US2944252A

US2944252A - Intruder alarm system

Info

Publication number: US2944252A
Application number: US632881A
Authority: US
Inventors: Manfred W Muehter
Original assignee: American District Telegraph Co
Current assignee: American District Telegraph Co
Priority date: 1957-01-07
Filing date: 1957-01-07
Publication date: 1960-07-05
Anticipated expiration: 1977-07-05

Description

July 5, 1960 M. w. MUEHTER 2,944,252

INTRUDER ALARM SYSTEM 2 Sheets-Sheet 2 suascnllal-:n 19 2 July 5, 1960 M. w. MUEHTER INTRUDER ALARM SYSTEM Filed Jan. 7, 1957 susscmeen #l G51 and G32, respectively. A resistor r11 is connected between one end of each of capaci-tors K2 and K3, and a similar resistor riz is connected between one end of each of capacitors K22 and B132. Capacitor Kisv'connected across relay coil TR ,through the night position contacts D2 of Day-Night switch 15.

Relay BR, which may be of the so-called slow-to-reg position in which contacts D1 and N are closed and conlease type, also has a crystal diode RC5 connected across Y its coil to keep the relay-energized during the interval etween successive half cycles. The relay BR, which may be termed the break sustaining relay, is provided for obtaining proper reception of break impulses in case of double drop alarms, i.e., 'those in which both a break (open) and a ground occur. The operation of this relay is described in detail in copending application Serial No. 556,633, tiled December 30, 1955.

`In case of a break alarm, as for example when a metal foil is broken by an intruder smashing a window on the premises of subscriber #1, only current iiow of the positive polarity is interrupted on line 10. Such interruption causes break drop coil B1 to drop out giving a break alarm at the central station. In the case of a ground in `the protection-circuit of subscriber #1, an increase of current flow of positive polarity only occurs on line 10, causing ground drop coil G1 to respond giving a ground alarm'at the central station. In the case of both a break and a ground, both alarms will be given at the central station by operation of both drops B1 and G1. In the case of a break or ground on the line 10, the corresponding drops B1 and B2 or G1 and G2, as the case may be, will be operated. Breaks and grounds of short duration are suppressed by capacitors K21, K31, K22 and KS2 connected across the drop windings.

When a protective device with both normally closed and normally open contacts, such 'as the door contacts 14', is put into alarm condition, a break is first produced as the normally closed contact opens. In this case, break sustaining relay BR will be deenergized after a time delay caused by its chanacteristics and the diode RC5 shunting it. This insures a long enough break impulse to overcome the delay caused by the capacitors K21 and K31. After the release of relay BR, the circuit is grounded Vthrough the normally open contacts of door switch 14',

the circuit extending from line 11B'l through rectifier RC3,

:resistor DR, day circuit 13, back contacts BR1, contacts N, the normally open contacts of switch V14y day circuit 16 and back contacts TR1, to ground, causing operation of the ground drop.

When a subscriber enters his premises a-t the end of a il' protected period, eg., in the morning, a double drop signal will be received at the central station from the open- Ving and closing, respectively, of the normally closed and normally open contacts of door switches 14. The subscriber then operates Day-Night switch 15 to the dayv i position in which contacts N are opened, contacts D1 are closed and contacts D2 are operated to the opposite position from the one illustrated. Relay BR, which will have. dropped out upon opening of the door and picked up upon subsequent closing of the door, will again drop out upon opening of contacts N. This sets up the day condition circuit which extends from line 10 through rectifier RC3, resistor DR, day circuit 13, back contacts BR1, contacts D1, a resistor r6, day circuit 16, and back con- 'tacts TR1 to ground. rl`he resistance of DR should be adjusted so that the current flow therethrough will be adequate to keep ground drop coil G1 energized, indicating the day condition at the central station. During the day, a break in the circuit will cause break drop coil B1 torbe -deenergized, giving a break indication at the central station.

When the subscriber wishes to restore protection, for example before closing up his premises for the night,.he irst puts all his protective devices in operation, as by closing doors and Windows, setting traps, etc. He then places the Day-Night switch 15 in an intermediate or test tacts D2 are in a position opposite the' one illustrated. If the night circuit is in its normal condition, a circuit is complete extending from line 10 through rectifier RC3, ristor DR, day circuit 13, back contacts BRI, contacts N, back contacts 14', nightcircuit 14, back contacts BRZ, contacts D2, the coil of relay TR, day circuit 16 and back contacts TR1 to ground. A parallel path KVthrough contacts D1 and resistor r6 also exists. Since night resistor NR and the coil of relay BR are shunted by operated contacts D2., sufficient current will ow lthrough the coil of relay TR to energize this relay.l VBack contacts TR1 thereupon open, placing the bell coil BE in the circuit. The bell BE thus becomes energized, but does not -operate as a vibrating bell since its bell contacts BB1 are shunted by contacts D2 (in the test position thereof). Since the make contacts D2 are open in the test position, capacitor K is disconnected from relay coil TR, so that the latter may follow the low frequency positive pulses supplied over the linet10. The bell coil BE will in turn follow the low frequency pulses, producing a distinctive vfasttapping sound indicating to the subscriber that the night protection circuit is in order. V The operating circuits for the relay TR and the bell coil BE will not be completed if the night protection circuit or the day circuit 13 is either open or grounded. A ground or open in day circuit 16 will prevent bell coil BE from operating, even though a ground in this circuit Will permit operationy of relay TR.

