US2650665A

US2650665A - Fire responsive mechanism

Info

Publication number: US2650665A
Application number: US135863A
Authority: US
Inventors: Melville F Peters
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-12-30
Filing date: 1949-12-30
Publication date: 1953-09-01
Anticipated expiration: 1970-09-01

Description

Sept. 1, 19534 M. F. PETERS FIRE RESPONSIVE MECHANISM Filed Dec. 30. 1949 IN V EN TOR. MEL VALLE F ,DET'ER5 A T'T'OE/VEX Patented Sept. 1, 1953 UNITED STATES PATENT OFFICE 6 Claims.

This invention relates to fire-responsive mechanism, and particularly to the detection, signalling, and extinguishing of fires originating near the power plant or other vital part of an airplane or other automotive vehicle.

An object of the invention is to provide a hollow element formed and treated in a novel manner enhancing its suitabilit and efficiency as a fire detecting element capable of transmitting an alarm signal electrically to one or more observation stations at a distance therefrom.

A second object of the invention is to provide a fluid conduit equipped with inlet and outlet points for the introduction and discharge of firefighting fluids, such as those commonly used in fire extinguishers; the said fluid conduit also serving as a fire detecting element capable of participating in the transmission of operating energy to an alarm signal device located at a distant observation station.

A third object of the invention is to provide a novel signalling system responsive to the presence of fire, and characterized by the use of a fluid conduit as a component part of the electric current flow controlling means by which the transmission of a fire alarm signal is effected.

A fourth object of the invention is to provide electric current flow controlling means of novel construction, including the provision of a layer of thermistor material on the outer surface of a metallic conductor, said thermistor layer serving to resist completion of an electric circuit therethrough in the presence of moisture, and further serving to accelerate completion of an electric circuit therethrough in the presence of fire or heat of such an intensity as to signify the presence of an elevated temperature.

A fifth object of the invention is to provide a fire-fighting fluid distributing conduit having an outer layer of thermistor material adapted to control electric current flow for operation of a fire alarm signal device, and having the characteristics indicated.

A sixth object is to provide a fluid distributing conduit having a layer of thermistor material interposed between layers of metal, the inner layer of metal serving as the basic conduit and the outer layer of metal co-operating with the thermistor layer to control .fiow of signal current in the presence of fire or intense heat.

A seventh object is to provide a fluid distributing conduit having inner and outer layers of thermistor material adapted to cause completion of a signalling circuit only when the intervening metal of the conduit becomes heated to a degree suggestive of fire.

These and other objects of the invention will be better understood upon examination of the following description of the particular embodiments of the invention illustrated in the accompanying drawings wherein:

Fig. 1 is a diagram illustrating a fluid distributing conduit surrounding and supported on the casing of an internal combustion engine or other vehicle component susceptible to attack by fire;

Figs. 2 and 3 are diagrams illustrating a fire alarm signalling circuit having a fluid distributing conduit as one of its component parts; the said conduit being constructed in a manner embodying the principles of the invention; and

Fig. 4 shows a section of a conduit constituting another form in which the invention may be embodied.

In Fig. 1 is shown the simplest type of thermistor fire detector, so designed that it may be used to distribute the carbon dioxide or other extinguishing material. It consists of a metal tube I, the walls of which may be plain, fluted, or corrugated in any common manner, and of sufficient thickness to withstand mechanical handling. It is supported by insulators 5. The holes 4 are so placed that when 002 enters through 6, the extinguishing material will be distributed throughout the confining chamber I. The fire signal is given when a flame 8 makes contact simultaneously with the tube I and the engine or metallic body 3. The chief objection to this simple type of fire detector is that a false alarm may be given if moisture collects on the insulation 5, or fail to give an alarm if the flame fails to contact both the tube I and the engine 3 simultaneously.

