CA2186341A1 - Electrochemical sensor - Google Patents
Electrochemical sensorInfo
- Publication number
- CA2186341A1 CA2186341A1 CA 2186341 CA2186341A CA2186341A1 CA 2186341 A1 CA2186341 A1 CA 2186341A1 CA 2186341 CA2186341 CA 2186341 CA 2186341 A CA2186341 A CA 2186341A CA 2186341 A1 CA2186341 A1 CA 2186341A1
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- Prior art keywords
- electrode
- sensing
- electrodes
- potential
- counter
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Classifications
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- 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
- G01N27/48—Systems using polarography, i.e. measuring changes in current under a slowly-varying voltage
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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)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
The invention provides an electrochemical sensor of the type having a sensing electrode (12), a reference electrode (14) and a counter electrode (16) all in contact with an electrochemical medium, an amplifier (18) capable in operation of maintaining a first potential between the sensing electrode and the reference electrode, and means for detecting a current flowing at the sensing electrode or at the counter electrode in response to an electrochemical reaction at the sensing electrode due to the presence of a material of the type being monitored.
According to the invention, there is an array of the sensing electrodes and a corresponding array of one of the reference electrodes and the counter electrodes, and means (30, 32) are provided for cycling an applied potential between the different electrodes in at least one of the arrays whereby each sensing electrode is in turn subjected to (a) a sensing potential at which detection can take place, and (b) a refreshing potential at which a discarge current flows between the associated counter electrode and sensing electrode to clean the surface of the sensing electrode.
According to the invention, there is an array of the sensing electrodes and a corresponding array of one of the reference electrodes and the counter electrodes, and means (30, 32) are provided for cycling an applied potential between the different electrodes in at least one of the arrays whereby each sensing electrode is in turn subjected to (a) a sensing potential at which detection can take place, and (b) a refreshing potential at which a discarge current flows between the associated counter electrode and sensing electrode to clean the surface of the sensing electrode.
Description
~ wo gs/26500 I P~ . r -~J
~.
ELECTI~O--HFI~IC~L ~F.I~ISOR
The present invemion relates to el~ lu.i..,.n;~i sensorS.
Elc~u~h~ i~l sensors arc i~nown for use in the d.,~. of species in aqueous solutions and for use in the deoection of gas in an atnnosphere being monitored.
5 In particular, ~Ic~hv-,l-c.l.i~l sensors employing IlliLlU.,~ ,iJUL~ haYing small physicai dimensions including a diameter of the order of 10 l~m are presently employed in solid state gas detectors. Such sensors, in which the electrodes are effectively point electrodes, have the advantage over other w.,~...iul~l sensors in that the current obtdinable is much higher than would normally be expeaed for their surface area because the molecular flu~
10 per unit area is higher.
Electrochemical sensors of the type employed in solid state gas detectors and ineiectrolytic gas detectors have a sensing (or working) electrode which is in ~.""",...".~;.", with the atmosphere being sensed. a counter-electrode and a reference electrode and all three electrodes are in contact with an CIC~IlULl~.)liLdi medium within the sensor and are connected via respective ter~ninais to the circuitry within the detector.
The potentiai difference between the sensing electrode and the reference electrode may be controlled dnd in some sensors this is done by connecting these two electrodes to the inputs of an operational amplifler either directly or through a resistor, see e.g. U.K.
Patent Sp~cifir ~ir~n Nos. 1 101 101, U.S. Patent Cr~rifr~ m No. 3 776 832, European Patent Application ~o.0 220 896 and International Patent Application No. WO90/12315 A circuit generally in accordance with the above patents is shown in Figure I ofthe dLw.~ t; drawings, in which the sensor is indicated by the generai referencenumber 10 and includes an electrolyoe (sulphuric acid). A sensing electrode 12, a reference electrode 14 and a counter eiectrode 16 are ail in contact vith the electrolyte.
The sensing eiectrode 12 and the reference electrode 14 are joined via ter~ninais 12a and 14a to respective inputs of an operational arnplifier 18 whose output is connected to the counter electrode 16 via a terminal 16a. A resistor 20 is present between the sensing electrode 12 and its input to the operationai amplifier 18. and is connected via a line 22 to a ground or other fixed reference potentiai.
The sensing electrode 12 is in contact with an atrnosphere that is being monitored and when the atmosphere contains a gas of the type being detected, this gas undergoes -; . 21 86341 woss/26soo ~ .1 691 sn el~ u-h~..,h,.,l reaction which depolarises the sensing electrode 12, causing the potential of that electrode to alhr. This causes sn imbalance bet veen the pohntial of the sensing eiectrode 12 and the refe~ence electrode 14 and henoe bet veen the inputs of the operational amplifier 18. The potentisl difference betveen these inputs causes the 5 operational amplifier to supply current through its output to the counhr electrode 16 snd hence causes a current to flow in the sensor cell 10 betveen the counhr electrode 16 snd the sensing electrode 12 ~however ' "~ no current llOws bet~veen the reference electrode snd the sensing electrode). The curreM flowing through the sensor cell, which is directly related to the amount of gas in the atmosphere, can be measured, for exsmple, 10 by including a resistor between the amplifler output and the counhr electrode 16 and messuring the voltsge drop across the resistor (see U.S. Pahnt No. 3 776 832);
alh..~ ly, the current flowing through the cell may be measured by a current follower connected to the line 22 connected to the resistor 20 or by measuring the pohntial difference across a resistor between the line 22 and a ground or other fixed pohntial (see European Patent Application No.0 220 896), ~ l,r, the voltage drop across the resistor 20 may be measured (see U.K. Pahnt No. I 101 101). The resistor 20 is included between the sensing electrode and the operational amplifier in order h slow the response time of the sensor and thus provide immunity from electronic noise and fluctuations in the potential of the sensing electrode; the value of the resis~or 20 is generally chosen to 20 be between 0 and 500 ohms.
