SE542640C2 - Gas sensor with thermopile - Google Patents

Gas sensor with thermopile

Info

Publication number
SE542640C2
SE542640C2 SE1850181A SE1850181A SE542640C2 SE 542640 C2 SE542640 C2 SE 542640C2 SE 1850181 A SE1850181 A SE 1850181A SE 1850181 A SE1850181 A SE 1850181A SE 542640 C2 SE542640 C2 SE 542640C2
Authority
SE
Sweden
Prior art keywords
thermopile
sensing element
gas sensor
gas
radiation
Prior art date
Application number
SE1850181A
Other languages
Swedish (sv)
Other versions
SE1850181A1 (en
Inventor
Anders Jansson
Niklas Kvist
Pavel Zyrianov
Original Assignee
Jondetech Sensors Ab Publ
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 Jondetech Sensors Ab Publ filed Critical Jondetech Sensors Ab Publ
Priority to SE1850181A priority Critical patent/SE542640C2/en
Priority to PCT/EP2019/054052 priority patent/WO2019158768A1/en
Publication of SE1850181A1 publication Critical patent/SE1850181A1/en
Publication of SE542640C2 publication Critical patent/SE542640C2/en

Links

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
    • G01J3/28—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
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
    • G01J5/12—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using thermoelectric elements, e.g. thermocouples
    • 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
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/10—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects
    • H10N10/17—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects characterised by the structure or configuration of the cell or thermocouple forming the device

Abstract

There is provided a gas sensor comprising an optical source (1), a sensing element (7) comprising a thermopile (8) and an optical focusing device (5) with a focal point, where the optical source (1) emits radiation (3) through a space where gas is to be detected, and the optical focusing device (5) is arranged to focus radiation (3) from the optical source (l)on to the sensing element (7), where there radiation (3) travels along an optical axis (18) onto a detection surface (4) of the sensing element (7), where the thermopile (8) comprises leads (11, 12) arranged to generate voltage with the use of the thermoelectric effect characterized in that the leads (11, 12) of the thermopile (8) are arranged parallel to the optical axis (18).

