U.S. patent application number 12/889876 was filed with the patent office on 2011-10-06 for electrochemical sensor.
This patent application is currently assigned to Georg Fischer Signet LLC. Invention is credited to Gert Burkhardt, Anthony Thai, Steven Wells.
Application Number | 20110240470 12/889876 |
Document ID | / |
Family ID | 39247048 |
Filed Date | 2011-10-06 |
United States Patent
Application |
20110240470 |
Kind Code |
A1 |
Wells; Steven ; et
al. |
October 6, 2011 |
ELECTROCHEMICAL SENSOR
Abstract
An electrochemical sensor is provided that includes a housing
defining a cavity for a reference electrolyte and defining an
opening to the cavity configured to be proximate to a target fluid.
The sensor further includes a junction plug comprising a porous
material and a cross member impermeable to a target fluid
positioned between the junction plug and the cavity. The cross
member is disposed proximate to the junction plug, defining an
aperture to enable electrochemical communication between the target
fluid and the reference electrolyte.
Inventors: |
Wells; Steven; (Huntington
Beach, CA) ; Burkhardt; Gert; (Pasadena, CA) ;
Thai; Anthony; (Orange, CA) |
Assignee: |
Georg Fischer Signet LLC
El Monte
CA
|
Family ID: |
39247048 |
Appl. No.: |
12/889876 |
Filed: |
September 24, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11533989 |
Sep 21, 2006 |
7867371 |
|
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12889876 |
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Current U.S.
Class: |
204/435 |
Current CPC
Class: |
G01N 27/4035
20130101 |
Class at
Publication: |
204/435 |
International
Class: |
G01N 27/30 20060101
G01N027/30 |
Claims
1. An electrochemical sensor, comprising: an elongated housing
defining a longitudinal axis, the housing having a proximal end and
a distal end configured to be exposed to a target fluid, the
housing further defining a cavity containing a gelled or liquid
reference electrolyte, the housing having an outer tubular wall
axially aligned with the longitudinal axis of the housing, the
outer wall impermeable to the reference electrolyte and the target
fluid, an inner tubular wall disposed within the outer wall, and
axially aligned with the longitudinal axis of the housing, the
inner wall impermeable to the reference electrolyte and the target
fluid, the inner wall defining an axial bore, and a cross member
extending between the outer wall and the inner wall proximate the
distal end of the housing, the cross member including a planar
portion defining an aperture to enable electrochemical
communication between the target fluid and the reference
electrolyte within the cavity, wherein the cavity is bounded by the
outer wall, the inner wall and the cross member, the cross member
of the housing formed of unitary construction with at least one of
the inner tubular member and the outer tubular wall; a measuring
electrode disposed in the axial bore of the inner wall and having
an tip extending beyond the distal end of the housing to be exposed
to a target fluid; a reference electrode disposed within the cavity
of the housing, submerged in the reference electrolyte; and a
junction plug comprising a porous material, the junction plug
disposed in the distal end of the housing such that a distal
surface of the plug is configured to contact the target fluid and a
proximal surface of the junction plug is disposed adjacent to the
cross member of the housing such that electrochemical communication
between the target fluid and the reference electrolyte must pass
through the aperture of the cross member.
2. An electrochemical sensor as defined in claim 1, wherein the
housing is formed of unitary construction of molded plastic,
including the outer wall, the inner wall and the cross member.
3. An electrochemical sensor as defined in claim 1, wherein the
cross member defines only a single aperture to enable
electrochemical communication between the target fluid and the
reference electrolyte.
4. An electrochemical sensor as defined in claim 3, wherein the
cross member covers between about 50 percent to 95 percent of the
proximal surface of the junction plug.
5. An electrochemical sensor as defined in claim 1, wherein the
cross member includes a stepped portion disposed about the axial
bore to receive an o-ring disposed about the measuring electrode to
inhibit target fluid from the axial bore.
6. An electrochemical sensor as defined in claim 1, wherein the
cross member is integrally formed with the inner tubular wall,
extending between the axial bore of the inner wall and the outer
wall.
