CA2097456A1 - Oxygen monitoring devices - Google Patents
Oxygen monitoring devicesInfo
- Publication number
- CA2097456A1 CA2097456A1 CA002097456A CA2097456A CA2097456A1 CA 2097456 A1 CA2097456 A1 CA 2097456A1 CA 002097456 A CA002097456 A CA 002097456A CA 2097456 A CA2097456 A CA 2097456A CA 2097456 A1 CA2097456 A1 CA 2097456A1
- Authority
- CA
- Canada
- Prior art keywords
- gas
- main body
- environs
- electrode
- oxygen
- 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.)
- Abandoned
Links
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
- G01N27/403—Cells and electrode assemblies
- G01N27/406—Cells and probes with solid electrolytes
- G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
Abstract
OF INVENTION An oxygen sensor having a main body member with an interior chamber, made from material which is an oxygen ion conducting solid electrolyte when at specified temperatures. Electrodes made from material which is porous to oxygen molecules axe positioned opposite each other on the main body member, within the interior chamber and on the outside of the main body. Via a port which extends through the main body, changes in the absolute pressure of gas to be tested in the environs of the outer electrode are transmitted to the gas in the environs of the inner electrode. As a result of reference gas being introduced into the interior chamber of the main body through an orifice at a pressure sufficient to maintain the rate of flow at its critical (and therefore constant) rate of flow, the environs of the inner electrode are occupied by reference gas and a flow of gas results, through the main body member from the region of the inner electrode and out through the port. In optional embodiments, only a portion of the test gas directly impinges upon the outer surface of the outer electrode to minimize it being cooled, the main body member is heated to specified temperatures, means are provided to ensure a flow of test gas past the sensor, and/or the outside electrode periodically is exposed to reference gas to calibrate the sensor for cell constant.
Description
(1~
BACKGROUND OF INVENTION
~l~g7 '1~ , In certain applications, it i~ desired to monitor the oxygen content of gases more or less continuously. A system which does thi~ effectively may be used, for example, to monitor ~he gaseous effluent from lndustrial boilers, kilns, ovens, internal combustion engines, driers, heat treating furnaces, incinerators, refinery process units, ga~ turbines ~crubbers and the like. Based on the information ~o gleaned, the amount of oxygen present may be adju~ted to desired level~. For example, the air being introduced into the combustion pha~e of a boiler may be xegula~ed to achieve optimum efficiency, and to reduce nitrous oxide and/or sulphur dioxide emissions. Insufficient oxygen, which can cause too high smoke opacity, slag buildup, boiler tube fouling, decrea~ed heat transfer, excessive maintenance, and wasted fuel, may be avoided, as also can an excess of oxygen which can cause waste of energy by heat lo~s.
Such monitoring ~y~tems can also be adapted to act as source~ to enable feedback sy~tem~ to effectuate ~uch adjustment~
automatically and continuously.
One means for so monitoring the oxygen content of such gases work~ on the principle of a zirconium oxide fuel cell oxygen sen~or. Typically, such sensors consist of a ceramic tube made from zirconium oxide that has been stabilized with yytrium and has porous platinum electrodes coated opposite each other on both itq inner and its outer Rurfaces at it~ sen~ing end. When the cell i3 heated to a temperature above 600 C (1100 F) the ceramic material becomes permeable to oxygen ions. Vacancies in it~ lattice ~tructure permit ~uch ions to pass through it, thus -rendering the cell into an oxygen ion conducting ~olid electrolyte. When the number of oxygen molecules per unit volume is ~reater at one plate of the cell tha~ at the other, oxygen ions will migrate from the former to the latter. The platinum electrodes on each ~ide of the cell wall provide catalytic ;;~
surfaces for the change of oxygen molecule~ into oxygen ionB and vice versa. Thus, oxygen molecules entering the cell through an electrode gain electrons to become ions whioh enter the electrolyte. Simultaneou~ly, at the other electrode, the oxygen ions 108e electrons and are released from the surface of the electrode as oxygen molecules. Thi~ flow creates an electron imbalance which produces a voltage potential between the electrode~. The magnitude of that potential is a function of the temperature of the cell and the relative partial pre~sure on each side of the cell. Partial pres~ure is defined as the pressure exerted by each component in the mixture that goes to make up the gas. It may be calculated as follows:
12~
~ 7 ~
Pi= Ni x R x T/V
where Pi = the partial pressure, Ni = the number of molecule~ of the ~pecie, R = the Universal Gas constant, T = temperat~re (absolute scale), and V = volume.
The partial pressure of the component gas "i" i8 then the same as if it occupie~ the same volume at the same temperature in the absence of other ga~es.
The relationship between the oxygen partial pre~sure at the monitored ~ide and that at the reference ga~ side (typically air, which i~ 20.95 % oxygen by volume), the temperature, voltage output, and cell constant of the individual cell are defined by the "Nernst" equation as follows~
E = RT/4F x ~n(Pl/P2) ~ C
::
where E - Voltage out T = Absolute temperature of cell = Universal Gas Con~tant F = Faraday's Constant P1=Partial Pre~sure oP oxygen in the reference ga~
P2=Partial Pre~sure of oxygen in the monitored ga~
C = a Cell Con~tant for each individual cell, and Ln(P1/P2) i~ the natural logarithm of ratio Pl/P2.
The electrical voltage output of such a cell may be utilized, for example, in a closed loop combustion control system which use~ the oxygen ~en~or output ~ignal to "trim" the fuel/air mixture ratio. In such system~, the reading~ for actual stack gas oxygen content are compared with a de3ired ~et point. An appropriate control system output is generated to adjust automatically the fuel/air ratio, by such means as changing the amount of combu~tion air to the burner and/or the amount of fuel admitted to the burner, adding diluents and/or oxygen, etc., thereby as~uring that the desired oxygen ~et point i8 maintained. The desired effect of thi~ iB to achieve optimum combustion efficiency by regulating exactly the amount of oxygen to achieve complete combustion of the fuel. The Nernst equation "C" factor iQ to ad~ust output readings for peculiarities of the individual cell, ~uch as those which may be induced by physical characterl~tia~, damage, and/or conditions which are unique to that particular cell. Its value may be determined and utilized
BACKGROUND OF INVENTION
~l~g7 '1~ , In certain applications, it i~ desired to monitor the oxygen content of gases more or less continuously. A system which does thi~ effectively may be used, for example, to monitor ~he gaseous effluent from lndustrial boilers, kilns, ovens, internal combustion engines, driers, heat treating furnaces, incinerators, refinery process units, ga~ turbines ~crubbers and the like. Based on the information ~o gleaned, the amount of oxygen present may be adju~ted to desired level~. For example, the air being introduced into the combustion pha~e of a boiler may be xegula~ed to achieve optimum efficiency, and to reduce nitrous oxide and/or sulphur dioxide emissions. Insufficient oxygen, which can cause too high smoke opacity, slag buildup, boiler tube fouling, decrea~ed heat transfer, excessive maintenance, and wasted fuel, may be avoided, as also can an excess of oxygen which can cause waste of energy by heat lo~s.
Such monitoring ~y~tems can also be adapted to act as source~ to enable feedback sy~tem~ to effectuate ~uch adjustment~
automatically and continuously.
One means for so monitoring the oxygen content of such gases work~ on the principle of a zirconium oxide fuel cell oxygen sen~or. Typically, such sensors consist of a ceramic tube made from zirconium oxide that has been stabilized with yytrium and has porous platinum electrodes coated opposite each other on both itq inner and its outer Rurfaces at it~ sen~ing end. When the cell i3 heated to a temperature above 600 C (1100 F) the ceramic material becomes permeable to oxygen ions. Vacancies in it~ lattice ~tructure permit ~uch ions to pass through it, thus -rendering the cell into an oxygen ion conducting ~olid electrolyte. When the number of oxygen molecules per unit volume is ~reater at one plate of the cell tha~ at the other, oxygen ions will migrate from the former to the latter. The platinum electrodes on each ~ide of the cell wall provide catalytic ;;~
surfaces for the change of oxygen molecule~ into oxygen ionB and vice versa. Thus, oxygen molecules entering the cell through an electrode gain electrons to become ions whioh enter the electrolyte. Simultaneou~ly, at the other electrode, the oxygen ions 108e electrons and are released from the surface of the electrode as oxygen molecules. Thi~ flow creates an electron imbalance which produces a voltage potential between the electrode~. The magnitude of that potential is a function of the temperature of the cell and the relative partial pre~sure on each side of the cell. Partial pres~ure is defined as the pressure exerted by each component in the mixture that goes to make up the gas. It may be calculated as follows:
12~
~ 7 ~
Pi= Ni x R x T/V
where Pi = the partial pressure, Ni = the number of molecule~ of the ~pecie, R = the Universal Gas constant, T = temperat~re (absolute scale), and V = volume.
