US 3924688 A
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Description (OCR text may contain errors)
United States Patent [191 Cooper et al.
[ FIRE FIGHTING SYSTEM  Assignee: G & H Technology, Inc., Santa Monica, Calif.
 Filed: Apr. 5, 1974  Appl. No.: 458,221
Primary Examiner-Lloyd L. King Assistant Examiner-Michael Mar Attorney, Agent, or Firm-Dan R. Sadler  ABSTRACT A fire control system is disclosed herein having a plurality of hot wire electromechanical activators for non-explosive initiation of a corresponding plurality of fire extinguishers. The activators may be connected either in parallel for increased reliability or in series for increased ease in testing for continuity. Each activator-has a split collet formed of two spool halves with a restraining wire wrapped around it having a hook at one end attached to a hot wire which is connected to electrical leads mounted on one of the spool halves. A
shaft contacts the split collet in such a manner so as to cause the spool halves to separate when not restrained by the restraining wire. Displacement of the shaft is obtained by applying an actuation current to the leads which reduces the tensile strength of the hot wire until it falls below the tensile stress applied by the restraining wire. When the hot wire fails in tension, the restraining wire is released to thereby permit the spool halves to separate to permit the shaft to be displaced by an internal spring or external force. The shaft is connected either directly to a utilization device such as a fire extinguisher for displacement thereof in a direction parallel to the centerline of the shaft or through a cylinder having fingers for displacement at an angle to the centerline of the shaft.
l7'Claims, 12 Drawing Figures Sheet 1 of 6 U.S. Patent Dec. 9, 1975 US. Patent Dec. 9, 1975 Sheet 2 of6 3,924,688
U.S. Patent Dec. 9, 1975 Sheet 3 of6 3,924,688
y f 38 m g US. Patent Dec. 9, 1975 shw 4 of6 3,924,688
mumnom Ou U.S. Patent Dec. 9, 1975 Sheet 6 of6 3,924,688
FIRE FIGHTING SYSTEM BACKGROUND The present invention relates to a fire control system and more particularly to a non-explosive initiating device having a plurality of hot wire control mechanisms for initiating a corresponding plurality of fire extinguishers.
Fire control systems for complex equipment have generally proven to be too slow to respond to a fire in the equipment. As a result, even though the fire may be eventually brought under control, it nevertheless causes early extensive damage to the equipment before being put out. For example, a fire in a computer system may do millions of dollars in damage in a few minutes. If the fire were extinguished in a fraction of a second, the damage would be limited to a very small amount.
Various prior art devices have been used for initiating actuation of fire control systems. One type of such prior art devices uses electro-explosive pyrotechnic mechanisms. Such devices have proven to be undesirable for various aerospace and and commercial applications particularly when such devices are used on fire suppression systems. These pyrotechnic devices increase the probability of fire damage and thereby aggravate the situation. The explosive characteristic of pyrotechnic devices causes shock to the system when operated. The chemical characteristics of the exploding substances may change due to electromagnetic radiation or the passage of time. This reduces the reliability and stability of such systems. This reduced reliability is particularly aggravated in aerospace systems wherein the response time is critical. The explosive aspect scatters particles in the immediate environment of the system. These particles must be cleaned away in order to refurbish such a system to permit it to be reused. Testing of such devices is particularly difficult if they are scattered throughout a complex system.
Non-explosive initiating devices have therefore been developedparticularly for aerospace and commercial applications to avoid the aforedescribed disadvantages of pyrotechnic devices. Such devices are typically formed of a split collet formed of two spool halves which are wound with a spring temper stainless steel wire. After winding, the wire is anchored to both ends of the spool. A short reduced diameter section of the 'wire is located approximately in the center of the wire equidistant from the spool ends. The reduced diameter section presents local increased electrical resistance and reduced tensile strength. The spool is configured to permit compressive axial loading from a shaft to cause the spool halves to separate when not restrained by the wrapped wire element.
