An alarm and monitoring system provided with a central console having a bank of relay-actuated light indicators. Associated with each relay is a solid-state control circuit having a pair of normally non-conductive transistors, one of which is coupled by wires to an external, normally-open sensor switch at a remote station, the other being coupled by wires to an external, normally closed sensor switch at the same station. The arrangement is such that when either switch is actuated, a bias is applied to the base of the related transistor through a resistor of relatively high value to render it conductive and thereby energize the associated relay. Because the bias is determined by the voltage drop across the resistor, the relatively low resistance in the wires going to the external switches has no material effect on the operation of the system even though this resistance is in series with the resistor.

Current U.S. Class:	340/525 ; 340/502; 340/514; 340/532; 340/594; 361/203
Current International Class:	G08B 25/14 (20060101); G08b 023/00 ()
Field of Search:	340/409,213R,176,248B,248C,249,412,276,227,227.1

Michael Ebert

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Claims

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1. An alarm and monitoring system comprising: A. a central console provided with a bank of light indicators and a relay coupled to each indicator to control the operations thereof, B. a solid-state control circuit associated with each relay, said circuit including a pair of normally nonconductive transistors each of which is coupled to said relay such that when either transistor is rendered conductive, current is supplied to said relay to energize same, thereby to operate the indicator coupled thereto, C. a first bias resistor connected at one end to the base of a first of said pair of transistors, and a second bias resistor connected at one end to the base of the second of said pair of transistors and at the other end to a first source of potential capable of biasing said second transistor into conduction, D. and a first normally open sensor switch connected to the other end of said first bias resistor and to said first source of potential, and a second normally closed sensor switch connected to the base of said second of said pair of transistors and to another source of potential capable of biasing said second of said pair of transistors into a nonconductive state, whereby closing of said first normally open sensor switch will cause conduction of said first of said pair of transistors, and opening of said second normally closed sensor switch will cause conduction of said

2. A system as set forth in claim 1, further including an alarm buzzer

3. A system as set forth in claim 1, further including a diode in series

4. A system as set forth in claim 1, further including a flasher circuit coupled to said relay and activated when the relay is energized to

5. A system as set forth in claim 1, further including holding circuits for said relays to maintain them operative subsequent to a momentary actuation of the associated sensors.

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Description

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RELATED APPLICATIONS

This application is related to my copending applications Ser. No. 818,677, filed Apr. 23, 1969, and Ser. No. 827,744, filed May 26, 1969, now U.S. Pat. No. 3,643,244.

This invention relates generally to monitoring and alarm systems, and in particular to a system in which the existence of fire, smoke, an illegal intrusion, or any other abnormal condition is sensed at any station in a multiple-station installation to produce a switching action functioning to identify the responsible station at a central console.

In one known form of fire-alarm system, detector heads are placed at various stations throughout a facility, the heads all being linked by lines to a common alarm circuit. The heads, which are usually constituted by bimetallic switches or equivalent elements, are temperature-sensitive and operate in response to an abnormal rise in temperature to actuate the alarm circuit. In a similar intruder alarm system, switches are associated with doors or windows located at various points in a structure, such that when a door or window is violated, the switch related thereto is actuated, the switches being linked by wires to a central alarm box.

While in prior-art systems of this type, the alarm calls attention to a hazardous condition somewhere in the installation, it does not actually identify the activated detector and hence does not point to the location of the violation. This is a serious drawback when the installation is made in a multiple-story building, a large warehouse, or in any other elaborate structure, for precious time may be lost in finding the exact source of the violation.

To overcome these drawbacks, systems have been proposed in which each station or door detector is coupled to an indicator on a central annunciator board which identifies the activated detector. In such systems, when a given detector switch is closed, current flows through the line extending from the switch to the associated annunciator relay to actuate the relay. The difficulty with this prior-art arrangement is that where the detector lines are distributed among various stations throughout a large building or other installation, the length of the lines may introduce substantial resistance in the circuit. Consequently, the voltage established at the annunciator board may fall below the level necessary to actuate the associated indicator relay.