In sensors of the type described with reference to Figure 1, the el~u~
action at the surface of the sensing electrode 12 tends to result in o~idstion snd eventual d~,h.iul~-~iu-- of the efficiency of the sensor 10 over time, which is a significant problem in applications requiring a precisely accurah output at all times. Periodic elc~L,u.,l~
25 cleaning and refreshing of the electrode surface are thus required, which means an interruption and introduces a further problem in applications requiring a continuous output.
The present inveMion seeks to oYercome the above problems and to provide an Cl~ ' ' sensor in which electrode cleaning can take place without affecting the senso ~ output.
~ w095/26500 ` ` 21 8 6341 r ~
According to the present invention, there is proYided an cl~.L u-L~...;~I sensorsensor having a sensing elearode, a reference electrode and a counter elearode all in contact with an ~ LI U~ ;~I med ium, means capable in operation of maintaining a first potential betwoen the sensing and the reference electrodes, means for deteaing a current 5 flowing at the sensing electrode or at the counter electrode in response to anr,~.L~u.,l.~,...;.al reaction at the sensing electrode due to the presence of a material of the type being monitored, ~I-~...~i,cd in that there is an array of the sensing electrodes and a w~c~,uu..lil~g array of one of the reference elearodes and the counoer electrodes, and means are provided for cycling an applied potential betwoen differeM elearodes in 10 at least one of said arrays whereby each sensing electrode is in turn subjected to a sensing potential at which deteaion can take place An ad~antage of this ~ 116~ ,.1L is that each sensing electrode and counter elearode in the associated array is subjected in rurn to a sensing or a ll,~ul~
potential at which detection can take place. As the l-l-~,u-~ potential is cycled round 15 the electrodes, the elearodes not at the required -~u-~ ,potential can undergo cleaning and refreshing to provide an accurate output and, if required, the output from the array can be continuous.
Preferably, the cycling means comprise an electronic gating ~-, t, for example a multiplexer ,1 ~
2û The present invention is described further, by way of example, with reference to the ~ u--~ lg drawings, in which:
Figure I is a known circuit for a gas detector;
Figure 2 is a circuit diagraJn of a portion of an ~ u~l-.,., ~1 sensor accordingto the present invention illustrating the connections betwoen a single sensing electrode, 2~ a reference electrode, a single counter electrode and an operational amplifier;
Figure 3 is a circuit diagram showing further portions of the ~Ic~l., ' sensor of Figure 2, which has a 3 x 3 array of sensing electrodes and a co--,, "array of counter electrodes;
Figure 4 is a signal diagram showing how the current at each of the sensing electrodes or ' ~ each of the counter elearodes in the ~I~,.,u, ' sensor of Figur~ 3 varies with the applied voltage and, at a particular time, has a different value;
W0 9s/26500 ` 2 1 8 6 3 4 l r~ g~ ~
Figure 5 is a circuit diagrarn showing a variation on the circuitry of Figures 2 and 3;
Figure 6 is a circuit diagram showing how the ~ U~ I;~I sensor of Figures 2 to 5 can be modified such that the output from the operational amplifier can be cycled 5 for an array of n by m counter electrodes, and Figure 7 is a di~ view illustrating an array of n by m counter electrodes.
Figure 1 relates to the prior art and Figures 2 to 6 illustrate ~ r 1 ~ ~t~ of the preseM invention. The sarne reference numbers will be used throughout, however, to 10 indicate comparable rr~mr~n.~nrc Referring initially to Figure 2, the circuit shown in this Figure is similar to the circuit of Figure I except in the following key respects:
Figure 2 shows only one of each of the sensing electrode 12r the reference electrode 14 and the counter elearode 16 but in fact there are an array of the sensing 15 electrodes 12 and a ~UII~ /U.~dill~ array of the counter electrodes 16 with a single reference electrode 14 all connected to one operational arnplifier 18.
The output of the operational arnplifier 18 is coMected to the illustrated counter electrode terminal 16a, and thence to the illustrated counter electrode 16, by way of a multiplexer 30 to be described in greater detail below. Essentially, the multiplexer 30 20 enables the output from the operational amplifier 18 to be cycled round all of the counter electrodes 16, although only one is shown in Figure 2 for the sake of sirnplicity.
Another difference over the Figure I circuit lies in the provision of a capîcitor 32 connected to the illustrated terminal 16a so that a potential applied by way of the multiplexer 30 to the illustrated counter electrode 16 can be stored, and indeed a 25 respective capacitor 32 is connected to each of the terminals 16a for storing the potential applied to the associated counter electrode 16.
As shown, the illustrated sensing electrode 12 is connected by way of the resistor 2û to the line 22, and each of the other sensing electrodes in the array of such electrodes is connected by way of a respective further resistor 20 to the line 22. A measuring device is connected across the resistor 20, and either respoctive measuring are associated with each of the resistors 20 or a further, ,1~ All ~, ~ WO95126500 2 1 8 634 I r~ r-~s 5.
