US2244955A - Electric sign contact - Google Patents

Description

' June 10, 1941, J, E, LONG 2,244,955

I ELECTRIC SIGN CONTACT Filed Dec. s, 1938 ooooooooooooos llllii' I "915 J66 E.: A an;

Patented June 10, 1941 UNITED srn'rss ar n' c rcles ELECTRIGSIGN CONTACT John E. Long, Portland, Greg. Application December 3, 1938, Serial No. 243,688

(01. amp-4e) 2 Claims.

The object of my invention is to provide an improved electrical contact which is particularly adapted for use in the control mechanism for intermittent electric signs. For this purpose itis necessary to open and close electric circuits r'apidly, and it has heretofore been found that said opening and closing can best be accomplished by means of mercury contacts. This type of makeand-break is not so abrupt as to cause radio interference, and other deleterious effects of sparking are thereby minimized.

In that type of electric sign wherein moving letters are formed by lighting certain lamps while others remain dark in the background, it has been customary to arrange a plurality of contacts on a small panel forming the bottom or floor of a mercury tank. One side of each lamp is then connected to a separate contact, and the other side of all of said lamps are connected, thru a suitable source of power, to the mercury in said tank. A tape, usually'made of paper, isthen moved along the bottom of said tank between the mercury and the contacts. Said tape separates the mercury and the contacts, thus opening the circuits and preventing the lighting of the lamps, except where small holes have been punched in said tape. These small holes are arranged in the form of letters, or other desired configurations, to be displayed on the sign; and, as the tape moves on to successive contacts, the letters move along to successive lamps. It is thus possible to spell out words by a succession of moving letters, and the sign is ordinarily long enough that several words are visible at once.

My invention is particularly directed to overcoming the difficulty that has been encountered with the contacts that extend thru the bottom panel of the mercury tank hereinbefore described. In order that the circuit shall be opened and closed thru mercury to mercury, rather thru mercury to some other metal, the aforesaid apparatus is arranged so that a small particle of mercury lies on top of the contact, and the circult is made and broken between this small particle and the main body of mercury in the tank.

The difiiculty ordinarily encountered is that of making contact between this small particle of mercury and the contact that is inserted thru the bottom panel.

The material that is ordinarily used for such contacts is copper, and this material is'peculiarly adapted for use in this structure wherein there is no arcing to the contact and no mechanical friction thereon. C pper amalgamates readily with mercury,

than 4 and the electrical current then flows from the copper contact to a thin layer of amalgain, thence to the small particle of mercury, thence, when a hole in the tape is over the contact, to the main pool of mercury and around the circuit. The said layer of amalgam is desired for reasons hereinafter set forth.

' It would seem that, in the aforesaid service, the copper contact would not wear out, but would last indefinitely. However, it has been found that such is not the case, and ordinary copper contacts are short lived. Furthermore, said wear occurs in such a way that the operation of the contact is unsatisfactory after a short time. The aforesaid wearing away of copper contacts seemingly is caused by the action of mercury and some chemical within the Bakelite, or other insulating material of which the bottom panel is made, or within the paper tape used immediately above the contact. Said chemical may react with copper or amalgam. In either case, it has been observed that copper contacts wear away more rapidly when used in Bakelite and other phenolresin panels than when used in some forms of fiber panels, which fiber panels, however, are not satisfactory for other reasons. Also, said copper contacts seemingly wear faster when paper tape is used than when Celluloid is used.

In some cases, copper contacts have worn away to such an extent that the mercury has leaked out'of the tank around them. However, in most cases the life of the copper contacts has been limited by the difiiculty in keeping them clean. This difficulty is caused by the shape to which the copper contact wears, said shape being invariably convex. That is, the outside of the electrode wears away more rapidly than the core portion, leaving an annular cavity around the top of the contact in which dirt accumulates. It is difficult to clean this dirt out, and unless it is cleaned out it interferes with the electrical contact between the copper and mercury or amalgam.

There are various other metals that will not be worn away, when used for contacts, as copper is. Nickel is an example of these noncorrosive metals. But nickel can not be satisfactorily used for the main body of the contacts because it does not amalgamate noticeably with mercury, and a layer of amalgam seems necessary for good elec trical conductivity. With clean mercury, nickel contacts give satisfactory operation for a short time. Then the surface of the nickel becomes slightly corroded, or a layer of dirt accumulates thereon, and the electrical conductivity becomes so low as to interfere with the operation of the lamps. A far greater accumulation of dirt would not interfere with copper contacts because of the layer of amalgam formed thereby.

