US2302271A - Alarm system - Google Patents

Description

Nov. 17, 1942. p, N, SMITH 2,302,251

ALARM SYSTEM Filed April 27, 1940 Patented Nov. 17, 1942 UNlTED STAT attrait ALARM lSYSIEIW Application April 27, 1940, Serial No. 332,026

7 Claims.

The present invention relates to alarm systems and more particularly to burglar alarm systems inr which responsive devices located at one or more local stations are arranged to transmit signals to a central office.

Such systems involve responsive devices of a variety of' types, one of the common types being the photoelectric cell which is continuously energized b-y a beam of lightv directed thereon so that the presence of an intruder is indicated by interruption of the beam. Another type of responsive device is the radiometer described in thev patent to Hayes No. 1,954,204 and the patent to Hall No. 2,115,578, which operates by the radiant energy emitted from the intruder himself, and is therefore particularly useful for this service because of its ability to pick up radiation from any point withinv its field of vision.`

Burglar alarm systems involving responsive devices of any type may be made self-supervising to the extent of indicating failure of electrical connections to the central oiiice and other faults of, similar nature, but are frequently defective in failing to guardV against other inoperative conditions, such as diminishing sensitivity of the responsive devices themselves, malicious disablement thereof bypersons who have gained legitimateaccess to the premises in` order to prepare for a subsequent illegal` entry, etc.

The principal object of 'the present invention is to provide means for routine supervision of the equipment whereby the effect of an intruder may be completely simulated so that the equipment cannot be left in inoperative condition for any extended period.

Since the local station orI stations may be separated from the central oiiice by considerable distances, it is desirable that4 the wiring connections be kept to a minimum, and another object of my invention is to provide means whereby the above-mentioned test may be effected without the necessity of connections in addition to the actual signal transmitting circuits.

With these objects in view, the present inven tion comprises the system hereinafter described and particularly defined in the claims.

In the accompanying drawing Fig. l is a diagram of the'preferred form of the system involving radiometers of the type disclosed in the Hayes and Hall patents, and Fig. 2-is a diagram of a modication of the system to employ photoelectric cells.

As shown in Fig. 1, the apparatus at the central station is indicated to ther left of the dot-and 55 dash line, and that at the premises tobe protected is showny at the right thereof. A single wire connects the central station equipment with the equipment at the premises.

The space to be protected is provided with one or more radiant energy sensitive devices indicated at 4 and 6 herein, such devices being preferably of the type described in the Hayes and Hall patents above referred to. Such devices are operated b-y the radiant energy emitted by the intruder himself. Preferably, each device is provided with a grating or screen of the type described'in the Smith Patent No. 2,198,725', to insure that the radiant energy impinging on the receivers will be varied or modulated during movements of the intruder about the space to be protected. The receivers are sensitive to changes in radiant energy no matter how generated, and are therefore useful to detect an incipient re in the protected space.

Each receiver is provided with a local amplifier designated at 8 and I li, and the outputs of these ampliiers are connected to the input of a main amplier I2, the output of which is Connected to the coil I4 of a balanced relay. The relay has a movable contact I5, which under normal conditions is held midway between two fixed contacts IB. Upon de-energization or increased energization of the coil Ill, the movable contact engages one or the other of the xed contacts I8. Connected with the contacts I8 is a relay 26 having a movable contact 22 normally engaging a iixed contact 2li, and adapted to close on another xed contact 26 when the relay is energized.

The foregoing circuits are under the control of a double-throw switch 28 adapted to be thrown into either the nigh or day position. One of the blades of the switch is connected by a wire Sllwith the positive terminal of a local battery, as indicated by a plus sign. The contact with which this blade engages in the night position is connected by Wiring 32 to the circuits for energizing the ampliers. A wire 34 con- .nects the wire 32 with the movable contact l day position is connected directly to ground and also through a wire d and variable resistor 62 with the connection 35.

The movable contact 22 of the relay 20 is ccnnected by a wire dll with a relay coil 46 to be presently described. From the relay i5 a line 58 runs to the central station.

The central station includes a battery 5G connected at one side to ground and at the other side to the line 68 through a current-adjusting resistor 52, a manual switch 54 to permit opening of the line, a current meter 5G, and two signal relays 58 and E9, all in series. The relay 53 has contacts S2 which are normally open, but are adapted to close upon an increase in line current to operate a suitable signal, and the relay 60 has normally closed contacts Gl which are adapted to open upon a decrease in line current to operate another signal. The signals may be any suitable type and are not shown in the drawings.