The probability of false alarm may be great- 1y reduced by covering the steel tube I with thermistor material 2. The tube does not become grounded by moisture on the insulators 5, because the thermistor material may be made to have a high resistance below the boiling point of water. When the tube is heated the resistance rapidly decreases and becomes a relative- 1y good conductor. By selecting the composition of the thermistor material the temperature at which the material becomes a good conductor can be controlled. The term thermistor material is intended to include any material having a negative temperature coefiicient of electrical resistance, such as porcelain or analagous glazing and enamelling materials. This arrangement of covering the steel tube with thermistor material has the advantages of an insulated tube when the detecting element is below some predetermined temperature and the advantages of a noninsulated tube in the presence of an elevated temperature. It still has the disadvantage of requiring the flame to make contact simultaneously with the steel tube I and the engine 3. Both types, one without thermistor material and the second with it are essentially flame detectors, in that the flame 8, upon making simultaneous contact with the tube and the engine housing 3, may thereby complete an electric circuit leading to a fire. alarm signal device, or'fire indicator, such as 'the'indicator'l3 of Fig. 2.

In Figure 2 is shown a unit which may serve in a dual capacity: first, as a heat or flame detecting unit, and secondly, as a means-fordistribut' ing the extinguishing material. It will actuate the indicating mechanism when some portion of the tube reaches a predetermined temperature,

whether this temperature is caused by a flame or the ambient atmosphere. same as a two wire thermistor, with the added feature that the conductivity of the flame. may play animportant part in determining theactual'resistance between the steeltube land the metal braid 9, shown-in Figure 2. The braid may be made of round or flat wire, or may be.-merely astrip. of tape orwire wrapped around the tube. Using the same notationas in Figure 1, the tube is covered with thermistor material 2,. a. few. thousandths inch'thick, and over this is. stretched aimetal braid-or wrapped conductor 9, which is grounded by supports The steel tube. 1 is connected to the CO2 or other extinguishing material supply tank by means of an electrically insulating coupling H The coefiicient of expansi-on of-themetaltube I, the thermistor material 2.. andthewire braid is the same, so that when the ambient temperature increases moderatelyfast, the braid remains in contact with the thermistor material and the signal'is actuated by conduction from braid to; tubethrough the thermistor material. When a hot flamestrikes the metal braid it will-heat". more rapidly than the-thermistor material and-the steel tube. Because of theunequal heating and consequentlyunequal expansion, some. parts of thebraid will failto-make contact with thethermistor material by a few thousandths of an.inch,.but the flame :will complete the circuit between the braid and-thermistor material where this; separation ocours;

The metal braid or circumventing conductor serves as a protection for the thermistor mate-- rial and radio shields the tube,- so that-for a cheap installation the voltagefor actuating; the signal maybe 'obtainedby capacitance coupling to the ignition cable without causing radio interference. Sucha signalling-unit is shown in Figure 2. The metal tube H isslipped over the ignition cable I2. A wirefrcmthe-metal tube isconnected to one. terminal of the neon light [3' and the other terminal is connected to the steel tube bymeans of the'conductor l5. The-condenser: I4- is connected acrossthe neonlight I3, so that the voltage across the neon light will not be great enough tocause breakdbwnuntilthe thermistor material becomes conducting. It'isto be pointed out thata better'type of indicator is recommended when the installation can stand the cost; but this indicator l3 will be-satisfactory for a cheap installation'.

A further improvement may be obtained by using the combination shown in Figure 4. In this arrangement, t is the steel tube, 2 the thermistor material which is only a few thousandthsinch thick, and iron wire braid or other In principle, it: is the.

suitable metal covering 9, and IS a covering of thermistor material over the complete unit. When a flame 8 strikes the thermistor material, a section AX is heated so that the current is conducted from the braid wire, or its equivalent, 9, to the steel tube I. This lowers the resistance and actuates the signal.