The partial pressure of the component gas "i" i8 then the same as if it occupie~ the same volume at the same temperature in the absence of other ga~es.
The relationship between the oxygen partial pre~sure at the monitored ~ide and that at the reference ga~ side (typically air, which i~ 20.95 % oxygen by volume), the temperature, voltage output, and cell constant of the individual cell are defined by the "Nernst" equation as follows~
E = RT/4F x ~n(Pl/P2) ~ C
::
where E - Voltage out T = Absolute temperature of cell = Universal Gas Con~tant F = Faraday's Constant P1=Partial Pre~sure oP oxygen in the reference ga~
P2=Partial Pre~sure of oxygen in the monitored ga~
C = a Cell Con~tant for each individual cell, and Ln(P1/P2) i~ the natural logarithm of ratio Pl/P2.
The electrical voltage output of such a cell may be utilized, for example, in a closed loop combustion control system which use~ the oxygen ~en~or output ~ignal to "trim" the fuel/air mixture ratio. In such system~, the reading~ for actual stack gas oxygen content are compared with a de3ired ~et point. An appropriate control system output is generated to adjust automatically the fuel/air ratio, by such means as changing the amount of combu~tion air to the burner and/or the amount of fuel admitted to the burner, adding diluents and/or oxygen, etc., thereby as~uring that the desired oxygen ~et point i8 maintained. The desired effect of thi~ iB to achieve optimum combustion efficiency by regulating exactly the amount of oxygen to achieve complete combustion of the fuel. The Nernst equation "C" factor iQ to ad~ust output readings for peculiarities of the individual cell, ~uch as those which may be induced by physical characterl~tia~, damage, and/or conditions which are unique to that particular cell. Its value may be determined and utilized
2 0 9 r~ ~ 3 ~ ( 3) to corr~ct the output readings by such means a~ a solenoid actuated bypass conduit through which rleference ga~ may be periodically introduced to the environs of the outer electrode ~urface. The "reading" while that is being done will then be that of the 'C" factor alone; a]1 other factors affecting the cell output at that instant thereby having then been eliminated or at lea3t so minimized as to have no material effect on the resulting reading~
It is also de~ired to effectuate such monitoring by comparable means and mechanism~ to those previou~ly described in ~ituations where ambient phenomena may induce false output reading~ which render the cell i~effectual as a practical matter. One example of thi~ is where there i8 a di~ferential between the absolute pressure of the gas at one of the electrodes from that at the other. An even more difficult example is where ~uch a differential in absolute pressure is pulsating. Thus, in an internal combustion diesel engine, the effluenk gas not only is at an absolute pressure differential with respect to the rèference, but al~o, because of the valving in the engine, that pre~sure pulsates through the exhaust system. Conditions of this type can cause a ~ensor of the type described to exhibit erroneous readings.
An explanation of this begins by noting that the principle involved in the operation of cells of the type described above i~ the migration of oxygen ions through the walls of the cell ;~
that i9 motivated by a disparity in the oxygen pres~ure as between the two ma3ses of gas. To be an accurate indicator of the proportion of oxygen content in the test gas, this migration, and the resulting imbalance in electrical potential, should be 501ely the result of he differential between the partial pressure of the oxygen in the gas that is on the test ~ide and that of the oxygen in the gas that is on the reference side of the cell. However, the magnitude of such migration may be influenced as well by a differential in the absolute pressure of the reference environment and that of the environment being sampled. The reason for this result is that the effect of an increase in absolute pressure is to compress the gas and thus "densify" it; i.e., to concentrate a greater number of oxygen molecules into an equivalent volume. But the sensor i~ capable only of reacting to oxygen pressure differentials. Its outer electrode now being expo~ed to more oxygen molecules over the same area for that electrode due to the "densification" which has occurred, the ~ensor "reads" this as if the composition of the test gas had changed through an increase in the proportion of its oxygen constituent, which it has not. To interpret the ~7~ 6 (4) resulting output a~ indicative of an oxygen partial pres~ure differential reading therefore, is erroneous since it has not been factored to take this absolute pressure differential element into account. While theoretically it might be po~sible to factor the cell output to take ~uch absolute pressure differentials into account, this would be an unrealistically complex approach as a practical matter. In a pulsating pressurized environment particularly, such as that present in an internal combustion engine e~hau~t ~y~tem, not only is ~uch an aberration produced by the addition in absolute pressure, but the aberration produced i~ unstable since the added pres~ure 80 applied is constantly changing due to the exhaust valve operation of the engine. It will be apparent then why, although the u~e of devices of the type descri~ed i~ desired, that has not been practical in some situations because of the inaccuracy of the re~ults produced.
ccordingly, it i8 an object of thl~ invention to provide meanq to detect the oxygen content of a gaseous environment.
Another object of this invention is to provide such mean3 for use ln monitoring ~uch oxygen content on a more or less continuou~ ba~
Yet another object of thi~ invention iB to provide means for achieving one or more of the foregoing objectives that is adapted for use in context3 wherein such gaseous environments are at differing absolute pres~ure~.
Still another object of thi~ invention is to provide ~eans for achieving one or more of the foregoing objectives that is adapted for use in contexts wherein ~uch gaseou6 environments are pulsating.
... .. ~;, , .
Yet another object of this invention is to provide means for achieving one or more of the foregoing objectives that is adapted for producing repetitive output signal~ to be utilized as corrective feedback ~ource~.
; ' Another object of thi~ invention is to provide means for achieving one or more of the foregoing objective~ that is adapted for u~e in internal combustion engines.
.
S~TATE~ENT OF INVENTION
According to a broad aspect, the present invention provides an oxygen sPnsor comprising an elongated main body member which is made from yy~rium stabilized zirconium oxide and has an internal chamber at one end, two electrodes that are ` ;~
made from platinum and are in con~act with sald main body, one of which is an inner electrode positioned within said chamber at one end of said main hody, and the othar of which is an outer electrode positioned on the outside surface of said main body member substantially opposite said inner electrode, electrical conductor means hy which said electrodes are rendered electrically accessible from the other end of said ;~
main body, an opening into said chamber from the outside of said main body via which the absolute pressure of gas in the -~ environs of said outer electrode is transmitted to gas in the environs of said inner electrode, isolation means for isolating the environs of said inner electrode from infiltration by gas being tested via said openinys, and supply means including an orifice for supplying reference gas to the environs of said inner electrode at a pressure to cause it to flow at its ;
critical flow rate through said orifice.
. :
Optionally, embodiments may include (1) means by `-~
.
which only a selected portion of said streams of gas impinges directly upon said outer electrode; (2) means for heating said main body member to such specified temperatures; (3) means for periodically calibrating the sensor for its "C" factor; ~4) means to ensure that the environs of said outer electrode are ~.
occupi.ed by gaæ to be tested; and/or (5) means to ensure that there is a positive flow of gas outward from said internal ~
cavity. ~ ;
The invention also provides a method of detecting the proportion of oxygen as a constituent part of a mass of gas ~, 5~ 67930-28 using an oxygen sensor comprisinq a main body member which has an tnterior chamber and is made from material which is an oxygen ion conducting solid electrolyte when within a specified temperature range; a~ least two electrocles that are porous to oxygen molecules, at least one oE which is an inner electrode positioned on a wall of said interior chamber and at least one other of which is an outer electrode positioned on the outside : surface of said main body member substantially opposite said inside electrode; electrical conductor means by which said electrodes are rendered electrically accessible at the outside of said main body; at least one opening into said interior chamber from tha outside of said main body via which the absolute pressure of gas in the environs of said outer electrode is transm:l.tted to gas in the environs of said inner :~
elec~rode; isolation means for isolating the environs of said inner electrode from infiltration by gas being tested via said ~:
openings; and supply means including an orifice for supplying xeference gas to the environs of saicl inner electrode at a -~
pressure to cause it to flow at its crltical flow rate through :~
.
said orifice; comprising the steps of establishing the temperature of said main body to within said specified kemperature range, causing the environs of said outside electrode to be occupied by 0as to be tested, supplying reference gas to th~ environs of said inner slectrode at a pressure to cause it to flow at its critical flow rate through said orifice and detecting the electrical output of said electrodes and translating said output into a value for the oxyyen compositlon of said gas being tested. :~
DESCRIPTION OF DRAWINGS
This lnvention may be understood from the description which follows and from the accompanying drawings in which :
.. .
