US2393014A - Time delay circuit - Google Patents

Description

Jan. 15, 1946. F. E. BARTHOLY 2,393,014

TIME DELAY CIRCUIT Filed March 20, 1943 WITNESSES: INVENTOR 44 p. 7M 4 W We,

ATTORNE Patented Jan. 15, 1946 UNITED STATES PATENT OFFICE rnvm DELAY cmcurr Frederick E. Bartholy, Wilkinsburg, Pa., assignor to -Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania This invention relates to electrical relay circuits and more particularly to a time delay circuit operating in connection therewith.

In electrical and industrial operations sensitive relay devices are frequently employed for indicating the occurrence of certain phenomena. For example, capacity operated relays or photoelectric devices are used to indicate the presence on the passing of diflerent objects, by the control of lights or by soundingan alarm. It is often desirable that the effect produced by the energization of the sensitive relay or the photocell be prolonged, particularly if the energlzation is of a very short duration. I

In the control of lights for display purposes or in the sounding of alarms used in protective installations the control effect may only be momentary such as the passing of a person in front of a show window, etc. If lights are to be lit or an alarm is to be sounded, it is necessary to provide means whereby the above eflects are produced not only during the energization of the relay system while the presence of the person within a narrow confine is observed but also that after the cause is removed the effect shall persist for a predetermined time and thereafter the system shall again be responsive to repeated enersizations.

This application is a continuation-in-part of application, Serial No. 388,105 and is directed to a particular feature of the invention which permits a cumulative time delay action upon momentary impulses which may arrive in succession following the first actuating impulse and during the delay time preset for the ensuing operation.

A particular feature of this invention is that in delay systems of the type mentioned the desired eifect caused by energization of short duration may be extended for a predetermined time and thereafter the system is restored automatically to a receptive condition for a successive enerization.

Another feature of thisinvention is that while the desired eifect is produced within the predetermined delay period energization of the system during such time will automatically extend the time interval until no energization appears within the delay period whereupon the system isagain automatically restored to receptive condition.

An advantage of the system in accordance with this invention is that the system may also be restored at any time during operation to a receptive condition without interfering with the predetermined time for the emu-m8 operation.

.eflect of momentary closures.

The invention contemplates a circuit arrangement for a time delay device in connection with a primary actuating element whereby the actuation thereof closes the circuit and simultaneously initiates the operation of the time delay element.

The circuit is automatically held closed until the time delay device ceases to function whereupon the circuit is automatically opened and the time delay device restored. Meansare provided for restoring the system at will at any time during the function of the time delay device to its starting condition without interfering with the predetermined time intervals of successive operations.

The invention also provides for cumulative excitation of the time delay element if the primary actuating means is momentarily closed or as long as it is closed, whereby the delay time is only eflective when the primary actuating means remains open over the entire delay period.

Other features and advantages will be apparent from the following description of the invention, pointed out in particularity by the appended claims, and taken in connection with the accompanying drawing in which the single figure diagrammatically illustrates an embodiment of the invention applied to an electrical circuit closim: element.

The electrical circuit closing element in the application above referred to was represented by a capacity operated relay in order to show a do vice which may operate only momentarily. The object of the invention in the former case as well as in this instance is to register an extended For the sake of simplified illustration, the circuit closing element is shown here merely as a manually operable switch. It is to be understood that this switch may represent various types of circuit closing devices and forms no part of the present inventionnor is it considered a limitation regarding the application of the time delay circuit about to be described.

In its broad aspect, the invention provides an impulse actuated device which upon energization by a first impulse will perform a certain operation for a certain allotted time. The time is preset and every successive impulse arriving within the preset time will extend the time to begin anew until no other impulse is received after the last impulse, during the time preset for operation. The device is automatically reset after the time element has completed its full or cumulative actuation period.