Description

Gas sensor with thermopile Field of the invention.
This invention relates to a gas sensor comprising a thermopile.
Background Gas sensors with thermopiles are known. These are based on shining IR radiation througha volume where gas is to be detected on to a heat sensor comprising a thermopile. ln thepresence of gas, radiation is absorbed, and this can be detected as a change in tempera- ture by the thermopile.
The use of thermopiles in gas sensors typically involves the use of |enses or mirrors to fo-cus the IR radiation onto the sensor, in order to generate a temperature difference that is large enough to be detected by the thermopile.
Prior art gas sensors have sensor elements with thermopiles with a radia| design, that isthermopiles where the hot junctions and the heat sink is placed centrally, and the coldjunctions and the cold sink is placed in the periphery as shown in Fig. 2. One example is the thermopile of US20050081905.
Fig. 1 shows a side view of a sensor element for a gas sensor according to prior art, whichcomprises a housing 100, a thermopile 101 where the optical beam 102 is focused on aspot in the centre area 104 comprising the hot junctions of the thermopile 101. The planeofthe surface ofthe thermopile 101 is in the focal point of the optical beam 102.GB2391310 is an example of a gas sensor where the thermopile is placed in the focus of the beam.
The housing 100 has a window 103 that may comprise a filter. Window 103 forms a part of housing 100. The cold junctions 106 ofthe thermopile 101 is located in the same plane as the surface ofthe thermopile 101 and towards the periphery ofthe sensing area. Theleads 107 ofthe thermopile 101 are typically on the surface ofthe sensor, making the sen-sor vulnerable to physical damage. The housing 100 protects the leads 107 of the thermo-pile 101 from damage and also shades the cold junctions 106 from incoming radiation. Thehousing 100 results in a bulky design. Fig. 2 is top view of a thermopile 101 according toprior art with a radial design where the cold junction 106 of the leads 107 are in the pe-riphery ofthe thermopile 101 and the hot junctions are in the centre area 104. Optical beam 102 is focused on a spot in the centre area 104.
The gas to be detected is in the space outside housing 100. lt is difficult to make the hous-ing 100 gas tight. At the same time housing 100 is often poorly ventilated. This may cause gas to be trapped inside housing 100, which may cause erroneous readings.
Summary of invention. ln a first aspect there is provided a gas sensor comprising an optical source, a sensing ele-ment comprising a thermopile, the gas sensor comprising an optical focusing device with afocal point, where the optical source emits infrared radiation through a space where gas isto be detected, and the optical focusing device is arranged to focus radiation from the op-tical source on to the detection surface of the sensing element, where there radiationtravels along an optical axis onto the detection surface of the sensing element, where thethermopile comprises leads arranged to generate voltage with the use of the thermoelec-tric effect, where the leads of the thermopile are embedded in a matrix and arranged par-allel to the optical axis and in that the distance from the focal point to the surface of thesensing element is at least 5 % of the distance from the focusing device to the focal pointand where the where the optical source, the focusing device and the sensing element are comprised in a housing that comprises the gas to be analysed.
Because the leads ofthe thermopile are parallel to the optical axis, the heat sensing areacan be made larger, because the surface ofthe sensing area is not crowded with the leads ofthe thermopile.
The small hot sink area in centre area 104 of the prior art must be placed in the focal pointofthe optical beam 102 in order to produce a signal. This has the following results: 1) lt isdifficult to consistently manufacture the gas sensor with a precision where the hot sink isin the focal point, and 2) the light source may move slightly from its original place whenswitched on and heated, thereby moving the focal point ofthe optical beam 102 from the hot sink in centre area 104.
With the inventive design, a larger sensing area is achieved. This makes the gas sensormuch less sensitive to relative movement of the radiation source, the focusing device andthe sensing element, and solves the problem of having to calibrate each individual gas sensor. Also, the sensing area is scalable.
Previously imaging optics has been used in the design of gas sensors. The inventive gas sensor can be designed using non-imaging optics, which is much easier to use.
Furthermore, because the cold junctions are placed on the reverse side ofthe thermopile,it is not necessary to have a housing 100 that shades the cold sink 106. The housing 100 isalso made unnecessary because the leads of the thermopile can be at least partially em-bedded in a matrix that protects them from physical damage. The housing is bulky andmay also trap gas, which results in errors as described above. Thus, the use of leads thatare parallel to the optical axis and embedded in a matrix provides better accuracy during sensing.
