US3701985A

US3701985A - Fire detection system and unit

Info

Publication number: US3701985A
Application number: US131122A
Authority: US
Inventors: John S Davies
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-04-05
Filing date: 1971-04-05
Publication date: 1972-10-31
Anticipated expiration: 1989-10-31

Abstract

A fire detection system includes an elongated heat sensing element which may be extended throughout the area to be protected, and it also includes a multiplicity of spot detector units which are spaced along the heat sensing element at critical points in the area to be protected. The spot detector units respond instantaneously to abnormal temperature conditions to complete an electric circuit through the aforesaid heat sensing element for alarm and control purposes.

Description

United States Patent Davies [54] FIRE DETECTION SYSTEM AND UNIT [72] Inventor:

Drive, Monrovia, Calif. 91016 [63] Continuation-impart of Ser. No. 735,006, June 6, 1968, abandoned.

[22] Filedi John S. Davies, 1010 Norumbega [52] Us. Cl. ..340/22s, 338/26, 340/227c [57] [51] Int. Cl. ..G08b 17/06 58] Field ofSearch.....340/227, 228, 227.1; 338/26; A fire detectwn System Includes elm/gated heat 323/68; 324/105 sensing element which may be extended throughout the area to be protected, and it also includes a mul- [56] References Cited tiplicity of spot detector units which are spaced along the heat sensing element at critical points in the area UNITED STATES PATENTS to be protected. The spot detector units respond instantaneously to abnormal temperature conditions to 3257530 6,1966 Dawes "340/228 X complete an electric circuit through the aforesaid heat 232;; sensing element for alarm and control purposes. 2:75l,550 V 6/1956 Chase ..323/68 X 4 Claims, 7 Drawing Figures am/ var! 32K 10 33 Ma/n/af/ JZ Z4 fpflbi/er 1 (A /4wr Ca afra 4. 26' EM- ak Ala/IA! l fl'redel/ a #64. 33 k (1:44) /j6 og (am/rid! j! 40 f r/m/er 1 4' "cf :2 a T e M 4M1- d l. f; 7 m.

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[45 Oct. 31, 1972 Tolliver ..324/ l 05 Primary Examiner-John W. Caldwell Assistant Examiner-Scott F. Partridge Attorney-Jessup & Beecher ABSTRACT v PATENTEDHBTSI m2 3,701,985

sum 3 M3 FIRE DETECTION SYSTEM AND UNIT RELATED PATENTS AND APPLICATIONS This is acontinuation-in-part of copending application Ser. No. 735,006 filed June 6,1968 and now abandoned. l

US. Pat. No. 3,257,530, which issued .Ian. 21, 1966, in the name of the present inventor is concerned with an electrical control system, which is capable of responding to fire conditions for automatically actuating .watersprinklers or other fire extinguishing means, and/or for initiating an appropriate alarm.

, BACKGROUND OF THE INVENTION The system described in the aforesaid patent includes an elongated heat'sensing element which is intended to be strung around the area to be protected, when the area, for example, is a home or establishment in a wooded or brush area; or to be strung throughout the area to be protected, when the system is-to be used internally, for example, in a warehouse, stable, barn, factory, or the like. i

' The aforesaid heat sensing element used in the system of the patent comprises a pair of electric wires which are held under tension in atwisted condition. The wires are normally held apart by suitable insulation. However, the insulation is sufficiently softened when a particular temperature threshold is exceeded, so that the wires may twist together into electrical contact and complete an electric circuit to appropriate water sprinkler and/or alarm control apparatus.

. The system and apparatus of the present invention is intended to be used in conjunction with the aforesaid system, and it comprises a multiplicity of spot detector units which are adapted to be connected at critical points to the wires of the elongated heat sensing element. These spot detector units respond instantaneously to abnormal rises in temperature, so as to create the desired alarm and/or control] effect at critical points, even before the insulation between the two wires is sufficiently softened to permit the wires themselves to come together and initiate the control. The overall system, modified in accordance with the present invention, finds particular utility, for example, in highly inflammable environments, such as warehouses, barns, race horse stables, fuel plants, ex plosive storage areas, and the like, where an instantaneous response to tire is essential.

