US3832675A

US3832675A - Electrode comprising a head and a detachable plug

Info

Publication number: US3832675A
Application number: US00296968A
Authority: US
Inventors: H Hubner; J Oswald; M Detemple
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-03-03
Filing date: 1972-10-12
Publication date: 1974-08-27
Anticipated expiration: 1991-08-27
Also published as: DE7208139U; CH541150A

Abstract

A connection between an electrode head and a cable plug to form an electrode plug head. The connection is a good electrical connection of a first contact and a second contact coaxially arranged about the first contact of the electrode head respectively with an inner terminal and an outer terminal of the cable plug similarly arranged. Further, a plastic casing enveloping the whole unit of electrode head clampingly engages another plastic casing enveloping the entire cable plug. The casings cause simultaneous engagement of an outer thread and an o-ring of the electrode head respectively with an inner thread and a shoulder of the cable plug. Thus, a fluid-proof electrode plug head is obtained. The electrode head is also provided with a thin metallic shield which is slidably mounted on the inner wall of the plastic casing and which is electrically connected to the second contact to serve as an electric shield so that the electrode plug head will be leak-proof when the electrode head and the cable plug are connected.

Description

Detemple et al.

[ ELECTRODE COMPRISING A HEAD AND A DETACHABLE PLUG [76] Inventors: Manfred F. Detemple, 65 Mainz,

Josefstr. 65, Mainz; Horst Hubner, 6203 Hochheim, Herderstr. 8, Hochheim; Johann Oswald, 65 Mainz, Sommerringplatz 6, Mainz, all of Germany [22] Filed: Oct. 12, 1972 [21] Appl. No.: 296,968

[30] Foreign Application Priority Data Mar. 3, 1972 Germany 7208139 [52] U.S. Cl 339/143 R [51] Int. Cl l-l0lr 13/46 [58] Field of Search 339/143 R, 177, 60, 94

[56] References Cited UNITED STATES PATENTS 2,1 l9,452 5/l938 Woodhead 339/60 R 2,742,622 4/l956 Stevens, Jr. 33 /94 R 3,l24,406 3/1964 Cook 339/l43 R 3,643,208 2/1972 Massa, Jr. 33 /143 R "ll l lli Aug. 27, 1974 Primary Examiner-James R. Boler Assistant Examiner-Peter Nerbun Attorney, Agent, or Firm'Littlepage, Quaintance, Murphy & Dobyns ABSTRACT A connection between an electrode head and a cable plug to form an electrode plug head. The connection is a good electrical connection of a first contact and a second contact coaxially arranged about the first contact of the electrode head respectively with an inner terminal and an outer terminal of the cable plug similarly arranged. Further, a plastic casing enveloping the whole unit of electrode head clampingly engages another plastic casing enveloping the entire cable plug. The casings cause simultaneous engagement of an outer thread and an o-ring of the electrode head respectively with an inner thread and a shoulder of the cable plug. Thus, a fluid-proof electrode plug head is obtained. The electrode head is also provided with a thin metallic shield which is slidably mounted on the inner wall of the plastic casing and which is electrically connected to the second contact to serve as an electric shield so that the electrode plug head will be leak-proof when the electrode head and the cable plug are connected.

PATENTEU M19 2 7 7 FIG. 2

FIG.1

ELECTRODE COWRISING A IEAD AND A DETACI-IABLE PLUG DISCLOSURE The present invention relates to a novel electrode such as a combined measuring electrode and single-rod measuring chains. In such measuring electrodes, it is customary to provide in one part, i.e., in the so-called electrode head, by soldering or welding together, a fixed electric connection between the contact wires located in the electrode, and the so-called contact or connection cable. Occasionally the electrical connection is provided by pressure contacts or by soldered-on or welded-on contacts at the contact cable and at the contact wires located in the electrode. In all cases, however, the contact cable is fixed in the electrode head in such a manner that cable and electrode together form a unit.