While it is possible to compensate for the effect of line resistance, the resultant arrangement becomes relatively complicated and costly. Moreover, in some situations, particularly where the lines go through an environment which may contain explosive gases or chemicals, the current-carrying lines themselves constitute a possible hazard, for the current therethrough is relatively heavy and may produce sparking at the detector contacts or elsewhere in the line, should there be a failure in line insulation.

BRIEF DESCRIPTION OF THE INVENTION

In view of the foregoing, it is the main object of this invention to provide an improved monitoring and alarm system wherein a plurality of external switching sensors at various remote stations, which sensors are either normally open or normally closed, are coupled by individual lines to pilot lights or other indicators on a central console so that the existence of an abnormal condition at any station is indicated at the console, and a general alarm is given.

More specifically, it is an object of this invention to provide a system of the above type, in which the status of each station is indicated at a central console by means of individual light indicators, each operated by a separate relay, the relay being actuated by a solid-state control circuit connected to an external sensor by a line whose length and resistance have virtually no effect on the behavior of the control circuit, whereby the system operates reliably with highly extended lines.

Also an object of the invention is to provide a monitoring system in which the lines connecting the external sensors to the central console operate at low voltage and carry minute electrical currents and hence offer no danger to building personnel and constitute no fire hazard.

Yet another object of the invention is to provide an alarm system of simple, reliable and efficient design which may be manufactured at low cost.

Because the system lends itself to use with switching type sensors or detectors which are either normally open or normally closed, the system is highly versatile and has many practical applications. The sensors may be made sensitive to fire, smoke, or any other abnormal condition whose existence creates an emergency, or the sensors may be simple switches responsive to an unauthorized entry such as at a window or door.

Briefly stated, these objects are accomplished in a system having a bank of relay-actuated light indicators at a central console. Associated with each relay is a solid-state control circuit having a pair of normally non-conductive transistors, one of which is coupled by wires to an external, normally-open sensor switch at a remote station, the other being coupled by wires to an external, normally closed sensor switch at the same station.

The arrangement is such that when either sensor switch is actuated, a bias is applied to the related transistor in the control circuit through a resistor of relatively high ohmic value, to produce a voltage drop thereacross which renders the transistor conductive and thereby energizes the associated relay. Because the bias is determined by the voltage drop across the resistor, the relatively low resistance of the wires going to the external sensor switches, even when of great length, has no material effect on the operation of the system.

OUTLINE OF THE DRAWING

For a better understanding of the invention, as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawing, in which:

FIG. 1 is a schematic representation of a monitoring system in accordance with the invention; and

FIG. 2 is a schematic circuit diagram of the system.

DESCRIPTION OF THE INVENTION

The General Arrangement

Referring now to FIG. 1, there is shown a monitoring and alarm system in accordance with the invention, the system being constituted by a console 10 located at a central point and operatively linked to a plurality of stations A, B, C, D, etc., disposed at various remote points in a warehouse, a factory, or other building having sensors installed therein to detect a condition or conditions to be monitored, such as fire, smoke or illegal entry.

The purpose of the system is to provide centralized indications of the individual status of the stations. Each station is provided with a normally-open switch Sx and a normally closed switch Sy. If, for example, the station is intended to protect a door and an adjacent window, a normally-open switch may be so mounted on the door whereby when the door is forced open illegally, switch Sx is closed thereby, whereas when the window is opened without authority, normally closed switch Sy is opened thereby. Because each station has switches Sx and Sy it is capable of tying in with any existing type of normally-open or normally closed sensor.

Console 10 is linked to the various stations by a plurality of lines W extending between switches Sx and Sy at each station and terminal boards 11 and 12. The boards are each provided with a bank of terminal pairs, board 11 functioning in conjunction with the normally-open switches Sx and board 12 with the normally closed switches Sy.

Switch Sx in the first station A is connected to the first terminal pair NOa in board 11, while switch Sy in the same station is connected to the first terminal pair NCa of terminal 1. Corresponding connections are made for the Sx and Sy switches in the other stations with respect to terminal pairs NOb, NOc, etc., and terminal pairs NCb, NCc, etc.