When the required electrical current is passed through the wire, the reduced section heats rapidly to a point where the unit tensile strength is reduced to the point of hoop stress rupture. The restraining wire unwinds and springs outwardly from the spool permitting the spool halves to be separated by the shaft which applies compressive axial loading. The shaft may be coupled to any utilization device for initiation of operation thereof.
Such devices have proven exceedingly useful for nonexplosive initiation of an actuator as shown in US. Pat. No. 3,388,933 to John Phillips entitled Electromechanical Activator Package. The inherent non-explosive initiation avoids the type of shock caused by pyrotechnic devices are prevents the possibility of aggravating a fire when the activator initiates operation of a fire extinguisher. They do not contain any volatile substances such as those used in pyrotechnic devices. Their operation is therefore not affected by electromagnetic radiation and they can be stored for long periods of time under a wide range of atmospheric conditions. The response time is relatively constant for a given actuation current.
Since these non-explosive initiators do not scatter particles in the course of actuation, they may be easily refurbished without having to clean the area immediately surrounding the devices. Testing the non-explosive actuators may be accomplished by a simple resistance check whereas pyrotechnic devices may not be easily tested in a non-destructive manner. Furthermore, a plurality of such actuators may be tested by connecting their respective hot wires in series and applying a single test current. They are also relatively light in weight.
The tensile strength of wires which are suitable for being reduced in diameter and wrapped around the collet are characteristically low. This low tensile strength of the wrapping wire reduces the axial load which may be safely applied to the collet without rupturing the wires before initiation of the actuation. Although such devices may be readily constructed, it is desirable to further simplify the construction.
SUMMARY The general purpose of this invention is to provide a fire control system which responds rapidly to extinguish a fire in a complex system. To attain this, the system provides a plurality of hot wire control mechanisms for non-explosive initiation of a corresponding plurality of fire extinguishing actuators. The plurality of hot wire actuators are spaced strategically throughout the complex mechanism and each is adapted to control a discharge nozzle of a source of fire extinguishing substance. Each of the hot wires is connected to a fire control box. A further plurality of fire sensor pickups are also located strategically throughout the device to be protected and are each connected to the fire control box. When one of the fire sensors detects a fire, the control box initiates actuation of the hot wire control mechanisms which in turn actuate the sources of fire extinguishing substance.
To attain this, each hot wire control mechanism includes a split collet formed of two spool halves wound with a restraining wire formed of spring temper stainless steel. One end of the wire has a hook attached to a hot wire which is short and has a diameter which is small relative to the diameter of the restraining wire. The hot wire is connected to suitable electrical terminals mounted on one of the spool halves. The collet is configured to permit compressive axial loading by a shaft so as to cause the spool halves to separate when not restrained by the restraining wire.
Initiation of each of the actuators may be affected by the application of current from the fire control box in response to a signal from one of the fire detectors. The current is of a sufficient level to reduce the tensile strength of each of the hot wires until it falls below the tensile stress applied by the associated restraining wire. When the hot wire fails in tension, the restraining wire uncoils to thereby permit the spool halves to separate under the axial load of the shaft. The shaft is then displaced by either an internal spring or external force.
The shaft may be connected toany suitable utilizaformed on a joint at the end thereof for displacement at an angle to the centerline of the shaft.
2 A system having a plurality of such hot wire mechanisms lends itself to ease of testing when each of the actuators is in a hard-to-get location in the complex mechanism which the fire suppression system protects. Ordinarily, pyrotechnic explosive initiators would have to be retrieved individually from the system and tested individually in some non-destructive manner in order to determine the operability of each such initiator. However, a system having a plurality of hot wire mechanisms may be tested by applying a simple test current having an amplitude below that which would actuate the mechanism and checking each of the hot wires for continuity. A continuity tester may be built into the fire control box with a test lamp means to signal continuity in each of the hot wires. If the hot wires are connected in series, they could be checked simultaneously with a single test lamp. In such a series connection, it would not be necessary to check each of the individual hot wires if the lamp displayed a signal in response to a test current.
