US3889221A

US3889221A - Protector unit

Info

Publication number: US3889221A
Application number: US447587A
Authority: US
Inventors: Robert Frederick Heisinger
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1974-03-04
Filing date: 1974-03-04
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10
Also published as: CA1035412A

Abstract

A protector unit includes a conductive cage electrically connected to a ground terminal and surrounding a carbon block arrangement. A contoured bimetallic disk contacts an input terminal of the unit and responds to heat generated by excessive currents between the input terminal and an output terminal or the ground terminal by deflecting into engagement with the cage thereby establishing a ground path for the excessive current.

Description

United States Patent Heisinger June 10, 1975 PROTECTOR UNIT 3,743,888 7 1973 Baumbach 3l7/l6 [75] Inventor: Robert Frederick Heisinger,

Parsippany-Troy Hills Township, Primary Examiner-J. D. Miller NJ. Assistant ExaminerFred E. Bell [73] Assignee: Bell Telephone Laboratories, Attorney Agent or Firm-A Hooper Incorporated, Murray Hill, NJ.

[22] Filed: Mar. 4, 1974 [57] ABSTRACT Appl. No.: 447,537

US. Cl. 337/15; 337/l4; 337/33;

337/34 Int. Cl. HOlh 61/00 Field of Search 337/l2, l4, l5, l6, 3l,

References Cited UNITED STATES PATENTS 6/l958 Hasselhorn 337/16 A protector unit includes a conductive cage electrically connected to a ground terminal and surrounding a carbon block arrangements A contoured bimetallic disk contacts an input terminal of the unit and responds to heat generated by excessive currents between the input terminal and an output terminal or the ground terminal by deflecting into engagement with the cage thereby establishing a ground path for the excessive current.

7 Claims, 3 Drawing Figures PATENTEDJUN 10 ms H 8 89 .221

FIG. 3

llllllllllll I llllllllll ll FIG. 2

FIG.

IIIIIIIIIIA r7 I II I III II II II 111! II I11 I PROTECTOR UNIT BACKGROUND ()F 'l HIE INVENTION 1. Field of the Intention This invention relates to protector units. and more particularly to a protector unit utilizing a bimetallic disk as a switch element.

2. Description of the Prior Art Protector units are widely used in the telephone industry for providing voltage and current protection between outside plant conductors and central office equipment. For example. commonly utilized protector units such as the well-known 3A protector unit and the 4A protector unit are mounted on frames within the central office and provide protection for a single outside plant pair of conductors. These protector units normally include a pair of input terminals to which the outside plant pair is connected. a pair of output terminals to which conductors connected to switching equipment or the like are connected. and a ground terminal. A pair of carbon blocks establishes a spark gap between an input terminal and the ground terminal across which any excess voltage appearing on the input terminal is dissipated. Some of these existing units also include means for providing a conductive path for grounding excess currents appearing on the input terminal. In one existing embodiment a grounding pin is held in spaced relationship to one of the carbon blocks by a thin layer of solder within a heat coil. Excess currents appearing on the associated input terminal generate heat in the heat coil or through the carbon blocks which softens the layer of solder thereby allowing the pin to slip through one block and contact the other block to bridge the spark gap and ground the circuit. One major disadvantage of this existing pin-heat coil arrangement is that the solder layer tends to creep or relax over the life of the protector unit and may eventually cause failure of the unit even though no excess current has appeared on the input terminals. Another disadvantage is that it is difficult to control the properties and physical dimensions of the solder layer accurately enough to provide reliable operation of the unit. Another embodiment of existing protector units utilizes a fusible metal disk which holds a conductive cage in spaced relationship to a ground plate. Excess currents through the protector unit cause the metal disk to melt and thereby allow movement of the cage to contact the ground plate. This embodiment as well as the previously discussed pin-heat coil embodiment requires the use of a substantially large spring to bias or urge the grounding pin or cage toward engagement with the carbon block or ground plate. This spring adds substantially to the size of the protector unit. Still another disadvantage of both of these embodiments is the fact that the pin or cage and associated spring must move within the protector housing in order to contact the ground surface. Corrosion products or other contaminants may form on the protector housing. the pin or cage or the associated spring during the extended life of the protector unit. These contaminants then tend to lock up these items and prevent movement thereof which causes the protector unit to fail to perform its required function.

