DE102004028551A1 - Reducing non-stationary temperature effects in electrochemical gas sensors, useful for miniaturized carbon monoxide or dioxide sensors, by applying a temperature-dependent potential to the sensor - Google Patents

Reducing non-stationary temperature effects in electrochemical gas sensors, useful for miniaturized carbon monoxide or dioxide sensors, by applying a temperature-dependent potential to the sensor

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Publication number
DE102004028551A1
DE102004028551A1 DE200410028551 DE102004028551A DE102004028551A1 DE 102004028551 A1 DE102004028551 A1 DE 102004028551A1 DE 200410028551 DE200410028551 DE 200410028551 DE 102004028551 A DE102004028551 A DE 102004028551A DE 102004028551 A1 DE102004028551 A1 DE 102004028551A1
Authority
DE
Germany
Prior art keywords
temperature
sensors
sensor
electrode
potential
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.)
Ceased
Application number
DE200410028551
Other languages
German (de)
Inventor
Christoph Dr. Bernstein
Rigobert Chrzan
Stephan Dr. Haupt
Dieter Krüger
Andreas Nauber
Michael Sick
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Draeger Safety AG and Co KGaA
Original Assignee
Draeger Safety AG and Co KGaA
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 Draeger Safety AG and Co KGaA filed Critical Draeger Safety AG and Co KGaA
Priority to DE200410028551 priority Critical patent/DE102004028551A1/en
Publication of DE102004028551A1 publication Critical patent/DE102004028551A1/en
Application status is Ceased legal-status Critical

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means
    • G01N27/26Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403Cells and electrode assemblies
    • G01N27/404Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors
    • G01N27/4045Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors for gases other than oxygen

Abstract

Method for reducing non-stationary temperature effects in electrochemical gas sensors that include a potentiostat comprises applying a potential (U) (a) between reference and measuring electrodes, in a 3-electrode sensor, or between counter and measuring electrodes, in a 2-electrode sensor, and varying this potential depending on the changes in environmental temperature.

