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Publication numberUS2088295 A
Publication typeGrant
Publication dateJul 27, 1937
Filing dateOct 24, 1934
Priority dateOct 24, 1934
Publication numberUS 2088295 A, US 2088295A, US-A-2088295, US2088295 A, US2088295A
InventorsHubble Grover C
Original AssigneeHubble Grover C
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electric control system
US 2088295 A
Abstract  available in
Images(3)
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Claims  available in
Description  (OCR text may contain errors)

July 27, 1937. s. c. HUBBLE 088,295

ELECTRIC CONTROL SYSTEM Filed Oct. 24, 1954 3 Sheets-Sheet 1 Jul 27, 1937.

G. c. HUBBLE 2,088,295

I ELECTRIC CONTROL SYSTEM Filed Oct. 24, 1954 s Sheets-Sheet 2 gy mm Filed Oct. 24, 1934 5 Sheets-Sheet 3 Patented July 27, 1937 UNITED STATES PATENT OFFICE 17 Claims.

This invention relates broadly to sensitive electrical circuits adapted to respond to the approach or contact of a foreign body to initiate a change in current flow in the circuit. It may be employed for various purposes but for purposes of illustration it is described herein as applied to a safety system for detecting the presence of burglars or other intruders in a protected space.

A broad object of the invention is to provide a sensitive electrical circuit capable of responding to the approach and/or contact of a foreign body, which circuit is stable and reliable in operation and is capable of handling control or alarm conductors of substantial length and capacity.

Various other more specific objects and-features of the invention will become apparent from the detailed description with reference to the drawings which follow.

This is a continuation in part of my application Serial No. 691,090, filed September 26, 1933 on Electronic discharge systems, which has now become abandoned.

In accordance with my invention, I employ as the main element of my system a glow tube having a cathode, anode and control grid, in an atmosphere of a rare gas, such as neon or argon. It is well known that such tubes have the characteristic of being substantially non-conductive at anode-cathode potentials below a definite value but suddenly become conductive if the anodecathode potential is increasedabove that value or if the potential of the grid is varied beyond definite limits. Because of this characteristic, such tubes have been employed by others in delicate detection circuits so arranged that the mere presence of a foreign body adjacent a conductor connected to the grid of the tube would alter the potential of the grid sufliciently to initiate a discharge in the tube, the resultant current flow being employed to control a switch in an alarm circuit, alighting circuit, or the like.

All these prior circuits of which I have knowledge have definite limitations in use. I have found in general that they are relatively insensitive and unreliable and lack sensitivity when employed with detecting conductors of any appreciable length.

The present invention involves novel circuits and apparatus in combination with a grid glow tube whereby the stability, reliability and sensitivity are greatly improved. My circuit and apparatus will now be described in detail with reference to the accompanying drawings, in which Fig. 1 is a wiring diagram of a double unit auto-matic alarm system embodying my inven tion? Fig. 2 is an elevation view of the double unit with the enclosing wall and cover of the containcr shown in section;

Fig. 3 is a plan view of the double unit disclosed in Figs. 1 and 2;

Fig. 4 is a transverse sectional view of the unit taken in the plane 'IVIV of Fig. 2;

Fig. 5 is a section-a1 view of a transformer employed in the unit; and

Fig. 6 is a schematic diagram of the detecting circuit employed in each of the units disclosed in Fig. 1.

Referring first to Figs. 1, 2, 3 and 4, my automatic alarm system apparatus comprises a metal container l divided into two compartments A and B, respectively, by a metal partition 2. A plug 3 is provided in one side wall of the container l for making connection to an external source of alternating current, which source is preferably the 110-volt commercial lighting circuit.

Each compartment A and B contains apparatus which is substantially identical with th-at'in the other compartment. This apparatus will be described with reference to the contents of com partment A. Corresponding elements of the apparatus in compartment B bear the same reference numeral with the prime mark added.

Thus referring to Fig. 1, compartment A contains a special transformer 4, three relays 5, 6

and 1, respectively, four variable condensers 8,

9, l0 and H, respectively, a .variable inductive resistance l2, 2. grid glow tube 13, a voltage control unit l4, and other minor elements which will be described in connection with the circuit description.

As disclosed in Figs. 2, 3 and 4, the metal container l is in the form of a staunch steel box containing the previously listed parts which are held in definite spaced relation within the box.

