AU2005200839A1 - Photoacoustic gas sensor - Google Patents
Photoacoustic gas sensor Download PDFInfo
- Publication number
- AU2005200839A1 AU2005200839A1 AU2005200839A AU2005200839A AU2005200839A1 AU 2005200839 A1 AU2005200839 A1 AU 2005200839A1 AU 2005200839 A AU2005200839 A AU 2005200839A AU 2005200839 A AU2005200839 A AU 2005200839A AU 2005200839 A1 AU2005200839 A1 AU 2005200839A1
- Authority
- AU
- Australia
- Prior art keywords
- gas sensor
- microphone
- photoacoustic gas
- printed circuit
- circuit board
- Prior art date
- Legal status (The legal status 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 status listed.)
- Abandoned
Links
- 238000005259 measurement Methods 0.000 claims description 28
- 238000005516 engineering process Methods 0.000 claims description 2
- 238000007789 sealing Methods 0.000 claims 1
- 210000004027 cell Anatomy 0.000 description 34
- 239000012528 membrane Substances 0.000 description 10
- 0 *CCC(C1)C2C1CC(**)C2 Chemical compound *CCC(C1)C2C1CC(**)C2 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000000034 method Methods 0.000 description 4
- 230000005855 radiation Effects 0.000 description 3
- 238000004026 adhesive bonding Methods 0.000 description 2
- 210000005056 cell body Anatomy 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 230000003595 spectral effect Effects 0.000 description 2
- 239000004593 Epoxy Substances 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000002457 bidirectional effect Effects 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000004512 die casting Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000005476 soldering Methods 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
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
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
-
- 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
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
- G01N2021/1704—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in gases
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
Description
S&FRef: 710358
AUSTRALIA
PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Siemens Building Technologies AG, of Bellerivestrasse 36, 8008, Ztirich, Switzerland Rolf Pleisch Peter Steiner Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Photoacoustic gas sensor The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c Photoacoustic gas sensor Description The present invention relates to a photoacoustic gas sensor having a measurement cell and a reference cell, Cc a radiating element and a differential microphone for 00 measurement of the pressure difference between the Smeasurement cell and the reference cell.
V) A photoacoustic gas sensor of this type as described in 18 393 has scarcely ever been used until now because virtually no suitable microphones were available, and normal suitable microphones are suitable only to a very restricted extent for the typical low signal frequencies. For this reason, two microphones are generally used in an electrical differential circuit, in order to suppress interference sound sources (in this context, see EP-A-0 855 592). However, this results in the problem of having to find microphones with a suitably lower cut-off frequency, because suitable microphones from audio applications have a typical lower 3 dB frequency of 20 to 30 Hz, that is to say in the region of the signal frequency of the gas sensor, which leads to cut-off frequency scatter, and to the cut-off frequency being varied by environmental influences. Furthermore, the differential design is difficult, because the microphones must be matched in pairs to a measurement accuracy in the region of one percent. Together with the drift of the 3 dB frequency mentioned, this leads to effective interference suppression being virtually impractical.
The aim of the invention is now to specify a photoacoustic gas sensor of the type mentioned initially whose differential microphone is costeffective and is suitable for the low signal frequencies typical for photoacoustic gas sensors.
2 According to the invention, this object is achieved by the differential microphone being formed by a so-called noise canceling microphone of the type used in mobile telephones.
Since these microphones have a frequency response which 00 is completely unusable in the open air, they appear to be unsuitable for the typical signal frequencies from 20 to 30 Hz. However, practical trials have led to the Ssurprising result that the microphones have very good characteristics, with a flat frequency response as far as the 3dB point, for the intended application in photoacoustic gas sensors. The cut-off frequency is generally at about 1 to 4 Hz, that is to say considerably below 10 Hz, so that this only insignificantly influences the signal at the useful frequency. Furthermore, the microphones are extremely cost-effective and are available in very widely differing miniaturized forms.
A first preferred embodiment of the gas sensor according to the invention is characterized in that the differential microphone has electrodes in the form of concentric circular rings. The lower cut-off frequency of the differential microphone is less than 10 Hz, and is preferably between 1 and 4 Hz.
A second preferred embodiment is characterized in that the differential microphone has a housing which is in the form of a box and whose base forms the front face of the microphone, while its rear face has a flange for the fixing of a rear plate.
A third preferred embodiment is characterized in that the differential microphone is mounted on a printed circuit board which has a first annular groove for the positioning of said flange.