Since measuring electrodes normally have a high internal resistance 2 lOMQ), it is customary to employ, for the purpose of electrostatic shielding, a shielded cable, a so-called coaxial cable, as constant cable. The cable core is connected to the measuring system proper, and the electrostatic shield surrounding the cable core and usually constructed as a dense copper lattice, is electrically connected either to the electrostatic shield, which in the electrode surrounds the measuring system concentrically, or in the case of singlerod measuring chains, to the reference system which functions also as a shield.

In similarly constructed measuring systems, such as conductivity cells, double platinum electrodes for polarization current or polarization voltage titrations, and thermometer probes, the connection is frequently produced in the manner described above.

A further possibility of providing a connection consists in the use of electrode heads shaped as plug sockets or screw clamps. In this case, coaxial connections may also be involved, the contact for the measuring electrode being arranged, corresponding to the structure of the coaxial cable, in the plug center. The contact surface for the shield, which usually constitutes also the outer casing of the plug head, is surrounded by an insulating material and is arranged concentrically about the middle contact.

Electrodes having a rigidly connected cable present the following disadvantages: Cable replacement is not possible complicating contact plug replacement. When the electrode becomes defective, the cable and usually also the connecting plug are thrown away. Due to the permanent fixation of the cable, the electrode cannot easily be stored in a state ready for measurement. This is especially troublesome when the cable is long.

Prior art electrode connections present at least one of the following disadvantages:

First, the shield, i.e., in single-rod measuring chains the reference electrode contact, is not an insulated outer casing. When a moisture layer from the measuring solution or from a reinforcement in conductive connection to the electrode head is present, the reference system is short-circuited by way of the resulting shunt resistance.

Second, the known plug connections are not sufficiently moisture vapor tight to maintain the insulation resistance between cable core and shield necessary for the measurement and amounting to B 5 X 10 ohm cannot be maintained in the plug head.

To be sure, the electrode heads are insulated toward the outside but the shield located in the head is not sufficient, so that in the case of strong field changes, e.g., when the head is touched, the accuracy of the measuring result is adversely influenced. The known construction is so complicated and so difficult to manufacture and to connect that the expenditure affects the price of the electrode disadvantageously.

It is an object of the present invention to provide an improved electrode substantially free of one or more of the disadvantages of prior electrode connections. These disadvantages are overcome according to the present invention in that:

1. The connection between the electrode head and the electrode cable is a plug and screw connection;

2. The plug and head are both embedded in plastic. The screw thread also consists of plastic;

3. An additional shield is provided in the electrode head in the form of a metal casing which is arranged coaxially about the two contacts of the electrode head and is electrically connected to the coaxial portion of the coaxial socket; and

4. The connection of the electrode head to the inner conductors thereof is a plug connection.

The plug and screw connection of the present invention is a coaxial one: One of the contacts of the cable plug inserted in a plastic cap, which contact in the cable constitutes a central wire, ends in the plug in a narrow metal casing surrounded by an insulating cover. The second contact of the cable plug forms a wider metal casing which is slid upon this insulating cover.

Correspondingly, one of the contacts in the electrode head consists of a central wire, which at its end is preferably fanned out, so that it clampingly engages the narrow casing of the cable plug, and the second contact consists of a metal casing which is so wide and provided with slots in such a way that the wider casing of the cable plug engages likewise clampingly this casing of the electrode head.

The screw threads provided on the plug and head are of such dimensions that in the manufacture of the connection the contacts described above, of the two parts must first he slid into each other over a certain length, e.g. about 2 mm, before the screw threads engage each other. Then the two parts are screwed together. For sealing purposes an O-ring of rubber or other plastic material is slid upon the outer thread. This O-ring has an outer diameter substantially equal to the outer diameter of the plastic casings of the head and the plug.

The arrangement described above of the contacts and threads, in which the central contact of the plug, shaped as a narrow casing, is slid upon the wire-shaped middle contact of the electrode head, and the casingshaped outer contact of the cable plug is inserted into a wider casing of the electrode head, and in which arrangement further an inner thread cut into the plastic casing of the cable plug is screwed upon an outer thread cut into the electrode head, may be entirely or partially reversed.

