WO2004083842A1 - Dispositif et procede de mesure de la concentration en nox dans un gaz de mesure - Google Patents

Dispositif et procede de mesure de la concentration en nox dans un gaz de mesure Download PDF

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Publication number
WO2004083842A1
WO2004083842A1 PCT/EP2004/000076 EP2004000076W WO2004083842A1 WO 2004083842 A1 WO2004083842 A1 WO 2004083842A1 EP 2004000076 W EP2004000076 W EP 2004000076W WO 2004083842 A1 WO2004083842 A1 WO 2004083842A1
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WO
WIPO (PCT)
Prior art keywords
pump current
measuring
reference electrode
gas
solid electrolyte
Prior art date
Application number
PCT/EP2004/000076
Other languages
German (de)
English (en)
Inventor
Tim Walde
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 WO2004083842A1 publication Critical patent/WO2004083842A1/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
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/417—Systems using cells, i.e. more than one cell and probes with solid electrolytes
    • G01N27/419—Measuring voltages or currents with a combination of oxygen pumping cells and oxygen concentration cells

Definitions

  • the invention relates to a device for measuring a gas concentration in a measuring gas, which has an outer electrode which is connected to a solid electrolyte and exposed to the measuring gas, and a reference electrode connected to the solid electrolyte, over which by means of a through the solid electrolyte flowing pump current, a constant oxygen concentration can be set, which differs from the oxygen concentration in the measurement gas, a pump current unit driving the pump current being connected between the reference electrode and the outer electrode and the device being heated by an electrical heating device.
  • the invention further relates to a method for measuring the NOx concentration in a measuring gas, wherein in an electrically heated device with an outer electrode, which is connected to a solid electrolyte and exposed to the measuring gas, and a reference electrode also connected to the solid electrolyte a pump current driven by the outer electrode to the reference electrode is transported from the measuring gas from the outer electrode to the reference electrode.
  • a thick-film sensor To measure the NOx concentration in a measurement gas, for example the exhaust gas of an internal combustion engine, it is known to use a thick-film sensor. Such a sensor is described for example in DE 199 07 947 AI. This sensor has two measuring cells and a body made of zirconium oxide that conducts oxygen ions. He realizes the following measurement concept: in a first measuring cell, to which the sample gas is supplied via a diffusion barrier, a first oxygen concentration is set by means of a first oxygen ion pump current, with no decomposition of NOx taking place. In a second measuring cell with the first is connected via a further diffusion barrier, the oxygen content is further reduced by means of a second oxygen ion pump current.
  • the decomposition of NOx on a measuring electrode located in the second measuring cell leads to a third oxygen ion pumping current, which is a measure of the NOx concentration.
  • the entire sensor is brought to an elevated temperature, eg 750 ° C, using an electric heater.
  • a Nernst voltage is tapped in the respective measuring cells, reference always being made to an oxygen content to which a reference electrode is exposed, usually that of the ambient air.
  • oxygen pumps from the outer electrode exposed to the measuring gas to the reference electrode above the reference electrode can be used to set an increased oxygen concentration which is independent of fluctuations and then serves as a reference concentration.
  • Reference electrode is of minor importance for the measuring process, as long as this value is only constant. lies, since the sensor concept explained at the beginning only makes relative measurements with respect to the chemical oxygen potential at the reference electrode in the Nernst voltage measurement.
  • the invention is based on the object of developing the device described at the outset or the method explained at the outset in such a way that a more precise measurement is possible.
  • a device for measuring a gas concentration in a measuring gas which has an outer electrode which is connected to a solid electrolyte and exposed to the measuring gas, and a reference electrode connected to the solid electrolyte, above which by means of a solid electrolyte flowing pump current, a constant oxygen concentration can be set, which differs from the oxygen concentration in the measurement gas, a pump current unit driving the pump current being connected between the reference electrode and the outer electrode, the device being heated by an electrical heating device and the pump current unit detecting one or more operating parameters of the heating device and the like Sets pump current depending on the measured value.
  • the invention is based on the knowledge that, in the case of gas sensors, a measurement signal falsification can sometimes result from influences of the sensor heating.
