U.S. patent application number 15/989499 was filed with the patent office on 2018-09-27 for electrochemical sensor.
The applicant listed for this patent is Endress+Hauser Conducta GmbH+Co. KG. Invention is credited to Christian Fanselow, Stefan Paul.
Application Number | 20180275092 15/989499 |
Document ID | / |
Family ID | 52478383 |
Filed Date | 2018-09-27 |
United States Patent
Application |
20180275092 |
Kind Code |
A1 |
Fanselow; Christian ; et
al. |
September 27, 2018 |
ELECTROCHEMICAL SENSOR
Abstract
An electrochemical sensor comprising a probe immersible in a
measured medium and having at least two electrodes of a first
electrically conductive material and at least one probe body of a
second, electrically non-conductive material. The electrodes are at
least partially embedded in the probe body and insulated from one
another by the probe body, wherein the at least two electrodes are
embodied of at least one conductive material and the probe body of
at least one electrically insulating ceramic, wherein the
electrodes are embodied of thin, measuring active layers of a
conductive material and sit in an end face of the probe body of a
ceramic material, and wherein the electrodes are electrically
contacted via connection elements extending through the probe
body.
Inventors: |
Fanselow; Christian;
(Geringswalde, DE) ; Paul; Stefan; (Dobeln,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Endress+Hauser Conducta GmbH+Co. KG |
Gerlingen |
|
DE |
|
|
Family ID: |
52478383 |
Appl. No.: |
15/989499 |
Filed: |
May 25, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14479595 |
Sep 8, 2014 |
|
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|
15989499 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 2457/00 20130101;
G01N 27/07 20130101; B32B 38/0036 20130101; G01N 27/403 20130101;
G01N 27/4062 20130101 |
International
Class: |
G01N 27/406 20060101
G01N027/406; G01N 27/403 20060101 G01N027/403; G01N 27/07 20060101
G01N027/07; B32B 38/00 20060101 B32B038/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2013 |
DE |
10 2013 110 042.2 |
Claims
1. A probe for an electrochemical sensor, comprising: a probe body
embodied of an electrically insulating ceramic, the probe body
having a cross-sectional area and a length; at least two electrodes
composed of an electrically conductive material, the at least two
electrodes embedded in the probe body and insulated from each other
by the probe body, wherein each electrode is embedded in a
corresponding cavity in an end face of the probe body such that an
outer surface of each electrode is flush with the end face of the
probe body and each electrode fills the corresponding cavity; and
at least two connection elements, each connection element
electrically connected to a corresponding electrode of the at least
two electrodes and extending through the length of the probe body
from the corresponding electrode, wherein the probe is produced by
producing a green probe body of the electrically insulating
ceramic, pressing each electrode connected to its corresponding
connection element into its corresponding cavity in the green probe
body, and sintering together the green probe body, the at least two
electrodes, and the at least two connection elements, wherein the
sintering produces a material bonding between the electrodes and
the probe body making a gap-free material transition between each
electrode and the probe body.
2. The probe of claim 1, wherein a thermal coefficient of expansion
of the electrically insulating ceramic and a thermal coefficient of
expansion of the electrically conductive metal differ by not more
than 2.times.10.sup.-6 K.sup.-1.
3. The probe of claim 1, wherein the electrically insulating
ceramic is one of a zirconium oxide (ZrO.sub.2) ceramic, an
aluminum oxide (Al.sub.2O.sub.3) ceramic, a chromium oxide
(Cr.sub.2O.sub.3) ceramic, a titanium dioxide (TiO.sub.2) ceramic,
and a tialite (Al.sub.2TiO.sub.5) ceramic.
4. The probe of claim 1, wherein the electrically conductive
material is one of electrically conductive ceramic, electrically
conductive enamel, platinum, titanium, and stainless steel.
5. The probe of claim 1, wherein the electrically conductive
material is platinum and the electrically insulating ceramic is
zirconium oxide ceramic stabilized with magnesium.
6. The probe of claim 1, further comprising: a temperature sensor
disposed within the probe body and attached to the probe body using
a thermally conductive adhesive.
7. The probe of claim 1, wherein each electrode has thickness
defined in the direction of the length of the probe body and the
thickness of each electrode is from 10 micrometers (.mu.m) to 3
millimeters (mm).