~ ,luu~ d with the multipiexer 30 allows the voltage drop across each of the resistors 20 to be measured in turn.
Finally, a reference diode 34 is connected betwoen the illustrated resistor 20 and the input of the operational amplifler 18 associated with the sensing electrode 12 in order 5 to provide a ~ t ~ rd offset voltage betwoen the two inputs of the operationalamplifier 18 for generating a ~ ' potential V, at its output. In place of the reference diode 34, an èlectronic circuit proYiding a defined potential or a digitai to an analogue converter driven from a ~h,~ulJIu~ul could equaily well be used.
The operation of the circuitry shown in Figure 2 is essentially the same as the 10 operation of the circuitry shown in Figure I apart frûm the cycling of the potential generated at the output of the operational ampliher 18, round the array of counter electrodes 16. This will now be described further with reference to Figure 3.
Figure 3 shows a specific example of the present invention having a 3 X 3 array of the counter electrodes 16 and a 3 X 3 array of the sensing electrodes 12.
As shown in Figure 3, the output of the operationai amplifier 18 is connected toeach of the counter electrode terminals 16a,," 16a,.,...16a33 and thence to a respective counter electrode 16,,,, 161,~...163.3 by way of the ~ .o~,.-l~,... 30. 3 ach of the counter electrode terminals 16a,,,.. 16a3,3 is also connected to an associated capacitor 32 as shown. CUl-~l uI-d;~5 to each counter electrode 16 is a respective serlsing electrode 12, and the sensing electrodes 12,,,.. 123,, are connected respectiYely to sensing electrode ~erminals 12a,,,...... 12a3,3. The sensing electrode terrninals 12al,1.. 12a33 are connected by way of respective resistors 20 to the line 22 and tbence through the reference diode 34 to the operationai amplifier 18 as mentioned above.
It will be noticed that there is only a single reference electrode 14 connected 25 directly to the operational ampliher 18, although there is both an array of sensrng electrodes 12 and an array of the counter electrodes 16.
The ~ s~ l 30 comprises a first multiplexer 40 having a single input. which is provided by the output of the operational amplifier 18 and is controlled by a control bus X. The multiplexer 40 has three outputs each connected to the input of a respective further multiplexer 42, 44, 46 also controlled by way of the com~non control b~ X. Again, each of the ~ 42, 44, 46 has three outputs connected to a s ~ 21 86341 Wo ss/~6soo 6.
respective one of the termina3s 16a. By way of example the outputs of the multiple~er 42 are connecte(3 to the terminals 16a" 16a, 2 and 16a, 3.
13y virtue of this ~ the potentia3 V~ obtained at the output of the operational arnplifier 18 is supplied by way of the multiplexer 40 first to the multiple~er 42 which in turn firsl applies the potentia3 V, to tbe counter electrode termina3 16a,, and begins to charge up the associated capacitor 32. When the capacitor 32 associate(3 with the termina3 16a" is partially charged the multiplexer 40 switches the signal under the control of the control bus X to the multiplexer 44 which applies the potential V, to the counter electrode termina3 16a2, to start charging the associated capacitor 32. Ne~t the potential V, is applied by way of the multiplexer 46 to the terminal 16a3, for charging the capacitor 32 associated with this terminal. The signal is switched sub~u~ ly to the terminals 16al 2, 16a2,2 and 16a3 2 and then to the terminals 16a, ,. 16a3 2 and 16a3 J.
In this way the potential V, at the output of the amplifier 18 is repeatedly cycled round the counter-electrode terminals 16a, ,....16a3 3 and the capacitors 32 are charged 15 au-,ccaal~ . At any one moment each of the counter electrodes 16 will be at a different potentia3 V according to the charge stored on the associated capacitor 32. Only one of the counter-electrode 16 is at a potential V which is a sensing or I~ a~l-CII.~ potentia3 at which detection can take place. When detection occurs in this situation. the current at the respective opposed sensing electrode 12 is picked up and the potential difference 20 across the respective resistor 20 connected thereto is measured.
The potentia3 V, at the output of the operational amplifier 18 is selected to be such that when the charge stored on any given capacitor 32 reaches a level to bring the associated counter electrode 16 also to the potential V,. then a cleaning or refreshing peak current flows through the sensor berween that counter electrode 16 and the opposeo 25 sensing electrode 12 to clean the associated sensing electrode 12. This results in a discharge of the relevant capacitor 32. following which charging begins of this capacitor 30 anew in the next cycling of the potentia3 generated at the output of the amplifier 18 applied by the multiplexers 40 to 46.
Figure 4 shows the relationship between current I and voltage V in each w"~ pair of sensing and counter-electrodes 12 16 and a3so shows how the potentia3 attained at each counter-electrode 16 varies according to the position of that WOss/26500 21 8 6341 r~ . s ~
7.
