Note: Descriptions are shown in the official language in which they were submitted.
` 1106~46
) Background of the Invention ¦ .
Field o~ the Invention
This invention relates to a probe ~or an electrochemical oxygen
measurement pickup having a solid3 oxygen ion-conducting
electrolyte with electrodes, and contact points at the end, ..
which are connected to the electrodes in an electron-conducting
manner.
Description of the Prior Art
Probes (sensor elements) for oxygen measurement pickups often
consist of an ion-conducting solid-electrolyte tube which is
closed on one end and the inner and outer surfaces of which
.are provided with ~lectrodesO These electrodes extend up to .
the open end of khe solid-electrolyte tube and form there the
electrical contact points, from which the electric probe voltage
is taken and is conducted ~o exter~al terminals. If su~h .
mea~uring pick~lps are used~ there is danger of fals~ measure-
men~s~ as the solid-elec~rolyte tube which usually protrude~ !
;~ ~ransver~ely into ~he hot gas stream has a temperature gradient
:; ~rom it~ tip to its end and there~ore has dlfferent ion '~.
conductivity. As a ~esult; a voltage which decreases from the
: prob~ tip toward the end is delivered and the resultant electric
v41~age whlch i~ taken off at the contact points is thereby
inaccurate and~cannot be related unequivocally to a definite
ox~gen content o~ the gas ko be measuredO
in addltlon3 the electrode exposed to the gas to be measured
must be catalytically effective and must bring the gas compo-
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nents into chemical equilibrium, ~hen the chemical equilibrium
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¦ is adjusted differently alDng the probe in accordance with the
., temperature gradient. Fr~m this, dif~erent gas concentrations
result~and therefore~ different electric electrode voltages (mixed
potentials), which additionally falsify the electrical signal of
the probe.
Summary o~ the Invention
An object of the invention is to provide a probe ~or oxygen measure-
ment pickups of the type mentioned which will deliver a more
accurate voltage measurement, i.e. a measurement substantially
free of the errors resulting ~rom temperature gradient and vari-
ances in chemical equilibrium.
With the ~oregoing and other obJects in ~iew~ there is provided
in accordance with the invention a probe ~or an electrochemical
oxygen measurement pickup having an oxygen ion-conducting solid
electrolyte with electrodes, and electrical contact points con-
nected to the electrodes, the combination therewith of a tubular-
shaped probe having an electrochemically active region o~ the
probe which has the electrodes and the oxygen ion-conducting solid
electrolyte for passage of oxygen ions through the solid electro-
lyte, and an electrochemically passive region of the probe which
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carries the contact points as well as their electrical connectionsto the electrodes, with the passive region having a solid electro-
lyte on which the contact points and electrical connections are
arranged, and with the contact points spaced from each other as
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1~ 446
well as the electrical connections consisting of conductor runs to
the electrodes spaced from each other, with the conductor runs
arranged diametrically opposite to each other on the tubular probe
to require ions moving ~rom one contact point to another and one
connection to another to t-ravel a long path thereby reducing
an interfering current.
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11~64~6
Brie~ Description of ~he ~rawings
~he invention, howeverJ together with additional ob~ects .
and advantages thereo~ will be best understood from the
follo~ng description when read in connection wlth the accom- i
panying drawings, in which:
- ~IG. 1 shows an axial longitudinal cross section through a
tubular probe, closed on one side, in accordance with the
invention; and .
~IGc 2 i~ a cross section through the tubular probe along
llne I~-~X o~ ~XG~ l; and
~X~ 3 is a cross section through the tubular probe along
line III-XII o~ ~G. l; and
FIG. 4 i~ a variant of the tubular probe shown in ~XG. l; and
~G. 5 ls a~ a~lal lo~gitudinal sectlon o~ another variant of
~he tubular probe ~hown ~n ~IG. l; and
~XG~ 6 is the ~ubular probe of ~IG. 5 with another des1gn o~
~he lnsula~ing body.
