US2224873A - Mercury switch relay - Google Patents

Description

Dec. 17, 1940. c. H. LARSON 2,224,873

MERCURY SWITCH RELAY Filed March '7, 1938 5 Sheets -Sheet l Dec; 17, 1940. Q LARSON 2,224,873

MERCURY SWITCH RELAY Filed March '7, 1938 3 Sheets-Sheet 2 Iii F ii 25 1 I/ IIIIIIIIIIIIIIIIIIII IIlI--II-- III Patented Dec. 17, 1940 UNITED STATES MERCURY SWITCH RELAY Carl ll. laraon,

Adlake lnd., a-ignor to The Illinois mm, Company, a corporation of Application March 7, 1938, Serial No. 194.273

24 Claims. '(01. zoo-a7) This invention relates broadly to mercury switches, for certain features or parts of it can be used to advantage with almost any type of mercury switch. But more specifically, the invention pertains to that type of mercury switch in which spaced electrodes, together with a quantity of mercury and a magnetically responsive displacer are hermetically sealed within a. glass envelope, afterwhich the switch is associated with a. coil which controls the movement of the displacer within the envelope to change the mercury level and thereby cause the electrical circuit between the spaced electrodes to be clam or opened according to the particular construction of the switch.

In general, the objects of the invention are to improve the mechanical strength of relays of this type, and particularly the electrode and time delay structure; to protect vulnerable parts of the relay from breakage due to blows, or if broken to confine the mercull within a jacket tightly fitted over the envelope so that adjacent property will not be damaged by mercury leaking out; to simplify manufacturing practices;

to provide a switch structure which can meet rigid and difiicult specifications for perfumance; and to provide means for obtaining uniform time delays, special contact opening and closing conditions, specified time delays even when-the relay is quickly recycled, and a quick and positive resetting of the time delay element 36 which follows. particularly when read in conjunction with the accompanying drawings, in which Fig. l is a perspective view showing a preferred mounting for the relay;

Fig. 2 is a vertical, sectional view taken along the line 2-2 of Fig. 1; a

Fig. 3 is a bottom plan view of the mounting with a portion of the bottom cover broken away to expose the interior of the base; I

5 Fig. 3a is a fragmentary, perspective view of the switch base retaining sleeve;

Fig. 4 is a vertical, sectional view taken on the line 4-4 of Fig. 2, the switch itself, however, being shown in elevation;

Fig. 5 is an enlarged vertical, sectional view taken through a front contact switch embodying certain features of this invention, the switch being shown in its normal de-energired position;

Fig. 6 is a view corresponding to Fig. 5, the

switch parts, howzver, being shown in the position which they take immediately after the relay coil has been energized, but before the time delay element in the switch has permitted the spaced electrodes to be bridged with mercury;

Fig. '1 is a fragmentary, sectional view through 5 the time delay thimble looking down upon the intermittently immersed electrode, the section line'being indicated at 1-1 in Fig. 8;

Fig. 8 is a horizontal, sectional view taken on the line 8-8 of Fig. 6; 10

Fig. 9 is an enlarged, vertical, sectional view taken through a back contact switch which incorporates a modification of the time delay element shown in Fig. 5, the time delay element position which they take substantially instantaneously after the associated relay coil has been 2 de-energized and the displacer has dropped to the floor of the switch envelope.

Fig. 10 is a view corresponding to Fig. 9, but showing the relationship of the mercury fill to the time delay element and associated electrodes 25 immediately after the displacer has been raised by the relay coil;

Fig. 11 is a view looking down upon the top of the time delay element;

Fig. 12 is a fragmentary, vertical section 30 through the time delay element; and

Figs; 13 and 14 are views corresponding to Figs.-

11 and 12, respectively, but showing a modified form of the time delay element.

The relay choun to illustrate a preferred embodiment of the invention comprises a mercury switch generally designated 20,-operatively associatedwithacoil 2| andmountedwithinahousing 22 which not only facilitates the moimting of the relay as a whole, but also provides the 40 I necessary mechanical protection for the switch from accidental blows.

