US2567473A - Time interval circuit - Google Patents

Description

Sept. 11, 1951 D w 2,567,473

TIME IQNTERVAL. CIRCUIT Filed Dec. 13, 1946 157 r ezzfor Sept. 11, 1951 PATENT OFFICE 'rnu: INTERVAL cntcUrr 7 Albert J. ml... Milwaukee, wa., asalgnor to Allen-Bradley Company, Milwaukee, Wis., a eerperatielefwbeonliu Application December 1:, 1946. Serial No. 110,038

' a cm (01. 175-373) This invention relates to delayed response electrical apparatus and resides more particularly in an improved form of delayed-action or interval timing circuit in which a grid-controlled gasfilied glow-discharge tube or grid-glow tube is related with other circuit elements in such fashion that firing of the .tube is regulated by gradual charging of thegrid and the interval during which the tube remains conducting upon firing is reduced to'a minimum.

An object of this invention is to provide delayed-action interval timing circuit apparatus dependent for its action upon a grid-glow tube in which tube life is greatly extended by reason of a very low ratio of active to inactive time of use of the tube. 1

Another object of this invention is to provide a delayed-action interval timing circuit apparatus dependent for its action upon a grid-glow tube in which increased dependability and consistency of response of the tube is obtained due to the comparatlvely brief periods during which the tube is loaded.

Another object of this invention is to p OYide a delayed-action interval timing circuit apparatus possessed of the advantages of constantreadiuses to perform without a "warm up delay and of freedom'from standby current requirements. Another object of this invention is to provide a simplified delayed-action interval circuit apparatus adapted for operation with filternating current supply and capable of repetitive timing of-successive intervals through ifg'ingle interval determining instrumentallty. Delayed-action circuit apparatuses of various forms, depending upon the controlled function of thermionic or gaseous discharge devices have been extensively used. In the case of ap paratus depending for operation upon thermionic devices, disadvantages are involved because of the necessity of maintaining standby conditions involving continuous supply of filament or heater current and because of the large expenditure of available tube life during idle conditions. A further disadvantage also is the waiting .period for warm up" that may be involved. The two element glow-discharge tube as heretofore employed has also suffered a disadvantage in that the quantity of energy available for actuation of a relay actuated thereby is limi to the charge prevailing in the capacitor at the moment of "striking" of the tube. If for any reason the relay does not react positively to the quantity of energy thus delivered, unreliable response is encountered. Such circuits are. therefore, dependent upon undesirably delicate relays lacking in the ruggedness preferred for industrial equipment. The grid-glow or three element gaseous discharge tube has heretofore been little used for g delayed-action circuits because its behavior in the circuits employed has been considered fickle and unreliable. Such unreliability has been attributed to shifting of tube characteristics as a result of the history of treatment to which the tube has been subjected. The grid-glow tube, however, is possessed of the advantage of being able to perform without standby demand and without "warm up" delay and may be controlled to continue supply of energy to a relay for any interval which may be required to cause its positive operation.

Through this invention consistent and dependable response is obtained in a delayed-action or interval timing circuit apparatus which is dependent upon a grid-glow tube for its operation by a novel circuit arrangement in which load is imposed upon the tube only so long as is required for positive relay operation. By reason of the very brief intervals during which load is imposed upon the grid-glow tube, shifting of tube characteristics is held well within limits such that practical consistency of operation is obtained. Furthermore, the total time of functioning required of the grid-glow tube for a large number of cycles is so short that the life of the tube in use is greatly extended.

This invention is herein described by reference to the accompanying drawing in which there is set forth by way of illustration and not of limitation one form in which the circuit of this invention may be embodied.