  • the inventor recognized that, in particular in the case of sensors based on zirconium oxide, insufficient electrical insulation of the heater from the rest of the sensor body can result in a shift in the voltage potential as a function of the operating parameters of the heater.
  • other operating parameters such as the level or duty cycle of a heating current, can also cause such a voltage potential shift.
  • the oxygen concentration serves as a reference point for other pumping and concentration determination processes in the sensor, a change in the oxygen concentration at the reference electrode automatically results in an undesired and unknown shift in the operating points in the sensor or on the individual electrodes of the sensor. This not only disadvantageously changes the measuring accuracy of the sensor, but also the cross-sensitivity and the aging behavior.
  • the above-described solution to the problem mentioned at the outset has the additional advantage that the voltage potentials do not shift in the first place, since the operating parameter of the heating device is taken into account when selecting the pump current for the reference electrode ensures a constant oxygen concentration at the reference electrode and consequently a shift in the voltage potentials related to it is excluded.
  • the accuracy of the sensor is improved by keeping the oxygen concentration constant at the reference electrode.
  • the individual operating points that must be observed during the operation of the sensor are approached more precisely, which has an advantageous effect on the cross-sensitivity and aging behavior of the sensor.
  • the supply voltage of the heating device can be directly proportional to the level of the pump current in a suitable transmission ratio.
  • the pulse duty factor or the pump current level can be coupled proportionally to the supply voltage.
  • other operating parameters of the heating device can also be taken into account when selecting the Pu p current. For example, the amount of a current flowing in the heating device or, in the case of a heating device operated in a clocked manner, the corresponding clock ratio can be taken into account.
  • the pump current unit detects the level of the supply voltage and selects the level of the pump current depending on the level of the supply voltage.
  • the pump current unit can be equipped with a measuring device which does not have to be integrated directly into the sensor or its circuitry; an external measuring device with suitable transmission of a value representing the level of the supply voltage is also suitable.
  • a measuring device can be provided as an internal or independent unit in the sensor or its connection.
  • the pump current unit In addition to an external measurement of the pulse duty factor, it is possible to design the pump current unit in such a way that it receives, appropriately evaluates and takes into account information about the pulse duty factor from a device controlling the heating device.
  • the pump current can be controlled both with regard to the level of a uniformly operated pump current and with regard to the timing of a pump current driven in a clocked manner.
  • the clocking will usually be suitably influenced, for example by changing the pulse duty factor.
  • Fig. 1 is a schematic sectional view through a NOx sensor with associated wiring and
  • FIG. 2 shows a block diagram of the circuitry of the sensor of FIG. 1.
  • Fig. 1 shows a schematic section through a NOx sensor that detects the NOx concentration in the exhaust tract of an internal combustion engine.
  • This sensor formed from a solid electrolyte, in the example Zr0 2 , receives the exhaust gas to be measured, the NOx concentration of which is to be determined, via a diffusion barrier 3.
  • the entire measuring sensor 1 is controlled by an electric heater 13 controlled by a heating controller H to the operating temperature. brought.
  • the exhaust gas diffuses through the diffusion barrier 3 into a first measuring cell 4.
  • the oxygen content in this measuring cell 4 is measured by tapping a first Nernst voltage VO between a first electrode 5, which is located in the first measuring cell 4, and a reference electrode 11, which is in a reference cell 12 is arranged.
  • the reference cell 12 is largely sealed off from the ambient air, suitable measures being taken to equalize the pressure when the ambient pressure changes.
  • a pressure compensation opening 14 in the form of a pinhole is provided for this purpose.
  • the Nernst voltage VO is therefore related to the oxygen content in the reference cell 12 in which the reference electrode 11 is located. The importance of this will be explained in more detail later.
  • a first circuit arrangement sets a predetermined oxygen concentration in the first measuring cell 4.
  • the first Nernst voltage V0 is tapped by a regulator which provides a driver voltage VpO which drives a first oxygen ion pump current IpO through the solid electrolyte 2 of the sensor 1 between the first electrode 5 and an outer electrode 6.
  • a predetermined oxygen concentration is set up in the first measuring cell 4, which is measured via the Nernst voltage V0 between the electrode 5 and the reference electrode 11.