,:
5b 6793Q-28 Figure I is a cross-sectional view of a prior art fuel cell oxygen sensor, : :
Figure 2 i5 a cross-sectional view of an embodiment ; of this invention, :
Flgure 3 is a cross-sectional view of a detailed portion of the embodiment of ~his invention shown in Figure 2, .
and Fi~ure 4 is another cross-sectional view of the - . .
embodiment of ~his invention shown in Figures 2 and 3, and Figure 5 is a cross-sectional view of another embodiment of this invention.
~' ~ '-,, , ,.`', ' ~, -:~, , ' ,~
., .
.
~ ~ ~3 '7 ~ ~ ~ (6~
DESCRIPTION OF PRE~ERRED_EMBODIMENTS
In Figure 1 there is depicted a cros~-sectional view of a prior art fuel cell oxygen sensor. It includes a central main body in the form of a ceramic tube made from yytrium stabi1ized zirconium oxide, with porou~ pla~inum electrodes coated on its inner and its outer surfaces. When the cell is heated, as by the heaters ~hich ~urround it, to a temperature above 600 C (llOO F) it become~ perrneable to oxygen ions. Vacancies in its lattice structure permit ~uch ions to pass through it, thu~ rendering the cell into an oxygen ion conducting ~olid electrolyte. The platinum electrodes on each ~ide of the cell provide the catalytic surfaces for the change of oxygen molecules into oxygen ions and vice versa. Oxyge~ molecule~ on the (outer~
reference gas cide of the cell, where the number of oxygen molecules is higher per unit volume, gain electrons and become ions when they are caused by the higher partial pressure on that side of the cell to pa~ through the outerj porous platinum coating and to enter the electrolyte. When such ions pas~
through the inner electrode, they are caused to lose electron~, rendering ~hem back into oxyg~n molecules tha~ are then released from the ~urface of the inner electrodeO Thus, whenever the partial pres~ure of oxygen i8 diferent at one ~i~e of the cell compared to that at the other, as when one slde i~ exposed to flue gases while the other is exposed to normal atmosphere, oxygen ion~ will migrate from the higher partial pre~sure side to the lower oxygen pressure side. The electron additions and deletion~ which take place as the oxyg2n passes through each of the platinum coating~ generate a net imbalance of electrons as between the two electrode~, and that produces a voltage potential between them. The magnitude of that potential is a function (among other things) of the oxygen partial pressures on each side of the cell. ~y eliminating or compensating for tho~e other factors, the oxygen density per unit volume on the te~t Bample side may thereby be detected. The relationship between the partlal pressure of the oxygen in the monitored ga~ and the reference gas (typically air, which is 20.95% oxygen by volume), and the temperature, vol~age output, and cell constant of the indivirlual cell are defined by the "Nernst" equation, a~
previously noted.
This detection approach i8 basically a partial pressure differential phenomenon. However, aa ha~ also been previously noted, phenomena which can affect the el0ctrical potential so generated may not be restricted to differential~ in partial pressure, Therefore, ~uch prior art device~ cannot measure 2~ (7) accurately the oxygen content of ga~ in a te~t zone when it is at an absolute presGure different from that of the ga~ in the reference zone. This deficiency iB even more unsatisfactory where, aq with internal combustion engine exhau~t system~, the absolute pres~ure in the ~e~t zone i~ con~tantly pulsing or otherwi~e changing with fair rapidity.
, ~
Fiqure 2 illustrates, in cro~s-~ection, an embodiment of this invention in the form of a ~ensor 10 which overcomes the~e shortcomings. A~ such, it includes a ceramic main body member 12 made from yytrium stabilized zirconium oxide, with porous platinum electrodes 14, 16 coated on the inside and out~ide re~pectively of the sensing end of ~he sensor. These electrodes 14, 16, have ~trlp-like exten~ion~ 14A and 16A respectively, which extend along the length of the out~ide and inside re~pectively of the main body member 12, as a mean~ to conduct the electrical output of the electrode~ to a point where it can be picked up out~ide the sensor itself. This iA shown in Figure
It is also de~ired to effectuate such monitoring by comparable means and mechanism~ to those previou~ly described in ~ituations where ambient phenomena may induce false output reading~ which render the cell i~effectual as a practical matter. One example of thi~ is where there i8 a di~ferential between the absolute pressure of the gas at one of the electrodes from that at the other. An even more difficult example is where ~uch a differential in absolute pressure is pulsating. Thus, in an internal combustion diesel engine, the effluenk gas not only is at an absolute pressure differential with respect to the rèference, but al~o, because of the valving in the engine, that pre~sure pulsates through the exhaust system. Conditions of this type can cause a ~ensor of the type described to exhibit erroneous readings.
An explanation of this begins by noting that the principle involved in the operation of cells of the type described above i~ the migration of oxygen ions through the walls of the cell ;~
that i9 motivated by a disparity in the oxygen pres~ure as between the two ma3ses of gas. To be an accurate indicator of the proportion of oxygen content in the test gas, this migration, and the resulting imbalance in electrical potential, should be 501ely the result of he differential between the partial pressure of the oxygen in the gas that is on the test ~ide and that of the oxygen in the gas that is on the reference side of the cell. However, the magnitude of such migration may be influenced as well by a differential in the absolute pressure of the reference environment and that of the environment being sampled. The reason for this result is that the effect of an increase in absolute pressure is to compress the gas and thus "densify" it; i.e., to concentrate a greater number of oxygen molecules into an equivalent volume. But the sensor i~ capable only of reacting to oxygen pressure differentials. Its outer electrode now being expo~ed to more oxygen molecules over the same area for that electrode due to the "densification" which has occurred, the ~ensor "reads" this as if the composition of the test gas had changed through an increase in the proportion of its oxygen constituent, which it has not. To interpret the ~7~ 6 (4) resulting output a~ indicative of an oxygen partial pres~ure differential reading therefore, is erroneous since it has not been factored to take this absolute pressure differential element into account. While theoretically it might be po~sible to factor the cell output to take ~uch absolute pressure differentials into account, this would be an unrealistically complex approach as a practical matter. In a pulsating pressurized environment particularly, such as that present in an internal combustion engine e~hau~t ~y~tem, not only is ~uch an aberration produced by the addition in absolute pressure, but the aberration produced i~ unstable since the added pres~ure 80 applied is constantly changing due to the exhaust valve operation of the engine. It will be apparent then why, although the u~e of devices of the type descri~ed i~ desired, that has not been practical in some situations because of the inaccuracy of the re~ults produced.
ccordingly, it i8 an object of thl~ invention to provide meanq to detect the oxygen content of a gaseous environment.
Another object of this invention is to provide such mean3 for use ln monitoring ~uch oxygen content on a more or less continuou~ ba~
Yet another object of thi~ invention iB to provide means for achieving one or more of the foregoing objectives that is adapted for use in context3 wherein such gaseous environments are at differing absolute pres~ure~.
Still another object of thi~ invention is to provide ~eans for achieving one or more of the foregoing objectives that is adapted for use in contexts wherein ~uch gaseou6 environments are pulsating.
... .. ~;, , .
Yet another object of this invention is to provide means for achieving one or more of the foregoing objectives that is adapted for producing repetitive output signal~ to be utilized as corrective feedback ~ource~.
; ' Another object of thi~ invention is to provide means for achieving one or more of the foregoing objective~ that is adapted for u~e in internal combustion engines.
.
S~TATE~ENT OF INVENTION
According to a broad aspect, the present invention provides an oxygen sPnsor comprising an elongated main body member which is made from yy~rium stabilized zirconium oxide and has an internal chamber at one end, two electrodes that are ` ;~
made from platinum and are in con~act with sald main body, one of which is an inner electrode positioned within said chamber at one end of said main hody, and the othar of which is an outer electrode positioned on the outside surface of said main body member substantially opposite said inner electrode, electrical conductor means hy which said electrodes are rendered electrically accessible from the other end of said ;~
main body, an opening into said chamber from the outside of said main body via which the absolute pressure of gas in the -~ environs of said outer electrode is transmitted to gas in the environs of said inner electrode, isolation means for isolating the environs of said inner electrode from infiltration by gas being tested via said openinys, and supply means including an orifice for supplying reference gas to the environs of said inner electrode at a pressure to cause it to flow at its ;
critical flow rate through said orifice.
