US2269340A

US2269340A - Burglar alarm

Info

Publication number: US2269340A
Application number: US293730A
Authority: US
Inventors: Finn H Gulliksen
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1939-09-07
Filing date: 1939-09-07
Publication date: 1942-01-06
Anticipated expiration: 1959-01-06

Description

Jan. 6, 1942. F. H. GULLIKSEN 2,269,340

- BURGLAR ALARM Filed Sept. 7, 19:59

WITNESSES: INVENTOR M v 54 BY 7 Mina Patented Jan. 6, 1942 BURGLAR ALARM Finn H. .Gulliksen, Pittsburgh, Pa., assignor to WestinghouseElectric & Manufacturing Company, East Pittsburgh, Pa., 'a corporationbf Pennsylvania Application September 7, 1939, Serial No. 293,730

g 10 claims. My invention relates to electric discharge apparatus and has particular relation to burglar alarm systems.

An essential desideratum in a burglar alarm system is that it shall resist any attempt of the burglar to render it inoperative. Electrostatic systems provided in accordance with the-teachings of the prior art, of which I am aware, to a certain extent, atisfy this condition. In apparatus of this type, the capacity to groundof a conductor of extensive area is varied when the burglar approaches; However, the electrostatic equipment has a rather undesirable feature in that the capacity varies over a substantial range in response to changing atmospheric conditions.

To remedy the deficiency of capacity burglar alarm systems, photo-sensitive apparatus has been suggested. However, in this case, difiiculty is encountered because the burglar may, with facility, render the system inoperative, by replacing the source which supplies the radiation for energizing the photo-sensitive device by another source, such as a flashlight.

It is accordingly an object of my invention to provide a photo-sensitive burglar alarm system that shall resist any attempt of a burglar to render it inoperative.

Another object of my invention is to provide a burglar alarm system that shall not be afiected by varying atmospheric conditions.

A further object of my invention is toprovide a burglar alarm system of simple structure that shall resist every attempt of a burglar to render it inoperative.

A general object of my invention is to so interlock a photo-sensitive system'with a source of radiant energy that thesystem shall respond only to the. radiant energy from the source.

Another general object of my invention is to provide electric discharge apparatus so interlocked with a physical disturbance that it shall respond only to the disturbance.

More specifically stated, it is an object of my invention to provide a photo-sensitive arrangement which shall have the selective properties thatare particularly essential in burglar alarm apparatus.

In accordance with my invention, a screen of radiant energy is provided'at the entrance of the region to be protected. The radiation is derived from a source, the luminous intensity of which varies with the potential impressed thereon and impinges on a photo-electric cell. The cell is connected to the control circuit of an is energized from an alternating-current system.

The source of radiant energy is supplied. with alternate half-waves of the potential from the alternating-current system.

The interconnection between the photo-cell and. the valve is such that" the current flow through the valve is small as long as the-excitation of the cell is constant. To increase the current flow through the valve, the excitation of the cell must be varied at least at a rate which is of the'same order of magnitude as the .varia-' tion produced by the source. As long as the radiation from the source continues to excite the cell, the valve is conductive andthe burglar alarm signal is' inactive. When a burglar interrupts the radiation, the valve is rendered non-conductive and the signal is actuated. If a burglar, understanding the operation of a photo-electric cell, energizes the photo-electric cell with 'a flashlight while heis' entering the protected region, the signalling equipment operates in spite of the'fiashl'ight. The valve remains non-c'onductivewhen the radiation on the cell is uniform as would be the case for a flashlight.

' It may happen that a particular clever burglar realizes that interrupted light is necessary to prevent operation of the signalling equipment.

To preclude the successful" use of interrupted lightythe polarity of the'potential impressed on both the radiant energy source and the valve is reversed at intervals of the order of one .minute. The phase relationship between the potential impressed on the valveand the interrupted light,

used by the burglar is thus changed periodically, and the signalling equipment operates for one phase position'or the other.