A particular characteristic of the present invention is that the electrode head is provided with an electric shield which, in the shape of a thin metallic casing, is mounted coaxially about the two aforementioned terminals of the electrode head. This metal casing abuts on the inside directly to the plastic wall of the electrode head, and in the manufacture of the electrode head the plastic material is suitably injected directly into the metal casing.

A further characteristic of the present invention is that the connection between the contacts of the electrode head and the contact wires issuing from the electrodes proper is a plug connection, that is to say, the contacts of the electrode head end toward the inside in thin slotted metal casings into which the wires issuing from the electrodes are clamped.

The shield casing described above is preferably shaped in such a way that it envelops also this plug connection inside the electrode.

By means of the present invention various advantages are achieved: The combination of a plug connection and screw connection assures a good electrical contact between electrode head and cable plug and a safe damp-proof packing, to which result especially the O- ring contributes, and the long creepage path from the O-ring support by way of the plastic thread to the outer contact assures a safe protection. A liquid-proof closure is of decisive importance for many fields of application of measuring electrodes. For transportation or storing purposes, the plug head may likewise be closed, in a moisture-proof manner, with a closure cap capable of being screwed on. The packing is so good that, when a sufficiently temperature-proof O-ring, eg from silicon plastic of fluorelastomer is used, the packing assures, even in steam sterilization, the required high dielectric resistance in the electrode head. The novel electric shield in the electric head prevents, as already mentioned, outer electrical fields, which may occur when the electrode head is being touched, from changing the measuring potential. The novel plug connection inside the electrode head makes possible an easy assembly of the entire measuring electrode and simplifies electrode manufacture.

The invention may be better understood by reference to the drawings where FIG. 1 is a partially cut away view of a head and FIG. 2 is a partially cut away view of a plug. Referring now to FIG. 1 it can be seen that the head comprises an inner contact 11 in the form of a fanned-out wire which extends toward the inside into a thin casing 12. The latter holds the conductor 20 which is electrically connected to the electrode (not shown). The head it further comprises a contact 13, a metal casing which changes likewise inside the electrode into a thin casing 14 capable of holding the second conductor of the head 10. Between the two contacts 11 and 13, a highly resistive insulator 19 is provided. A metal casing 15 is mounted coaxially about the two contacts ll and 13, which metal casing 15 serves as a shield and is connected in an electrically conductive manner to the outer contact 13. The whole unit is enveloped by a plastic casing 16 having an outer thread 17. An O-ring i8 is slid upon the shoulder between the outer thread 17 and the outer wall of the plastic casing 16.

Referring now to FIG. 2 there is shown a plug 30 comprising an inner contact 21, a narrow metal casing 22 to which the central wire (not shown) of the electrode cable is connected. The outer terminal consists again of a wider metal casing 23 which is electrically connected to the outer conductor of the cable. The whole unit is enveloped by a plastic casing 26 into which the inner thread 27 is cut. Between the two contacts 21 and 23 a highly resistive insulator 29 is inserted. The plastic casing 28 is pressed by the metal part in a packing manner against the upper opening of the plastic casing.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that'variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.

What is claimed is:

1. An electrode comprising:

A. an electrode head comprising:

1. a first contact forming the core of the electrode head comprising a fanned-out wire which ex tends toward the inside of the electrode head into a thin casing;

2. a second contact which is a metallic casing arranged coaxially about the first contact and provided with a slot formed by a thin bent wire extending inside the electrode head into a thin cas- 3. an insulating plastic casing enveloping the whole unit of electrode head comprising an outer thread and a shoulder on an outer wall, and an O-ring upon the shoulder;

4. a highly resistive insulator disposed between the two said contacts;

5. a thin metallic casing electrically connected to the second contact and mounted coaxially about the two said contacts and abutting an inside wall of the plastic casing; and

