US2847662A - Signalling system for automatic fire alarm installation - Google Patents

Description

12, 1958 E. G. LINDGREN 2,8

SIGNALLING SYSTEM FOR AUTOMATIC FIRE ALARM INSTALLATION Filed March 25, 1955 f/VVEA/FOR ER/K Cusrwr A /NDGREA/ HM WNW firromvs rs United States Patent SIGNALLING SYSTEM FOR AUTOMATIC FIRE ALARM INSTALLATION Erik Gustaf Lindgren, Stockholm, Sweden, assiguor to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a corporation of Sweden Application March 25, 1955, Serial No. 496,880

Claims priority, application Sweden April 1, 1954 7 Claims. (Cl. 340-227) The present invention relates to a signalling system for an automatic fire alarm installation. There are known signalling systems for fire alarm installations in which one or more two-wire circuit systems are continuously kept under current and normally open temperature responsive alarm switches bridge the two wires of the circuit systems. These alarm switches close their contacts in response to an excessive temperature caused by fire, thereby short-circuiting the two wires whereby an energizing circuit is closed for an alarm device.

One of the objects of the present invention is to provide a signalling system for fire alarm installations of the general kind above referred to, which discriminates between changes in the circuit system caused by a line fault and changes caused by closing of an alarm switch due to fire and which indicate the cause of the change in the circuit by different signals. Such arrangement affords the advantage of eliminating the annoyance of a false fire alarm.

Another object of the invention is a signalling system the signals of which indicate the approximate location of the fire thereby expediting the required steps for extinguishing the fire.

Still another object of the invention is to provide a signalling system in which the total area to be supervised is divided in sectional areas each of which is individually supervised by the associated detecting and indicating means whereby the approximate location of a fire or another cause causing an excessive temperature can be more readily located.

Other and further objects, features and advantages of the invention will be pointed out hereinafter and set forth in the appended claims forming part of the application.

In the accompanying drawing, several preferred embodiments of the invention are shown by way of illustration and not by way of limitation.

In the drawing:

Fig. 1 is a diagrammatic circuit system of the entire installation according to the invention,

Fig. 2 shows a network modifying the detecting means of the installation, and

Fig. 3 shows another modification of the detecting network.

Referring now to the figures more in detail, the signalling system and installation according to the invention comprises a two-wire circuit system, the two wires or branches of which are designated by a and b, and a central control installation including four relays 1, 11, 12, 13 and four signalling lamps 14, 15, 16 and 17. Relay 1 is a common control relay controlling contact arms 20, 8, 9, and 21. Relay 1 is shown energized and it is assumed that in accordance with the conventions used for the diagrammatic showing of relays and the contact arms thereof, the contact arms move into the direction away from the relay coil when the relay deenergizes, that is, contact arm 20 will move to the left and the other contact arms to the right. As is evident, the contact 2,847,662 Patented Aug. 12, 1958 "ice arms of relay 1 and the contacts 2, 3, 4 and 5 controlled thereby divide the total area supervised by wires a and 11 into three sections, but of course a greater number of sections may be provided such as five to ten sections. Relays 11, 12 and 13 constitute supervisory or indicating relays, each being assigned to one section. Each section further encloses an alarm or detecting switch 7. These switches are connected across wires a and b and are parallel with each other. The switch contacts of switch 7 are normally open, but close in response to an excessive temperature caused, for instance, by a fire, thereby directly short-circuiting wires a and 12. Temperature responsive switches of this kind are well known in the art and any suitable conventional type may be used.

The indicating means of the installation comprise a lamp 14 controlled by a relay 1 and lamps 15, 16 and 17 controlled by relays 11, 12 and 13 respectively.

To simplify the illustration, only one circuit system is shown but obviously several may be provided. In such arrangement each installation has its own control relay 1 but the indicating relays 11, 12 and 13 may be common to several circuit systems a and b, in which event they are connected to the several systems as shown for one system.

The operation of the arrangement is as follows:

A direct current circuit is normally closed from the positive pole of a source of current through branch a, the coil of relay 1, branch b including relay contacts 2, 3, 4 and 5 connected in series and a resistance 6 to the negative pole. If there is a break in line branches a and b or a short-circuit between them, the flow of current through the coil of relay 1 is interrupted or at least decreased. As a result the relay releases and its contacts 2, 3, 4 and 5 are opened due to the movement of contact arms 8, 9, 10 and 21 to the right. Branch b is now divided into three sections each of which is connected through contact arms 8, 9 and 10 to supervisory relays 11, 12 and 13. As is evident, the release of control relay 1 due to a break in the circuit will not close an energizing circuit for any of the supervisory relays as the circuit of each of the relay coils includes one of the alarm switches 7 which are still open. However, signalling lamp 14 is closed due to a movement of contact arm 20 to the left as previously described. Ignition of lamp 14 indicates that there is a fault in the circuit.

