US2728904A - Supervised fire detection and alarm system - Google Patents

Description

Dec.27,1955 W.J.SCHAFER 2,728,904

SUPERVISED FIRE DETECTION AND ALARM SYSTEM Fi led June 29, 1954 2 Sheets-Sheet 1 61 X I'M:

INVENTOR.

W\\.L\AM JSQHAFER ATT OKNEYS Dec. 27. 1955 w. J. SCHAFER SUPERVISED FIRE DETECTION AND ALARM SYSTEM 2 Sheets-Sheet 2 Filed June 29, 1954 INVENTOR. W\LL\AM d. SCHAFER ATTO RNEYS and bearing the same title.

United States Patent Oflice SUPERVISED FIRE DETECTION AND ALARM SYSTEM William Joseph Schafer, Cleveland, Ohio, assignor to Arthur J. Waldorf, Beachwood Village, Ohio Application June 29, 1954, Serial No. 440,009

3 Claims. (Cl. 340-227) This invention relates in general to an electrically energized system for sensing abnormal conditions of temperature, and is a continuation-in-part of my copending application, Serial No. 402,745, filed January 7, 1954 More particularly, this invention relates to a fire alarm or signalling system having improved means for sensing and signalling the existence of operative defects and disturbances in the system so that the operative condition of the system is automatically and continuously supervised.

It is apparent that an automatic fire detection system, which is incapableof functioning properly when the need arises, is worse than having no system at all. The existence of an inoperative automatic. fire detection system on occupied premises gives the occupants a false sense of security which blunts their vigilance and alertness and thus can easily result in a condition where total reliance is placed in the system, with tragic consequences.

It is a primary object of my invention to provide an automatic fire detection system of the character described which is self-supervising, whereby it will detect and indicate any serious condition of inoperativeness of the system.

Another object of my invention is to provide a fire detection system in which said supervision is automatically and continually maintained.

Still another object of my invention is to provide a tire detection system in which the signal indications for tire conditions are distinct from the signal conditions resulting from operative defects or disturbances.

Other objects and advantages of my invention will be apparent during the course of the following description.

in the accompanying drawings forming a part of this specification and in which like numerals are employed to designate like parts throughout the same,

Fig. 1 is a schematic wiring diagram of a supervised fire detection system embodying the features of my invcntion.

Fig. 2 is a plan view of a thermal unit which may be utilized in the fire detection system.

Fig. 3 is a view similar to Fig. 2, with the cover of the thermal unit removed to show the arrangement of the circuit elements.

Fig. 4 is a diagrammatic view showing the operation of the fuse element which is employed in the thermal unit.

Referring more particularly to Fig. l of the drawings, 1 have shown a fire detection system which includes 'a source of power supply 10 which is preferably independent of the usual power supply of the structure to be protected, and can conveniently be a low voltage dry cell battery rated, for example, at nine volts.

The system may, for convenience, be considered as consisting of a power circuit, a detection and control circuit, and the subsidiary signal or alarm circuits, all of which are fully described hereinafter.

The power circuit is connected in series with the battery 10 and includes a control relay 11, a voltage relay 2,728,904 Patented 27, 1955 of current to cause energization of relay 12. It will be understood that in selecting the resistor to be used,.con-

sideration must be given to the electrical characteristics of the other power circuit elements so as to obtain the functional condition, mentioned above. Such selection is within,the knowledge of one skilled in the art. In the illustrative example of Fig. 1, the resistor 13 may have a value of 2000'ohms in relation to relay 11 of 50 ohms and relay 12 of 2500 ohms.

For clarity of description, the conductors in the power circuit will be identified as follows: 14 is the bus line from the positive side of the battery 10; 15 is the bus line from the negative side of the battery; 16 is the lead connecting relay 11 to the positive side of battery 10; 17 is the conductor connected to the negative side of relay 11; 18 is a lead connecting relay 12 to lead 17; 19 is the lead between relay l2 and resistor 13; and 20 is a lead connecting resistor 13 to negative bus line 15. v The detection and control circuit is connected across the battery 10 in series with the relay 11 and in parallel with the relay l2 and resistor 13. This circuit includes a Wheatstone bridge connected at 21 to lead 17 and connected at 22 to the negative side of the power circuit. The resistance value of the Wheatstone bridge prevents energization of the relay 11 through this circuit.