Description

  • The The invention relates to a method for reducing transient temperature effects when using electrochemical gas sensors with potentiostats. The Procedure can be anywhere find there advantageous use where electrochemical gas sensors fast temperature changes are exposed.
  • at electrochemical anperometric gas sensors becomes the potential difference for three-electrode sensors between reference and measuring electrode and in the case of two-electrode sensors between the counter and measuring electrodes a Potentiostatenschaltung fixed. This setting is independent of the ambient temperature in the prior art. This principle has also changed with strong changes in the ambient temperature proven. For each ambient temperature there is a specific zero current. Does that change? Ambient temperature, the zero current drifts gradually from its initial value to a new steady state value to the new ambient temperature belongs. This temperature dependence The zero current of electrochemical sensors is known and generally good to compensate.
  • at Miniaturization of such sensors has been found that the temperature dependence of Nullstromes partially considerably from the above behavior differs. In changing Ambient temperatures show some miniaturized sensor types, which are operated at potentials not equal to 0V, significant changes of the zero current, which do not compensate each other in a conventional way to let.
  • at fast changes the ambient temperature, z. B. at a temperature jump from 20 ° C to 30 or 50 ° C, The zero current drifts to positive or negative values, the like can be high, that faults or false alarms are triggered in connected evaluation devices can. Before the zero current is a new temperature-dependent steady-state final value achieved, can in such cases a few minutes pass. During this time, the affected sensor is in conventional Arrangements not for evaluable measurements available.
  • possibly hang the observed highly transient Effects with the opposite larger sensors changed Geometry and the associated different setting a stationary one Condition after a temperature change together.
  • Affected are specifically sensor types whose reference electrode is from another Material as the measuring electrode consists. Under miniaturized electrochemical In the following, sensors are understood to be sensors whose volume about the order of magnitude of a cubic centimeter or slightly lower. Significantly smaller Sensor volumes are conceivable.
  • When examples for possible Disadvantages of wiring miniaturized electrochemical sensors According to the prior art, the following behavior is given. One miniaturized CO sensor is operated at 150 mV. Does that rise? Ambient temperature of 20 ° C to 50 ° C, so shows up for a few minutes a zero current of up to 10μA. This corresponds to a CO concentration of about 1000 ppm, with the CO-MAK value being 30 ppm. A miniaturized CO2 sensor also shows extremely strong transient temperature effects, which hardly make it possible to use it in practice. Another miniaturized CO sensor, which was also operated at 150 mV, showed after an identical temperature jump for a few minutes a negative Zero signal of up to -1,5μA, whereby error messages are usually triggered in measuring arrangements.
  • The The object of the invention is to provide a method which it allows, with miniaturized electrochemical gas sensors to work without being during or after quick changes the ambient temperature calculated with strongly faulty measured values must become. The miniaturized sensors should be similar in temperature jumps Drifting of the zero current show like conventional larger sensors.
  • Is solved the object by a method having the features of the claim 1. Advantageous embodiments can be found in the subclaims.
  • investigations Prototypes have shown that with miniaturized electrochemical gas sensors under stationary Temperature conditions similar accuracies can be achieved as with conventional huge Sensors.
  • Surprised has shown that the above - described transient courses of the Zero current after a change the ambient temperature can be almost completely avoided if at the same time with the temperature change the potential at the measuring electrode raised or lowered by a few millivolts. In this way can be miniaturized electrochemical gas sensors with similar Use measurement performance as well-known larger sensors.
  • The invention then comprises a method for reducing transient temperature effects when using electrochemical gas sensors with potentiostats, in which a potential is applied at preielektrodensensoren between reference and measuring electrode and two-electrode sensors between the counter and measuring electrode, which is changed in response to changes in the ambient temperature of the gas sensor. The type of potential change according to the invention depends on the type of sensor used and can be determined in simple experiments.
  • A simple and convenient design of the method consists in three-electrode sensors between Reference and measuring electrode and in the case of two-electrode sensors between Counter electrode and measuring electrode to attach a constant potential, too the one of changes the ambient temperature of the gas sensor dependent correction voltage added becomes. This correction voltage may be a fixed voltage value when crossing a thermal ambient criterion is added.
  • It are also configurations with miniaturized electrochemical Gas sensors have been found in which a temperature-induced overshoot to positive zero current values avoided by a potential reduction can be.
  • The solution The object set at the outset thus takes place in that the potential difference between measuring and reference electrode of the temperature change the ambient temperature made dependent becomes. In many cases enough it, the setpoint voltage of the potentiostat a small correction potential to overlay, which depends only on the ambient temperature, time constants of temperature changes but except Consider.
