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WO2003001195A1 - Controle de detecteurs de gaz - Google Patents

Controle de detecteurs de gaz Download PDF

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Publication number
WO2003001195A1
WO2003001195A1 PCT/GB2002/002939 GB0202939W WO03001195A1 WO 2003001195 A1 WO2003001195 A1 WO 2003001195A1 GB 0202939 W GB0202939 W GB 0202939W WO 03001195 A1 WO03001195 A1 WO 03001195A1
Authority
WO
WIPO (PCT)
Prior art keywords
sensor
pulse
current
electrode
monitor
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
PCT/GB2002/002939
Other languages
English (en)
Inventor
John Chapples
Martin Legg
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.)
Honeywell Analytics Ltd
Original Assignee
Zellweger Analytics Ltd
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 Zellweger Analytics Ltd filed Critical Zellweger Analytics Ltd
Publication of WO2003001195A1 publication Critical patent/WO2003001195A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • G01N27/4163—Systems checking the operation of, or calibrating, the measuring apparatus
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/004—CO or CO2

Definitions

  • the present invention relates to the monitoring of sensors for detecting and measuring quantities of gases or vapours in an ambient atmosphere.
  • the present specification will refer to such sensors as "gas sensors", although throughout the present specification that term also applies to the measurement of vapours.
  • the present invention is especially concerned with the monitoring of electrochemical gas sensors, e.g. for measuring toxic gases such as carbon monoxide.
  • Gas sensors are incorporated within gas sensing equipment (called herein "monitors") which include circuitry for analysing the sensor output and, for example, displaying the level of gas in an atmosphere and/or triggering alarms if excessive levels of gas are detected (either instantaneously or when integrated over time).
  • gas sensors One use of gas sensors is to monitor the level of carbon monoxide in a dwelling, particularly in temporary accommodation.
  • Various national and international standards apply to the detection of carbon monoxide in dwellings, including a requirement to measure with reasonable accurately up to 600 parts per million (ppm) of carbon monoxide. It is also a requirement that the monitor tests each sensor within the monitor to ensure that it is operational (viable) for the whole of its expected lifetime, generally 5 years.
  • EP-0 039 549 discloses the imposition of a pulse of potential across the electrolyte of an electrochemical cell, the potential being sufficient to electrolyse the electrolyte. The resulting current is observed and taken to be an indication of the viability of the sensor.
  • the potential may be applied as an alternating or direct current, although the latter is very much preferred.
  • US-5,202,637 discloses a method of monitoring three electrode sensors by applying a pulse of potential between the reference electrode and the sensing electrode (also known as the working electrode) of a sensor.
  • the working electrode of a two-electrode sensor is connected to the inverting terminal of an operational amplifier while a current pulse is applied periodically to the non-inverting terminal of the amplifier.
  • the application of such a pulse can cause a bias voltage to be built up and the readings to drift.
  • Drift affects the accuracy of the readings and can cause a false alarm to be generated if especially severe. Recalibration is rarely possible with domestic monitors.
  • the present invention is based on the realisation that the long term drift in the output of two electrode sensors can be at least reduced.
  • a monitor for monitoring an atmosphere for the presence of a target gas comprising: a) two terminals for connection, respectively, to the working (sensing) electrode and the counter electrode of a two electrode electrochemical gas sensor, the sensor providing a current between the terminals that is indicative of the amount of target gas in the atmosphere; b) a circuit applying successively a pulse of positive potential between the electrode terminals and a pulse of negative potential between the electrode terminals (the pulses can be applied in either order); and c) a detector for monitoring the current of the sensor, including perturbations therein caused by the pulses applied in step b) and generating an alarm signal when the perturbations are less than a predetermined threshold, which is indicative of a malfunctioning sensor or the absence of a sensor.
  • a stream of negative and positive pulses may be applied but they should be limited so that they are not, in effect, the application of a steady state alternating current.
  • a number of pulses e.g. up to about 10 (5 positive and 5 negative) may be applied successively. However, it is preferred that only one such pair of pulses is applied at any instance.
  • the perturbation measured is preferably the change in the output signal during the course of each positive pulse and each negative pulse.
  • An operational amplifier is preferably connected between the sensor electrode terminals to generate an output signal according to the current flowing between the terminals, including perturbations therein caused by the applied pulses; in these circumstances, the detector can monitor the output of the amplifier for detecting the said perturbations.
  • the pulses are advantageously substantially identical.
  • the duration of each pulse may be between 100 and 1000 milliseconds, e.g. 300 to 800 milliseconds and preferably about 600 milliseconds.
  • the potential of each pulse should be insufficient to electrolyse the sensor electrolyte.
  • the present invention also provides a method of monitoring an atmosphere for the presence of a target gas using the monitor as described above.
  • both positive and negative pulse also provides a method of testing the sensor while measuring gas within the normal range of the instrument.
  • Typical low cost domestic gas sensors operate from a single ended supply rail (typically 0V to 4.5V) When no gas is present and hence output is 0V, one of the current pulses cannot be measured since it would tend to produce a negative signal and the amplifier cannot output a values below 0V. However, the other pulse can be measured since it would tend to produce a signal greater than 0V.
  • the second type of pulse will not be detected since the output is already saturated and so the imposition of the second type of pulse will not affect the output signal but the first type of pulse can be measured since it would tend to lower the output signal below the maximum and so can be detected.
  • the presence of at least one of the pulses can be seen.
  • Figure 1 is a schematic circuit diagram showing a circuit of the present invention
  • Figure 2 is a detailed circuit diagram of the circuit of Figure 1;
  • Figure 3 shows the change of current flowing through point 19 of the circuit of Figure 2 when a double pulse is imposed on that point
  • Figure 4 shows the change of output of the circuit of Figure 2 when a double pulse is imposed on the point 19;
  • Figure 5 shows the change of output of the circuit of Figure 2 when a double pulse is imposed on the point 19 and there is no operational sensor included in the circuit;
  • Figure 6 shows the change of output of the circuit of Figure 2 when a double pulse is imposed on the point 19 and the sensor is short circuited
  • Figure 7 shows the change of output of the circuit of Figure 2 when a single pulse is imposed on the point 19.
  • the sensor includes a sensing electrode 11a and a counter electrode 1 lb separated by an intervening body of electrolyte.
  • the sensing electrode 11a is exposed to the atmosphere being monitored and accordingly any toxic gas (in this case carbon monoxide) in the atmosphere comes into contact with the sensing electrode 11a.
  • the sensing electrode 11a is an anode and oxidises the carbon monoxide to carbon dioxide. This oxidation causes a current to flow through the sensor between the working electrode 11a and the counter electrode lib.
  • a pair of resistors 16a and 16b is connected between the sensing electrode 11a and the inverting input of an operational amplifier 12. The non-inverting input of the amplifier is connected to the earth 14.
  • the operational amplifier 12 is acting as a transimpedance amplifier, the gain of which is defined by V out / I ⁇ m and given by the value of the feedback resistor between the negative input and output of the operational amplifier.
