US2295602A

US2295602A - Switching device

Info

Publication number: US2295602A
Application number: US402727A
Authority: US
Inventors: Jr Charles E Pollard
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1941-07-17
Filing date: 1941-07-17
Publication date: 1942-09-15
Anticipated expiration: 1959-09-15
Also published as: FR938833A; GB553329A

Description

Sept. 15, 1942. v c. E. POLLAR D, JR 2,295,602

' SWITCHING DEVICE Filed July 17, 1941 IN 5 N TOR By c. 5. POLL/1RD, JR.

ATTORNEY Patented Sept. 15, 1942 SWITCHING DEVICE Charles E. Pollard, Jr., Hohokus, N. J assignor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application July 17, 1941, Serial No. 402,727

7 Claims.

This invention relates to electrical switching devices and relays and, more particularly, to those in which a conducting liquid, such as mercury, is used as the contact making medium.

The object of the invention is to render devices of this type capable of producing slow-make and quick-break, quick-make and slow-break, slow-make and slow-break or continuity contact closures.

It is well recognized that mercury has distinct advantages over solid elements as the contact making medium for electrical circuits. For instance, a body of mercury presents a fresh surface for each successive contact closure and is not subject to the pitting and corroding effects that gradually reduce the usefulness of solid contact elements. With these advantages in view, several forms of mercury switches have been devised in the past. These generally fall into one or the other of two classes. In one of these classes the container is tilted or otherwise moved to cause the body of mercury within it to shift in position thus opening or closing the desired connection. In the other class, an armature or other movable element is forced into a pool of mercury, the free surface of the mercury being displaced into engagement with circuit making contacts. In either case, it is necessary to move all or a considerable part of the mercury mass into a position in which itphysically engages or disengages the desired contact or contacts.

In many circuits, it is often required that normally open relay contacts shall be slow to close after the relay winding becomes energized and quick to open following the deenergization of the relay winding or that a normally open relay contact shall be quick to close after the relay winding becomes energized and slow to open following the deenergization of the relay winding or, in other cases, slow both to close and open. Furthermore, continuity contacts are often required which will enable a circuit transfer to be effected without any interruption.

In accordance with Patent No. 2,247,493, granted July 1, 1941, to Mr. H. C. Harrison and to me, certain advantages over prior mercury contact devices were achieved by means of a switch in which the stationary contacts were of solid material and in which circuits were either made or broken between such contacts by a globule of mercury carried upon and movable by a magnetically actuated armature. The structure of this switch could be altered as disclosed in such patent to provide contact closures and openings having different time characteristics. This structure did not, however, lend itself readily to the securing of time delays either in making or breaking a contact closure of any appreciable duration nor did it lend itself to the securing of continuity contact closures.

It is therefore the object of the present invention to improve switching devices of this character whereby longer delay intervals may be measured and whereby continuity contact closures may be effected in a simple and reliable manner.

In accordance with the present invention, the switch element comprises an envelope of glass or other suitable material through the upper end of which a front contact member and a back contact member depend, each having a horizontally disposed contact portion between which the contact portion of a movable contact member is operable. The movable contact member comprises a pair of parallel wires extending vertically into a pool of mercury in the bottom of the envelope and secured to the inner surface of a hollow cylindrical armature which floats with its lower end partially submerged in a pool of mercury. Mercury from the pool is conducted by capillary action along the wires of the movable contact member to the contact portion thereof and is transferred by the engagement of such contact portion with the contact portions of the front and back contact members to the latter contact portions. The armature cylinder is surrounded by a stationary cylinder or guide sleeve having its lower end immersed in the pool of mercury and supported by a terminal lead which is sealed through the lower end of the envelope. The guide sleeve and armature being made of a material wettable by mercury, the mercury enclosed between the sleeve and armature and within the armature positions the armature with the contact portion of the contact member carried thereby held firmly in engagement with the contact portion of the back contact member.