Considering the parts thus far described and assuming the switch 2B to be thrown to night position, it will be seen that the amplifiers are energized and that the relay I4 is suiiciently energized to hold the movable contact I6 in its midposition, the relay 2S being then de-energized. A continuous circuit may be traced from ground through the battery 50, the central station equipment, the line 48, the relay 46, wire M, contacts 22, 24, resistor 38, resistor 42, and wire 40 to ground. The resistors 38 and 42 as well as the resistor 52, are adjusted to maintain a standard line current which is indicated by the meter 56, this current being just suicient to maintain the relay 6i) energized, and insuicient to pick up the contacts of the relay 58. Under such conditions a change of radiant energy falling on either or both of the receivers will result in a change in energization of the relay I4, thus either attracting or releasing the movable Contact I3 to close on one of the fixed contacts I8 and establish an energizing circuit for the relay 2D. Contact 22 then closes on 26 so that resistors 38 and 42 are shunted, thereby increasing the line current and giving an indication on the meter 5B, as well as on the signal controlled by the relay 58.

When the premises are to be opened for business, the switch is thrown to day position, thereby disconnecting the local battery. Also, the resistor i2 is shunted, thereby increasing the line current. The increase of current to the standard day value is indicated on the meter 56 and may also, if desired, be indicated by the signal controlled through the relay 53. The central station operator is thus advised that the premises are occupied and he need pay no further attention to the equipment until he receives an indication of establishment of standard night current when the switch 28 is thrown to night position.

The apparatus as thus far described is selfi' supervising to the extent of automatically indieating any failure in the line or in the power and output circuits of the ampliers. Thus a break in the line is indicated by operation of the underload relay E9, and a ground fault by operation of the overload relay 5S. Failure of the amplifiers to maintain the relay I4 continuously energized causes closure of the contacts I 6, I8 with consequent operation of the central station signal equipment.

The invention also provides for supervision of the receivers 4 and 6, as well as the input circuits of the amplifiers 8 and I0, and in fact, any other equipment not subject to the automatic supervision above noted. This is accomplished by a routine test which may be carried out on regular schedule at the central oice. For this purpose the relay iii which is continuously energized under normal conditions is provided with a movable contact 6G adapted to close on a fixed contact 68 when the relay is de-energized. The contact 56 is connected to the wire 32 which as previously described is connected to the positive terminal cf the local battery through the switch 28 when the latter is set to night position. The contact G8 is connected through a resistor 13 and a lamp i2 with the negative terminal of the local battery. The lamp T2 is arranged in the protected space so that radiant energy emitted therefrom is picked up by both of the receivers 4 and 6. The relay 46 is shunted by a large condenser TG., preferably not less than 40 microarads in capacitance.

For the routine test the central station operator simply opens the switch 54 momentarily. The switch 54 is held open long enough to insure cle-energization of the relay 46, usually two or three seconds. The switch 54 is then closed. The relay 66 does not re-energize immediately because of the time constant aiorded by the condenser i4. Consequently, the lamp I2 remains energized for a short period after the line is again closed. If all parts are in working order, the relay I4 will usually operate to transmit a signal to the central office when the switch 54 is closed. It is to be noted that, as stated in the Hall patent, the receivers operate on changes of radiant energy rather than on actual quantities of radiant energy impinging thereon, and consequently a signal may not be transmitted at this time if the switch 54 has been held open so long that the lamp 'I2 has come up to full brilliance before the switch 54 is closed. It has geen found, however, that due either to mechanical oscillation of the receiver diaphragms or to electrical oscillations in the amplicrs, a number of swings usually occur and one or more signals will ordinarily be given unless the switch 54 has been held open for too extended a period. But whether or not a signal is given at the time of closure of the switch Sli, a signal will certainly be given shortly thereafter when the magnetic eld of the coil 46 builds up sufiiciently to attract its contact and open the lamp circuit. The extinction of the lamp results in a change of radiant energy which is effective to give the desired signal if the parts are in working order; in fact, several signals may be given due to the oscillating effect above mentioned. In any event, the central ofice will receive a denitive signal that all parts of the equipment are in proper condition. Immediately thereafter equilibrium conditions are established and the system is in normal condition for nre and burglar detection.

If for any reason the equipment is not in proper working order, no signals will be given at the central o'ice after the closure of the switch 54. This is an indication that attention is required at the premises.

If only a single detector is used for the protected space the resistor 70 may be omitted. When two detectors are used the purpose of the resistor is to adjust the lamp current to such a value that the radiant energy emitted from the lamp will be just sufcient to operate the equipment if both receivers are in working order, but will be insufficient to give a signal if only one of the receivers is in working order.

It will be noted that this method of routine supervision is accomplished without the necessity A'of any additional wiring between Vthe central office and' the premises. In practice the central oiice will have equipment fora number of establishments, in which case a line 48 will run from the central o'ihce to each of the premises 'to be protected. Since the centraloice may be ferred system, a routine check 'test is madefonce each hour through the night for each installation.

The routine check test system is equally appli-l cable to otherforms of radiant-energy detectors. For example, in the use of the photoelectric cell a similar arrangement is used except that the relay connections are reversed. As shown in Fig. 2, .a photoelectric cell 'l5 is continuously energized by a beam of light from a lamp 76. The beam is directed past a door or window and the detection of an intruder depends upon the interruption of the beam. The energizing circuit for the lamp 16 includes contacts I8 and 8S, similar to the contacts 66 and S8 of Fig. 1, except that they are maintained normally closed by the relay winding 46. The remainder of the connections are similar to those of Fig. 1.