8. An electrochemical sensor, comprising: a probe, comprising: a
probe body embodied of an electrically insulating ceramic, the
probe body having a cross-sectional area and a length; at least two
electrodes composed of an electrically conductive material, the at
least two electrodes embedded in the probe body and insulated from
each other by the probe body, wherein each electrode is embedded in
a corresponding cavity in an end face of the probe body such that
an outer surface of each electrode is flush with the end face of
the probe body and each electrode fills the corresponding cavity;
and at least two connection elements, each connection element
electrically connected to a corresponding electrode of the at least
two electrodes and extending through the length of the probe body
from the corresponding electrode, wherein the probe is produced by
producing a green probe body of the electrically insulating
ceramic, pressing each electrode connected to its corresponding
connection element into its corresponding cavity in the green probe
body, and sintering together the green probe body, the at least two
electrodes, and the at least two connection elements, wherein the
sintering produces a material bonding between the electrodes and
the probe body making a gap-free material transition between each
electrode and the probe body; and a measuring electronics connected
to the at least two connection elements and embodied to determine
an electrochemical property of a liquid medium.
9. An electrochemical sensor comprising: a probe immersible in a
measured medium, the probe comprising: a probe body composed of an
electrically insulating ceramic, the probe body having a
longitudinal axis, at least two electrodes and a corresponding
connection element for each electrode, each electrode electrically
connected to its corresponding connection element and each
electrode embodied as a layer of electrically conductive material
having a thickness defined in the direction of the longitudinal
axis, the thickness being in a range from 10 micrometers to 3
millimeters, wherein the at least two electrodes and the
corresponding connection elements are at least partially embedded
in the probe body and insulated from one another by the probe body,
and the at least two electrodes are disposed in an end face of the
probe body such that an end face of each electrode is flush with
the end face of the probe body, wherein each electrode is
electrically connected to its corresponding connection element and
each connection element extends from its corresponding electrode
through the probe body, and wherein the probe body and the
electrodes are formed such that intermolecular interactions between
the electrically conductive metal and the electrically insulating
ceramic provide a material bonding between the electrodes and the
probe body and a gap-free material transition between the
electrodes and the probe body.
10. The electrochemical sensor of claim 9, wherein the electrically
insulating ceramic is one of a zirconium oxide (ZrO.sub.2) ceramic,
an aluminum oxide (Al.sub.2O.sub.3) ceramic, a chromium oxide
(Cr.sub.2O.sub.3) ceramic, a titanium dioxide (TiO.sub.2) ceramic,
and a tialite (Al.sub.2TiO.sub.5) ceramic.
11. The electrochemical sensor of claim 9, wherein the electrically
conductive material is one of electrically conductive ceramic,
electrically conductive enamel, platinum, titanium, and stainless
steel.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is related to and claims the
priority benefit of U.S. Non-Provisional Patent Application Ser.
No. 14/479,595, filed on Sep. 8, 2014, the entire contents of which
are incorporated herein by reference.
TECHNICAL FIELD
[0002] The invention relates to an electrochemical sensor
comprising a probe immersible in a measured medium and having at
least two electrically conductive electrodes embedded in a ceramic
probe body.
BACKGROUND
[0003] Electrochemical sensors are used in many fields, such as
e.g. in clinical analysis or laboratory analysis, environmental
protection, and process measurements technology. Electrochemical
sensors work either according to a conductive, a potentiometric or
an amperometric, measuring principle, such that the measured
variable is ascertained in the medium via the electrodes.
[0004] Known from the state of the art, e.g. from EP 990 894 B1,
are conductive conductivity sensors comprising at least two
electrodes, which for measuring are immersed in the measured
medium. For determining the electrolytic conductivity of the
measured medium, the resistance or conductance of the electrode
measuring path is determined in the measured medium. In the case of
known cell constant, the conductivity of the measured medium can be
ascertained therefrom.
[0005] Shown in German Patent DE 10 2006 024 905 A1 is an electrode
arrangement of a conductive conductivity sensor, in the case of
which an inner and an outer electrode are isolated and insulated
from one another by a shaped seal and a seal support body. The
shaped seal serves to prevent penetration of measured medium into
an annular gap between the electrodes.
