US2064994A - Alarm system - Google Patents

Description

Dec. 22, 1936. s-n ET AL v 2,064,994

ALARM SYSTEM Filed Dec. 28, 1955 2 Sheets-Sheet 1 Fig.1.

W W W IN V EN TORS.

A TTORNEYS.

' Dec. 22, 1936. E. D. STIRLEN ET AL 2,064,994

ALARM SYSTEM INVENTORS. EUGENE D. ST/RLEN, AND BY FREDERICK 6. KELLY.

ATTORNEYS.

Patented Dec. 22, 1936 UNITED STATES PATENT OFFICE ALARM SYSTEM of Connecticut Application December 28, 1933, Serial No. 704,214

11 Claims.

This invention relates to a structurally and functionally improved detecting and signaling system, capable of use in numerous different associations, but primarily intended for employment in connection with the detection of burglars or intruders, or where it is attempted by means of an implement to gain access to premises which are to be safe-guarded.

Numerous attempts have heretofore been made to provide detecting and signaling systems by means of which an intruder or an implement introduced by a person would result in a signal being actuated. Prior systems of this nature have included actuating units or elements which would be actuated by an intruder or by an implement. Such apparatus-even though attempts have been made to conceal the samewould be relatively conspicuous and apparent. As such, they-might readily be avoided or nullifled by a person seeking oreffecting entry. Further systems have been developed in which, by means of inconspicuous or concealed wiring, the presence of a person or implement was detected, and a signaling indication given. These latter systems, however, have ofiered numerous objections, among which are, first, that they include units which are expensive to manufacture, install and maintain; second, that certain of these systems are inherently dangerous; third, that in the case of a change in atmospheric conditions they have automatically operated,. and that such operation has also frequently occurred due to various types of radiated energy, slight motions of the antenna, objects such as bushes 0 and window shades swaying near the antenna,

etc.; and fourth, where attempts have been made to prevent such accidental operation, these attempts have been successful to only a very small extent, despite the provision of cumbersome and expensive apparatus.

With the foregoing in mind, it is an object of the invention to provide apparatus of this character the parts of which will be relatively few in number and rugged in construction, these parts being capable of ready assemblage to furnish a relatively inexpensive system which, when onceinstalled, will operate over long periods of time with freedom from dimculties, but which. at the same time, will function forthwith andduring any instant of such period if an attempt is made to violate the premises. 1

Moreover, by means of the present invention, such wiring as is necessary may be inconspicuously placed, or, in fact, wholly concealed in such manner that it will be virtually impossible for and cause an alarm to be sounded.

an intruder to detect the presence thereof. However, even if such intruder is cognizant of the existence of the system, it will be substantially impossible for him to nullify any portion of the same or to otherwise render the system ineffective to detect unauthorized entry.

An additional object is that of providing a system in which no dangerous condition will be present and which will not function in response merely to atmospheric or other natural or unavoidable changes and influences, and in which such non-functioning is achieved by a simple and positively operating construction.

With these and other objects in mind, reference is had to the attached sheets of drawings illustrating one practical embodiment of the invention, and in which:

Fig. 1 shows schematically a layout for an alarm system;

Fig.- 2 is a diagrammatic view of the wiring and apparatus which forms a part of one unit of the system; and

Fig. 3 is a similar view showing a further unit which is employed in conjunction with the unit illustrated in Fig. 2.

As afore brought out, theinvention is primarily intended to be employed in connection with the detecting of unauthorized entrance, and in the following specification and drawings the description has been accordingly limited. It will, however, be appreciated that the invention might be employed for the detection of any desired capacity variations, whether these be caused by foreign bodies entering the heldof the system, moisture variations, temperature variations, etc. Accordingly, this description is to be taken merely in an illustrative sense except where the appended claims would indicate that a more specific interpretation is in order.

with the foregoing in mind, Fig. 1 shows a schematic layout of the system, and in this figure the windows are designated by W and a door by D". All of these openings are to be protected so that an intruder will be detected "A" indicates the antenna which may consist of a wire arranged near the windows and the door as shown. The antennas are grouped'in sections and each section is connected to a partial detecting and amplifying unit P. For the sake of brevity this device will hereinafter be called a "packet. Each packet is connected by an inter-connecting cable C to the main detecting and amplifying device F. For the sake of brevity, this device will be called the "central set. The central set has a ground connection G and is also connected to the alarm which may be a bell, as shown, or floodlights, or any other device that will serve as an alarm.