Extending from each of the compartments A and B of the metal container I I preferably provide a flexible conduit 16a leading to a metallic alarm or gong box I6, which conduit carries \three conductors 59, 60 and 82, respectively.

Each alarm box 16 contains'a battery I! which may consist of four standard dry cells, an electric bell l8 and a siren l9.

Referring now to the apparatus within compartment A, it will be observed that transformer 4 comprises a primary winding 2| connected to the terminals of the plug 3. Thus the upper end of winding 2| is connected through a conductor 3| and one of the windings of the reactance element IE to one terminal of the reversing switch Hit). The lower end of winding 2! is connected through a conductor 285a and the other winding of reactance element M to another terminal of the reversing switch ltd. One of the remaining terminals of switch llld is connected through a switch 30 to a conductor 29 nected through conductor 28 to the other terminal of the plug 3. Line potential connected to plug 3 will therefore be appliedto the primary winding 2| when the switch 38 is closed and} by manipulating the reversing switch I88, the direction of the current in the winding 2| may be reversed. The purpose of providing the reversing switch I 88 will be explained later.

The secondary winding 22 of transformer 4 contains a great many more turns than the primary winding 2| and is provided with numerous taps thereon, these taps being preferably so spaced along the winding as to provide a diiference of potential of substantially 500 volts between each adjacent pair of taps. Several of the taps on the upper end of the winding are shown connected to the contacts 81, 88, 88 and 88 associated with a pair of switch blades 12 and 88, respectively. The switch blade 88 is connected through a lead 33 and the variable inductive resistance element l2 to the cathode 31 of the glow tube l3. The other switch blade 12 is connected through a conductor 8|, winding of relay 5, and conductor 48 to the anode 48 of tube I3. The tube I3 is preferably a Westinghouse grid glow tube, type KU-618, in the actual construction oi! which the cathode 31 comprises a cylinder with the anode 48 constituting a point projecting from a glass tube positioned substantially in the middle oi the cylindrical cathode. The grid 28 consists of a point protruding from a glass tube immediately adjacent the anode 48. The electrodes, of course, are positioned in a sealed bulb containing a rare gas at suitable pressure.

The grid 28 is connected through a conductor 4i and a high resistance 42, having a resistance of the order of a million ohms, to a detecting conductor 43 which is extended through an insulating bushing in the metal case I to the exterior where it may be connected to an object to be protected, such as a cash register 44.

The variable condensers 8, 8, I8 and II each have one terminal connected to the conductor M and have their other terminals connected to taps 83, 84, and 85 adapted to be successively connected by a movable contact 38, which is connected through a conductor 38 to the cathode 31 of tube I3. By shifting the movable blade 38, the condensers 8, 8, l8 and II may be successively connected into the circuit.

Condensers 8, 8 and I8 are manually variable, being connected to control knobs on the exterior of the case. The condenser II is adapted to be automatically varied by a solenoid Ila con-- nected directly to the conductors 28 and 28.

The anode 48 of tube I3 is connected through a high resistance element I8 I, having a resistance of the order of a million ohms, to a conductor I82 which is extended through an insulating bushing in the metal case I to the exterior and may, like conductor 43, be connected to an object to be protected such as a safe I83. A switch I84 is provided within the case I for connecting,

the conductor I82 to the metal case itself when desired.

When the circuit described is energized by connecting a -volt alternating current supply to the plug 3, the system can be adjusted to a state of equilibrium, in which substantially no current flows through the tube I3, by adjusting one or more of the condensers 8, 8 and I8. Thereafter, assuming no change takes place in the condition of the detecting conductors 43 and I82 extending from the case, equilibrium will be maintained despite variations in the potential across conductors 28 and 28 by the action of the solenoid IIa which varies the capacity of the variable-condenser II to compensate for voltage variations in the power source.

However, the state of equilibrium may be terminated by a change in the electrical condition of either conductor 43 or conductor I82 extending from the metal case. It is found that contact of almost any external object with the conductor I82 or an object connected thereto (such as the safe I83) initiates a discharge between the cathode and anode within the tube l3. The conductor 43 is even more sensitive. Thus even the approach, without actual contact, of a foreign object to the conductor 43 or an object connected thereto is suflicient to initiate a discharge in the tube I3.