3 The microphone electrodes in the form of concentric circular rings have the advantage that the parts do not need to be aligned while being fitted to the printed circuit board, thus allowing simple assembly by means of a robot. The simple assembly process is additionally simplified by the first annular groove, because this 00 0 results in the microphone, together with its housing Sflange, being automatically guided to the correct position.
Further preferred embodiments and advantageous developments of the photoacoustic gas sensor according to the invention are claimed in the dependent claims to 9.
The invention will be explained in more detail in the following text with reference to an exemplary embodiment and to the drawings, in which: Figure 1 shows an exploded illustration of a photoacoustic gas sensor according to the invention, Figure 2 shows a detail of the gas sensor shown in Figure 1; Figure 3 shows a first schematic sketch in order to explain the production of the gas sensor; and Figure 4 shows a second schematic sketch in order to explain the production of the gas sensor.
The photoacoustic gas sensor illustrated in Figure 1 comprises a measurement cell 1, a reference cell 2, a bidirectional differential microphone 3 arranged between the two cells 1 and 2, a miniature incandescent lamp 4 associated with the measurement cell 1 and a reflector housing 5 with a reflector for focusing the radiation emitted from the miniature incandescent lamp 4 on a window which is arranged in the side wall of the 4 Qmeasurement cell 1 facing the miniature incandescent lamp 4 and into which an infrared bandpass filter 6 is inserted. The measurement cell 1 and the reference cell 2 are absolutely identical in terms of their design and dimensions. Both the measurement cell 1 and the reference cell 2 are provided on one outer side wall o with a hole into which a gas-permeable membrane 7 or S7', respectively, is inserted. The differential Smicrophone 3 is mounted on a printed circuit board 8 V3 10 and is provided with a seal 9 (optionally) on each of Cthe two sides of the differential microphone 3. The miniature incandescent lamp 4 is likewise mounted on a printed circuit board, which is denoted with the reference symbol The miniature incandescent lamp 4 emits light over a broad spectrum into the infrared band; in most cases, a spectral line in the infrared band is used for gas detection. The infrared bandpass filter 6 has a pass band which is characteristic of the gas to be detected and is in the form of a narrow spectral band which is around 4.25 Am for detection of CO 2 10 Am for NH 3 and 3.4 Am for CH 4 The gas to be detected is passed through the two gas-permeable membranes 7 and 7' into the measurement cell 1 and into the reference cell 2, respectively. The gas in the measurement cell 1 is illuminated by modular light from the miniature incandescent lamp 4. The gas absorbs the light radiation and is thus heated. This results in thermal expansion and, corresponding to the modulation of the light radiation, in a periodic pressure fluctuation, thus causing an acoustic pressure wave whose intensity is in direct proportion to the concentration of the gas.
The interference sound which strikes the membranes 7, 7' from the outside is attenuated by them and in each case appears with an identical intensity in the 5 measurement cell 1 and in the reference cell 2. This interference sound is thus directly compensated for on the membrane of the microphone 3 without large signals being produced which would have to be electronically subtracted. Since the same pressure fluctuations occur on both sides of the microphone membrane, the signals caused by the interference sound are directly 0 physically subtracted on them, so that the microphone membrane is initially not deflected at all. The 13 0 microphone membrane thus produces the acoustic pressure Ccaused by the gas in the measurement cell 1 directly, and thus the sought concentration.
The microphone 3 is a so-called noise canceling microphone, as is used in mobile telephones. If this microphone is used as a differential microphone and is installed between two acoustically virtually closed cells, specifically between the measurement cell 1 and the reference cell 2, it has very good characteristics, matched to the objective.
Figure 2 shows a section through the microphone 3. As can be seen from the illustration, this comprises a housing G which is open on one side and is in the form of box, whose base forms the front face of the microphone. Holes 11 are provided in this base for the sound to pass through to the microphone membrane 13, which is clamped in between the base of the housing and a metal back electrode 12 and is composed of metalized plastic. The side wall of the housing 18 is peened over on the rear face of the microphone and fixes a rear wall 14 which is provided with small equalization holes, so-called back ports 15, and is fitted on its inner face, facing the metal back electrode 12, with an FET 16, and on its outer face with two circular electrodes 17 and 19.
The back ports 15 are sufficiently large for low 6 frequencies and make the frequency response of the D microphone 3 flat as far as the lower cut-off -frequency. This lower cut-off frequency is governed by y the capacitance of the membrane 13 and by the input impedance of the impedance converter that is used and is considerably below 10 Hz, preferably between 1 and n 4 Hz, so that the signal is influenced only 0 insignificantly by the lower cut-off frequency at the useful frequency of about 20 to 30 Hz.