Accordingly, an object of the present invention is to provide a fire suppression system.
Another object is to provide a plurality of hot wire control mechanisms throughout a complex expensive system to initiate actuation of a source of fire extinguishing substance in response to the sensing of a fire.
A further object is to provide a plurality of hot wire control mechanisms strategically spaced throughout a complex system with each of the hot wires connected in series for ease of testing of the hot wire initiators.
Yet another object is to provide a hot wire initiator having a split collet formed to withstand heavy compressive axial loading.
Still another object is to provide means for displacing a member in response to the application of an electrical current to a hot wire.
These and other features and advantages of the present invention will become readily apparent from the following detailed description of the invention wherein like reference numerals refer to like parts when considered in conjunction with the accompanying drawings.
DRAWINGS FIG. 1 is a perspective view of the present invention armed for displacement inwardly before actuation;
FIG. 2 is a perspective view of the present invention in the expended position;
FIG. 3 is a cross-sectional view of an internally spring loaded embodiment of the actuator of the present invention armed for displacement inwardly;
FIG. 4 is a cross-sectional view of the actuator of FIG. 3 in the expended position;
FIG. 5 is a cross-sectional view of an internally spring loaded embodiment of the actuator of the present invention armed for displacement outwardly;
FIG. 6 is a cross-sectional view of FIG. 5 in the expended position;
FIG. 7 is a cross-sectional view of a redundant system using an externally loaded embodiment of the present invention armed for displacement outwardly;
FIG. 8 is a view of FIG. 7 in the expended position;
FIG. 9 is a cross-sectional view of an externally loaded embodiment of the actuator of the present invention armed with a cylinder formed for displacement at an angle to the centerline of the shaft;
FIG. 10 is a cross-sectional view of FIG. 9 in the expended position;
FIG. 11 is a view of the fire control system of the present invention adapted for a parallel connected hot wire configuration; and
FIG. 12 is a view of the fire control system of the present invention adapted for a series connected hot wire configuration.
DESCRIPTION Referring now to FIG. 1, there is shown the electromechanical actuator of the present invention in the armed position and having a split collet formed of spool halves l1 and 12 with a hot wire 13 coupled to terminals 14 and 16 mounted onspool half 11. The spool halves are retained together by a wrapping wire 17 which applies circumferential stress to -the spool halves 11 and 12 and has a bent portion 18 formed at the end thereof and hooked to hot wire 13. The spool halves l 1 and 12 have tapered surfaces 21 and 22 respectively as shown in greater detail in FIGS. 3 and 4. The shaft 19 has a conical surface for engaging the tapered surfaces of the spool halves 11 and 12.
The bent portion 18 is disengaged from hot wire 13 by the application of an actuating current. The actuating current applied to the terminals 14 and 16 must be of sufficient magnitude to heat hot wire 13 to thereby reduce the tensile strength of the hot wire to a magnitude below the tensile stress exerted by wrapping wire 17 at bent portion 18 to thereby cause the hot wire 13 to be broken. When bent portion 18 is disengaged, the circumferential stress applied by wrapping wire 17 is released. The axial force of the shaft 19 urges the two spool halves 11 and 12 apart as shown in FIG. 2 to permit the displacement of the shaft 19 inwardly.
A spring loaded embodiment of theelectromechanical actuator is shown in FIGS. 3 and'4 for operating a abutment 27 of the housing 23. A butterfly valve 28 may be positioned to engage the shaft 19 at the end thereof.
When the hot wire breaks, the spring 24 compressibly loads the shaft 19 to displace it inwardly to release the butterfly valve 28 as shown in the expended position in FIGS. 2 and 4. The butterfly valve may be positioned in a nozzle for transmitting a fire extinguishing substance. Thus, the utilization device such as a fire extinguisher is activated by the application of a current to the hot wire 13 to permit the internal spring loading of the shaft 19 to displace the shaft inwardly.