7. An electrochemical sensor as defined in claim 1, further
comprising an upper seal positioned proximate to the proximal end
of the housing, the upper seal configured to engage the inner wall
and the outer wall to define an upper boundary of the cavity within
the housing.
8. An electrochemical sensor as defined in claim 1, wherein the
outer wall includes an inwardly facing flange disposed about a
distal opening of the outer wall, the flange sized such that the
junction plug can be securely seated in place proximate to the
distal opening to directly contact the target fluid.
9. An electrochemical sensor as defined in claim 8, wherein an
o-ring is disposed about the junction plug to engage the outer wall
to provide a secure seal.
10. An electrochemical sensor as defined in claim 1, further
comprising a cap disposed on the proximal end of the housing.
11. An electrochemical sensor, comprising: an elongated housing
defining a longitudinal axis, the housing having a proximal end and
a distal end configured to be exposed to a target fluid, the
housing further defining a cavity containing a gelled or liquid
reference electrolyte, the housing having an outer member formed of
unitary construction, the outer member including an outer tubular
wall axially aligned with the longitudinal axis of the housing, the
outer member impermeable to the reference electrolyte and the
target fluid, an inner member formed of unitary construction having
an inner tubular wall and a cross member disposed at a distal end
of the inner tubular wall, the inner member disposed within the
outer member and impermeable to the reference electrolyte and the
target fluid, the inner tubular wall axially aligned with the
longitudinal axis of the housing, the inner wall defining an axial
bore, and the cross member extending between the outer wall and the
inner wall proximate the distal end of the housing, the cross
member defining an aperture to enable electrochemical communication
between the target fluid and the reference electrolyte within the
cavity, wherein the cavity is bounded by the outer wall, the inner
wall and the cross member; a measuring electrode disposed in the
axial bore of the inner wall and having an tip extending beyond the
distal end of the housing to be exposed to a target fluid; a
reference electrode disposed within the cavity of the housing,
submerged in the reference electrolyte; and a junction plug
comprising a porous material, the junction plug disposed in the
distal end of the housing such that a distal surface of the plug is
configured to contact the target fluid and a proximal surface of
the junction plug is disposed adjacent to the cross member of the
housing such that electrochemical communication between the target
fluid and the reference electrolyte must pass through the aperture
of the cross member.
12. An electrochemical sensor as defined in claim 11, wherein the
cross member defines only a single aperture to enable
electrochemical communication between the target fluid and the
reference electrolyte.
13. An electrochemical sensor as defined in claim 12, wherein the
cross member covers between about 50 percent to 95 percent of the
proximal surface of the junction plug.
14. An electrochemical sensor as defined in claim 11, wherein the
cross member includes a stepped portion disposed about the axial
bore to receive an o-ring disposed about the measuring electrode to
inhibit target fluid from the axial bore.
15. An electrochemical sensor as defined in claim 11, further
comprising an upper seal positioned proximate to the proximal end
of the housing, the upper seal configured to engage the inner wall
and the outer wall to define an upper boundary of the cavity within
the housing.
16. An electrochemical sensor, comprising: an elongated housing
defining a longitudinal axis, the housing having a proximal end and
a distal end configured to be exposed to a target fluid, the
housing further defining a cavity containing a gelled or liquid
reference electrolyte, the housing having an outer tubular wall
formed of plastic, axially aligned with the longitudinal axis of
the housing, the outer wall impermeable to the reference
electrolyte and the target fluid, an inner tubular wall formed of
plastic, disposed within the outer wall, and axially aligned with
the longitudinal axis of the housing, the inner wall impermeable to
the reference electrolyte and the target fluid, the inner wall
defining an axial bore, and a cross member extending between the
outer wall and the inner wall proximate the distal end of the
housing, the cross member defining an aperture to enable
electrochemical communication between the target fluid and the
reference electrolyte within the cavity, wherein the cavity is
bounded by the outer wall, the inner wall and the cross member, the
cross member of the housing formed of unitary construction of
plastic with at least one of the inner tubular member and the outer
tubular wall; a measuring electrode disposed in the axial bore of
the inner wall and having an tip extending beyond the distal end of
the housing to be exposed to a target fluid; a reference electrode
disposed within the cavity of the housing, submerged in the
reference electrolyte; and a junction plug comprising a porous
material, the junction plug disposed in the distal end of the
housing such that a distal surface of the plug is configured to
contact the target fluid and a proximal surface of the junction
plug is disposed adjacent to the cross member of the housing such
that electrochemical communication between the target fluid and the
reference electrolyte must pass through the aperture of the cross
member.