One arm 23 of the bridge includes one coil 24a of a differential relay 24, the other coil 24b of the relay being disposed in an arm 25 of the bridge. A third arm 26 includes a resistor 27, a'variable resistance or rheostat 28 and an external alarm relay 29. The fourth arm 30 of the bridge includes one or more thermal detector units 31 (as shown in Fig. 3) connected in series with each other and with signal units 32 which, in this example, are lamps 32a, 32b, 32c and 32d.

Each thermal unit 31 is physically located in a specific detection area of the structure to be protected, and as many thermal units may be used as are necessary to provide adequate overall protection. Fig. 1 illustrates four of such thermal units 31a, 31b, 31c and 31d. The arm 30 also includes a fusible link 33.

Each thermal unit includes a resistor 34 connected in series with a second larger resistor 35 which is, in turn, in series with a fusible link 36. The resistor 34 may, for example, have a value of i5 ohms and the resistor 35 may be 300 ohms. Connected in parallel across each resistor 35 is a thermo-mechanical fuse or circuit breaker 37, which will be described in more detail hereinafter. Each thermal unit is in series with one of the lamps 32, which are preferably centrally located and consolidated on a control panel which is remote from the thermal units 31.

In addition to the series arrangement of the thermal units 31, an alternate parallel circuit is provided in which the units 31 are individually connected across the bus lines 14 and 15. These parallel circuits are established by the closing of the normally-open plural contacts 11a, 11b, 11c and 11d of relay 11.

A sensitive relay 38 of the galvanometer type is connected across the Wheatstone bridge, as at 39 and 40,

' flow in one direction or the other.

7 in the Wheatstone bridge circuit.

amends switch arm 44 which will indicate the condition of balance or unbalance existing in the Wheatstone bridge circuit. .The relay 38 has double contacts 44a and 44b which are engageable by arm 44 in response to current The pointer 44 is connected to positive conductor 17 by means of a lead 45. The contact 44a is connected in parallel with relay 12 by means of lead 46. The contact 44b is connected to negative bus line 15 by means of a lead 47 to provide a shunt circuit across relay 12 and resistor 13.

A second diode 48 is connected across the sensitive relay 38 and also connects with a resistor 49 which is connected across diode 41. V

The foregoing describes the essential elements of the detection and'control circuit.

The signal or alarm circuits may be designated as an internal alarm circuit 50, an external alarm circuit 51 and a trouble alarm circuit 52.

The internal alarm circuit 50 includes a bell 53, or other suitable audible alarm, which may be located in a convenient central location in the building or structure to be protected. The bell andrelay 29 are circuit elements of the arm 26 of the Wheatstone bridge. The internal alarm circuit is closed by the relay-actuated contacts 11c and 111 which serves to energize the bell 53 and relay 29, respectively. During normal operation, there is insufiicient current flow through the arm 26 to cause actuation of the bell 53 or relay 29.

The external alarm circuit 51 includes any form of signal or indicator element, which may be physically remote from the protected structure. As exemplary of such an element, I have shown a siren 54 which is connected in series with an independent power supply 55. The circuit includes a relay-actuated switch arm 29a which is normally maintained in open position, but which closes the circuit when relay 29 is energized.

The trouble alarm circuit 52 is also preferably provided with an independent power supply 56 which may be a mercury cell or the like, and which serves to en-' ergize an audible alarm such as a buzzer 57. A singlepole single-throw normally open switch 58 is provided in the circuit. The circuit is closed by a relay-actuated switch arm 12a which is usually maintained in open position in response to energization of relay 12.

Although it is not an electrical element of the trouble alarm circuit 52, I have diagrammatically indicated at 59 a drop flag or target which may be utilized as a visual indication of deencrgization of the relay 12 in a manner well known in the art. The drop flag 59 is useful in recording the fact that a trouble condition has existed,

even though the condition may have somehow remedied itself and thus reopened the trouble alarm circuit.

The alarm operation of the above-described system is based upon the creation of a condition of unbalance Therefore, when the system is operating normally, the Wheatstone bridge is in balance, i. e., the resistance values of the arms 23 and 26 is equal to that of arms 25 and 30. The rheostat 28 which may be rated, for example, at -300 ohms, has a sufiicient range to permit the system to be adjusted to a balanced condition so that no current will flow through relay 38, and therefore pointer 44 will lie intermediate the contacts 444 and 44b.