  • the amplifier has a negative feedback including a resistor 17 such that the gain on the operational amplifier 12 is about 125,000 fold.
  • the presence of carbon monoxide at the sensing electrode 11a causes the sensing electrode to generate a current proportional to the amount of gas present.
  • the potential difference between the electrodes floats until it reaches a level that is sufficient to generate the current concerned between the sensing and counter electrodes.
  • Such current causes a potential difference across the resistors 16a and 16b, causing a change of potential at the inverting input of the amplifier 12.
  • the operational amplifier 12 generates a signal at its output 15 that is proportional to the potential between its inputs and so the output signal is proportional to the current flowing in the sensor 10 and hence the amount of gas in the atmosphere being monitored.
  • the output signal can be fed to a display and an alarm (neither shown) to display the concentration of carbon monoxide in the atmosphere and to generate an alarm if the concentration exceeds a pre-set threshold.
  • the integrated concentration can be computed over different time periods to generate alarms based on the rate that the human body absorbs a particular concentration of gas.
  • the monitor includes two sources of current 24 and 25 of opposite polarity.
  • a switch 28 controlled by a microprocessor 22 periodically connects the sources of current 24 and 25 successively to point 19 which changes the potential between the working and the counter electrodes 11a and l ib of the sensor and alters the signal on output 15.
  • the microprocessor 22 includes a square wave generator 22' (PWM Output) that is connected to the base of transistor Ql that is connected to a supply rail 21.
  • Resistor Rl and capacitor C3 provide a low frequency filter that filters out the frequency of the square wave and so a voltage is applied to the base of the transistor that is the weighted average of the peaks and troughs of the applied square wave, i.e. if the peaks and troughs are of equal duration, the voltage applied to the base will be half that voltage of the peak voltage and if the peaks are of much longer than the troughs, the voltage supplied to the base is a little less than the voltage of the supply.
  • the transistor Ql acts as an emitter follower so that the voltage of the emitter is 0.7 volts less than that applied to the base of Ql.
  • the voltage applied by the transistor Ql to a diode D3 can be set by altering the ratio of the durations of the peaks and troughs from the square wave generator 22'.
  • the emitter of transistor Ql is connected via diode D3 and a resistor R3 to a point 33 and so the current supplied to the point 33 from the transistor Ql can be controlled by adjusting the ratio of the peaks of the square wave from generator 22' to the troughs.
  • Section 32 of the circuit is a charge pump deriving power from the square wave generator and providing a constant voltage of approximately -3 volts at point 31 of the circuit.
  • Section 34 containing transistors Q2 and Q3 is a constant current source providing a current of -30 ⁇ A to point 33 at the voltage of point 31, i.e. -3V, irrespective of the ratio of peaks to troughs of the square wave generator 22'.
  • the charge pump section 22 When the square wave generator 22 is dormant, i.e. does not provide a square wave signal for an extended period, then the charge pump section will not be charged and so no voltage is applied to point 31 and no current is supplied to point 33. However, the charge pump section 32 is not discharged immediately and so, if the square wave generator 22 produces no peaks for a short period, then a current of -30 ⁇ A is still provided to point 33 at a voltage of -3V for a time.
  • the sensor In the case of a CO sensor 10, the sensor is only periodically tested for viability and between the tests, the normal state of affairs will be for the square wave generator to be set to be dormant and produce no peaks, whereupon the current supplied by sections 32 and 34 to point 33 is zero; the transistor Ql will also not supply any current to point 33 and the overall effect is that no current is supplied at point 19. However, periodically the sensor will undergo testing. Once the charge pump section 32 is charged, the microprocessor 22 produces no square waves and so the transistor Ql will supply no current to point 33 causing a pulse of -30 ⁇ A to be applied to point 19 from the charge pump and the constant current source 32,34.
  • a current of +60 ⁇ A is supplied by transistor Ql, under the influence of the square wave generator, to point 33 causing a pulse of +30 ⁇ A to be applied to point 19.
  • the square wave generator is set to be dormant as described above. The double pulses can be applied periodically, e.g. every minute, to ensure that the sensor is functioning properly.
  • the change in current at point 19 is shown in Figure 3.
  • the two pulses will impose a positive and a negative current on the normal current A flowing though point 19.
  • the sensor acts a capacitor and the pulses will change the potential across the sensor 10, causing current to flow at the sensing electrode as the sensor charges or discharge.
  • Such charging or discharging current will change the potential at the sensing electrode 11a over the course of a positive or negative pulse and will also change the current applied to the operational amplifier over the course of each pulse.
  • the increase in the signal from Vi to V 2 and from V 3 to V over the duration of the two pulses indicates that the sensor is correctly operational since it indicates that charge is flowing at the sensing electrode as a result of the imposed pulses. If (a) the electrolyte in the sensor has dried up e.g. due to leakage, or (b) the sensor is absent or (c) the sensor terminals are not correctly connected to the circuit, or (d) the sensor is short circuited, the sensing electrode will not accept charge and the above change of current over the course of a pulse will not occur or will occur to a much lower extent, indicating that the sensor is no longer correctly functioning. This state of affairs will be detected by the microprocessor 20 and an appropriate error signal generated.
  • Figure 5 shows the change in amplifier output 15 when there is no operational sensor present.
  • the whole of the pulses are applied to the inverting input of the amplifier and there will be no change in the signal over the duration of a pulse.
  • part of the pulse current flows via the short circuit to earth and the output from the operational amplifier will be smaller ( Figure 6) than in the case of the situation described in connection with Figure 5.
  • Figure 6 shows the output from the operational amplifier.
  • the present invention can distinguish between a fault occurring when there is no operational sensor present and a fault occurring when there is a short circuit across the sensor.
  • the signal 15 After a double pulse has been applied, the signal 15 returns to its normal value according to the amount of gas in the atmosphere. However, if only a single pulse is applied, there is an offset in the signal once the pulse has finished (see Figure 7).
  • One advantage of the present invention is that the double pulse will still indicate the viability of the sensor even when the operational amplifier is saturated since the positive current pulse will decrease the current flowing to the amplifier input and will cause a change in the output.
  • the negative current pulse will not be observed since the operational amplifier is already saturated and the increase in the signal at the amplifier input will not alter the amplifier output.
  • the sensor produces no current.
  • the amplifier cannot output a negative signal and so only the application of the negative current to the inverting input of the amplifier will change the current.
  • both positive and negative pulse the presence of at least one of the pulses can be seen.
  • the microprocessor 22 When the microprocessor 22 detects a reversed current, it can apply such voltage pulses to bring the sensor back to its normal operational state more quickly.
  • square wave generator 22' is part of the microprocessor chip 22.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • General Health & Medical Sciences (AREA)
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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
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  • General Physics & Mathematics (AREA)
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Abstract