The contact portion of the movable contact member is widened out to provide upper and lower surfaces for increasing the area of the mercury film adhering thereto and the contact portions of the front and back contact members may be made narrow to decrease the area of the mercury film adhering thereto if a quick break of the mercury film formed between such portions and the contact portion of the movable contact member is desired, or such contact portions may be widened to increase the area of the mercury film adhering thereto if a slow break of the mercury film formed between such portions and the contact portion of the movable contact member is desired. In this manner a switch element may be made slow to make a front contact closure and fast to break such closure, fast to make a front contact closure and slow to break such closure or slow both to make and break a front contact closure. Delays of several seconds duration may be secured with switch elements of this type and quick recycling is assured.

With this contact structure, it is possible by decreasing the spacing between the contact portions of the front and back contact members and by providing all of the contact portions with widened surfaces, to enable the movable contact member to establish a front contact closure before the mercury film between the contact por tion of the movable member and the contact portion of the back contact member becomes disrupted whereby a continuity contact closure is effected.

Furthermore, if the bottom of the armature cylinder is closed except for a small opening, it is possible to further delay the movement of the armature contact member in both its attractive and retractive operations whereby delay intervals of several seconds may be obtained, since the attractive movement of the armature is restrained by the weight of the mercury enclosed therein and such mercury can run out of the armature through the opening only at a slow :1;

rate as the armature is lifted and on its retractive movement the armature can settle down into the mercury pool only at the slow rate at which the mercury can reenter through the opening into the armature.

For a clearer understanding of the invention reference may now be had to the following detailed description thereof taken in connection with the accompanying drawing in which:

Figs, 1 and 2 are side views partly in cross section of a relay switch element in accordance with the present invention which is rendered slow to make and slow to break its front contact closure, Fig. 1 being a front view of the element and Fig. 2 being a side view thereof;

Fig. 3 is a cross-sectional view taken along the section line 3-3 of Fig. 2;

Fig. 4 is a view of the upper end of a switch element with its contacts constructed to effect a fast front contact closure but a slow break of such closure;

Fig. 5 is a view of the upper end of a switch element with its contacts constructed to effect a slow front contact closure but a fast break of such closure; and

Figs. 6A, 6B and 60 show the successive operating stages of contacts of the type disclosed in Figs. 1 and 2 arranged to effect a continuity contact closure.

While the invention is not limited to a switch of any given size or proportion, it may be noted that the switch or relay in accordance therewith is particularly useful in electrical systems where relatively small currents are involved, such for example, as currents of the order generally used energizing coil (not shown), such a magnetic circuit being disclosed, for example, in the patent hereinbefore referred to.

Positioned within the envelope is a cylindrical guide sleeve 4 entirely open at its upper end and partially closed at its lower end to add rigidity thereto and supported on and secured to the upper end of terminal wire 5. The wire 5 is sealed through the bottom of the envelope I. The guide sleeve 4 is made of a material, such as nickel, which is wettable by mercury. Sealed through the upper end wall of the envelope are two paralielly disposed

contact members

6 and 1 having their ends which extend into the envelope bent at right anlges toward each other to form two stationary contact portions 9 and 8, the upper one of which serves as a front contact and the lower one 9 of which serves as a back contact.

Movable within the guide sleeve 4 is a cylindrical tubular armature III, the upper end of which is entirely open and the lower end of which is closed except for the small opening ii therein. The armature is made of magnetic material but its surfaces are such that they are readily wetted by mercury. Secured to the inner surface of the armature is a movable contact member l2 which may be formed by doubling a length of wire, bending the looped end at right angles and flattening the same to provide a widened contact portion l3 for engagement with the contact porons 3 and 9 of the front and back contact members and G. A contact of this type has the property of conducting mercury along the capillary ducts formed therein to its upper contact portion from which a small amount of mercury is transferred to the surfaces of the contacts with which it cooperates,

