WO1993002352A1 - Device for analysing gases by the heat conductivity process - Google Patents

Device for analysing gases by the heat conductivity process Download PDF

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Publication number
WO1993002352A1
WO1993002352A1 PCT/DE1992/000528 DE9200528W WO9302352A1 WO 1993002352 A1 WO1993002352 A1 WO 1993002352A1 DE 9200528 W DE9200528 W DE 9200528W WO 9302352 A1 WO9302352 A1 WO 9302352A1
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WO
WIPO (PCT)
Prior art keywords
temperature
gas
dependent
resistor
measuring
Prior art date
Application number
PCT/DE1992/000528
Other languages
German (de)
French (fr)
Inventor
Eckhard Aidam
Günter Marcaux
Johann Weinel
Original Assignee
Siemens Aktiengesellschaft
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 Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Publication of WO1993002352A1 publication Critical patent/WO1993002352A1/en

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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
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
    • G01N27/18—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature caused by changes in the thermal conductivity of a surrounding material to be tested

Definitions

  • the invention relates to a device for analyzing gases according to the thermal conductivity method according to the preamble of claim 1.
  • Such a device is described in European patent application 0 039 956.
  • An electrical conductor heated with constant current is spanned in a measuring chamber through which a measuring gas flows, the temperature and thus its resistance of which depend on the thermal conductivity of the measuring gas surrounding it.
  • a comparison chamber with a likewise heated, temperature-dependent comparison resistor contains a comparison gas.
  • a measurement value is formed from the difference between the resistance values of the measurement and comparison resistance, from which the composition of the measurement gas is derived.
  • the resistance wires consist of platinum and are clamped in the chambers, which can be designed as glass capillaries or glass tubes, and melted into them. With these measures, short time constants for warming up or cooling down depending on the measurement gas are achieved, however, this requires a large manufacturing effort and the finished resistance temperature sensors are difficult to handle.
  • a gas analyzer which has two temperature-dependent resistors which are connected in two different branches of a measuring bridge and one of which is heated, the other which serves for temperature compensation and is not heated. Both are exposed to the sample gas.
  • the bridge current is set so that the ratio of the values of the heated and the unheated, temperature-dependent resistance is kept constant.
  • the sample gas is supplied to both temperature-dependent resistors in pulses.
  • the present invention has for its object to shorten the time constant of the device according to the preamble of claim 1, especially when the temperature-dependent resistors in addition to the resistance wire additional masses increasing the time constant, eg. B. a carrier for the resistance wire, ent ent.
  • FIG. 1 illustrates an embodiment of the invention
  • FIG. 2 shows the structure of temperature-dependent resistors used in the embodiment of FIG. 1.
  • MK denotes a measuring chamber which contains a temperature-dependent measuring resistor RM.
  • the measuring gas flows into the measuring chamber via a gas inlet GE, flows around the measuring resistor RM and passes through a gas outlet GA out again.
  • a comparison chamber VK which is filled with a comparison gas, contains a temperature-dependent comparison resistor RV. Both chambers are housed in a common block and therefore connected to each other in a heat-conducting manner.
  • Resistors are heated, as described in detail below.
  • the measuring resistor RM is cooled depending on the thermal conductivity of the measuring gas. If, as in known measuring devices, the heating power were constant, its temperature and thus its resistance would change accordingly. However, a measurement would only make sense when the entire measuring resistor RM has adjusted to the new temperature.
  • FIG. 2 shows a resistor that can be used in the device according to FIG. 1. It essentially consists of a carrier TR designed as a glass tube, onto which a resistance wire WD is wound bifilarly. In the example shown, the resistance wire WD is led through the interior of the carrier TR to the winding. The winding and the end faces of the carrier are covered with a GH glass skin as a protective layer. A heating current is sent through the resistance wire WD, which heats the entire temperature sensor to a temperature that depends on the thermal conductivity of the surrounding gas. In a 'change in the thermal conductivity, the Canada ⁇ changes output of the temperature sensor, so that also its temperature, initially only on the surface changes. Even if the new thermal conductivity remains constant over a long period, the temperature of the
  • a gas analyzer with such a temperature sensor fed with constant heating current therefore has a large time constant.
  • the time constant is shortened in that the heating current is not constant, but in that the temperature sensor is regulated to a constant temperature.
  • the carrier TR is therefore no longer heated or cooled.
  • the time constant therefore only corresponds to the time in which the heat transfer through the glass skin GH adjusts to a new balance of heat generation and heat dissipation. It is therefore possible to use commercially available resistance temperature sensors, such as those used for. B. are known under the name PtlOO, even if a short time constant is required.
  • the protective layer made of glass ensures a high corrosion resistance.
  • the measuring resistor RM and the comparative resistor RV are each connected in a measuring bridge R1, R2, R3 or R4, R5, R6 (FIG. 1).
  • the voltages at the bridge diagonals are amplified by differential amplifiers DV1, DV2, to the outputs of which control inputs of transistors TS1, TS2 are connected, via which the measuring bridges are fed from a supply voltage UB.
  • the feed currents are set so that the bridges are balanced by heating the temperature-dependent resistors RM, RV.
  • the current through the measuring resistor RM or the voltage dropping across it is a measure of the thermal conductivity of the gas surrounding it.
  • the voltage between the diagonal of the bridge and the mass, which is fed to a measuring amplifier MV, is proportional to this heating current.
  • This voltage is connected across the diagonal of the bridge containing the comparison resistor RV, so that the difference between the voltages at the bridge diagonals is used as the measured value, which is displayed in a registration device RG connected to the measuring amplifier MV.

