US1768452A - Time-delay controlling device and system - Google Patents

Description

June 24, 1930. B. w. JONES TIME DELAY CONTROLLING DEVICE AND SYSTEM Filed Dec. 29, 1926 Inventor: Benjamin W. Jones,

His Attorne g.

Patented June 24, 1930 UNITED STATES PATENT OFFICE BENJAMIN W. JONES, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK TIME-DELAY CONTROLLING DEVICE AND SYSTEM Application filed December 29, 1926. Serial No. 157,815.

The invention relates primarily to electrically operated circuit controlling devices that respond automatically a time interval after the occurrence of some predetermined condition such' as undervoltage or the like,

as well as to circuit controlling systems employing such devices. However, electrically operated time delay apparatus and systems embodying the present invention also may be adopted with advantage to accomplish other time delay controlling, signalling or similar functions.

One of the princi al objects of the invention is to provide or substantially instantaneous operation of the electrically operated time delay device, as well as time delay operation thereof. In this way either a time delay operation of the device or an instantaneous operation thereof may be obtained in accordance with difl'erent controlling conditions. Moreover it is intended that the instantaneous operation be effected entirely independently of the occurrence of the abnormal or other conditions to which the device is arranged to respond with a time relay operation. Preferably the instantaneous operation is under manual control.

Thus, as specifically applied to switching apparatus for controlling electric circuits,

the present invention makes it possible to obtain automatic time delay protection against the continuous of abnormal conditions in the circuit, and at the same time permits substantially instantaneous manual 85 control of the opening and closing of the circuit at will. In this connection one of the particular objects of the invention is to provide a special master control station for remotely controlled electrically operated cir- 4 cuit controlling devices such as motor starters, contactors, or the like which in the mast er control station itself, provides automatic time delay undervoltage protection as well as instantaneous manual push button control of the circuit; Furthermore, as will be pointed out more fully hereinafter, the special combined automatic time element undervoltage and push button master controlstation embodying the preferred form of the invention is of a relatively simple and inexpensive construction and may be applied almost universally to control the operation of all ordinary forms of remotely controlled motor starters, contactors or other electrically operated devices.

With the invention embodied in the preferred form of master control station indicated above, the closure of the line contactor for the motor or other circuit is effected by operation of a normally open, starting or circuit closing push button switch in the usual manner. However, the arrangement of the master control station is such that at the same time an electromagnet located in the control station itself is connected to be energized in accordance with the. voltage of the controlled circuit. With normal voltage in the circuit the movable armature of the electromagnet serves to close immediately a second normally open contact through which 70 holding circuits for the main line contactor and also the voltage responsive electromagnet are established. Some suitable form of time delay mechanism, such for example, as a flywheel or a gear escapement is normally connected to delay the return operation of the voltage responsive electromagnet armature to open the holding circuit switch con tact for a time interval after the occurrence of undervoltage conditions.

In order, however, to permit the motor stop or circuit opening push button to efiect instantaneous opening of the main line contactor whenever desired, provision is made whereby the stop button not only disconnects the timing device but also opens the holding circuit switch contact and thereby de-energizes both the voltage responsive electromagnet as well as the main line contactor. In the preferred forms of control stations described hereinafter a resilient spring connection between the armature of the voltage electro-magnet and the holding circuit switch contact serves as a lost motion connection to allow the necessary opening movement of the latter by the stop push button. With the time delay device disconnected and the holding circuit contact open, the main line contactor is at once opened and the armature of the voltages responsive Fri) i undervolte o control station time delay provided with mechanism ot the flywheel Fig. 2 shows a modification e ing a. gear escapement type of time delay device, and fig. 3 a schematic diagram cult comiections used with either er control stations shown in Fig.

and E2 in controlling an electromagnetic h for a motor circuit.

to i construction shown in Fig. l, the combined pr button and automatic time delay undervoltage control station has a base of insulating material, upon which the undervoltage electromagnet 11; the start or circuit closing push button mechanism 12; the stop or circuit opening push button mechanism 13; and the rotatable flywheel timing element 1% are respectively mounted.

Electromagi it 11 may be of any ordinary type, and as shown has a movable magnetic core or armature 15 which is lifted when the electromagnet 11 is energized and falls when the electron agnet is ale-energized. A racl: arm 16 is pivotally connected to the lower and of the armature 15 by the pin 17 and is biased by the spring 18 to engage with the toothel shaft 19 of the flywheel The arrangement is such that the teeth on the raclr arm 16 mesh firmly with the teeth on the J reel shaft 19 only when the racl; arm 16 nov s downwardly, but are freely disengaged to allow unrestrained upward movement of the raclr arm 16. This readily may be accomplished by slightly sloping the raclt arm teeth in the downward direction.