[0006] Such an electrode arrangement with additional seals is
constructively relatively complex and disturbance susceptible, so
that medium can penetrate into the gap between electrode and seal
support body. The structural complexity is especially great in the
case of conductivity sensors for application in foods technology or
in the pharmaceutical industry. The sensors of process automation
technology, which are applied in the foods and/or pharmacy
industries, must fulfill very high requirements as regards hygiene.
For example, the probes of such sensors, to the extent that they
come in contact with the measured medium, must not have difficultly
accessible gaps, in order that a cleaning and/or sterilizing of the
total probe surface contacting the measured medium is possible.
Conventional seals or a shaped seal can according to DE 10 2006 024
905 A1, indeed, basically fulfill this purpose. They lead, however,
to a complex construction with corresponding assembly complexity.
Furthermore, with age and wear, these seals can fail and then
medium can get into the gap between electrodes and seal support
body.
[0007] In general, the probe bodies of the probe of an
electrochemical sensor are produced from a synthetic material by
means of various manufacturing methods, such as e.g. injection
molding, impression molding, and hot stamping, into which the metal
electrodes are installed. A great disadvantage of combining
synthetic material, such as a plastic, and the metal electrodes are
their different coefficients of thermal expansion. In the case of
high loadings due to high surrounding pressures, respectively
temperature fluctuations, gaps form between the different materials
of the probe body and the electrodes. This can lead to lack of
sealing of the sensor element, whereby medium can penetrate into
the sensor interior. Furthermore, germs can get into these gaps,
whereby the sensor cannot be qualified for hygienic uses. Another
undesired characteristic of synthetic materials is their poor long
term durability, since they age. Aging as a result of aggressive
media or repeated strong temperature changes increases the porosity
of the applied synthetic materials. In this way, it is possible
that liquid medium can diffuse through the synthetic material into
the sensor interior.
[0008] Shown in Published International Application, WO 2010/072483
A1 is a conductive conductivity sensor having a probe immersible in
a measured medium. The probe comprises at least two electrodes of a
first electrically conductive material and at least one probe body
of a second electrically non-conductive material. The electrodes
are embedded in the probe body and insulated from one another by
the probe body. Thus, the electrodes and the probe body are
embodied as a sintered, composite piece. To accomplish this, the
probe body and/or the electrodes are produced by means of a
multicomponent injection molding process.
SUMMARY OF THE INVENTION
[0009] It is, consequently, an object of the invention to provide
an electrochemical sensor having a probe immersible in a measured
medium, which overcomes the disadvantages of the state of the art
as regards sealing between the electrodes and the probe body,
whereby the availability of the sensor is greatly increased, while
manufacturing costs are reduced.
[0010] This object is achieved by an electrochemical sensor
comprising a probe immersible in a measured medium and having at
least two electrodes of a first electrically conductive material
and at least one probe body of a second, electrically
non-conductive material, wherein the electrodes are at least
partially embedded in the probe body and insulated from one another
by the probe body, wherein the at least two electrodes are embodied
of at least one conductive material and the probe body of at least
one electrically insulating ceramic, wherein the electrodes are
embodied of thin, measuring active layers of a conductive material
and sit in an end face of the probe body of a ceramic material, and
the electrodes are electrically contacted via connection elements
extending through the probe body.
[0011] The embodiment of the electrodes as thin material layers
with connection elements extending through the probe body and their
embedding in a ceramic probe body achieves a gap-free material
transition and therewith also a gap-free sealing between the
electrodes at least partially embedded in the probe body and the
probe body.
[0012] In an advantageous embodiment, the measuring active layer of
the conductive material of the electrodes has a coating thickness d
of, for example, 10 .mu.m-3 mm. This measuring active layer of the
electrodes sits gap-freely in the ceramic material of the probe
body, so that the end faces of the electrodes and the probe body
form a plane. The coating thickness of the electrodes is, in such
case, preferably in the range, 10 .mu.m to 200 .mu.m, whereby
through minimal use of noble metals, such as e.g. platinum,
titanium and stainless steel, also costs can be saved. These thin
layers of concentrically arranged ring-electrodes are electrically
contacted via corresponding connection elements.
[0013] In an additional embodiment, the conductive material
comprises an electrically conductive ceramic, electrically
conductive enamel or a metal, especially platinum, titanium or
stainless steel.