To complete the switch element a measured amount of mercury I4 is deposited in the bottom of the envelope and the envelope is then evacuatod and refilled with a gas, such as hydrogen, to a required operating pressure. With the measured amount of mercury in the envelope the mercury rises within the guide sleeve 4 and within the tubular armature III to the positions illustrated in Figs. 1 and 2 and the mercury is also conducted by the capillary action of the inner surface of the guide sleeve 4 and the outer surface of the armature I0 to fill the entire space between such surfaces. The surface tension of the mercury between the upper edges of the guide sleeve 4 and armature l0 and the surface tension of the mercury within the armature exerts a downward pull upon the armature to normally hold the contact portion 13 of the armature contact member l2 firmly against the contact portion 9 of the back contact member 6. The mercury within the armature also engages the lower end of the contact member 12 whereby mercury is carried along such member to its upper contact portion l3 and in the normal position of the armature to the contact portion 9 of the back contact member 6 thereby establishing a mercury contact between the contact portions l3 and 9 and thus between the terminal wire 5 and the back contact member 6.

By referring to Fig. 3 it will be noted that the contact portions 8, 9 and I3 all have wide surfaces for increasing the area of the mercury film adhering thereto and thus delaying the disruption of the film of mercury enclosed between the contact portions 9 and I3 in the normal position of the armature l0 upon the attractive movement of the armature, and delaying the disruption of the film of mercury enclosed between the contact portions I3 and 8 in the fully attracted position of the armature upon the retractive movement of such armature.

If now the relay coil is energized to establish a difference of magnetic potential between the pole-

piece plates

2 and 3, the armature I!) will attempt to rise within the guide sleeve 4 to center itself within the magnetic field thus created but will be restrained in such movement by the surface tension of the mercury pool, by the surface tension of the film of mercury between the contact portion I3 of the armature contact member I2 and the contact portion 9 of the back contact member 6 and by the weight of the mercury within the armature. If the energization of the relay coil is continued, the armature I will slowly rise as the mercury runs out of it through the opening I I and mercury will be drawn up the ducts of the member I2 to increase the amount of mercury in the film between the contact portions 9 and I3 until sufficient mercury will have run out of the armature to permit the contact portion I3 of the armature contact member to move away from the contact portion 9 of the back contact member 6 sufficiently to disrupt the mercury film between them, thus opening the back contact closure of the switch element. When the mercury film breaks the excess mercury in the film will run back down the ducts of member I2 into the pool I4. The armature It will then continue its upward movement until the contact portion I3 of its contact member engages the contact portion 8 of the front contact member I thereby effecting a delayed front contact closure. This delayed closure may, for example, be effective up to thirty seconds following the energization of the relay coil.

Upon the deenergization of the relay coil, the surface tension of the mercury pool tends to pull the armature I0 back into its normal or retracted position and as the armature moves downwardly mercury flows back at a slow rate through the opening II into the armature, the retractive movement of the armature being restrained by .such rate of fiow of the mercury through such opening. As the contact portion I3 of the armature contact member I2 moves downwardly away from the contact portion 8 of the front contact 7 member I, the film of mercury between such contact portions is supplied by mercury drawn up the ducts of the member I2 and the film is drawn out thereby retaining the front contact closure until such film finally is disrupted. The excess mercury in the film then runs back down the ducts of the member I2 into the pool I4. When the armature reaches its normal position the back contact closure again becomes established. A delayed breaking of the front contact closure is thereby effected, which delay may also be of several seconds duration.

A delay in the establishment of the front contact closure of several seconds may thus be obtained particularly if the energization of the relay coil is intermittent and of such a periodicity that between successive energizations the armature I0 has sufficient time to become retracted to a less degree than the attractive movement in response to the preceding impulse. In this manner the armature of the switch element in effect advances in its attractive movement step by step and is tuned to the periodicity of the energizing current to establish a front contact closure after i If a quick recycling of the switch element is required, the bottom wall of the armature I0 may be omitted and the upper end of the armature may be formed with an inturned rim to render it more rigid as disclosed in Figs. 4 and 5.