The system described in the aforesaid patent, and the system modified in accordance with the present invention, are particularly advantageous in that the single or combined systems are simple and economical to manufacture and install. Moreover, the system has the ability to protectextremely large areas, such as race tracks,

sensing element may have any desired length, and, as noted, it is strung throughout or around the area to be protected. As pointed out, whenever a fire occurs, the resulting temperature rise softens the insulation which normally holds the two wires on the heat sensing element apart, so that the wires may quickly twist together into electrical contact. The resulting electrical connection serves to actuate the fire extinguishing equipment or to sound the alarm, as described in detail in the aforesaid patent.

The f re detector unit of the present invention is intended to be used in conjunction with the aforesaid system and, as explained, a plurality of such units may be connected into the system at critical points, each providing a rapid response spot-type fire detector. As will be described, any desired number of the detector units may be used in a single circuit, and each may be set to respond to the same or different temperature thresholds. That is, the detector units in the circuit can be used alone to detect a given temperature threshold; or in a group, each being set to detect the same or different temperature thresholds. Moreover, the fire detector units of the invention may be used, if desired, in connection with an ambient temperature compensator, so that the detecting threshold of the fire detector units may be made dependent upon ambient temperature levels.

Thefire detector units of the invention, therefore, find utility in connection with the system described in the aforesaid patent, to provide a rapid response detector means in spots where the outbreak of fire may be BRIEF DESCRIPTION OF THE DRAWINGS FIG. is aschematic diagram, partly in block form, showing the system described in the aforesaid patent, modified to incorporate the teachings of the present invention;

homes in wooded or brush areas, fair grounds, industrial plants, .dock yards, military plants, and so on. The

FIGS. 2A and 2B are circuit diagrams of the respective circuitry involved in two embodiments of the fire detection unit used in the system of the invention;

FIG. 3 isa circuitdiagram of an ambient temperature compensating circuit used to render the aforesaid spot detector units essentially independent of prevailing ambient temperature conditions;

FIG. 4 is a side elevation of a spot detector unit constructed in accordance with one embodiment of the invention;

FIG. 5 is a side section of an ambient temperature compensator suitable for use in the system; and

FIG. 6 is a side elevation, partly in section, of a combined spot detector and ambient temperature compensator unit.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT The block diagram of FIG. 1 shows a fire control system incorporating a variety of different types of protective circuits. The system includes a series of terminal boards 10, l2, 14, 16 and 18. A first fire prevention circuit is connected to the terminal board 10. This first circuit includes an elongated heat sensing element 20 which extends throughout or around, for example, a first area to be protected. The elongated heat sensing element 20 is constructed, as explained in the aforesaid patent, to include a pair of wires which are supported under tension in a twisted condition, so that they may be brought together into electrical contact when an abnormal temperature condition causes the insulation of the heat sensing element to soften.

The two wires of the elongated heat sensing element 20 are connected to the terminals 3 and 4 of the ter minal board 10. One of these terminals is connected, for example, to the positive terminal of a 6-volt source, and the other is connected to a fire area control module (A) 22. This module responds to the completion of the circuitbetween the wires of the heat sensing element 20 to apply a control signal to a control valve 24. The control valve is then caused to turn on a sprinkler system so as to innundate the area protected by the heat sensing element 20 with water or other fire extinguishing fluid. The fire area control module 22 may also activate a common fire bell 26 to indicate a fire in the overall area.

As explained above, the elongated heat sensing element20 extends throughout the area to be protected, and it completes its circuit normally when an abnormal temperature condition softens the insulation between the two wires of the element. The wires are terminated at the remote end of the element by, for example, an 8.2 kilo-ohm resistor 28.

A plurality of manually operated fire control stations designated F.C., and indicated as 30 may be located at different points along the heat sensing element. These stations include appropriate switching means .so that the connection between the two wires of the heat sensing element 20 may be completed manually, upon the visual observation of fire, so as to initiate the alarm and sprinkler control. Likewise, spot detector units (S.D.U.) 32b are included in the system at critical points along the heat sensor element, in accordance with the concept of the present invention. These units 32b are connected to the wires of the heat sensing element 20. A pair of monitoring leads 34 for the spot detector units 32b extend along the heat sensing element 20, and these leads are terminated, for example, by a 1.6 kilo-ohm terminating resistor 33. One of the leads 34 may be connected, forexample, to a monitoring source, and the other may be connected to a common or ground lead. The spot detectors 32b are a combined ambient compensating and heat detecting unit, as will be described in conjunction with FIG. 6.