Accordingly. it is an object of this invention to improve protector units to insure satisfactory operation thereof over an extended life.

Another object is to decrease the size of protector units.

Still another object is to reduce the complexity of protector units to provide better control over the functioning thereof.

SUMMARY OF THE INVENTION The foregoing objects and others are achieved in accordance with this invention by a protector unit having a carbon block arrangement establishing a spark gap between an input terminal and a gound terminal. A conductive cage in electrical contact with the ground terminal surrounds the carbon blocks. One carbon block rests against a contoured bimetallic element such as a disk which is in electrical contact with the input terminal so that the bimetallic disk makes no contact with the conductive cage in its normal configuration. The bimetallic disk is responsive to the heat generated by excessive currents through the unit to change its contour and contact the conductive cage thereby establishing a grounding path for the excessive current between the input terminal and the ground terminal. The bimetallic disk is the only moving component of the protector unit and the characteristics of this disk can be very accurately controlled to give very accurate operation of the protector unit. The relatively large spring previously required to actuate the protector unit and accommodate tolerances can be replaced by a very small spring to accommodate tolerances only within the protector unit. Accordingly, the size of the protector unit can be reduced substantially. The bimetallic disk may automatically revert to its original configuration upon removal of the excess current, and thus the protector unit may be reused if desired.

BRIEF DESCRIPTION OF THE DRAWING The invention will be more fully comprehended from the following detailed description and accompanying drawing in which:

FIG. 1 is a broken away front elevation view of a protector unit in accordance with this invention;

FIG. 2 is a broken away side elevation view of the protector unit of FIG. 1; and

FIG. 3 is a partly broken away front elevation view of a second embodiment of the invention.

DETAILED DESCRIPTION Referring now to FIG. 1 there is shown a protector unit [01 comprising a housing 2 and a base 4 which are made of suitable plastic or other insulative materials well known in the art. Base 4 includes two pairs of pins such as

line pins

6A and 6B and central office pins 8A and 83 extending therefrom.

Pins

6A and 8A might. for example. be associated with the ring conductor and pins 6B and 88 might be associated with the tip conductor of a telephone pair. Base 4 also includes a ground pin 10 extending therefrom.

Pins

6A and 6B are connected to respective line plates 12 and 13 by respective straps 14. Heat coil terminals 20 and 21 having

respective heat coils

22 and 23 thereon establish paths between line plate 12 and I3 and

output pins

8A and 8B. respectively.

Line plates 12 and 13 contact the end of respective

carbon block arrangements

24 and 26.

Carbon block arrangements

24 and 26 are well known in the art and advantageously comprise two carbon blocks arranged in an end-to-end configuration and surrounded by a ceramic sleeve.

Carbon block arrangements

24 and 26 include spark gaps as is well known in the art. Conductive cages 28 and 30 surround

carbon block arrangements

24 and 26, respectively. and are connected to ground plate 16 by

springs

32 and 34, respectively. Ground plate 16 is connected to ground pin by a conductive strap 18.

Contoured

bimetallic disks

36 and 38, respectively, are mounted between line plates 12 and 13 and

carbon block arrangements

24 and 26.

Bimetallic disks

36 and 38 are formed by sandwich construction of two materials having different coefficients of expansion. Accordingly, the contour of these disks will change when their temperature changes as is known in the art.

Disks

36 and 38 present a convex contour to

carbon block arrangements

24 and 26, respectively in their normal configuration. The

fingers

29 and 31 of cages 28 and 30, respectively, are shorter than the length of

carbon block arrangements

24 and 26. Accordingly in their

normal configuration disks

36 and 38 do not contact cages 28 and 30.