17. An electrochemical sensor as defined in claim 16, further
comprising an upper seal positioned proximate to the proximal end
of the housing, the upper seal configured to engage the inner wall
and the outer wall to define an upper boundary of the cavity within
the housing.
18. An electrochemical sensor as defined in claim 16, further
comprising a cap disposed on the proximal end of the housing.
19. An electrochemical sensor as defined in claim 16, wherein the
cross member defines only a single aperture to enable
electrochemical communication between the target fluid and the
reference electrolyte.
20. An electrochemical sensor as defined in claim 16, further
comprising an upper seal positioned proximate to the proximal end
of the housing, the upper seal configured to engage the inner wall
and the outer wall to define an upper boundary of the cavity within
the housing.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of U.S.
application Ser. No. 11/533,989, filed Sep. 21, 2006, which is
herein incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to electrochemical
sensors and, more particularly, to such sensors having a reference
electrode and a measuring electrode for measuring parameters of a
target fluid.
BACKGROUND OF THE INVENTION
[0003] Electrochemical sensors have long been used to measure
properties of fluids. Such sensors typically include a measuring
electrode assembly and a reference electrode assembly, both which
are electrically coupled to an instrument that senses the
difference in electrical potential between the electrodes. In
sensors of this kind, the measuring electrode assembly typically is
exposed directly to the target fluid; whereas the reference
electrode assembly is immersed in a stable electrolytic solution,
i.e., a reference electrolyte. Sensors of this kind further include
an ion-permeable separator, commonly referred to as liquid junction
or salt bridge, disposed between the reference electrolyte and the
target fluid, to enable a closed circuit between the
electrodes.
[0004] In use, the measuring electrode generates a potential that
varies as a function of prescribed parameters of the target fluid.
The potential difference between the measuring electrode and the
reference electrode provides a basis for measuring the prescribed
parameters of the target fluid. For a precise reading, the
reference electrode must provide a stable potential.
[0005] The liquid junction plays an important role in achieving and
maintaining a stable potential for the reference electrode.
Ideally, the liquid junction should enable ionic communication
between the reference electrolyte and the target fluid, while
otherwise preventing transfer or intermingling of the fluids.
Contamination or dilution of the reference electrolyte can unduly
inhibit performance of the reference electrode. Moreover,
contamination or reaction with the reference electrode or
electrolyte is of particular concern when used in harsh chemical
environments. The ability of the liquid junction to inhibit
diffusion of the measured fluid, and ions therefrom, can be
generally referred to as its resistance factor.
[0006] Much attention has been given to designing effective liquid
junctions having a high resistance factor. Many approaches attempt
to establish a tortuous path for ions through the junction by
confining travel through relatively complex structural
configurations that incorporate multiple components assembled
together. For example, certain approaches include multiple layers
held together with wood dowels. Although generally effective, such
approaches are relatively expensive and time-consuming to
manufacture. Moreover, performance of such approaches can
deteriorate with time.
[0007] It should be appreciated that there remains a need for an
electrochemical sensor that addresses these concerns. The present
invention fulfills this need and others.
SUMMARY OF THE INVENTION
[0008] In general terms, the present invention provides an
electrochemical sensor comprising a housing defining a cavity for a
reference electrolyte and defining an opening to the cavity
configured to be proximate to a target fluid. The sensor further
includes a junction plug comprising a porous material and a cross
member impermeable to a target fluid positioned between the
junction plug and the cavity. The cross member includes a planar
portion disposed against the junction plug that defines an aperture
to enable electrochemical communication between the target fluid
and the reference electrolyte. Thus, ionic exchange must pass
through the aperture, thereby enhancing the resistance factor of
the sensor assembly.