. :
Optionally, embodiments may include (1) means by `-~
.
which only a selected portion of said streams of gas impinges directly upon said outer electrode; (2) means for heating said main body member to such specified temperatures; (3) means for periodically calibrating the sensor for its "C" factor; ~4) means to ensure that the environs of said outer electrode are ~.
occupi.ed by gaæ to be tested; and/or (5) means to ensure that there is a positive flow of gas outward from said internal ~
cavity. ~ ;
The invention also provides a method of detecting the proportion of oxygen as a constituent part of a mass of gas ~, 5~ 67930-28 using an oxygen sensor comprisinq a main body member which has an tnterior chamber and is made from material which is an oxygen ion conducting solid electrolyte when within a specified temperature range; a~ least two electrocles that are porous to oxygen molecules, at least one oE which is an inner electrode positioned on a wall of said interior chamber and at least one other of which is an outer electrode positioned on the outside : surface of said main body member substantially opposite said inside electrode; electrical conductor means by which said electrodes are rendered electrically accessible at the outside of said main body; at least one opening into said interior chamber from tha outside of said main body via which the absolute pressure of gas in the environs of said outer electrode is transm:l.tted to gas in the environs of said inner :~
elec~rode; isolation means for isolating the environs of said inner electrode from infiltration by gas being tested via said ~:
openings; and supply means including an orifice for supplying xeference gas to the environs of saicl inner electrode at a -~
pressure to cause it to flow at its crltical flow rate through :~
.
said orifice; comprising the steps of establishing the temperature of said main body to within said specified kemperature range, causing the environs of said outside electrode to be occupied by 0as to be tested, supplying reference gas to th~ environs of said inner slectrode at a pressure to cause it to flow at its critical flow rate through said orifice and detecting the electrical output of said electrodes and translating said output into a value for the oxyyen compositlon of said gas being tested. :~
DESCRIPTION OF DRAWINGS
This lnvention may be understood from the description which follows and from the accompanying drawings in which :
.. .
,:
5b 6793Q-28 Figure I is a cross-sectional view of a prior art fuel cell oxygen sensor, : :
Figure 2 i5 a cross-sectional view of an embodiment ; of this invention, :
Flgure 3 is a cross-sectional view of a detailed portion of the embodiment of ~his invention shown in Figure 2, .
and Fi~ure 4 is another cross-sectional view of the - . .
embodiment of ~his invention shown in Figures 2 and 3, and Figure 5 is a cross-sectional view of another embodiment of this invention.
~' ~ '-,, , ,.`', ' ~, -:~, , ' ,~
., .
.
~ ~ ~3 '7 ~ ~ ~ (6~
DESCRIPTION OF PRE~ERRED_EMBODIMENTS
In Figure 1 there is depicted a cros~-sectional view of a prior art fuel cell oxygen sensor. It includes a central main body in the form of a ceramic tube made from yytrium stabi1ized zirconium oxide, with porou~ pla~inum electrodes coated on its inner and its outer surfaces. When the cell is heated, as by the heaters ~hich ~urround it, to a temperature above 600 C (llOO F) it become~ perrneable to oxygen ions. Vacancies in its lattice structure permit ~uch ions to pass through it, thu~ rendering the cell into an oxygen ion conducting ~olid electrolyte. The platinum electrodes on each ~ide of the cell provide the catalytic surfaces for the change of oxygen molecules into oxygen ions and vice versa. Oxyge~ molecule~ on the (outer~
reference gas cide of the cell, where the number of oxygen molecules is higher per unit volume, gain electrons and become ions when they are caused by the higher partial pressure on that side of the cell to pa~ through the outerj porous platinum coating and to enter the electrolyte. When such ions pas~
through the inner electrode, they are caused to lose electron~, rendering ~hem back into oxyg~n molecules tha~ are then released from the ~urface of the inner electrodeO Thus, whenever the partial pres~ure of oxygen i8 diferent at one ~i~e of the cell compared to that at the other, as when one slde i~ exposed to flue gases while the other is exposed to normal atmosphere, oxygen ion~ will migrate from the higher partial pre~sure side to the lower oxygen pressure side. The electron additions and deletion~ which take place as the oxyg2n passes through each of the platinum coating~ generate a net imbalance of electrons as between the two electrode~, and that produces a voltage potential between them. The magnitude of that potential is a function (among other things) of the oxygen partial pressures on each side of the cell. ~y eliminating or compensating for tho~e other factors, the oxygen density per unit volume on the te~t Bample side may thereby be detected. The relationship between the partlal pressure of the oxygen in the monitored ga~ and the reference gas (typically air, which is 20.95% oxygen by volume), and the temperature, vol~age output, and cell constant of the indivirlual cell are defined by the "Nernst" equation, a~
previously noted.
This detection approach i8 basically a partial pressure differential phenomenon. However, aa ha~ also been previously noted, phenomena which can affect the el0ctrical potential so generated may not be restricted to differential~ in partial pressure, Therefore, ~uch prior art device~ cannot measure 2~ (7) accurately the oxygen content of ga~ in a te~t zone when it is at an absolute presGure different from that of the ga~ in the reference zone. This deficiency iB even more unsatisfactory where, aq with internal combustion engine exhau~t system~, the absolute pres~ure in the ~e~t zone i~ con~tantly pulsing or otherwi~e changing with fair rapidity.
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Fiqure 2 illustrates, in cro~s-~ection, an embodiment of this invention in the form of a ~ensor 10 which overcomes the~e shortcomings. A~ such, it includes a ceramic main body member 12 made from yytrium stabilized zirconium oxide, with porous platinum electrodes 14, 16 coated on the inside and out~ide re~pectively of the sensing end of ~he sensor. These electrodes 14, 16, have ~trlp-like exten~ion~ 14A and 16A respectively, which extend along the length of the out~ide and inside re~pectively of the main body member 12, as a mean~ to conduct the electrical output of the electrode~ to a point where it can be picked up out~ide the sensor itself. This iA shown in Figure
3. There, in a cros~-~ection of the sensor end of the sensor device shown in Figure 2, the inner electrode 16 i~ ~hown to have a continuation ribbon 16A which extends from that electrode along the in~ide of the length of the main body 12 to it~
opposite end, where it extends across the end of the wall o$ the main body 12 and doubles back for a short di~tance. Throuqh a soldered connection 20, it~ output iB carried off via an insulated conductor 19. Similarly, a ribbon of platinum 14A
conduct~ the output of the inner electrode 14 along the outside of the length of the main body to a connector 20A, through which it~ electrical output i8 conducted via another soldered connection 20A to another insulated electrical conductor 1~. The shape of the boay member in thi~ embodiment i~ like that of a test tube, in that it i~ clo~ed at the sensing end o~ the sensor where the electrode~ are located, and ha~ a central chamber.
Other structures, however, may al~o be utilized, ~uch a~ ~quare, rectangular, or other shaped boxe~ with internal cavitie~
adapted for particular use~. AB shown in Figures 2, 4, and 5, the main body member 12 has a port or bleed hole 32 which extends through its ~ldewall, by meanA of which absolute ~pressures at the outside of the main body will be transmitted to its internal cavity. The sen30r also lnclude~ a central tube which has two internal conduits 28, 29 which extend the length of the interior chamber. The~e conduits open to the reference gas ~ource at the non-sensing end of the tube, and open into the region of the inside electrode 16 within the main body member 12 at it~ clo~ed end. ~y means of these conduit~, reference gas may be introduced directly to the envlronG of the inner el~ctrode as 2~7~5~8~
will be describad. Surrounding the central tube ~, at spaced intervals along its length, are spacer~ 24, 26 made from ceramic material of the type a~ is the main body 12. It should be noted that tho~e spacers marked "24" have a space between their tops and the in~ide of the main body 12, while those marked "24" have comparable spaces at their bottoms. These may be formed by chording what are otherwise circular spacers, alternating top and bottom. The effect of thi~ alternating gap pattern i8 to create tortuou~ paths which tend to dampen or attenuate the flow of ga~ linearly through the body member 12 and, more importantly, ~erve to increase the length of the travel path which gas would have to travel from the port 32 to the environs of the inner electrode 16. The significance of this latter, in particular, will be elaborated upon later, from which it will be apparent that desired result~ may be achieved with other forms of such isolation mean3 (e.g., fibrous "wool") in addition or in -~
the alternative. A plug 30 or other means seals the open end of the main body member 12 while allowing the various electrical leads to be brought out to the outside of the main body 12.
Included among them are electrical conductor leads 21, 22 which conduct the output of a thermocouple 17. sy this mean~, the temperature of the sensor may be monitored to facilitate maintaining it above the 600 C level necessary for the ceramic component of the wall of the main body 12 to function as a solid electrolyte a~ previously described.