In the drawing the figure shows diagrammatically a circuit constructed in accordance with this invention applied to the regulation of the starting function of an alternating current induction motor. 7 a

As depicted in the drawing the time delay apparatus of this invention depends for its operation upon a cold cathode grid-controlled gasfilled glow-discharge tube I. The cathode of tube 1 constituting one of its main electrodes is connected by a lead 2, a resistor 3, normally closed switch contacts I and lead I with an adjustable tap 8 of an auto transformer I. The anode of tube I constituting the other main electrode is connected by lead I and lead I 'with one end of the winding of a relay II. The opposite endof the winding of the relay II is connected by lead H with terminal I! of the auto transformer I. In this manner a plate circuit is provided through which current may be passed to the relay III for energizing the same whenever the tube I becomes conducting. I

The grid I3 oi! tube I is arranged to be charged at a regulated rate through the action or half wave rectifier I4. Rectifier I4 is connected on one side by lead I5 and lead II with terminal I2 of the auto transformer 1 and on'the opposite-side through-leads I5 and I1 with a capacitor I8. 'The capacitor I3 is connected on its opposite side through a lead I9 with resistor 3 and thence through switch'contacts 4 and lead 5 with the tap-5 of transformer 1. In this way, with trans former 1 supplied with alternating current through leads 29 and 2I, the capacitor I3 be- 4 cycle and then immediately drops to start a new timing interval. For each energization of the relay III the tube I remains excited for only a very brief period. Usually two or three current cycles are sufl'lcient to cause the relayIfl to move. The life of tube I thus is greatly extended even though a large number of timing cycles is employed since even under conditions of. repeated timing cycles the total active time 01' the tube I is extremely small.

The interval timing circuit above described may be employed for any purpose which requires a switching function automatically regulated to occur -at pre-determined intervals. One such comes charged through the action oi! the rectifier v resistor 22 having a movable side tap which is connected in turn through switch contacts 23 and lead 24 with one side 01 a capacitor 25. Alternatively connected to lead I1 is a variable resistor requirement is the successive reduction or the secondary resistance of a wound rotor induction motor during starting. The drawing shows the timing circuit of 'this invention thus applied.

' As shown in the drawing a motor 39 is connected 22' which is connected in turn through switch contacts 23' and lead 24 with the capacitor 25 as shown. The opposite side of capacitor 25 is connected through lead 25v with lead I9 and, consequently, with-the cathode of tube I. Lead 24 is connected by lead 21, resistor 29 and lead 29 with the grid I3 of tube I. Thus when current is supplied to the auto transformer 1 and lead I1 becomes negative, current fiows through the relatively high resistance of resistor 22 .(or resistor 22' depending upon the position of switch contacts 23 and 23') at a limited rate with the result that capacitor 25 gradually becomes charged. The rate at which capacitor, 25 becomes charged may be altered by adiustment oi resistor 22 or resistor 22' as the case may be so that the time required for the ,grid I3 to reach a charge which will cause firing of tube I may be adjusted.

Having selected an adjustment for the resistor 22 and having applied current to the auto trans-1 Iormer 1 the grid I3 or tube I will at some prethrough leads 40, M and with a load contactor -43 which is connected in turn with power supply mains 44, 45 and 45. Control current for closing the contactor 43 is supplied from main 46 and from thence passes through normally closed stop switch 41, normally open start switch 49, lead 52 and overload control 49 to the coil of contactor 43 from which connection to supply main 45 is provided by lead 59. Upon closure of the starting switch 48 the contactor 43 closes-and in so doing establishes a maintaining circuit through stop switch- 41, lead 5|, auxiliary contacts 53,

I lead 52', overload control 49 to the coil of condetermined interval after commencement of excitation of transformer 1 reach a potential at which the tube I fires thus admitting current to the winding oi. relay I0.

Upon excitation of the winding'of relay ID the movable member of contact 4 is shifted into engagement with stationary contact '4' which is connected through lead 30 with the grid lead 21. In this way the capacitor 25 is caused to discharge through the resistor 3 which reduces the charge on the grid I3 of tube I, thus preparing the same for a succeeding timing function. At the same time normally open contacts 3| become closed and this establishes a circuit through leads 32 and 33 which causes the capacitor I8 to empty its charge through the resistor 3 likewise. At the same time normally closed contacts 4 open thus breaking the supply of current to the cathode of tube I.

In order that the relay III remain excited when desired after a single timing interval a maintain- I ing circuit is provided which extends from line tactor 43.thus causing the contactor 43 to remain closed until the stop switch 41 is opened.