  • Especially advantageous the process of the invention To run, if over a temperature sensor dependent on the ambient temperature voltage is generated, which has a analog or digital electronics, possibly software-based, for Target voltage of the potentiostat is added. This is done in this way an automatic potential correction after temperature jumps.
  • The ambient temperature can be determined with an NTC element, a Pt-100 resistor, a thermocouple or other temperature sensors. The output voltage of the temperature sensor can be multiplied in the simplest case by a factor and used directly for potential correction by adding it to the output voltage of the potentiostat. The factor can usually be determined in the course of a calibration by simple experiments. In an advantageous embodiment of the method according to the invention, the voltage to be added to the setpoint voltage of the potentiostat is obtained from a linear dependence on the ambient temperature, which is chosen so that it is at standard conditions, for example, an ambient temperature of 20 ° C, is just 0 mV. A multiply proven calculation rule for the potential correction can be represented by the following formula: U (θ) = 0V + dU / dθ · (θ - 20 ° C)
  • U is the voltage that adds to the setpoint voltage of the potentiostat is, θ is which describes the prevailing ambient temperature and dU / dθ, How an optimal potential correction depends on the height of the temperature jump to be compensated. This Quotient is typically around 1 mV / K and is for individual Sensor types once to be determined or from time to time to check and if necessary to correct.
  • vicarious for many applications the method according to the invention are listed below Examples.
  • Associated shows:
  • 1 the potential profile and the associated course of the zero current of a small CO 2 sensor during a temperature jump, wherein the sensor is connected according to the prior art,
  • 2 the potential profile and the associated course of the zero current of a small CO 2 sensor during a temperature jump, wherein the sensor is connected according to the invention,
  • 3 the potential profile and the associated course of the zero current of a small CO sensor during two temperature jumps, wherein the sensor is connected according to the prior art,
  • 4 the potential profile and the associated course of the zero current of a small CO sensor during two temperature jumps, wherein the sensor is connected according to the invention,
  • 5 a block diagram of an apparatus for performing the method according to the invention.
  • Example 1:
  • A large CO 2 sensor (eg standard Pac XS CO 2 sensor) is operated with a voltage of 400mV between the measuring and reference electrodes. at a temperature jump from 20 ° C to 50 ° C increases the zero current in the form of a stage within a few, typically about 10 minutes to a steady end value. This zero current rise can be stored in your table and compensated if necessary.
  • Will, as in 1 If a miniaturized CO 2 sensor (1 cm diameter, 4 mm height) is exposed to the same temperature jump, the zero current shows a strong increase to a multiple of the full scale value. After some time, for example after about 15 minutes, the zero current slowly decreases and gradually assumes a stable final value. The exact course of this form of strong overshoot of the zero current can be difficult to predict and therefore hardly compensate as a transient zero current effect.
  • However, as in 2 shown during the temperature jump, the voltage between the reference and measuring electrode by 20mV from 400mV to 420mV increases, so this sensor, the unsteady zero current effect no longer occurs. The zero current slowly drifts to the new stationary end value after the temperature jump, without showing a strong overshoot in the meantime. This process is known from larger sensors ago. The potential change has no influence on the actual measurement signal, which indicates the concentration of CO 2 to be measured.
  • Example 2:
  • Similar Observation can also be made when measuring other gases. Will be a great CO sensor with a voltage of 150mV between measuring and reference electrode operated, then rises in a temperature jump from 20 ° C to 50 ° C, the zero current in the form of a stage within a few minutes to a steady end value at. This zero current increase leaves put in your table in a memory chip and at Compensate for demand.
  • Will, as in 3 If a miniaturized CO sensor (1 cm in diameter, 4 mm in height) is exposed to the same temperature jump, the zero current initially shows a sharp drop to negative values, for example -2 μA. After some time, the zero current slowly increases and gradually assumes a stable positive end value. When the ambient temperature jumps from 50 ° C to 20 ° C, the zero current initially rises to a few μAμm and then slowly drops to the steady end value within several minutes, which corresponds to an ambient temperature of 20 ° C. The exact course of this form of a strong overshoot of the zero current can also be difficult to predict and therefore hardly compensate as a transient zero current effect.
  • However, as in 4 shown, during the temperature jump from 20 ° C to 50 ° C, the potential of the measuring electrode of 20mV increased by 20mV to 170mV from 150mV and on return from 50 ° C to 20 ° C again reduced from 170mV to 150mV, the transient zero current effects are greatly reduced , This potential change also has no influence on the actual measurement signal, which indicates the concentration of the CO to be measured.
  • 5 shows the block diagram of an apparatus for carrying out the method according to the invention. A temperature-dependent measured variable of a temperature sensor 1 (eg the resistance value of a Pt - 100 sensor) is connected to a circuit 2 converted into a temperature-dependent voltage U (θ), which in an adder 3 to the constant setpoint voltage U is to be added. The sum of the setpoint voltage U soll and the temperature-dependent voltage U (θ) is used as an input to the potentiostat 4 conducts and controls the potential adjustment of the measuring electrode of the electrochemical sensor 5 ,