The spot detector units 32b, as will be described, respond to temperatures above a particular threshold to complete the circuit between the wires of the heat sensing element 20, so as to initiate the sprinkler control and alarm effects. The response of the spot detector units is almost instaneous, so that they constitute a sensitive and rapid means for detecting fires at sensitive points in the area to be monitored.

The circuit connected to the terminal board 12 is essentially the same as the circuit described above and includes a similar heat sensing element designated 20a. Theenergizing leads for the spot detector units in the second circuit are designated 34a. The second circuit differs from the circuit described above in the inclusion of a single ambient temperature compensating circuit unit 36 in the circuit of the leads 34a; and by the inclusion of heat detecting unit 32a such as will be described in conjunction with FIG. 4. The ambient temperature compensating circuit 36, as will be described in conjunction with FIG. 5, responds to different ambient temperature levels to control the threshold voltages supplied to the associated spot detector units 32a. This is so that the thresholds of the spot detector units 32a will respond to temperatures of a particular value above the ambient level, so as to avoid false indications of abnormal temperature conditions. The circuit associated with the terminal board 12 operates generally in the same manner as the circuit described above, with the alarm signal being applied to a fire area control module 38. The latter module responds to the alarm signal to activate a sprinkler control valve 40, and also to energize the common fire bell 26.

The third circuit includes a similar fire sensing element 20b which is connected to the terminal'board 14. This circuit is shown to contain, where desired, simplified spot detector units 32, shown in FIG. 2A, and in the aforesaid patent, and which are set to operate at any desired fixed temperature that will respond earlier than the liniar detector 20b. The-alarm signal from the sensing element 20b is applied to a fire area control module 42, and the module responds to the alarm signal to activate a sprinkler control valve44, and also to energize the common fire bell 26.

The overall system of FIG. 1 also-includes a fourth circuit which, in turn, includes a heat sensing element 200. The heat sensing element 20c is similar to those described above, except that it includes a third wire 46 which may be used, for example, for police signaling purposes. The wire 46 is connected at its remote end through a 1.6 kilo-ohm terminating resistor 48 to the +6 volt wire of the heat sensing element 20c.

In addition to the components and elements described above, a series of police call boxes 50 designated P.C. may be connected to the wire 46 and to the +6 volt wire of the heat sensing element 200. These boxes may be actuated manually by closing a switch in the particular box, and thereby completing a circuit through the terminal board 18 to the police area control module 52. The latter module responds to the alarm control signal from the terminal board 18 to sound a police alarm 54. This police alarm signifies assistance is needed in the area monitored by the heat sensing element 20c. Similar alarms, of course, can be established in the other heat sensing elements, so that a selective police alarm system can be provided.

The fire sensing element 200 itself is connected through the terminal board 16 to a fire area control module 56. The latter module responds to the alarm signal from the terminal board 16to activate the sprinkler control valve 58,- and also to energize the fire bell shown in FIGS. 2A and 28, comprise solid state transistor circuits which respond to the abnormal temperature condition to complete the circuit across the wires of the heat sensing element 20.

It will be appreciated that the transistor circuit of FIG. 2A is merely a simplified version of the transistor circuit of FIG. 2B. The transistor circuit shown in FIG. 28 includes, for example, an NPN transistor Q1 which may be of the type presently designated 2N3648, and a PNP transistor Q2 which may be of the type presently designated 2N3638. The +2.4 volt energizing lead from the terminal board is connected to the emitter of the transistor Q1, and the common lead is connected through a balancing resistor 100 to the base of the transistor Q1. The balancing resistor 100 permits a plurality of the spot detectors to be connected to the same leads 34, a without affecting the operation of one another. The balancing resistor 100 is installed to give the correct operating temperature of thermistor 102.