The detection surface ofthe sensing element may be arranged between the focusing de-vice and the focal point. This results in a more compact sensor. For example, the distancefrom the focal point to the surface ofthe sensing element is at least 20% ofthe distance from the focusing device to the focal point (focal length).
The radiation beam may have a cross section with a size and shape such that the entire surface of the sensing element is illuminated by the radiation from the focusing device.
This makes it less important to calibrate the sensor, since it is enough only to check that the entire surface is illuminated.
The sensing element comprises a heat sink arranged between the thermopile and the in-coming radiation. The heat sink may comprise a heat absorbing layer arranged perpendic-ular to the direction of the conductors of the thermopile. The heat sink may cover the hot junctions of the thermopile.
The gas sensor may have a cold sink on the cold side ofthe sensing element.
The optical source, the focusing device and the sensing element, in particular the detec-tion surface ofthe sensing element, may be comprised in a housing that comprises the gasto be analysed. This provides a simple and cost-efficient way to build the gas sensor and minimizes the problem with gas trapped in a separate housing.
The leads of the thermopile are preferably at least partially or completely embedded, forexample at least partially or completely embedded in a matrix. This has the advantage that the thermopile is protected against physical damage.
Brief description of drawings The accompanying drawings form a part of the specification and schematically illustratepreferred embodiments of the invention and serve to illustrate the principles of the inven- tion.
Fig. 1 and 2 shows sensing elements according to the prior art, where the thermopile has aradial design.
Fig. 3 is a schematic drawing of a gas sensor.
Fig. 4 is a schematic side view of a sensing element.
Fig. 5 is a front view of a cut through along line A-A in Fig. 4 Fig. 6 is a schematic representation of a how a sensing element is arranged in relationshipto an optical beam.
Fig. 7 is a schematic drawing of a gas sensor comprising a gas container.
Detailed description Fig. 3 schematically show an example of a gas sensor according to one embodiment oftheinvention. Optical source 1 typically emits visible light or IR radiation, preferably IR radia-tion. The optical source 1 may be any suitable radiation source, such as an IR source, forexample an IR LED. The optical source 1 may be powered by a battery or by mains power(optionally via a transformer). Gas inside housing 2 is detected in the space covered by theoptical beam 3 emitted from optical source 1. Focusing device 5 focuses the optical beam3 towards a focal point 6. In Fig. 3 the focusing device 5 is a lens but any suitable arrange-ments of lenses, such as Fresnel lenses, mirrors, or the like may be used. For example, theoptical source 1 and the sensing element 7 may be placed opposite a mirror that focuses the radiation from the optical source 1 towards the sensing element as in GB2391310.
Housing 2 is preferably common for the optical source 1, focusing device 5 and sensing el-ement 7. The housing 2 is preferably well ventilated, preferably having several openings21 for allowing gas to be analysed into housing 2. The space that comprises the gas maythus comprise the sensing element 7, as shown in Fig. 3, in particular the detection surface4 ofthe sensing element 7. The housing 2 may be made in for example sheet metal or apolymer material. Preferably there is no housing that separates the sensing element 7 from the optical source 1 and the focusing device 5 (like the housing 100 of the prior art).
Sensing element 7 comprises a thermopile 8, i.e. a number of thermocouple leads as dis-cussed below with reference to Figs. 4-5. Sensing element 7 may comprise a heat sink 9arranged in contact with thermopile 8 such that heat from beam 3 can be absorbed by theheat sink 9 and transferred to leads 11, 12 ofthermopile 8. The heat sink 9 may be a heatabsorbing layer. The heat absorbing layer is preferably arranged perpendicular to the di- rection ofthe leads 11, 12 ofthe thermopile 8. The heat sink 9 should be able to absorb heat and conduct heat to the thermopile 8. Suitable materials for the heat sink includes athermally conducting polymer or a metal, for example copper. The heat sink 9 preferably covers the hot side 23 ofthe thermopile 8, thus being arranged between the focusing de-vice 5 and the thermopile 8. The cold side 24 side of the sensing element 7 may comprise a cold sink 20.
There may be a band pass filter 10 arranged between the sensing element 7 and the opti-cal source 1. The filter 10 may be a band pass filter chosen depending on the gas to be de-tected, as every gas has its own specific absorption spectrum. The choice of filter 10 thuscan make the gas sensor specific for one gas. There are suitable filters 10 for C02, me- thane, nitrogen, etc.