The photoelectric system is self-supervising in most respects, but would not automatically indicate some conditions of intentional tampering. For example, a person who had gained access to the premises during the day might introduce an extra source of illumination which would keep the cell 15 energized notwithstanding interruption of the beam from the lamp 76; or he might disable the relay 2t so that the system would not respond to a subsequent intrusion. Such conditions are guarded against by routine tests, carried out by opening of the central oice switch 541. The switch 54 is opened long enough to drop the contact 89, thus extinguishing the light l5. Upon closure of the switch 54 the relay is not immediately energized so that the lamp 16 remains dark for a short period. If the equipment is in working order, the central oi'ce equipment indicates this short dark period, followed by the normal current flow. On the other hand, an immediate indication of normal current after closure of the switch 54 is a warning of trouble, requiring immediate attention at the premises.

It will be observed that the manual supervising devices, in either form of the invention, simulate an actual intruder and therefore render it impossible for the system to be inoperative for a period greater than the time between routine tests. Not only is the system protected against loss of sensitivity in the equipment, but also against intentional disablement by persons who have gained access to the local equipment under day conditions. In the preferred operation of the system a manual test is made within a few minutes after the system has been converted for night operation, whereby any such disablement may be immediately detecte-d, and other tests are made at regular intervals during the night. It will be understood that the night setting is used for Sunday and holiday conditions, or to any other conditions under which the premises are unoccupied.

Having thus described the invention, I claim:

1. An alarm system comprising a local station having a radiant-energy-sensitive device responsive to radiant energy emitted from any source within the space to be protected, a central cnice having a signal device, a single normally closed signaling circuit between the local station and the central oice, test means at the local `station including a normally extinguished source of radiant energy and a relay in said signaling circuit having a, large time constant and energized while the circuit remains closed, said relay having contacts to Venergize said source when the relayis di-energized, 'and control switch' at the central office for opening and closing the signaling circuit to .de-energize and slowly re-energize vthe relay and thereby vbriefly to energizeI the Vsource of radiant energy in time-lagging relation to the opening and'closing of the circuitr- 2. An alarm system comprising a local? station having a radiant-energy-sensitive device responsive to radiant energy emitted from any source within the space to Ybe protected, a central office having a signal device, a single normally closed signaling circuit between the local station'and the central oiiice, test means at the local station including a normally extinguished source of radiant energy and a relay in said signaling circuit energized while said circuit remains closed, a condenser shunting the relay to delay energization and de-energization thereof, relay contacts to energize said test source when the relay is deenergized, and control switch at the central oiTlce for opening and closing the signaling circuit to cause the source of radiant energy to be energized briefly following an opening and re-closing of the circuit.

3. An alarm system comprising a local station having a photoelectric cell and a source of light directed thereon, a central office having a signal device, a single normally closed signaling circuit between the local station and the central ofiice, a relay in said circuit at the local station and energized while the signaling circuit remains closed, the relay having a large time constant to delay energization and de-energization thereof, relay contacts operative when the relay is deenergized'to cut off the illumination from the cell, and means at the central oflice operative to control the relay by opening and thereafter closing the signaling circuit to cause the relay to be de-energized and re-energize-d in time delayed relation to the circuit opening and closing.

4. An alarm system comprising a local station having a photoelectric cell and a source of light directed thereon, a central office having a signal device, a single normally closed signaling circuit between the local station and the central oiiice, a relay in said circuit at the local station and energized while the circuit remains closed, the relay having a large time constant to delay energization and de-energization thereof, relay contacts operative when the relay is fle-energized to cut off the illumination from the cell, and a switch in said circuit at the central ofce operative upon a single opening and closing to control the relay to cause the same to cut off the illumination from the cell for a brief period after the circuit is re-closed.

5. An alarm system comprising a local station having a responsive device operable upon the relay contact after opening and closing of the circuit to hold the test means operative for a short time after switch closure.

6. An alarm system comprising a local station having a responsive device operable upon the presence of an intruder, a central station having a signal device, a normally closed signaling circuit connecting the local station and the central station, test means at the local station operable to simulate the presence of an intruder, a. normally energized relay in the circuit and having a movable contact to operate the test means when the relay is de-energzed, a switch at the central station to open and close said circuit, and means shunting the relay to delay re-energization of the relay following an opening and closing operation of the switch to hold the test means operative for a short time after switch closure.

7. An alarm system comprising a local station having a responsive device operable upon the presence of an intruder, a central station having a signal device, a normally closed signaling circuit connecting the local station and the central station, test means at the local station operable to simulate the presence of an intruder, a normally energized relay in the circuit and having a movable contact to operate the test means when the relay is de-energized, a switch at the central station to open and close said circuit, and a condenser shunting the relay to delay reenergization of the relay following an opening and closing operation of the switch to hold the test means operative for a short time after switch closure.

PHILJP N. SMITH.

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