[0014] In an advantageous embodiment, the ceramic material
comprises at least a zirconium oxide (ZrO.sub.2) ceramic, an
aluminum oxide (Al.sub.2O.sub.3) ceramic, a chromium oxide
(Cr.sub.2O.sub.3) ceramic, a titanium dioxide (TiO.sub.2) ceramic,
and/or a tialite (Al.sub.2TiO.sub.5) ceramic.
[0015] In an especially suitable further development, the
electrodes comprise platinum and the probe body comprises a
zirconium oxide ceramic stabilized by means of magnesium. The
platinum of the electrodes and the zirconium oxide ceramic
partially stabilized or stabilized with magnesium have
approximately the same thermal coefficients of expansion, for
example, zirconium oxide stabilized with magnesium ZrO.sub.2MgO at
9.3.times.10.sup.-6 K.sup.-1 and platinum Pt at 8.8.times.10.sup.-6
K.sup.-1. For equalizing the thermal coefficients of expansion of
the ceramic material of the probe body and the coefficients of
expansion of the metal material of the electrodes, stabilizing
materials, such as, for example, magnesium, iridium and/or aluminum
are added into the ceramic material of the probe body. These
additions of stabilizing materials stabilize or at least partially
stabilize the ceramic material, so that the thermal coefficients of
expansion of the probe body and the electrodes are approximately
equal and also other properties of the material of the probe body,
such as, for example, greater chemical durability, better fracture
behavior, etc., result. For this reason, the solid composite of
electrodes and probe body remains stable over a large temperature
range of, for instance, -30.degree. C. up to 300.degree. C. This
solid composite of the metal material of the electrodes and the
ceramic material of the probe body results at least partially from
intermolecular interactions or chemical bonds between regions of
the metal material of the electrodes and regions of the ceramic
material of the probe body. In this way, there results a high
quality, material bonded connection between the electrodes and the
probe body, which provides a gap-free seal. Because of the almost
equal coefficients of expansion of the two materials, these bonding
forces are also not overcome by otherwise arising mechanical
stresses upon temperature changes, so that gap formation between
the electrodes and the probe body is prevented.
[0016] In an additional advantageous embodiment, the probe body is
connected with a process connection. By connecting the probe body
to the process connection, an option is provided for applying the
probe in process measurements technology directly and sealingly on
the process container.
[0017] In an alternative embodiment, the process connection is
embodied as one-piece with the probe body of the same electrically
insulating ceramic. Ideally, the process connection is a component
of the basic body of the probe, i.e. embodied as one-piece with the
probe body, respectively embodied as a single molded part. This has
the advantage that also the process connection is gap-free, due to
the one-piece embodiment, so that the total conductivity sensor has
no gaps. In a further development, for improving mechanical
stability, respectively for securement of the sensor, metal parts
or parts of synthetic material can be provided on the side of the
process connection facing away from the process.
[0018] In a special further development, the process connection is
connected at a joint mechanically and sealingly with the probe body
by means of a joining means. Applied as joining means is an
adhesive, which connects the metal process connection with the
ceramic probe body and seals the joint, respectively the joining
gap, gap-freely.
[0019] In an additional embodiment, the electrochemical sensor is
embodied as a conductive conductivity sensor. Conductive
conductivity sensors are applied in varied applications for
measuring conductivity of a medium. The most known conductive
conductivity sensors are the so-called two, or four, electrode
sensors. Two electrode sensors have two electrodes in measurement
operation immersed in the medium and supplied with an alternating
voltage. A measuring electronics connected to the two electrodes
measures an electrical impedance of the conductivity measurement
cell, from which then, based on a cell constant determined earlier
from the geometry and character of the measuring cell, a specific
resistance, respectively a specific conductance, of the medium
located in the measuring cell is ascertained. Four electrode
sensors have four electrodes immersed in the medium during
measurement operation, of which two are operated as so called
electrical current electrodes and two as so called voltage
electrodes. Applied between the two electrical current electrodes
in measurement operation is an alternating voltage, so that an
alternating electrical current flows through the medium. This
electrical current creates between the voltage electrodes a
potential difference, which is determined by a preferably
currentless measurement. Also here, a measuring electronics
connected to the electrical current, and voltage, electrodes
determines from the introduced alternating electrical current and
the measured potential difference the impedance of the conductivity
measurement cell, from which then, based on a cell constant
determined earlier from the geometry and character of the measuring
cell, a specific resistance, respectively a specific conductance,
of the medium located in the measuring cell is determined.