The switch mounting The upper portion of the housing 22 serves as 5 the iron circuit for the coil 2| and it comprises a cylinder 23 of seamless, soft, cold-drawn steel tubing fitted at both ends with soft cold-rolled steel annuli 24 in the center openings of which top and bottom pole sleeves 25 and 2., respec- 5o tively, are drive fitted leaving an air gap 21 between their inner ends. The top of the housing is covered by a cap 28 held in place by screws 29, and a terminal box 30 is then attached to the lower face of the iron circuit by means of screws 55 2 aaaasrs ii. The terminal box is preferably an aluminum casting having an inturned flange 32 at the top through which the screws ll pass. The rear and bottom of the casting are left open, the

6 former being closed by a Bakelite plate 33 formed with an integral X-shaped projection having horizontal webs and vertical webs 35 which form insulating barriers between half hard nickel silver terminal prongs 36 and 31 which are mounted on the plate I3 and are connected to the switch terminals and coil terminals, respec-.

tively, The plate 33 is held in place by screws 38 which enter enlargements or bosses 38 in the 7 base casting. A cover plate 40 closes the bottom ll of the base casting and is held in place by screws 4i.

The lower portion of the switch III is fitted with a Bakelite sleeve 42 which projects below the bottom of the switch envelope and is filled 80 with sealing wax, as indicated at 48. When assembling the switch with the coil 2|, the cover is removed and the switch inserted from the bottom until the base sleeve 42 of the switch strikes the lower margin of the bottom pole as sleeve 26. A wire clip 44 is then sprung into place within slots formed in a metal sleeve 45 which is soldered or otherwise secured to the outer periphery of the downwardly projecting portion of the lower pole sleeve 28. The clip has 30 a head 48 which fits within an opening 41 in the sleeve and the two ends of the clip when pressed together enter a bayonet slot 48 on the other side of the sleeve where they are retained by shoulders 48 when pressure on the free ends of 8B the clip is released. Preferably the clip 44 is made of music wire, or other suitable resilient material. Notches 50 are formed in the lower margin of the sleeve 45 to accommodate the lead wires from the switch.

so The relay as a whole is adapted to be mountedonawallbymeansofabracket Ii of cold rolled steel which is rigidly attached to the coil cylinder 23, and a special plug (not shown) is used to receive the relay terminals and the X 4| shaped insulating barrier associated with the plate 33. The housing furnishes full protection to the switch Ill from accidental blows.

vSwitch having delayed make u ugh the switch electrodes is closed. switchmaybeeitherofthefront contact orth The switch comprises a switch envelope 'II' 68 coveredforatleastaportionoftheirlengthby glassinsulatingsleeveslltheoneassociated leavinganexposedendorcontactio. Theup perendoftheins'ulatingsleeveisflaredout. as indicatedatihtoform aseatforaceramiccup 1g 02, and when the materials for the cup I and sleeve it are properly selected, the two may bev fused together to form a firm bond.

A time delay element, generally designated 63 is supported by at least one and preferably both of the electrodes, and it comprises a glass thim- 6 trode i1 is preserved.

The thimble '4 has a relatively large opening 8' in one of its side walls, the area of this opening preferably being at least as great as the cross sectional area of the thimble. A smaller opening 01 in the upper portion of the thimble receives a porous plug ll of suitable ceramic material, and again when proper materials are used, the porous block-may be sealed into place by fusion with the enveloping glass wall Bl of the thimble 84.

The switch contains a mercury flll 10, a magnetically responsive displacer generally designated 1| consisting of an ironsleeve 12, an inner 25 glass sleeve 13, guide washers l4 and top and bottom springs 15 and 16, respectively, the latter being tightly telescoped over the projecting ends of the irmer glass sleeve 13 to hold the ironsleeve I2, and guide washers 14 in proper relationship to the glass sleeve '13.

The swtich contains a gas fill preferably inciuding helium and hydrogen, and after the switch parts have all been assembled in the a switch blank (which includes the tube through the base of which electrodes 56 and 51 with their associated insulating sleeve and superposed thimble are sealed) and the gas illl inserted, the upper end oi the envelope is sealed 0 oil, as indicated at 11 to hermetically seal the switch parts within the envelope.

-The air gap 21 between the pole sleeves 25 and 26 is so positioned with reference to the displacer II that when the coil II is energized, 5 the displacer is drawn downwardly by magnetic force to the position in which it is shown in Fig.