The initiation of a discharge in tube l3 causes current to flow through the relay 5, closing the armature 41 of that relay on its front contact 48, which completes a circuit between conductor 68 and conductor 58. This applies current from battery II to the bell I8 and the siren I8, thereby producing an alarm signal. This action continues so long as the foreign object is in contact with conductor I82 or adjacent conductor 43. However, if the object is removed the discharge in tube I3 ceases and relay 5 releases, stopping the bell l8 and siren I8.

In some instances, however, it is desired to produce an alarm signal continuously upon initiation thereof. .It is for this purpose that relay 8 is provided. It will be observed that relay 8 has an energizing winding 48 adapted to be connected through a switch 52 with conductor.

82, which is connected to one side of the battery I1 in the alarm box It. The other side of battery I! is connected to conductor 58, which in turn is connected to the other side of winding 48. Therefore, closure of switch 82 completes a circuit from one side of the battery I! through the conductor 82 up to the contact 48 of relay 5. Immediately upon actuation of relay 5 a circuit is completed through winding 48 and contact 48 and armature 41' of relay 5 to the conductor 88 which is connected to the other side of battery I! and the relay 48 pulls up. When it pulls, this relay closes a pair of holding contacts 5i and 52 connected in shunt to the contact 48 and armature 41 so that the relay 48 remains locked up until the switch 52 is opened. The closure of contacts 5I and 52 of course completes the energizing circuit to the bell l8 and the siren I8 in the same manner as did relay 5.

Relay G'is also provided with a pair of contacts 54 and 55 and a switch blade 53 adapted to close contacts 54 and 55 when said relay 8 is energized. This completes a circuit from conductor 28 to contact 55, switch member-53, contact 54, and conductor 84 to one terminal of a receptacle 83 positioned in the exterior wall of the case I. The other terminal of this receptacle is permanent-ly connected to the conductor 28. By connecting an external circuit to the receptacle 83 by a suitable plug, the circuit may be controlled in response to the actuation of the tube I3. This external circuit may consist of the lighting circuit of the building so that in the case of an alarm the building is flooded with light.

Inan alarm system dependent upon the continuity of current from a commercial power systern, it is-desirable to provide means for giving an alarm in case of failure of the power supply. To this end, relay I is provided. This is an alternating current relay bridged directly across the conductors 28 and 29 and is provided with an armature 51 and a back contact 58, which are connected to the conductors 60 and 59, respectively, so that release of relay 1 actuates the bell l8 and the siren I9. Ordinarily the armature 57 is held clear of the contact 58' by current from the source conductors 28 and 29.

r The layout of the apparatus in compartment A as a unit and its operation have been briefly reviewed. Certain elements of the apparatus will now be described in greater detail.

The transformer 4 constitutes a very important element of my apparatus and the success of the system depends in large measure on the characteristics of this transformer. As previously indicated, the primary winding 2| is so proportioned as to normally substantially completely saturate the core. proportioning the primary winding as to saturate the core, the stability of the system is greatly increased and the magnitude of the secondary potential is affected to a much lesser degree by variations in the line potential across conductors 28 and 29. Considerable experimentation was required to produce a transformer having the desired characteristics and for this reason the construction of a suitable transformer will be described in detail with reference to Fig. 5.

It will be observed that the transformer is provided with a core 28 of H shape consisting of lamination's of. silicon steel. The external dimensions of the core are approximately 3 3% inches andthe laminations are built up to a depth or 35 thickness of about 1% inches. Both windings are placed on the central cross bar, the primary winding 2| consisting of 394 turns of No. 24 enameled wire. The secondary winding is placed on top of the primary and is Wound in sections, 40 which are preferably separated from each other by layers of insulating material. The first or inner section 23a of the secondary winding may consist of 880 turns of No. 37 enameled wire; the second section 231) consists of 1760 turns; the third section 230 consists of 3520 turns; the fourth section 23d consists of 5280 turns; the fifth section 23c consists of 7040 turns; and the sixth section 23; consists of 8080 turns, all of No. 37 enameled wire. It is found that with the Various sections of the secondary proportioned as described, approximately 500 volts will be developed between the ends of each section, which is the desired object.

In part because of the small number of turns in the primary winding 2|, this winding would draw excessive current from the line were it connected directly thereto; Therefore, to prevent excessive current flow and to provide a means for regulating the current flow in the pri- 0 mary winding, vI provide the variable reactance element |4 connected in series with the winding- 2| and the supply conductors 28 and 29. Reactances of the general type which I prefer to use are fully described in my United States Letters Patent No. 1,628,148; The essential features of this reactance are that it comprises two independent windingsfone connected in each side of the line and both windings closely adjacent each other. Variation in reactance is preferably obtained by means of a movable core 34 r In Fig. 6 of the drawingsone of the conductors "be understood that in actual construction .both

conductors would be of the-same dimensions.