Operation in the manner above stated is often ample, in automatic gate opening controlled by photocells, timing detilized to keep the gate open for a defiafter energization of the cell in order ow for the person to reach and pass through te. During this predetermined time interer'ore the closure of the gate another person the first one may cause a photocell and the time delay for closure must be ended until the last named person will pass through the gate. In such cases, cumulative time delay is necessary since the actuating impulses cannot be so distributed as to appear after each closure of the gate.

ring to the drawing the switch repre- "he impulse device which when closed coms a circuit between power supply conductors it to the winding 2| of the electromagnetlc switch 2E, The latter has a plurality of contacts among which 28 and 28 are in parallel with contacts 3 and 3 and lock the circuit so that the winding 2i remains energized after the switch I is released from engagement with contacts 3 and 2. Contacts 29 and 29 of the switch 20 complete the circuit to the load elements shown h re by of example as lamps I8.

is desired that upon momentary actuation of the switch l, the lamps l8 shall remain energized for a definite period of time, and that after this time elapses and no other closure of the switch i occurs, the load shall be disconnected and the circuit returned to its original receptive condition. Moreover, it is desired that should the switch i be energized again during the time interval of operation, the time preset for the energization of the lamps l8 shall be extended again to the source predetermined time starting from the last actuation period. In other words, each actuation of the switch causing only momentary bridgin of contacts 3 and 3' and D and 50' shall renew the time period irrespective of the time elapsed since the energization of the lamps l8. This feature shall be further described in connection with the operation of the time delay circuit. The contacts 3B and 30 of the switch 20 when the winding 2% is not energized maintain the grid of an electron discharge device 32 connected to the conductor l4. The discharge deinay be of the type including a rectifier porcomprising an anode 33 and cathode 34 and trode portion comprising the cathode 35, con.-

EL bu trol rid screen grid 36 and the anode 31. his type of tube, due to its compactness, is suitc for the application here intended, although tubes may as well be used, and it is not c rectifier portion is utilized to provide di current potential for the elements of the tetrcde portion and is connected between conductors i4 and M in series with a load resistor hich is shunted by a filter condenser 39 of St. hole size. The filament 3 may also be energized directly from the lines M and I4 through a suitable series resistor IS. The cathode 35 is connected to a point on the load resistor 38 by slider anode 3? is connected in series with the Winding All of the relay 25 to the cathode 34, which is the highest positive potential or the rectified voltage output. The screen grid 36 is also connected to this point. The potential for e anode supply will he in effect the portion of sister designated by the letter A between 3-! and the slider 35' whereas the portion between the conductor I4 and the slider 35' designated by the letter B will be of I. potential more negative than the cathode 35. Consequently, the connection through the contacts 30 and 30 of the magnetic switch 20 or through the contacts 50 and 50' of the switch I will place the grid 3| at a potential which is negative with respect to the cathode 35. The grid 3| is also connected through a resistance capacity network comprising the resistor 4| shunted by the condenser 42 to the cathode 35.

Describing the operation of the time delay circuit, let it be assumed that the contacts 3 and 3' of the switch l are open and the switch 20 is in the open position as shown in the figure. Only contacts 30 and 30 are closed whereby the grid 3| is connected to the negative terminal 0! the anode supply source, thatis, the resistor ll. The voltage drop across portion B of the resistor 38 is so chosen that the grid is biased sufliclently negative to reduce the anode current either to zero or to such a small value which will not energize the winding 40 of the relay 25. The con tacts 24 and 24 of the latter are, normally, closed similarly as the contacts 22 and 22 of the push button switch 23. The load circuit to be controlled comprising the lamps I8 is deenerglzed from the line H and I4 due to the open contacts 29 and 29' of the switch 20. The entire system is at rest.

A momentary closure of the switch bridging the contacts 3 and 3' will energize the winding 2| and contacts 28 and 28' close the circuit permanently to the winding 2| so that further opening of the contacts 3 and 3' have no eilect as far as the switch 20 is concerned, which now is locked in position, being energized directly from the line. Simultaneously the contacts 29 and 23 are also closed and the lamps I8 are now supplied with current from the conductors ll andll. The closure of contacts 28 and 28' and 29 and 29, is accompanied by the opening of contacts 30 and 30', whereby the grid 3| is disconnected from the negative side of the supply source. The grid circuit has now a return path solely to the cathode 35 through the resistor I. The latter in combination with the condenser 42 provides the necessary time constant since the charge accumulated by the condenser 42 when the contacts 30 and 30 were closed must first discharge through the resistor 4|, and until such time as the discharge takes place'there is a progressive decreasing negative bias on the grid 3|. The