  • the measurement of the first oxygen ion pump current IpO required for regulation is carried out via a measuring resistor RO and a voltmeter VO. These are implemented using an A / D converter with an internal resistance.
  • the second measuring cell 8 is connected to the first measuring cell 4 via a further diffusion barrier 7.
  • the gas present in the first measuring cell 4 diffuses into the second measuring cell 8 through this diffusion barrier 7.
  • a second circuit arrangement sets a second oxygen concentration in the second measuring cell.
  • a second Nernst voltage VI is tapped between a second electrode 9 and the reference electrode 11 and fed to a controller which provides a second drive voltage Vpl, with which a second oxygen ion pump current Ipl is driven out of the second measuring cell 8 in order to reduce the oxygen content in the to further reduce the second measuring cell 8.
  • a measuring resistor Rlm and a voltmeter Vlm are used to control the second oxygen ion pumping current Ipl.
  • the second circuit arrangement regulates the second oxygen ion pump current Ipl in such a way that a predetermined oxygen concentration is established in the second measuring cell 8. This is so large that NOx is not affected by the processes taking place, in particular it is not decomposed.
  • the NOx is now pumped in a second oxygen ion pump current Ip2 from the measuring electrode 10 to the outer electrode 6 in the second measuring cell 8 at a measuring electrode 10, which can be configured catalytically. Since the residual oxygen content in the measuring cell 8 has been reduced to such an extent that the oxygen ion pumping current Ip2 is essentially carried only by oxygen ions which originate from the decomposition of NOx at the measuring electrode 10, the pumping current Ip2 is on
  • the third oxygen ion pump current Ip2 is determined via a measuring resistor R2m and a voltmeter V2m, and, like the previous pump currents, is driven by a driver voltage, in this case Vp2, which is specified by a controller which has a third Nernst voltage V2 between the measuring electrode 10 and the reference electrode 11 taps.
  • the sensor 1 is fed from a battery B, from which the driver voltages etc. are also derived.
  • the battery B is suitable via lines (not shown) connected to all active components 13, in particular to the heating controller H.
  • the reference cell 12 In order to have a constant reference potential available in the reference electrode 11 when measuring the Nernst voltages, the reference cell 12 is essentially sealed off from the ambient air. Furthermore, due to unavoidable diffusion processes, an increased partial oxygen pressure compared to the environment is set in the reference cell 12 by driving a fourth oxygen ion pump current Ip3 from the outer electrode to the reference electrode 11 by means of a controlled current source UI, which pumps oxygen into the reference cell 12.
  • the current source UI is controlled by means of a control voltage Vs, which is output by a controller C.
  • Vs which is output by a controller C.
  • a different, analog circuit is also optionally possible.
  • the controller C is connected for setting the fourth pump current Ip3 according to the diagram shown in FIG. 2 as a block diagram.
  • the controller C is controlled by a measuring device M via control lines SI and S2.
  • the controller C and the measuring device M are therefore part of a pump current unit.
  • the controller C takes the signals transmitted via the control lines S1 and S2 into account when setting the control voltage VS, which sets the fourth oxygen ion pump current Ip3.
  • the controller C varies the maximum level of the fourth oxygen ion pump current Ip3.
  • the measuring device M detects operating parameters of the heating controller H via measuring taps M1 and M2 and outputs a corresponding signal on the control lines S1 and S2.
  • the operating parameter detected by the measuring device M is the supply tensioner of the heater 13.
  • the heating controller H controls the heater 13 in a clocked manner according to a pulse duty factor, and the measuring device M uses the measuring taps Ml and M2 the duty cycle set by the heating control H.
  • the operating parameter of the heater 13 determined in this way is converted by the measuring device M into the control information, which is supplied to the controller C via the control lines S1 and S2, according to a previously determined relationship between the operating parameters and the pumping of oxygen to the reference electrode 11.
  • a linear relationship between operating parameters e.g. Battery voltage and pump current are assumed.
  • More complex relationships can be realized as suitable functions or through suitably stored maps.
  • the measurement takes place using the heating controller H.
  • the heating controller H energizes the heater 11 according to a pulse duty factor.
  • the measuring device is then implemented in such a way that the heating controller H reports the pulse duty factor directly to the controller C for appropriate consideration when setting the fourth oxygen pump current Ip3.
  • the measuring device M as part of the pump current unit, does not directly record values of the heating controller H, but rather senses the voltage of the battery B.