It is found that by so' The condensers are preferably proportioned about as follows: condenser 8 may be a variable 23-blade midget variable condenser having a maximum capacity of 100 micro-microfarads; condenser 9 may be a 35.-blade large variable condenser having a maximum capacity of 325 mlcromicrofarads; condenser I!) may be a small variable condenser having a capacity variation from .0001 to .0005 microfarads; and the condenser H may have a capacity variation of .0003 to .001 microfarads.

By virtue of the fact that the lower end of the secondary winding 22 of transformer 4 (with reference to Figs. 1 and 6) is closely adjacent to the primary winding 2|, there is considerable capacity between primary winding 2| and the lower endof winding 22. Furthermore, since primary winding 2| is connected to a commercial power circuit, oneside of which is invariably grounded, one end of primary winding 2| will be substantially at ground potential and by virtue of the capacity between the windings the lower end of the secondary winding 22 will be maintained to a greater or less extent at ground potential. If desired, the potential of the lower end of winding 22 may be definitely fixed by grounding it, as shown by the dotted connection 0 in Fig, 6. However, in actual practice I have not found it necessary to provide this ground connection.

As previously stated, the secondary Winding is so proportioned that substantially 500 volts are developed between adjacent taps thereon so that regardless of which set of taps the conductors 8| and 33 are connected to the same voltage will be impressed between the anode 20 and cathode 31 of the tube |3. However, the potential of the tube electrodes considered as a unit with respect to ground will depend upon which set of taps on winding 22 the conductors 33 and 8| are connected across.

This feature of maintaining the tubes as a whole, including the detecting conductors 43 and I02, at a potential substantially above ground potential, is an important novel feature of the invention and one that contributes greatly to the superior performance of my system as compared to prior known systems. As previously indicated, the potential of the tube as a unit with respect to ground may be varied without varying the potential difference impressed between the cathode and anode by manipulating the switch to connect the switch blades 12 and 80 to different pairs of the taps 81,08, 89 and 90, since the transformer is designed to develop the same potential, approximately 500 volts, between each adjacent pair of taps. With different external circuit conditions of the conductors 43 and I02, different positions of the switch 80 may be found to give best results, the best position in each case being determined by experiment.

It is important to note that despite the fact that the conductors 43 and I02 are maintained substantially above ground potential, no injury can result to a person touching them and no injury to the tube or other apparatus can result from a ground on these conductors because of the high resistance elements 42 and IM connected in series with the respective conductors within the case these resistances limiting any current flow in the conductors to an extremely small value.

I am unable to offer any definitely correct detailed explanation of the theory of operation of mysystem because I have been unable to obtain from the literature relating to grid glowtubes any definitely correct detailed explanation of what takes place within the tubes. I am inclined to believe that there is normally (with voltage impressed across the electrodes but no discharge) an accumulation of electrons on the grid 20 (Fig. 6) which imparts to the grid a negative charge, the average potential of the grid with respect to the cathode and anode being dependent upon the rate of accumulation of electrons thereon and the rate of leakage therefrom through the conductor 43 and the objects and apparatus connected thereto. Alternating potentials are also impressed upon the grid through thecondenser 8 connecting'the grid to the cathode and through the inherent capacity between the conductor 43 and ground. These alternating potentials on the grid probably control to a large extent the rate of accumulation of electrons on the grid and henceindirectly control the average potential of the grid. By suitable adjustment of the condenser B with respect to the capacity to ground and leakage conductance to ground of the con ductor 43, the average potential of the grid may be adjusted to a value only slightly different from that required to produce a discharge in the tube. Thereafter a slight change in the capacity or conductance to ground of the conductor 43 produced by the approach or contact of a foreign body produces sufllcient change in the potential of the grid to initiate .a discharge in the tube. Likewise a change in the conductivity of the air surrounding the conductor 43 or an object connected there to, such as might be produced by the ionizing effect of a flame, is sufficient to start the discharge. This feature renders the invention useful for fire alarm purposes as well as burglar alarm.

A discharge may also be started in the tube, without varying the potential of grid 20, by increasing the potential drop between the cathode 31 and anode 40 above predetermined limits.