Upon closure of start switch 48 or of maintaining contacts 53, current also becomes supplied to the transformer 1 by reason of lead 54 which joins with lead 2I and by reason of the connection of lead 29 to switch 55, which in turn is connected through lead 55, normally closed contacts 51,--to' be described in greater detail later, and lead 58 with main 45. As a result of theclosure oi. contactor 43,'assuming switch 55 is in closed position, a timing interval is initiated inthe timing circuit, and at the same time the motor 39 becomes energized with a maximum of resistance in its secondary circuit.

At the end of the first timing interval, assuming switch 34 to be open, normally 'open contacts 59 become closed momentarily and in so doing establish a circuit extending from line 45 through lead-53, lead 59, lead H to the winding of contactor 52 and thence through leads 53, 54, 55 and the contacts 59 to the lead 85 and thence through lead 54 and maintaining contacts 53, lead Ill and stop switch 41 back to power line 45. The establishment of this circuit causes contactor 52 to close and to short out the resistances 51 in the secondary of motor 39.

Upon closure of contactor 52 a maintaining circuit for causing the same to be retained in closed position is established through auxiliary contacts 58' and lead 59. At the same time through mechanical interlock 52' contacts 23ware opened and contacts 23' closed.

Following the first momentary closure of relay I0, normally closed contacts 19 re-engage and upon such re-engagement a subsequent step circuit, prepared by the closure of the auxiliary contacts 53, becomes completed. This subsequent step circuit extends from contacts .58 through lead 55 and through the contacts 10 and leads II and 12 to the winding of interlock relay 13, the

other end of which winding is joined with lead upon closing maintains itself in closed position through the action of auxiliary contacts I4 connected by lead with lead 64 as shown.

The closure of relay I3 through closure of its contacts 16 then sets up but does not complete an energizing circuit for a contactor 11. The circuit thus prepared extends through lead 13, the winding of contactor 11, lead 19, contacts 13, lead 90 to a pair of normally open contacts 9|. The contacts 8| are joined in turn through a lead 33 with lead 66. By reason of this preparatory action upon occurrence of the second succeeding closure of relay In at the end of the second timing interval, contactor l1 closes and in so doing eliminates the remaining resistances 93 from the secondary of motor 39. It will be understood that the duration of the first timing interval will be determined by the adjustment of resistor 23 while the duration of the following interval will be determined by the adjustment of resistor 22. These two intervals may thus be independently varied within the limits of adjustment available.

Closure of contactor I1 also establishes its own maintaining circuit through maintaining contacts 84 and lead 85 causing it to remain closed after re-opening of relay l0. At the same time upon closure of contactor 11 the normally closed contacts 51 previously referred to are caused to open, thus interrupting power supply to the transformer I so as to terminate further repetition of timing intervals by the timing circuit. The motor 39 thus is brought up to operating speed through three successive stages of resistance in its secondary circuit and this sequence is performed automatically without intervention of the operator once the starting switch 48 is closed. In order to stop the motor the stop switch 41 is opened causing contactors 43, 62 and 11 to drop open closing contacts 51 and also deenergizing relay 13. The circuit is thus brought into condition for execution of a new starting sequence whenever start switch 48 is again closed.

If it is desired that the motor 39 be run at reduced speed switch 55 may be opened before closing of the starting switch 49. In this case the motor 39 will continue to run with maximum resistance in the secondary circuit. If it is desired that the motor run at an intermediate rate the switch 55 may be closed and the switch 34 also. Under such circumstances a single timing sequence only will -occur and the motor 39 will be caused to run with the resistance 83 only in the secondary circuit. It will be understood that for normal starting, switch 55 is closed and switch 34 is allowed to remain open.

It will be observed that the tube i is subjected, in the operation of the circuit of this invention, to load carrying conditions only for so long as is required for the relay Hi to positively close, an action aided by the capacitor 96. Immediately on closing of relay ID the opening of contacts 4 terminates passage of current through the tube I. The actual period of loading of tube I need not be more than 2 or 3 current cycles and this interval is so short that no perceptible change in the characteristics of the tube results. The response on repetition of successive timing intervals, therefore, remains reasonably constant- I claim: v

1. In an interval timing circuit a current source adapted to be controllably activated; a grid-glow tube having main electrodes and a grid; a charging circuit for said grid including a resistor and a grid charging capacitor; said capacitor being connected on one side to one of the main electrodes of said tube and to one side of said'current source and connected on its other side through said resistor to the other side of said current source to said current source and to said grid for charging the same to a'striking potential at a pre-determined interval after activation of said current source: and a relay connected through said main electrodes of said grid-glow tube to a source of actuating current, said relay including contacts interposed in the connections joining said relay with said actuating current source to interrupt the supply of actuating current for said relay and including contactsconnected in discharging relationship to said capacitor to discharge said grid charging capacitor upon excitation of said relay, whereby said relay on closing immediately reopens torestore the circuit to a conditionpermitting repetition of a timing cycle.