The switch element partially disclosed in Fig. 4 has the contact portion I3 of its armature contact member I2 widened, has the contact portion 8 of its front contact member I also widened but the contact portion 9' of its back contact member 6 is not widened. With this contact structure, when the armature is moved in its attractive movement, the film of mercury between the contact portion 9 of the back contact member and the contact portion I3 of the armature contact member will disrupt quickly since the crosssectional area of the film adjacent to the contact portion 9 will be small and the armature having no further restraint against its movement except the surface tension of the mercury pool in which it is partly immersed, will move the contact portion I3 of the contact member I2 quickly into engagement with the contact portion 8 of the front contact member I. When the operating winding of the relay becomes deencrgized, since the contact areas of the contact portions 8 and I3 are both large, the film of mercury between them will persist unbroken due to mercury drawn into the film up the ducts of the member I2 while the armature moves in its retractive movement under the influence of its weight and the surface tension of the mercury pool until the film finally breaks, whereupon the contact portion I3 snaps quickly into engagement with the contact portion 9 of the back contact member 6. The snap action reduces the tendency to produce an arc when the contact portions separate. This switch element, therefore, effects a quick make and a slow break of its front contact closure. The delay in breaking the front contact closure may be in the order of several seconds.

The switch element partially disclosed in Fig. 5 has the contact portion I3 of its armature contact member I2 widened, has the contact portion 9 of its back contact member 6 also widened, but the contact portion 8 of its front contact member "I is not widened. With this contact structure, when the armature is moved in its attractive movement, the film of mercury between the contact portion 9 of the back contact member 6 and the contact portion I3 of the armature contact member I2 will be drawn out, but, due to its relatively large cross-sectional area, will not become disrupted for an interval which may be of several seconds duration, and, consequently, a slow make of the closure between the contact portion I3 of the armature contact member and the contact portion 8 of the front contact member 'I will be effected. When, however, the mercury film does break, the contact portion I3 snaps into engagement with the contact portion 8. .When the operating winding of the relay becomes deenergized and the contact portion I3 of the armature contact member I2 starts to move away from the contact portion 8 of the front contact member I the film of mercury between such contact portions will become disrupted quickly since it will have a small crosssectional area adjacent to the contact portion 8. This switch element, therefore, effects a slow make and a quick break of its front contact closure.

If a switch element of the type disclosed in Figs. 1 and 2 but with the lower end of its armature I entirely open, has the contact portions 8 and I3 of its front and back contact members spaced nearer to each other, it is possible to secure a continuity closure action as illustrated in Figs. 6A, 6B and 6C. Fig. 6A shows the normal position of the contact members of the switch element in which the contact portion l3 of the movable contact member [2 is engaged with the contact portion 9 of the back contact member 6 through a film of mercury. When the relay coil becomes energized and the armature moves upwardly in its attractive movement, the contact portion l3 of the armature contact member [2 moves away from the contact portion 9 of the back contact member 6 thereby drawing out the film of mercury which interconnects them as disclosed in Fig. 63, until the portion l3v approaches near enough to the contact portion 8 of the front contact member 1 to become connected therewith through a film of mercury.

At that instant, the three contact members are interconnected. Upon the further attractive movement of the armature, however, the film of mercury between the contact portions 9 and I3 becomes disrupted and the contact closure between the contact portions l3 and 8 through the mercury film enclosed between them becomes more firmly established as illustrated in Fig. 60. Thus a continuity transfer is effected from the back contact member 8 to the front contact member 1. Obviously, a similar but reverse transfer is effected upon the retractive movement of the armature.

What is claimed is:

1. In an electric switch, an envelope having a pool of mercury therein, a tubular armature movable within said envelope having its lower end immersed in said mercury, a contact member carried by said armature, other contact members for engagement by said armature contact member, said contact members all having widened contact surfaces to which mercury easily adheres, and electromagnetic means for moving said armature to disengage its contact member from one of said other contact members and to engage it with the other of said contact members, whereby due to the adherence of mercury to the contact surfaces thereof, said three contact members become momentarily bridged by films of mercury during the movement of said armature contact member.