B. a cable plug comprising:

6. an inner terminal, centrally disposed inside the electrode plug, in the form of a narrow metallic casing that fits into the fanned-out end of the first contact of the electrode head;

7. an outer terminal, arranged coaxially about the inner terminal, having a wider metallic casing extending inside the cable plug;

8. an insulating plastic casing enveloping the entire cable plug comprising an inner thread and a shoulder;

9. a highly resistive insulator disposed between the two said terminals,

wherein means for establishing an electrical connection between said electrode head and cable plug comprising clampingly engaging the two said plastic casings after the following connections take place:

a. the narrow metallic casing of the inner terminal of said cable plug clampingly engaged by the fanned-out end of the first contact of said electrode head,

b. the wider metallic casing of the outer terminal of said cable plug clampingly engaged by the slot provided in the second contact of the electrode head,

c. the inner thread of the insulating plastic casing of the cable plug screws into the outer thread of the insulating plastic casing of the electrode head so that the O-ring of the electrode head rests against the shoulder of said plastic casing of the cable plug.

Claims

1. An electrode comprising: A. an electrode head comprising: 1. a first contact forming the core of the electrode head comprising a fanned-out wire which extends toward the inside of the electrode head into a thin casing; 2. a second contact which is a metallic casing arranged coaxially about the first contact and provided with a slot formed by a thin bent wire extending inside the electrode head into a thin casing; 3. an insulating plastic casing enveloping the whole unit of electrode head comprising an outer thread and a shoulder on an outer wall, and an O-ring upon the shoulder; 4. a highly resistive insulator disposed between the two said contacts; 5. a thin metallic casing electrically connected to the second contact and mounted coaxially about the two said contacts and abutting an inside wall of the plastic casing; and B. a cable plug comprising: 6. an inner terminal, centrally disposed inside the electrode plug, in the form of a narrow metallic casing that fits into the fanned-out end of the first contact of the electrode head; 7. an outer terminal, arranged coaxially about the inner terminal, having a wider metallic casing extending inside the cable plug; 8. an insulating plastic casing enveloping the entire cable plug comprising an inner thread and a shoulder; 9. a highly resistive insulator disposed between the two said terminals, wherein means for establishing an electrical connection between said electrode head and cable plug comprising clampingly engaging the two said plastic casings after the following connections take place: a. the narrow metallic casing of the inner terminal of said cable plug clampingly engaged by the fanned-out end of the first contact of said electrode head, b. the wider metallic casing of the outer terminal of said cable plug clampingly engaged by the slot provided in the second contact of the electrode head, c. the inner thread of the insulating plastic casing of the cable plug screws into the outer thread of the insulating plastic casing of the electrode head so that the O-ring of the electrode head rests against the shoulder of said plastic casing of the cable plug.

2. a second contact which is a metallic casing arranged coaxially about the first contact and provided with a slot formed by a thin bent wire extending inside the electrode head into a thin casing;

3. an insulating plastic casing enveloping the whole unit of electrode head comprising an outer thread and a shoulder on an outer wall, and an O-ring upon the shoulder;

4. a highly resistive insulator disposed between the two said contacts;

5. a thin metallic casing electrically connected to the second contact and mounted coaxially about the two said contacts and abutting an inside wall of the plastic casing; and B. a cable plug comprising:

9. a highly resistive insulator disposed between the two said terminals, wherein means for establishing an electrical connection between said electrode head and cable plug comprising clampingly engaging the two said plastic casings after the following connections take place: a. the narrow metallic casing of the inner terminal of said cable plug clampingly engaged by the fanned-out end of the first contact of said electrode head, b. the wider metallic casing of the outer terminal of said cable plug clampingly engaged by the slot provided in the second contact of the electrode head, c. the inner thread of the insulating plastic casing of the cable plug screws into the outer thread of the insulating plastic casing of the electrode head so that the O-ring of the electrode head rests against the shoulder of said plastic casing of the cable plug.