40 This explains the action of the tube when the conductor I02 is contacted by a body connected to or having appreciable capacity to ground, as under these conditions the relatively high potential developed in the lower portion of the transformer secondary winding 22 is applied through ground, the foreign body H5, and conductor I02 to the anode 40. It should be noted that the conductor I02 is much less sensitive than the conductor 43 but has the advantage that it may be extended to much greater distances. Thus I have found that the conductor I02, if reasonably well insulated from ground, may be extended for miles whereas the length of conductor 43 is limited to a few hundred feet under most conditions.

It is to be understood that it is not necessary to use both conductors 43 and I02 unless conditions make it desirable to do so. Either one may be eliminated without effecting the operation of the other.

The conductor I02 may, if desired, be connected to the metal of the apparatus by closing switch I04 (Fig. 1), thereby sensitizing the case so that if anyone attempts to tamper with the system and touches the case, an alarm will be produced.

If it is desired to render the case of the instrument sensitive to the approach without actual contact of a person, the case may be connected to conductor 43 by closing switch I20 (Fig. 1).

The adjustable inductive resistance, I2 functions as a safety device to limit the current flow through the tube I3. However, it is also useful "In balancing the system.

The variable reactance I4 in the primary circult of the transformer 4 is employed to regulate the current in the primary winding M. This is necessary, in part, because the transformer primary has so few turns that excessive current would flow therein if no regulating apparatus were employed. The particular type of reactor described, in which the two windings are coextensive and alongside each other, has been found by experiment to be particularly effective in the system-increasing its sensitivity-although I have not yet determined the explanation for this peculiar efficacy.

Referring back to Fig. l, the apparatus in compartment B is substantially identical with that in compartment A and may be employed independently thereof. However, it is sometimes advantageous to employ them both in combination and there are two ways of doing this.

One method is to connect the two conductors 43 and 43 together and to the same objects, as by closing switch 85, and so positioning the reversing switch I00 in compartment A as to cause the alternating current applied to the tubes I3 and I3, respectively, to be in phase. With this arrangement approach of a body to either conductor 43 or 43 will initiate a discharge in one or both of tubes I3 and I3, dependent on whether or not either associated circuits are balanced with equal precision. The important advantage of this connection, however, is that a break in either conductor 43 or 43' upsets the balance of the system and initiates a discharge in one or. both tubes, thereby making it practically impossible to open the broken circuit without giving an alarm.

It is to be understood that the conductors I02 y and I02 may also be connected together and to the same objects, the reversing switch I00 being so positioned that the potentials applied to the anodes 40 and 40 are in phase with each other. This connection may be effected by closing switch I02a. The system will then respond to an open circuit condition on either the conductors I02 or I02 as well as to contact of a foreign object with either conductor.

The other method is to maintain the two conductors 43 and 43' electrically insulated from each other and position them on opposite sides of an area to be guarded and adjust the reversing switch I00 so that the alternating current applied to the tubes I3 and I3 are opposite in phase. Thus in Fig. 1 the conductors 43 and 43 are shown extended respectively above and below a window 86 and the switch 85 is open. Under these conditions the conductors 43 and 43' have alternating potentials impressed thereon through their associate tubes, which potentials are of radically different instantaneous values so that a slight change in the capacity and/or conductance characteristics produced by the interposition of any body therebetween causes a change in the potential of one or both of the grids 20 or 20 sufllcient to initiate a discharge in the associated tube, the superior sensitivity of the conductors 43 and 43' with respect to detection of a body therebetween, as compared to a body approaching only one of the conductors, being due to the fact that the alternating current potential difference between the twov conductors is substantially equal to the sum of the potentials. of the two conductors with respect to ground.

It is to be understood that although I have described what I now consider to be the preferred embodiment of the invention that it is not ess ntial that the system be reproduced exactly as described. Various modifications will occur to those skilled in the art and may be employed without departing from the essential features of the invention, which are set forth in broad terms in the appended claims.

I claim:

1. In a system for controlling an electric circuit in response to change of a body with respect to a portion of said circuit; a source of alternating current, a load device, an electric valve havinga pair of electrodes spaced apart from each other, said device conducting substantially no current below a predetermined critical potential and becoming conductive above said critical potential, means connecting said electrodes and said load device in series with said source, means for impressing a potential between ground and all parts of the series circuit including said source, said load device, and said electrodes, a detecting conductor connected to one of said electrodes and insulated from ground, said source impressing a potential across said electrodes slightly less than said critical potential whereby contact between said detecting conductor and an external body applies a potential from said last named means i through ground and said external body to said detecting conductor, thereby varying the potential of said conductor suflicient to render said valve conductive.