. ~ led_Descrlptlon Or the Invention
~o r~he probe has ~ least one electrochemlcally active region
prov.ld~d wlkh ~he electrodes a~d an electrochemically passive~
or at lPast largely passive reg~on which is provided with the
contact points as well as wi~h their electrical co~nections
to the electrodes. The active regio~ can therefore be chosen
independently of the total length of the probe ~nd be adapted
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11064A.6
specially for the intended application. Here, di~ferent
temperatures of the passive part are without, or at least
wlthout appreciable effect on the voltage delivered by the
probe.
A m~nimum o~ structural means is required if both regions of
the probe have a solid electrolyte, on which the contact
points as well as the connections are arranged with a large
mutual distance for forming the passive region. Although
in this embodiment, the contact points as well as the connec-
~ion~ are arranged on the solid electrolyte, their ef~ect as
active electrodes is very small, as the path which i~ very
long as compared to ~he active reglon, for the ions in the
~olld electro~yte of the passive region results in a high
lnternal resistance and thus in a small delivered current,
whlch hardly causes inter~erence. The active region e~fects
the voltage delivered by the probe. The passive reglon is
wl~houk appreciable e~rect on the voltage delivered by the
probeO, I
In ~rde~ to reduce the influence of the passlve part further,
~n insulatlng layer which does not conduct ion~ or electrons
i~ in~erted bet~een ~he two regions. This elimlnates part- .
lcularly the effects of the junctions rrom the electrodes to
~he connec~lons. The in~luence of the pass1ve part on the
measureme~t is p~actically completely eliminated by forming
- the passi~e region with an insulatlng part~ preferably of
eeramicD which does not conduct electrons or ions.
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The connections consist advantageously of conductor runsO I~
the probe is of tubular design, it is advisable to arrange the
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i conductor runs approximately diametrically. For a good
compromise between the requirement o~ an active region as
large as possible and the requirement of a measurement s~b-
~tantlally una~ected by in~luence of temperature gradient
and chemical reaction, it is advisable to have the passive
region o~ the probe disposed in that part of the probe
which is to extend in a probe housing.
~n the drawings, identical parts in the individual f~gures have
the same reference symbols.
~e~erring to FIG~ 1, the probe comprises a solid-electrolyte
~ube 10 with a closed le~t and an open right end. Zirconium
diox~de serves as the oxygen ion-conducting solid electrolyte.
~n ~he actLve region 11 of the probe which is provided ror
del~vering the measurement signal a~d which extends from khe
t~p Or the solid-electrolyte tube 10 in the axial dlrection~
the entire outer ~urface ls pre~erably provlded with an outer
electrode 13 and ~he entire inside surface with an inner
e~ectrode 14. In so~e cases it ma~ also be su~flcient to make
one or both electrodes as mutually opposite stripsO The act~ve
reglon 11 i~ deslgned as to its electrode areas and the e^ectro
l~te thickness so that at the operating temperature a suf~icient-
ly ~.OW inte~nal electric resistance is obtalned5 ~or instance,
be~ een :lO and 10~000 K-Q3 and preferably 10 to 100 K~. The
passive region 1~ formed with the same solid electrolyte
carrles an outer connection 15 connected to the outer elec~rode
13 and an lnner connect~on 16 connected to the inner electrode
14, the ends of which form the c~ntact points 17 and 18.
The connections are electron-conducting and, as can be seen
clearly ~rom FIG. 3, co~sist of conductor runs~ the width
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llQ6~A~fi
which is between l and lO mm, depending on the probe
diame~er, but preferably between 2 and 4 mm. It is important
here that the path for the ions from the one to the othe~
connectlon through the solid-electrolyte tube i5 very long, `
as thereby ~he ln~ernal electric resis~ance is increased
considerably and the passive region 12 cannot therefore deliver
an appreciably inte~fering current and thus, for all practlcal
purposes, cannot falsify the measurement voltage. ~he connec-
tlons 15 and 16 may be made of any electron-conducti~g,
corrosiorl-resistant materlal but preferably, they conslst of
extensions of the respective electrodes. In order to ensure
good contact with the potential leads which go on from there,
the conductors can be widened at the contact polnts.