2. In an interval timing circuit a current source comprising means adapted to be supplied with alternating current and to rectify the same; a grid-glow tube having main electrodes and a grid; a charging circuit for said grid including a resistor and a grid charging capacitor, said capacitor being connected on one side to one of the main electrodes of said tube and to one side of said current source and connected on its other side through said resistor to the other side'of said current source to said current source and to said grid for charging the same to a striking potential at a pre-determined interval after activation of said current source; and a relay connected through said main electrodes of said grid-glow nections joining said relay with said actuating current source to interrupt the supply of actuating current for said relay and including contacts connected in discharging relationship to said capacitor to discharge said grid charging capacitor upon excitation of said relay, whereby said relay on closing immediately reopens to restore the circuit to a condition permitting repetition of a timing cycle.

3. In an interval timing circuit a currentsource adapted to be controllably activated; a grid-glow tube having main electrodes and a grid; a resistor; a grid charging capacitor connected to one side of said current source through said resistor and to said grid for charging the same to a striking potential at a pre-determined interval after activation of said current source: a connection joining the other side of said current source to one of the main electrodes of said tube; a relay having an actuating coil connected through said main electrodes of said grid-glow tube to asource of actuating current, said relay including contacts interposed in the connection joining said relay coil to said actuating current source to interrupt the supply of actuating current for the actuating coil of said relay when I said relay is actuated, and contacts connected in shunt relationship to said grid charging capacitor to discharge the same upon excitation of said relay, said contacts acting immediately upon closing of said relay to cause the same to reopen to placethe circuit in condition for repetition of a timing cycle; load contacts operatively concurrent source and to said grid and on its other side to one of the main electrodes of said tube and to the other side of said current source for charging said grid to a striking potential at predetermined intervals aiter commencement of charging of said capacitor; a relay having an actuating coil connected through said main electrodes of said grid-glow tube to a source of actuating current, said relay including contacts interposed in the connections joining said coil to said actuating current source to interrupt the supply of actuating current for the actuating coil ot'said relay upon actuation of said relay. contacts connected in shunt relation to said ca pacitor, to discharge said grid charging capacitor upon excitation of said relay, and load contacts; and a control circuit responsive to the actuation of said load contacts by said relay coil including shiitable means responsive to successive closures of saidzload contacts cooperatively engaging said time interval regulating variable resistor means to successively vary the same upon successive actuations oi said relay whereby the duration of successive timing intervals is altered successively.