2. In an electric switch, an envelope having a pool of mercury therein, a tubular armature movable within said envelope having its lower end immersed in said mercury, a contact member carried by said armature, front and back contact members for engagement by said armature contact member, said contact members all having widened contact surfaces to which mercury easily adheres, and electromagnetic means for moving said armature to move its contact member away from said back contact member thereby drawing out the film of mercury enclosed between them and to move its contact member towards said front contact member until a film of mercury is formed between them, whereby said three contact members become momentarily joined by said films of mercury until said first film becomes disrupted upon the termination of the attractive movement of said armature.

3. In an electric switch, an envelope having a pool of mercury therein, a tubular armature movable within said envelope having its lower end immersed in said mercury, a contact member carried by said armature, front and back contact members for engagement by said armature contact member, said contact members all having widened contact surfaces to which mercury easily adheres, and electromagnetic means for moving said armature, said armature upon its retractive movement moving its contact member away from said front contact member thereby drawing out the film of mercury enclosed between them and moving its contact member towards said back contact member until a film of mercury is formed between them whereby said three contact members become momentarily joined by said films of mercury until said first film becomes disrupted upon the termination of the retractive movement of said armature.

4. In an electric switch, an envelope having a pool of mercury therein, a tubular armature movable within said envelope having its lower end immersed in said mercury, a contact member carried by said armature, front and back contact members for engagement by said armature contact member, said contact members all having widened contact surfaces to which mercury easily adheres, and electromagnetic means for moving said armature to move its contact member away from said back contact member thereby drawing out a film of mercury between them until it becomes disrupted just prior to the engagement of said armature contact member with said front contact member, and whereby upon the retractive movement of said armature, the film of mercury between said armature contact member and said front contact member is drawn out until it becomes disrupted just prior to the engagement of said armature contact member with said back contact member thereby effecting a slow make of the front contact closure and a slow break thereof.

5. In an electric switch, an envelope having a pool of mercury therein, a tubular armature movable within said envelope having its lower end wall closed except for a small opening therethrough and immersed in said mercury, a contact member carried by said armature, front and back contact members for engagement by said armature contact member, said contact members all having widened contact surfaces to which mercury easily adheres and electromagnetic means for moving said armature at a speed determined by the outflow of mercury from said armature through said opening for moving its contact member away from said back contact member thereby drawing out the film of mercury between them until it becomes disrupted just prior to the engagement of said armature contact member with said front contact member, and whereby upon the refractive movement of said armature at a speed determined by the inflow of mercury thereinto through said opening, the film of mercury between said armature contact member and said front contact member is drawn until it becomes disrupted just prior to the engagement of said armature contact member with said back contact member thereby effecting a slow make of the front contact closure and a slow break thereof.

6. In an electric switch, an envelope having a pool of mercury therein, a tubular armature movable within said envelope having its lower end immersed in said mercury, a contact member carried by said armature, front and back contact members for engagement by said armature contact member, said armature and front contact members having widened contact surfaces and said back contact member having a narrow contact surface to which surfaces mercury easily adheres, and electromagnetic means for moving said armature to move its contact member into engagement with said front contact member thereby quickly disrupting the film between said armature contact member and said back contact member, and whereby upon the retractive movement of said armature, the film between said armature contact member and said front contact member is drawn out until it becomes disrupted just prior to the engagement of said armature contact member with said back contact member thereby effecting a quick make of the front contact closure and a slow break thereof.

7. In an electric switch, an envelope having a pool of mercury therein, a tubular armature movable within said envelope having its lower end immersed in said mercury, a contact member carried by said armature, front and back contact members for engagement by said armature contact member, a plurality of said contact members having widened contact surfaces to which mercury easily adheres and electromagnetic means for moving said armature to move its contact member away from said back contact member into engagement with said front contact member thereby drawing out a film of mercury between said armature contact member and said back contact member and whereby upon the retractive movement of said armature contact member, the film of mercury between the armature contact member and said front contact member is drawn out, the degree to which each film is drawn out and consequently the time elapsing before its disruption being dependent upon the comparative areas of the contact members between which the film is established.

CHARLES E. POLLARD, JR.