Figure 2 shows the details of a packet. This particular one is designed to carry an antenna not exceeding a capacityof 200 m. m. f. The connecting cable between the packet and the central set has six conductors in it and connects to terminals ii through 16 inclusive. Referring to Fig. 3 which shows the details of the central set, there are shown terminals HA through iBA, inclusive, arranged in vertical rows of six, Each vertical row connects to the connecting cable from a packet, the wires in the cable being arranged so that the terminal H in the packet connects to terminal HA in the central set, i2 to 12A, etc. There will be one such vertical row for each packet, the number of rows being determined by the number of packets.

Terminals l3A connect through wire 60 to ground. An oscillator in the central set supplies five volts at 200,000 cycles between terminals HA and ground. The details of the oscillator will be described later. Terminals 14A and 15A connect to battery 48 which supplies current for heating the filaments of the vacuum tubes in the packets. One side of the filament supply is grounded. Terminals ISA are connected to battery 6! of minus three volts, the plus side of battery 6| being grounded. As will be noticed from Fig. 3, all the like numbered terminals of all packets are connected in parallel at the central set with the exception of terminal I i, which connects to a separate terminal HA, one for each packet. Each terminal HA connects through a resistance 49 of 35,000 ohms to the plus side of battery 62 of volts, the negative side of the battery being grounded.

Referring again to Figure 2, it will be noted that the oscillator output from the central set is supplied across a circuit including a condenser 20 of 500 m. m. f. capacity, resistance 2| of 250 ohms, inductance 22 of 3.75 m. h. and variable condenser 23 of 200 m. m. i. capacity. The antenna is connected to terminals I9, and consequently the antenna capacity may be considered as a condenser in parallel with condenser 23. I

It is apparent that there is a point of resonance in the above circuit when the capacity of the antenna and condenser 23 are such that their reactance equals the reactance of inductance 22. This occurs when the combined capacity of antenna and condenser 23 is approximately m. m. f. At that point the voltage across the portion of the circuit in resonance will be substantially zero, neglecting the resistance of inductance 22, which is low. As the combined capacity is increased, the voltage across the above mentioned portion of the circuit will gradually rise and it will be found that between a capacity of m. m. f. and 220 m. m. f. the curve will approximate a straight line. Above 220 m. m. f. the voltage increases at an increasing rate.

The above described voltage is connected to a. transformer 24 through coupling condenser 30 of .0025 m. f. capacity. Transformer 24 is a tuned transformer, being tuned by variable condenser 25. It has a 1: 6 step up ratio, this high ratio and efficiency being possible because it is tuned to the frequency of the voltage it must amplify. One side of the transformer is connected to anode 28 of vacuum tube l8, and the other side is connected to ground through a parallel circuit of condenser 26 of .1 m. f. capacity and resistance 21 of 6 megohms. Whenever the voltage swings positive, anode 28 will draw electrons from cathode 29, the heater being designated by IT. In this way condenser 26 will be kept charged at a negative potential almost equal to the peak of the alternations. A small part of the charge will leak off through resistance 2'! and consequently the potential of condenser 26 never quite reaches the peak value of the alternations. If the voltage on the transformer changes, the potential of condenser 26 will follow and adjust itself to the new peak almost instantly.

The negative side of condenser 26 is connected to the grid 3i through coupling condenser 32 of 4 m. f. capacity. Grid 3! is also connected to terminal I6 through resistance 33 of 3 megohms. Terminal I6 supplies minus 3 volts bias. When equilibrium is reached, grid 3| will be at minus 3 volts, the difierence between its bias and the potential of condenser 26 appearing as a potential across condenser 32.

The suppressor grid of tube [8 is indicated by 63 and is connected to ground. The screen grid is marked 64 and receives a potential of plus 50 volts from battery 62. The same wire that supplies the high frequency current to the packet also supplies the plus 50 volts. This is accomplished by inserting chokes 65 and 66 in the 50 volt circuit which keeps out the high frequency current. Similarly, condensers 41 and 20 prevent the 50 volt direct current from getting into the oscillator or the resonator circuit. Condenser 61 of .1 m. f. capacity acts as a shunt for radio frequency currents, so that screen grid 64 will not fluctuate.