6 and the immediate result of this movement is that mercury is displaced from the low level shown in Fig. 5 to the level in which the merso cury is shown in Fig. 6. The gas trapped within the thimble 44 restrains the movement of mercury within the thimble to circuit closing position and the time that it takes the mercury within the thimble '4 to reach the edge 14 of 66 the cup 02 after energization of the coil II is the time delay interval of the switch in its delayed circuit closing action.

As the mercury within the thimble l4 gradually rises due to the escape of gas through the 60 porous plug It, (the difference between the outside mercury level and the level of mercury within the thimble creates a head which forces gas from the thimble through the plug 68), it will the thimble '4 will immediately fall below the top of the opening 66 with the result that the mercury within the thimble will substantially instantaneously fall from the thimble and away 7;

from the contact 80 to break the circuit through the electrodes 56 and II.

The switch which has been described has certain inherent advantages over earlier types of 5 switches, and these will be briefly mentioned:

(a) The method of attaching the time delay element 83 to the insulating sleeve surrounding venlent method of fabrication and at the same time gives great stability to the electrode structure. It is far superior in mechanical strength to the method of attachment shown in my earlier Patent No. 1,967,946, and the desired time delay characteristic of the switch can be much more 18 easily obtained and maintained than was heretofore possible. The rigidity which is furnished by supporting the time delay element by both of the spaced electrodes contributes itsshare to the perfection of the switch as a whole. 20 (b) It will be noticed that the intermittently immersed contact 60 is at one side of the thimble 84 and that the opening 66 is on the other side. The purpose of this arrangement is so that the mercury can fall away from the contact 60 with as little restraint as possible because in some electrical circuits, the breaking of the electrical circuit controlled by the switch must bewithin a very few thousandths of a second after the coil has been de-energized. It is for this reason that the opening 80 is made equal to or greater than the cross sectional area of the thimble. It has also been found by experimentation that the time required for the mercury to drop away from the electrode 6. was substantially less 85 when a side opening, such as the opening 66 is used instead of the body opening shown in my prior Patent No. 1,967,946.

(0) The slight pitch given to one edge of the refractory cup 62 insures that gas will not be trapped within the cup since the mercury will flow in from the low side of the cup and gas will flow out of the high side.

(d) The time delay element 63 can be given any desired time delay characteristic by proper 5 selection for the material of the plug 68. Preferably the plug is made of a product known as Alundum, and grades RA 98, RA 360 and RA 84, for short, medium and long time delays, respectively. have been found satisfactory, particularly since this type of ceramic material will fuse readily with the particular type of glass that is used in the switch, namely 733 A.

(e) It should be noticed that the displacer ll when in the position it takes upon energization of the coil II, has its lower spring 16 resting on the floor of the switch envelope and the parts of the switch are proportioned so that the displacer will occupy this position when the coil is energized. The result is that the outside mercury level will always rise the same distance above the top of the opening 66 so that the gas pressure differential between the inside and outside of the thimble, due to the head of mercury, will be the same for all operations of the switch. Uniformity of 05 results is thereby assured unless, of course, the voltage on the coil is lower than that for which the relay was designed. However, since the displacer is completely submerged in the mercury fill, variations in the voltage of the coil will have 70 little or no eifect on the'uniformity oi switc operation.

(I) It sometimes happens that when the relay coil is operating on an alternating current voltage which is lower than that specified for the relay, the displacerwill have a certain amount of reciprocating movement due to voltage changes which necessarily affect the outside mercury level and would cause false makes or breaks in the circuit in the event that the time delay element were carried by the displacer. In the switch 5 shown, however, these oscillations. of the displacer have no perceptible effect on the inside I one of the electrodes (or both) constitutes a conmercury level, and the switch, therefore, functions according to specification under these adverse conditions. 10

(a) The mercury cup 82 is formed so that it not only is assured of being filled on each operation of the switch, but the flare 6| which joinsthe sleeve 58 with the cup tends to throw mercury away from the cup in the event that excess voltage on the coil should lower the displacer II with such speed that a wave of mercury is thrown upwardly within the thimble 64 with suflicient force to momentarily compress the gas within the thimble. The flare 6| avoids a false make 20 if such a situation should arise.

(h) Although a glass insert "I3 is shown in conjunction with the magnetic sleeve 12, it is unnecessary to use a liner of this type to protect the magnetic sleeve from deterioration due to the effect of the are at the electrodes, since the thimble 84 serves this function. The liner in such cases is used merely to give the displacer additional buoyancy.

The switch shown in Figs. 5-8 inclusive can be readily made into a slow make, slow break switch merely by proportioning the mercury fill, height of the electrodes, shape of the glass thimble, etc. so that the opening 88 is at all times below the outside mercury level. A switch so'constructed very clearly illustrates the advantage which this type of construction has over switches in which the time delay element is carried by the displacer, particularly with respect to relaw tively small displacer oscillations produced by voltage changes in the coil, and when the mercury level on the inside of the time delay element is closely adjacent to the level at which it changes .the condition of the electrical circuit through the 45 switch. It also has the inherent advantage in that when the mercury level on the inside of the thimble is falling away from the intermittently immersed electrode, the heat created by the are at the moment the circuit is broken instan- 60 taneously expands the gas in the thimble and accelerates the breaking of the circuit so that the arc is held down to a minimum. The thimble in a sense becomes an explosion chamber in which the expanding gas accelerates the movement of 55 mercury away from the contact being broken, thereby extinguishing the are.

In order to protect adjacent property from damage due to leaking mercury in the event that the switch should become broken, the switch 60 envelope is preferably encased within a sealing jacket 81 made of a material known as Sealon. This Jacket is applied to the envelope while in a wet condition, and as it dries, it shrinks radially, but not longitudinally, to tightly encase the envelope. The Bealon jacket is transparent so that the switch parts can be inspected through the Jacket and it is strong and tough with great rev sistance to tearing.

Preferably a metal cap 8| is held in place by 70 a suitable cement 82 over the tip 11 of the envelope so that the jacket 00 when shrunk into place will completely-'encase the envelope and seal the mercury within it. even though the glass envelope may become broken. 7

Switch having quick make and delayed break The switch shown in Figs. 8-14 inclusive is a back contact switch characterized by the fact that it immediately closes the electrical circuit through the electrodes whenever the associated relay coil is de-energized and delays the opening of the circuit for a given period of time when the coil is energized. In addition to this, how- 1 ever, the switch has the unusual and imporant property or attribute that it will always give the desired time delay on the breaking of the circuit no matter what the recycling period for the relay coil may be.

The principles of this switch may also be incorporated in a front contact switch. as will readily be understood by reference to Figs. 5-8 inclusive, but as here shown, the switch comprises a switch envelope 88 having electrodes 88 and 81 sealed through the base in a manner very similar to the switch disclosed in Figs. 5-8 inclusive. The time delay element 88 is rigidly attached to both of the'electrodes' 88 and 81,- the latter extending into the thimble 88 and terminating in an exposed end 88 surrounded by a refractory cup 8] containing a quantity of mercury. The

. thimble 88, as before, is preferably made of glass and has anopening 82 on the opposite side from the cup 8 I-.-

The top of the thimble 88 is equipped with a mercury check valve, generally designated 88,

which allows gas to freely pass from the interior of the thimble to the exterior of the thimble but restricts the flow of gas in the opposite direction.

The check valve comprises a porous seat 88 of coarse ceramic material (such asAlundum, grade BA 98) andan upwardly extending short tube 88 (preferably Alundum grades RA 360 or BA 84 v according to the time delay desired) the tube 88 forming with the seat-88 a cup adapted to '48 retain a small quantity of mercury 88 over the seat 84. The seat and the tube are both fused to the top of the glass thimble 88 and preferably the tube 98 is cut away, as best shown in Fig. 12. The switch envelope contains a mercury fill 81 and a magnetically responsive displacer 88,

the form of which is somewhat different from the displacer II of the front contact relay shown in Figs. 5-8 inclusive, because of the need of additional weight in the displacer for obtaining 58 positive action of the switch. Theopening 88 in the top of the displacer is of sufilcient size so that it does not in any way modify the movement of either the displacer or the mercury within the envelope. As before, springs I8 and I8 88 are attached to the top and bottom of the dispiacer to cushion the movement of the displacer within the envelope.

When the coil associated with the switch is ole-energized, the parts assume the position in so which they are shown. in Fig. 9, and it should be noted that the mercury level is such that the check valve cup 88 is assured of a filling of mercury. The notch I88 formed in the cup prevents any entrapment of gas in the cup which 85 might hinder the cup in filling. In this podtion of the switch parts, the electrical circuit between the electrodes 88 and 81 is closed through the mercury fill 81.

When the clisplacer is raised, by energi- 78 zation of the coil II, the outside mercury level immediately falls to the position in which it is shown in Fig. 10, but the measured quantity of mercury within the mercury chamber in the thimble 88 (the same quantity 1; is always assured because the high mercury levelasshown inFig. 9isabovethetopofths mercury chamber in the thimble) is retarded in, its downward movement due to the slow entry of gas through the walls of the tube 88 and the porous seat 84, as shown by the arrows in Fig. 12. s In effect, the mercury valve is by-pdssed by'the e of gas through the walls of the tube and through the seat. The mercury level finally recedes until a mercury level is established with both the inside and outside mercury levels rest- 10 ing at the position indicated by the line.I8I, the contact, however. being broken at the instant when the mercury within the thimble falls below the edge I88 of the refractory cup. 8| associated with the bared end so of the electrode :1. l6

Upon lie-energizing the coil 2|, the displacer raises the mercury level to the position in which it is shown in Fig. 9, and the mercury 88 in the check valve 88 readily passes the gas within the thimble through the coarse ceramic material con- 28 stituting the seat 84 with the result that the circuit through the electrodes 88 and 8'! is made substantially instantaneously upon release of the coil 2|.

It is important to note at this point that the as desired time delay on the breaking of the electrical circuit is always obtained no matter what the period of recycling for the relay may be. In other words, a minimum time delay period will always exist between the energization of the relay coil 8| and the opening of the circuit through the electrodes 88 and 81, although de-energization of the coil 8| before the minimum time delay period has expired will cause the time delay element to be reset for subsequent 35 energization of the relay coil. This desirable result is achieved without any possibility of a false contact being made due to unexpected short cycling of the relay.

A slight modification of the mercury check a; valve arrangement is shown in Figs. 13 and 14 in which the time delay element consisting of a cylindrical plug I88 of suitable ceramic material is physically separated from the mercury valve. In this case, the seat is the same as before, a but the tube I88 which forms the cup for' the mercury is made of molybdenum, or other suitable non-porous material. Molybdenum is preferred because it will seal with glass and because itpermitstheseatfltobefusedwiththetubing 80 by glass indicated at I88.

The action of the modified form of time delay element Is substantially the same as before: Gas within the thimble can escape quickly through the coarse ceramic seat 88 and out as through the mercury 88 in the cup without any appreciable impedance. but gas can only enter the thimble through the time delay element I88 which measures the minimum amount of time required for breaking of the circuit through the so electrodes 88 and 81. Throughout the specification and claims, the expression "low mercury level is used to designate the level of the mercury when the displacer is in its raised position and the columns of mer- 88 cury within the time delay thimble is in equilibrium with the column of mercury on the outside of the thimble. Byway of example, the mercury fill in'Fig., 5 is shown at its "low mercury level" and in Fig. 18, the reference numeral I II 10 indicates the low mercury level. Similarly, the expression high mercury level" throughout the specification and claims is used to designate the level of the mercury fillwhen the displacer is in its lowered position (see Figs. 6 and 8) and the 1g inside and outside mercury columns are at rest. The reference line II in Fig. 6 indicates the high mercury level for the switch there disclosed, and in Fig. 9, the mercury is shown at its high mercury level. a

The plug 94 in the form of the invention shown in Figs. 9-14 inclusive may, if desired, be made of somewhat denser material, so that a certain time delay is efiected on the making of the circult through the electrodes as well as on the breaking oi the circuit, the latter, oi course, being accomplished by the still denser material constituting either the tubing 99 (Fig. 12) or the plug I03 (Fig. 14).

Iclaim:

1. In a mercury switch, a switch envelope, a

mercury fill, a gas fill. spaced electrodes in the envelope, one c! which projects upwardly through the mercury fill and is surrounded by an insulating sleeve to a point above the low mercury level, leaving an expom end, a thimble telescoped over the exposed end and having its lower portionbonded to the sleeve, said thimble having a large opening adjacent to the bond for the free e of mercury to and from the interior of the thimble, and a small opening adjacent to the top oi the thimble for the restricted passa e of gas between the interior and the exterior oi the thimble in at least one direction.

2. In a mercury switch, a switch envelope, a mercury fill, a gas fill, spaced electrodes in the envelope. one of which projects upwardly through themercuryfillandissurroundedbyaninsulating sleeve to a point above the low mercury level, leaving an exposed end, a time delay thimble telescoped over the exposed end and having its lower portion bonded to the sleeve. said thimblehavingalargeopeningadiacenttothebond for the tree passage oi. mercury to and from the interior of the thimble, and a small opening adjacent to the top of the thimble tor the restricted passage of gas to and/or from the interior of the thimble, and means for having the second electrode assist in the support of the thimble.

3. In a mercury switch, a switch envelope, a mercury fill, a gas fill. spaced electrodes in the envelope, one of which projects upwardly through the mercury fill and is surrounded by an insulating sleeve to a point above the low mercury lewl, leaving an exposed end, a time delay thimble telescoped over the exposed end and having its lower portion bonded to the sleeve, said thimble having a large opening adjacent to the bond for the tree passage of mercury in and from the interior of the thimble, and a small opening adjacent to the top of the thimble for the restricted passage of gas to and from the interior oi the thimble, and a refractory cup mounted on the exposed end of said one electrode.

4. In a mercury switch, a switch envelope, a mercury fill, a gas fill, spaced electrodes in the envelope, one of which is adapted to, be intermittently placed in electrical contact with the mercury fill, a thimble telescoped over the end of said one electrode, and rigidly supported in .fixed position by attachment to both of said mittently placed in electrical contact with the? mercury fill, a thimble telescoped over the end oisaid one electrode, and rigidly supported in fixed position by attachment to at least one of said electrodes, a porous plug constituting at least a portion of the wall of the thimble for restricting the how of gas therethrough, and a mercury valve associated with said plug.

6. In a mercury switch, a switch envelope, a mercury fill, a gas fill, spaced electrodes in the envelope, one of which is adapted to be intermittently placed in electrical contact with the mercury fill, means for raising and lowering the mercury fill, and a time delay element supported by and rigidly attached to at least one of said spaced electrodes, said element comprising a restricted gas passage, and means for by-passing the restricted passage when the gas is moving in one direction.

7. In a mercury switch, a switch envelope, a

' mercury fill, a gas fill, spaced electrodes in the the mercury fill, a time delay element associated with one of said electrodes for delaying the movement of mercury in one direction in the vicinity 01' said one electrode, said time delay element comprising a thimble telescoped over said one electrode and having an opening in a horizontal wall thereof, a ceramic cup in the opening having gas pervious side and bottom walls, and m'ercury in the cup restricting the flow of gas into the thimble to that which permeates the side walls of the cup.

8. In a mercury switch, a switch envelope, a mercury fill, a gas fill, spaced electrodes in.the envelope, one oi which is adapted to be intermittently placed in electrical contact with the mercury fill, means for raising and lowering the mercury fill, and a time delay element associated with one oi said electrodes for delaying the movement of mercury in one direction in the vicinity of said one electrode, said time delay element comprising a thimble telescoped over said one electrode and having an opening in a horizontal wall thereof, a mercury cup in the opening having its bottom wall of material that is impervious to mercury, but which offers substantially no resistance to the passage of gas, positive means for filling the mercury cup for each cycle 0! switch operation, and means for slowly admitting gas to the thimble.

9. In a mercury switch, a switch envelope, a mercury fill, a gas fill, spaced electrodes in the envelope, one of which is adapted to be intermittently placed in electrical contact with the mercury fill, means for raising and lowering the mercury fill, and a time delay element associated with one 01 said electrodes for delaying the movement of mercury in one direction in the vicinity of said one electrode, said time delay element comprising a thimble telescoped over said one electrode and having an opening in a horizontal wall thereof, a mercury cup in the opening having gas pervious side and bottom walls, mercury in the cup restricting the flow of gas into the thimble to that which permeates the side walls of the cup, and means for filling the mercury cup upon each operation of the switch, said cup having a portion of its side wall of greater height than the remaining po to facilitate the filling oi the cup with mercury.