The novel features that I consider characteristic of my invention are set forth with particuasymmetrically conductive discharge valve which 5 larity in the'appended claims. The invention itself,"however, both as to its organization, and its method of operation, together with additional objects and advantages thereof, will best' be understood from'the following description of a specific embodiment when read in connection withthe accompanying drawing, in which the single figure is a diagrammatic view showing an embodiment of my invention.

In the drawing, the invention is shown as used for the purpose of protecting a safe I. proach to the safe is covered by a screen of radiant energy produced by a lamp 3. The lamp 3 is preferably of the tungsten filament type, but the broader aspects of my invention maybe practiced with other luminous sources, such as glow tubes, carbon lamps and the like. The

The al light from the lamp is reflected back and forth, at the approach to the safe by suitable mirrors 5 and disposed above and below the safe.

The light emerging from the approach to the safe I impinges on a photo-electric cell 9 of the usual emissive type. The cell 9 is connected in a closed circuit with a resistor H and a directcurrent potential l3 derived from a suitable alternating-current generator l5, preferably of the usual commercial GO-cycle type, through the secondary section ll of a suitable transformer l9.

To amplify the output of the cell 9, an electric discharge valve 2| is provided. Thevalve has an anode 23, a cathode 25, and a control electrode 21, and is supplied from the alternating-current source |5 through a secondary section 29 of the transformer I9, which is provided with an intermediate tap 3|. The anode 23 of the valve is connected to one terminal of the secondary section 29 through the exciting coil 33 of an auxiliary relay 35, and the cathode is connected to the intermediate tap 3|. The control electrode 21 of the valve is connected to the other terminal through a suitable grid resistor 31. The photo-electric cell circuit is coupled to the control circuit of the valve 2| through a capacitor 39. The capacitor 39 and the grid resistor 31 are connected in parallel with the resistor H in the cell circuit. The lamp is connected across the terminals of the secondary section 29 through a half-wave rectifier 4|, which is preferably of the copper copper-oxide type.

The auxiliary relay 33 controls a main relay 43 which, in turn, opens and closes the signalling circuit 45. pendently of the generator |5 from a battery 41 or any other suitable source.

The polarity of the potential impressed on the lamp 3 and the valve 2| is reversed at intervals by a drum switch 49 provided with suitable reversing segments 50 and cooperative brushes 5| and 52. The brushes 5| interconnect the segments and the line conductors 53, and the brushes 52 connect the segments'to the primary 54 of the supply transformer Ill. The reversing segments 59 are interrupted in the region in which the reversal takes place, and at this point the switch is provided with auxiliary segments 55 which may be used to maintain any connections which would be opened by the interruption.

When the protecting apparatus'is to be used,

a master switch 51 is closed. The generator I5' is connected to the line conductors 53 through two of 'the contacts 59 of the switch, while the signalling circuit 45 is closed through a third contact 6|. If the apparatus is in proper condition for operation, potential is supplied between the

electrodes

23, 25 and 21 of the valve l. The potential impressed between the control electrode 21 and the cathode 25 by the left-hand portion of the secondary section 29 is in opposite phase to the anode-cathode potential impressed by the right-hand portion, and is of sufficient magnitude to maintain the valve 2| non-conductive in the absence of a counteracting potential.

Counteracting potential is provided by the photo-electric circuit when the light from the lamp 3 impinges on the cell 9. Current is supplied to the lamp only during alternate half periods of the source. During the intervening zero current intervals, the lamp filament cools substantially so that light from the lamp fluctuates over a substantial range and the periodicity of the source and the current flow through the cell The latter circuit is supplied indecircuit fluctuates correspondingly. The periodic photo-cell current flow through the resistor and the corresponding potential drop are impressed between the control electrode 21 and the cathode 25 through the capacitor 39. The relationship between the lamp circuit and the anodecathode circuit of the valve is such that the potential impressed from resistor H counteracts the blocking potential when the anode-cathode potential is positive, and, therefore, the valve 2| is conductive while the light is impinging on the cell.

