Membrane Support Structure for Electrochemical Sensing Probe

U.S. Pat. No. 3,826,730 describes an electrochemical sensing probe for determining oxygen concentration. This probe includes a membrane 52 held against an end of an electrode 54 by a cap 50. There have been problems insuring uniform pressure of such membrane against the electrode. If too much pressure is exerted, it is difficult for the electrolyte to reach the electrode. Conversely, if not enough pressure is exerted, electrolyte will build up at the electrode face causing excessively long response time of the probe.

In addition to the above mentioned reference, another sensing probe is described in my co-pending patent application entitled "Electrochemical Sensing Probe," filed Dec. 19, 1978, Ser. No. 970,890, which illustrates at the membrane-electrode contact area the general problem described above.

The above problems have been overcome with the present invention which includes a roughened surface on the electrode support. Preferably, an annular groove and connecting channel system is also used to insure sufficient electrolyte flow to the electrode. A retaining cap has a protruding annular section which uniformly presses the membrane against the electrode support. Thus, improved reproducability is achieved during manufacturing and assembly.

FIG. 1 is a fragmentary view showing the membrane supporting section of an electrochemical sensing probe;

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1; and

FIG. 3 is an enlarged sectional view of the retaining cap portion in contact with the membrane.

In FIG. 1, a sensing probe is shown which generally includes a connector 1, which can be reusable, joined to a disposable electrolyte housing 2. Within this housing is an electrolyte 3 contained in an annular chamber surrounding an electrode support 4 that includes in its center section an electrode 5 which can be a cathode. Anode 6 protrudes into the electrolyte 3. Retaining a membrane 7 in contact with electrode 5 is a cap 8. Cap 8 includes a central opening 9 to the atmosphere being tested. Surrounding opening 9 is an upstanding annular rib 10 with a convex cross-sectional shape in contact with membrane 7. Thus, a more predictable and uniform pressure is exerted on the membrane to hold it against electrode support 4. This provides better reproducability in manufacture and assembly.

To insure there is electrolyte contact at cathode 5, the bottom of rounded electrode support 4 is preferably roughened. This can be done by sanding the rounded end of electrode support 4 after it has been molded. Also, to insure electrolyte wetting of cathode 5, an annular groove 11 is molded into the end of electrode post 4. Groove 11 has a smaller diameter than the cap 8. Connecting the electrolyte chamber 3 with annular groove 11 are a series of radial channels, such as 12 and 13. Channels 12 and 13 extend across the pressure point at the membrane caused by annular rib 10 of the cap.

The above description has used specific embodiments to describe the invention. However, it is understood by those skilled in the art that certain modifications can be made to these embodiments without departing from the spirit and scope of the invention.