Abstract

In prior art devices for analysing gases by the heat conductivity process, temperature-dependent resistors (RM), generally thermistors, are heated by a constant current and exposed to the gas to be measured. The measuring resistor (RM) is cooled dependently upon the heat conductivity of the gas to be measured. Such devices have the drawback that, when the gas to be measured is changed, the temperature-dependent resistor (RM) with the bearer and a protective layer must be heated or cooled to the new temperature, resulting in a considerable time constant. In the present invention, the temperature of the measuring resistor (RM) is kept constant, thus considerably shortening the time constant. The invention is used in gas analysers using the heat conductivity process.

Description

Siemens AktiengesellschaftSiemens Aktiengesellschaft
Vorrichtung zur Analyse von Gasen nach dem Wärmeleitfähig¬ keitsverfahrenDevice for analyzing gases according to the thermal conductivity method
Die Erfindung betrifft eine Vorrichtung zur Analyse von Gasen nach dem Wärmeleitfähigkeitsverfahren gemäß dem Oberbegriff des Anspruchs 1.The invention relates to a device for analyzing gases according to the thermal conductivity method according to the preamble of claim 1.
Eine derartige Vorrichtung ist in der europäischen Patent¬ anmeldung 0 039 956 beschrieben. In einer von einem Meßgas durchströmten Meßkammer ist ein mit konstantem Strom be¬ heizter elektrischer Leiter aufgespannt, dessen Temperatur und damit sein Widerstand von der Wärmeleitfähigkeit des ihn umgebenden Meßgases abhängt. Eine Vergleichskammer mit einem ebenfalls beheizten, temperaturabhängigen Vergleichs¬ widerstand enthält ein Vergleichsgas. Aus der Differenz der Widerstandswerte von Meß- und Vergleichswiderstand wird ein Meßwert gebildet, aus dem die Zusammensetzung des Meßgases abgeleitet wird. Zur Erhöhung der Ansprechge¬ schwindigkeit ist vorgeschlagen, die Meßwerte zyklisch zu ermitteln, indem die Meßkammer rasch mit dem Meßgas ge¬ füllt, dann die Meßgaszufuhr unterbrochen und die Messung durchgeführt wird, wenn das Meßgas in der Meßkammer zur Ruhe gekommen und der Meßwiderstand sich auf einen kon¬ stanten Widerstandswert eingestellt hat. Die Widerstands¬ drähte bestehen aus Platin und sind in den Kammern, die als Glaskapillaren oder Glasröhrchen ausgeführt sein können, aufgespannt und in diese eingeschmolzen. Mit diesen Maßnahmen werden zwar kurze Zeitkonstanten für die Aufwärmung oder Abkühlung in Abhängigkeit des Meßgases erreicht, allerdings ist dazu ein großer Fertigungsaufwand erforderlich, und die fertigen Widerstandstemperaturfühler sind schwierig zu handhaben. Aus der US-PS 3 913 379 ist ein Gasanalysator bekannt, der zwei temperaturabhängige Widerstände aufweist, die in zwei verschiedenen Zweigen einer Meßbrücke geschaltet sind und von denen der eine beheizt, der andere, der Temperatur- kompensation dienende, nicht beheizt ist. Beide sind dem Meßgas ausgesetzt. Der Brückenstrom wird so eingestellt, daß das Verhältnis der Werte des beheizten und des nicht- beheizten, temperaturabhängigen Widerstandes konstant¬ gehalten wird. Das Meßgas wird beiden temperaturabhängigen Widerständen impulsweise zugeführt.Such a device is described in European patent application 0 039 956. An electrical conductor heated with constant current is spanned in a measuring chamber through which a measuring gas flows, the temperature and thus its resistance of which depend on the thermal conductivity of the measuring gas surrounding it. A comparison chamber with a likewise heated, temperature-dependent comparison resistor contains a