It will be evident that the subscriber can determine the integrity of his protection circuits Without enlisting the 'aid of a central station operator or causing transmission of a signal to the central station since, when switch 15 is in the test position, the day current still continues to iiow through contacts D1 and resistor r6 even if there is an open in the night circuit.

If the subscribertfails to get the distinctive sound from the bell BE, he knows that his protection circuit is not vin order and that it must be checked, for'example for open doors or windows or loose trap connections. To facilitate such checking-of a night protectioncircuit eX- tending to points remote from the bell BE, one or more vextension bells 17 may be provided at appropriate locations about th'e protected premises," As shown, Vthe bell v17 maybe providedl with power from a Vcommercial Ysource through a transformer-13, the-,transformer secondary circuit being completed through 4front contacts -TR1. -With switch 15 in thetest'position thereof, the

f tion contacts D1 are open while contacts N are momentarily opened and then closed. Contacts D2 are operated to the make position illustrated. The momentary opening Vof contacts N causes a break signal to be received at the central station, advising the operator that the subscriber is ready to close. During the day condition-switch GS1 (and also' switch GSZ) had been open so that capacitor K21 (and R22) had been disconnected, reducing the retardation-of the lbreak coil B1 (and B2) to make it more responsive to the momentary break signal transmitted as the Day-Night switch 15 is operated to its night position. i v

Upon receiving the break -sign alY the4 operator o'perates the test switch of the unit associated with the particular subscriber; inthe case of'subscriber #l this is a switch Tf1. The switchITl has vcontacts TTI, and TI`12 and is ganged with switch L1 (-havingcontacts The switches TT1 ,and L1 may be a In? one position (the normal position), contacts L11`are open,

vcontacts L12 are closed, and contactsTTll and "Ijl`12 arranged to connectthe individual equipment at said central station and associated with the set not being tested to said circuit means, a normally charged capacitor, and a switching element associated with said manually operable means for causing said capacitor to discharge through the coil of said relay to energize the latter when said manually operable means is operated.

5. An intruder alarm system as set forth in claim 4 in which the discharge time constant of said capacitor is less than one second.

6. In an intruder alarm system for protecting premises connected to a remote station over a conductive path, the remote station having equipment separately responsive to circuit breaks and circuit grounds, the combination comprising a minimumprotection circuit, a maximum protection circuit, a protection testing circuit, and switch means for selectively connecting said protection circuits to said path, said minimum and maximum protection circuits having some common elements including a local indicating device which normally is prevented from operating, said minimum protection circuit having a resistance in that portion thereof not common to said maximum protection circuit sufiicient to maintain current ow in said path at a level at which said break and ground responsive equipment will not be actuated, said protective testing circuit including, in parallel connection, the noncommon portions of said minimum and maximum protection circuits and said local indicating device, said switch means having contacts which, in a test position thereof, permit operation of said local indicating device provided the maximum protection circuit is operative.

7. In an intruder alarm system for protecting premises connected to a remote station over a conductive path, the remote station having equipment separately responsive to circuit breaks and circuit grounds, the combination comprising a minimum protection circuit, a maximum protection circuit, a protection testing circuit, and switch mean-s for selectively connecting said protection circuits to said path, said minimum and maximum protection circuits having some common elements including a local indicating device which normally is prevented from operating, said minimum protection circuit having a resistance in that portion thereof not common to said maximum protection circuit suflicient to maintain current flow in said path at a level at which said break and ground responsive equipment will not be actuated, said protective testing circuit including, in parallel connection, the non-common portions of said minimum and maximum protection circuits and said local indicating device, said switch means having contacts which, in a test position thereof, permit operation of a relay included in said maximum protection circuit and having normally closed contacts shunting said local indicating device, said switch means, in Isaid test position, also causing said local indicating device to operate in a distinctive manner, said relay being operable by a high current liow initiated as a test from said central station when said switch means is Y in the maximum protection position thereof, the local indicating device operating in a manner other than said distinctive manner in said last-mentioned connection.

8. In an intruder alarm system for protecting premises connected to a remote station over a conductive path carrying alternating current, the remote station having equipment separately responsive to circuit breaks and circuit grounds, the combination comprising a minimum protection circuit, a maximum protection circuit, a protection testing circuit, and switch means for selectively connecting said protection circuits to said path, said minimum and maximum protection circuits having some common elements including a local indicating device which normally is prevented .from operating, and a rectifier which permits only one polarity of current to fiow through said protection circuits, said minimum protection circuit having a resistance in that portion thereof not common to said maximum protection circuit sufficient to maintain current flow inV said path at a level at which said break and ground responsive equipment will not be actuated, said protective testing circuit -including -in parallel connection the non-common portions of said minimum and maximum protection circuits and said local -indicating device, said switch means having'contacts which, in a test position thereof, permit operation of said local indicating means provided the maximum protection circuit is operative.