[0020] The object is achieved, furthermore, by a method for
manufacturing a conductive conductivity sensor in one of the above
described embodiments, comprising steps as follows:
[0021] producing in a first step a green body of the probe body
from the electrically insulating ceramic,
[0022] in a second step, pressing the electrodes with their
connection elements into the green body or introducing the
electrodes with their connection elements into corresponding
cavities in the green body,
[0023] sintering in a third step the green body with the
introduced, respectively pressed in, electrodes and connection
elements.
[0024] For manufacturing the ceramic green body, all known methods
can be used. Examples include:
[0025] ceramic slip casting
[0026] injection molding or temperature-inverse injection
molding
[0027] sheet casting
[0028] extrusion
[0029] assembly of plates
[0030] chip removing methods, e.g. in a lathe or milling
machine
[0031] pressing (uniaxial pressing, cold isostatic pressing, hot
isostatic pressing)
[0032] With this method, it is possible to produce the desired
solid composite of the electrodes of metal and the ceramic probe
body, at least in a portion of a material transition, especially by
intermolecular interactions or chemical bonds, such as earlier
described.
[0033] In a further embodiment of this method, the process
connection is mechanically stably and sealingly connected with the
probe body at a joint by means of a joining means, especially by
means of an adhesive connection, and the region of the joint after
the joining together and/or the end face of the probe body with the
therein gap-freely embedded electrodes are/is ground or machined.
Thus, the probe end face 7 and the joint 8 of the adhesive
connection between the probe body 3 and the process connection 6
are ground, respectively machined, so that a planar, gap-free
surface is obtained for the end face 7 and the joint 8.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] The invention will now be explained in greater detail based
on the examples of embodiments shown in the drawing, the figures of
which show as follows:
[0035] FIG. 1 is a probe of an electrochemical sensor, especially a
conductivity sensor, according to a first embodiment of the
invention;
[0036] FIG. 2 is a probe of an electrochemical sensor, especially a
conductivity sensor, according to a second embodiment of the
invention; and
[0037] FIG. 3 is a probe of an electrochemical sensor, especially a
conductivity sensor, according to the second embodiment of the
invention of FIG. 2 with a diameter expansion of the process
connection at the joint.
DETAILED DISCUSSION IN CONJUNTION WITH THE DRAWINGS
[0038] FIG. 1 shows a probe 1 of the invention for an
electrochemical sensor, especially a conductivity sensor, with a
probe body 3 of an electrically non-conductive, ceramic material
and, according to the invention, therein embedded electrodes 5 of a
thin, electrically conductive material. The coating thickness of
the material of the electrodes 5 of the invention, which are
provided in FIG. 1 as concentric rings, respectively sleeves,
sintered into the probe body 3, lies in a range of 10 micrometer to
3 millimeter, whereby material for the manufacture of the probe 1
and, thus, costs, are saved. The end faces of the electrodes 5 lie
freely exposed on the end face 7 of the probe body 3 and in the
case of a measuring of conductivity they are in contact with the
measured medium. FIG. 1 shows a perspective view of the probe 1 and
shows, concentrically arranged around the rotational symmetry axis
Z, the ring elements of the electrodes 5, which in the case of a
measuring of conductivity are immersed in the measured medium.
Electrodes 5 are embodied as ring elements coaxially arranged
around the shared rotational symmetry axis Z and are embedded in
the sensor body 3 insulated from one another. Probe 1 is embodied
as a measuring probe of a 4-electrode sensor. In the case of this
type of sensor, in measurement operation, an alternating voltage is
applied to the two electrodes 5 of the electrical current
electrodes and the potential difference determined on the other
two, remaining electrodes of the voltage electrodes. Using a
measurement transmitter (not explicitly shown) connected with the
electrodes 5, the impedance of the conductivity measurement cell
formed by the probe 3 immersed in the measured medium is
ascertained. Taking into consideration the cell constants, the
specific resistance, respectively the specific conductivity, of the
measured medium can be ascertained therefrom. The ascertained
measured values can either be displayed by the measurement
transmitter or output to a superordinated control system. A part
the functions of the measurement transmitter can be executed by a
measuring electronics accommodated in a separate housing outside of
the measurement transmitter. This measuring electronics can, at
least in part, be accommodated, for example, in a plug head
connected with the probe 1, which plug head is available from the
applicant under the mark, MEMOSENS.RTM..