comparison gas. A measurement value is formed from the difference between the resistance values of the measurement and comparison resistance, from which the composition of the measurement gas is derived. To increase the response speed, it is proposed to determine the measured values cyclically by quickly filling the measuring chamber with the measuring gas, then interrupting the measuring gas supply and carrying out the measurement when the measuring gas has come to rest in the measuring chamber and the measuring resistor has risen has set a constant resistance value. The resistance wires consist of platinum and are clamped in the chambers, which can be designed as glass capillaries or glass tubes, and melted into them. With these measures, short time constants for warming up or cooling down depending on the measurement gas are achieved, however, this requires a large manufacturing effort and the finished resistance temperature sensors are difficult to handle. From US Pat. No. 3,913,379 a gas analyzer is known which has two temperature-dependent resistors which are connected in two different branches of a measuring bridge and one of which is heated, the other which serves for temperature compensation and is not heated. Both are exposed to the sample gas. The bridge current is set so that the ratio of the values of the heated and the unheated, temperature-dependent resistance is kept constant. The sample gas is supplied to both temperature-dependent resistors in pulses.
Der vorliegenden Erfindung liegt die Aufgabe zugrunde, die Zeitkonstante der Vorrichtung gemäß dem Oberbegriff des Anspruchs 1 zu verkürzen, und zwar vor allem auch dann, wenn die temperaturabhängigen Widerstände außer dem Wider¬ standsdraht zusätzliche, die Zeitkonstante vergrößernde Massen, z. B. einen Träger für den Widerstandsdraht, ent¬ halten.The present invention has for its object to shorten the time constant of the device according to the preamble of claim 1, especially when the temperature-dependent resistors in addition to the resistance wire additional masses increasing the time constant, eg. B. a carrier for the resistance wire, ent ent.
Diese Aufgabe wird gemäß der vorliegenden Erfindung mit den im kennzeichnenden Teil des Anspruchs 1 angegebenen Maßnahmen gelöst.This object is achieved according to the present invention with the measures specified in the characterizing part of claim 1.
Anhand der Zeichnung werden im folgenden die Erfindung sowie Ausgestaltungen und Ergänzungen näher beschrieben und erläutert.The invention and the refinements and additions are described and explained in more detail below with reference to the drawing.
Figur 1 veranschaulicht ein Ausführungsbeispiel der Erfin¬ dung, Figur 2 zeigt den Aufbau von im Ausführungsbeispiel nach Figur 1 eingesetzten temperaturabhängigen Wider¬ ständen.FIG. 1 illustrates an embodiment of the invention, FIG. 2 shows the structure of temperature-dependent resistors used in the embodiment of FIG. 1.
In Figur 1 ist mit MK eine Meßkammer bezeichnet, die einen temperaturabhängigen Meßwiderstand RM enthält. Das Meßgas strömt über einen Gaseinlaß GE in die Meßkammer, umspült den Meßwiderstand RM und tritt über einen Gasauslaß GA wieder aus. Eine Vergleichskammer VK, die mit einem Ver¬ gleichsgas gefüllt ist, enthält einen temperaturabhängigen Vergleichswiderstand RV. Beide Kammern sind in einem gemeinsamen Block untergebracht und daher wärmeleitend miteinander verbunden. Die beiden temperaturabhängigenIn FIG. 1, MK denotes a measuring chamber which contains a temperature-dependent measuring resistor RM. The measuring gas flows into the measuring chamber via a gas inlet GE, flows around the measuring resistor RM and passes through a gas outlet GA out again. A comparison chamber VK, which is filled with a comparison gas, contains a temperature-dependent comparison resistor RV. Both chambers are housed in a common block and therefore connected to each other in a heat-conducting manner. The two temperature-dependent