'A main switch 60 is provided in the power circuit, and preferably it is fused as at 61. When switch 60 is closed, current will flow through the power circuit to energize relay l2 and thus keepswitch arm 12a from closing the trouble alarm circuit 52. However,

I the current value in the power circuit is insuflicient to provided by the lamps 32. In the absence of the alternate parallel thermal unit circuit previously described.

any failure of the circuit elements of the thermal arm 30 of the Wheatstone bridge or of relay 11 would cause the lamps 32 to be extinguished and thus indicate such failure. However, it is desired not only that the system indicate that a failure has occurred, but also that it indicate, whenever possible, the approximate locationof the failure as well as its nature or character, so that it can be distinguished from a fire failure. This attribute of the supervised system is best explained by describing the operation of the system under the various conditions to which it may be subjected.

First, I will discuss some of the trouble or failure conditions which might occur independently of a firc condition, and which would generally cause the system to be inoperative unless the condition is noted and remedied.

One of the conditions which might occur, is that resulting from a complete failure of the power supply circuit. This might be caused by a break in the power circuit lines, such as line 15, for example. Or it might result from a short circuiting of the battery 10. Or, if a community power supply is being used, it may be caused by some external source. Upon power supply failure, the voltage relay 12 is deenergized, and the switch arm 12a is thereby released to close the trouble alarm circuit 52, and cause the buzzer 57 to be energized. At the same time, the flag 59 will drop. As soon as notice has been taken of the buzzer 57, the circuit 52 may be opened by means of normally-closed manual switch 58, as illustrated in Fig. l, to prevent unnecessary depletion of the cell 56. It will be noted that the power failure causes no actuation of the, sensitive relay 38. Therefore, an inspection of the position of the pointer 44a will clearly show that the trouble does not lie in an arm of the Wheatstone bridge, but elsewhere in the system. If the power failure is only temporary or of short duration, the trouble'alarm'circuit 52 will be opened by the energization of relay 12 as soon as the power supply is restored, and the buzzer will be silenced. However, the position of the flag 59 will indicate that a temporary power interruption has occurred.

In the event the battery 10 weakens or deteriorates through age or use, the system will react in the same manner as it does to power failure. The relay 12 may be selected to be inoperative when the power voltage decreases below a certain percentage of its normal rating. Thus, for example, when the battery power drops from a normal nine volts to about five volts, the relay 12 will no longer be eliectively energized and the trouble circuit 52 will be established. In this manner, the eventual failure of the. battery can be anticipated, and timely replacement can be made. It is to be noted, however, that the control relay 11 may be selected to be operative at voltage levels which will exist when relay 12 and resistance 13 are shunted out of the power circuit (in a manner to be described more fully hereinafter) so that, in effect, the system will still be operative for fire detection even when the trouble circuit 52 indicates that the battery 10 needs replacement.

Another form of trouble condition could be caused by a short circuit inthe thermal arm 30 of the Wheatstone bridge, which would eliminate some of the resistance elements in this arm. Under such circumstances, the cathode of the diode 41- is negative and the diode acts like a relatively low resistance permitting current to flow through relay 38 and cause deflection of pointer 44 toward contact 44a. When-the contacts are closed, a shunt circuit is established across relay 12 which short circuits the relay and causes it to become inoperative. This, in turn, causes the trouble circuit 52to be established in the manner previously described. After the short circuit is found and remedied, the pointer 44 is reset to its neutral position and the relay 12 will then become energized to cause the trouble alarm circuit 52 to be opened. The shunting effect of diode 48 on sensitive relay 38 is negligible due to the relatively low resistance of the relay 38.

When there is a break in the alarm arm 26 of the circuit, the anode of the diode 41 becomes positive and the system reacts in the same manner as it does to a shortcircuit in the thermal arm 30.

Another trouble condition may occur when there is a break in the thermal arm 30. This causes the cathode of diode 41 to go positive thus causing it to become nonconducting. However, some current will flow through the parallel resistor 49 and this will cause a very slow movement of pointer 44 toward contact 441). At the same time, the open thermal arm will cause effective elimination of the bucking fiux of the coil 24b of the differential relay 24 which holds contact arm 24c against contact 42. The arm 240 is thereby actuated to make contact with a contact lead 42a which connects diode 41 with the negative side of the power supply through a high resistance 62 which is provided to prevent a dangerous level of current flow through the sensitive relay 38. The diode then will permit current to flow through relay 38 to cause the pointer arm 44 to swing in the opposite direction and make contact with 44a before there has been time for it to make contact with 44b. The relay 12 is thus shorted out and the circuit 52 is established to visually and audibly indicate the existence of the difficulty.