Claims (4)

  1. A method for reducing transient temperature effects when using electrochemical gas sensors with potentiostats, characterized in that in three-electrode sensors between the reference and measuring electrode or two-electrode sensors between the counter and measuring electrode, a potential is applied, which is changed in response to changes in the ambient temperature of the gas sensor.
  2. Method according to claim 1, characterized in that in the case of three-electrode sensors, between the reference electrode and the measuring electrode or in the case of two-electrode sensors between the counter and measuring electrodes constant potential, to which one of changes the ambient temperature of the gas sensor dependent correction voltage is added.
  3. Method according to claim 2, characterized in that that the correction voltage linearly from the ambient temperature of Gas sensor is dependent.
  4. Method according to claim 2, characterized in that that the correction voltage according to the rule U (θ) = 0V + dU / dθ · (θ - 20 ° C) where U is the voltage corresponding to the setpoint voltage of the potentiostat is added and θ the describes each prevailing ambient temperature.
DE200410028551 2004-06-12 2004-06-12 Reducing non-stationary temperature effects in electrochemical gas sensors, useful for miniaturized carbon monoxide or dioxide sensors, by applying a temperature-dependent potential to the sensor Ceased DE102004028551A1 (en)

Priority Applications (1)

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DE200410028551 DE102004028551A1 (en) 2004-06-12 2004-06-12 Reducing non-stationary temperature effects in electrochemical gas sensors, useful for miniaturized carbon monoxide or dioxide sensors, by applying a temperature-dependent potential to the sensor

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE200410028551 DE102004028551A1 (en) 2004-06-12 2004-06-12 Reducing non-stationary temperature effects in electrochemical gas sensors, useful for miniaturized carbon monoxide or dioxide sensors, by applying a temperature-dependent potential to the sensor

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DE102004028551A1 true DE102004028551A1 (en) 2006-01-05

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3116884A1 (en) * 1980-04-28 1982-01-28 Kuraray Co A method and circuit for measuring the ionenaktivitaet in liquids
DE3109454A1 (en) * 1981-03-12 1982-09-23 Schott Glaswerke Probe for measuring oxygen partial pressures in highly aggressive media
DE3786127T2 (en) * 1986-08-28 1993-12-02 Ngk Insulators Ltd Oxygen concentration measuring device.
DE4403909A1 (en) * 1994-02-08 1995-08-10 Max Planck Gesellschaft Reference electrode for galvanic cells having an ion-conducting solid electrolyte
DE19512117A1 (en) * 1995-04-04 1996-10-10 Itt Ind Gmbh Deutsche measuring device
DE68927566T2 (en) * 1988-07-25 1997-05-15 Honeywell Inc Temperature compensation for potentiometric working ISFETS
DE10129344A1 (en) * 2000-06-20 2002-05-23 Denso Corp A method for the output characteristics of a gas sensor element based on the supply of electric power setting of this sensor element

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3116884A1 (en) * 1980-04-28 1982-01-28 Kuraray Co A method and circuit for measuring the ionenaktivitaet in liquids
DE3109454A1 (en) * 1981-03-12 1982-09-23 Schott Glaswerke Probe for measuring oxygen partial pressures in highly aggressive media
DE3786127T2 (en) * 1986-08-28 1993-12-02 Ngk Insulators Ltd Oxygen concentration measuring device.
DE68927566T2 (en) * 1988-07-25 1997-05-15 Honeywell Inc Temperature compensation for potentiometric working ISFETS
DE4403909A1 (en) * 1994-02-08 1995-08-10 Max Planck Gesellschaft Reference electrode for galvanic cells having an ion-conducting solid electrolyte
DE19512117A1 (en) * 1995-04-04 1996-10-10 Itt Ind Gmbh Deutsche measuring device
DE10129344A1 (en) * 2000-06-20 2002-05-23 Denso Corp A method for the output characteristics of a gas sensor element based on the supply of electric power setting of this sensor element

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
HAMANN, VIELSTICH, Elektrochemie, Wiley-VCH Verlag Weinheim, 3. Aufl., 1998, S. 81f *

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