2. A system as described in claim 1 in which the said means for impressing a potential between said electrodes and ground-is also a source of alternating current.

3. A system as described in claim 1 in which said source of current and said means for impressing a potential between said electrodes and ground are constituted by a transformer having a secondary winding with taps thereon, one end of said winding being substantially at ground potential and a tapped portion of said winding remote from said one end constituting said source connected to said electrodes.

4. In a system for controlling an electric circuit in response to change of a body with respect to a portion of said circuit; a load device, an electric valve having a pair of electrodes spaced apart from each other, said valve conducting substantially no current below a predetermined critical potential and becoming conductive above said critical potential, a transformer having a core of paramagnetic material, a primary winding and a secondary winding, means for connecting said primary winding to a source of alternating current, means for maintaining one end of said secondary winding substantially at ground potential, said secondary winding comprising a tapped portion remote from said grounded end connected in series with said load device and the electrodes of said electric valve, said tapped portion of said secondary winding delivering a potential to said electrodes slightly less than said critical potential, a detecting conductor connected to one of said electrodes and insulated from ground whereby contact of an object with said conductor increases the potential applied to said electrodes above said critical value and initiates a discharge through said valve, the secondary winding of said transformer having a plurality of taps there- 70 on and the number of turns'between the taps being so proportioned that the potential delivered between any adjacent two of said several taps is slightly below said critical potential whereby said electrodes may be connected across different taps to apply the same voltage across said electrodes While applying different potentials between the electrodes and ground.

5. In a system for controlling an electric circuit in response to change of a body with respect to some portion of said circuit; a source of a1- ternating current, a load device, an electric valve having a cathode, an anode and a control electrode, means connecting said cathode, anode and load device in series with said source, means other than said source of alternating current for impressing a potential between ground and said entire series circuit containing said cathode, anode, load deviceand source, a detecting conductor connected to said control electrode and insulated from ground, and variable impedance means connected directly between said control electrode and cathode for adjusting the potential of said control electrode to a critical value with respect to said cathode and anode such that a slight change in the potential of said control electrode produced by approach of a body to said detecting conductor renders said valve conductive.

6. A system as described in claim 5 in which said means for impressing a potential between ground and all parts of the said series circuit, supplies alternating current substantially in phase with the alternating current supplied by said source.

. 7. A system as described in claim 5 in which said means for impressing a. potential between ground and all parts of the series circuit including said source, said load device and said electrode is a source of alternating current and in which said variable impedance means comprises a variable condenser.

8. In a system for controlling an electric circuit in response to change of a body with respect to some portion of said circuit; a source of alternating current, a transformer having a primary winding and means for connecting said primary winding to said source, said transformer having a core of paramagnetic material and a secondary winding, means for maintaining one end of said secondary winding substantially at ground potential, a load device, an electric valve having a cathode, an anode and a control grid, means connecting said cathode, anode and load device in series with a portion of said secondary winding remote from the grounded end thereof, a detecting conductor connected to said control grid and insulated from ground, and variable impedance means connected directly between said grid and cathode for adjusting the potential of said grid to a critical value with respect to said cathode and anode such that a slight change in the potential of said grid produced by approach of a body to said detecting conductor renders said valve conductive.

9. A system as described in claim 8 in which the said source of alternating current is subject to potential fluctuations and in which the pri-. mary winding of said transformer has so few is cumulative, and means for varying the reluctance of the magnetic circuit of the windings.

10. A system as described in claim 8 in which the secondary winding of said transformer has a plurality of taps thereon adjacent the end remote from said grounded end, the number of turns between successive taps being such as to provide substantially equal potentials between any two successive taps thereon, whereby the same potential may be applied between thecathode and anode of the valve but the valve as a whole maintained at different potentials with respect to ground by connecting to different taps on said transformer.

11. A system as described in claim 5 in which a high resistance is connected between said detecting conductor and said control grid circuit whereby the current that can be drawn from said detecting conductor is limited to a value not dangerous to human life.