L'invention concerne un appareil de mesure destiné à contrôler une atmosphère afin d'y détecter la présence d'un gaz cible et comprenant: (a) un détecteur (11) de gaz électrochimique à deux électrodes présentant une électrode de travail (détection) (11a) et une contre-électrode (11b), le détecteur fournissant un courant entre les électrodes indiquant la quantité du gaz cible dans l'atmosphère; (b) un circuit (24, 25, 28) appliquant successivement une impulsion de potentiel positif entre les bornes des électrodes ainsi qu'une impulsion de potentiel négatif à un point (19) provoquant un changement de potentiel entre les bornes des électrodes; et (c) un amplificateur opérationnel (12) connecté entre les bornes des électrodes du détecteur pour générer un signal de sortie selon le courant passant entre les électrodes, notamment les perturbations s'y trouvant provoquées par les impulsions appliquées. Un détecteur contrôle la sortie de l'amplificateur et détecte les changements se produisant dans le courant au cours des impulsions et il génère un signal d'alarme lorsque la valeur dudit changement est inférieure à une valeur de seuil.
PCT/GB2002/002939 2001-06-26 2002-06-26 Controle de detecteurs de gaz Ceased WO2003001195A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0115586A GB0115586D0 (en) 2001-06-26 2001-06-26 Monitoring of gas sensors
GB0115586.0 2001-06-26