Figure 4 illu~trate~ in cro~s-section the embodiment of this invention ~hown in Figure~ 2 and 3 with other components with which it may be used. These added components include an outer housing 31, a sample gas inlet 33, and an exit tube 34 which extend~ from thP compartment surrounding the sensor 10. Thefie several components are held in place and sealed by means of known per ~e means, such as the retention nut 38 and the O ring seal 40. The heating coil 36 i8 supplied with electrical enerqy by means of the power leads 42, 44 a~ a means to maintain the unit at a desired 600+ C temperature level. There i8 also an outer box 45 with a screw-on cover for access which i9, nevertheless, ga9 tight 80 that reference gas admitted to it via ~ ;~
the gas inlet 23 may be cau~ed to flow into the open ends of the conduits 28, 29 and along their length into the environs of the inner electrode 16 as herein de~cribed.
.
The apparatus shown in Figuxe 5 as well as that shown in Figure
opposite end, where it extends across the end of the wall o$ the main body 12 and doubles back for a short di~tance. Throuqh a soldered connection 20, it~ output iB carried off via an insulated conductor 19. Similarly, a ribbon of platinum 14A
conduct~ the output of the inner electrode 14 along the outside of the length of the main body to a connector 20A, through which it~ electrical output i8 conducted via another soldered connection 20A to another insulated electrical conductor 1~. The shape of the boay member in thi~ embodiment i~ like that of a test tube, in that it i~ clo~ed at the sensing end o~ the sensor where the electrode~ are located, and ha~ a central chamber.
Other structures, however, may al~o be utilized, ~uch a~ ~quare, rectangular, or other shaped boxe~ with internal cavitie~
adapted for particular use~. AB shown in Figures 2, 4, and 5, the main body member 12 has a port or bleed hole 32 which extends through its ~ldewall, by meanA of which absolute ~pressures at the outside of the main body will be transmitted to its internal cavity. The sen30r also lnclude~ a central tube which has two internal conduits 28, 29 which extend the length of the interior chamber. The~e conduits open to the reference gas ~ource at the non-sensing end of the tube, and open into the region of the inside electrode 16 within the main body member 12 at it~ clo~ed end. ~y means of these conduit~, reference gas may be introduced directly to the envlronG of the inner el~ctrode as 2~7~5~8~
will be describad. Surrounding the central tube ~, at spaced intervals along its length, are spacer~ 24, 26 made from ceramic material of the type a~ is the main body 12. It should be noted that tho~e spacers marked "24" have a space between their tops and the in~ide of the main body 12, while those marked "24" have comparable spaces at their bottoms. These may be formed by chording what are otherwise circular spacers, alternating top and bottom. The effect of thi~ alternating gap pattern i8 to create tortuou~ paths which tend to dampen or attenuate the flow of ga~ linearly through the body member 12 and, more importantly, ~erve to increase the length of the travel path which gas would have to travel from the port 32 to the environs of the inner electrode 16. The significance of this latter, in particular, will be elaborated upon later, from which it will be apparent that desired result~ may be achieved with other forms of such isolation mean3 (e.g., fibrous "wool") in addition or in -~
the alternative. A plug 30 or other means seals the open end of the main body member 12 while allowing the various electrical leads to be brought out to the outside of the main body 12.
Included among them are electrical conductor leads 21, 22 which conduct the output of a thermocouple 17. sy this mean~, the temperature of the sensor may be monitored to facilitate maintaining it above the 600 C level necessary for the ceramic component of the wall of the main body 12 to function as a solid electrolyte a~ previously described.
Figure 4 illu~trate~ in cro~s-section the embodiment of this invention ~hown in Figure~ 2 and 3 with other components with which it may be used. These added components include an outer housing 31, a sample gas inlet 33, and an exit tube 34 which extend~ from thP compartment surrounding the sensor 10. Thefie several components are held in place and sealed by means of known per ~e means, such as the retention nut 38 and the O ring seal 40. The heating coil 36 i8 supplied with electrical enerqy by means of the power leads 42, 44 a~ a means to maintain the unit at a desired 600+ C temperature level. There i8 also an outer box 45 with a screw-on cover for access which i9, nevertheless, ga9 tight 80 that reference gas admitted to it via ~ ;~
the gas inlet 23 may be cau~ed to flow into the open ends of the conduits 28, 29 and along their length into the environs of the inner electrode 16 as herein de~cribed.
.
The apparatus shown in Figuxe 5 as well as that shown in Figure
4 also includes a reference ga~ conduit 60 through which reference gas may flow periodioally according to a predetermined program a~ regulated by a solenoid valve 62, for example, lnto 2û~5~(9) the environs of the out3ide electrode 14. ~y this means, the sensor device may periodically be "zeroed" as to all affecting factor~ except for the "C" factor of individual cel] vari3tions according to ~he Nernst formula. This effect i~ achieved because when both electrode~ in the sen~or are expoqed to gas o~ the same oxygen compo~ition and the same absolute pressure, any read-out that occurs will be a reflection of any aberration that is peculiar to that cell and it~ environment, and ~o may be used to compensated test readings for those peculiarities. In both cases, the calibration gas solenoid 62 receives it~ gas supply directly from the pressurized reference ga6 plenum, and the flow of calibration gas to the sensing cell i3 controlled by an appropriately sized orifice built directly into the solenoid body. ~:
In the embodiment ~hown in Figure 4, reference gas from the end housing flows at a controlled rate into an aspirator tube 72 that is positioned more or lesB coaxial to and within the exhaust tube 74. The latter terminate~ in a nozzle 74 which vents this exhaust in the direction of flow of the te~t gas as it passes through the manifold 76. A similar, but alternative structure i8 shown in Figure Sj with corresponding elements identified by the ~ame reference numerals. While other structure~ may be used to achieve comparable ends, these embodiments are illustrative of eduators which may be used as a means to ensure a positive flow of gas outward from the interior chamber of the sen~or device. The high pre~sure reference gas supply furni3hes the motive power for the a~pirator. The exhaust conduit and the test gas inlet are located in close proximity to each othex to en~ure that the two tube~ are at substantially the ~ame absolute pressure where they are open to the mass of gas being sampled. The exhaust tube i~ located downstxeam of the test gas inlet to eliminate pollution of the test ga~ inlat by the exhaust flow. The aspirator flow control orifice limits the flow to the aspirator 80 that a ~ufficient test gas flow rate is maintained. The negative presaure created by the aspirator iB a driving force that cau~es a sample of test gas to be drawn into the test gas inlet, past the ~ensor and out through the exhaust conduit 34, and al~o carri0s away gas exiting the ~en~or main body v~a the port 32. Thus, during te~ting, the outer electrode "sees" te~t gas that is representative of the mas~ of gas being tested, and the inner electrode "~ees" reference gas.
The eductor assembly and the reference gas conduits preferably are located in the heated area~ of the sensor since thi~
eliminates condensation and minimizes temperature "excurqion~"
at the sen~ing cell.
In the embodiment ~hown in Figure 4, reference gas from the end housing flows at a controlled rate into an aspirator tube 72 that is positioned more or lesB coaxial to and within the exhaust tube 74. The latter terminate~ in a nozzle 74 which vents this exhaust in the direction of flow of the te~t gas as it passes through the manifold 76. A similar, but alternative structure i8 shown in Figure Sj with corresponding elements identified by the ~ame reference numerals. While other structure~ may be used to achieve comparable ends, these embodiments are illustrative of eduators which may be used as a means to ensure a positive flow of gas outward from the interior chamber of the sen~or device. The high pre~sure reference gas supply furni3hes the motive power for the a~pirator. The exhaust conduit and the test gas inlet are located in close proximity to each othex to en~ure that the two tube~ are at substantially the ~ame absolute pressure where they are open to the mass of gas being sampled. The exhaust tube i~ located downstxeam of the test gas inlet to eliminate pollution of the test ga~ inlat by the exhaust flow. The aspirator flow control orifice limits the flow to the aspirator 80 that a ~ufficient test gas flow rate is maintained. The negative presaure created by the aspirator iB a driving force that cau~es a sample of test gas to be drawn into the test gas inlet, past the ~ensor and out through the exhaust conduit 34, and al~o carri0s away gas exiting the ~en~or main body v~a the port 32. Thus, during te~ting, the outer electrode "sees" te~t gas that is representative of the mas~ of gas being tested, and the inner electrode "~ees" reference gas.
The eductor assembly and the reference gas conduits preferably are located in the heated area~ of the sensor since thi~
eliminates condensation and minimizes temperature "excurqion~"
at the sen~ing cell.
5 ~ 1 0) From these Figures, the operation of this embodiment of this invention may be seen. When the complete a~sembly i~ installed in place for u~e; sample gaa ~i.e., that gas whose oxygen content i~ to be ascertained), ~uch a~ exhaust gas from a diesel engine, iq admitted through the sample gas inlet 33, so that it impinges upon and occupies the environs of ~he outer electrode l4 of the ~en~or lO. Sample gas so admitted to the unit pa~se~
along the length of the outslde of the outer main body 12. A~ a result, any differential in ab~olute pres~ure between that of the body of sample ga~ being tested and that of the reference gas which i8 in~ide the device and in the environs of the inner electrode 16 is transmitted via the hole 32 to the inside of the mai~ body member 12. ~he effect of thls effectively is to nullify any differential between the ab301ute pre~sures of the two bodie~ of gas other than the differential in partial pre~sure between them which, of course, are what is desired to be detected.