In the internally spring loaded embodiment shown in FIGS. 5 and 6, a shaft 29 is positioned in an axial bore formed between collet spool halves 31 and 32. Each spool half has a tapered surface 33 and 34 respectively. The shaft 29 has a frustoconical shaped head 36 formed at the end thereof for engaging tapered surfaces 33 and 34 as shown. The shaft 29 has a spool portion 35 with a shoulder 37 and a housing 38 has a shoulder 39. A spring 41 is positioned to engage the shaft 29 at shoulder 37 to urge it outwardly. When an actuating current is applied to the hot wire to reduce its tensile strength to a magnitude less than the tensile stress of the wrapping wire, the wrapping wire hook is released from the hot wire to permit collet spool halves 31 and 32 to be urged apart by the axial force imparted by spring 41 transmitted through spool 35 and fustoconical shaped head 36 of shaft 29 as shown in the expended positionin FIG. 6. Thus, the actuator in FIGS. 5 and 6 is operative to displace the shaft 29 outwardly in response to the application of an actuating current to the hot wire and the internal spring loading imparted by spring 41.
FIGS. 7 and 8 show a pair of externally laoded actuators 42 and 43 in a unitary housing 46 coupled to a single source of current 44 for redundant operation to provide increased reliability. Actuators 42 and 43 each have collets 47 and 48 respectively and shafts 49 and 51 respectively. Each shaft is positioned through an axial bore in the associated collet as shown in the armed position in FIG. 7. When current is applied through current source 44 to the respective hot wires (not shown) of actuators 42 and 43 to reduce the tensile strength thereof to a magnitude below the tensile stress of the associated wrapping wire, the book of each wrapping wire breaks the associated hot wire to permit the axial loading of shafts 49 and 51 to separate the spool halves of the associated collet to displace them outwardly as shown in the expended position in FIG. 8.
The externally loaded embodiment shown in FIGS. 9 and is operative to actuate a utilization device positioned at an angle to the centerline of the shaft. As shown in the armed position in FIG. 9, a collet having spool halves 53 and 54 has a shaft 56 positioned axially therethrough. The spool halves 53 and 54 have tapered surfaces 57 and 58 which contact the fustoconical head 59 of the shaft 56. A hot wire 61 is secured to one of the spool halves 53 and a wrapping wire 62 has a bent portion 63 formed at the end thereof for. engaging the hot wire 61. The shaft 56 has a slot 64 which engages a pin 66. The shaft has a cam head 67 formed atthe end thereof which engages the fingers 68 of a cylinder 69. In the armed position shown in FIG. 9, the cam head and fingers are retained in a bore 71 inthe actuator housing 72.
When an actuating current is applied to hotwire 61 to decrease the tensile strength below the tensile stress of the wrapping wire 62, the hook 63 breaks the hot wire. The wrapping wire 62 is thereby released from circumferential compression of the spool halves 53 and 54. An external axial load (not shown), applied through the fingers 68 of cylinder 69 to shaft 56 causes the shaft to be displaced to the right as shown in the expended position in FIG. 10. The displacement of the shaft to the right causes the fingers 68 to release outwardly into a cavity in the housing 72 to permit the cylinder 69 to move at an angle with respect to the centerline of the shaft 56. This angular movement of the cylinder 69 permits actuation of a utilization device which is not perfectly aligned with the centerline of shaft 56.
Since the wrapping wire is separate and apart from the hot wire asopposed to prior art devices, the wrapping wire may be formed of wire having a thickness greater than that of wrapping wire in prior art devices and greater in thickness than the hot wire. The axial load on the collets may therefore be in the order of 6 2,000 lbs., which is substantially greater than that of similarly employed prior art devices. Typical hot wires have an electrical resistance in the order of 1 ohm. It has been found, for example, that a 4.5 ampere current applied to the hot wire will initiate actuation in the order to 20 to 30 milliseconds under axial loads in the order of 1,000 to 2,000 lbs. A 2.5 ampere current applied to the hot wire will initiate actuation in the order of 60 milliseconds under an axial load of approximately 300 lbs. Thus, the initiation time of the actuator may be carefully controlled by the actuating current for any given axial load. Furthermore, the period of time required for displacing the shaft may be controlled by adjusting the axial load, whether it is an internal spring load in the collet housing or an external load.