The manual start or circuit closing push button mechanism 12 is of a quite simple construction having the bridging contact member 20 biased out of engagement with the cooperating stationary contacts 21 by the spring 22. The bridging contact 20 is secured to the bent member which slides along the stationary support and guide 24 and carries at its outer end the start push button 25.

The manual stop or circuit opening push button mechanism 13 operates upon the bridging contact 26 which is held in circuit closing engagement with the cooperating stationary contact 27 through the lost motion connection formed by the tension spring 18 when the armature 15 is attracted by the voltage responsive electromagnet 11. At its center the bridqing contact 26 is loosely secured to the lever arm 28 mounted electromagnet operates ins rntaneously to upon the pivot pin 29 extending from the maintain the honing circuit cont-act its support 30, the latter being suitably secured open position, 1 reoaratory to subsequent to the base 10. An operating member 31 operation of the start or circuit closing push having the stop push button 13 fixed upon button. the end thereof is pivotally connected to the In the d embodiments oi" the inupper end of the lwer arm by the pin 33 vention il l in the accompanyin and as shown is provided with an elongated drawings, 'llustr tes the combined slot 34% through which a. reduced section of push button and nton at ic tine element the flywheel shaft 19 loosely passes and series as a guide therefor. The operating member 31 has a bent up portion 01 which engages with the end of the raclr as to move the rack teeth out at sh with the toothed shaft 19 when the bringing contact member 26 is operated to the circuit opening position by the stop push button. Hence, with the time delay flywheel l l entirely disconnected and thus rendered ineffective to retard the descent of the arma ture 15, substantially instantaneous operation instead of time delay operation of the armature 15 to engage with the pin 18 and thereby open contact 26 inherently occurs.

The actual operation of the combined manual and automatic control station construction just described may be more clearly understood by reference to the circuit diagram shown in Fig. In Fig. 3 a plurality of control stations 35, 36 and 37 are shown schematically, each of which may be of the construction shown in Fig. l, and are connected to control the opening and closing of the electromagnetic contactor 38 which in turn controls the energizing circuit of motor 39 from the supply lines 40. To start motor 39, any one of the start buttons 12 with which each of the master control stations is provided may be operated to the closed position. With the supply lines 40 energized at normal voltage from a suitable source not shown in the drawing, this results in energizing the motor line eontactor 38 in parallel circuit with each of the undervoltage electromagnets 11 in the respective control stations 35, 36 and 37, the energizing circuits being obvious. Line contactor 38 at once responds to close the motor circuit. Each of the voltage responsive electromagnets 11 at once responds to raise its armature l5 and through the agency of the spring 18 close the respective holding circuit contact 26 controlled thereby. With all of the holding circuit contacts 26 closed, the starting push buttons 12 are shunted toestablish a holding circuit for maintaining line contactor 38 as well as electromagnets 11 energized from the supply lines 40.

Under these conditions the voltage responsive eleetromagnets 11 each function to provide time element undervoltago protection to the motor circuit. For example, in case a temporary decrease in the voltage of the supply lines L0 should occur, the energi-- zation of the line cont-actor 38 and also of the voltage responsive electromagnets 11 may be reduced 'sufiiciently to allow the opening of the line contaetor and operation of the armatures 15 of the voltage responsive electromagnets to open the holding circuit contact 26 controlled thereby. However, with the armature 15 of each of the voltage electromagnets 11' connected with a .time delay device in the manner illustrated and described in connection with Fig. l, the opening of the corresponding holding circuit contact 26 is delayed for. a time interval after the occurrence of undervoltage conditions on the supply lines while the armature 15 is operated slowly to take up the lost motion in the spring 18 and finally engage with the pin 18 If the undervoltage condition continues for suflicient interval to permit the armature of the several voltage responsive electromagnets 11 to operate the corresponding holding circuit contact 26 to the open posi tion, the holding circuit of course is interrupted. Thereafter operation of one of the start push buttons 12 is required to reclose the motor line contaetor 88 as previously described.