9. An intruder alarm system as set forth in claim 8 in which another protected premises is connected to said conductive path, said other protected premises having similar protection circuits including an oppositely poled rectiiier so that the opposite polarity current ows through the protection circuits thereof.

l0. In an intruder alarm system for protecting premises connected to a remote station over a conductive path, the remote station having equipment separately responsive to circuit breaks and circuit grounds; the combination ccmprising a maximum protection circuit including, in series connection, first switch contacts of a manually operable switch, protective devices, a first relay coil, -two sets of normally open contacts of said lirst relay, vibrating bell contacts, the coil of a second relay and the bell coil, said second relay being unoperated by the current 4through said maximum protection circuit and having normally closed contacts shunting said bell coil; a minimum protection circuit including, in series connection, a set of normally closed contacts of said lirst relay, a setof normally open switch contacts of said manually operable switch, a resistor adapted to provide Sufficient current flow through Said minimum protection circuit to prevent circuit break or circuit ground indications at said remote station, and said shunted bell coil; and a test circuit comprising the parallel combination of the non-common portions of said minimum andV maximum protection circuits connected in series with the remainder of said maximum protection circuit, a further set of switch contacts of said manually operable switch being arranged to shunt the coil of said rst relay and to decrease the resistance of said maximum protection circuit sufficiently to operate said second relay thereby removing the shunt from said bell coil, said further set of switch contacts also shunting said bell contacts so that said bell coil produces a distinctive sound, a break in the circuit of said protective devices preventing energization of said second relay and hence preventing removal of the' shunt from said bell coil.

ll. In an intruder alarm system for protecting premises connected to a remote station over a conductive path carrying a low frequency alternating current, the remote station having equipment separately responsive to circuit breaks and circuit grounds; the combination comprising a maximum protection circuit including, in series connection, a rectifier element, first switch contacts of a manually operable switch, protective devices, a first relay coil, two sets of normally open contacts of said first relay, vibrating bell contacts,.the coil of a second relay and the bell coil, said second relay being unoperated by the current through said maximum protection circuit and having normally closed contacts shunting said bell coil; a minimum protection circuit including, in series connection, said rectifier, a set Vof normally closed contacts of said first relay, a set of normally open switch contacts of said manually loperable switch, a'resistor adapted to provide sufficient current flow through said lminimum protection circuit to prevent circuit break or circuit ground indications at said remote station, and said shunted bell coil; and a test circuit comprising the parallel combination of the noncommon portions of said minimum and maximum protection circuits connected in series with the iremainder of said maximum protection circuit, a further set of switch contacts of said manually operable switch'being arranged to shunt the coil of said first relay and ltodecrease the resistance of said maximum protection circuit sufficiently to operate said second relay thereby removing the shunt from said bell coil, said further set of switch contacts also shunting said bell contacts so that said bell coil'produces a distinctive sound, a break in the circuit of said protective devices preventing energization of said second relay and hence preventing removal of the shunt from said bell coil; said record relay also being energized upon presence of a direct current of suti'lcient magnitude in said path whereby said bell operates in a normal manner, consequent vibration of said bell contacts providing a test -indication at said remote station.

12. In an intruder alarm system for protecting two premises connected to a remote station over a conductive path carrying a low frequency alternating current, the remote station having equipment separately responsive to circuit breaks and circuit grounds at each premises; each premises having protective equipment comprising a maximum protection circuit including, in series connection, a uniquely poled rectifier element, rst switch contacts of a manually operable switch, protective devices, a rst relayv coil, two sets of normally open contacts of said first relay, vibrating bell contacts, the coil of a second relay and the bell coil, said second relay being unoperated by the current through said maximum protection circuit andY having normally closed contacts shunting said bell coil; a minimum protection circuit including, in series connection,

said uniquely poled rectifier, a set of normally closed contacts of said first relay, a set of normally open switch contacts of said manually operable switch, a resistor adapted to pfrovide suicient current ow through said minimum protection circuit to prevent circuit break or circuit ground indications at said remote station, and said shunted bell coil; and a test circuit comprising-the parallel combination of the non-common portions of said minimum and maximum protection circuits connected in series with the remainder of said maximum protection circuit, a further set of switch contacts of said manually operable switch being arranged toshunt the coil of said first relay and to decrease the resistance of said maximum protection circuit sulliciently to operate said second relay thereby removing the shunt from said bell coil, said further set of switch contacts also shunting said bell contacts so that said bell coil produces a distinctive sound, a break in the circuit of said protective devices preventing energization of said second relay and hence preventing removal of the shunt from said bell coil.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Principles and Method of Telemetering by Borden et al., New York, Reinhold Publishing Corp., 1948, pp. 122, 123.