counter electrode within the array of such electrodes. Al a given time Tl the potential of each counter electrode 16 is represented by _ and at a given time T2 the potential at each counter-electrode 16 is represented by Q. As can be seen at any particular time only one of the counter-electrodes 16 will be at the l~lc~ulc,~ i potential V,~ . Further 5 as can be seen the counter-electrodes 16 ,u~ c,,i~ attain the potential V~ at which a discharge current flows and cleaning of the opposed sensing electrode 12 occurs.Figure 5 shows a 3 x 3 array of the counter electrodes 16 and a 3 x 3 array of the sensing electrodes 12 like Figure 3. In the present instance however a respective capacitor 32 is connected between the terminals 16a and 12a of each associated pair of counter and sensing electrodes 16 12 for storing potential~ and a respective resistor 20 is connected between each sensing electrode terminal 12a and the line ~2. A l ... lli~.l. i -~
~I~'b'~ "' 50 is connected to all of the terminals 12a for cycling round the sensing electrodes 12 for the pick-up of currents for detecling purposes and is connectcd by vvay of an arnmeter 52 to the line 22 for measuring the current Referring now to Figure 6 this figure shov~s how the same principle can be applied to an I~ r.. -: of CIC~ sensor having an array of n by m counter electrodes 16 and an array of n by m sensing electrodes 12. In this case the output of the operational arnplif er 18 is connected to a first multiplexer I~L0 controlled by a control bus X and having a set of m outputs each connected to a respective further multiplexer 142" .. 14~" . The further IIIUIL;~ ACIS are again controlled by the common control bus X and each has a further n outputs connected to a respective counter electrode termirlal 16a"....16a l c and to a respective capacitor 132. The array of sensing electrodes 12 are connected by way of sensing electrode terminals 12a, ,.. 12a,.~ through respective resistors 20 and the reference diode 34 to the operational arnplifier 18. As before there 25 is a single reference electrode 14.
The array of counter electrodes 16 is illustrated in Figure 7 which shows how the outputs of a each of the IIIUIL;~ .ACI~ 142 are connected IC~ L;~d.1 to a column of the counter electrode terminals 16a,.,...16a,~ and how each counter electrode terminal 16a, I to 16a, ~ in the respective column being connected to the respective capacitor 132.
In the described circuitry the voltage drop across the respective resistor 20 is in ach ~e measured for detecting the current flowing through the associated pair of Wogs/26500 P~~ 9 8.
counter and sensing electrodes in sensor cell 10. Of course, an alternative possibility is to rnsert respectiYe resistors in the conneaions leading to the counter-elearodes 16 and to measure the voltage drop there.
Various other ~ ;r;,~ are also possible in the circuitry described. In 5 particular, the capacitor 3~ is optional if a storing funaion and elc~-u-,h~.l.cal cleaning is not required.
The IllU~ .,Ael~ may of course be replaced by an alternative elearonic gating u~ ... or by an appropriate central processing unit and software.
Further, the surface or surfaces of individua~ or plural elearodes in the array may 10 be modified by techniques such as ion ~u~ ~dlll~llL or elc.,l~u~,h,~ or by coating techniques such as screen or inA jet printing to give respective electrodes differeM aaivity or specifity to chemical species.
It will readily be perceived that the advantage of the present invention is in the provision at all times of a pair of sensing and counter electrodes at an appropriate 15 potential for measuring the ele~lu.;.~...h,dl parameter for which the sensor is being employed, whilst at the same time allowing other pairs of sensing and counter elearodes to reach an appropriate applied potential for cleaning purposes.
The present invention is primarily applicable to sensors in which the senstng electrodes are l";~lu~ lludcs, a I~ u~lc~lul~ includes a srnall exposed area of an inert 20 conduaive material, for example platinum or some other said elc.~lu~ d~Lic material.
Mi.luelc~I.udcs are lAnown that consist of a platinum wire that is enclosed within a glass sheath that has been drawn, cut to si2e and the exposed cut end polished. The diameter of the exposed platinum wire will generally be 15 - 30 I~m but smaller diameters are Anov~n and indeed diameters up to Imm are also lAnov~n. Naturally, the cross seaion of 25 the exposed area need not be circular and any cross seaion of comparable area could be used.
Although the present invention has been discussed in terms both of the senstng of both gaseous and dissolved species, it is primarily concerned with the sensing of dissolved species, particularly dissolved gases, eg. oxygen.
... .
~.
ELECTI~O--HFI~IC~L ~F.I~ISOR
The present invemion relates to el~ lu.i..,.n;~i sensorS.
Elc~u~h~ i~l sensors arc i~nown for use in the d.,~. of species in aqueous solutions and for use in the deoection of gas in an atnnosphere being monitored.
5 In particular, ~Ic~hv-,l-c.l.i~l sensors employing IlliLlU.,~ ,iJUL~ haYing small physicai dimensions including a diameter of the order of 10 l~m are presently employed in solid state gas detectors. Such sensors, in which the electrodes are effectively point electrodes, have the advantage over other w.,~...iul~l sensors in that the current obtdinable is much higher than would normally be expeaed for their surface area because the molecular flu~
10 per unit area is higher.
Electrochemical sensors of the type employed in solid state gas detectors and ineiectrolytic gas detectors have a sensing (or working) electrode which is in ~.""",...".~;.", with the atmosphere being sensed. a counter-electrode and a reference electrode and all three electrodes are in contact with an CIC~IlULl~.)liLdi medium within the sensor and are connected via respective ter~ninais to the circuitry within the detector.
The potentiai difference between the sensing electrode and the reference electrode may be controlled dnd in some sensors this is done by connecting these two electrodes to the inputs of an operational amplifler either directly or through a resistor, see e.g. U.K.