It ~hould be noted that thi~ result occurs as to any differential in ab~olute pressure betwean the two regions, which may be more or le88 con~tant, or it may pul~ate as does the exhau~t from a diesel or other internal combu~tion engine.
Further, the presqure in the test or sample zone may be negative compared to that in the reference zone, and likewise may be -constant or pul~ate compared to that of the reference zone. As will presently be seen, embodlments of this invention may be made to operate in all such 3ituations.
These regultB are assured by the manner in which the reference gas is introduced into the environ~ of the inside electrode 16 via the ducts 28, 29 in the inner tube-~. According to well ~nown principles of physic~, the general rule is that the flow rate of gas through an orifice i8 a function of the difference in pressure between the two ~ide~ of the orifice. However, when the ratio of pre~sure on the "out" ~ide is about 53% of that on its "in" ~ide, the critical flow rate for that orifice is reached. At that point, the rate of flow will stabilize and will not increase or d0crease so long as the ratio of "out" to "in"
pressure~ is maintained at or above that 53+~ level. The flow of gas from these ducts is maintained at the level of critical flow for the orifices through which it flows. As a result, the voluma of reference gas entering the internal cavity of the main body will not decrease or increase, even when changes occur in ~he ab~olute pre~sure of the ga~ being tested. To that end, the 2~ tll) pressure at the "in" side of the inlet orifices is maintained at a level such that a pressure equal to 53% of that level (iOe., the pressure at the "out" side of that same orifice) is at least ~lightly greater than the ac~ual constant pre~sure or the peak of the pulsating pre~sure (a~ the case may be) of the sample gas. This maintain~ a net outflow of the reference gas from the exposed surface of the inner electrode 16 inside the main body 12 out through the port 32, from whence it can move along to and out through the exhaust tube 34. This result is enhanced by the previously de~aribed isolation means which, in addition to the dampening or attenuation functions, lengthen~ the travel path for this outflow of reference gas. As a result, any invasion of of test ga~ into the inner cavity via the port 32 due to a tran~ient exce~s of test gas absolute pressure over that of the reference ~a5 ~ and contamination of the re~erence gas in the environs of the inner electxode, is precluded. Correspondingly, if the ab~olute pressure, constant or pul~ating, of the test gas is negative ~i.e., is a partial vacuum) with respect to that of the reference gas, the nPt outflow will remain substantially constant due to the throttling effect inherent in the constancy of the critical flow phenomenon at the reference gas injection orifices. Since thiq al~o ensures a net outflow of reference gas from the interior of the sensor, it is as~ured that the environs of the inner electrode 16 will always be occupied by reference gas, uncontaminated by sample ga~ leaking through the port 32 lnto the interior of the main body member 12, thu~ preservinq the basis upon which accurate readings of partial pressure differential~ (and therefore of oxygen content~ may be premi~ed.
Some consideration mu~t be given to the hole sizes of the inlet and outlet orifice~, ~lnce thi~ may ha~e an effect on the accuracy of the readings obtained. Thus, the inlet orifice must be suffi~iently large to introduce a volume of gas that will a~ure a positive net outflow from the inner chamber while, at the same time, not being so large as to permit so much gas to enter the chamber ~hat it will have a cooling effect on the device or otherwise affect its output. Such adjustment are within the capability of one skilled in these art~ once given these teachings of this invention. It should also be noted that thP outlet orifice ordinarily ~hould be somewhat larger in size than the inlet orifice to ensure that it relieves quickly any pressure built up in the inner chamber. It is recognized, too, that some pressure drop normally wlll be exhibited across the outlet orifice which may effect the accuracy of the device.
}lowever, the effect of this, if any, is taken into account when a reading is taken a8 previously described to calibrate the device for it~ "C" factor. In eEfect, this element becomes part of the read cell factor.
~ ~ ~3 r~ 2 ) Sometimes, ~gain a~ in the case of an internal com~ustion diesel engi~e, the p~ e~ in the ~ample (exhau~t) ~one are ~o frequent in tim~ d~ration and of such a m~gnitude that the sample qas impinging upon the outer electrode 14 doe~ 80 at high velocities and volume~ and ~o can produce false readings. To ameliorate this,the embodiment of this invention ~hown in Figure 5 may be used. It include~ a sensor 10 within a heated housing 31.
)lowever, lnstead of ~he ~ample gas coming at the ~ensor through a sample gas inlet of the type ~hown a~ 33 in Figure 4, a sample gas inlet tube 47 is positioned within the sample gas inlet and ~ealed with re~pect to it by means of a seal ring nipple 48, ~o that the sa~ple ga~ admitted to the unit comes entirely through the tube 47~ The ~ube 47 ie made ~o that lt ha~ a ~mall tap hole 52 at its end that is juxtaposed to the electrode l4/ a~d has comparatively large cro~-sectional area hole~ 50 in the ~ides of the inlet tube 47 but within the ~ealed off region. By thi~
means, only a ~mall portion of the total incoming test gas, which nevaxthele~s compositionally i5 ~tatistically representative of the test ga~ but of small volume and low veloaity, actually impinge~ upon the electrode 14, thus eliminating or at least minimizing any readout aberrations that would otherwise be volume and/or velocity induced. At the same time the unit still ha~ large volume test ~ample capability by virtue of the side hole~ 50 which permit mo~t of the san)ple ga~
to bypa~s the electrode 14 but to pa~s through the test apparatu~ anyway. Such large volume capacity for the unit as a whole may be necessary in order to en~ure, particularly with a pulsating source, that the sample testea i3 representative, and not merely the re-injection of a previou~ly monitored or otherwi~e unrepresentative sa~ple.
It should be noted that the calibration air circuit which ~ncludee the conduit 62 and the ~olenoid 60 of the embodiment as shown in Figure 5, while otherwise comparable in da~ign and function with that shown in Figure 4, discharges into the tube 47 in th~ region of the nipple 48, well ahead of the lateral tube slots 50. This discharge po~ition is selected to provide sufficient time for the calibration gas, as it travels along the tube in the direction of the sensor eleatrode 14, to heat sufficiently for it not to introduce any temperature induced errors in the sensor reading~. However, given the distanGe involved in assuring that result, con~ideration must be given to en~uring that a sufficient volume of calibration gas i8 introduced ~o that the callbration ga~ which the sensor electrode 14 "~ees" is sub~tantially undiluted with test gas and is truly repre~entative of the composition of the calibration 2~97~, ~13) gaY. Such concepts are not limited to embodiment~ of the type ~hown in ~igure 5, but are applicable to other embodiments of thi~ invention a~ well. Such adjustments are within the skills of per~ons knowledgeable in the cognizant art~.
Figure~ 4 and 5 also illustrate means for heating the entire sen30r unit in the form of a heating coil 36 that i9 energized by electrical energy through conductor leads 42, 44. Normally, given the high temperature (600+ C) that mu~t be established and maintalned in order for zirconium oxide to become oxygen ion conductive, such supplementary heating means is required in the current state of this technology. However, it i~ within the contemplation of thi~ invention that technological advance~ may be made such that -the nece~sity for such supplementary heating is reduced or negated.
From the preceding description and the accompanying drawings, it will be clear that many different embodiment~ and variants thereof may be employed within the contemplation of this invention. For example, although single pres~ure relief ports and pair~ of electrode~ have been described and di~cus~ed in the embodiments, it is within the contemplatlon of this inv6ntion that multiple port~ and/or combinations of electrodes may be used within recognized engineering con~iclerations and practices.
Thu~, it is to be understood that the embodiment~ illustrated and discussed are by way of illustration and not of limitation, and that a wide variety of embodiment3 may be made without departing from the ~pirit or scope of thi~ invention.
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~ WE CLAIM ~
: .
: : : ::
along the length of the outslde of the outer main body 12. A~ a result, any differential in ab~olute pres~ure between that of the body of sample ga~ being tested and that of the reference gas which i8 in~ide the device and in the environs of the inner electrode 16 is transmitted via the hole 32 to the inside of the mai~ body member 12. ~he effect of thls effectively is to nullify any differential between the ab301ute pre~sures of the two bodie~ of gas other than the differential in partial pre~sure between them which, of course, are what is desired to be detected.