The resistance of enamel covered metal tubes to withstand mechanical abuse at elevated temperatures, has been demonstratedby; the long life of exhaust stacks when covered with ceramic material. Their resistance to mechanical abuse atlow temperatures has been amply demonstrated-by the increased life of steel coal chutes when covered with enamel. These enamels are all thermistor: materials. By the use of thermistor Iintend toincludeall enamels responding to the same law of resistance decrease with rise in temperature.- The enamel material commonly used as a covering for kitchen pots and pans has been found to be very satisfactory as a thermistor material, and willbesuitable for the purposeszof the present invention; For further identification'of thermistor materials; which are now well known, reference may be hadto many patents. issued to Bell TelephoneLaboratories, wherein thermistorsandthermal transitors are described; one such patent being the Koch patent of September 19,- 1950.

The electrical resistance of. the braid over the steel tube, with a few thousandths of thermistormaterialbetween the two, will be" many. times lower than two wire thermistors. This means,- with the same operating voltage the. currents will be many times greater inthe braid-tube; type comparedv to the two-wire type. This reduces the probability of false alarm'by groundingdue to moisture.

The tubel may be made of steel from. thestandpoint of economy. The cost of thetube. per foot will depend uponthe diameter and thickness'of the wall. The cost of covering itwith thermistor material in largecquantities is. relatively cheap. As aconcrete example akitchenpot covered with'an enamel which is thermis-- tor material may beproducedfon less than 25 cents. The steel braid. is cheap and: may be slippedinto place over thetube; If it is desired. to insulate both tubeand. braid a heavy cheap. connector may be used, since resistance to ground isnot critical. Instead ofbraid, a metal ribbon maybe wrapped around the tube. The indicators for these heat and flame detectors are similar toother thermistor indicators. Because of. the lower resistance thecircuit constants in the indicator would be changed. The one in Figure 2 is recommended for cheap installation-only.

Fora cheap indicator for automotive or bus service, the; steel, tube covered with thermistor material'shown in Figure 1, with the indicating circuit as'shown in Figure 2, would'suffi'ce.

The alarm control circuits maybe employed independently of the fluid discharging feature, where the-latter is not needed. Also, if desired,

, each of the fluid discharge holes in the conduits sourceto said-indicator element, said electric cir- Similarly; othercuit including a metallic tube having a coating of thermistor material which is a ceramic enamel and whose thickness is only a few thousandths of an inch, said coating being of high resistance at norma1 temperature and thereby preventing flow of electric current sufiicient to actuate said indicator element, but of low resistance at abnormally high temperatures and thereby causing flow of electric current sufiicient to actuate said indicator element.

2. Means for indicating the presence of flames, comprising an indicator element, a source of electrical energy, means including an electric circuit for delivering operating energy from said source to said indicator element, said electric circuit including a tubular element having a coating of thermistor materia1 which is a ceramic enamel of less than twenty thousandths of an inch, and means for electrically grounding said tubular element and coating during any period when the thermistor material is hot enough to conduct electric energy, said grounding means including a metallic covering surrounding said coating.

3. Means for indicating an abnormal temperature rise occurring in the vicinity of an internal combustion engine power plant having its ignition circuit enclosed in metallic shielding, comprising an indicating element and electrical connections extending from said shielding to said indicating element, said electrical connections ineluding a metallic element having a thin coating of thermistor material, which is a ceramic enamel, forming part of the path of current flow leading to said indicating element.

4. A system as defined in claim 1, wherein the system is applied to an internal combustion engine having electrical conductors supplying ignition current thereto, and wherein said energy source comprises the electrical shielding encasing said conductors.

5; A fire detecting circuit including a signal element, a source of electric energy, a conduit having a very thin coating of thermistor material, which is a ceramic enamel and means for contacting said coating for grounding said coating when it becomes hot enough to be electrically conductive.

6. A circuit as defined in claim 5, wherein said conduit is in the form of a tube, to facilitate flow of fire-fighting fluid therethrough.

MELVILLE F. PETERS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,493,327 Dunbar May 6, 1924 2,315,872 Kernen Apr. 20, 1943 2,487,526 Dahm Nov. 8, 1949 2,495,867 Peters Jan. 31, 1950