Patent Sp~cifir ~ir~n Nos. 1 101 101, U.S. Patent Cr~rifr~ m No. 3 776 832, European Patent Application ~o.0 220 896 and International Patent Application No. WO90/12315 A circuit generally in accordance with the above patents is shown in Figure I ofthe dLw.~ t; drawings, in which the sensor is indicated by the generai referencenumber 10 and includes an electrolyoe (sulphuric acid). A sensing electrode 12, a reference electrode 14 and a counter eiectrode 16 are ail in contact vith the electrolyte.
The sensing eiectrode 12 and the reference electrode 14 are joined via ter~ninais 12a and 14a to respective inputs of an operational arnplifier 18 whose output is connected to the counter electrode 16 via a terminal 16a. A resistor 20 is present between the sensing electrode 12 and its input to the operationai amplifier 18. and is connected via a line 22 to a ground or other fixed reference potentiai.
The sensing electrode 12 is in contact with an atrnosphere that is being monitored and when the atmosphere contains a gas of the type being detected, this gas undergoes -; . 21 86341 woss/26soo ~ .1 691 sn el~ u-h~..,h,.,l reaction which depolarises the sensing electrode 12, causing the potential of that electrode to alhr. This causes sn imbalance bet veen the pohntial of the sensing eiectrode 12 and the refe~ence electrode 14 and henoe bet veen the inputs of the operational amplifier 18. The potentisl difference betveen these inputs causes the 5 operational amplifier to supply current through its output to the counhr electrode 16 snd hence causes a current to flow in the sensor cell 10 betveen the counhr electrode 16 snd the sensing electrode 12 ~however ' "~ no current llOws bet~veen the reference electrode snd the sensing electrode). The curreM flowing through the sensor cell, which is directly related to the amount of gas in the atmosphere, can be measured, for exsmple, 10 by including a resistor between the amplifler output and the counhr electrode 16 and messuring the voltsge drop across the resistor (see U.S. Pahnt No. 3 776 832);
alh..~ ly, the current flowing through the cell may be measured by a current follower connected to the line 22 connected to the resistor 20 or by measuring the pohntial difference across a resistor between the line 22 and a ground or other fixed pohntial (see European Patent Application No.0 220 896), ~ l,r, the voltage drop across the resistor 20 may be measured (see U.K. Pahnt No. I 101 101). The resistor 20 is included between the sensing electrode and the operational amplifier in order h slow the response time of the sensor and thus provide immunity from electronic noise and fluctuations in the potential of the sensing electrode; the value of the resis~or 20 is generally chosen to 20 be between 0 and 500 ohms.
In sensors of the type described with reference to Figure 1, the el~u~
action at the surface of the sensing electrode 12 tends to result in o~idstion snd eventual d~,h.iul~-~iu-- of the efficiency of the sensor 10 over time, which is a significant problem in applications requiring a precisely accurah output at all times. Periodic elc~L,u.,l~
25 cleaning and refreshing of the electrode surface are thus required, which means an interruption and introduces a further problem in applications requiring a continuous output.
The present inveMion seeks to oYercome the above problems and to provide an Cl~ ' ' sensor in which electrode cleaning can take place without affecting the senso ~ output.
~ w095/26500 ` ` 21 8 6341 r ~
According to the present invention, there is proYided an cl~.L u-L~...;~I sensorsensor having a sensing elearode, a reference electrode and a counter elearode all in contact with an ~ LI U~ ;~I med ium, means capable in operation of maintaining a first potential betwoen the sensing and the reference electrodes, means for deteaing a current 5 flowing at the sensing electrode or at the counter electrode in response to anr,~.L~u.,l.~,...;.al reaction at the sensing electrode due to the presence of a material of the type being monitored, ~I-~...~i,cd in that there is an array of the sensing electrodes and a w~c~,uu..lil~g array of one of the reference elearodes and the counoer electrodes, and means are provided for cycling an applied potential betwoen differeM elearodes in 10 at least one of said arrays whereby each sensing electrode is in turn subjected to a sensing potential at which deteaion can take place An ad~antage of this ~ 116~ ,.1L is that each sensing electrode and counter elearode in the associated array is subjected in rurn to a sensing or a ll,~ul~
potential at which detection can take place. As the l-l-~,u-~ potential is cycled round 15 the electrodes, the elearodes not at the required -~u-~ ,potential can undergo cleaning and refreshing to provide an accurate output and, if required, the output from the array can be continuous.
Preferably, the cycling means comprise an electronic gating ~-, t, for example a multiplexer ,1 ~
2û The present invention is described further, by way of example, with reference to the ~ u--~ lg drawings, in which:
Figure I is a known circuit for a gas detector;
Figure 2 is a circuit diagraJn of a portion of an ~ u~l-.,., ~1 sensor accordingto the present invention illustrating the connections betwoen a single sensing electrode, 2~ a reference electrode, a single counter electrode and an operational amplifier;
Figure 3 is a circuit diagram showing further portions of the ~Ic~l., ' sensor of Figure 2, which has a 3 x 3 array of sensing electrodes and a co--,, "array of counter electrodes;
Figure 4 is a signal diagram showing how the current at each of the sensing electrodes or ' ~ each of the counter elearodes in the ~I~,.,u, ' sensor of Figur~ 3 varies with the applied voltage and, at a particular time, has a different value;
W0 9s/26500 ` 2 1 8 6 3 4 l r~ g~ ~
Figure 5 is a circuit diagrarn showing a variation on the circuitry of Figures 2 and 3;
Figure 6 is a circuit diagram showing how the ~ U~ I;~I sensor of Figures 2 to 5 can be modified such that the output from the operational amplifier can be cycled 5 for an array of n by m counter electrodes, and Figure 7 is a di~ view illustrating an array of n by m counter electrodes.