Let it now be assumed that there is a fire within the area supervised by the installation. Then one or several of the temperature responsive alarm switches '7 will close thus short-circuiting lines a and b and closing an energizing circuit for the respective supervisory relay 11, 12 or 13. If for instance relay 12 is energized in a circuit from the positive pole through the a branch, the respective alarm switch 7, relay contact arm 9 and the coil of relay 12 to the negative pole, the relay will attract its contact arm 22 thereby closing a circuit for signal lamp 16.

As is apparent, in the circuit system according to Fig. 1 any direct short-circuit between the line branches at and [2 due to causes other than fire, but electrically equivalent to a closing of a switch 7, will set off a false fire alarm signal. Experience shows that faults of this nature are extremely rare and in any event occur much less than faults caused by a break in the circuit and resulting merely in a lighting of signal lamp 14.

In a further development of the invention, Figs. 2 and 3 show networks which eliminate the aforementioned rare but possible source of false alarm.

According to Fig. 2 a current direction dependent impedance means 18 shown as a rectifier is connected in series with each of the alarm switches 7. If new the supervisory relays 11, 12, and 13 are connected to a source of current producing a polarity shifting direct current or an alternating current, release of control relay 1 due to deenergization by the closing of an alarm switch 7 willpermit fiow of'current in one direction only through the closed alarm switch and the respective supervisory relay. However, when current is supplied due to a direct short-circuit between theline branches a flow of current in-both directions will reach the respective supervisory relays. The supervisoryrelays used in this arrangement are of the well-known kind which does not respond to current flowing in both directions, but to unidirectional current only. Consequently a direct short-circuit caused by a'fault rather than by a fire effecting closing of an alarm switch will be correctly indicated as a line fault by the closing of circuit of lamp 14 by relay 1.

According to Fig. 3 a voltage dependent resistance19 is connected in series with each of the alarm switches 7. Such resistance, for instance a siliceous carbide resistance, decreases its resistance value as the voltage across the resistance increases. A source of current supplies the supervisory circuit including relays 11, '12 and 13 with current of varying voltages, namely a normal voltage and a voltage higher than normal. If the current strengths, which in the event of a short-circuit reach a supervisory relay, are proportional to the voltages that occur through a short-circuit due to a line fault; the respective supervisory relay cannot respond due to its arrangement. However, when the relation between the current strengths is greater than the relation between the voltages which occur when alarm switch 7 is closed, the respective supervisory relay responds and closes the circuit of its signal lamp 15, 16 or 17.

As is evident the arrangements of Figs. 2 and 3 both prevent a false fire alarm signal due to a line fault.

What is claimed is:

l. A signalling system for an automatic fire alarm installation, said system comprising, in combination, a closed two-wire energizing circuit means, a plurality of cross connections across the two wires each including a detecting temperature sensitive switch contact biased into the open position but closing in response to an ambient temperature above a predetermined value, a common control relay means having and controlling a plurality of pairs of relay contacts, the coil of said relay means and one contact of each pair being included in series in said two-wire circuit means, the said series contacts being closed in the energized state of said relay 0nd contact of a respective pair, and a plurality of indicating means each controlled by a respective one of said supervisory relay means whereby, upon deenergization of said control relay means only due to a fault in said twowire circuit means, said circuit means is separated in a plurality of networks by opening of said series contacts, each network including a respective supervisory relay means and at least one open detecting contact and whereby, upon. closing of one of said detecting contacts and deenergization of said control relay means due to an excessive ambient temperature, said two-wire circuit means are separated in said several networks and the respective supervisory relay means is energized for actuating its signal means over said other contact of the respective pair of relay contacts.

2. A system according to claim 1, wherein said common control relay means controls an indicating means, said indicating means being actuated upon deenergization of said control relay means.

3. A system according to claim 1, wherein a unidirectional impedance means is included in each of said connections across the wires of said circuit means, each of said supervisory relay means being arranged to be actuated in response to a flow of current ina predetermined direction only due to the closing of the respective detecting contact.

4. A system according to claim 3, wherein said impedance means comprises a rectifying means.

5. A system according to claim 1, wherein said twowire circuit means are energized with different voltages, and wherein each of said cross connections includes a voltage responsive impedance means, said supervisory relay means being arranged to be actuated only in response to a current strength caused by a voltage due to a closing of a detecting contact.

6. A system according to claim 5, wherein said impedance means comprises a resistance means having a characteristic decreasing the resistance value thereof in response to an increasing voltage.

7. A system according to claim 6, wherein said resistance means comprises a siliceous carbide resistor.

References Cited in the file of this patent UNITED STATES PATENTS 1,537,211 Wooton May 12, 1925 2,605,342 Spurling July 29, 1952 2,695,994 Lode Nov. 20, 1954

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