It ~hould be noted that thi~ result occurs as to any differential in ab~olute pressure betwean the two regions, which may be more or le88 con~tant, or it may pul~ate as does the exhau~t from a diesel or other internal combu~tion engine.
Further, the presqure in the test or sample zone may be negative compared to that in the reference zone, and likewise may be -constant or pul~ate compared to that of the reference zone. As will presently be seen, embodlments of this invention may be made to operate in all such 3ituations.
These regultB are assured by the manner in which the reference gas is introduced into the environ~ of the inside electrode 16 via the ducts 28, 29 in the inner tube-~. According to well ~nown principles of physic~, the general rule is that the flow rate of gas through an orifice i8 a function of the difference in pressure between the two ~ide~ of the orifice. However, when the ratio of pre~sure on the "out" ~ide is about 53% of that on its "in" ~ide, the critical flow rate for that orifice is reached. At that point, the rate of flow will stabilize and will not increase or d0crease so long as the ratio of "out" to "in"
pressure~ is maintained at or above that 53+~ level. The flow of gas from these ducts is maintained at the level of critical flow for the orifices through which it flows. As a result, the voluma of reference gas entering the internal cavity of the main body will not decrease or increase, even when changes occur in ~he ab~olute pre~sure of the ga~ being tested. To that end, the 2~ tll) pressure at the "in" side of the inlet orifices is maintained at a level such that a pressure equal to 53% of that level (iOe., the pressure at the "out" side of that same orifice) is at least ~lightly greater than the ac~ual constant pre~sure or the peak of the pulsating pre~sure (a~ the case may be) of the sample gas. This maintain~ a net outflow of the reference gas from the exposed surface of the inner electrode 16 inside the main body 12 out through the port 32, from whence it can move along to and out through the exhaust tube 34. This result is enhanced by the previously de~aribed isolation means which, in addition to the dampening or attenuation functions, lengthen~ the travel path for this outflow of reference gas. As a result, any invasion of of test ga~ into the inner cavity via the port 32 due to a tran~ient exce~s of test gas absolute pressure over that of the reference ~a5 ~ and contamination of the re~erence gas in the environs of the inner electxode, is precluded. Correspondingly, if the ab~olute pressure, constant or pul~ating, of the test gas is negative ~i.e., is a partial vacuum) with respect to that of the reference gas, the nPt outflow will remain substantially constant due to the throttling effect inherent in the constancy of the critical flow phenomenon at the reference gas injection orifices. Since thiq al~o ensures a net outflow of reference gas from the interior of the sensor, it is as~ured that the environs of the inner electrode 16 will always be occupied by reference gas, uncontaminated by sample ga~ leaking through the port 32 lnto the interior of the main body member 12, thu~ preservinq the basis upon which accurate readings of partial pressure differential~ (and therefore of oxygen content~ may be premi~ed.
Some consideration mu~t be given to the hole sizes of the inlet and outlet orifice~, ~lnce thi~ may ha~e an effect on the accuracy of the readings obtained. Thus, the inlet orifice must be suffi~iently large to introduce a volume of gas that will a~ure a positive net outflow from the inner chamber while, at the same time, not being so large as to permit so much gas to enter the chamber ~hat it will have a cooling effect on the device or otherwise affect its output. Such adjustment are within the capability of one skilled in these art~ once given these teachings of this invention. It should also be noted that thP outlet orifice ordinarily ~hould be somewhat larger in size than the inlet orifice to ensure that it relieves quickly any pressure built up in the inner chamber. It is recognized, too, that some pressure drop normally wlll be exhibited across the outlet orifice which may effect the accuracy of the device.
}lowever, the effect of this, if any, is taken into account when a reading is taken a8 previously described to calibrate the device for it~ "C" factor. In eEfect, this element becomes part of the read cell factor.
~ ~ ~3 r~ 2 ) Sometimes, ~gain a~ in the case of an internal com~ustion diesel engi~e, the p~ e~ in the ~ample (exhau~t) ~one are ~o frequent in tim~ d~ration and of such a m~gnitude that the sample qas impinging upon the outer electrode 14 doe~ 80 at high velocities and volume~ and ~o can produce false readings. To ameliorate this,the embodiment of this invention ~hown in Figure 5 may be used. It include~ a sensor 10 within a heated housing 31.
)lowever, lnstead of ~he ~ample gas coming at the ~ensor through a sample gas inlet of the type ~hown a~ 33 in Figure 4, a sample gas inlet tube 47 is positioned within the sample gas inlet and ~ealed with re~pect to it by means of a seal ring nipple 48, ~o that the sa~ple ga~ admitted to the unit comes entirely through the tube 47~ The ~ube 47 ie made ~o that lt ha~ a ~mall tap hole 52 at its end that is juxtaposed to the electrode l4/ a~d has comparatively large cro~-sectional area hole~ 50 in the ~ides of the inlet tube 47 but within the ~ealed off region. By thi~
means, only a ~mall portion of the total incoming test gas, which nevaxthele~s compositionally i5 ~tatistically representative of the test ga~ but of small volume and low veloaity, actually impinge~ upon the electrode 14, thus eliminating or at least minimizing any readout aberrations that would otherwise be volume and/or velocity induced. At the same time the unit still ha~ large volume test ~ample capability by virtue of the side hole~ 50 which permit mo~t of the san)ple ga~
to bypa~s the electrode 14 but to pa~s through the test apparatu~ anyway. Such large volume capacity for the unit as a whole may be necessary in order to en~ure, particularly with a pulsating source, that the sample testea i3 representative, and not merely the re-injection of a previou~ly monitored or otherwi~e unrepresentative sa~ple.
It should be noted that the calibration air circuit which ~ncludee the conduit 62 and the ~olenoid 60 of the embodiment as shown in Figure 5, while otherwise comparable in da~ign and function with that shown in Figure 4, discharges into the tube 47 in th~ region of the nipple 48, well ahead of the lateral tube slots 50. This discharge po~ition is selected to provide sufficient time for the calibration gas, as it travels along the tube in the direction of the sensor eleatrode 14, to heat sufficiently for it not to introduce any temperature induced errors in the sensor reading~. However, given the distanGe involved in assuring that result, con~ideration must be given to en~uring that a sufficient volume of calibration gas i8 introduced ~o that the callbration ga~ which the sensor electrode 14 "~ees" is sub~tantially undiluted with test gas and is truly repre~entative of the composition of the calibration 2~97~, ~13) gaY. Such concepts are not limited to embodiment~ of the type ~hown in ~igure 5, but are applicable to other embodiments of thi~ invention a~ well. Such adjustments are within the skills of per~ons knowledgeable in the cognizant art~.
Figure~ 4 and 5 also illustrate means for heating the entire sen30r unit in the form of a heating coil 36 that i9 energized by electrical energy through conductor leads 42, 44. Normally, given the high temperature (600+ C) that mu~t be established and maintalned in order for zirconium oxide to become oxygen ion conductive, such supplementary heating means is required in the current state of this technology. However, it i~ within the contemplation of thi~ invention that technological advance~ may be made such that -the nece~sity for such supplementary heating is reduced or negated.
From the preceding description and the accompanying drawings, it will be clear that many different embodiment~ and variants thereof may be employed within the contemplation of this invention. For example, although single pres~ure relief ports and pair~ of electrode~ have been described and di~cus~ed in the embodiments, it is within the contemplatlon of this inv6ntion that multiple port~ and/or combinations of electrodes may be used within recognized engineering con~iclerations and practices.
Thu~, it is to be understood that the embodiment~ illustrated and discussed are by way of illustration and not of limitation, and that a wide variety of embodiment3 may be made without departing from the ~pirit or scope of thi~ invention.
, ~
~ WE CLAIM ~
: .
: : : ::
Claims (20)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An oxygen sensor comprising an elongated main body member which is made from yytrium stabilized zirconium oxide and has an internal chamber at one end, two electrodes that are made from platinum and are in contact with said main body, one of which is an inner electrode positioned within said chamber at one end of said main body, and the other of which is an outer electrode positioned on the outside surface of said main body member substantially opposite said inner electrode, electrical conductor means by which said electrodes are rendered electrically accessible from the other end of said main body, an opening into said chamber from the outside of said main body via which the absolute pressure of gas in the environs of said outer electrode is transmitted to gas in the environs of said inner electrode, isolation means for isolating the environs of said inner electrode from infiltration by gas being tested via said openings, and supply means including an orifice for supplying reference gas to the environs of said inner electrode at a pressure to cause it to flow at its critical flow rate through said orifice.
2. The device described in Claim 1 including calibration means for periodically introducing reference gas to the region of said outside electrode.