If an excess voltage appears on either line pin 6A or 68 such voltage will be transmitted through the respective

carbon block arrangements

24 or 26 and springs 32 or 34 to ground terminal 16 as is known. A portion of the currents generated by such excessive voltage and appearing in either the talking path, i.e., the path between 21 line pin and a central office pin. or the sparking path. i.e., through the carbon block arrangements. of unit 101 will be converted to heat. For example, currents through the talking paths are converted to heat in heat coils 22 and 23 while the spark currents generate heat in associated

carbon block arrangements

24 and 26, respectively. A portion of this heat will be transferred to

bimetallic disks

36 and 38 causing these disks to change contour. if the amount of heat transferred to

disks

36 and 38 exceeds a predetermined threshold level these disks will change contour sufficiently to establish contact with respective cages 28 and 30 as shown in phantom for disk 38 to FIG. 1. This threshold level of heat is chosen to correspond with the maximum allowable currents through unit 101. When

disk

36 or 38 establishes contact with its respective cage 28 or 30 a ground path for grounding the excess current is established through straps 14, plates 12 or 13, cage 28 or 30

spring

32 or 34 to ground plate 16 for a respective one of input terminals or line pins 6A or 6B. If desired the contour of the bimetallic element can be designed to provide a snap action" change in contour.

When the excess current is removed from the protected line, i.e.. when the excessive voltage is removed. the heat generated is reduced and the contour of

disk

36 or 38 reverts to its original configuration. This interrupts the grounding path and allows the protector unit to remain in service.

It should be apparent from the foregoing description that the only moving parts in protector unit 101 are the bimetallic disks. The movement of these disks is in the form of a change in contour. Therefore. there is little likelihood of this movement being prevented by corrosion or other contaminants appearing within the protector unit.

Since cages 28 and 30 are not required to move within protector unit 101 the size of

springs

32 and 34 can be greatly reduced as compared with the springs utilized in the present unit. The primary function of

springs

32 and 34 is to provide a conductive path and to compensate for tolerances within the other components. Accordingly, these springs can be made quite short and small. The indicated coil springs could be replaced by a single leaf spring or cantilever spring which is mounted to ground plate 16 in the center thereof and which contacts respective cages 28 and 30 on the ends thereof.

The composition and physical dimensions of

disks

36 and 38 can be controlled very accurately thereby providing very accurate operation of protector unit 101. Accordingly high reliability of operation for

disks

36 and 38 can be readily obtained for very extended lifetimes.

FIG. 3 indicates a second embodiment of a protector unit 102 having a reset feature which insures the return of

disks

36 and 38 to their original positions after operation of unit 102. Such a feature advantageously might be employed where it is intended to utilize protector unit 102 repeatedly. In this embodiment cage 50 is extended in length to directly contact ground plate 16. Spring 32 is mounted within cage 50 between the end thereof and the top of carbon block arrangement 24.

Openings

52 and 54 are formed through housing 2 and ground plate 16, respectively. A button or plunger 56 is slidably mounted in holes 52 and S4 in engagement or contact with cage 50. Depression of plunger 56 moves cage 50 along carbon block arrangement 24 until fingers 51 contact the outer periphery of disk 36 forcing disk 36 toward its original convex configuration with respect to carbon block arrangement 24. When the operating force is released from plunger 56 spring 32 returns cage 50 to its original position out of contact with disk 36.

While the invention has been described with respect to specific embodiments thereof it is to be understood that various modifications thereto might be made by those skilled in the art without departing from the spirit and scope of the appended claims. For example. heat coils 22 and 23 could readily be replaced by other resistive heat generating means or the heat could be generated by the resistance of the bimetallic element itself. The layout of the parts within protective unit 101 can be changed without departing from the principles of operation described in the foregoing.

What is claimed is:

l. A protector unit comprising an input terminal, an output terminal, a ground terminal, a carbon block means for shunting voltages exceeding a preselected voltage level on said input terminal to said ground terminal, and a cage of conductive material about said carbon block means in electrical contact with said ground terminal and adapted for providing a current path between said input terminal and said ground terminal, said path normally being in an open condition, CHARACTERIZED lN THAT:

said unit includes a bimetallic disk in electrical contact with said input terminal and responsive to currents through said input terminal in excess of a preselected current level to deflect into engagement with said cage to close said path.