- time of discharge of the condenser can be regulated by the slider 45 of the resistor ll which will vary the effective resistance through which the capacity 42 must discharge. As the condenser discharges the negative bias on the grid 3| will be progressively diminshed and anode current oi the tube 32 will correspondingly rise until a value is reached which is sufilclent to actuate the winding 40 of the relay 25 to open the contacts 2Land 24. When these contacts are opened, the winding 2| of the switch 20 is deenergized being disconnected from the conductor H and the switch 20 will resume the position shown in the drawing, closing the contacts 30 and 30' and opening the others. Closure oi these contacts instantaneously puts a negative bias on the grid 3|, The opening or the other contacts disconnects the short circuit of the contacts 3 and 3' and removes the load circuit from the lines I4 and H.

The switch I also actuates contacts III and 30' which are essentially in parallel with contacts ll and 80' or the switch 20. Consequently closure of the iormer contacts will connect the'grid- II to the conducto ll thereby placing the negative side of the voltage dividersection B on the grid electrode II which will instantly charge the condenser IL The purpose 0! this operation oi the switch I is to produce the desired cumulative eiiect and cause resetting of the time element every time the switch I is actuated. When the contacts 3| and III are open and the condenser 42 begins to discharge through the resistance ll, the time constant oi the circuit determined by these elements will be reset every time the switch I is de- Consequently, whenever the contacts I! and BI are momentarily closed, the preset time element determined by the condenser 42 and resistor It shall begin anew and will hold the energization oi the load it until ior the time preset no actuation of the switch I occurs. As described before. when the condenser 42 discharses through the resistor ll, the grid ll is eiiectively at cathode potential which permits the desired anode current conductivity to actuate the reset relay II disconnecting the load ll irom the energizing circuit and also causing complete resetting of the 5 system for the next ensuing impulse by the swikhl.

The entire system may also be reset any time if desired by opening momentarily the switch 23.

In a practical embodiment of the. invention, the following circuit constants were utilizedr Resistor l l-5 megohms Portion 3-5.000 ohms Condenser 42-42 microiarads Condenser 38-16 microiarads.

The tube used was an RCA type 12A7, diodevpentode. A maximum delay of approximately one hour'was obtained between the time of operation 01 the relay I to the resetting of the system.

I claim as my invention: 1. In an electrical control system, a circuit closing element operable ior momentary action. a circuit energized thereby including a current ment, means tor extending thev actuation time of said circuit after momentary actuation-oi said circuit closing element comprising contact actuated by said switch for connecting said energizing coil to said source, normally closed contacts in series between said source and said energizing coil, delay action means having a predetermined time interval of operatiommeans actuated by said switch for initiating the start of operation time of said delay action means upon closure oi said switch and means actuated by said vdelay action means for opening said contacts and thereby deenergizing said circuit after said lapse of time, said initiating means being operable to condition said delay action means for recurrent operation and contact means operable in conjunction with the actuation of said circuit closin element for restoring the start oi operation time 01 said delay action means whereby the delay action of said delay action means is cumulative for repeated momentary actuations.

2. In an electrical control system, a circuit clos ing element operable for momentary action, a circuit energized thereby including a current source, a switch, an energizing coil for said element, means for extending the actuation time of said circuit aiter momentary actuation 0! said circuit closing element comprising contact means actuated by said switch ior connecting said energizing coil to said source, normally closed contacts in series between said source and said energizing coil, delay action means comprising a vacuum tube having anode, cathode and grid electrodes, a source of operating potentials therefor including a voltage for biasing said grid electrode negative with respect to said cathode whereby space current flow through said tube is substantially prevented, a circuit of predetermined time constant connected between said grid and said cathode, means for disconnecting said grid from said bias source upon closure of said switch thereby eflectively placing said time constant circuit in 'operation and means operable upon space current flow in said tube for opening said contacts thereby de energizing said first-mentioned circuit, and means to;- connecting said grid to said bias source upon opening or said circuit closing. element for restorcs ing the start-oi operation time of said delay acsourcc, a switch, an energizing coil tor said ele- I FREDERICK E. BARTHOLY.

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