In case, however, the undervoltage condition exists only for a short interval and normal voltage is restored on the supply lines 40 before any one of the holding circuit contacts 26 have been operated to the open position, due to action of the time delay device, the motor line contaetor is immediately reclosed through the holding circuit that is maintained established through the contacts 26. At the same time the voltage responsive electromagnets 11 are re-energized with full voltage and their armatures 15 are at once attracted to maintain the corresponding holding circuit contact 26 in the closed position through the agency of the tension springs 18'.

If at any time it should be desired to voluntarily open the motor line contaetor 38, this readily is accomplished by operation of any one of the stop push buttons 13'. As previously pointed out in connection with Fig. 1, the tension spring 18 permits the holding circuit contact 26 to be manually operated to the open position even though the armature 15 is maintained in the attracted position. Simultaneously with the opening of the holding circuit. contact 26, the time element device of the particular controlled station involved is disconnected in the manner previously described in detail in connection with the control station structure illustrated in Fig. 1. Thus with the holding circuit contact 26' opened and the time delay device disconnected, the armature 15' immediately and without any time delay, drops to maintain the holding circuit contact 26 in the open position. This insures that even though the stop push button 13 is only operated momentarily still the holding circuit is effectively interrupted during this short interval. With the holding circuit once permanently interrupted by the dropping of armature 1-5 the line contaetor 88 necessarily is de-energized and opens the motor circuit at once.

The modified construction of the combined time delay undervoltage and manual push button master control station shown in Fig. 2 embodies substantially the same elements as the control station shown in Fig. 1, namely, a base 10, a' voltage responsive electromagnet 11*, a start or circuit closing push buttonmechanism 12*, a stop or circuit opening push button mechanism 13, as Well as a time delay mechanism 14 which in this case is of the gear escapement type. Moreover the armature 15 of the voltage responsive electromagnetll is connected to the rack arm 16 by the pin 17, and the spring 18 serves to bias the teeth on the rack arm 16 into meshing engagement with the toothed shaft 19 of the gear escapement time device 14* in a quite similar manner to the arrangement of Fig.1.

The start or circuit closing push button mechanism 12 in Fig. 2 is of somewhat different construction and has a bridging contact 60 for the stationary contact 61 loosely supported at its center upon the arm 62 which is pivotally supported upon the pin 63. The spring 64: shown in dotted lines is arranged to bias the arm 62 into engagement with the stop 65 and thereby maintain the bridging contact 60 in its normally open position.

The stop or circuit opening push button mechanism 13* operates upon the bridging contact 26 for the two stationary contacts 27 In the construction shown in Fig. 2 the contact 26 is loosely supported at its center upon one end of the ball crank lever arm 28* which is rotatable about the pivot pin 29 and the stop push button is loosely connected to the other end of the bell crank arm 68 by the links 71 and the pin 72. a

In order that operation of the stop push button 70 may disconnect the clock escapement timing device 14 simultaneously with the opening of the bridging contact 26 an extension arm 73 is connected with the end of the pin 7 2 and the bent up portion 7 4 of the arm is disposed so as to engage with the finger 75 formed integral with the rack 16" and thereby move the rack teeth out of meshing engagement with the toothed shaft 19 of the gear escapement time delay mechanism.

. The gear escapement time delay mechanism 14 in the form shown is fully described and claimed in the pending application of Homer Golf, Serial No. 161,919 filed January 18, 1927, and assigned to the assignee of my present invention. Briefly,the Gofli" form of time delay mechanism comprises a toothed wheel 7 6 formed of a moulded composition of spinnable textile material with a double acting escapement pawl 77 in cooperating relation therewith The end of the toothed shaft 19 on which the escapement gear 7 6 is mounted, together with the pivot pin 78 upon which the pawl 77 is mounted are carried by the support 79 which is suitably secured to base 10. The pawl 77 has a threaded pendulum arm 80 extending therefrom upon which the two threaded nuts 81 may be adjusted to produce the desired pendulum effect. The whole arrangement is such that upon rotation of the wheel 7 6 the opposing faces of the pawl 77 on either side of the pivot pin 78 alternately engage with the teeth on the wheel 7 6 and thereby rapidly oscillate the pendulum arm 80. Obviously the rate of oscillation of the pendulum arm 80 is dependent upon the distance of the nuts 81 from the pivot pin 78. With the nuts 81 set close to the pivot pin the rate of oscillation is quite rapid while with the nuts 81 at the end of the pendulum arm 80 the rate of oscillation is relatively slower. As more fully pointed out in the above mentioned Golf patent application this type of time delay mechanism is capable of providing definite time delay action throughout an extended period of service without material variation. At the same time the time delay mechanism is of such simple construction that it may be manufactured cheaply and installed and maintained in adjustment with very little trouble. Moreover the time delay action of this form of mechanism may be adjusted over a quite considerable range, simply by varying the position of the nuts 81 on the pendulum arm 80.