With reference to Figs. 4 and 5, the sensing element 7 comprises thermopile 8. A thermo-pile 8 comprises at least two thermocouples. Each thermocouple each consisting of a firstlead 11 of a first metal and a second lead 12 of a second metal, where the first lead 11 andthe second lead 12 have different Seebeck coefficients. Thus, there is at least a first lead11 that has a first Seebeck coefficient and a second lead 12 that has a second Seebeck co-efficient. Examples of suitable pairs of metals include chromel-constantan (type E therm-nocouple), iron-constantan (type J), chromel-alumel (type K). The leads 11, 12 of the ther-mopile is preferably embedded in matrix 17. When there is a temperature difference be-tween the hot side 23 and the cold side 24 a voltage potential will be generated. Matrix 17is made from a non-conductive material such as, for example, an epoxy polymer. Matrix17 is preferably a poor conductor of heat and electricity. The material ofthe matrix 17 canbe selected by a person skilled in the art. The leads 11 and 12 may be connected with con-nectors 19 on the hot side 23 and the cold side 24 of the thermopile 8. The individual ther-mocouples pairs 11,12 and 11', 12' ofthe thermopile 8 are coupled to provide a voltage potential that is sufficient to be detected.
The detection surface 4 of the sensing element 7 may have any suitable shape. Fig. 5shows a square configuration ofthe thermopile 8, but a circular detection area may be preferred.
The leads 11,12 are arranged parallel to the optical axis 18 ofthe radiation 3 that is incom-ing towards the sensing element 7 from the focusing device 5. ”Parallel” as used in thiscontext comprises an angle of up to 10°, more preferably 5°, between the optical axis 18and the leads 11, 12 ofthe thermopile. This arrangement makes it possible to provide alarge and scalable detection surface 4. The matrix 17 moreover protects leads 11, 12 from physical damage and shades junctions 19 on the cold side 24 from radiation 3. ln a preferred embodiment, the detection surface 4 ofthe sensing element 7 is not in thefocal point 6 but placed at a distance along the optical axis 18 from the focal point 6, pref-erably between the focal point 6 and the focusing device 5. Preferably the detection sur-face 4 of the sensing element 7 is placed between the focal point 6 and the focusing de-vice 5. Preferably the distance D between the detection surface 4 ofthe sensing element 7and the focusing point 6 is at least 5%, more preferably 10 %, more preferably 20% andmost preferably 30% of the distance F from the focusing device 5 to the focal point 6 (the focal length).
The optical beam 3 from the focusing device 5 that illuminates the sensing element 7 pref-erably has a cross section with a size and shape such that the entire detection surface 4 ofthe sensing element is illuminated by the radiation 3 from the focusing device 5. The en-tire heat absorbing layer 9 or, when a heat absorbing layer 9 is not present, the entire sur-face of the thermopile 8 may be illuminated. Some radiation, indicated with 22 in Fig. 6, from the radiation source may fall outside surface 4 of the sensing element 7.
Fig. 7 shows an embodiment where the gas to be analysed is provided in a gas container13 which lets in gas from a space where gas is to be detected, trough inlet 14. The arrowsindicate flow of gas. Gas may leave the gas container trough outlet 15. |nlet 14 and outlet15 can be combined in one channel or opening. The gas inside gas container 13 is beingsensed by the gas sensor. The use of a gas container 13 may be useful because it isolatesthe gas being detected, which may be corrosive, from the electronics and other sensitive parts of the of the sensor. Windows 16, 25 in gas container 13 enables the radiation from optical source 1 to enter and leave the gas container 13. ln the embodiment shown in Fig.7, the optical source 1 and the sensing element 7 is provided in the same housing 2, andthe gas container 13 is arranged between the optical source 1 and the sensing element 7 in the housing 2.
Generally, the thermopile 8 is typically electrically connected to one or more of the follow-ing: amplifier, analog to digital converter, processor, memory, output means for transmit-ting a signal to another device (by wire or wireless means), alarm, as is known in the art.Thus, the leads ofthe thermopile 8 may be electrically connected to an amplifier that am-plifies the signal from the thermophile 8. The signal from the amplifier may be digitalizedby an analog to digital converter and then further processed by the processor. The signalmay be provided to other devices, systems, such as alarms, displays and communication devices.
The gas sensor may comprise a reference cell that contains a known gas that is also al-lowed to absorb IR, as is known in the art. Preferably the same optical source 2 is used forthe reference cell. The reference cell and the gas in housing 2 or gas container 13 may be alternatively illuminated and analysed using a radiation chopper.
While the invention has been described with reference to specific exemplary embodiments,the description is in general only intended to illustrate the inventive concept and should notbe taken as limiting the scope of the invention. The invention is generally defined by the claims.