Publications (1)

Publication Number Publication Date
WO2003001195A1 true WO2003001195A1 (fr) 2003-01-03

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WO (1) WO2003001195A1 (fr)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102004018289A1 (de) * 2004-04-15 2005-11-03 Abb Patent Gmbh Verfahren zur Bestimmung des Ansprechverhaltens und der Empfindlichkeit eines Sauerstoffsensors in einer Messeinrichung
US7840699B2 (en) 2003-02-28 2010-11-23 Nec Corporation Name resolution server and packet transfer device
EP2261649A1 (fr) * 2009-06-10 2010-12-15 Novar GmbH Procédé et circuit pour la vérification d'un capteur de monoxyde de carbone
CN102706932A (zh) * 2012-05-31 2012-10-03 成都安可信电子股份有限公司 一种电化学气体传感器正反向电流适配电路及方法
CN102706931A (zh) * 2012-05-31 2012-10-03 成都安可信电子股份有限公司 电化学气体传感器偏压与非偏压工作电路及偏压配置电路
US8877035B2 (en) 2005-07-20 2014-11-04 Bayer Healthcare Llc Gated amperometry methods
US9005527B2 (en) 2006-10-24 2015-04-14 Bayer Healthcare Llc Transient decay amperometry biosensors
US9110013B2 (en) 2005-09-30 2015-08-18 Bayer Healthcare Llc Gated voltammetry methods
US9410917B2 (en) 2004-02-06 2016-08-09 Ascensia Diabetes Care Holdings Ag Method of using a biosensor
US9933385B2 (en) 2007-12-10 2018-04-03 Ascensia Diabetes Care Holdings Ag Method of using an electrochemical test sensor

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3809107A1 (de) * 1988-03-18 1989-09-28 Licentia Gmbh Verfahren zur automatischen ueberpruefung der kennwerte eines im messbetrieb befindlichen, auf der basis einer widerstandsaenderung arbeitenden sensors
US5202637A (en) * 1989-04-04 1993-04-13 Neotronics Limited Fault detection in electrochemical gas sensing equipment
US5611909A (en) * 1994-12-22 1997-03-18 Dragerwerk Aktiengesellschaft Method for detecting source of error in an amperometric measuring cell
EP0840112A1 (fr) * 1996-10-29 1998-05-06 Zellweger Analytics Limited Surveillance de l'état d'un détecteur de gaz
US6096186A (en) * 1998-08-18 2000-08-01 Industrial Scientific Corporation Method for determining exhaustion of an electrochemical gas sensor