Thus, the electromechanical actuator of the present invention provides for non-explosive initiation thereof. The actuator may operate a utilization device such as a fire extinguisher by displacement of the shaft. The shaft may be internally spring loaded as shown in FIGS. 3 through 6 or externally loaded as shown in FIGS. 7 through 10. Furthermore, the shaft may be positioned external of the split collet halves to split them apart at their tapered surfaces as shown in FIGS. 1 through 4. Alternatively, the shaft may be positioned in an axial bore formed between the spool halves of the collet to split them apart on displacement as shown in FIGS. 5 through 10.
In FIG. 11, there is shown a fire control system having a plurality of hot wire actuators through each connected in parallel to a control box 116. A plurality of sensors 117 are each connected to the control box and are responsive to a fire in a complex mechanism 100. Each of the sensors is connected to a current source (not shown) which actuates each hot wire in each of the actuators 11 0 through 115. A source of fire extinguishing substance 118 is operative to transmit carbon dioxide or any other suitable fire extinguishing substance through conduits 120 through respectively. Each conduit has a suitable nozzle mounted at the end thereof through which the fire extinguishing substance is transmitted to the complex mechanism 100.
When any of the sensors 117 senses a fire in the complex mechanism 100, it energizes the current source in the control box 116 to initiate actuation of each of the actuators 1 10 through 115. Each of the actuators opens a separate valve in the associated conduit to enable the transmission of fire extinguishing substance through each of the conduits and the associated discharge nozzle into the mechanism 100 to extinguish the fire.
The control box 116 has a plurality of test lamps through each associated with one of the actuators. A plurality of test buttons through are each associated with one of the test lamps 130 through 135 respectively and each energize a separate current source (not shown). Each test lamp is responsive to the current source associated with the associated test button to signal electrical continuity in the hot wire of the associated actuator. The continuity of each of the hot wires may thereby be tested by depressing the associated test button and observing whether the associated test lamp is lit.
The parallel connection of the hot wires shown in FIG. 1 1 is particularly reliable in view of the fact that if any one actuator is inoperative for any reason, the remaining actuators are not affected. They are thereby still capable of dispensing fire extinguishing substance 'tem 100 to extinguish the'fire therein.
7 through the associated nozzle to the complex mechanism 100.
In the embodiment shown in FIG. 12, a plurality of hot wire actuators 150 through- 155 are, shown connected to thecontrol box 156 in series. Each of the sen I "siveinitiation of an actuator, said mechanism includsors 157 is connected to the control box .to sense a fire or other undesirable condition. Each-actuator-is connected to an associated conduit 160 through 165 which is connected to the sourceof fire extinguishing substance 158 to open the nozzle of the associated conduit in response to the application ated hot wire.
of -a current to the associ- "The "control box-156 has a current source (not shown) which is connected in series to the hotwires.
When any of the sensors 157 senses'afire in the mechanism'l00, the current source applies an electrical current to each of thehot wires to initiate actuation of the .;vention which is defined only by the claims which folassociated actuator. The current mustbe ofsufficient magnitude to heat each of the hot wires to enablethem to besimultaneously ruptured by the associated hook of the associated wrapping wire. This rupturing of the hot wire releases fire extinguishing substance in the sys- The control box 156 has a test lamp 170 which is responsive to a current in series with each of the hot wiresfThe continuity of the series connection of the hot wires 'of each of the actuators may be tested by depressing a button 171 to initiate a test current from a test current source (not shown) through each of the hot wires. Lamp 170 isthen operative to signal a continuity through the s'eriesconnected' hot wires. The embodiment shown in FIG. 12 is therefore operative to display a continuitythrough" the entire series connection of hot wires in responsie'tothe depression of one button. This simultaneous testing of the continuity of the series connected*hot wires" enables them to be tested quickly.