S CThe microphone 3 is mounted on the printed circuit board 8, which has an annular groove 19 for the positioning of the flange on the microphone 3, annular contact webs 20 and 21 for the two circular electrodes 17 and 18, respectively, as well as an annular groove 22 with a number of holes 23 which are passed through the printed circuit board 8 from the base of the annular groove. The holes 23 and the annular groove 22 allow air and sound to be supplied from the rear to the back ports 15 without them having to be aligned with any holes in the printed circuit board 8.
The microphone 3 and the printed circuit board 8 do not need to be aligned during the fitting process, thus making it easy to assemble them using a robot. The assembly process is also simplified by the annular groove 19, which automatically guides the housing flange on the microphone 3 to the correct position for fitting. The circular electrodes 17 and 18 are adhesively bonded and electrically connected to the printed circuit board 17 by means of conductive epoxy.
The external contour of the measurement cell 1, the reference cell 2 and the reflector housing 5 is completely the same, so that the parts can be produced cost-effectively as extruded profiles, reducing the necessary machining to a minimum.
The individual components of the sensor, that is to say 7 Qof the reflector with its housing 5, of the two cell bodies for the measurement cell 1 and the reference cell 2, of the bandpass filter 6, of the microphone 3 and of the miniature incandescent lamp 4 are produced/provided in the course of the production process for the gas sensor. The bandpass filter 6 is adhesively bonded into the measurement cell 1, and the 00 0 microphone 3 is then mounted on the printed circuit Sboard 8. The measurement cell 1 and the reference cell Vt 10 2 are preferably aluminum or zinc diecastings.
These components are then joined together to form a measurement module M, as can be seen in Figure 4, which is done by batch processing as illustrated in Figure 3.
One reference cell 2 with the fitted microphone printed circuit board 8, the measurement cell 1, reflector housing 5 which contains the reflector 24 and in which the miniature incandescent lamp 4 is inserted, and the populated miniature incandescent lamp printed circuit board 10 are in each case connected to form a stack, which is done either by adhesive bonding or by clamping them together. In the former case, the seals 9 (Figure 1) are not required, because the adhesive join seals the interior of the cell bodies 1 and 2. The clamping together is carried out by means of a spring element, for example a clip, which acts in the longitudinal direction of the sensor (direction of the arrows in Figure 3).
The membranes 7, 7' are then inserted into the measurement cell 1 and the reference cell 2 of the complete measurement module M, and, finally, the measurement module M is fitted to a module printed circuit board P, which can be done by adhesive bonding or soldering. The preassembled measurement module M is complete and functional and can be tested in advance as a unit before it is mounted on the module printed circuit board P. The measurement module M can be 8 O installed as a sub-module, like a component, on any desired other printed circuit boards, without any Stolerance or alignment problems for the microphone 3, the reflector 24 and the miniature incandescent lamp 4.
It is obvious that the described production of the 0%sensor is considerably simpler and more cost-effective 00 than the previously known production methods, in which Sthe microphone and the miniature incandescent lamp are 1 0 mounted on a base printed circuit board, and the measurement cell is then fitted individually around C- these components.
Claims (11)
1. A photoacoustic gas sensor having a measurement cell and a reference cell, a N radiating element and a differential microphone for measurement of the pressure difference between the measurement cell and the reference cell, wherein the differential Cc microphone is formed by a noise canceling microphone of the type used in mobile 00 0 telephones.
2. The photoacoustic gas sensor as claimed in claim 1, wherein the lower cut-off S 10O frequency of the differential microphone is less than 10 Hz.
3. The photoacoustic gas sensor as claimed in claim 2, wherein the lower cut-off frequency of the differential microphone is between 1 and 4 Hz.
4. The photoacoustic gas sensor as claimed in claim 2 or 3, wherein the differential microphone has electrodes in the form of concentric circular rings.
The photoacoustic gas sensor as claimed in claim 4, wherein the differential microphone has a housing, which is in the form of a box and whose base forms the front face of the microphone, while its rear face has a flange for the fixing of a rear plate.
6. The photoacoustic gas sensor as claimed in claim 5, wherein the differential microphone is mounted on a printed circuit board, which has a first annular groove for the positioning of said flange.
7. The photoacoustic gas sensor as claimed in claim 6, wherein equalization holes are provided in the rear plate and the printed circuit board has a second annular groove with holes, which pass through the printed circuit board, with the second annular groove and said holes allowing access for sound from the outside area to the equalization holes.