[0039] The electrodes 5 are platinum and the probe body 3 a
zirconium oxide ceramic stabilized, respectively partially
stabilized, by means of magnesium. The platinum of the electrodes 5
and the zirconium oxide ceramic of the probe body 3 stabilized with
magnesium possess approximately the same thermal coefficients of
expansion, for example, with magnesium stabilized zirconium oxide
ZrO.sub.2MgO being at 9.3.times.10.sup.-6 K.sup.-1 (per degree
Kelvin) and platinum Pt at 8.8.times.10.sup.-6 K.sup.-1. There are,
however, other such material combinations for the electrodes 5 and
the probe body 3, whose thermal coefficients of expansion differ
only little from one another, i.e. preferably deviating from one
another by only 1.times.10-6 to 2.times.10.sup.-6 K.sup.-1. Thus,
for example, in the case of platinum as material for the electrodes
5, which has a thermal coefficient of expansion of
8.9.times.10.sup.-6 K.sup.-1, such can be combined with an aluminum
oxide ceramic with a coefficient of expansion of 6 to
8.times.10.sup.-6 K.sup.-1. In the case of titanium with a
coefficient of expansion of 10.8.times.10.sup.-6 K.sup.-1 as
electrode material, such can be used with, for example, zirconium
oxide ceramic with a coefficient of expansion of 10 to
12.times.10.sup.-6 K.sup.-1 as material for the probe body 3. A
zirconium oxide ceramic for the probe body 3 is likewise suitable
for combination with stainless steel as material for electrodes 5,
since stainless steel has a thermal coefficient of expansion of
about 13.times.10.sup.-6 K.sup.-1.
[0040] Through the situating of metal in a ceramic shape, e.g. by
sintering, the metal of the electrodes 5 is surrounded in a
shape-interlocking manner by the ceramic material of the probe body
3 and there arises also, such as earlier described, a material
bonding between the two materials. For situating the electrodes 5
in the probe body 3, the electrodes are seated in cavities provided
in the probe body 3 or slightly pressed into the green body of the
probe body 3. After insertion of the electrodes 5 into the ceramic
green body of the probe body 3, the assembly is sintered by means
of a predetermined temperature regimen.
[0041] The electrodes 5 can also be produced by deposition of the
conductive material into corresponding cavities in the probe body
3. The following methods can be used for the deposition:
[0042] vapor deposition of metals
[0043] sputtering of metals
[0044] screen printing with metal pastes
[0045] In supplementation, also the probe body 3 can be produced by
the following deposition methods from a gas phase or liquid
phase:
[0046] Chemical vapor deposition (CVD)--In such case, a plurality
of gases react with one another at a certain pressure and high
temperatures and deposit a ceramic material.
[0047] Physical vapor deposition (PVD)
[0048] Chemical vapor infiltration (CVI)
[0049] Since the coefficients of expansion of ceramics, such as
e.g. zirconium oxide and metal, preferably platinum, are almost
identical, gap formation can be minimized. Furthermore, such a
ceramic is suited due to its poor electrical conductivity as a
support material for electrical measurements between the electrodes
5. Furthermore, ceramics are very suitable support material due to
their very good chemical durability. Ceramics have the property
that they age very much slower than synthetic materials, which
leads to a very much longer service life of the sensor. The surface
roughness of the end faces 7 of the electrodes and/or of the probe
body 3, as well as the joint 8 between probe body 3 and process
connection 6, is further reduced by polishing processes after the
manufacture, so that possibly arising gaps and openings on the
outer surface of the ceramic probe body 3 are removed and, thus,
the high hygienic requirements of the probe 1 can be durably
fulfilled.
[0050] Used as electrically conductive material can also be an
electrically conductive ceramic, respectively enamel, which is
cast, injected, respectively introduced into the corresponding
cavities in the green body of the probe body 3 and after
introduction sintered together with the green body of the probe
body 3. This embodiment has the advantage that the used materials
and, thus, the coefficients of expansion are very similar.