Figure 1 relates to the prior art and Figures 2 to 6 illustrate ~ r 1 ~ ~t~ of the preseM invention. The sarne reference numbers will be used throughout, however, to 10 indicate comparable rr~mr~n.~nrc Referring initially to Figure 2, the circuit shown in this Figure is similar to the circuit of Figure I except in the following key respects:
Figure 2 shows only one of each of the sensing electrode 12r the reference electrode 14 and the counter elearode 16 but in fact there are an array of the sensing 15 electrodes 12 and a ~UII~ /U.~dill~ array of the counter electrodes 16 with a single reference electrode 14 all connected to one operational arnplifier 18.
The output of the operational arnplifier 18 is coMected to the illustrated counter electrode terminal 16a, and thence to the illustrated counter electrode 16, by way of a multiplexer 30 to be described in greater detail below. Essentially, the multiplexer 30 20 enables the output from the operational amplifier 18 to be cycled round all of the counter electrodes 16, although only one is shown in Figure 2 for the sake of sirnplicity.
Another difference over the Figure I circuit lies in the provision of a capîcitor 32 connected to the illustrated terminal 16a so that a potential applied by way of the multiplexer 30 to the illustrated counter electrode 16 can be stored, and indeed a 25 respective capacitor 32 is connected to each of the terminals 16a for storing the potential applied to the associated counter electrode 16.
As shown, the illustrated sensing electrode 12 is connected by way of the resistor 2û to the line 22, and each of the other sensing electrodes in the array of such electrodes is connected by way of a respective further resistor 20 to the line 22. A measuring device is connected across the resistor 20, and either respoctive measuring are associated with each of the resistors 20 or a further, ,1~ All ~, ~ WO95126500 2 1 8 634 I r~ r-~s 5.
~ ,luu~ d with the multipiexer 30 allows the voltage drop across each of the resistors 20 to be measured in turn.
Finally, a reference diode 34 is connected betwoen the illustrated resistor 20 and the input of the operational amplifler 18 associated with the sensing electrode 12 in order 5 to provide a ~ t ~ rd offset voltage betwoen the two inputs of the operationalamplifier 18 for generating a ~ ' potential V, at its output. In place of the reference diode 34, an èlectronic circuit proYiding a defined potential or a digitai to an analogue converter driven from a ~h,~ulJIu~ul could equaily well be used.
The operation of the circuitry shown in Figure 2 is essentially the same as the 10 operation of the circuitry shown in Figure I apart frûm the cycling of the potential generated at the output of the operational ampliher 18, round the array of counter electrodes 16. This will now be described further with reference to Figure 3.
Figure 3 shows a specific example of the present invention having a 3 X 3 array of the counter electrodes 16 and a 3 X 3 array of the sensing electrodes 12.
As shown in Figure 3, the output of the operationai amplifier 18 is connected toeach of the counter electrode terminals 16a,," 16a,.,...16a33 and thence to a respective counter electrode 16,,,, 161,~...163.3 by way of the ~ .o~,.-l~,... 30. 3 ach of the counter electrode terminals 16a,,,.. 16a3,3 is also connected to an associated capacitor 32 as shown. CUl-~l uI-d;~5 to each counter electrode 16 is a respective serlsing electrode 12, and the sensing electrodes 12,,,.. 123,, are connected respectiYely to sensing electrode ~erminals 12a,,,...... 12a3,3. The sensing electrode terrninals 12al,1.. 12a33 are connected by way of respective resistors 20 to the line 22 and tbence through the reference diode 34 to the operationai amplifier 18 as mentioned above.
It will be noticed that there is only a single reference electrode 14 connected 25 directly to the operational ampliher 18, although there is both an array of sensrng electrodes 12 and an array of the counter electrodes 16.
The ~ s~ l 30 comprises a first multiplexer 40 having a single input. which is provided by the output of the operational amplifier 18 and is controlled by a control bus X. The multiplexer 40 has three outputs each connected to the input of a respective further multiplexer 42, 44, 46 also controlled by way of the com~non control b~ X. Again, each of the ~ 42, 44, 46 has three outputs connected to a s ~ 21 86341 Wo ss/~6soo 6.
respective one of the termina3s 16a. By way of example the outputs of the multiple~er 42 are connecte(3 to the terminals 16a" 16a, 2 and 16a, 3.
13y virtue of this ~ the potentia3 V~ obtained at the output of the operational arnplifier 18 is supplied by way of the multiplexer 40 first to the multiple~er 42 which in turn firsl applies the potentia3 V, to tbe counter electrode termina3 16a,, and begins to charge up the associated capacitor 32. When the capacitor 32 associate(3 with the termina3 16a" is partially charged the multiplexer 40 switches the signal under the control of the control bus X to the multiplexer 44 which applies the potential V, to the counter electrode termina3 16a2, to start charging the associated capacitor 32. Ne~t the potential V, is applied by way of the multiplexer 46 to the terminal 16a3, for charging the capacitor 32 associated with this terminal. The signal is switched sub~u~ ly to the terminals 16al 2, 16a2,2 and 16a3 2 and then to the terminals 16a, ,. 16a3 2 and 16a3 J.
