US 3708411 A
A compact construction for ion selective electrodes and reference electrodes, and a combination of both, is proposed wherein a plastic shrink tubing is employed for enclosing an integral assembly incorporating an attachment to an electrical cable; the shrink tubing also confines and supports the specific active membrane; the combination of specific ion and reference electrode is formed in a unitary compact assembly convenient for process applications.
Description (OCR text may contain errors)
United States Patent 1191 Vanslette 1 Jan. 2, 1973 154] CONSTRUCTION OF ION ELECTRODE 3,442,782 5/1969 Shiller et a1. ..204/195 3,461,055 8/1969 Staunton ..204/195  Invent when vanslem' Medfield 3,035,113 5/1962 Danchuk ..174/D1G. 8 Mass- 3,492,216 1/1970 Riseman et al ..204/195 3,530,056 9/1970 Haddad ..204/195  9 3,562,130 2/1971 116616 61a1..... ..204/195 3,575,834 4/1971 H6616 6:61. ..204/195  1969 FOREIGN PATENTS OR APPLICATIONS  App! 763,082 7/1967 Canada ..204/195  US. Cl. ..204/195 M 7 Primary Examiner-T. Tung  Int.,Cl. ..G0ln 27/46 yL wr n 1-l. P n - Field of Search ..l74/75 R, DIG. 8; 204/1 T,
204/195, 195.1 ABSTRACT q A compact construction for ion selective electrodes References Clled and reference electrodes, and a combination of both,
' is proposed wherein a plastic shrink tubing is em- UNITED STATES PATENTS ployed for enclosing an integral assembly incorporat- 2,755,243 711956 Beckman et a1 ..204/195.1 ing an attachment to an electrical cable; the shrink 3,049,118 8/1962 Arthur et a1 204/195.1 tubing also confines and supports the specific active 3,081,250 3/1963 Hall etal. ..204/195 1 membrane; the combination of specific ion and 3,103,480 1963 Watanabe et a1 --2 4/l reference electrode is formed in a unitary compact as- 3,151,052 9/1964 Arthur 61 3.1 204/195 sembly convenient for process applications. 3,334,039 8/1967 Vlasak ..204/195 3,339,411 9/1967 Riffie ..174/DlG. 8 5 Claims, 4 Drawing Figures I 1| 441?: 719. 11 46. 617 @Q/ 1 11a Ev/1 47 iii? \42 56. s a 6 34 -32 426 /!1/Q1,= a a, 1 \a 49 /'jy PATENTEDJM 2 I975 SHEET 1 BF 3 I M'Illlllfl INVENTOR- ROBERT A. VANSLETTE DH i ATTORNEY PAIENTEUJAI ems I "3.708.411 I FIG. 4
I NVEN TOR.
ROBERT A. VANSLETTE ATTQRNEY 1 CONSTRUCTION OF ION ELECTRODE This invention relates to construction of ion selective and reference electrodes, and in particular to a combination construction containing both measurement and reference junctions.
It is desireable in electrode construction to provide a compact unitary assembly which may be readily employed in process applications. The invention is for an assembly enclosed and attached to an electrical conductor by a shrink tubing, whereby the finished product is in the form of an electrical cable having a firmly attached electrode assembly at its tip. The construction of the'electrode is simple compact, inexpensive, conveniently handled and replaced, and suitable for a variety of applications. The arrangement of the invention in particular permits a combination electrode application employing a salt solution for an electrolyte which is not saturated with silver chloride. In this application, the silver is internal to the electrode, and the salt solution appearing at the process junction consequently contains little silver to cause precipitation at the junction with the consequent plugging and fouling common to electrodes of conventional construction. Consequently, an electrode constructed in accordance with the invention will require minimal maintenance during its life.
These and other advantages of the invention will be apparent from the following specification taken together with the various FIGS. in which;
FIG. 1 is a three-dimensional outline view of a combination electrode;
FIG. 2 is a cross-sectional view of the combination electrode in combination with a cell;
FIG. 3 is a detailed view in cross-section of a portion of the combination electrode;
FIG. 4 is a cross-sectional view of a construction of a measurement electrode in which the which the reference junction is omitted.
I Referring to FIG. 1, a three dimensional outline view of a combination electrode 20 is represented, which is a unitary construction covered overall by a shrink tubing 30 extending from circumference 53a of active face 53 up to end 52 of tubing 30 which is shrunk fit over coaxial cable 36. The portion of shrink tubing 30 between shoulder 13 and end 52 makes a close shrink fit with coaxial cable 36 to serve in sealing and retaining the electrode 20 in integral relationship with coaxial cable 36. Shoulder 23, together with faces 11 and 12 thereof,
serve as mounting and retaining means for electrode 20, to be placed in an appropriate receptacle 210 such as is shown interior. to cell 21 in FIG. 2. Indentation 47 is provided in the region that wick end 31a is extended from shrink tubing 30, the space provided for by indentation 47- being filled with electrolyte solution under operating conditions. Indentation 34 is provided Referring to FIG. 2, combination electrode assembly 20 is shown installed in cell 21, combination electrode 20 being held in place by means of threaded collar 22 which clamps shoulder 23 of electrode 20 against shoulder 24 of the cell 21 receptacle 21a. The process.
stream is injected into inlet 25 of cell 21 passing through channel 26 and exiting from outlet of cell 21. The salt solution, conveniently one molar potassium chloride, is injected into inlet port 28 at a small positive. pressure. The salt solution flow along channel 29 into the interior receptacle 21a of cell 21 comes in contact with shrink tubing 30 of combination electrode 20, and flows therealong following the outside of combination electrode 20, coming in contact with wick end 31a, in a electrolyte region provided for by indentation 47 of electrode 20. The salt solution continues therefrom through porous fiber gasket 32 into the process stream. Porous fiber gasket 32 provides for the process junction, providing an interface between the salt solution and the process solution. It will be seen that the process solution will enter into annular channel 33 between the combination electrode 20 and the inside diameter of the lower part of receptacle 21a. Porous gasket 32 has a size such as forms a sealable contact between the body of combination electrode 20 at indentation 34 thereof and inner wall 35 of cell receptacle 21a.