The base of the transistor O1 is connected through a temperature. sensitive impedance 102 which may be a usual and well known type of thermistor, the impedance being connected to the emitter of the transistor Q2, and through a 5.6 kilo-ohm resistor 104 to the base of the transistor Q2. The collector of the transistor Q1 is connected through a kilo-ohm resistor 106 to the base'of the transistor Q2. The collector of the transistorQZ is connected to one of the wires of the heat sensing element 20, and the emitter of the transistor O2 is connected to the other wire.

Under normal operating conditions, the transistor 02 is non-conductive, due to the bias on its base electrode exertedby the combined effect of the impedance 102 and resistor 104. Therefore, under these conditions, there is no current flow between the emitter and collector of the transistor. However, when the temperature exceeds a particular threshold, the resistance means 102 drops to a value such that current begins to flow in the-transistor Q2. This causes the transistor O1 to become conductive which serves further to increase the current through the transistor Q2, so that the latter transistor rapidly reaches its fully conductive condition. The conductivity of the transistor Q2 effectively provides a connection across the wires of the heat sensing element 20, so that the desired alarm signal is supplied to the central station.

As mentioned above, in the circuit of the heat sensing element a, an ambient temperature compensating unit 36 is included. This compensating unit serves to compensate the 2.4 volt supply voltage supplied to the spot detector 32a, so that the voltage varies in accordance with variations in the ambient temperature conditions. As shown'in FIG. 3, the circuit of the ambient temperature compensator 36 supplies a compensated voltage to the leads 34b, and this voltage rises and falls with changes in ambient temperature conditions, so that the trigger point of the circuit of FIG. 2B is correspondingly adjusted. I

The ambient temperature compensator 36 circuit includes a pair of

resistors

200 and 202 which are connected between the +6 volt lead and the common lead which connect to the terminal board 12 of FIG. 1. The resistor 200 may, for example, have a resistance of 27 kilo-ohms, and the resistor 202 may have a resistance of lS kiIo-ohms. A diode 204 connects the common junction of the resistors 200 and202 to the common junction of a resistor 206 and of a heat sensitive impedance means 208, the latter also being, for example, of the thermistor type. v

The impedance means 208 is connected to the common lead, whereas the resistor 206 is connected through a kilo-ohm resistor 210 to the +6 volt lead. The aforesaid junction is also connected to the base of an NPN transistor Q3 which may, for example, be of the type designated 2N3643. The collector of the transistor Q3 is connected to the base of a similar NPN transistor Q4, and to a 30 kilo-ohm resistor 212. The emitter of the transistor 03 is connected to a 20 kiloohm resistor 214. The resistor 212 is connected to the 6 volt lead, whereas the resistor 214 is connected to the common lead. I

The collector of the transistor Q4 is connected directly to the 6 volt lead, whereas its emitter is connected through a pair of 3.9 kilo-

ohm resistors

216 and 218 to the common lead. The junction of the latter resistors is connected to the base of a similar transistor Q5 and to a 10 kilo-ohm resistor 220. The resistor 220 is connected to the +6 volt lead, and the collector of the transistor Q5 is connected to that lead through a l kilo-ohm resistor 222.

The emitter of the transistor Q5 is connected to the threshold voltage lead 34b, and the collector is connected to the base of a PNP transistor Q6. The latter transistor may be of the type designated 2N3638. The emitter of the transistor 06 is connected to the +6 volt lead, and the collector is connected through a 220 kiloohm resistor 224 to one of the leads 34a, the other lead 34a being connected to the common lead which is connected to the terminal board 12 (FIG. 1). j The circuitry described in conjunction with FIG. 3 is connected, and the circuit parameters arechosen, so that under a predetermined ambient temperature condition, the voltage across the leads 34a is 2.4 volts, for example. However, whenever the ambient temperature changes, the resulting changein resistance of the impedant temperature sensitive impedance means 208 changes the voltage amplification characteristics of the circuit, so that the output voltage across the leads 34b changes accordingly.

