Patent Application
20080073210
Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings in which:
Referring now to the drawings, and particularly to
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.
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.
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.
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.
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.
As best seen in
With reference to
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.
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.
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.
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.
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.
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.
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.
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.
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.
The reference electrode 14 is not directly exposed to the target fluid; rather it is surrounded by a reference electrolyte within a cavity 18 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.
With reference now to
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.
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.