Referring to Figure 3, it will be noted that terminal HA is connected through condenser 52 of 4 m. f. capacity to anode 50 of vacuum tube 5i. This vacuum tube serves merely as a. coupling device. It has a cathode 56 and filament 54, the filament being heated by battery 55. Cathode 56 is connected to one side of filament 54, but is not grounded. Anode 50 is also connected to a bias of minus 3 volts, the bias being supplied by battery 68, through resistance 53 of 3 megohms, the plus side of battery 66 being grounded. The difference between the potential of terminal HA and the potential of anode 50 appears as a potential across condenser 52. Cathode 56 connects by wire 69 through resistance 10 of 1 megohm to the grid H of vacuum tube 12. Grid H is supplied with a bias through resistance I3 of 6 megohms from battery 14 of minus 6 volts, the plus side of battery 14 being grounded. It will be apparent that, under normal conditions, grid H and cathode 56 will be at the same potential, namely, minus 4 volts, the 6 megohm leak being unable to draw them lower because any drop greater than 1 volt between cathode 56 and anode 50 will cause more electron current than leak I3 can supply. Tube 12 has a cathode I5, filament 16, and plate 11. Heating current for filament I6 is supplied from battery 84. The plate circuit is completed through relay H and battery I6 of 65 volts, the negative side of battery 18 being grounded. Contact 19 of relay 'I'I closes a circuit through alarm device 86 and battery 8|, causing the alarm to sound when relay 11 operates. This relay has a time delay characteristic of about one-half second, so that the pull in current mus.

flow ror that length of time before contact 19 closes.

The second packet is connected to the second vertical row of terminals. The plate circuit of the second packet goes through a separate resistor 49 of 35,000 ohms to the second anode 51 of tube Similarly, the third packet is connected to the grid 58 which serves as a third anode. The number of packets connected to one tube is limited only by the number of anodes built into vacuum tubes. As illustrated, this number at present practice is three. The second group of three packets is coupled thru a second tube 59 and further packets would require additional tubes. Condenser 82 of .01 m. f. capacity and condenser 83 of .l m. f. capacity act as by-pass circuits for any stray alternating currents.

The oscillator which supplies the 200,000 cycle supply to the packets is shown in Fig. 3. The oscillator coil 35 has an inductance of 126.5 micro-henries, and the oscillator condenser 36 has a capacity of .005 m. f. The feed back coil is marked 31. One side of the oscillator tank circuit is connected to the positive terminal of a 90 volt battery, the other side to the plate 38 of vacuum tube 39. The feed back coil is connected to the grid 40. The cathodeis grounded and the heater element 42 is heated by battery 43. Feed back coil 31 is connected to ground through a parallel circuit consisting of condenser 44 of .001 m. f. capacity and resistance 45 of 100,000 ohms. This parallel circuit acts as an automatic bias for grid 40. The output is tapped oil from point 46 and is connected through condenser of .5 m. f. capacity to terminals |2A.

It will now be possible to describe thecomplete sequence of operations of the system, which is as follows:

As long as the combined capacity of the antenna and condenser 23 is between 180 and 220 m. m. f. the change in voltage produced by a fixed change in capacity, such as caused by the approach of an intruder, will be substantially the same. Condenser 23 is set so that the combined capacity of. antenna and condenser 23 equals 200 in. m. I. Then the antenna capacity may vary plus or minus 20 in. m. f. and the change in voltage produced by the approach of an intruder will be the same. In other words, the gradual and seasonal'variations may be as great as plus or minus 20 m. m. f. without affecting the sensitivity of the system. In most applications a practical antenna can be built with such limits and accordingly no greater variations need be provided for although any other limits can be obtained by choosing the proper circuit constants.

If an intruder approaches the antenna, causing an increase in antenna capacity, the voltage supplied to transformer 24 will increase, causing an increase in the negative potential of condenser 26. The charge on condenser 32 cannot change instantly since it must come through resistance 33 and consequently the potential of grid 3| is made more negative. This results in a decrease in the plate current of vacuum tube ill, the plate current being from battery 62, resistance 49, terminals HA and plate 34, and cathode 23 to ground.