Widerstände sind, wie weiter unten im einzelnen beschrie¬ ben, beheizt. Der Meßwiderstand RM wird in Abhängigkeit der Wärmeleitfähigkeit des Meßgases gekühlt. Wäre, wie bei bekannten Meßvorrichtungen, die Heizleistung konstant, würde sich daher seine Temperatur und damit sein Wider¬ stand entsprechend ändern. Eine Messung wäre aber erst dann sinnvoll, wenn sich der gesamte Meßwiderstand RM auf die neue Temperatur eingestellt hat.Resistors are heated, as described in detail below. The measuring resistor RM is cooled depending on the thermal conductivity of the measuring gas. If, as in known measuring devices, the heating power were constant, its temperature and thus its resistance would change accordingly. However, a measurement would only make sense when the entire measuring resistor RM has adjusted to the new temperature.
Figur 2 zeigt einen in der Vorrichtung nach Figur 1 ein¬ setzbaren Widerstand. Er besteht im wesentlichen aus einem als Glasröhrchen ausgebildeten Träger TR, auf den ein Widerstandsdraht WD bifilar gewickelt ist. In dem gezeig¬ ten Beispiel ist der Widerstandsdraht WD durch das Innere des Trägers TR zu der Wicklung geführt. Die Wicklung sowie die Stirnseiten des Trägers sind mit einer Glashaut GH als Schutzschicht überzogen. Durch den Widerstandsdraht WD wird ein Heizstrom geschickt, der den gesamten Temperatur¬ fühler auf eine Temperatur aufheizt, die von der Wärme- leitfähigkeit des umgebenden Gases abhängt. Bei einer 'Änderung der Wärmeleitfähigkeit ändert sich die Wärme¬ abgabe des Temperaturfühlers, so daß sich auch dessen Temperatur, und zwar zunächst nur an der Oberfläche, ändert. Auch wenn die neue Wärmeleitfähigkeit über längere Zeit konstant bleibt, stellt sich die Temperatur desFIG. 2 shows a resistor that can be used in the device according to FIG. 1. It essentially consists of a carrier TR designed as a glass tube, onto which a resistance wire WD is wound bifilarly. In the example shown, the resistance wire WD is led through the interior of the carrier TR to the winding. The winding and the end faces of the carrier are covered with a GH glass skin as a protective layer. A heating current is sent through the resistance wire WD, which heats the entire temperature sensor to a temperature that depends on the thermal conductivity of the surrounding gas. In a 'change in the thermal conductivity, the Wärme¬ changes output of the temperature sensor, so that also its temperature, initially only on the surface changes. Even if the new thermal conductivity remains constant over a long period, the temperature of the
Widerstandsdrahtes WD bei konstanter Heizleistung erst dann auf einen neuen Wert ein, wenn der gesamte Tempera¬ turfühler auf gleicher Temperatur ist, also wenn auch die verhältnismäßig große Masse des Trägers TR auf der neuen Temperatur ist. Ein Gasanalysator mit einem derartigen, mit konstantem Heizstrom gespeisten Temperaturfühler hat daher eine große Zeitkonstante. Gemäß -der vorliegenden Erfindung wird die Zeitkonstante dadurch verkürzt, daß der Heizstrom nicht konstant ist, sondern daß der Temperaturfühler auf eine konstante Tem¬ peratur geregelt wird. Der Träger TR wird daher nicht mehr erwärmt oder abgekühlt. Die Zeitkonstante entspricht daher nur noch der Zeit, in