; The construction of the probe according to FIG. 4 is slmilar
to that of the probe of FIG. 1. The difference between the
probe o~ FIG. 1 and the probe Or FIG. 4 consists merely in
the ~olid electrolyte Or the active region ll being separated
~rom the solid electrolyte of the passive region 12 by an
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1nterposed clrcular insulatlng layer 19 (FIG. 4). This
o~ measure creates a clean separation Or the two regions.
; The 1nsula~ing layer consists preferably o~ gas~tightJ sintered
glass ceramic which does not conduct ~ons or electrons, such
as ceramic Or the ~ollowlng composition: SiO2, 35 to 50%;
MgOg 50 to 30~, and A1203, 15 to 20~. The insulating layer
.s conneGted b~ a sintering or fusing process to the tw~ parts
o~ ;the tube~ which, incidentally, may also have dirferent
outside diameters, as shown in FIG. 6.
e probe shown in FIG. 5 corresponds generally to the probe
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~ IG. l. The probe shown in FIG. 5 corresponds generallyto the probe of ~G. 1. The difference between the probes is
tha~ the passive region 12 is bullt up on an insulating part
of kubular shape 20 (FIGo 5) which ls fastened to ~he solid-
electrolyte tube ~0, and the outside and inside d~ameter o~
the insulating part 20 corresponds approximately to the diameters
o~ the solid-electrolyte tube lO. As this insulating part 20 ..
consists of a material that does not conduct ions or electrons,
there is practically no danger that the measurement result
is influenced in any way by the passive region. This would
not he the case i~ the connections 15 and 1~ did not . .
consist of narrow c~nductor runs but were simply ~ormed by an
ex~enslon o~ the electrodes 13 and 14 covering the entlre lnside
and outside sur~aces. The insulating part 20 preferably
cons~sts of magnesium silicate Mg2(SiO4), magnesium-aluminum
spinel MgO-A1203 or the sintered-glass ceramic mentioned above.
The elect;x~olyte tu~e is ~astened to the lnsulating part either
b~ dlrec~l~ sintering together the two par~s or by inserting
a co.nnec~ng layer of glass solder or sintered~glas~ ceram~c.
20 The ba~ic design of the probe shown in FIG. 6 corresponds to
thak o~ ~IG. 5~ However9 the insulat~ng part 20.o~ FIGo 6 ls
made ln the shape o~ a circular flange, the outside diameter
of which i~ larger than the corresponding diameker o~ ~he
so~.id-electrolyte tube lO. In order to center this tube with
~espect to the f`lange, it is inserted into a step-l~ke expansion
of ~he flange opening and fastened there. me free end o~ the
flange has likewise an lnner s~ep ~or forming the shoulder ~l,
on which the connec~ions 15 and 16 end and form the contact
points 17 and 18. To this end, the outer connection 15 is
30. brou~sht on the ~lange on the outside up to the shoulder 21,
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-~ as can be seen in ~IG. 6, and the inner connection 15 runs on
the inner wall of the flange up to the shoulder 21. However,
i~ would also be possible to also arrange the connection 15 on
the inside wall Or the flange approximately diametrically oppo-
- s~te to the connectlon 16 and to let it end on the shoulder 21.
To this end it is necessary to bring the connection 15 at the
~oint o~ the tube and the flange from the outside to the inside,
which can be done easily part~cularly if a connecting layer is
in~erposed at this pointO In order to avold shor~ clrcults,
the ~nner electrode 14 should not quite extend to the end Or the
solid-electrolgte tube 10 at this feedthrough poi~t. The inside
diameters of the solid-electrolyte tube and the flange are
app~o~imately equal and the ratio o~ the outside diameters ls
aboul; 1 0 1~5 to 1: 2. The choice o~ the material ~or the
~lange may be the same as those made in connection wi~h FIG. 5.
For determining the size and length relations of the active to
the passlve regionJ the rule generally applies that the active
reglon is ma~e only large eno~gh so that a suf~iciently low
lnternal resistance of the probe is provided. The remaining
part o~ the probe is'made passive. me slze will vary dependlng
on ~he glven measuremen~ problem. As a minimumj however, at least
the region o~ the probe which is intended to be inserted in a
probe houslng, should be designed as passive.
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