As soon as the transient condition in the antenna circuit has ceased, condenser '32 will be charged through resistance 33 and eventually grid 3| will again reach a bias of minus 3 volts and the original plate current will be re-established. 1

The operation of the central set is as follows: When the plate current of the packet decreases, due to the approach of the intruder, the potential drop across resistance 49 decreases and consequently the potential of terminal HA connected to the afiected packet rises. The potential of condenser 52 cannot change instantly, any change having to pass through resistance 53 and consequently the potential of anode 50 rises and lifts the potential of cathode 56, causing a rise in potential of grid II. This will cause an increase in the plate current of tube 12 and if this change is suificient, relay 1'! will operate. In the meantime, current has been flowing into condenser 52 from battery 68 and the normal potential of anode 50 will eventually be re-established, which will cause the grid H to resume its former bias and re-establish the normal plate current in tube 12, dropping out relay I1. I

The above describes the complete sequence of functions resulting from the approach of a body towards the'antenna. It will be noted that the change in capacity must be at least a certain amount in order to cause a sufficient increase in the plate current of tube 12 so that it will operate relay '|1'. Furthermore, any change must occur above a certain minimum rate of m. m. f. per second because the circuit has restoring actions for grids 3| and 1|, (and coupler anodes) proportional to their displacements from steadystate potentials. If the change in antenna capacity is at a lower rate the potentials of grids 3| and II will not change sufficiently to cause the output relay-hence the alarm-to work. It therefore becomes apparent that this is the way the slow seasonal variations in antenna capacity are distinguished from the relatively rapid changes produced by the approach of a body.

Now suppose that the various packets connected to the central set are receiving interference impulses as described above. The resultant fluctuation in each section is only a portion of the larger total that would have occurredif all sections had been connected together. The corresponding fluctuations of coupling anodes 50, 51, 58, etc. tend to raise the potential of grid 1|. However, due to unidirectional conductivity of the electron streams commandable by each coupler anode, only the most positive anode passes any current through the coupler and consequently the potential of cathode 56 has to follow the most positive anode, all other anodes being at an insuflicient positive voltage above the cathode for conduction. Hence, the largest interference impulse received on anyone packet is the size of the interference impulse received by the entire system. The capacity interferences are similar to the changes produced by an intruder except that, in general, their intensity per foot of antenna length is very much smaller than the eifect of an intruder, who, at most, aifects one or two feet of antenna. However, if the antenna is long enough, the sum total of the capacity impulses on one antenna may be great enough to cause an alarm. Accordingly, in practice the sections are preferably made small enough so that the largest impulse apt to be received will not be large enoughv to 'icause an alarm. Naturally, the sensitivity of the. system to an intruder is not affected because the sensitivity along the entire length of the antenna is independent of its length.

Some interferences, such as those due to lightning, may still be so large as to cause alarms. These, however, are usually of extremely short duration and are eliminated by the slow pull-in characteristic of relay Tl.

Changes in sensitivity of a particular packet may be accomplished by changing the size of resistance 49. Decreasing the size of the resistor decreases the sensitivity because the change in voltage drop for the same change in current will be less. Accordingly the rise in the potential of anode 50 will be less. Accordingly, the sensitivity may be increased by increasing the size of the resistance.

The packet shown in Fig. 2 will carry an antenna of a capacity not exceeding 200 m. m. f. If an antenna of larger capacity is to be carried on one packet, the constants of the resonating circuit are changed. For example, if an antenna of 400 In. in. f.' is to be carried on one packet, condenser 20 would be changed to .001 m. m. f., resistance 21 to 125 ohms, and inductance 22 to 1.87 m. h. Condenser 23 need not be changed because its only function is to supply the difference in capacity between the packet capacity of 400 m. m. f. and the antenna capacity.

Referring to Fig. 2, antenna capacity variations produce changes in the D. C. voltage across condenser 26. This voltage, being rectified radio frequency power, is directly proportional to the oscillator voltage, and hence to the voltage of the oscillator plate supply batteryall other conditions remaining constant. Hence, if that batterys voltage should change, a change would occur across condenser 26, which, if rapid and large enough, would cause an alarm just the same as a capacity change. Consequently, while all batteries shown may be replaced if desired with alternating current rectifiers, the rectifier replacing the oscillator supply battery must be very accurately regulated.