welcher der Wärmeübergang durch die Glashaut GH sich auf ein neues Gleichgewicht von Wärme¬ erzeugung und Wärmeabfuhr einstellt. Es können daher han¬ delsübliche Widerstandstemperaturfühler, wie sie z. B. unter der Bezeichnung PtlOO bekannt sind, eingesetzt werden, auch wenn eine kurze Zeitkonstante verlangt ist. Die Schutzschicht aus Glas sorgt für eine hohe Korrosions¬ beständigkeit.Resistance wire WD with a constant heating power only at a new value when the entire temperature sensor is at the same temperature, ie when the relatively large mass of the carrier TR is at the new temperature. A gas analyzer with such a temperature sensor fed with constant heating current therefore has a large time constant. According to the present invention, the time constant is shortened in that the heating current is not constant, but in that the temperature sensor is regulated to a constant temperature. The carrier TR is therefore no longer heated or cooled. The time constant therefore only corresponds to the time in which the heat transfer through the glass skin GH adjusts to a new balance of heat generation and heat dissipation. It is therefore possible to use commercially available resistance temperature sensors, such as those used for. B. are known under the name PtlOO, even if a short time constant is required. The protective layer made of glass ensures a high corrosion resistance.
Zur Temperaturregelung sind der Meßwiderstand RM und der Vergleichswiderstand RV in je eine Meßbrücke Rl, R2, R3 bzw. R4, R5, R6 geschaltet (Fig. 1). Die Spannungen an den Brückendiagonalen werden von Differenzverstärkern DVl, DV2 verstärkt, an deren Ausgänge Steuereingänge von Transi- stören TS1, TS2 angeschlossen sind, über welche die Me߬ brücken aus einer Versorgungsspannung ÜB gespeist werden. Mit den Transistoren TS1, TS2 werden die Speiseströme so eingestellt, daß durch Aufheizen der temperaturabhängigen Widerstände RM, RV die Brücken abgeglichen sind. Der Strom durch den Meßwiderstand RM bzw. die an diesem abfallende Spannung ist ein Maß für die Wärmeleitfähigkeit des ihn umgebenden Gases. Zu diesem Heizstrom ist die Spannung zwischen Brückendiagonale und Masse proportional, die einem Meßverstärker MV zugeführt ist. Dieser Spannung wird die an der Diagonale der den Vergleichswiderstand RV ent¬ haltenden Brücke gegengeschaltet, so daß die Differenz der Spannungen an den Brückendiagonalen als Meßwert verwendet wird, der in einem an den Meßverstärker MV angeschlossenen Registriergerät RG angezeigt wird. For temperature control, the measuring resistor RM and the comparative resistor RV are each connected in a measuring bridge R1, R2, R3 or R4, R5, R6 (FIG. 1). The voltages at the bridge diagonals are amplified by differential amplifiers DV1, DV2, to the outputs of which control inputs of transistors TS1, TS2 are connected, via which the measuring bridges are fed from a supply voltage UB. With the transistors TS1, TS2, the feed currents are set so that the bridges are balanced by heating the temperature-dependent resistors RM, RV. The current through the measuring resistor RM or the voltage dropping across it is a measure of the thermal conductivity of the gas surrounding it. The voltage between the diagonal of the bridge and the mass, which is fed to a measuring amplifier MV, is proportional to this heating current. This voltage is connected across the diagonal of the bridge containing the comparison resistor RV, so that the difference between the voltages at the bridge diagonals is used as the measured value, which is displayed in a registration device RG connected to the measuring amplifier MV.