In this way the potential V, at the output of the amplifier 18 is repeatedly cycled round the counter-electrode terminals 16a, ,....16a3 3 and the capacitors 32 are charged 15 au-,ccaal~ . At any one moment each of the counter electrodes 16 will be at a different potentia3 V according to the charge stored on the associated capacitor 32. Only one of the counter-electrode 16 is at a potential V which is a sensing or I~ a~l-CII.~ potentia3 at which detection can take place. When detection occurs in this situation. the current at the respective opposed sensing electrode 12 is picked up and the potential difference 20 across the respective resistor 20 connected thereto is measured.
The potentia3 V, at the output of the operational amplifier 18 is selected to be such that when the charge stored on any given capacitor 32 reaches a level to bring the associated counter electrode 16 also to the potential V,. then a cleaning or refreshing peak current flows through the sensor berween that counter electrode 16 and the opposeo 25 sensing electrode 12 to clean the associated sensing electrode 12. This results in a discharge of the relevant capacitor 32. following which charging begins of this capacitor 30 anew in the next cycling of the potentia3 generated at the output of the amplifier 18 applied by the multiplexers 40 to 46.
Figure 4 shows the relationship between current I and voltage V in each w"~ pair of sensing and counter-electrodes 12 16 and a3so shows how the potentia3 attained at each counter-electrode 16 varies according to the position of that WOss/26500 21 8 6341 r~ . s ~
7.
counter electrode within the array of such electrodes. Al a given time Tl the potential of each counter electrode 16 is represented by _ and at a given time T2 the potential at each counter-electrode 16 is represented by Q. As can be seen at any particular time only one of the counter-electrodes 16 will be at the l~lc~ulc,~ i potential V,~ . Further 5 as can be seen the counter-electrodes 16 ,u~ c,,i~ attain the potential V~ at which a discharge current flows and cleaning of the opposed sensing electrode 12 occurs.Figure 5 shows a 3 x 3 array of the counter electrodes 16 and a 3 x 3 array of the sensing electrodes 12 like Figure 3. In the present instance however a respective capacitor 32 is connected between the terminals 16a and 12a of each associated pair of counter and sensing electrodes 16 12 for storing potential~ and a respective resistor 20 is connected between each sensing electrode terminal 12a and the line ~2. A l ... lli~.l. i -~
~I~'b'~ "' 50 is connected to all of the terminals 12a for cycling round the sensing electrodes 12 for the pick-up of currents for detecling purposes and is connectcd by vvay of an arnmeter 52 to the line 22 for measuring the current Referring now to Figure 6 this figure shov~s how the same principle can be applied to an I~ r.. -: of CIC~ sensor having an array of n by m counter electrodes 16 and an array of n by m sensing electrodes 12. In this case the output of the operational arnplif er 18 is connected to a first multiplexer I~L0 controlled by a control bus X and having a set of m outputs each connected to a respective further multiplexer 142" .. 14~" . The further IIIUIL;~ ACIS are again controlled by the common control bus X and each has a further n outputs connected to a respective counter electrode termirlal 16a"....16a l c and to a respective capacitor 132. The array of sensing electrodes 12 are connected by way of sensing electrode terminals 12a, ,.. 12a,.~ through respective resistors 20 and the reference diode 34 to the operational arnplifier 18. As before there 25 is a single reference electrode 14.
The array of counter electrodes 16 is illustrated in Figure 7 which shows how the outputs of a each of the IIIUIL;~ .ACI~ 142 are connected IC~ L;~d.1 to a column of the counter electrode terminals 16a,.,...16a,~ and how each counter electrode terminal 16a, I to 16a, ~ in the respective column being connected to the respective capacitor 132.
In the described circuitry the voltage drop across the respective resistor 20 is in ach ~e measured for detecting the current flowing through the associated pair of Wogs/26500 P~~ 9 8.
counter and sensing electrodes in sensor cell 10. Of course, an alternative possibility is to rnsert respectiYe resistors in the conneaions leading to the counter-elearodes 16 and to measure the voltage drop there.
Various other ~ ;r;,~ are also possible in the circuitry described. In 5 particular, the capacitor 3~ is optional if a storing funaion and elc~-u-,h~.l.cal cleaning is not required.
The IllU~ .,Ael~ may of course be replaced by an alternative elearonic gating u~ ... or by an appropriate central processing unit and software.
Further, the surface or surfaces of individua~ or plural elearodes in the array may 10 be modified by techniques such as ion ~u~ ~dlll~llL or elc.,l~u~,h,~ or by coating techniques such as screen or inA jet printing to give respective electrodes differeM aaivity or specifity to chemical species.
It will readily be perceived that the advantage of the present invention is in the provision at all times of a pair of sensing and counter electrodes at an appropriate 15 potential for measuring the ele~lu.;.~...h,dl parameter for which the sensor is being employed, whilst at the same time allowing other pairs of sensing and counter elearodes to reach an appropriate applied potential for cleaning purposes.
The present invention is primarily applicable to sensors in which the senstng electrodes are l";~lu~ lludcs, a I~ u~lc~lul~ includes a srnall exposed area of an inert 20 conduaive material, for example platinum or some other said elc.~lu~ d~Lic material.
Mi.luelc~I.udcs are lAnown that consist of a platinum wire that is enclosed within a glass sheath that has been drawn, cut to si2e and the exposed cut end polished. The diameter of the exposed platinum wire will generally be 15 - 30 I~m but smaller diameters are Anov~n and indeed diameters up to Imm are also lAnov~n. Naturally, the cross seaion of 25 the exposed area need not be circular and any cross seaion of comparable area could be used.