From the foregoing, it will be seen that a system is provided which, among others, achieves the objects specifically set forth at the beginning of this specification. It is apparent that the antenna might be located as desired, and also be of any configuration which might seem best suited to the needs of any particular installation. The seasonal weather and daily temperature variations cause the antenna capacity to change at a slow rate, so that accordingly no accidental operation will result. On the other hand, a capacity change caused by the approach of a person or object would result in an immediate functioning of the system, even though such change would be but fractional as compared to a change which might result from atmospheric variations. Moreover, the system is substantially immune to accidental operation incident to lightning striking in the vicinity. A sudden mechanical shifting of the antenna, bushes and hedges swaying near the antenna, and other similar effects, are not discriminated against in the present system. However, interferences of this nature are reduced to a negligible intensity, due to the manner that the antenna is connected to the detecting portion of the system. By dividing the antenna into sections, a part of the detecting is done by each section, the several packets feeding into a main detector in such a manner that the interference impulses are received in parallel. In this manner the total interference impulses can be no greater than the largest individual one. Of course, each section of the system may be adjusted so that it has exactly the proper sensitivity. In other words, the antenna protecting a smaller window need not be very sensitive, because it is obvious that an intruder, in efiecting passage through such window, must pass very close to the antenna. In the case of an antenna protecting a large open areaway, that branch of the system would have to be adjusted in such manner as to be relatively and extremely sensitive, because the intruder might not pass immediately adjacent to the antenna.

It is apparent that numerous changes in construction and rearrangement of the parts might be resorted to without departing from the spirit of the invention as defined by the claims, and that, moreover, the method of detection as herein taught might be varied in numerous different respects.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

l. A device for detecting capacity changes including, in combination, a constant frequency oscillator, a circuit energized by said oscillator, said circuit including an antenna, means to am plify changes in the voltage across a portion of said circuit, means associated with said amplifying means to cause the latter to have a relatively poor amplification characteristic for slow rates of change and a good amplification characteristic for rapid rates of change, and means for indicating certain of such changes.

2. A detecting system including an antenna, means for supplying constant frequency current to said antenna, indicating means and means for connecting said antenna to saidindicating means to render the latter responsive only to capacity changes in said antenna which occur at and above a predetermined rate.

3. A device for detecting capacity changes including, in combination, a constant irequency output oscillator, a circuit including an antenna connected to and energized by said oscillator, and means to indicate rate of change of voltage across a portion of said circuit.

4. A device for detecting capacity changes including, in combination, a constant frequency output oscillator, a circuit including an antenna connected to and energized by said oscillator, distribution of the total voltage across said circuit being dependent upon the impedance of each portion, and means to indicate rate of change of voltage across a portion of said circuit.

5. A device for detecting capacity changes including, in combination, a constant frequency output oscillator, a circuit including an antenna connected to and energized by said oscillator, distribution of the total voltage across said circuit being dependent upon the impedance of each portion, the impedance of one portion varying with changes in antenna capacity, and means to indicate rate of change of voltage across a portion of said circuit.

6. A device for detecting capacity changes including, in combination, a constant frequency output oscillator, a circuit including an antenna connected to and energized by said oscillator,

the voltage across a portion of said circuit varying with changes in antenna capacity, and means connected to said circuit to indicate voltage chtanges occurring at and above a predetermined ra e.

'7. A device for detecting capacity changes including, in combination, a constant frequency output oscillator, a circuit including an antenna connected to and energized by said oscillator. the

voltage across a portion oi' said circuit varying with changes in antenna capacity, means to amplify and rectify the voltage across a portion of said circuit, and means to indicate changes in said rectified voltage occurring at and above a predetermined rate.

8. A device for detecting capacity changes including, in combination, a constant frequency output oscillator, a circuit including an antenna connected to and energized by said oscillator, the voltage across a portion of said circuit varying with changes in antennacapacity, means to amplify and rectify the voltage across a portion of said circuit, said amplifying means having a relatively poor amplification characteristic for,

slow rates of change and a good amplification characteristic for rapid rates of change, and means for indicating certain of such changes.

9. A device for detecting capacity changes including, in combination, a constant frequency output oscillator, a plurality of circuits connected to and energized by saidoscillator, each said circuit including an antenna, the voltage across a portion of each circuit varying with changes in capacity of the antenna, and indicating means'connected to said circuits and operable by voltage changes in any circuit occurring at and above a predetermined rate.

10. A device for detecting capacity changes including, in combination, a constant'frequency output oscillator, a plurality of circuits connectedto and energized by said oscillator, each said circuit including an antenna, the voltage across a portion of each circuit varying with changes in capacity of the antenna, means connected to each said circuit and adapted to amplify said voltage changes, and further means connected to said last mentioned means to indicate voltage changes in any circuit occurring at and above a predetermined rate.

11. A detecting system including a plurality of antennas individual to diiferent property 10- cations, means for supplying constant frequency current to each of said antennas, indicating means, and means common to a plurality of said antennas and connected to the indicating means to cause said indicating means to register changes in capacity in said antennas occurring at and above a predetermined rate.

EUGENE D. S'IIRLEN.

FREDERICK G. KELLY. as

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