The decreased electrical conductivity of nickel contacts, or contacts made of other metal that does not readily amalgamate with mercury, is objectionable because of the energy loss at the contacts and because of the ineflicient operation of theJamps at subnormal voltage. But there is a more serious result peculiar to this particular device. After the circuit is opened so there is no more heating eflect of the electric current, the filament of the lamps remains hot for a short period of time, and the light therefrom graduallydies out. When letters move across the sign, due

to difierent lamps being lighted, they appear to leave a tail behind them due to this residual glow of the lamps just previously lighted. If the lamps are brightly lighted by having full voltage applied to them, this residual glow is not very noticeable. On the other hand, if the voltage applied to the lamps is low due to the poor conductivity of the nickel contacts, the brightness of the filaments is reduced much more than in direct proportion to the reduction of voltage and the residual glow, which is only slightly decreased by the lower voltage, becomes conspicuous. Thus, the tailing effect which may be barely noticeable with-copper contacts becomes very objectionable when nickel contacts are used. 1

I have found that all of the advantages of copper contacts can be retained, without any of the disadvantages thereof, by the use of compositecontacts having a copper. core and a shell made of nickel or similar material. Instead of wearing away to form a convex point, like copper does, such a composite contact wears to aconcave poirit, that is, a small crater forms on the top of. the contact. This crater does not continue to wear away; it wears only to a certain depth and then seemingly remains unchanged indefinitely. The crater will have a layer of amalgam at its bottom, and, on top of this, a small particle of mercury.

The crater formed in the top of a composite contact is, to a large extent, self-cleaning. The action of the tape moving thru the mercury tends to scrape foreign matter out of said crater. This is thereverse of the result with the convex points of copper contacts in which the accumulated dirt is scrubbed into the deeper marginal depressions from which it is difficult or impossibleto be removed. Thus,-the composite contacts have the advantages of copper contacts in that they have a layer of amalgam to assure good conductivity with the mercury, and they have the further advantage, unique in themselves, because of said protective nickel sheathing, of forming a crater at their top which is largely self-cleaning. If it becomes necessary to clean the dirt out of said craters, this is easily done.

Other objects and advantages of my invention will be described with reference to the accompanying drawing in which:

Fig. 1 is a longitudinal vertical section thru a control box, together with a more or less diagrammatic view of an electric sign adapted for use therewith, portions of the electrical circuit being shown schematically;

Fig. 2 is an enlarged fragmentary view of the end portion of the control box of Fig. 1 showing details thereof;

Fig; 3 is an enlarged fragmentary detail View showing a new contact embodying my invention in position in the control box of Fig. 2, the circuit being shown closed;

visible.

Fig. 4 is a view similar to Fig. 3, showing a contact that has been worn by use;

Fig. 5 is a view similar to Fig. 4, the circuit being shown open'f and,

Fig. 6 is an enlarged fragmentary detail view showing a worn copper contact not provided with a shell in position in a control box, the circuit being shown closed.

A common type of electric sign is shown at I, Fig. 1, having a plurality of lamps 2 distributed more or less uniformly over a rectangular area on which letters or other configurations are to be One side of each lamp is electrically connected to a metallic copper face plate through binding post 3 thence to one side of alternating current generator 4. The other side of generator 4 is connected to binding post 5 which extends thru the ends of tank 1 into mercury 8. Each of wires 9 is connected to the other side of one of lamps 2 and to contacts I0. Thus when a contact I0 makes contact with mercury 8, the circuit is completed thru the corresponding lamp and generator 4 and the lamp is thereby lighted.

It will be understood that any suitable source of power, such as the ordinary transmission line, might be substituted for generator 4, and various combinations of series or parallel groups of lamps might be operated thru a single contact. The electric sign hereinbefore described doesnot form part of my invention; it is illustrated and described to show the use for my invention, for which it was particularly devised, and the problems involved therein. Said sign and electric wiring connected there-to are not shown in detail and reference is made to my United States Patent Reissue No. 16,809, entitled Electric circuit controlling apparatus, and issued December 6, 1927, for details of such a sign.

An endless paper tape H is adapted to travel over rollers I2, I3, and I4- Said rollersM, in operating position, are submerged in mercury 8, recesses I5 being provided in bottom panel I6 or tank I to permit said rollers to lie slightly below the top of said bottom panel or floor. A tape II is thereby caused to travel along the top of said bottom panel underneath the mercury. The high surface tension of mercury prevents its seeping under the tape. An electric motor I! is adapted to'drive one of rollers I2 by means of belt I8 and suitable reduction gears I9.