[0009] More specifically, and by way of example, the
electrochemical sensor comprises a housing having an outer member
and an inner member disposed within the outer member. The inner
member includes an axial bore configured to receive a measuring
electrode. A junction plug of porous material positioned such that
a first surface contacts the target fluid and a second surface is
proximate to the cavity of the housing. The housing includes a
cross member impermeable to the target fluid positioned between the
junction plug and the cavity. The cross member defines an aperture
in a single prescribed region of the cross member to enable
electrochemical communication between the target fluid and the
reference electrolyte.
[0010] In another embodiment of the invention, the electrochemical
sensor includes a housing of unitary construction defining a cavity
for a reference electrolyte and having a cross member between the
cavity. The sensor further includes a junction plug having a first
surface that contact a target fluid and a second surface that
contacts the cross member.
[0011] In another embodiment, the housing includes an outer
cylindrical member and an inner member disposed within the outer
member. The outer member includes the cross member. Alternatively,
the cross member can be provided as a separate component or even
affixed to the junction plug. The cross member covers between about
50 percent to 95 percent of the second surface of the junction
plug.
[0012] In a detailed aspect of an exemplary embodiment of the
invention, the cross member includes a stepped portion and a planar
portion disposed against the junction plug. The stepped portion and
the junction plug define a void.
[0013] For purposes of summarizing the invention and the advantages
achieved over the prior art, certain advantages of the invention
have been described herein. Of course, it is to be understood that
not necessarily all such advantages may be achieved in accordance
with any particular embodiment of the invention. Thus, for example,
those skilled in the art will recognize that the invention may be
embodied or carried out in a manner that achieves or optimizes one
advantage or group of advantages as taught herein without
necessarily achieving other advantages as may be taught or
suggested herein.
[0014] All of these embodiments are intended to be within the scope
of the invention herein disclosed. These and other embodiments of
the present invention will become readily apparent to those skilled
in the art from the following detailed description of the preferred
embodiments having reference to the attached figures, the invention
not being limited to any particular preferred embodiment
disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Embodiments of the present invention will now be described,
by way of example only, with reference to the following drawings in
which:
[0016] FIG. 1 is a cross-sectional view of a first embodiment of an
electrochemical sensor in accordance with the present invention,
depicting a reference electrode disposed within a cavity.
[0017] FIG. 2 is a partially exploded view of the electrochemical
sensor of FIG. 1.
[0018] FIG. 3 is a cross-sectional view, taken along the line 3-3
of the electrochemical sensor of FIG. 1, depicting an aperture
defined by the cross member of the housing assembly.
[0019] FIG. 4 is a partially exploded view of a second embodiment
of an electrochemical sensor in accordance with the present
invention, depicting a reference electrode disposed within a
cavity.
[0020] FIG. 5 is a cross-sectional view, similar to FIG. 3, of the
electrochemical sensor of FIG. 4, depicting an aperture defined by
the cross member of the housing assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Referring now to the drawings, and particularly to FIGS. 1
and 2, there is shown an electrochemical sensor assembly 10, for
measuring parameters of a target fluid (not shown), such as ORP or
specific ions, e.g., pH or sodium. The sensor assembly 10 includes
a measuring electrode 12 (e.g., glass pH electrode) and a reference
electrode 14 coupled to a housing 16. The reference electrode is
disposed within a cavity 18 of the housing and is surrounded by a
reference electrolyte. The sensor assembly includes a liquid
junction comprising a plug 20 disposed at distal end of the housing
and further includes a cross member 22 disposed between the plug
and the cavity. The cross member defines an aperture 24 that
enables electrochemical communication between the target fluid and
the reference electrolyte. Thus, ionic exchange must occur through
the aperture, thereby enhancing the resistance factor of the sensor
assembly.