The construction of combination electrode 20 may be seen, referring to FIGS. 2, and the detail shown in FIG. 3, in that a coaxial cable 36 is employed for the electrical-connections. Annular insulator 37 is fitted over the outside insulation of coaxial cable 36. A silver sleeve 38 is also fitted over the outside insulation of cable 36, sleeve 38 being cemented to insulator 37 at abutment 39 therebetween. The insulation of coaxial cable 36 is stripped from the sensing end up to sleeve 38, and annular ferrule 40 is inserted underneath braid 41, so that braid 41 contacts end 38a of sleeve 38. Insulator 42 is slipped over the inner insulator 43 of coaxial cable 36, in a manner to compress braid 41 and annular insert 40 against sleeve end 38a. Insulator 42 is cemented to abutting region 44 between sleeve 38 and insulator 42. The region 45 annular to sleeve 48 provided for between insulator 37 and insulator 42 is filled with a silver chloride powder or paste, such as may be conveniently applied circumferentially to sleeve 38 prior to the application of shrink tubing 30. End 31b of wick 31 is in contact with silver chloride region 45, and wick 31 runs therefrom along threaded grooves 46 on the body of insulator 42 down to indentation 47 of insulator body 42.
For the sensing end of the electrode, an active membrane 60 is cemented, such as by' epoxy to end 42a of insulator 42. Active membrane 60, employing material such'as pressed silver sulfide for sulfide measurement,
is backed by silver backing 48 and connected by wire 49, preferably silver, to center conductor 50 of the a coaxial cable. Some suitable non-hardening sealant is may be circumferential or alternatively a small opening for the wick, is made in the body of tubing 30 at indentation 47 of insulator 42, and end 31a of wick 31 pulled out therefrom for contacting the salt solution supplied to the annular region defined by indentation 47 and walls 14 and 15 thereof. Shrink tubing 30 is trimmed to present a flush uniform with face 53 of membrane 60.
In operation, the electrolyte solution is wicked into electrode by wick end 31a extending into the electrolyte solution in the region of indentation 47, the electrolyte wicking up the length of wick 31 along screw thread 46 to wick end 31b wetting the silver chloride powder 45 thereby creating a wet silver chloride half cell reference junction. The electrical signal therefrom is taken via coaxial braid 41 and supplied to conventional measuring equipment, not shown. Inasmuch as any silver is internal to the electrode 20, the solution entering into the process contains very little silver at junction 32, thus reducing precipitation at junction 32. The signal from the ion sensing membrane 60 is taken via center conductor 50 of coaxial cable 36 and supplied to conventional measuring equipment, not shown.
Referring to FIG. 4, a construction of an electrode is shown in which the reference junction is omitted, and in which only the ion selective measurement function is provided. An electrode body 56 is placed over coaxial cable 36, electrode body being of any suitable material. Ferrule 40 is inserted under braided shield 41 and a lower body piece 57, made of some suitable insulating material, is slipped over the braid end and the inner coaxial insulator, body piece 57 being cemented to body piece 56. Alternatively, the body pieces 56 and 57 may be formed as part of a molded assembly in which the molded assembly provides a strain relief for the electrical cable 36 and support for the pellet 60. The ion selective membrane 60, such as a silver sulfide pellet, is epoxied to end 57a of lower body piece 57, and a silver backing 48 of pellet 60 is connected by thin wire 49 to center conductor 50 of the coaxial cable. As an alternative form of construction, not shown, a conventional liquid electrical connection may be employed, such as the saturated potassium chloride used with pH electrodes. A non-hardening sealant is applied to circumferential portion 51 of pellet 60 and a shrink tubing 30 applied over the entire assembly, extending from pellet 60 face 53 up to point 52 on coaxial cable 56. The finished assembly includes a shoulder 23 for mounting to the appropriate application. It is to be noted that the resilient tubing in the region of shoulder 23 provides means for sealing the electrode with the receptacle employed without requirement for additional seals or gaskets.
What is claimed is:
1. An ion electrode assembly comprising:
a tubular body of insulating material,
an ion selective membrane supported in contact with one end of said tubular body,
a coaxial electrical cable disposed in said body and being solidly electrically connected to said ion selective membrane,
a resilient tubing being sealably shrinkfitted over the outside of said tubular body and said electric ca-- ble, said tubing extending from a seal with the outside of said electrical cable to said membrane and over the circumference of said membrane to its exposed sensing face,
and a non-hardening sealant disposed between said resilient tubing and said circumference of said membrane,
whereby said membrane is supported by said resilient tubing.
2. The ion electrode assembly as claimed in claim 1 further including: f
a reference junction enclosed within said resilient tubing, said reference junction being electrically connected with the outside conductor of said coaxial electrical cable.
3. The ion electrode assembly as claimed in claim 2 further including:
a wicking means incorporated with said reference junction having an end protruding through said tubing.
4. The ion electrode assembly as claimed in claim 1 wherein said tubular body includes a shoulder portion adapted to provide means for sealably mounting said assembly to a receptacle.
5. The ion electrode assembly as claimed in claim 1 wherein one end of said resilient tubing is substantially flush with' exposed sensing face of said membrane.