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3809107A1 (de) * 1988-03-18 1989-09-28 Licentia Gmbh Verfahren zur automatischen ueberpruefung der kennwerte eines im messbetrieb befindlichen, auf der basis einer widerstandsaenderung arbeitenden sensors
US5202637A (en) * 1989-04-04 1993-04-13 Neotronics Limited Fault detection in electrochemical gas sensing equipment
US5611909A (en) * 1994-12-22 1997-03-18 Dragerwerk Aktiengesellschaft Method for detecting source of error in an amperometric measuring cell
EP0840112A1 (fr) * 1996-10-29 1998-05-06 Zellweger Analytics Limited Surveillance de l'état d'un détecteur de gaz
US6096186A (en) * 1998-08-18 2000-08-01 Industrial Scientific Corporation Method for determining exhaustion of an electrochemical gas sensor

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
KITZELMANN D ET AL: "ELECTROCHEMISCHE GASSENSOREN - WIRKUNGSWEISEN UND MOEGLICHKEITEN ZUR FUNKTIONSUEBERWACHUNG. ELECTROCHEMICAL GAS SENSORS- PRINCIPLES AND PERSPECTIVES OF A CONTINUOUS SENSOR CHECK", TECHNISCHES MESSEN TM, R.OLDENBOURG VERLAG. MUNCHEN, DE, vol. 62, no. 4, 1 April 1995 (1995-04-01), pages 152 - 159, XP000516378, ISSN: 0171-8096 *

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7840699B2 (en) 2003-02-28 2010-11-23 Nec Corporation Name resolution server and packet transfer device
US10067082B2 (en) 2004-02-06 2018-09-04 Ascensia Diabetes Care Holdings Ag Biosensor for determining an analyte concentration
US9410917B2 (en) 2004-02-06 2016-08-09 Ascensia Diabetes Care Holdings Ag Method of using a biosensor
DE102004018289A1 (de) * 2004-04-15 2005-11-03 Abb Patent Gmbh Verfahren zur Bestimmung des Ansprechverhaltens und der Empfindlichkeit eines Sauerstoffsensors in einer Messeinrichung
US8877035B2 (en) 2005-07-20 2014-11-04 Bayer Healthcare Llc Gated amperometry methods
US9110013B2 (en) 2005-09-30 2015-08-18 Bayer Healthcare Llc Gated voltammetry methods
US9835582B2 (en) 2005-09-30 2017-12-05 Ascensia Diabetes Care Holdings Ag Devices using gated voltammetry methods
US10670553B2 (en) 2005-09-30 2020-06-02 Ascensia Diabetes Care Holdings Ag Devices using gated voltammetry methods
US11435312B2 (en) 2005-09-30 2022-09-06 Ascensia Diabetes Care Holdings Ag Devices using gated voltammetry methods
US9005527B2 (en) 2006-10-24 2015-04-14 Bayer Healthcare Llc Transient decay amperometry biosensors
US10190150B2 (en) 2006-10-24 2019-01-29 Ascensia Diabetes Care Holdings Ag Determining analyte concentration from variant concentration distribution in measurable species
US11091790B2 (en) 2006-10-24 2021-08-17 Ascensia Diabetes Care Holdings Ag Determining analyte concentration from variant concentration distribution in measurable species
US9933385B2 (en) 2007-12-10 2018-04-03 Ascensia Diabetes Care Holdings Ag Method of using an electrochemical test sensor
US10690614B2 (en) 2007-12-10 2020-06-23 Ascensia Diabetes Care Holdings Ag Method of using an electrochemical test sensor
EP2261649A1 (fr) * 2009-06-10 2010-12-15 Novar GmbH Procédé et circuit pour la vérification d'un capteur de monoxyde de carbone
CN102706931B (zh) * 2012-05-31 2014-07-09 成都安可信电子股份有限公司 电化学气体传感器偏压与非偏压工作电路及偏压配置电路
CN102706931A (zh) * 2012-05-31 2012-10-03 成都安可信电子股份有限公司 电化学气体传感器偏压与非偏压工作电路及偏压配置电路
CN102706932A (zh) * 2012-05-31 2012-10-03 成都安可信电子股份有限公司 一种电化学气体传感器正反向电流适配电路及方法

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