Claims

Patentansprüche Claims
1. Vorrichtung zur Analyse von Gasen nach dem Wärmeleitfähig¬ keitsverfahren mit mindestens einem elektrisch beheizten, temperaturabhängigen Meßwiderstand, der in einer Meßkammer dem zu analysierenden Gas ausgesetzt ist, d a d u r c h g e ¬ k e n n z e i c h n e t , daß der temperaturabhängige Wider¬ stand (RM) auf eine konstante Temperatur geregelt ist und der Meßwert vom Heizstrom oder von der Heizspannung abgeleitet ist.1. Device for analyzing gases according to the thermal conductivity method with at least one electrically heated, temperature-dependent measuring resistor which is exposed to the gas to be analyzed in a measuring chamber, characterized in that the temperature-dependent resistor (RM) regulates to a constant temperature and the measured value is derived from the heating current or from the heating voltage.
2. Vorrichtung nach Anspruch 1, d a d u r c h g e k e n n ¬ z e i c h n e t , daß ein elektrisch beheizter, temperatur¬ abhängiger Vergleichswiderstand (RV), der einem Vergleichsgas ausgesetzt ist, auf eine konstante Temperatur geregelt ist und der Meßwert von der Differenz der Heizströme oder der Heiz¬ spannungen abgeleitet ist.2. Device according to claim 1, characterized in that an electrically heated, temperature-dependent comparison resistor (RV) which is exposed to a reference gas is regulated to a constant temperature and the measured value is derived from the difference in the heating currents or the heating voltages is.
3. Vorrichtung nach Anspruch 2, d a d u r c h g e k e n n ¬ z e i c h n e t , daß die beiden te perturabhängigen Wider- stände (RM, RV) je einen Zweig einer Widerstandsbrücke (Rl, R2, R3; R4, R5, R6) bilden, die über einen Transistor (TS1; TS2) gespeist ist, der so gesteuert ist, daß die Brücke abgeglichen ist, und daß die Differenz der Potentiale an den beiden Brückendiagonalen als Meßwert abgenommen ist. 3. Device according to claim 2, characterized in that the two te temperature-dependent resistors (RM, RV) each form a branch of a resistance bridge (R1, R2, R3; R4, R5, R6) which are connected via a transistor (TS1 ; TS2) is fed, which is controlled so that the bridge is balanced, and that the difference in the potentials on the two bridge diagonals is reduced as a measured value.
PCT/DE1992/000528 1991-07-22 1992-06-26 Device for analysing gases by the heat conductivity process WO1993002352A1 (en)

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Cited By (5)

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GB2306662A (en) * 1995-10-25 1997-05-07 Hewlett Packard Co Thermal conductivity detector
DE19624683C1 (en) * 1996-06-20 1997-10-16 Siemens Ag Thermal conductivity detector apparatus for thermal conductivity determination of medium under study
US5817611A (en) * 1992-12-03 1998-10-06 Jeyes Group, Plc Lavatory cleansing blocks
WO2003091718A1 (en) * 2002-04-26 2003-11-06 Siemens Aktiengesellschaft Thermal conductivity gas analyser
CN100403017C (en) * 2005-07-12 2008-07-16 赵飞 Constant temperature combustable gas concentration detector

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DE4320781A1 (en) * 1993-06-23 1994-03-03 Praessl Wendl Maria Theresia Differential thermal conductivity measurement of solid. liquid or gas samples - comparing heat flows of parallel paths containing sample and reference respectively, measured simultaneously by Peltier device
DE102007031869A1 (en) 2007-07-05 2009-01-08 Kerkow, Hartmut, Dr. Photoelectric temperature controller for measuring wire sensor, has infrared phototransistor for measuring emitted heat radiation of thin and hot measuring wire by electronically processed photoelectric current of transistor

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5817611A (en) * 1992-12-03 1998-10-06 Jeyes Group, Plc Lavatory cleansing blocks
GB2306662A (en) * 1995-10-25 1997-05-07 Hewlett Packard Co Thermal conductivity detector
US5772321A (en) * 1995-10-25 1998-06-30 Hewlett-Packard Company Compensation for spacial and temporal temperature variations in a thermal conductivity detector
GB2306662B (en) * 1995-10-25 1999-12-08 Hewlett Packard Co Thermal conductivity detector
DE19624683C1 (en) * 1996-06-20 1997-10-16 Siemens Ag Thermal conductivity detector apparatus for thermal conductivity determination of medium under study
WO2003091718A1 (en) * 2002-04-26 2003-11-06 Siemens Aktiengesellschaft Thermal conductivity gas analyser
CN100403017C (en) * 2005-07-12 2008-07-16 赵飞 Constant temperature combustable gas concentration detector

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