lVith the modified construction illustrated in Fig. 2 embodied in a motor control system such as illustrated in Fig. 3, exactly the same control functions may be obtained as previously described. The voltage electroresponsive magnet 11 is energized whenever any one of the start push buttons 12 is operated to close the motor line contactorand at once attracts its armature 15 With the teeth on the rack arm 16 suitably formed to permit unrestrained upward movement in the sameway as previously described, the bridging contact 26 is at once closed and completes the holding circuits for the motor line contactor as well as the voltage responsive electromagnets. Upon the occurrence of undervoltage conditions, the armature 15 is released and drops slowly due to the engagement of the rack l6 with the .toothed shaft 19 of the time delay device 14. If normal voltage conditions are restored before the downward movement of the rack 16* is sufficient to engage and open the bridging contact 26', the full energization of the voltage responsive electromagnet 11 at once returns the armature 15 to the attracted position. If the undervoltage condition continues for a sufficient interval, the final downward movement of the rack 16 effects the opening of the bridging contact 26 which is in the holding circuit of the motor line contactor and also the voltage responsive electromagnet 11. The resulting opening of the line contactor disconnects the motor and the contact 26 remains open until after the starting push button 12 is again operated.

The manual opening of the motor line contactor may be accomplished at any time by operation of the stop push button 13"*. In this case not only the bridging contact 26 is opened, but also the gear escapement time delay mechanism M is disconnected and thereby rendered ineffective to delay downward movement of armature l5 and rack arm 16. Consequently, the undervoltage time mechanism is operated substantially instantaneously to maintain the holding circuit contact 26 in the open position.

From the foregoing it will be seen that the present invention makes it possible to provide time delay automatic protection against the continuance of abnormal conditions in an electric circuit, and at the same time provides for substantially instantaneous manual control of the circuit at will, all with a relatively simple, compact and inexpensive form of master control station. \Vhile the control apparatus illustrating the prefered embodiment of the invention is designed and intended primarily for controlling electrically operated motor starting switch mechanism or the like, the apparatus readily may be modified for adaptation to other controlling functions, such, for example, as signalling, indicating or the like. Moreover, other embodiments of the invention than the specific forms illustrated in the drawing may be devised by those skilled in the art.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In a controlling device, the combination of a movable controlling member, means tending to move the member in one position, means for maintaining the member in another position and for automatically releasing the member in response to predetermined conditions for operation by said first means, time delay means for retarding the movement of the member by said first means from said other position to said one position, and means for controlling said automatically responsive holding means and said movement retarding means to effect substantially instantaneous movement of the memher from said other position to said one position by said first means independently of said conditions.

2. In a controlling device, the combina tion of a movable controlling member, electroresponsive means for controlling the operation of the said member in response to a predetermined variation in the energization of said means, time delay means for retarding operation of the member for a time interval after the said variation in the energization of said means, and means for simultaneously controlling both the energization of said electroresponsive means and said time delay means to effect substantially instantaneous operation of said member.

3. In a controlling device, the combination of a movable controlling member biased to one position, electrically controlled means for holding the member in another position, said means being operable with a time delay action in response to the occurrence of certain conditions for releasing the member from said other position for operating in accordance with its bias andmeans including a circuit controlling element for controlling said electrically controlled time delay means to effect substantially instantaneous release of the member from said position independently of said conditions.

4:. In a circuit controlling device, the combination of a movable circuit controlling member, electrically controlled time delay means for maintaining the member in one position and operable with a time delay action to release the member therefrom, and means comprising said movable circuit controlling member for controlling said electrically controlled time delay means to eiiect substantially instantaneous release of the member from said position.

5. In a controlling device, the combination of a movable controlling member, electrically controlled means having a movable element, a yielding connection between said member and said element through which the member is maintained in one position and released therefrom after a limited movement of said element, time delay means for delaying the said limited movement of the element, and independently operable means for rendering said time delay means ineffective to permit thereby substantially instantaneous release of the member.

