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 method for rubbing a sensor for determining the concentration of oxidizing gases, in particular for determining the nitrogen oxide concentration in exhaust gases from internal combustion engines, according to the preamble of claim 1.
• Such a sensor can be seen, for example, from EP 0 791 826 AI.
• the method according to the invention with the features mentioned in claim 1 offers the advantage over the fact that the measurement errors resulting from the mutual coupling of the electrodes via electric fields and currents in the solid electrolyte and the measurement errors resulting from the voltage drops at the lead resistances can be eliminated or at least minimized.
• the functionally applied voltages depending on the currents flowing in the electrode feed lines and / or between the electrodes so that the voltages applied to the electrodes inside the sensor correspond to the specified target values, it is possible to reduce the voltages at the Adjust electrodes precisely without errors being distorted by voltage drops on the electrode leads or due to mutual coupling of the electrodes. It is particularly advantageous that the setting is independent of the current intensity with which the individual electrodes are applied.
• An advantageous embodiment provides that voltages are added to the voltages at the electrodes, one of which is weighted by factors Correspond to feedback of voltage components that are proportional to the currents.
• the moving average values of the voltages proportional to the currents and / or their derivation of even higher degrees and / or also their moving average values or linear combinations formed by means of known electrical circuit elements can be fed back therefrom. In this way it is also possible to eliminate capacitive couplings.
• the voltage at the electrodes is advantageously adjusted by changing these factors, these factors being increased until the system begins to oscillate due to the feedback.
• the oscillation occurs when the feedback factor is> 1 in magnitude and at the same time the phase is greater than or equal to 180 °.
• the factors are then reduced slightly, and only to the extent that no more vibration occurs. As a result, almost the entire voltage drops occurring at the electrode feed lines as well as the voltage drops occurring within the solid electrolyte due to a fictitious resistance network can be compensated.
• FIG. 1 shows a schematic sectional illustration through a sensor known from the prior art for determining oxides in gas mixtures
• FIG. 2 schematically shows a circuit arrangement known from the prior art for a sensor shown in FIG. 1;
• Fig. 3 shows an embodiment of a circuit arrangement suitable for carrying out the method according to the invention for a sensor shown in Fig. 1 and
• Fig. 4 schematically shows the coupling of the voltages / currents applied to the electrodes of a sensor shown in Fig. 1 in matrix form.
• a double-NOx sensor shown in FIG. 1, has five electrodes, one oxygen pump electrode 9 exposed to the exhaust gas, one arranged in a first chamber 1, the oxygen pump electrode 9 exposed to the exhaust gas essentially opposite, one arranged in a second chamber 2 Oxygen pump electrode 8, an NO pump electrode 10 likewise arranged in the second chamber 2 and an air reference electrode 6 arranged in a third chamber 3.
• the first chamber 1 is connected to the exhaust gas via a diffusion barrier 4, the second chamber 2 is connected to the first via a further diffusion barrier 5.
• the third chamber 3 is connected to the atmosphere via a channel.
• the oxygen pump electrodes 7 and 8 pump oxygen from the first chamber 1 and from the second chamber 2, respectively.
• the outer pump electrode 9 serves as the counter electrode.
• Nitrogen oxides are pumped out of the NO pump electrode 10. All electrodes are arranged on an ion-conducting solid electrolyte 20, which may consist of zirconium oxide, for example, and are connected to it in an electrically conductive manner.
• An insulated heater 11 is provided to heat the sensor to the required operating temperature.
• An evaluation circuit is used to operate the sensor, which provides various electrical voltages and obtains the measurement signal from a current measurement.
• a block diagram of such a circuit known from the prior art is shown schematically in FIG. 2.
• the three voltages for the oxygen pump electrodes 7, 8 located in the first chamber 1 and the second chamber 2 and for the NO pump electrode 10 are determined via voltage references 31, 32, 33 and drivers 41, 42, 43 generated and shifted by the potential of the air reference.