12. In a system for controlling an electric circuit in response to change of a body with respect to some portion of said circuit, two sets of apparatus each comprising: a transformer having a primary winding and a secondary winding, one end of which is maintained substantially at ground potential, a load device, an electric valve having a cathode, anode and control grid, means connecting said cathode, anode and load device of each set in series with a portion of the secondary winding, remote from the grounded end thereof, of the transformer in that set, each set also comprising a detecting conductor connected to the control grid of that set and insulated from ground, the two detecting conductors being spaced from each other across an area to be sensitized, each set comprising variable impedance means connected between the grid and cathode of that set for adjusting the potential of the grid of each set to a critical value with respect to its associated cathode and anode such that a slight change in the potential of the grid renders the valve conductive, a single source of alternating current and means connecting the primary windings of the transformers in said two sets of apparatus to said source with such polarity that the said two detecting conductors are maintained at opposite potentials with respect to each other and with respect to ground.-

13. In a system for controlling an electric circuit in response to change of a body with respect to some portion of said circuit, two sets of apparatus each comprising, a transformer having a primary winding and a secondary winding, one end of which secondary winding is maintained substantially at ground potential, aload device, an electric valve having a cathode, anode and control grid, means connecting said cathode, anode and load device ofeach set in series with a portion of the secondary winding remote from the grounded end thereof of the transformer in that set, each set also comprising a detecting conductor connected to the control grid of that set and insulated from ground, the two detecting conductors being connected together, each set comprising variable impedance means connected between the grid and cathode of that set for adjusting the potential of the grid of each set to a critical value with respect to its associated cathode and anode such that a slight change in the potential of the grid renders the valve conductive, a single source of alternating. current and means connecting the primary windings of the transformers in said two sets of apparatus to said source with such polarity that the said two detecting conductors are maintained at substantially the same potentie whereby a slight change in the potential of said grids produced by approach of a body to one of said detecting conductors renders said valves conductive and whereby a break in the connection between said two detecting conductors or a break in any part of either one of said conductors upsets the balanced condition of one of said valves suiliciently to initiate a discharge therein.

14. A system as described in claim 1 in which said apparatus is contained in a metal box connectedto said detecting conductor.

15. In a system for controlling an electric circuit in response to change of a body with respect to some portion of said circuit, a source of alter nating current, a load device, an electric valve having a cathode, anode and control grid, means connecting said cathode, anode and load device in series with said source, means other than said source for impressing a potential between ground and all parts of theseries circuit including said source, said load device and said electrode, variable impedance means connected directly between said grid and cathode for adjusting the potential of said grid to a critical value with respect to said cathode and anode such that a slight change in the potential of said grid renders said valve conductive, a detecting conductor connected to said grid, a second detecting conductor connected to said anode, said first detecting conductor functioning in response to approach of a foreign object thereto to change the potential of said grid sufilciently to render said valve conductive, and said second detecting conductor being relatively less sensitive than. said first conductor but functioning in response to contact thereof by a foreign object to render said valve conductive.

16. In a system for controlling an electric circuit in response to contact of a foreign body with respect to some portion of said circuit, two sets of apparatus each comprising a transformer having a primary winding and a secondary winding, one end of which secondary winding is maintained substantially at ground potential, a load device, an electric valve having a cathode and anode, means connecting said cathode, anode and load device of each set in series with a portion of the secondary winding of the transformer of that set, said portion being remote from the grounded end ofthe winding, each set also comprising a detecting conductor connected to the anode of that set and insulated from ground, the two detecting conductors being connected together, a single source of alternating current, and means connecting the primary windings of the transformers in said two sets of apparatus to said source with such polarity that the said two detecting conductors are maintained at substantially the same potentials whereby an increase in the potential of either anode produced by contact of a foreign body with one of said detecting conductors renders said valves conductive and whereby a break in the connection between said two detecting conductors or a break in any part of either one of said conductors upsets the balanced condition of one of said valves sufficient to initiate a discharge therein.

17 A system as described in claim 5, in which said apparatus is contained in a metal box. said box being connected to said control electrode.

I GROVER C. HUBBLE.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3155953 *Sep 27, 1960Nov 3, 1964Dehavilland AircraftProtected remote alarm system
US4222045 *May 4, 1979Sep 9, 1980Firetek CorporationCapacitive shift fire detection device
Classifications
U.S. Classification340/562, 307/652, 361/181, 336/155, 336/182
International ClassificationG08B13/26, G08B13/22
Cooperative ClassificationG08B13/26
European ClassificationG08B13/26