The spot detector unit 32a may take the form shown in FIG. 4. As illustrated, the particular embodiment includes a tubular base 300, having a plug 302 attached thereto in coaxial relationship therewith. The plug 302 may be threaded, so that the detector may conveniently be screwed into a socket, permitting the necessary electrical connections to be made. In this manner, the units may be easily unscrewed for replacement or servicing purposes. A disc-like circuit board 304 is supported in the tubular base 300, and extends across the base as shown. The circuitry described in conjunction with FIG. 2B, including the transistors Q1 and Q2 are supported on the circuit board 304.

A tubular wire mesh cage 306 is mounted in the tubular base 300, and extends out from the base in coaxial relationship therewith. The cage 306 for example, may be formed of Va inch by Vs inch wire mesh. An elongated support 308 is supported on the circuitboard 304 and extends along the cage 306 towards its remote end. The thermistor 102 is supported on the end of the support 308 adjacent the remote end of the cage 306.

The thermistor 102 is connected to the circuit on the board 304 through appropriate electrical connections, including the

leads

104, 106 from the thermistor, the leads being soldered to corresponding leads on the support member 308.

The ambient temperature compensator unit 36 may likewise be formed, as shown in FIG. 5, with a threaded base, so that it too may be screwed into an appropriate plug for easy replacement purposes. The compensator circuit of FIG. 3, including the transistors Q3, Q4, Q and Q6, are supported on a disc-like circuit board 400 ,which, in turn, is supported in the base 402 of the compensator unit, and extends across the base, as shown in FIG. 5.

If desired, and as shown in FIG. 6, each of the spot detector units 32a may have a temperature compensator unit 36 incorporated into its base so as to constitute the spot detectors 32b. Such a construction, for example, is shown in FIG. 6. In FIG. 6, the circuit board designated 400 extends across the base of the combined units and supports the various circuit components of the compensator 36 as designated in FIG. 5. A central aperture is provided in the board 400, and the circuit board 304 is fitted across the aperture in the board 400, and the board 304 supports the various components of the spot detector 32a of FIG. 4. The necessary electrical connections are made between the circuits, and the result is a spot detector unit 32b with its own built-in ambient temperature compensator.

The system of the invention is most advantageous because of its very small thermal log, this being due to the low thermal mass or heat capacity of the detector. The system also features an adjustable or programmable remotely-controlled detector which can optimize the trip joint as a function of ambient temperature or other variable, so that trip time may be further reduced.

All circuits used in the system of the invention, including the detectors, may be highly reliable solid state, transistorized circuits so that there are no problems of contact erosion arising. Moreover, both detection and contact circuits in the system are monitored.

In the system of the invention, the spot detectors 32a are independent units which can be located at any point along the linear detecting circuit; and in which a low-voltage power source supplied to the unit detector 32a (FIG. 4) is controlled and varied by a compensating circuit 36 (FIG. 3) which itself is controlled by the ambient temperature.

The compensator unit 36 (FIG. 5) can be combined with the spot detector unit 32a (FIG. 4) to form a single operating unit 32b (FIG.6), as described.

In either case, the purpose of the compensating unit 36 is to detect ambient temperature, and to supply a varying degree of low voltage (designated herein as pressed voltage) to the detector unit 32a. The compensating circuit 36 prevents the detector unit 32a from transmitting a current of sufficient strength to the master control until the temperature at the detector unit 32a rises a predetermined amount above the control level established by the compensator circuit 36.

An important and prime feature of the system of the invention is that the heat detecting unit 320 can be made to operate at any number of degrees above ambient, by the readjustment of the value of resistor 100 in FIG. 28. Likewise the compensating circuit 36 can be adjusted to operate the detector unit 32a at any number of degrees above ambient by adjustment of its

resistors

200 or 202.

Thus the spot detector unit 32a can be made to operate at any desired incrementabove ambient temperature, regardless of the actual ambient temperature level.

The invention provides, therefore, an improved electrical heat detecting system which has all the attributes, characteristics and advantages of the system described in the aforesaid copending application and patent. In addition, the improved system of the present invention includes spot detector units which may be located at sensitive points in the system, and which respond instantaneously to abnormal temperatures, so as to set up the appropriate control effects. As described, these units may be controlled by an ambient temperature control unit, so as to be independent of ambient temperature changes.