8. The photoacoustic gas sensor as claimed in one of claims 1 to 7, wherein the radiating element is formed by a miniature incandescent lamp, which is mounted on a printed circuit board, and by a reflector, which is provided in a reflector housing. [R:\LIBCC]04618.doc:wxb CN
9. The photoacoustic gas sensor as claimed in claim 8, wherein the measurement cell, the reference cell and the reflector housing have the same external contours. C
10. The photoacoustic gas sensor as claimed in one of claims 1 to 9, wherein a small sealing plate is provided on each of the two sides of the differential microphone. 00 00
11. A photoacoustic gas sensor substantially as hereinbefore disclosed with reference 1 to any one or more of Figs. 1 to 4 of the accompanying drawings. S 10 DATED this Twenty-third Day of February, 2005 Siemens Building Technologies AG Patent Attorneys for the Applicant SPRUSON FERGUSON [R:\LIBCC]04618.doc:wxb
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP04005482.7 | 2004-03-08 | ||
| EP04005482A EP1574841A1 (en) | 2004-03-08 | 2004-03-08 | Photoacoustic gas sensor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| AU2005200839A1 true AU2005200839A1 (en) | 2005-09-22 |
Family
ID=34814267
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU2005200839A Abandoned AU2005200839A1 (en) | 2004-03-08 | 2005-02-24 | Photoacoustic gas sensor |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP1574841A1 (en) |
| KR (1) | KR20060043530A (en) |
| CN (1) | CN100514031C (en) |
| AU (1) | AU2005200839A1 (en) |
| PL (1) | PL373064A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2604998A1 (en) * | 2011-12-12 | 2013-06-19 | ABB Research Ltd. | Gas analysis device |
| US8848191B2 (en) | 2012-03-14 | 2014-09-30 | Honeywell International Inc. | Photoacoustic sensor with mirror |
| KR20160061492A (en) | 2014-11-21 | 2016-06-01 | 삼성디스플레이 주식회사 | Portable dust senser and cellular phone using the same |
| EP3550286B1 (en) | 2019-04-17 | 2021-01-27 | Sensirion AG | Photoacoustic gas sensor device |
| CN110596236A (en) * | 2019-09-27 | 2019-12-20 | 湖北晟正汽车零部件有限公司 | Urea solution concentration detection device who optimizes |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4019056A (en) * | 1975-04-28 | 1977-04-19 | Diax Corporation | Infrared laser detector employing a pressure controlled differential optoacoustic detector |
| US4067653A (en) * | 1976-08-27 | 1978-01-10 | Nasa | Differential optoacoustic absorption detector |
| JPS622879Y2 (en) * | 1981-03-25 | 1987-01-22 | ||
| DK155269C (en) * | 1986-07-17 | 1989-07-24 | Brueel & Kjaer As | Pressure gradient |
| CH679076A5 (en) * | 1989-06-13 | 1991-12-13 | Oscar Dr Sc Nat Oehler | |
| US5651074A (en) * | 1995-05-11 | 1997-07-22 | Lucent Technologies Inc. | Noise canceling gradient microphone assembly |
| NO308228B1 (en) * | 1997-11-26 | 2000-08-14 | Presens As | Dynamic pressure sensor |
| JP3360254B2 (en) * | 1999-07-27 | 2002-12-24 | エヌイーシーインフロンティア株式会社 | Microphone holder for noise canceling handset, noise canceling handset, and method of mounting noise canceling microphone on handset |
-
2004
- 2004-03-08 EP EP04005482A patent/EP1574841A1/en not_active Withdrawn
-
2005
- 2005-02-22 PL PL05373064A patent/PL373064A1/en not_active Application Discontinuation
- 2005-02-24 AU AU2005200839A patent/AU2005200839A1/en not_active Abandoned
- 2005-03-08 CN CNB2005100545004A patent/CN100514031C/en not_active Expired - Fee Related
- 2005-03-08 KR KR1020050019244A patent/KR20060043530A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| PL373064A1 (en) | 2005-09-19 |
| EP1574841A1 (en) | 2005-09-14 |
| CN1667396A (en) | 2005-09-14 |
| KR20060043530A (en) | 2006-05-15 |
| CN100514031C (en) | 2009-07-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PC1 | Assignment before grant (sect. 113) |
Owner name: SIEMENS AKTIENGESELLSCHAFT Free format text: FORMER APPLICANT(S): SIEMENS BUILDING TECHNOLOGIES AG |
|
| MK4 | Application lapsed section 142(2)(d) - no continuation fee paid for the application |