• the voltage output by driver 40 is added or subtracted to the voltage output by drivers 41, 42, 43 in adder elements 61, 62, 63 in a manner known per se.
• the potential of the outer pump electrode 9 is set via a two-point controller 50 until the voltage difference between the oxygen pump electrode 7 and the air reference electrode 6 corresponds to a predefinable target value.
• the other electrode potentials are set directly.
• the NO pump current can be measured via a current-voltage converter 80 known per se and output as a measurement signal.
• the basic idea of the invention is to enable the required voltages to be set directly on the electrodes without the voltage drop at the lead resistances R L or the mutual coupling of the electrodes via the resistors R E falsifying these electrode voltages.
• This is solved by a method for operating a sensor, which is explained below in connection with a circuit shown in FIG. 3.
• a method for operating a sensor which is explained below in connection with a circuit shown in FIG. 3.
• FIG. 3 those elements which are identical to those of the circuit shown in FIG. 2 are provided with the same reference numerals, so that with regard to their description, reference is made in full to the explanations regarding the circuit shown in FIG. 2 is taken.
• the circuit shown in FIG. 3 differs from that in FIG.
• circuit devices are provided, by means of which the voltages I IPE, ü_NO, U_02 applied to the electrodes 7, 8, 10, 9 are dependent on those in the measuring lines and / or currents flowing between the electrodes are changeable.
• These circuit devices include current-voltage converters 100, 110, 120 and circuit elements (compensation branches) 201, 202, 203, 204, 205, 206, which are weighted with compensation factors K1, K2, K3, K4, K5, K6, such that one Current proportional portion is fed back to the electrodes in such a way that the portions coupled over in the fixed electrolyte 20 and the lead losses are compensated.
• the potentials of the electrodes that can be measured on the feed lines become dependent on the currents in the solid electrolyte 20 and the feed lines.
• the currents in the solid electrolyte 20 are not accessible for measurement, but they result from a linear combination of the currents in the feed lines at each location.
• the entire system is considered to be electrically linear. tet. Due to the linear combination of the currents at each location, voltages are also obtained at the locations of the electrodes, which depend linearly on the supply currents.
• the feedback takes place in such a way that the factor Kl is first increased step by step until there is an oscillation due to the feedback. Then factor K1 is again reduced slightly until no more oscillation occurs. If necessary, the other factors K2 to K6 can be used accordingly.
• Fig. 4 shows schematically the coupling matrix.
• the rows are formed by the currents of the electrodes I_pump electrode 7, I_02 pump electrode 8 and I_N0 pump electrode 10.
• the current of the inner oxygen pump electrode I_pump electrode 7 is relatively large compared to the other two and therefore has a noticeable influence on the electrode voltages U_IPE or on the pump electrode 7, U_02 on the pump electrode 8 and U_N0 on the pump electrode 10.
• the spatial proximity of the oxygen Material pump electrode 8 and the NO pump electrode 10 to each other in the second chamber 2 leads to a pronounced coupling.
• the occupation of the main diagonal of the coupling matrix results from the lead resistance. Since the matrix is symmetrical, it is sufficient to consider only the compensation factors K2, K3, K5 and Kl, K4, K6 arranged on one side of the main diagonal.

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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)

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• 1999
  • 1999-12-23 DE DE19962912A patent/DE19962912C2/de not_active Expired - Fee Related
• 2000
  • 2000-12-20 EP EP00991104A patent/EP1250591B1/de not_active Expired - Lifetime
  • 2000-12-20 US US09/914,208 patent/US6767449B2/en not_active Expired - Lifetime
  • 2000-12-20 WO PCT/DE2000/004550 patent/WO2001048467A2/de not_active Ceased
  • 2000-12-20 JP JP2001548931A patent/JP4638647B2/ja not_active Expired - Fee Related
  • 2000-12-20 DE DE50015927T patent/DE50015927D1/de not_active Expired - Lifetime

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