While particular embodiments of the invention have been described, modifications may be made. It is intended in the claims to cover the modifications which come within the scope of the invention.

What is claimed is:

1. An electrical fire control system including: an elongated heat-sensing element comprising a pair of tensioned twisted electric wires and temperature-sensitive insulating material'normally holding said wires insulated from one another, said insulating material softening in the presence of a temperature rise above a particular temperature level to permit the wires to twist together into electrical contact, and at least one solidstate temperature responsive spot detector unit mounted at a selected location alongsaid heat-sensing element and electrically connected to said wires to establish an electrical connection therebetween prior to the aforesaid softening of said insulating material for temperatures above a particular threshold, electrical energizing leads extending to said spot detector unit and electrically connected thereto; and an ambient temperature compensating unit interposed in the circuit of said energizing leads to control the voltage supplied thereby to said spot detector unit in accordance with ambient temperature conditions, and thereby to render said particular threshold of said spot detector unit dependent upon ambient temperature conditions; said spot detector unit comprising a transistor circuit including a normally non-conductive transistor connected between said electric wires, and said transistor circuit including a temperature sensitive impedance means for rendering said transistor conductive in response to temperatures above said particular threshold; and said ambient temperature compensating unit comprising a transistor circuit including a temperature sensitive impedance means for controlling the voltage supplied by said energizing leads to said spot detector unit in accordance with ambient temperature conditions.

2. The electrical fire control system defined in claim 1, in which said spot detector unit includes a tubular base member, a disc-like circuit board mounted in said tubular base member and extending thereacross, control circuitry supported on said board, a tubular wire mesh cage mounted on said base and extending therefrom in coaxial relationship therewith; an elongated support member extending in said cage from said base toward the end of said cage remote from said base; Y

and temperature sensitive impedance means supported on said support member adjacent said remote end of said cage and electrically connected to said control circuitry.

3. The spot detector unit defined in claim 2, and which includes a threaded plug means attached to the end of said base opposite to said cage and in coaxial

Claims

1. An electrical fire control system including: an elongated heat-sensing element comprising a pair of tensioned twisted electric wires and temperature-sensitive insulating material normally holding said wires insulated from one another, said insulating material softening in the presence of a temperature rise above a particular temperature level to permit the wires to twist together into electrical contact, and at least one solidstate temperature responsive spot detector unit mounted at a selected location along said heat-sensing element and electrically connected to said wires to establish an electrical connection therebetween prior to the aforesaid softening of said insulating material for temperatures above a particular threshold, electrical energizing leads extending to said spot detector unit and electrically connected thereto; and an ambient temperature compensating unit interposed in the circuit of said energizing leads to control the voltage supplied thereby to said spot detector unit in accordance with ambient temperature conditions, and thereby to render said particular threshold of said spot detector unit dependent upon ambient temperature conditions; said spot detector unit comprising a transistor circuit including a normally non-conductive transistor connected between said electric wires, and said transistor circuit including a temperature sensitive impedance means for rendering said transistor conductive in response to temperatures above said particular threshold; and said ambient temperature compensating unit comprising a transistor circuit including a temperature sensitive impedance means for controlling the voltage supplied by said energizing leads to said spot detector unit in accordance with ambient temperature conditions.

2. The electrical fire control system defined in claim 1, in which said spot detector unit includes a tubular base member, a disc-like circuit board mounted in said tubular base member and extending thereacross, control circuitry supported on said board, a tubular wire mesh cage mounted on said base and extending therefrom in coaxial relationship therewith; an elongated support member extending in said cage from said base toward the end of said cage remote from said base; and temperature sensitive impedance means supported on said support member adjacent said remote end of said cage and electrically connected to said control circuitry.

3. The spot detector unit defined in claim 2, and which includes a threaded plug means attached to the end of said base opposite to said cage and in coaxial relationship therewith.

4. The spot detector unit defined in claim 2, and which includes a second circuit board supported in said base for said ambient temperature compensating unit, and temperature compensating circuitry mounted on said second circuit board forming said ambient temperature compensating unit and including temperature sensitive impedance means connected to the aforesaid control circuitry of said spot detector unit.