A number of holes 20 corresponding to the'numher and the patternof lamps 2 in sign I (or to the number of groups of lamps that are to be lighted at the same time) ;are drilled in bottom panel I6 of tank 7. Contacts Ill may, if desired, be pressed firmly in said holes 20. As described thus, tape II lies between mercury 8 and contact In and effectively prevents electrical communication therebetween. To permit contact between the mercury and a particular contact at certain times, small holes 2I are punched thrusaid tape. As said tape moves along, a small tip of mercury projects thru. each of said holes, rubbing along the top of bottom panel I6 until it reaches a contact II] whereupon the circuit is completed thru a lamp. It will be understood that the desired letter, or other configuratiom'will be formed by the lighted lamps because holes are punched in a corresponding configuration in tape II, and that said configuration of lighted lamps will move along sign I as tape II moves along bottom panel I6.

If, as holes 2I pass over contacts I0, the contact resistance between the mercury and said contact is high, the voltage on the lamps will be reduced and they will not burn with full brilliance. Then, as the letters move along the sign, they appear to leave a tail behind them. To prevent this tailing effect, without using con tacts having a short life due to pitting, I have devised contacts such as 1110., shown in Fig. 4.. Said contacthas a copper core 23 on which is electroplated a nickel shell 22. If desired, said shell may be otherwise attached to said core, but it should fit securely thereon. The contact may initially have a fiat top arranged flush with the top of bottom panel I6, as shown in Fig. 3.

After use for a period of several weeks, contact H3 will have been worn to the form of contact Nib, shown more clearly in Figs. 4 and 5. A copper contact, without a nickel shell might have worn to the form of contact I00, shown in Fig. 6. The concave surface automatically formed on the ends of the contacts of my invention are advantageous in effecting a proper contact with the mercury. Said concavity becomes filled with amalgam 24 and a small particle of mercury 25 which lies in said concavity in a favorable position to meet and coalesce with the tip of mercury projecting thru a hole 2! thereby to make contact therewith. This mercury contact will not break so suddenly as to give rise to transient electrical phenomena that might cause interference with radio reception, and sparking will be minimized.

I am unable to explain exactly why the composite contacts herein described wear in the form of a concave surface instead of the convex sun face that invariably appears on a solid copper contact under similar conditions of use. It might be expected that the copper would merely Wear away, leaving a thin shell of nickel. But this concave surface is not in itself the answer to the problem; the desired result is attained by the combination of a concave surface on a copper core. For example, a concave surface might be machined on a solid nickel contact, and, with clean mercury, this would give excellent results for a period of, say, one month. Thereafter, due to the deposit of foreign matter on the surface of the nickel or to the corrosion thereof, the objectionable tailing effect herein described would ensue. This effect does not occur when composite electrodes are used wherein the mercury makes contact with copper.

While, for convenience, I have described my invention as a composite contact having a nickel shell sheathing and a copper core, it should be understood that other non-corrodible materials, such as chromium, heavy enamel coatings, plastics which may be applied to coat copper and other similar materials which will not amalgamate with mercury and will not corrode copper, may be substituted for those named. The end result to be attained is to provide a sheathing which will space the copper rods or wires from the floor panel, will be securely bonded or secured to the copper, and will remain unaffected by mercury when serving as an electrode in direct electrical communication with the copper. Said sheathing thus constitutes a bounding wall or rim to hold copper-mercury amalgam and a droplet of mercury directly upon the end of the copper terminal for the purpose described. Said shell should be made of a material that will not pit, or wear, under the action of mercury and whatever 'iemical agents may be present in the insulating material, while the core is made of a metal that will readily amalgamate with mercury, thereby resulting in the formation of a crater, or concave surface, at the end of the contact. I have illustrated and described my invention in connection with electric sign, for which it was specifically devised, but it may be used with other similar equipment. For example, the contacts ordinarily used with electric pianos are subject to trouble similar to that of electric sign contacts, and said piano contacts may advantageously be replaced with those embodying my invention.

I claim:

1. In an electric make-ancl-break element comprising a receptacle open to atmosphere and adapted to hold a pool of mercury constituting an electrical connection for an electric circuit, a terminal element extending into said receptacle below the normal surface of said pool for electrical connection with said pool of mercury, an insulating breaker element adapted to pass between said terminal element and said pool of mercury to break the electrical connection therebetween, said terminal comprising a rod made of a material that will amalgamate with mercury and having a non-corrodible sheathing of substantial thickness covering the sides thereof.

2. In an electric make-and-break element comprising a receptacle open to atmosphere and adapted to hold a pool of mercury constituting one common electrical connection for a plurality of electric circuits, a plurality of spaced terminal elements extending into said receptacle below the normal surface of said pool thru the floor thereof and arranged in predetermined pattern for electrical connection with said pool of mercury, a perforated insulating breaker element adapted to pass along said floor and between said terminal elements and said pool of mercury to break the electrical connection therebetween, each of said terminals comprising a copper rod of substantial area having a nickel sheathing of substantial thickness, but with a cross-sectional area less than that of the copper rod, covering the sides thereof.

JOHN E. LONG.

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