The foregoing represents the principal trouble conditions which are detected by the system, and which are indicated by a signal which is distinct from the alarm which is given when a fire condition exists, so that there should be no undue panic due to false alarms.

If an uncontrolled fire condition should develop in any area which is supervised by a thermal unit 31, the increase in ambient temperature will cause the fuse element 37 to open. As best seen in Fig. 4, the element 3'7 includes three sections 37a, 37b and 37c which are joined or bonded to each other at their terminal junctures 63, 64 by a low-melting fuse metal 370'. The sections 37a and 372; which are each connected to the resistor 35 are made of electro-conductive material which interruption oriailure of the circuit established by the pointer arm 44 and contact 44b.

The actuation of the contacts 1la--11d establishes the parallel thermal unit circuits 31a-31d, previously described. If, for example, the fuse element 37 of thermal unit 310 has opencd,'the lamp 320 will be substantially extinguished. However, the remaining lamps 32a, 32b and 32d will be in parallel and will be lit. Thus, the affected area can be determined quickly.

The closing of contacts lie and 11 causes internal alarm circuit to be energized and causes bell 53 to sound. The energization of relay 29 closes the external alarm circuit 51 and causes the siren 54 to be actuated.

The short-circuiting of the relay 12 also causes the trouble circuit 52 to be established. Thus a fire condition will cause two separate independently powered alarm circuits to be activated, in addition to the trouble circuit 52. This condition (fire) is thus clearly and readily distinguished from the various trouble conditions.

The actuation of control relay 11 causes a momentary polarized voltage surge which tends to swing pointer 44 away from contact 44b. By placing the diode 48 in parallel with the relay 38, the diode absorbs the bulk of the surge and prevents the breaking of the connection with contact 441).

A manually operable sequential push-button switch 65 is provided for testing the external alarm circuit 51 and relay 29, as well as serving as a manual burglar alarm system or the like. One set of contacts 650', short-circuits the relay contact 11f and serves to close the circuit to relay 29. A second set of switch contacts 65b short is pre-stressed during the assembly so as to cause the sections 37a and 37b to diverge at points 63 and 64 when the fuse metal becomes plastic or melts. The intermedi ate section 370 is also 'electro-conductive and is prestressed during assembly so that its arms will converge toward each other when the fuse metal 37d becomes plastic. This arrangement provides a snap action fuse element which is not subject to the vagaries which are encountered in using a simple fusible link, such as 36, and which therefore responds more efiiciently and more precisely to the temperature condition to which it has been calibrated. However, fusible link 36 is retained in the circuit as an additional safeguard.

The fuse element 37 which normally short-circuits a resistor 35, causes the resistor 35 to be placed in series in the thermal circuit whenever a fuse element 37 opens, and thus adds about 300 ohms of resistance to the thermal arm 30. This increase in resistance causes the cathode of diode 41 to become positive and the diode becomes non-conductive. The current then flows through resistance 49 and relay 38, in the manner heretofore described, to cause pointer arm 44 to swing slowly toward contact 44b. In this instance, however, the increased resistance of the thermal arm 30 is not of great enough magnitude (as distinguished from the open condition) to 'cause actuation of contact arm 24c of differential relay 24. I

When contact 441; is made, a short-circuit is established across relay 1?; and resistor 13. The elimination of the resistance of the elements 12 and 13 from the power circuit causes actuation of control relay 11 to close the multiple contacts Ila-41f, previously described, as well as a contact 11g which serves to assure continued energization of relay 11 even if there should be a subsequent circuits the relay 38 and diodes in the Wheatstone bridge to prevent any actuation of the relay 38. The switch 65 is designed to close the contacts 65b before closing the contacts 65a.

From the foregoing it will be apparent that I have provided a supervised fire detection system which normally is in a condition of electrical balance. When the balance is destroyed by a moderate decrease in resistance in the thermal arm of the system or by an infinite increase (break) in the resistance of the thermal arm or alarm arm, a trouble alarm circuit will be actuated. However, a moderate increase in the resistance of the thermal arm will establish independent and distinctive local and re mote alarm bircuits in addition to the trouble alarm circuits, so that a fire condition is clearly emphasized and distinguished from a trouble condition.