By way of example only, the terminal boards in FIG. 1 have each been provided with seven pairs of terminals. In practice, the system may be made in any desired capacity (as few as two stations, or as many as 10, 20, 50 or even more). Mounted on the front panel of console 10 is a bank of lightbulb indicators La, Lb, Lc, etc., there being as many bulbs as there are station terminal inputs. Housed behind the panel is a buzzer Bz which gives a general alarm when any bulb in the console is activated. In practice, an external alarm may also be provided.

The arrangement is such that when either switch Sx or Sy at any station is activated, or both of them, this fact is indicated by illumination of the corresponding lamp La, Lb, etc., in the bank thereof, the illuminated lamp being caused to flash so that its operation is more noticeable.

THE ALARM CIRCUIT

The circuit arrangement of the monitoring and alarm system is shown in FIG. 2, in which, for purposes of simplicity, only three light indicators La, Lb, and Lc and their associated circuits are shown operating in conjunction with stations A, B and C. Power for the system, in one preferred embodiment thereof, is derived from an alternating-current (115 volt - 60 cycle) power line and is stepped down by a transformer 13 to 12 volts A-C or any other value appropriate to the components forming the electrical system.

The secondary of transformer 13 is connected to a bridge rectifier and filter circuit 14 whose 12-volt D-C output appears at terminals DC+ and DC-. The 12-volt A-C output of the transformer is directly available at terminals AC.sub.1 and AC.sub.2 to operate the buzzer Bz.

A 12-volt battery 15 is provided on a stand-by basis, the battery being automatically connected into service in the event of A-C power failure by means of a switch-over relay (not shown). The charge on the battery may be maintained by a trickle charger operating on the A-C power line.

The lightbulbs La, Lb, Lc, etc., are energized by the 12-volt D-C supply, one end of each bulb being connected to terminal DC-. A bank of light-operating relays Ra, Rb, Rc, etc., is provided, there being as many relays as there bulbs and associated station terminals. Initially, when the main power switch 16 in the primary of transformer 13 is turned on, all relays Ra, Rb and Rc remain de-energized.

Associated with relay Ra is a solid-state control circuit Ca, and similarly associated with relays Rb and Rc are solid-state control circuits Cb and Cc. Each circuit includes a pair of transistors 17 and 18 and a pair of isolating diodes 19 and 20. The coil of relay Ra is connected through diode 19 and the collector-emitter path of transistor 17 between the negative terminal DC- of the D-C power supply and the positive terminal DC+ thereof by way of the normally-closed contacts a of a single-pole, double-throw light-test and reset switch 21. The coil of relay Ra is similarly connected to the D-C power supply through diode 20 and transistor 18.

The base of transistor 17 and the base of transistor 18 in the control circuit are normally unbiased whereby these transistors are initially non-conductive and the associated relays Ra is initially de-energized. The other relays under the control of their respective control circuits are similarly initially de-energized.

When, however, either transistor 17 or 18 is rendered conductive, a path is completed between the coil of relay Ra and the power supply, and the relay is energized to actuate a ganged set of four single-pole, double-throw switches S1, S2, S3 and S4 whose poles P normally engage fixed contacts a but, when the relay is energized, engage fixed contacts b.

One terminal of the terminal pair NO.sub.a, connected by wires W to the normally-open external switch Sx at station A, is connected to power-supply terminal DC+. The other terminal of the pair NOa is connected via resistor 22 to the base of transistor 17. When, therefore, normally-open external switch Sx is caused to close by reason of an abnormal condition sensed at station A, a bias is applied to the base of transistor 17 whose value is determined by the voltage drop across resistor 22. In practice, resistor 22 as well as resistor 23 has a high ohmic value (16,000 ohms) and the resultant bias is sufficient to render transistor 17 conductive.

As a consequence, relay Ra is energized, thereby actuating relay switches S1 to S4. Relay Ra, once momentarily energized, is latched, this being accomplished by switch S2, whose pole P shifts from free contact a to contact b. Since pole P is connected to the DC+ terminal, this voltage is now applied to resistor 22 to maintain transistor 17 conductive even if external station switch Sx reopens.