3. The device described in Claim 1 including heating 14a means for heating said main body member to a temperature of at least 600 degrees centigrade.
4. The device described in Claim 2 including heating means for heating said main body member to a temperature of at least 600 degrees centigrade.
5. The device described in Claim 3 including monitoring means that is adapted for monitoring the temperature of said main body and is also adapted for being monitored by regulating means to maintain the temperature of said main body at at least 600 degrees centigrade.
(15)
(15)
6. The device described in Claim 4 including monitoring means that is adapted for monitoring the temperature of said main body and is also adapted for being monitored by regulating means to maintain the temperature of said main body at at least 600 degrees centigrade.
7. The device described in Claim 1 including control means for directing a selected portion of the gas to be tested to occupy the environs of the outer surface of said outer electrode.
8. The device described in Claim 2 including control means for directing a selected portion of the gas to be tested to occupy the environs of the outer surface of said outer electrode.
9. The device described in Claim 3 including control means for directing a selected portion of the gas to be tested to occupy the environs of the outer surface of said outer electrode.
10. The device described in Claim 4 including control means for directing a selected portion of the gas to be tested to occupy the environs of the outer surface of said outer electrode.
11, The device described in Claim 5 including control means for directing a selected portion of the gas to be tested to occupy the environs of the outer surface of said outer electrode.
12. The device described in Claim 6 including control means for directing a selected portion of the gas to be tested to occupy the environs of the outer surface of said outer electrode.
13. An oxygen sensor comprising a main body member which has an interior chamber and is made from material which is an oxygen ion conducting solid electrolyte when within a specified temperature range, at least two electrodes that are porous to oxygen molecules, at least one of which is an inner electrode positioned on a wall of said interior chamber and at least one other of which is an outer electrode positioned on the outside surface of said main body member substantially opposite said inside electrode, electrical conductor means by which said electrodes are rendered electrically accessible at the outside of said main body, at least one opening into said interior chamber from the outside of said main body via which the absolute pressure of gas in the environs of said outer electrode is transmitted to gas in the environs of said inner electrode, isolation means for isolating the environs of said inner electrode from infiltration by gas being tested via said openings, and supply means including an orifice for supplying reference gas to the environs of said inner electrode at a pressure to cause it to flow at its critical flow rate through said orifice.
14. The device described in Claim 13 including at least one from among the group consisting of calibration means for periodically introducing reference gas to the region of said outside electrode, heating means for heating said main body member to such specified temperature range, monitoring means that is adapted for monitoring the temperature of said main body and is also adapted for being monitored by regulating means to maintain the temperature of said main body at said specified temperature range, impeller means adapted to cause test gas to flow past the exterior of said main body, and control means for directing a selected portion of the gas to be tested to occupy the environs of the outer surface of said outer electrode.
15. A method of detecting the proportion of oxygen as a constituent part of a mass of gas using an oxygen sensor comprising a main body member which has an interior chamber and is made from material which is an oxygen ion conducting solid electrolyte when within a specified temperature range; at least two electrodes that are porous to oxygen molecules, at least one of which is an inner electrode positioned on a wall of said interior chamber and at least one other of which is an outer electrode positioned on the outside surface of said main body member substantially opposite said inside electrode, electrical conductor means by which said electrodes are rendered electrically accessible at the outside of said main body; at least one opening into said interior chamber from the outside of said main body via which the absolute pressure of gas in the environs of said outer electrode is transmitted to gas in the environs of said inner electrode; isolation means for isolating the environs of said inner electrode from infiltration by gas being tested via said openings; and supply means including an orifice for supplying reference gas to the environs of said inner electrode at a pressure to cause it to flow at its critical flow rate through said orifice; comprising the steps of establishing the temperature of said main body to within said specified temperature ranger causing the environs of said outside electrode to be occupied by gas to be tested, supplying reference gas to the environs of said inner electrode at a pressure to cause it to flow at its critical flow rate through said orifice and detecting the electrical output of said electrodes and translating said output into a value for the oxygen composition of said gas being tested.
16. The method described in Claim 15 wherein said step of establishing said temperature of said main body includes utilizing supplementary heating means.
17. The method described in Claim 15 including the added steps of periodically introducing reference gas into the environs of said outside electrode while monitoring the electrical output of said electrodes to determine the "C"
factor of said cell, and calibrating the electrical output of said sensor for said "C" factor.
factor of said cell, and calibrating the electrical output of said sensor for said "C" factor.
18. The method described in Claim 16 including the added steps of periodically introducing reference gas into the environs of said outside electrode while monitoring the electrical output of said electrodes to determine the "C"
factor of said cell, and calibrating the electrical output of said sensor for said "C" factor.
factor of said cell, and calibrating the electrical output of said sensor for said "C" factor.
19. The method described in Claim 17 including the added steps of utilizing said electrical output of said electrodes as a drive signal to adjust automatically the oxygen constituent of said gas being monitored.
20. The method described in Claim 18 including the added steps of utilizing said electrical output of said electrodes as a drive signal to adjust automatically the oxygen constituent of said gas being monitored.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/892,211 | 1992-06-02 | ||
| US07/892,211 US5296112A (en) | 1992-06-02 | 1992-06-02 | Oxygen monitoring devices |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2097456A1 true CA2097456A1 (en) | 1993-12-03 |
Family
ID=25399557
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002097456A Abandoned CA2097456A1 (en) | 1992-06-02 | 1993-06-01 | Oxygen monitoring devices |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US5296112A (en) |
| EP (1) | EP0573006A3 (en) |
| CA (1) | CA2097456A1 (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5585547A (en) * | 1994-01-06 | 1996-12-17 | Ssangyong Cement Industrial Co., Ltd. | Oxygen sensor probe for boiler |
| FR2735866B1 (en) * | 1995-06-22 | 1997-08-29 | Crevoiserat Jean Michel | PROBE FOR MEASURING THE PARTIAL PRESSURE OF OXYGEN IN DOMESTIC AND INDUSTRIAL CHIMNEYS |
| DE19609323B4 (en) * | 1996-03-09 | 2008-11-20 | Robert Bosch Gmbh | sensor element |
| DE19631501C2 (en) * | 1996-08-03 | 1998-09-10 | Bosch Gmbh Robert | Gas-permeable connection line for a sensor |
| JP2000065789A (en) * | 1998-08-25 | 2000-03-03 | Ngk Insulators Ltd | Carbon monoxide sensor, its production and its use |
| US6341519B1 (en) | 1998-11-06 | 2002-01-29 | Reuter-Stokes, Inc. | Gas-sensing probe for use in a combustor |
| US6277268B1 (en) * | 1998-11-06 | 2001-08-21 | Reuter-Stokes, Inc. | System and method for monitoring gaseous combustibles in fossil combustors |
| US6293093B1 (en) * | 2000-08-02 | 2001-09-25 | Ford Global Technologies, Inc | Method and system for directly monitoring the efficiency of a conditioning catalyst having negligible oxygen storage capacity |
| US7128818B2 (en) * | 2002-01-09 | 2006-10-31 | General Electric Company | Method and apparatus for monitoring gases in a combustion system |
| US20040149579A1 (en) * | 2002-12-19 | 2004-08-05 | General Electric Company | System for monitoring combustible gases |
| US7739924B2 (en) * | 2008-02-27 | 2010-06-22 | Caterpillar Inc. | Sensor assembly having a flow head |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4284487A (en) * | 1978-10-13 | 1981-08-18 | Milton Roy Company | Oxygen analyzer probe |
| DE2945698C2 (en) * | 1979-11-13 | 1989-09-21 | Brown, Boveri & Cie Ag, 6800 Mannheim | Electrochemical measuring device for the determination of the oxygen content in gases |
| JPS57192848A (en) * | 1981-05-25 | 1982-11-27 | Ngk Insulators Ltd | Regulator for oxygen concentration |
| AU561654B2 (en) * | 1981-08-21 | 1987-05-14 | Rosemount Analytical Inc | Solid electrolyte gas sensor |
| US4875990A (en) * | 1986-08-28 | 1989-10-24 | Ngk Insulators, Ltd. | Oxygen concentration measuring device |
| CA1273603A (en) * | 1986-10-10 | 1990-09-04 | Charles R. Masson | Solid electrolyte for oxygen sensor |
-
1992
- 1992-06-02 US US07/892,211 patent/US5296112A/en not_active Expired - Fee Related
-
1993
- 1993-06-01 CA CA002097456A patent/CA2097456A1/en not_active Abandoned
- 1993-06-02 EP EP93108864A patent/EP0573006A3/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| US5296112A (en) | 1994-03-22 |
| EP0573006A2 (en) | 1993-12-08 |
| EP0573006A3 (en) | 1995-09-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |