US2269856A - Direct current impulse operated selector switch - Google Patents

Description

2,269,856 DIRECT CURRENT IMPULsE oP'ERATEn sELEcTog swITcH- M. G. NELSEN ETAL Jamo 13, 1942. v

Filed Aug. 19, 1940 z'shgets-sheet 1 Sgm 13, 1942. M G. r-:LSEN ETAL DIRECT URRENT IMPULSE OPERATED SELECTOR SWITCH switch embodying Patented Jan. 13, 1942 DER/ECT CURRENT IMPULSE OPERATED SELECTOR SWITCH Marvin G. Nelson and 'Alhedore Obszarny, Chicago,

Ill., assignors to Guardian Electric Manufacturing Co., Chicago, Ill., a corporation of Illinois Appiaation August 19, 1940, serial No. 359,262

A2 Claims.

The present invention relates to a selector switch device or mechanism for controlling the make and break of portions of a plurality of branches of a main electrical circuit.

More particularly, the present invention is directed to a novel, direct current operated selector switch adapted to be actuated in step-by-step fashion, by the intermittent action of an electro'- magnet operated by pulsations of electrical current for selectively completing portions of one or more of a plurality of dierent electrical circuits, or portions of branches of a main circuit. Switches of this type also lend themselves for use in a relatively wide field in the selective and/or remote control of various types of Vmachines and apparatus.

One of the principal objects of this invention is to provide a novel form of direct current operated selector switch of the character indicated wherein a main electrical circuit may be completed and/or broken in a timed relation.

Another object is to provide an improved switch yof the character indicated for selectively completing and maintaining a main electrical circuit for a timed interval. l

A'further object is to provide a novel form of selector switch characterized by the provision of a direct current operated electro-magnetic timer control for effecting completion of a portion of a main electrical circuit-after a timed interval,`

subsequent lto completion of another portion of said circuit by the selector switch.

A still further object is' to provide a novel form of selector switch characterized by the provision -of a direct current operated electro-magnetic timing apparatus for controlling the period of completioniof a main or branch portions of a main electrical circuit, selected by adjustment of the switch.

Still another object is to provide a novel selector switch of the character indicated adapted to be actuated in step-by-step fashion by fpulsations of electrical current and` provided'with a novel arrangement of direct current operated electro-magnetic timing apparatus for controlling the period of completion of the main or branches of a main electrical circuit selected by the step-by-step adjustment ofthe switch.

Other objects and advantages of this invention will be apparent from the following description, taken in connection with the accompanying drawings, in which:

Figure 1 'is a plan View of the unitary selector the present invention. Figure 2 is a vertical sectional' view throughthe device, taken substantially as indicated at I line 2-2 of Figure 1.

` portions extending through the panel with their tion to a conductor wire indicated at Figure 3 is a staggered vertical sectional view, taken as indicated at line 3-3 on Figure 1 Figure 4 is a transverse vertical sectional View, taken at line 4-4 on Figure 1.

Figure is a front elevational view of the device showing the selector panel; and

Figure 6 is a wiring diagram including the electrical circuits for controlling the operation of the selector switch.

The switch structure illustrated in the drawings includes a main mounting frame l0, fabricated as a sheet metal stamping, of a 4generally U-shaped formation. Said frame serves to totally support all apparatus constituting the switch device to provide la unitary structure or assembly. Connected to the intermediate portion of the U-shaped frame l0 in spaced apart relation thereto and forwardly thereof, is a contact panel ll of insulating material, which is connected to the frame l0 by screws l2, with spacer elements |`4 interposed between said panel and the frame. Said panel is provided with an arcuate series of contacts I6, with the heads thereof exposed on the outer face of the panel and including body inner ends projecting to the rear side of the panel for connection to conductor wires, as indicated at Il, which wires it may be understood form portions of different electrical circuits tobe selectively controlled.

Also mounted on the front face of the panel il is an arcuate contact strip i9, having a ter- Aminal projecting through the panel for connec- Zil for completing portions of the different electrical circuits including the contact buttons I6, as will hereinafter be described. Said contact buttons drawings, of disc members `22a, and 23a,

I6 'and strip I9 are adapted to be engaged by a `'pair of yielding contact arms 22 and 23 respectively, as may be best seen in Figure 1 of the Saidarms are formed asextensions which are disposed in engagement with each other and mounted between a pair of insulating discs 25 which in turn are fixedly mounted upon the outer end of a shaft 2l, which extends through said panel Il and is journalled in a bearing 28 which is rigidly supported on the mounting frame l0 as seen in Figure 2 of the drawings. The inner end of said shaft, within said frame, has rigidly mounted thereon a ratchet wheel 39, adapted to be moved in step-by-step fashion for moving the contact arms 22 and 23 simultaneously, in stepped fashion, for sequentially engaging the respective contact buttons I6. It will be apparent that due to the arrangement of the contact arms 22 and 23, the conductor wire 2U is in series with the particular conductor wire l1 corresponding to the contact button I6, engaged by the arm 22 at a given time. In other words, when the contact arm 22 is in engagement with any one of the contact buttons l5 the portion of the electrical circuit connected through said contact button, is completed through the contact arm 23, the contact strip I9 and conductor wire 2B.

The means for rotating the ratchet wheel 3U in step-by-step fashion is accomplished by the intermittent energization of an electro-magnetic relay 32 supported on one of the legs of the U- shaped frame l0 by means of a mounting bracket 33 which constitutes an extension of the field piece 34 of the relay. As may be seen in the drawing, the relay 32 is disposed with its coil in upright position, and hingedly mounted on the upper end of the upright leg of the field piece 34, is an armature 36 which is normally urged in upward direction away from the core 32a of the coil of the relay by means of a coil spring 31 which is connected to the outer end of the armature and to a lug extension on the leg of the eld piece 34, as seen in Figure 2 of the drawings.

Pivotally mounted at 39 on a vertical axis, on top of the armature 36, adjacent said hinge connection thereof, is an actuating pawl 40, formed of a nat bar and supported directly upon the top of the armature, and extending in a direction parallel to the axis of the ratchet wheel. 'I'he forward end of said bar, beyond the armature, is twisted with respect to the main body of the bar so that the lower edge thereof is disposed adjacent to the toothed periphery of the ratchet wheel 30. Said lower edge of the bar is cut at an incline, as indicated at 48a, to insure proper engagement with the teeth of the ratchet wheel 30. Due to the pivotal connection 39 of the actuating pawl 4) to the armature, said pawl is permitted lateral movement with respect to the armature. To maintain the actuating pawl inproper position on the armature and for limiting its extent of lateral movement, we provide a guide inthe form of a strap 42 extending over the actuating pawl, adjacent the outer end of the armature, which strap is secured to the armature by means of studs 43.

Said relay 32 is adapted to be intermittently energized by pulsations of electrical current, thus imparting a step-by-step action to the pawl and ratchet wheel 30, for shifting contact arms 22 and 23 in a step-by-step manner so that arm 22 is sequentially stepped over a series of contact buttons I6. It is to be understood that said pulsations of current may be supplied directly or from a remote sending station, and in the latter case suitable receiving apparatus may be employed for use in transferring the wave impulse directly to said relay. Therefore, for convenience relay 32 may be termed a stepping relay.

Said pawl 40 is dimensioned so that its extreme outer end projects into an opening IDa formed in the intermediate portion of the U- shaped mounting frame Ill. Mounted on the outer face of said portion of the frame, in registration with said opening, is an adjustable guide block (0b having a slot or window therein for receiving the extreme end portion of the actuating pawl, as seen in Figure 3. It is to be unjusted with respect to the opening Illa so as to limit the extent of vertical and lateral movement of the actuating pawl, incident to the movement of the armature toward and away from the core of the relay 32. The purpose of providing for lateral movement of the actuating pawl is to permit the pawl to accommodate itself to the contour of the ratchet wheel during the vertical movement of said pawl in stepping the ratchet wheel, and thereby preclude binding of the ac tuating pawl and the ratchet wheel, which would otherwise occur as a result of the particular relationship of the pawl to the ratchet wheel.

To insure return of the pawl to a proper position to engage the next tooth of the ratchet wheel for successive stepping action, we provide a coil spring 46 which is connected to the outer end of the pawl and to a stud Inc on the inter mediate portion of the main frame so that the spring is disposed in an oblique angle, tending to draw the actuating pawl in an upward and inward direction, with respect to said ratchet wheel.

In the switch device herein illustrated it is intended that the portion of the circuit completed by the engagement of contact arm 22 with a certain contact button I6, be maintained only for a short period of duration after which the device is readjusted to a neutral or starting position. Accordingly, we provide a check pawl 5D pivotally mounted at 5| on the inside of the front or intermediate portion of the frame l, adjacent the lower edge. Said pawl includes a sharp, angularly formed nose 52 for engagement with the teeth of the ratchet wheel 3U, and the opposite end of the pawl terminates in an arm 53 to which is connected a coil spring 54, the opposite end of which spring is connected to the lower portion of the adjacent leg of the U-shaped frame I0, as shown in the drawings. The function of the spring 54 is to normally urge the pawl 50 in a direction to cause the nose portion 52 to engage the teeth of the ratchet wheel 30, and to serve to check or hold the ratchet wheel in various, stepped positions of adjustment, but permitting further step-by-step adjustment of the ratchet i wheel, by the action of the actuating pawl 40.

i piece 58. Connected to and derstood that said block lUb is adapted to be ad- Said check pawl5 is normally held out of engagement with the ratchet wheel 30, by means of a holding and reset relay 56 which is mounted on the leg of the U-shaped frame l0, opposite to that upon which the relay 32 is mounted. Said relay 56 is disposed in opposite relation to relay 32 in that its armature 51 is disposed at the lower end of the relay, and is hingedly mounted at one end on a field piece 58. Said armature 51 is normally urged in a downward direction, to the position seen in Figure 3, by means of a coil spring 59, which is connected to the heel end of the armature and to an extension lug on the field extending inwardly from one end of the check pawl 50 is a relatively rigid rod 6I, having an angularly bent offset portion positioned to engage beneath an insulating panel 62 secured to the lower surface of the armature 51. It is to be understood that the spring 59 of the armature 51 exerts a greater force than the spring 54 of the check pawl so that the armature 51 is normally maintained, when de-energized, in the position seen in Figure 3, and due to the engagement with the rod 6I holds the check pawl 50 out of engagement with the ratchet wheel 3U, as seen in Figure 4 of the drawings. As will hereinafter be described, the relay 55 is energized pawl 40, causing through an aperture lud yconnected in a manner tive contact buttons i during the period that ythe relay 32 is being energized by pulsations of electrical current for imparting a step-by-step action to the actuating step-by-step rotation of ratchet wheel 3|] and contact arms 22 and 23. Relay 56 may for convenience be termed a holding and reset relay because of its function in operation of the circuits being controlled.

In order that the selector switch be readjusted to a neutral or starting position after each adjustment for completing a preselected circuit, the ratchet wheel 38 is yieldingly urged in a counterclockwise direction with respect to the normal direction of operation by the actuating pawl 40. For this purpose we provide a coil Spring 65 surrounding a portion of the bearing 28, inside the frame IU, as seen in Figures 1 and 4 of the drawings, with one end of the spring extending in the intermediate portion of the main frame l and with the opposite portion of the spring anchored on a pin 36a on the adjacent face of the ratchet wheel. v

It will now be apparent that as the ratchet wheel is stepped by action of the pawl 49, the spring 55 becomes tensioned so that upon release of the ratchet wheel by check pawl 50, the spring 65 tends to rotate the ratchet wheel in counterclockwise direction. In order to arrest the ratchet wheel at a normal or starting position, which corresponds also drawings, the ratchet wheel is provided with a nubbin 39h adapted to engage a projecting shelf portion 89 of a bracket memberv E1, adjustably mounted on the inner portion of the main frame l0, so that when the nubbin engages said shelf portion, the ratchet Wheel will be adjusted at a neutral or starting position with the contact arm 22 likewise disposed in a neutral or starting position, as seen in Figure 5.

Mounted on the last mentioned leg of the U-shaped frame lil, immediately above relay 56, is a third relay 18 having its field piece 'Il rigidly attached to leg of said frame l0. Said relay is mounted with its coil extendingv horizontally and is provided with an armature 12 hingedly mounted at its lower end on the eld piece 1l, and the upper end portion being movable toward and away from the core 18a of the coil of the re'- lay. A spring 13 is connected to the heel end of the armature and to a lug extension of the eld piece for normally urging the armature away from the core of the coil. This relay may for convenience be termed a holding relay and is to control the electrical circuit including the relay 56, as will hereinafter be described.

Associated with the respective relays 32, 56 and 19 are switch devices connected in electrical circuits in a manner for controlling the make and break of a main electrical circuit sought to be energized and which in the present construction corresponds to a preselected circuit of the selector switch, namely, a circuit made through one of the contact buttons I6, when engaged by the contact arm 22, due to the step-by-step actuation of the ratchet wheel as above described.

It is to be understood that each of the different branch electrical circuits including the respeci, also include suitable mechanism adapted to be electrically energized or operated. For convenience in illustration we have shown in the wiring diagram represented in to a starting position ofthe Contact arm 22, as seen in Figure of the surface of the intermediate I to the respective contact buttons I6. Each branch circuit is shown as including a winding or coil indicated generally at 15, which it is to be y understood, may represent any suitable form of Figure 6 the branch circuit portions, connected 75 electrically energized device adapted to be operated when the particular branch circuit is completed through its corresponding contact button and the contact arm 22.

The switch devices associated with the respective relays will now be briefly described. Mounted on a bracket 11 attached to the iield piece 34 of the stepping relay 32 is a normally open switch including switch lingers 1.8 and 19 having their respective contact buttons 18a and 19a disposed in spaced-apart relation as shown in Figure 2 of the drawings. It is to be understood that these switch fingers are formed of yieldable material and are normally biased to closing position. Said ngers are supported between a plurality of blocks 11a of insulating material, carried on the upper end of bracket 11. The switch finger 19 includes an outer extension projecting beyond finger 18 and is provided with a depending plug of insulating material, adapted to be engaged by the stud `i3 connected to the armature 36 so that when the armature is free or in the position away from the core 32a of said relay 32, as seen in Figure 2 of the drawings, said plug 80 is raised to dispose the contact button 19a of switch finger 19, out of engagement with its cooperating contact button 18a of the other switch nger.

The hold and reset relay 56 has associated therewith a normally open switch including contacts 82 and 83, the former being mounted on the insulating member 62 and the latter being mounted between blocks of insulating material, indicated at 84, carried on an extension of the eld piece 58 as seen in Figure 3 of the drawings. It will be apparent that when the armature 51 is moved into engagement with the core 55a of said relay 5B, contact 82 is brought into cooperative engagement with contact 83 to complete a portion of an electrical circuit.

The holding relay 10 has associated therewith two switches; one being composed of a pair of contact members 8B and 81 normally disposed in engagement with each other and the other switch including a pair of contacts 88 and 89 normally disposed in spaced apart relation as seen vin Figure 4 of the drawings The contact fingers vlili and 88 of the respective switch are mounted in blocks of insulating material 98 secured to an extension of the eld piece 1| of the relay 18. The other respective switch members 81 and 89 are mounted on a panel 9| of insulating material secured to the outer surface of the armature 12. The switch fingers 81 and 89 are pivotallymounted at 81a and 89a respectively, adjacent the lower end of the insulating panel Sl and have springs 93 carried on studs 94 mounted adjacent the upper end of said panel. It will be noted that said springs are disposed in opposite relation, namely, so that contact arm B1 is urged away from the panel of insulating material, while the other spring tends to urge contact member 89 toward the panel of insulating material. By virtue of this arrangement, contact iinger 81 remains in engagement with the contact finger 86 during a portion of the initial movement of the armature toward its core 10a to maintain the portion of the electrical circuit including said switch members, for a short period after contact ringer 89 commences to engage and seat on its cooperating nger 88, for purposes as will hereinafter be described. Furthermore, when the armature 12 starts to move away from its core, switch nger 89 remains in engagement with finger 88, to maintain the portion of the circuit including said switch fingers for a short period after switch linger 81 engages its cooperating nger 86. Each of the respective relays 56 and 10 which are adapted to be energized by direct current, have associated with their coils a copper slug, indicated at 56D and 10b respectively. The function of the copper slugs is to obtain a timingaction by the induced current set up in the slugs immediately after the coils of the respective relays are deenergized.

The operation of the selector switch will now be described in conjunction with the wiring diagram illustrated in Figure 6. The stepping relay 32 is first energized intermittently by one or more pulsations of electrical current supplied by conductor wires and IUI, which pulsations are directly transmitted into mechanical movement by the armature 36, which in turn eiects step-by-step ratcheting action of the ratchet wheel 30, through the actuating pawl 40, and eiects step-by-step adjustment of the contact arms 22 and 23 so as to dispose Contact arm 22 in registration with a proper predetermined contact button |6 of a certain branch of a main electrical circuit sought to be energized, and which circuit includes any suitable form of electrically operated or controlled mechanism, to be actuated, as diagrammatically represented in Figure 6, by a coil 15. It will be apparent that as the armature 36 moves into engagement with the core 32a of the coil of the relay 32, the plug 80 is released so that switch nger 19 is free to move downwardly to dispose its contact 19a into engagement with contact 18a of switch finger 18 and thereby complete a portion of an electrical circuit through the direct current supply conductor wires |04, and |06 to energize the coil of the holding relay 1U.

Due to the intermittent action of stepping relay 32, the switch fingers 18 and 19are continuously moved into and out of engagement with each other for making and breaking the circuit to the relay 10, and similar pulsations of current are thus imparted to the relay 10 which ordinarily would cause intermittent movement of its armature 12 in a manner similar to the armature 36 of relay 32. Such intermittent operation of relay 10, however, is precluded by the use of the copper slug 10b which by induced magnetism retains the armature 12 attracted to the core 10a of the relay 10 for a period suicient to overlap the period between pulsations of the current supplied to said relay. Therefore, during the time that the relay 32 is being intermittently energized by pulsations of current, the armature 12 of relay 10 remains attracted to its core and during this time switch finger 81 is separated from its co operating nger 86, and switch finger 89 is in engagement with switch nger 88. This action of relay 10 serves to hold or complete ythrough switch fingers 88-89, a portion of an electrical circuit, during the interval that pulsations of electrical current are supplied to the `coil of relay 10 incident to the make and break action of switch fingers 18 and 19, resulting from the intermittent action of relay 32 by the pulsationof the electrical current supplied to said relay 32.

As may be seen in Figure 6, the hold and reset relay 56 is connected in shunt relation to relay 10 when the relay 10 is energized. This shunt circuit includes a conductor wire |08, connected to the direct currentl supply conductor wire I 04 and to the switch :finger 89. When the latter switch nger is in engagement with switch nger 88 it completes the electrical circuit through conductor wire I 09 through the coil of the hold and reset relay 56, and conductor Wire III) to the other supply conductor wire |06, for energizing said relay 56. Immediately after the relay 56 is deenergized, the copper slug 56h is built up with induced magnetism for holding the armature 56 attracted to the core of the coil of the relay 5B for a short interval period of time after opening of the shunt circuit, including said relay 55.

The devices represented by the coils 15, which may be selectively energized incident to adjustment of the selector switch, with the arm 22 engaging a predetermined contact button I6, may be energized by the same low current utilized for energizing the relays 10 and 56. Usually such devices as represented by the coils 15 often require a higher current and accordingly we have herein shown said devices connected in a separate high power circuit in which the main current supply lines are generally designated as line #1 and line #2. The circuit for the coils 15, representing devices to be selectively energized, includes a conductor wire I 2 for connecting current supply line #l to switch finger 81, and a conductor wire II4 connects switch nger 86 to the switch finger 82, associated with the relay 56, while a conductor wire |6 connects the cooperating switch linger 83 to conductor wire 20, which is connected to the contact strip 9, contact arm 23, through the contact arm 22 to a predetermined contact button I6, corresponding to the preselected circuit to be energized. Conductor wires I1, complete the circuit through the respective coils 15, to the other current supply line #2.

Normally when the selector switch is in inoperative position no current is permitted to ow through the main circuit including conductor wires I|2, H4 and I|6 and supply lines #l and #2, since the switch composed of members 82 and 83 is in open position. However, after pulsations of electrical energy are imparted to the stepping relay 32 for effecting selective adjustment of the arm 22 with a desired contact button I6, by the action above described, the main circuit, by the separation of switch ngers 88 and 81. remains open during the period that pulsating current is supplied to relay 32. Therefore, no current is permitted to flow through the main circuit including conductor wires |I2, H4 and IIS, and lines #l and #2, during the period that the contact arm 22 is moving from one contact to another.

Due to the fact that relay 56 functions as a hold and reset relay, which as above mentioned is energized during the time that the pulsations of current are being supplied to relay 32, the check pawl 50 is freed by the armature 51 moving out of engagement with the rod 6I so that said paw] 50, operatively engages the teeth of the ratchet wheel 30 and maintains the same in stepped positions of adjustment. Just as soon as pulsations of current cease to be supplied to relay 32, the switch members 18 and 19 are again opened by the armature 36 engaging plug 80 so as to break the circuit which supplies pulsating current to the relay 19. However, the relay 10, due to the copper slug 1912, causes the armature 12 to remain attracted to its core for a short interval of time after opening of said circuit, due to induced magnetism in the slug, vand during which interval current is still permitted to flow through the coil of relay S for maintaining said relay fully energized. After the armature T2 is permitted to move away from the core of the relay lli, upon dissipation of the induced magnetism in the copper slug 1Gb, the main electrical circuit may be energized to complete a preselected branch circuit including a coil 'i5 by reengagernent of switch fingers tt and 3l, just prior to separation of switch iingers S8 and 89, as above described, and current is then permitted to ow through said main circuit for a short interval of time. Said main circuit is maintained completed for the short interval of time by reason of the induced magnetism in the copper slug 56h of relay 56, by virtue of which the armature 5l is held in attracted position, with the switch fingers 32 and 83 in closed relation. After the induced magnetism in the copper slug 56D is dissipated, the armature El is permitted to move away from the coil oi said relay 5%, and thereby moves switch finger 82 out of engagement with switch iinger t3, breaking' the main electrical circuit. Such movementof the armature 5l again causes the rod 6i to move the check pawl 5i) out of engagement with the ratchet wheel 3i! so as to permit said ratchet wheel, under iniiuence of spring 55, to return to neutral or starting position, simultaneously returning the selector contact arm 22 to a neutral or starting position.

By virtue of the construction described, it will be apparent that there Will be no arcing as a result of contact arm 22 moving from one contact button to another since no current flows through the main electrical circuit, including the branch circuits, until the selector arm is arrested for a predetermined period of time in engagement with a predetermined contact button of a preselected circuit, after which period of time current is permitted to ow through such circuit for only a limited period of time, and the circuits are then broken and assume the normal inoperative condition.

Although we have herein shown and described a preferred embodiment of our invention, maniestly it is capable of modication and rearrangement of parts Without departing from the spirit and scope thereof. We do not, therefore, wish to be understood as limiting this invention to the precise embodiment herein disclosed, except as it may be so limited by the appended claims.

We claim as our invention:

1. In a direct current operated selector switch, the combination of a plurality of contacts connected in separate branches of a main electrical circuit, a movable contact arm, means including ratcheting mechanism connected to said arm, and electro-magnetic means adapted to be intermittently energized by impulses of electric current for actuating said ratcheting mechanism for shifting said arm in step-by-step Vfashion into engagement with a predetermined contact for completing a portion of a preselected branch circuit, spring means tending to return said ratcheting means and contact arm to a starting position, switch means adapted to be connected in the main electrical circuit, direct current operated time delay electro-magnetic means for controlling the switch means, said time delay means being subject to control by said impulse operated magneticmeans, for causing completion of said preselected branch circuit after the lapse of a timed interval, subsequent to engagement of the predetermined contact by said arm, a second direct current operated time delay electro-magnetic means, subject to control by said rst time delay means, for controlling said switch means to cause opening of said branch circuit after the lapse of a timed interval, and means controlled by the last mentioned time delay electro-magnetic means while the latter is energized for holding said ratcheting means and contact arm in stepped positions of adiustmen 2. In a direct current operated selector switch, the combination of a plurality of contacts connected in separate branches of a main electrical circuit, a movable contact arm, means including an electro-magnet adapted to be intermittently energized by impulses `of electrical current for shifting said arm in step-by-step fashion into engagement with a predetermined contact for completing a portion of a preselected branch circuit, a normally closed switch and a normally open switch connected in the main electrical circuit, direct current operated time delay electromagnetic means fcr controlling said closed switch, a normally open switch connected in the circuit of said time delay magnetic means and positioned to be controlled by said impulse operated electromagnet, a second direct current operated time delay electro-magnetic means for controlling the normally open switch of the main circuit, said last mentioned time delay means being connected in shunt relation to the first mentioned time delay means, and a normally open switch in said shunt circuit positioned to be controlled by said rst mentioned time delay electro-magnetic means, whereby the first time delay means serves to eiect energization of said preselected branch circuit after the lapse of a timed interval, subsequent to engagement of said predetermined contact by said arm, and the second time delay means serves to break said branch circuit after the lapse of a timed interval, said normally closed switch of the main circuit and said normally open switch in the shunt circuit being constructed and correlated in a manner to effect closing of one prior to effectively opening of the other to positively obtain said sequential timing of completion and breaking of said preselected branch circuit, in addition to the timing by said time delay electro-magnetic means.

MARVIN G. NELSEN. THEDORE OBSZARNY.

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