A similar action takes place should normally closed switch Sy at station A be caused to open by virtue of an abnormal condition. One terminal of terminal pair NCa associated with switch Sy is connected to the DC- terminal, the other terminal going through contact b and pole P of relay switch S1 to the base of transistor 18, thereby putting the base at ground level and cutting off this transistor.

But if normally-closed switch Sy is caused to open, this lifts the ground voltage from the base of transistor 18, and the base is then biased by the voltage drop produced across resistor 23 connected to the positive supply DC+, to render transistor 18 conductive and to energize relay Ra.

Relay Ra is latched by relay switch S1, for when this switch is actuated to cause pole P to move from contact b to free contact a, ground voltage remains disconnected from the base of transistor 18, even if external switch Sy at station A should re-close.

Thus in the event either normally-open switch Sx at station A or normally closed switch Sy is operated as a result of an abnormal condition, relay Ra will be energized and held in this state. This same action will occur should both external switches be operated.

When relay Ra is energized, bulb La is caused to flash. The reason for this is that bulb La is connected on one side to the negative terminal DC- and on the other side to pole P of relay switch S4 which, when the relay is energized, engages contact a. Contact a of relay switch S4 is connected through a normally closed switch S5 of a flasher relay FR to power-supply terminal DC+, thereby energizing bulb La.

The bulb is caused to turn on and off periodically at a rate determined by a solid-state relaxation oscillator constituted by transistors 24 and 25, resistors 26, 27 and 28, and capacitor 29. The R-C time constant of this circuit is such as to energize the coil of flasher relay FR connected in the collector-emitter path of transistor 25 at a desired flashing rate.

One terminal of the relaxation oscillator circuit is connected to DC- and the other to the b contact of relay switch S3 of relay Ra. Hence, when the relay is energized, the relaxation oscillator proceeds to actuate flasher relay FR periodically, thereby causing flasher switch S5 to operate intermittently and making and breaking the power circuit to bulb La.

Buzzer Bz is connected to A-C terminals AC.sub.1 and AC.sub.2 through a normally-open switch S6 actuated by flasher relay FR; hence, as the lights are caused to flash, the buzzer is similarly operated intermittently to produce an audible alarm calling attention to an abnormal condition. To test the buzzer, a switch 30 is provided which, when depressed, applies A-C power thereto.

To test the indicator lights and also to reset the system, one presses push-button switch 21 which causes the pole P thereof to engage contact b, thereby connecting the positive terminal DC+ of the supply to the lightbulbs La, Lb and Lc through the a contact of switch S4 in the relay bank. When pole P of bush-button switch 21 is lifted from its a contact, this breaks the coil circuit of relays Ra, Rb and Rc, thereby resetting these relays and preparing the system for a subsequent violation.

It is important to note that the bias voltages which are applied to the transistors of the control circuits for the relays are produced by a base current flow passing through resistors 22 and 23 as well as through the wires going to the external switches Sx and Sy. Since these base currents are extremely small, in the order of microamperes, they do not represent the slightest danger to those who make accidental contact with these wires, nor are these currents capable of producing hazardous sparks.

Moreover, since the resistance of the bias circuit is determined mainly be resistors 22 and 23 which have high ohmic values, the overall resistance thereof is not materially affected by the relatively low resistance of wires W, even if these wires are of great length. For example, while a resistance in the wires in the order of 100 ohms might be fatal to the operation of a conventional system, it has virtually no effect on the present system.

While there has been shown and described a preferred embodiment of a monitoring and alarm system, it will be understood that many changes and modifications may be made thereto without, however, departing from the essential spirit of the invention.

Where the sensors at the stations are not of the type producing a change in state from a normally-open to a normally closed switching condition, but rather give rise to a change in value to a degree depending on the condition being detected, the system disclosed herein may be adjusted to accommodate sensors of this type. For example, if the sensor is a smoke or fire detector whose quiescent impedance is very high (say 250,000 ohms), which is equivalent to an open circuit, but whose impedance when smoke or fire is detected is markedly reduced (say to 120,000 ohms), this change in impedance is sufficient with a bias resistor in the control circuit of appropriate value, to render the transistor conductive to an extent effecting energization of the relay, thereby to indicate the presence of smoke or fire at the sensor station.

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