[0022] The cross member 22 is formed of material impermeable to the
target fluid. In the exemplary embodiment, the cross member is
formed of molded plastic and is integrally formed with an inner
member 26 of the housing 16. The aperture 24 is provided in a
single prescribed region of the cross member. With the cross member
in place, ions traveling between the target fluid and the reference
electrolyte must migrate axially through and transverse across the
junction plug 20 to pass through the aperture of the cross member,
resulting in an increased effective path length through the
junction plug.
[0023] The cross member 22 includes a stepped portion 28 disposed
about a cylindrical bore 30 of the inner member and a planar
portion 32 that extends from the stepped portion and positioned
against the junction plug. The stepped portion and the junction
plug define a void 34 about bore for receiving an o-ring 54
disposed about the measuring electrode.
[0024] In the exemplary embodiment, the junction plug 20 defines a
central passage 36 that enables the measuring electrode 12 to
extend beyond the liquid junction, to contact the target fluid. The
junction plug includes a distal surface 38 that is exposed directly
to the target fluid and a proximal surface 40 abutting the cross
member 24.
[0025] The distal surface 38 of the junction plug 20 provides a
relatively substantial surface area, to enabling effective exposure
to the target fluid and minimizing clogging of the plug. The
junction plug 20 is confined in an opening defined by the
housing.
[0026] In the exemplary embodiment, the junction plug 20 is formed
of a unitary construction of porous ultra-high molecular weight
polyethylene. Nonetheless, other material having suitable
characteristics can be used. For example, effective materials
include ground glass, ceramic, other porous plastics, and wood. The
liquid junction can be formed of multiple components and
materials.
[0027] As best seen in FIG. 3, the cross member 22 effectively
substantially covers the proximal surface 40 of the junction plug.
Preferably, the cross member covers between about 50 percent to 95
percent of the proximal surface of the junction plug. In the
exemplary embodiment, the cross member covers about 90 percent of
the proximal surface. The aperture 24 is defined by the planar
portion of the cross member. In the exemplary embodiment, the cross
member defines a single circular aperture 23, however, other
configurations can be used in other embodiments. For example,
several apertures as well as other shapes, e.g., ring, rectangle,
and so on, can be used. Moreover, in other embodiments, the cross
member can be attached directly to the proximal surface of the
cross member.
[0028] With reference to FIG. 2, the housing 16 includes the inner
member 26 and an outer member 42. The outer member has a sidewall
44 and defines proximal and distal openings 46, 48, respectively.
The outer member includes an inwardly facing flange 50 disposed
about the distal opening. The flange is sized such that the
junction plug 20 can be securely seated in place proximate to the
distal opening to directly contact the target fluid. An o-ring 52
is disposed about the junction plug to engage the sidewall 44 of
the outer member, providing a secure seal about the plug.
[0029] The inner member 26 of the housing 16 is coupled to and
disposed within the outer member 42. The cylindrical bore 30 of the
inner member is aligned with a longitudinal axis of the housing and
configured to receive the measuring electrode 12. The sidewall 44
of the outer member is generally equidistantly spaced from the bore
about the circumference thereof.
[0030] As previously mentioned, the inner member 26 provides the
cross member 22. The cross member extends between the cylindrical
bore and the sidewall 44 of the outer member. In the exemplary
embodiment, the inner member is permanently affixed in place. The
sidewall of the outer member slope inwardly from the proximal
opening to the distal opening.
[0031] During assembly, the measuring electrode 12 is inserted into
the plug 20. The o-ring is put down over the back of the measuring
electrode 12, fitting snugly against the plug 20. The assembly is
then inserted through the proximal opening 46. The inner member 26
is inserted into the outer member 42 through the proximal opening.
The components are sized such that the diameter of the cross member
22 will correspond to the inner diameter of the outer member
proximate to junction plug, once the plug is in place. In this
manner, the cross member will directly contact the junction plug,
as well as, the sidewall 44 of the outer member 42. Adhesive
material can be provided, as needed. Nonetheless care should be
taken to ensure that the aperture 24 does not become blocked with
material that would bar electrochemical communication between the
target fluid and the reference electrolyte.
[0032] In other embodiments, the inner member can be coupled to the
outer cylindrical member in such manner to enable disassembly for
maintenance purposes. For example, the inner and outer members can
couple via cooperative attachments assemblies, e.g., threaded
portions, tongue and groove engagements, and other suitable
attachments.