When the switch 51 is closed, the reversing drum 49 is rotated by a motor 63 connected to the conductor 53. The reversal of the potential supplied to the primary 54 of the transformer |9 does not, however, affect the relationship between the valve 2| and the lamp 3, since both elements are supplied from the transformer.

When the valve 2| is rendered conductive, the auxiliary relay 33 in circuit with the valve is actuated, and its contact 65 closes a circuit through the exciting coil 61 of the main relay 43. The latter relay is then actuated and its contact 59 opens the signalling circuit 45. The auxiliary segments 55 of the reversing drum 49 short-circuit the contact 65 of the auxiliary relay 33 during the reversal, and thus assure that the main relay 43 remains energized in spite of the discontinuity in the supply of power to the transformer l9.

If there should be any defect in the system, as, for example, a burnt out lamp or a defective photo-cell or valve, the main relay 43 is deenergized and the signalling circuit 45 is closed. On the other hand, if there is no defect in the equipment, the

relays

33 and 43 are energized and the signalling equipment is deenergized.

Unauthorized entry into the protected region results in the interruption of the light impinging on the photo-electric cell 9. Under such circumstances, the supply of potential impulses by the resistor II in circuit with the cell 9 is discontinued, and the only potential impressed in the control circuit of the valve 2| is that derived from the secondary section 29. This potential is of sufficient magnitude to render the valve substantially non-conductive. The

relays

33 and 43 are then deenergized and the signalling equip ment is operated.

If the person desiring entry into the region should excite the photo-electric cell 9 with a flashlight, the valve 2| would still remain nonconductive. The current flow through the cell is, under such circumstances, constant, and the resultant potential dropped across the resistor H is constant. No varying potential is, therefore, impressed across the grid resistor 31 through the capacitor 39, and the only potential in the control circuit is blocking potential derived from the secondary section 29. If the person should produce interrupted light and use it for exciting the photo-cell 9, he'would still fail to prevent the signalling apparatus from operating. The interrupted light would not have the proper phase relationship for maintaining the valve conductive for one or the other of the positions of the reversing switch 49. To prevent a person seeking entry from suppling a lamp circuit similar to the circuit of lamp 3 from the transformer 9, the transformer should be disposed within the region covered by the light screen.

Although I have shown and described a certain specific embodiment of my invention, I am full aware that many modifications thereof are possible. My inventiongtherefore, is not to be restricted exceptinsofar-as is necessitated by the prior art and by, the spirit of the appended claims. l

I claim as my invention: 1 g

1. In combination, an electric discharge device having a principal circuit and'a control circuit, said control circuit being of the type wherein a control potential varying in a predetermined sense at at least a predetermined rate must be impressed to produce substantial current flow through said principal circuit, mens for impressing a periodic energizing potential in said principal circuit, means for impressing a periodic potential in said control circuit, said potential varying in amplitude at at least said predetermined rate and in said sense only during certain portions of the periods of said energizing poten' tial, and means for shifting the phase of both said potentials to the same extent with respect to a hypothetical reference potential.

2. In combination, an electric discharge device having a principal circuit and a control circuit, said control circuit being of the type wherein a control potential varying in a predetermined sense at at least a predetermined rate must be impressed to produce substantial current flow through said principal circuit, means for impressing a periodic energizing potential in said principal circuit, means for impressing a periodic potential varying in amplitude at at least said predetermined rate and in said sense only during certain portions of the periods of said energizing potential, and means for simultaneously reversing both said potentials.

3. In combination, an electric discharge device having a principal circuit and a control circuit, said control circuit being of the type wherein a control potential varying at at least a predetermined rate and in a predetermined sense must be impressed to produce substantial current flow through said principal circuit, means for impressing a periodic energizing potential in said principal circuit and means for impressing a periodic potential in said control circuit, said potential varying in amplitude at at least said predetermined rate and in said sense only during certain portions of the periods of said energizing potential.