[0051] Embedded in the probe body 3 and in the process connection 6
are the electrodes 5 of the probe 1, which are electrically
contacted via connection elements 2, respectively connection lines.
Provided for this, for example, in a region of the sensor body 3
and of the process connection 6 facing away from the process are
connection elements 2, via which the electrodes 5 can be connected
with a control or measuring electronics.
[0052] Used for measuring the current temperature of the medium can
be, furthermore, a temperature sensor 4. Temperature sensor 4 is
inserted via a cavity provided in the probe body 3 facing away from
the medium, respectively held in place with a thermally conductive
adhesive. By means of this temperature sensor 4, the current
temperature of the medium on the electrodes 5 can be ascertained
and, thus, a thermal correction of the conductivity measurement
performed.
[0053] Probe 1 shown in FIG. 2 forms the measuring probe of a
so-called 4-electrode sensor immersible in a measured medium. Two
electrodes 5, especially two electrodes 5 directly adjoining one
another, are operated as so called electrical current electrodes.
The two remaining electrodes 5 are operated as voltage electrodes.
Applied between the two electrical current electrodes in
measurement operation is an alternating voltage, in order to
introduce an alternating electrical current into the measured
medium. Measured between the voltage electrodes, especially using a
currentless measuring, is the resulting potential difference. Using
the introduced alternating electrical current and the measured
potential difference, the impedance of the conductivity measurement
cell formed through immersion of the probe 1 in a measured medium
is calculated, and from the impedance while taking into
consideration the cell constant, the specific resistance,
respectively the conductivity, of the measured medium can be
ascertained. Serving for control of the introduced alternating
current for measuring the potential difference of the voltage
electrodes and converting the measured values into a resistance,
respectively conductance or a specific resistance, respectively
specific conductivity of the measured medium is a measurement
transmitter (not explicitly shown) connected with the probe 1. The
measuring electronics can be a component of the measurement
transmitter or at least partially accommodated in a separate
module, for example, in a plug head connected with the probe 1. The
ascertained measured values can either be displayed by the
measurement transmitter or output to a superordinated control
system.
[0054] As described in WO 2010/072,483 A1, the probe 1 can also be
produced in a single method step by means of a two component,
injection molding method. In the case of this method, preferably an
injection molding machine with two injection units is used. In the
case of application of one injection unit for the electrode
material and an additional injection unit for the material of the
sensor body, the two injection units are preferably controlled
independently of one another, since, in this way, a larger variety
of electrode geometries can be produced. Two component injection
molding is a technology established especially for the manufacture
of components of different synthetic materials. The injection
molding of metals or ceramics, for example, by means of metal
powder injection molding (MIM--Metal Injection Molding) or ceramic
power injection molding (CIM--Ceramic Injection Molding), is a
known and established manufacturing method for technically
demanding and complex molded parts. Also, multicomponent injection
molding of metals and/or ceramics as individual components is, in
principle, known, however, previously not usual in the
manufacturing of composites of metal and ceramic.
[0055] In FIGS. 2 and 3 of the probe 1, the probe body 3 is joined
with a process connection 6. For this, the probe body 3 is
connected mechanically stably and sealingly with the process
connection 6, for example, by means of an adhesive. The joint 8
between the sensor body 3 and the process connection 6 can be
further worked by means of machining, grinding, and/or polishing.
In this way, also adhesive residues are removed. The diameter of
the process connection 6 and of the probe body 3 is enlarged at
least in this region of the subsequent working of the joint 8. In
order that the adhesive gap be as small as possible, thus, as
hygienic as possible, the lower end of the process connection 6 as
well as the ceramic sensor body 3 are provided with a diameter
larger than desired in the target application. Through subsequent
grinding or machining of the joint 8 of the connection between
sensor body 3 and process connection 6, a region with very much
smaller surface roughness is produced. Thus, also highest hygienic
requirements can be fulfilled.
[0056] The measuring active layer of the conductive material of the
electrodes 5 is embodied in a coating thickness d of, for example,
10 .mu.m-3 mm and so seated in the probe body 3 that its end faces
7 lie in a plane A. The thickness d, respectively height, of the
electrodes 5 as well as their diameter D amounts in the embodiment
of a four electrode measuring probe 1 of FIG. 2 or FIG. 3 to
preferably 1 to 2 millimeter.
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