'Alth oughon ly 6'hotwire actuators are shown, each. connected to associated discharge nozzle, it should be. appreciated that any number of actuators and discharge 'no zz'les' may be positioned throughout the mechanism 100 for added safety. In order for the systern to be useful, the hot wire actuators must be dispersed throughout the mechanism 100 in strategic flocations. Often theselocations are not readily accessible for inspection of the hot wire of the actuator mounted at the locationfl'hetest lamps and associated test buttons provide ease of testing of these hot wires at a convenient central location.
Although thedischarge nozzles are shown connected to a source of 'c'arbondioxide, they may be connected The system is therefore operative to extinguish a fire inside them'echanism 100 very rapidly before any sub- 55 stan tial amountpf damage could occur.
,While. only a limited number of embodiments have beendisclosed hereinit will bereadily apparentto persons skilled in the art that numerous changes maybe madethereto without departing from the spirit of the invention. For example, the system could be designed to initiate actuation of any system in response to any predetermined condition. Furthermore, the particular configuration of the package and its parts may be varied,. Also,the manner in which thepackage is coupled tothe loadand the nature of.the load may be modified to fit any particular application. Accordingly, the foregoing disclosure-and description thereof are for illustratiye purposes only and do:not;inany way-limit the inaying' described the invention, whatis claimed 1 electromechanical mechanism for a non-exploa. plurality-of separable spool sections secured together and formed to have a;recess therebetween,
a pair of electrical terminals on oneof said sections,
wrapping meanswwrapped around saidplurality of spool sections for applying circumferential tension thereto to maintain said sections together,
asecuring portion formed on said wrapping means,
an electrically conductive element engaged by said securing portion, said electrically conductive element being connected to said terminal,
a movable member disposed at one end in said recess, I I
- a utilization device coupled to said movable member whereby the movement of said utilization device and'said movable member are restrained by the application of circumferential tension by-said wrapping means tosaid plurality of separable spool sections, and
' a source of electrical current coupledto said electrically conductive element, saidelectricall-yconductive element having a'tension greater than: said circumferential tension applied by said "securing means to said plurality of separable members at ambient temperatures, said tension of said electrically conductiveelement being less than said circumferential tension when'said tension element is heated up by current'applied by said source of electricalcurrent,
whereby the application of current 'by said source of electrical current disengages said securing means from said electrically conductive t" nsion element to enable said movable memberf'to initiate actuation of said utilization device.
2; An electromechanical mechanism'for a non-explosive'initiation' of an actuator, said mechanism includl I i a plurality of separable spool'sections secured together and formed to'hav e a recess therebetween, wrapping means wrapped around said plurality of spool sections for applying circumferential tension fthereto to maintain said sections together,
a securing portion formed on said wrapping means,
an electrically" conductive element engaged by said securing portion,
- a movable member disposed at one end in said recess I r a utilization device coupled to said movable member whereby the movement of said utilization device and said movablemember are restrained by the application of circumferential tension by said wrapping means to said plurality of separable spool seca source'of electrical current coupled to said electri- .cally conductive element, said electrically conductive element having a tension greater than said circumferential tension applied by said securing means tosaid plurality of separable members at (ambientltemperatures said tension of said electrically conductive el'ement'ibeing less than said circumferential ,terisio'nfwherr said tension element is 9 heated up by current applied by said source of electrical current,
whereby the application of current by said source of electrical current disengages said securing means from said electrically conductive tension element to enable said movable member to initiate actuation of said utilization device, and
a cylinder having fingers for engaging said movable member at the end opposite to the end movably disposed in said recess for displacement of said cylinder at an angle to the centerline of said movable member when said movable member is displaced.
