable as a light source.
  • the optical filter 5 can be dispensed with.
  • a light interrupter is usually required to generate intensity-modulated radiation.
  • the use of such an element can be avoided if the thermal radiator 2 has a low thermal inertia and a low modulation frequency is selected.
  • the light source 1 is operated by a low-frequency oscillator 6 via the power amplifier 7.
  • a modulatable heat source in the present case in the form of an electro-thermal heat source 20 - for example a wire coil - which works at a very low power (even below 1 mW) is used to measure the speed of sound sensitivity and thus to control it the vote or for sound velocity calibration of the resonator.
  • an electro-thermal heat source is also possible.
  • bar for example an electrical resistance or a semiconductor element.
  • the oscillator 6 can be used via the power amplifier 22 to control the modulatable heat source 20.
  • the electro-thermal heat source 20 can be operated at a higher frequency (for example above 5 Hz) by means of the oscillator 21, since the thermal inertia of the source 20 can be kept low because of the low power requirement of the source 20.
  • the use of different frequencies for the light source 1 and the electro-thermal heat source 20 allows the tuning / calibration measurement and the photothermal measurement in one
  • Double modulation methods can be carried out simultaneously.
  • the periodic detuning of the resonator which occurs in the resonator 11 as a result of the temperature dependence of the speed of sound due to light absorption, provides information about the gas concentration in the cavity of the resonator and thus represents the sought-after photothermal signal.
  • Low frequency demodulation is used to detect the same 8, which takes over the rectified signal of the high-frequency demodulator 16, the signal of the low-frequency oscillator 6 being used as a reference.
  • the Demodulation of the photothermal signal resp. of the calibration signal can be carried out alternately with the same low-frequency demodulator 8.
  • the low-frequency demodulator 8 either a frequency change is required in the low-frequency demodulator 8, or it is necessary, in particular if the two sources 1, 20 are used simultaneously at different frequencies the low-frequency oscillators 6, respectively. 21 be ⁇ operated, in addition to the low-frequency demodulator 8, another low-frequency demodulator 23 in the circuit of the luch source 20 is required.
  • the evaluation of photothermal signals takes place in the evaluation unit 9, the signal from the calibration source preferably being used for calibration.
  • the evaluation unit contains a division element and a buffer, which supplies the latter with the calibrated gas concentration information of an external utilization unit (for example a gas concentration controller, an alarm system or display unit).
  • an external utilization unit for example a gas concentration controller, an alarm system or display unit.
  • the calibration source 20 can also be used to check the tuning with regard to a favorable speed of sound sensitivity of the ultrasound resonator 11. For example, after a major change in temperature or gas concentration, it is advisable to track the operating point of the resonator or even to determine it anew. This process is preferably carried out by optimizing the speed of sound sensitivity on the basis of the signal from the calibration source 20. In this case (in contrast to the optimization of the amplitude at the ultrasound receiver 14) it is ensured that the resonator has a high sensitivity to the speed of sound. That in the low-frequency demodulator 23, respectively. 8 resulting control signal can as already mentioned, for example the controllable oscillator 15, a piezo actuator, or a Peltier element 18, which in turn is connected to a thermal mass 19, or a heating element (as denoted by 35 in FIG. 2).
  • FIG. 2 shows an example of a gas sensor based on the paramagnctism of gases in front and side view.
  • Paramagnetic gases such as oxygen
  • the modulatable magnetic field is by means of an electromagnet 31 consisting of the coil 32, the
  • Power amplifier (7) controls the coil 32 of the electromagnetic 31 instead of the IR source.
  • FIG. 2 shows an optothermal element 25 for the thermal monitoring and calibration of the speed of sound sensitivity of the device.
  • This Element consists of a light guide 26, at one end of which there is a light source, for example a laser diode or an LED element 27.
  • An optical absorber 28 for example a blackened end surface, is attached to the other end of the light guide.
  • the opto-thermal element 25 can of course also be used in the photothermal gas detection device (according to FIG. 1).
  • This calibration device is particularly preferred when there is an explosive or aggressive gas in the resonator cavity 11, which gas must not be exposed to an electro-thermal element (20).
  • the control of the resonator can in turn be carried out with the aid of a controllable oscillator, a piezo actuator, or thermally, for example with a Peltier element or, as shown in FIG. 2, a heating element 35.
  • the magneto-sonar signal is evaluated in analogy to the photothermal signal with the aid of a low-frequency derodulator, where appropriate the signal from the electro-thermal calibration source 20 or. of the electro-optical element 25, 26, 27, 28 can be used for calibration.
  • 3 shows the photothermal signal as a function of the ultrasound frequency, taking thermal calibration into account.
  • the curve of FIG. 3a shows the frequency profile of the ultrasound amplitude at the ultrasound receiver 14 (in x ⁇ .25 in V) when the transmitter 13 is operated at a constant amplitude of 22 V. Since the ultrasonic frequency in the area of the resonance extends over a range of 5 kHz, the resonance character of the amplitude response is at the receiver 14 very pronounced.
  • the working point changes with gas temperature changes and changes in the gas composition at least for a short time. It is therefore advantageous to constantly control the speed of sound sensitivity of the ultrasonic resonator, respectively. to carry out a calibration.
  • a calibration measurement was carried out using a modulatable heat source 20 in the cavity of the resonator in the form of a wire coil
  • FIG. 3c shows the course of the photothermal signal when the values from FIG. 3b have been divided by the calibration values. The signal is largely independent of the operating point of the resonator. Further improvements in the results can be expected when optimizing the electro-thermal element 20 and the resonator cavity 11.
  • FIG. 4b shows the course of the photothermal signal when the values of FIG. 4a have been divided by the corresponding calibration measurements determined at a power of 0.33 mW.