[0033] In the exemplary embodiment, the outer and the inner members
26, 42, respectively, are formed of molded plastic, such as
polypropylene, PP. In other embodiments, other materials can be
used. Some examples of other material that can be used include
polyphenylsulfone PPS, polyvinyl chloride PVC, chlorinated
polyvinyl chloride CPVC, polyvinyldiflouride PVDF, or other
materials known in the art having appropriate chemical resistivity
for a particular application.
[0034] The sensor assembly 10 further includes an upper seal 56
positioned proximate to the proximal end of the outer member. The
upper seal is configured to engage the cylindrical bore of the
inner member and the sidewall 44 of the outer member 42 in such a
manner as to aid in defining the reference cavity 18. The reference
electrode is disposed within cavity, in this embodiment, opposite
the aperture 24 of the cross member.
[0035] In the exemplary embodiment, a gelled reference electrolyte
is used, such as, KCl saturated with AgCl acrylamide gel.
Nonetheless, other reference electrolytes, including gels and
liquids, can be selected as requirements dictate for particular
uses.
[0036] The measuring electrode 12 and a reference electrode 14 are
configured to be coupled to instrumentation, e.g., amplifier (not
shown), to sense the potential of the measuring electrode and the
reference electrode. The housing further includes a cap 58 received
atop the proximal opening 46 of the outer member. Wires attached to
the electrodes pass through the cap to couple to the
instrumentation.
[0037] In the exemplary embodiment, a glass pH electrode is used.
In use, the end portion of the measuring electrode 12 exposed to
the target fluid such that the measuring electrode is
electrochemically coupled to the target fluid. In the exemplary
embodiment, a sensor assembly is configured to detect pH and ORP.
However, other embodiments can configured to measure these or other
parameters, individual or in combination. For example, other types
of specific ions that can be measured include, for example,
ammonium, bromide, chloride, fluoride, sulfide, nitrate, and
sodium.
[0038] The reference electrode 14 is not directly exposed to the
target fluid; rather it is surrounded by a reference electrolyte
within a cavity 20 defined by the housing, enabling the reference
electrode to provide a stable potential for comparison against the
potential of the measuring electrode. In the exemplary embodiment,
an Ag/AgCl type reference electrode is used, nonetheless, various
other types of reference electrodes known in the art can be
used.
[0039] With reference now to FIGS. 4 and 5, a second embodiment of
a sensor assembly 70 is provided, having a housing 72 formed of a
unitary construction, e.g., molded plastic. Otherwise, the housing
is similarly configured to the housing of the first embodiment,
including a cylindrical sidewall 74 and a circular cross member 76
disposed proximate to a distal end 78 of the housing. The housing
defines a central bore 80 for the measuring electrode 12 and a
cavity 82 for containing the reference electrolyte. The cross
member 76 defines an aperture 84 aligned with the cavity for the
reference electrode. The cross member is disposed between the
junction plug 86 and the cavity to enable electrochemical
communication between the target fluid and the reference
electrolyte. In t his embodiment, the aperture is configured as a
single radial segment confined in a prescribed region of the cross
member.
[0040] It should be appreciated from the foregoing that the present
invention provides an electrochemical sensor that includes a
housing defining a cavity for a reference electrolyte and defining
an opening to the cavity configured to be proximate to a target
fluid. The sensor further includes a junction plug comprising a
porous material and a cross member formed of material impermeable
to a target fluid positioned between the junction plug and the
cavity. The cross member includes a planar portion disposed against
the junction plug that defines an aperture to enable
electrochemical communication between the target fluid and the
reference electrolyte. Thus, ionic exchange must pass through the
aperture, thereby enhancing resistance factor of the sensor
assembly.
[0041] Although the invention has been disclosed in detail with
reference only to the exemplary embodiments, those skilled in the
art will appreciate that various other embodiments can be provided
without departing from the scope of the invention. Accordingly, the
invention is defined only by the claims set forth below.
* * * * *