4. In combination, an electric discharge device having a control electrode and a plurality of principal electrodes, means for impressing an alternating potential between said principal electrodes, photo-sensitive means connected to said control electrode in such manner that the current flow between said principal electrodes is substantial only when the excitation of said photosensitive means is varied at a predetermined rate in a predetermined sense, a source for exciting said photo-sensitive means, means for energizing said source by impressing thereon alternate halfwaves of said potential and means for simultaneously reversing said potentials impressed on said principal electrodes and said source.

5. In combination, an electric discharge device having a control electrode and a plurality of principal electrodes, means for impressing an alternating potential between said principal electrodes, photo-sensitive means connected to said control electrode in such manner that the current flow between said principal electrodes is substantial only when the excitation of said photo-sensitive means is varied at a predetermined rate in a predetermined sense, a source comprising an incandescible filament of tungsten or the like for exciting said" 'pl'ioto s'ens'itive means, means forenergizi'ng said'sour'ce by inipressing thereon alternate halfewav'esjof said potential and means'for simultaneously reversing said potentials impressed on said principal electrodes and said source. g Y

, 6. In combination,..an.asymmetrically conductive electric discharge device having a control electrode and a plurality of principal electrodes, means for impressing an alternating potential between said principal electrodes, photo-sensitive means connected to said control electrode in such manner that the current flow between said principal electrodes is substantial only when the excitation of said photo-sensitive means is varied at a predetermined rate in a predetermined sense, a source for exciting said photo-sensitive means, means for energizing said source by impressing thereon alternate half-waves of said potential and means for simultaneously reversing said potentials impressed on said principal electrodes and said source.

7 For use in signalling an entry into a region, the combination comprising, a photo-sensitive device, a source of radiant energy, said source and device being so arranged that radiant energy passes from said source to said device and forms a screen before said region, an electric discharge device having a principal circuit and a control circuit, means for'impressing an alternating potential in said principal circuit, means for energizing said source by impressing alternate halfwaves of said alternating potential thereon, means for connecting said photo-sensitive device in said control circuit in such manner that the current flow in said principal circuit is substantial only when the radiant energy impressing on said photo-sensitive device has a rate of variation corresponding to that of said source and means for simultaneously reversing the polarity of the potentials impressed on said principal circuit and on said source at intervals.

8. For use in signalling an entry into a region, the combination comprising, a photo-sensitive device, a source of radiant energy, said source and device being so arranged that radiant energy passes from said source to said device and forms a screen before said region, an electric discharge device having a principal circuit and a control circuit, means for impressing an alternating potential in said principal circuit, means for energizing said source by impressing alternate halfwaves of said alternating potential thereon, means for connecting said photo-sensitive device in said control circuit in such manner that the current flow in said principal circuit is substantial only when the radiant energy impressing on said photo-sensitive device has a rate of variation corresponding to that of said source, means for simultaneously reversing the polarity of the potentials impressed on said principal circuit and on said source at intervals, signalling means, and means for actuating said signalling when said radiant energy is interrupted or when the supply of saidalternating potential is discontinued.

9. In combination, an electric discharge device having an anode, a cathode, and a control electrode, means for impressing an alternating potential between said anode and cathode, a photo-sensitive device, means including a capacitor for connecting said photo-sensitive device between said control electrode and cathode, a source for exciting said photo-sensitive device and means for energizing said source with alternate half-waves of said potential.

10. In combination, an electric discharge device having an anode, a cathode, and a control electrode, means for impressing an alternating potential between said anode and cathode, a photo-sensitive device, means including a capacitor for connecting said photo-sensitive device between said control electrode and cathode, a source for exciting said photo-sensitive device, means for energizing said source with alternate half-waves of said potential and means for simultaneously reversing the polarity of the potential impressed between said anode and cathode and on said source.

FINN H. GULLIKSEN.