Claims (7)

CLAll\/IS
1. A gas sensor comprising an optical source (1), a sensing element (7) comprising a
2.
3. thermopile (8), the gas sensor comprising an optical focusing device (5) with a focalpoint (6), where the optical source (1) emits infrared radiation (3) through a spacewhere gas is to be detected, and the optical focusing device (5) is arranged to focusthe radiation (3) from the optical source (1) on to a detection surface (4) of thesensing element (7), where the radiation (3) travels along an optical axis (18) ontothe detection surface (4) of the sensing element (7), where the thermopile (8)comprises leads (11, 12) arranged to generate voltage with the use of the thermo- electric effect characterized in that the leads (11, 12) of the thermopile (8) are embedded in a matrix (17) and ar-ranged parallel to the optical axis (18) and in that the distance from the focal point(6) to the surface of the sensing element (7) is at least 5 % of the distance (F) fromthe focusing device (5) to the focal point (6) and where the optical source (1), thefocusing device (5) and the sensing element (7) are comprised in a housing (2) that comprises the gas to be analysed. The gas sensor according to claim 1 where the detection surface the sensing element arranged between the focusing device _(§§_f¿__and the focal point__§'\§'§_}_. The gas sensor according to any one of claims 1 to 2 where the radiation beam (3)has cross section with a size and shape such that the entire surface (4) ofthe sens- ing element (7) is illuminated by the radiation from the focusing device (5). The gas sensor according to any one of claims 1 to 3 where the sensing element (7)comprises a heat sink (9) arranged between the thermopile (8) and the incoming radiation. The gas sensor according to claim 4 where the heat sink (9) is a heat absorbinglayer arranged perpendicular to the direction ofthe conductors (11, 11', 12, 12') of the thermopile (8). The gas sensor according to any one of claims 4 to 5 where the heat sink (9) covers the hot junctions of the thermopile (8). The gas sensor according to any one of claims 1 to 6 which has a cold sink (20) on the cold side of the sensing element (7).
SE1850181A 2018-02-19 2018-02-19 Gas sensor with thermopile SE542640C2 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
SE1850181A SE542640C2 (en) 2018-02-19 2018-02-19 Gas sensor with thermopile
PCT/EP2019/054052 WO2019158768A1 (en) 2018-02-19 2019-02-19 Gas sensor with thermopile

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE1850181A SE542640C2 (en) 2018-02-19 2018-02-19 Gas sensor with thermopile

Publications (2)

Publication Number Publication Date
SE1850181A1 SE1850181A1 (en) 2019-08-20
SE542640C2 true SE542640C2 (en) 2020-06-23

Family

ID=65529674

Family Applications (1)

Application Number Title Priority Date Filing Date
SE1850181A SE542640C2 (en) 2018-02-19 2018-02-19 Gas sensor with thermopile

Country Status (2)

Country Link
SE (1) SE542640C2 (en)
WO (1) WO2019158768A1 (en)

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8309211D0 (en) * 1983-04-05 1983-05-11 Edinburgh Instr Infra red absorption gas detectors
GB0213326D0 (en) 2002-06-11 2002-07-24 Edinburgh Instr Gas sensors
DE10315864B4 (en) * 2003-04-08 2006-01-12 Dräger Medical AG & Co. KGaA Apparatus and method for determining the concentration of at least one gas component in a breathing gas mixture
US20050081905A1 (en) 2003-10-17 2005-04-21 Lan Alex H. Thermopile IR detector package structure
DE102005061411A1 (en) * 2005-12-22 2007-06-28 Robert Bosch Gmbh Micromechanical thermopile sensor and method for its production
DE102006049258A1 (en) * 2006-10-19 2008-04-30 Robert Bosch Gmbh Micromechanical element for use as infrared image sensor, has thermocouple with two thermal side pieces that are provided columnar and perpendicular to main extending plane of substrate, where substrate is provided as plastic substrate
DE102009043413B3 (en) * 2009-09-29 2011-06-01 Siemens Aktiengesellschaft Thermo-electric energy converter with three-dimensional microstructure, method for producing the energy converter and use of the energy converter

Also Published As

Publication number Publication date
WO2019158768A1 (en) 2019-08-22
SE1850181A1 (en) 2019-08-20

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