Oxygen sensing cell

• US 4,435,268 A
• Filed: 08/26/1982
• Issued: 03/06/1984
• Est. Priority Date: 08/26/1982
• Status: Expired due to Fees

• Current Assignee: ABB Process Analytics, Inc. (ABB Limited)
• Original Assignee: The Bendix Corporation (Honeywell International Inc.)
• Inventors: Strohl, John, Martin, Gordon W.
• Primary Examiner(s): Kaplan, G. L.
• Application Number:
  US06/411,765
• Time in Patent Office: 558 Days
• Field of Search: 204/408, 204/411, 204/412, 204/415, 204/1 P, 128/635
• US Class Current: 204/408
• CPC Class Codes: G01N 27/404 Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid , e.g. Clark-type oxygen sensors

Abstract

An improved oxygen sensing cell, especially of the polarographic type, is intended for use primarily in a gaseous environment. The cell has a cathode located at the bottom of the cell body. The cathode comprises a gold mesh electrode laminated to a thin-film sense membrane. The electrode is thus made immobile relative to the membrane, thereby improving the response time and providing for long-term sensor stability. The cell further has a guard electrode for the cathode. The guard electrode operates continuously and scavenges any oxygen molecules which are dissolved in the electrolyte and diffused towards the cathode. As a result, the dynamic range of the cell is substantially increased. The anode comprises a silver wire wound about a spool retained within the main cavity in the cell body. A p.c. board, as well as a compensation membrane, are resiliently retained at the top of the cell body. The body carries conductors for electrically connecting the p.c. board with the anode, cathode, and guard electrode, respectively.

Claims

1. An oxygen sensing cell, comprising a body having a pair of end portions provided with respective first and second openings therein, the body further having a central bore forming a main cavity communicating with the openings, an electrolyte within the cavity, a compensation membrane mounted over the first opening in the body, an anode within the cavity in the body, a cathode across the second opening in the body and including an outer permeation sense membrane and an inner porous electrode bonded to the inner surface of said sense membrane, a guard electrode between the second opening and the cathode, said guard electrode being substantially coextensive with and overlying said inner porous electrode, a thin layer of insulating material which is pervious to said electrolyte interposed between said guard electrode and said porous electrode, the opposite sides of said insulating layer being in intimate contact with the adjacent surfaces of said guard electrode and said porous electrode so that said guard electrode is spaced from said porous electrode only by said insulating layer, the guard electrode operating continuously, whereby oxygen molecules dissolved in the electrolyte and diffusing towards the cathode will be scavenged by the guard electrode, thereby substantially increasing the dynamic range of the sensing cell, and means within the body for respectively establishing electrical connections to the anode, cathode and guard electrode.

2. An oxygen sensing cell, comprising a body having a central cavity with at least one opening communicating therewith, an electrolyte within the cavity, a spool concentrically mounted within the cavity and having an opening communicating with the opening in the body, a button having a sleeve portion mounted within the body opening and coaxially aligned with the spool opening, the button further having a head portion provided with at least one aperture communicating with the bore in the spool, an anode including a helical wire wound about the spool, a cathode outwardly of the head portion of the button and including an outer permeation sense membrane and an inner mesh electrode, and a guard electrode between the head of the button sleeve and the cathode and insulated therefrom.

3. In an oxygen sensing cell, the combination of a body having a bore and a connecting counterbore, an electrolyte within the bore, an annular ledge between the bore and counterbore, a compensation membrane mounted on the ledge, an O-ring on top of the membrane, a p.c. board on top of the O-ring, and a top disc secured within the counterbore of the body and having a portion bearing against the p.c. board, thereby resiliently retaining the p.c. board and the membrane in the body, and thereby forming a top seal for the electrolyte in the cell cavity.

4. In an oxygen sensing cell, the combination of a body having a bottom face with an opening formed therein, a guard electrode covering the opening, a filter insulator over the guard electrode, a cathode over the filter insulator, respective first and second electrical conductor means carried by the body and terminating at the bottom face thereof, means including a first wire disposed adjacent to the bottom face and electrically connecting the first conductor to the guard electrode, a first compression ring concentrically of the guard electrode and bearing against the first wire, means including a second wire electrically connecting the second conductor to the cathode, a second compression ring concentrically of the first ring and radially thereof, thereby retaining a portion of the second wire against the bottom face, the second wire running between the first and second compression rings and substantially along the outer face of the first compression ring, and a bottom disc secured to the body and retaining the cathode and the compression rings therebetween.

5. In an oxygen sensing cell, the combination of a body having a central cavity, the body further having an end face with an opening formed therein, the opening communicating with the cavity in the body, a button having a hollow sleeve portion press-fitted within the opening, the button further having a head portion with at least one aperture formed therein, a cathode covering the opening in the end face of the body outwardly of the head portion of the button, a spool in the central cavity of the body, the spool having an opening formed therein and press-fitted over the sleeve portion of the button, thereby retaining the spool in the cavity and coaxially of the button, and an anode comprising a helical wire wound about the spool.

6. A polarographic oxygen sensing cell, comprising a generally cylindrical body having respective top and bottom portions, the body having an enlarged bore forming a central cavity therein, the body further having a counterbore in its top portion, an annular ledge between the bore and counterbore, a compensation membrane mounted on the ledge, an O-ring on top of the compensation membrane, a p.c. board on top of the O-ring, a top disc secured within the top of the body, the disc having a portion bearing against the p.c. board, thereby resiliently retaining the p.c. board and the compensation membrane, the bottom portion of the body having an end face, the end face having an opening formed therein communicating with the cavity, a cathode across the opening in the body, the cathode including a permeation sense membrane and a mesh electrode secured thereto, a guard electrode between the opening and the cathode and insulated therefrom, whereby oxygen molecules dissolved in the electrolyte and diffusing towards the cathode will be scavenged by the guard electrode, means including a bottom disc secured to the body for retaining the cathode and the guard electrode, the bottom disc having a central opening therein communicating with the sense membrane, a hollow spool mounted within the cavity concentrically of the opening in the bottom portion of the body, an anode comprising a wire wound about the spool, an electrolyte within the cavity in the body, and respective conductor means carried by the body and electrically connecting the p.c. board to the anode, cathode, and guard electrode, respectively.