3. The mechanism of claim 2 wherein said securing portion is a bent portion which is secured to said tension element and is hooked thereon.
4. The mechanism as described in claim 2 including a housing for enclosing said actuator mechanism,
a spring mounted in said housing,
a shaft in said housing, and
a shoulder on said shaft for engaging said spring to effect displacement of said shaft when said electrically conductive tension element disengages said securing portion.
5. The mechanism as described in claim 2 wherein at least one of said plurality of separable spool sections has a tapered. surface and said movable member has at least one tapered surface for mating with said tapered surface of said one of said plurality of separable spool sections.
6. A non-explosive fire extinguisher actuator comprising:
a sensing element for sensing a fire,
a pair of members,
a tapered surface on the first of said members,
a movable element,
a tapered surface on said element for engaging the tapered surface on said first member,
a wire wrapped around said pair of members for applying circumferential tension stress to said members to retain them together,
a securing portion on said wire,
a hot wire responsive to said sensing element and engaged by said securing portion, said hot wire having a tensile strength greater than the tensile stress of said wrapped wire at ambient temperatures, said hot wire having a tensile strength less than the tensile stress of said wrapped wire at an elevated temperature,
a source of tire extinguishing substance responsive to the displacement of said movable element,
whereby the sensing by said sensing element of a fire activates the actuator by elevating the temperature of said hot wire to reduce the tensile strength thereof below the tensile stress of said wrapping wire to enable displacement of said shaft to initiate operation of said source of fire extinguishing substance, and
said source of fire extinguishing substance includes a throat through which said substance is transferred and a butterfly valve mounted in said throat for engaging said shaft.
7. The actuator of claim 6 and including a pair of terminals mounted on one of said pair of members,
said hot wire is coupled to said terminals, and
an electrical current source coupled to said terminals by a pair of electrical leads.
8. The actuator of claim 6 wherein said securing portion is a hooked portion which is hooked on to said hot wire.
9. The actuator of claim 6 wherein said means for applying axial force is a spring and said shaft is formed with a shoulder for engaging said spring.
10. An actuator including the combination of sensing means,
a plurality of members,
securing means for retaining said members together and having a latching extension thereon,
wire means responsive to said sensing means and secured to said latching extension, said wire means having a tensile strength greater than the tensile stress exerted thereon by said latching extension at ambient temperature, said wire means having a tensile strength less than the tension stress exerted thereon by said latching extension at an elevated temperature,
said securing means including a wire wrapped around said plurality of members and having a thickness greater than the thickness of said wire means, and
a utilization device positioned to engage said plurality of members and operative to be displaced when the temperature of said wire means is elevated by said sensing means.
11. The actuator of claim 10 wherein said plurality of members includes a split collet having a pair of spool members at least one of which has a relieved portion for engaging said utilization device.
12. The actuator of claim 10 wherein said utilization device includes a movable member having a tapered surface for engaging said relieved portion of said one of said spool members.
13. The actuator of claim 10 wherein one of said spool members includes a pair of electrical terminals and said wire means is connected between said pair of electrical terminals.
14. An actuator system comprising:
a plurality of hot-wire actuators,
control means to which each of said plurality of hotwires is responsive,
a second plurality of sensors for sensing a predetermined condition and each connected to said control means,
whereby the sensing by at least one of said sensors of said predetermined condition initiates actuation of at least one of said plurality of hot-wire actuators, and
testing means in said control means for testing said plurality of hot-wire actuators simultaneously.
15. The system as described in claim 14 including lamp means in said testing means for signaling continuity of each of said hot-wire actuators,
16. The system as described in claim 14 including means connecting said plurality of hot wires in series,
means in said testing means for applying an electrical current to said plurality of hot wire actuators.
17. The system as described in claim 14 including a lamp in said testing means for signaling continuity of each of said hot-wire actuators.