6. A circuit controlling device comprising a movable switch member, electroresponsive means having a movable element connected with the switch member for operating the same to and from a circuit controlling position, time delay means normally connected with said movable element for retarding one of said movements of the switch memher, and means for disconnecting said time delay means and simultaneously controlling said electroresponsive means to effect said one movement of the switch member substantially instantaneously.

7. In a circuit controlling device, the combination of a movable circuit controlling member, elcctroresponsive means having a movable element, a lost motion connection between said element and said movable controlling member through which the member is maintained in one position upon op eration of the movable element to a corresponding position and released therefrom after a limited movement of said element from said position, time element means for retarding the said limited movement of said element, and independently operable means for controlling said electrically operated means and rendering said time delay means ineifective to thereby effect substantially instantaneous release of the circuit controlling member from said position.

8. In a circuit controlling device, the combination of a movable switch member, electroresponsive means for effecting a circuit controlling movement of the switch member in response to predetermined electrical conditions, time delay means associated with said electroresponsive means for delaying said movement of the switch member for a time interval after the occurrence of said predetermined condition, and means for rendering said time delay means inactive and simultaneously controlling the energization of said electroresponsive means to effect said circuit controlling'movement of the switch member substantially, instantaneously, and independently of said predetermined electrical condition.

9. A circuit controlling device comprising a movable switch member, electroresponsive means having a movable element connected with the switch member for operating the same to a certain circuit controlling position upon a predetermined energization of the electroresponsive means and arranged to operate the switch member from said position upon a predetermined variation in the energization of the elcctroresponsive means, time delay means associated with said electroresponsive means for delaying operation of the switch member from said position for a time interval after the said variation in the energization of said electroresponsive means, and means for rendering said time delay means inactive and simultaneously varying the energization of said electroresponsive means to effect substantially instantaneous operation of said switch memher from said position.

10. A controlling device comprising a movable controlling member, electroresponsive means operably connected therewith to effect operation of the controlling member from one position to another position upon energization of said means, means for controlling the energization of said electroresponsive means to hold said controlling member in said other position, time delay means normally arranged to delay the return of said controlling member to said one rendering said time delay means ineffective and simultaneously operating said means controlling the energization of said electroresponsive means to effect a substantially in stantaneous return of the controlling member to said one position.

11. A circuit controlling device comprising a movable switch member, an electroinagnet having a movable magnetic member, a yielding connection between the said member and the switch member for operating the same to and from a circuit controlling position in accordance with movement of the magnetic member, a time delay mechanism normally connected with said movable magnetic member for retarding movement thereof to effect operation of the switch member from said circuit controlling position, and manually operated means for disconnecting said time delay mechanism and simultaneously controlling the energization of said electromagnet to effect substantially instantaneous operation of said movable magnetic member to operate the switch member from said position.

12. A circuit controlling device comprising a movable switch member, an electromagnet having a movable magnetic member, a lost motion connection between said switch member and said magnetic member through which the magnetic member controls the operation of the switch member to and from a circuit controlling position, a time delay mechanism normally connected with said movable magnetic member and arranged to permit instantaneous operation of the switch member to said circuitcontrolling position and to retard movement of the magnetic member to operate the switch member from said circuit controlling position and means for disconnecting said time delay mechanism and simultaneously controlling the electromagnet to effect movement of the magnetic member to operate the switch member from said circuit controlling position substantially instantaneously.

13. A combined automatic undervoltage and manual control station comprising a manual circuit controlling switch, electroresponsive means for maintaining said switch in the closed position under normal voltage conditions and operable with a time delay action to open said switch upon the occurrence of undervoltage conditions, and mechanism associated with said switch for effecting substantially instantaneous action of said electroresponsive means to open the switch upon manual operation of the switch to the open position.

1%. A combined automatic undervoltage and manual control station comprising a push button switch biased to the open position, electroresponsive means for maintaining said switch in the closed position under normal voltage conditions and operable with a time delay action for releasing said switch to open in accordance with its bias upon the occurrence of undervoltage conditions, and mechanism associated with said push button switch for effecting substantially instantaneous action of-said electroresponsive time delay means to release the switch upon manual operation of the switch to the open position.

15. A combined automatic undervoltage and manual control station comprising a push button switch, an electromagnet having a movable magnetic member connected with said switch for maintaining the same in the closed position under normal voltage conditions, said magnetic member being biased to open said switch upon the occurrence of undervoltage conditions, a time delay mechanism connected with said movable member and arranged to permit instantaneous operation thereof to maintain said switch closed and to retard operation thereof to open said switch, and means effective upon manual operation of said switch for rendering said time delay means inactive and thereby permit substantially instantaneous operation of said magnetic member to open said switch.