2. Apparatus in accordance with claim 1 including heat generating means between said input terminal and said output terminal and responsive to currents between said input and output terminals for generating heat proportional to the level of said currents whereby said bimetallic disk is responsive to currents between said input terminal and said output terminal or said ground terminal for closing said path.

3. Apparatus in accordance with claim 2 wherein said heat generating means comprises a coil of resistance wire.

4. Apparatus in accordance with claim 1 wherein said bimetallic disk comprises a contoured disk having a first surface contacting said carbon block means on a first end thereof. said first surface comprising a convex surface in its normal configuration with respect to said carbon block means. said cage having a recessed end with respect to said first end of said carbon block means to prevent contact with said disk in said normal configuration. said disk being responsive to said currents to change said convex surface to a concave surface which contacts said recessed end of said cage and closes said path between said input terminal and said ground terminal.

5. Apparatus in accordance with claim 4 including means for resetting said disk to said normal configuration after said current is removed.

6. Apparatus in accordance with claim 5 wherein said resetting means comprises a plunger contacting said cage on the end thereof opposite said recessed end, said plunger being responsive to a force thereon to move said cage with respect to said carbon block means and apply a force to said disk.

7. A protector unit comprising in combination:

a housing;

a base adapted for mating with said housing. said base including at least one of each of input. output and ground terminals;

signal transmitting means between said input terminal and said output terminal for transmitting signals therebetween;

a carbon block arrangement including a spark gap betweeen saidinput terminal and said ground terminal for shunting voltages on said input terminal which exceed a preselected threshold voltage to ground; and

a normally open-circuit conductor means in parallel with said carbon block arrangement between said input and said ground terminals, said conductor means including a bimetallic disk and a cage of conductive material about said carbon block arrangement and having a recessed end with respect to a first end of said carbon block arrangement, said bimetallic disk having a convex surface in its normal configuration electrically contacting said first end and electrically insulated from said recessed ends, said disk being responsive to currents through either said signal transmitting means or said carbon block arrangement to change said convex surface to a concave surface which contacts said recessed end to close said conductor means and ground said input terminal when said currents exceed a preselected threshold.

Claims

1. A protector unit comprising an input terminal, an output terminal, a ground terminal, a carbon block means for shunting voltages exceeding a preselected voltage level on said input terminal to said ground terminal, and a cage of conductive material about said carbon block means in electrical contact with said ground terminal and adapted for providing a current path between said input terminal and said ground terminal, said path normally being in an open condition, CHARACTERIZED IN THAT: said unit includes a bimetallic disk in electrical contact with said input terminal and responsive to currents through said input terminal in excess of a preselected current level to deflect into engagement with said cage to close said path.

4. Apparatus in accordance with claim 1 wherein said bimetallic disk comprises a contoured disk having a first surface contacting said carbon block means on a first end thereof, said first surface comprising a convex surface in its normal configuration with respect to said carbon block means, said cage having a recessed end with respect to said first end of said carbon block means to prevent contact with said disk in said normal configuration, said disk being responsive to said currents to change said convex surface to a concave surface which contacts said recessed end of said cage and closes said path between said input terminal and said ground terminal.

7. A protector unit comprising in combination: a housing; a base adapted for mating with said housing, said base including at least one of each of input, output and ground terminals; signal transmitting means between said input terminal and said output terminal for transmitting signals therebetween; a carbon block arrangement including a spark gap betweeen said input terminal and said ground terminal for shunting volTages on said input terminal which exceed a preselected threshold voltage to ground; and a normally open-circuit conductor means in parallel with said carbon block arrangement between said input and said ground terminals, said conductor means including a bimetallic disk and a cage of conductive material about said carbon block arrangement and having a recessed end with respect to a first end of said carbon block arrangement, said bimetallic disk having a convex surface in its normal configuration electrically contacting said first end and electrically insulated from said recessed ends, said disk being responsive to currents through either said signal transmitting means or said carbon block arrangement to change said convex surface to a concave surface which contacts said recessed end to close said conductor means and ground said input terminal when said currents exceed a preselected threshold.