5. In an interval timing circuit a current source'adapted to be controllably activated; a grid-glow tube having main electrodes and a grid; a relay having a winding, normally open resetting contacts closed when said relay is excited. normally closed resetting contacts opened when said relay is excited, and load contacts; relay circuit connections extending through the main electrodes of said grid-glow tube through said normally closed resetting contacts and through the winding of said relay to said source oi current; initial grid control circuit connections connected to one of the main electrodes of said tube and extending through said normally closed gresetting contacts of said relay to a first side oi said source of current; a capacitor; 9. resistor; intermediate grid control circuit connections joining a first side of said capacitor through said timing resistor to the other side of said cilrrent source and joining the other side of said apacitor through said initial grid control circ t connections to the first side of said ourrentsource to cause said capacitor to be gradually charged at a rate regulated by said timing r-.sistcr when said current source is activated; final grid control circuit connections joining the first side of said capacitor to the grid of said grid-glow tube adapted to apply a striking charge thereto when said capacitor becomes charged to a pre-determined potential; and discharging circuit connections connected through the nor-' mally open resetting contacts oi the relay to said capacitor in shunt'relation thereto for discharg ing the same when said relay moves to excited position whereby the timing circuit is prepared at the end of one timing function for a succeedingtiming function. v 6. In an interval timing circuit a source of alternating current adapted to be controllably acti- Y 8 vated: a grid-glow tube having main electrodes and a grid; a relay having a windingn rmally open resetting contacts closed when said relay is excited,normally closed resetting contacts opened when said relay is excited, and load contacts; relay circuit connections extending through the main electrodes of said grid-glow tube through said normally closed resetting contacts and through the winding 0! said relay to said source of alternating current; a first capacitor; a rectifier; initial grid control circuit connections joining said first capacitor through said rectifier and said normally closed resetting contacts of said'relay to said source of alternating current for charging said first capacitor upon activation 01' said alternating current source; a second capacitor; a timing resistor; intermediate grid control circuit connections Joining a first side of said second capacitor through said timing resistor to a first side of said first capacitor and joining the other side of saidsecond capacitor to the other side or said first capacitor and to one of the main electrodes of said tube to cause said second capacitor to be gradually charged at a rate regulated by said timing resistor when first capacitor becomes charged; final grid control circuit connections joining the first side of said second capacitor to the grid of said grid-glow tube adapted to apply a striking charge thereto when said second capacitor becomes charged to a pre-determined potential: and. discharging circuit connections connected through the normally open resetting contacts of the relay in shunt relation to said first and second capacitors for discharging the'same when said relay moves to excited position whereby the timing circuit is prepared at the end or one timing function for a succeeding timing function.

7. In an interval timing circuit a source 01' alternating current adapted to be controllably activated; a grid-glow tube having main electrodes and a grid; a relay having a winding, normally open resetting contacts closed when said relay is excited, normally closed resetting contacts opened when said relay is excited, maintaining contacts and load contacts; relay circuit connections extending through the main electrodes of said grid-glow tube said normally closed resetting contacts and through the winding of said relay to said source of alternating current; a first capacitor; a rectifier; initial grid control circuit connections joining said first capacitor through said rectifier and said normally closed resetting contacts ofisaid relay to said source of alternating current for charging said first capacitor upon activation oi said alternating current source; a second capacitor; a timing resistor; intermediate grid control circuit connections joining a first side of said second capacitor through said timing resistor to a' first side or said first capacitor and Joining the other sides of said capacitors to one another and to one of the main electrodes 01 said tube to cause said second capacitor to be gradually charged at a rate regulated by said timing resistor when said first capacitor maintaining circuit controlled by said maintains ing contacts adapted to maintain excitation of said relay after opening of said normally closed resetting contacts.

8. In an electrical apparatus adapted to assume a plurality of circuit positions and to shirt successively at pre-determined intervals subject to independent adiustment, from position to position, the combination comprising a grid controlled tube having main electrodes and a grid; a current source adapted to supply current at a grid charging potential sufllcient to render said tube conducting; a capacitor connected to a main electrode of said tube and the grid thereof; a plurality of independently adjustable resistor means each adapted to be selectively connected between said capacitor and said current source to cause charging oi said capacitor to a potential at which said tube will become conducting at rates determined by the particular resistor means and the position of adjustment thereof forming the connection between the capacitor and said current source; resistor selecting switching means adapted to be shifted to select the particular resistor means forming the connection between the current source and the capacitor; a relay having an actuating coil connected through the main electrodes of said tube to a source of actuating current to be excited thereby, said relay having a plurality of contacts movable upon excitation of its actuating coil; a first electro-magneticalLy actuated control switch connected through some otsaidrelaycontactstoacontrolcurrentsource 10 to be actuated thereby upon the first excitation of said relay, said electro-magnetically actuated switch having load contacts and shifting means cooperatively engaging said resistor selecting switching means to alter the selection of said resistor means forming the connection between said capacitor and said current source, and preparatory means operative to prepare a succeed- REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES F 'ATENTS Number Name Date 2,360,721 Rose Oct. 17, 19 2,370,727 Holden Mar. 6, 1945 2,379,262 Terry June 26. 1945 2,442,238 Haungs May 25, 1948 OTHER REFERENCES 3 Schmidt (A.P.C.), published May 18. 1943.

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