10. F'or use in a mercury switch of the class described, a switch. blank comprising an envemercury fill, a gas fill. spaced electrodes in the envelope, one or which projects upwardly through the mercury fill and is surrounded by an insulating sleeve to a point above the low mercury 10 level, leaving an exposed end, a time delaythimble telescoped over the exposed end and having its lower portion bonded to the sleeve, said thimble having -a large opening in one oi its side walls adjacent to the bond for the tree passage oi mercury to and from the interior 0! the thimble, and a small opening adjacent to the top 0! the thimble for the restricted passage of gas to and from the interior of the thimble, the exposed end 0! said one electrode being closely adjacent to. the side wall 01. the thimble opposite from that in which the mercury opening is provided.

12. In a mercury switch, a switch envelope, a mercury fill, a gas fill, spaced electrodes in the envelope, one 01' which projects upwardly through 26 the mercury fill and is surrounded by an insulating sleeve to a point above the low mercury level, leaving an exposed end, a time delay thimble telescoped over the exposed end and having its lower portion bonded to the sleeve, said thim- 80 ble having a large opening adjacent to the bond for the tree passage of mercury to and from the interior oi the thimble, and a small opening adjacent to the top of the thimble for the restricted e of gas to and from the interior of 86 the thimble, and a refractory cup mounted on the exposed end of said electrode and bonded to the insulation surrounding that electrode, the bond between the cup and the sleeve surrounding said one electrode being flared upwardly and a outwardly whereby mercury moving rapidly toward said one electrode is momentarily-thrown away from the cup.

13. In a mercury switch, a glass envelope, a mercury fill, a gas fill, spaced electrodes sealed as into one end of the envelope, a base fitted to the lower end of the envelope and held in place by a wan substance, and a light transmitting thin-walled inirangible jacket shrunk over the switch envelope and at least a portion oi the base for confining the mercury within the jacket in the event of breakage oi the glass envelope.

14. In a mercury switch, a switch envelope, a

mercury fill. a gas fill, spaced electrodes in the envelope. one of which projects upwardly through tilt the mercury fill and is surrounded by an insulating sleeve to a point above the low mercury level, leaving an exposed end, a time delay thimble telescoped over the exposed end and having its lower portion bonded to the sleeve, said thimso ble having a large opening adjacent to the bond for the tree passage of mercury to and from the interior of the thimble, and a small opening adjacent to the top of the thimble for the restricted passage of gas to and from the interior of the thimble, the opening for the mercury being substantially equal to or larger than the diameter of the thimble.

15. In a time delay mercury switch adapted to produce a relatively quick make and a slow break of the circuit which it controls, the combination of a switch envelope, a mercury fill, a gas fill,

spaced electrodes in the envelope, one of which is adapted to be intermittently placed in electrical contact with the mercury fill, a time delay element associated with said one electrode and comprising a thimble telescoped over that electrode and having a mercury valve in its upper portion, and means for raising and lowering the mercury fill to electrically connect the spaced electrodes through the mercury fill, the mercury 5 fill and said means bearing such relationship to each other that the mercury valve is automatically filled each time that the mercury level is raised to electrically connect the spaced electrodes.

' 18. In a mercury switch, a switch envelope, a gas fill, a merciuy fill, spaced electrodes in theenvelope, one of which is adapted to be intermittently placed in electrical contact with the mercury fill, means for raising and lowering the mercury fill between specified high and low levels, and means for positively preventing mercury from falling away from said'one electrode in less than a given time interval following the lowering 01' the mercury level, even though the mercury level is raised and lowered between said high and low levels in cycles which are shorter than the prescribed time interval, said latter means comprising a thimble telescoped over said one electrode and having a relatively large opening 25 for the free e of mercury to and from the interior or the thimble, and a one my time delay element permitting gas to escape relatively freely from the thimble but restricting the flow 0! gas into the thimble, said thimble bearingsuch relationship to the mercury fill and the associated switch parts that the high mercury level is at or above the top of the mercury chamberrwlthin the thimble whereby a measured quantity of mercury is always within the thimble subject to the 36 action of the restricted gas e when the mercury level is shifted from its high position to its low position.