16. A combined automatic undervoltage and manual control station comprising a circuit controlling push button switch biased to the open position, electroresponsive means for maintaining said switch in the closed position under normal voltage conditions and arranged to release the switch to open in accordance with the bias upon the occurrence of undervoltage conditions, time delay means cooperating with said electroresponsive means to delay the release of the switch from the closed position for an interval after the occurrence of undervoltage conditions and means for rendering said electroresponsive means and said time delay means both ineffective upon manual operation of the switch to the open position.

17. A combined automatic undervoltage and manual control station comprising a pair of circuit controlling push button switches each biased to the o en position, electroresponsive means control ed by one of said switches for maintaining the second switch in the closed position under normal voltage conditions, said electroresponsive means being operable with a time delay action to release said second switch to open in accordance with its bias upon the occurrence of undervoltage conditions, and mechanism associated with said second push button switch for effecting substantially instantane- 7 ans action of said electroresponsive means to release said second switch upon manual operation thereof to the open position:

18. A. combined automatlc undervoltage and manual control station comprising a pair of push button switches each biased to the open position, an electromagnet having a movable magnetic member connected with one of said switches for maintaining the same in the closed position under normal voltage conditions and operable with a time delay action to release said switch to open in accordance with its bias upon the occurrence of undervoltage conditions, time delay means cooperating with said electroresponsive means to delay the release of said switch for an interval after the occurrence of said under-voltage conditions, mechanism associated with said one push button switch for rendering said time delay means inefi'ective upon manual operation of said switch, and connections through which the electroresponsive means is energized upon operation of the second switch to the closed position and maintained energized upon the resulting closure of said first switch whereby manual operation of said first switch to the open position deenergizes said electroresponsive means and simultaneously renders said time delay means ineffective.

19. The combination with an electromagnetic switch, of time element electroresponsive means connected to be energized upon energization of said electromagnetic switch for establishing a holding circuit therefor, said electroresponsive means being operable in accordance withmpredetermined electrical conditions with a time delay action to interrupt said holding circuit, and means for effecting substantially instantaneous oporation of said time element electroresponsive means to interrupt said holding circuit independently of said predetermined electrical conditions.

20. A control system for an electrical device having an operating winding comprising a pair of se arately operable switches, the first switch or establishing an energizing circuit for said winding and the second switch for controlling a holding circuit for the winding, automatic time element electr oresponsive means under the control of said first switch for operating said second switch to establish the said holding circuit for said winding and to maintain the said holding circuit established for a time interval after the occurrence of predetermined electrical conditions, and means controlled by said second switch for rendering said time element electroresponsive means inactive substantially instantaneously upon independent operation of the second switch to interrupt the said holding circuit of said winding.

21. A combined automatic and manual control system comprising an electrically operated switch, a pair of manual control switches therefor, one for closing said electrically operated switch and the second for opening said electrically operated switch,

and automatic electroresponsive means for operating said second control switch a time interval after the occurrence of predetermined electrical conditions.

22. A combined automatic and manual control system comprising an electrically operated switch biased to the open position and having an electromagnet for operating the switch to and maintaining the switch in the closed position, a pair of manually operable control switches therefor, one for establishing an energizing circuit for said operating'electromagnet and the other for interrupting a holding circuit therefor at will, and automatic electroresponsive means for operating said second switch a time interval after the occurrence of predetermined electrical conditions.

23. A. combined automatic under-voltage and push button control system for an electric circuit comprising an electromagnetically operated switch biased to the open position, a pair of master push button control switches therefor each normally biased to the open position, the first for establish-' ing an energizing circuit for said electromagnetically operated switch and the second for controlling a holding circuit for the electromagnetically operated switch, an electromagnet having a movable magnetic member yieldingly connected with thesecond push button switch for biasing the same to the closed position upon energization of the electromagnet, a time delay mechanism normally connected with said movable magnetic member for retarding operation thereof to release said second push button switch upon a predetermined reduction in the energization of the electromagnet, connections through which the electromagnet is energized in accordance with the voltage of the circuit upon operation of the first push button switch to the closed position, and through which said electromagnet is maintained energized in accordance with the voltage of the circuit upon the resulting closure of the second push button switch, and means whereby the time delay mechanism is disconnected from the said movable magnetic member upon manual operation of said second switch to interrupt the circuits for said electromagnetically operated switch

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