Additionally, means have been provided for safeguarding continued operation of the control relay after a fire condition has been detected, and means have also been provided for testing or operating an external signal or alarm independently of the other circuit-s and without disturbing them.

In Figs. 2 and 3 I have shown a form of thermal detector unit 31 which may be utilized in the system herein described. The thermal unit 31 includes a base 66 which is adapted to be secured to a surface, such as a wall or ceiling, by means of fasteners 67. The base 66 is preferably molded of a rigid synthetic resin and has integrally formed thereon a centrally projecting stud 68. An aperture 69 is provided in the base for passage of the conductor wires or cable.

A circular cover 70, also preferably formed of molded synthetic resin, is threadedly secured to the stud 68. The cover is provided with an annular flange 71 having a larger diameter than the base 66, so that an unobstructed annular space 72 is provided for circulation of air.

Secured to terminal posts 73 on the base, are the resistor 34 in series with link 36 and with fuse element 37 which is connected in parallel with resistor 35. Conductor wires 74 serve to connect the thermal unit 31 with the other circuit elements of the system.

The cover prevents foreign articles or particles from accidentally injuring the elements of the thermal unit circulation of air It will be understood that all the components of the system, except the thermal units 31 and the external alarm 54, may be physically grouped in a central control box or the like. The lamps 32 may be associated with suitable indicia of area location.

It is to be understood that the form of my invention, herewith shown and described, is to be taken as a preferred example of the same, and that various changes in the shape, size and arrangement of parts may be resorted to, without departing from the spirit of my invention, or the scope of the subjoined claims.

Having thus described my invention, I claim:

1. In a fire detection system of the character described, the combination of an electrical power supply, a balanced resistance circuit connected to said power supply, an alarm element in one arm of said circuit, a first switch means for connecting said alarm element directly to said power supply, a thermo-responsive detection unit in an opposed arm of said circuit, a sensitive relay in said circuit energizable in response to a condition of unbalance resulting from a change in the resistance value of either of said arms of said circuit, a control relay in series with said balance resistance circuit and actuated in response to a current value greater than that of said circuit, and a second switch means responsive to actuation of said sensitive relay for connecting said control relay directly to said power supply for actuating said control relay, said first switch means being responsive to actuation of said control relay to actuate said alarm element.

2. In a fire detection system of the character described, the combination of an electrical power supply, a balanced resistance circuit connected to said power supply, an alarm element in one arm of said circuit, an external alarm relay in said arm of said circuit, a thermo-responsive detection unit inan opposed arm of said circuit, a control relay in series with said balanced circuit, said balanced circuit depressing the current flow through said control relay and said alarm element and said external alarm relay to an inoperative value, a normally-open external alarm circuit, switch means responsive to actuation of said external alarm relay for closing said external alarm circuit, means responsive'to a condition of unbalance in said circuit for actuating said control relay, and switch means responsive to actuation of said control relay for actuating said alarm element and said external alarm relay.

3. In a fire detection system of the character described,

the combination of an electrical power supply, a nor-" mally balanced Wheatstone bridge connected in series with said power supply, a thermo-responsive detection unit in one arm of said bridge, a directional relay connected across said bridge and energizable in response to a condition of unbalance in said bridge, a trouble alarm circuit, first switch means responsive to one direction of current flow through said relay for actuating said trouble alarm circuit, a normally-open fire alarm circuit, second switch means responsive to an opposite direction of current flow through said relay for establishing said fire alarm circuit, means for causing current fiow in said one direction in response to a decrease in the electrical resistance of said thermo-responsive detection unit, means for causing current flow in said opposite direction in response to an increase in the electrical resistance of said thermo-responsive detection unit, means for reversing said current flow in said opposite direction in response to an infinite increase in the electrical resistance of said thermoresponsive detection unit, and means provided in said thermo-responsive detection for adding electrical resistance to said unit in response to a predetermined value of temperature.

References Cited in the file of this patent UNITED STATES PATENTS 311,681 Sawyer Feb. 3, 1885 1,008,482 Lovejoy Nov. 14, 1911 2,074,262 Grant Mar. 16, 1937 2,094,211 Grant Sept. 28, 1937

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