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Measuring Oxygen Concentration In Cells (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)

Abstract

L'invention concerne un dispositif de mesure de la concentration en NOx dans un gaz de mesure. Ce dispositif comporte une électrode externe (6), reliée à un électrolyte solide (2) et exposée au gaz de mesure, ainsi qu'une électrode de référence (11), reliée à l'électrolyte solide (2) et par l'intermédiaire de laquelle une concentration en oxygène constante, se distinguant de la concentration en oxygène dans le gaz de mesure, peut être réglée au moyen d'un courant de pompage (Ip3) traversant l'électrolyte solide (2). Selon ladite invention, une unité à courant de pompage (UI3), propulsant le courant de pompage (Ip3), est montée entre l'électrode de référence (11) et l'électrode externe (6), laquelle unité enregistre et prend en compte un paramètre de fonctionnement d'un système de chauffage (13) chauffant ledit dispositif.
PCT/EP2004/000076 2003-03-18 2004-01-08 Dispositif et procede de mesure de la concentration en nox dans un gaz de mesure WO2004083842A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE10311816.0 2003-03-18
DE2003111816 DE10311816B4 (de) 2003-03-18 2003-03-18 Vorrichtung und Verfahren zur Messung der NOx-Konzentration in einem Messgas

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WO2004083842A1 true WO2004083842A1 (fr) 2004-09-30

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5340462A (en) * 1992-06-25 1994-08-23 Mitsubishi Denki Kabushiki Kaisha Air-fuel ratio sensor
EP0841562A2 (fr) * 1996-11-08 1998-05-13 Ngk Spark Plug Co., Ltd Méthode et appareil pour mesurer la concentration d'oxygène et d'oxyde d'azote
EP1014084A2 (fr) * 1996-05-16 2000-06-28 Ngk Insulators, Ltd. Procédé de détermination d'oxide d'azote
US6192874B1 (en) * 1997-01-31 2001-02-27 Sagem Sa Device for measuring oxygen content in a gas medium

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH063431B2 (ja) * 1984-02-08 1994-01-12 三菱電機株式会社 機関の空燃比センサ
DE4333231A1 (de) * 1993-09-30 1995-04-06 Bosch Gmbh Robert Verfahren zum Betrieb einer Sauerstoffsonde mit interner Referenzatmosphäre
DE19907947B4 (de) * 1999-02-24 2004-01-29 Siemens Ag Schaltung für einen NOx-Meßaufnehmer

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5340462A (en) * 1992-06-25 1994-08-23 Mitsubishi Denki Kabushiki Kaisha Air-fuel ratio sensor
EP1014084A2 (fr) * 1996-05-16 2000-06-28 Ngk Insulators, Ltd. Procédé de détermination d'oxide d'azote
EP0841562A2 (fr) * 1996-11-08 1998-05-13 Ngk Spark Plug Co., Ltd Méthode et appareil pour mesurer la concentration d'oxygène et d'oxyde d'azote
US6192874B1 (en) * 1997-01-31 2001-02-27 Sagem Sa Device for measuring oxygen content in a gas medium

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DE10311816B4 (de) 2005-12-29
DE10311816A1 (de) 2004-10-07

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