Although the present invention has been discussed in terms both of the senstng of both gaseous and dissolved species, it is primarily concerned with the sensing of dissolved species, particularly dissolved gases, eg. oxygen.
... .
Claims (7)
1. An electrochemical sensor having a sensing electrode (12), a reference electrode (14) and a counter electrode (16) all in contact with an electrochemical medium,means (18) capable in operation of maintaining a first potential between the sensing and the reference electrodes, means for detecting a current flowing at the sensing electrode or at the counterelectrode in response to an electrochemical reaction at the sensing electrode due to the presence of a material of the type being monitored, characterised in that there is an array of the sensing electrodes (12) and a corresponding array of one of the reference electrodes (14) and the counter electrodes (16), and means (30) are provided for cycling an applied potential between different electrodes in at least one of said arrays whereby each sensing electrode (12) is in turn subjected to a sensing potential at which detection can take place.
2. An electrochemical sensor according to claim 1 characterised by means (32) arranged to cooperate with the cycling means so as to subject each sensing electrode in turn to (a) the sensing potential, and (b) a refreshing potential at which a discharge current flows between the associated counter electrode and sensing electrode to clean the surface of the sensing electrode.
3. An electrochemical sensor according to claim 2 characterised in that said cooperating means comprise storing means associated respectively with each of the electrodes in said array.
4. An electrochemical sensor according to any preceding claim characterised in that the cycling means comprise an electronic gating arrangement.
5. An electrochemical sensor according to claim 4 characterised in that the gating arrangement comprises a multiplexing arrangement.
10.
10.
6. An electrochemical sensor according to any preceding claim characterised in that the two arrays constitute an array of the sensing electrodes and an array of the counter electrodes, and in that the cycling means are arranged to cycle the applied potential round different electrodes in the array of counter electrodes.
7. An electrochemical sensor according to any preceding claim characterised in that the means capable in operation of maintaining said first potential comprise an amplifier.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9406109A GB9406109D0 (en) | 1994-03-28 | 1994-03-28 | Electrochemical sensor |
| GB9406109.0 | 1994-03-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2186341A1 true CA2186341A1 (en) | 1995-10-05 |
Family
ID=10752627
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2186341 Abandoned CA2186341A1 (en) | 1994-03-28 | 1995-03-28 | Electrochemical sensor |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0753141A1 (en) |
| AU (1) | AU2077195A (en) |
| CA (1) | CA2186341A1 (en) |
| GB (1) | GB9406109D0 (en) |
| WO (1) | WO1995026500A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19916921A1 (en) * | 1999-04-14 | 2000-10-19 | Fraunhofer Ges Forschung | Electrical sensor array |
| FR2858414B1 (en) * | 2003-07-29 | 2008-02-08 | Centre Nat Machinisme Agricole | METHOD FOR ACTIVATION-REGENERATION OF A REDOX SENSOR IN A PURIFICATION STATION |
| DE102005048273A1 (en) * | 2005-10-08 | 2007-04-19 | Knick Elektronische Messgeräte GmbH & Co. KG | Measuring device for electrochemical measured variables in liquids, in particular pH or redox potential measuring device, and method for measuring such electrochemical measured variables |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4496454A (en) * | 1983-10-19 | 1985-01-29 | Hewlett-Packard Company | Self cleaning electrochemical detector and cell for flowing stream analysis |
| US4963245A (en) * | 1986-05-02 | 1990-10-16 | Ciba Corning Diagnostics Corp. | Unitary multiple electrode sensor |
| GB8907564D0 (en) * | 1989-04-04 | 1989-05-17 | Neotronics Technology Plc | Fault detection in electrochemical gas sensing equipment |
| JP2869866B2 (en) * | 1989-10-06 | 1999-03-10 | ティーディーケイ株式会社 | Container for electrochemiluminescence detection |
| US5120421A (en) * | 1990-08-31 | 1992-06-09 | The United States Of America As Represented By The United States Department Of Energy | Electrochemical sensor/detector system and method |
| DE4131731A1 (en) * | 1991-09-24 | 1993-05-19 | Raymond Glocker Gmbh Inst Fuer | Sensor for determining chemicals in liq. gps. or glass - has micro-electrode array on silicon@ chip useful e.g. for determining oxygen concn. in blood |
| DE4221847A1 (en) * | 1992-07-03 | 1994-01-05 | Martin Dipl Ing Klein | Current and voltage measurement arrangement for electrochemical cells - operates as ground-referenced current or voltage source by switching between potentiostatic voltage from instrumentation amplifier across measurement resistor, and galvanostatic voltage from reference electrode via multiplexer. |
-
1994
- 1994-03-28 GB GB9406109A patent/GB9406109D0/en active Pending
-
1995
- 1995-03-28 AU AU20771/95A patent/AU2077195A/en not_active Abandoned
- 1995-03-28 EP EP95913227A patent/EP0753141A1/en not_active Ceased
- 1995-03-28 CA CA 2186341 patent/CA2186341A1/en not_active Abandoned
- 1995-03-28 WO PCT/GB1995/000694 patent/WO1995026500A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO1995026500A1 (en) | 1995-10-05 |
| EP0753141A1 (en) | 1997-01-15 |
| GB9406109D0 (en) | 1994-05-18 |
| AU2077195A (en) | 1995-10-17 |
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