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  • Food Science & Technology (AREA)
  • Combustion & Propulsion (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Acoustics & Sound (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Abstract

L'invention concerne un procédé et un dispositif de surveillance et d'étalonnage permanent d'un dispositif de détection de gaz de type photothermique ou fondé sur le paramagnétisme de gaz. La détection de gaz repose sur la mesure du désaccord périodique des fréquences d'un résonateur ultrasonore (11). Ce désaccord des fréquences est dû à l'absorption du rayonnement incident périodique d'une source lumineuse (1) ou à l'action d'un champ magnétique dans le gaz de mesure du résonateur ultrasonore (11). L'étalonnage et la surveillance du dispositif interviennent thermiquement, soit à l'aide d'un élément électrothermique (20) monté dans la cavité résonante (11) et chauffé périodiquement, se présentant sous forme de conducteur électrique ou de semi-conducteur, soit à l'aide d'un élément optothermique actionné périodiquement, de préférence un guide d'ondes muni d'un absorbeur terminal.
PCT/CH1997/000244 1996-06-22 1997-06-20 Syntonisation et etalonnage d'un dispositif photothermique de detection de gaz WO1997049984A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP97925808A EP0846261A1 (fr) 1996-06-22 1997-06-20 Syntonisation et etalonnage d'un dispositif photothermique de detection de gaz

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
CH1572/96 1996-06-22
CH157296 1996-06-22
CH2335/96 1996-09-25
CH233596 1996-09-25

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WO1997049984A1 true WO1997049984A1 (fr) 1997-12-31

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4184768A (en) * 1977-11-04 1980-01-22 The Johns Hopkins University Self-calibrating photoacoustic apparatus for measuring light intensity and light absorption
EP0362307A1 (fr) * 1988-02-19 1990-04-11 Koch High Tech Ag Mesurage de la temperature par ultrasons et application en spectroscopie optique et en calorimetrie.
WO1991009306A1 (fr) * 1989-12-08 1991-06-27 Oscar Oehler Detection selective de gaz par separation de champ et mesure de la vitesse du son: detection d'o¿2?

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4184768A (en) * 1977-11-04 1980-01-22 The Johns Hopkins University Self-calibrating photoacoustic apparatus for measuring light intensity and light absorption
EP0362307A1 (fr) * 1988-02-19 1990-04-11 Koch High Tech Ag Mesurage de la temperature par ultrasons et application en spectroscopie optique et en calorimetrie.
US5141331A (en) * 1988-02-19 1992-08-25 Oscar Oehler Ultrasonic temperature measurement and uses in optical spectroscopy and calorimetry
WO1991009306A1 (fr) * 1989-12-08 1991-06-27 Oscar Oehler Detection selective de gaz par separation de champ et mesure de la vitesse du son: detection d'o¿2?
EP0456787A1 (fr) * 1989-12-08 1991-11-21 Oehler Oscar Detection selective de gaz par separation de champ et mesure de la vitesse du son: detection d'oxygene.

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EP0846261A1 (fr) 1998-06-10

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