1'7. In a mercury switch, a switch envelope, a

mercury fill, a gas fill, spaced electrodes in the 49 envelope, one of which is adapted to be intermittently placed in electrical contact with the mercury fill, a thimble telescoped over the end 01' said one electrode, and rigidly supported in fixed position by attachment to at least one or 45 said electrodes, a porous plug constituting at least a portion of the wall of the thimble for restricting the fiow 0! gas therethrough. and a mercury valve in another portion oi the thimble permitting as to by-pass the plug when the gas is moving in one direction.

18. In a mercury switch, a switch envelope, a mercury fill, a gas fill, spaced electrodes in the envelope, one of which is adapted to be intermittently placed in electrical contact with the mercury fill, a thimble telescoped over the end of said one electrode and rigidly supported in fixed position byattachment at its base to at least one of said electrodes, and means including a restricted gas e for retarding the movement of mercury away from said one electrode, said thimble having a mercury chamber 01 relatively small area forming an explosion chamber to accelerate the breaking of the circuit at said 65 one electrode at the instant when an arc is formed due tothe breaking of the circuit.

19. Ina mercury switch, a switch envelope, a mercury fill, a gas fill. spaced eiectrodes'in the envelope, one of which is adapted to be intermittently, placed in electrical contact with the 7 mercury fill, a fixed time delay element associated with said one electrode, and means for attaching the element to both of said electrodes whereby it has rigid and stable support.

20. In a mercury switch, a switch envelope, a

mercury fill, a gas fill, spaced electrodes in the envelope, one of which is adapted to be intermittently placed in electrical contact with the mercury fill, a fixed time delay element associated with and telescoped over said one electrode, a magnetically responsive displacer for shifting the mercury level, said displacer when in its lowered position being completely submerged within the mercury fill.

21. In a mercury switch, a glass envelope having a seal-off tip at its upper end, a mercury fill, a gas fill, spaced electrodes sealed into the lower end of the envelope, a base fitted to said lower end of the envelope and held in place by a waxy substance, a metal cap bonded with adhesive material over the seal-oil? tip, a light transmitting thin-walled infrangible jacket shrunk over the switch envelope and at least a portion of the base and the metal cap for confining the mercury within the jacket in the event of breakage of the glass envelope.

22. In a mercury switch relay, the combination of a vertical switch envelope, spaced electrodes sealed through the base of the envelope, a coil telescoped over the envelope, a magnetic circuit associated with the coil and including a cylinder of magnetic material encasing the coil, a top for enclosing the upper end of the envelope, and a terminal box mounted below the coil for receiving the lower end of the envelope.

23. In a mercury switch, a glass envelope, a mercury fill, a gas fill, spaced electrodes sealed into the envelope, a fluid-tight jacket telescoped over the switch envelope and sealed above and below the envelope to completely incase it and to confine the mercury within the jacket in the event of breakage of the glass envelope.

24. In a mercury switch, a switch envelope, a mercury fill, a gas fill, spaced electrodes in the envelope, one of which is adapted to be intermittently placed in electrical contact with the mercury fill, means for raising and lowering'the mercury fill, and a time delay element supported by and rigidly attached at its base to at least one 01 said spaced electrodes, said element comprising a restricted gas passage, and means for lay-passing the restricted passage when the gas is moving in one direction.

CARL H. LARSON.

CERTIFICATE OF CORRECTION. Patent No. 2321 75. Decenber 17, 191w.

' CARL H. mason.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 32, for swtich read --switch; page 5, first column, lines and 11.5, claim 2, for the words "to and/or from the interior of the thimble" read. "between the interior and the exterior of the thimble in at least one direction"; and that the said Letters Patent should be read with this correction therein that the same meg conform to the record of the 'case in the Patent Office.

Signed and sealed this 21st day of January, A. D. 19114.

Henry Van Arsdale, I Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION. Patent No. 2,22h,875. I Decanber 17, 191w.

CARL H. LARSON.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, sec- 0nd column, line 32, for "swtich" read --switch-- page 5, first column, lines and 4-5, laim 2, for the words "to and/or from the interior of the thimble" read between the interior and the exterior of the thimble in at least one direction"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 21st day of January, A. D. 19m.

Henry Van Arsdale, I Acting Commissioner of Patents.

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