US3476517A - Combustible gas detecting device - Google Patents

Description

Nov. 4, 1969 A. H. SMITH 3,476,517

COMBUSTIBLE GAS DETECTING DEVICE} Filed NOV. 22, 1965 FIG. 1

FIG. 2

INVENTOR Albert H.Smi1'h TORNEYS 3,476,517 COMBUSTIBLE GAS DETECTING DEVICE Albert H. Smith, Ossiuiug, N.Y., assignor, by mesne assignments, to Automation Industries, Inc., El Segundo,

Calif., a corporation of California Filed Nov. 22, 1965, Ser. No. 509,079 Int. Cl. G01n 33/22 US. Cl. 23-455 8 Claims ABSTRACT OF THE DISCLOSURE A gas detector which includes a platinum filament for producing a catalytic reaction wherein any combustible constituents in a potentially explosive mixture are oxidized and the temperature of the filament is increased by a corresponding amount. In addition, heating means, such as an incandescent lamp, are provided for producing a thermal siphon wherein the mixture is preheated to a stabilized level prior to detection and the heating current through the filaments is regulated.

The detecting device of the invention is of the type employing a heated filament of a material such as plati num which reacts with combustible gases or vapors to which it is exposed and thereby undergoes an increase in temperature and electrical resistance. This variation in the resistance of the filament may be utilized to actuate suitable signaling means to Warn of the presence of the combustible gas. Detectors relying upon such filament means may be located at selected positions in an area where explosive or combustible vapors may collect, such as in mines, adjacent natural gas storage tanks, and so on.

In conventional gas detecting equipment of this sort, the electrically conductive filament means are surrounded by an enclosure formed of a fine mesh Davy screen which serves to cool any burning gases ignited by the filament means and prevent the spread of combustion. The combustible gases must therefore seep through the screen before they can reach the detecting filament and be sensed. Many of the gases and vapors which are to be detected by these devices have a density greater than that of air, and consequently they do not reach the filament means and produce a warning signal until they have filled the area in question up to the filament means. Oftentimes a delay of this sort can be critical and should be avoided if at all possible.

It is the broad purpose of the present invention to produce a forced draft in the region of the sensing filament so that denser gases or vapors are carried directly up to the filament even though they may not have otherwise collected in critical quantities at the level of the detector. This is done by locating the filament at the top of what serves as a small chimney and forces the gas or vapors upwardly through the chimney by convection currents produced by a safe heat-emitting element.

Broadly stated, the combustible gas detecting device of the invention comprises a chimney adapted to be arranged substantially vertically and having upper and lower ends. Gas vapor inlet and outlet ports are defined at the lower and upper ends respectively of the chimney, and fine mesh Davy screen means are disposed across each of the inlet and outlet ports. An electrically powered heatemitting incandescent lamp, for example, a metal filament incandescent lamp is mounted within the chimney adjacent the lower end thereof above the inlet ports for forcing a draft through the chimney. Filament means for sensing the combustible gas are exposed within the chimney adjacent the upper end thereof. The device also includes circuit means for directing electrical current through the lamp and filament means so that the com- United States Patent "ice bustible gases drawn up through the chimney vary the filament resistance and are thus detected.

As a result of this construction, convection currents are induced in the environmental gases surrounding the detecting device and draw the gases upwardly into the chimney before the denser gases normally collect at that level, so that the earliest possible warning of combustible gases is achieved. The incandescent lamp responsible for the upward draft can be relied upon not. to warm a combustible gas to its ignition temperature and is therefore thoroughly safe. For these reasons, and others which will be apparent from the following detailed description of the new detecting device, the combination of the chimney with its Davy screens, incandescent lamp and filament means provided by the invention constitutes a marked improvement in the design of combustible gas detecting devices.

A preferred embodiment of the invention is described hereinbelow with reference to the accompanying drawing, wherein FIG. 1 is an elevation in section of the detecting device of the invention; and

FIG. 2 is a diagram of the circuit means employed therein.

With reference to the drawing, a cylindrical metal transducer tube defines a chimney 10 adapted to be arranged vertically when the device is mounted in operating position. The lower and upper ends of the transducer tube forming the chimney 10 are open as shown in FIG. 1. A first cap 11 is welded to the lower end of the chimney 10 and defines a plurality of gas inlet ports 12. A second cap 13 is attached to and covers the upper open end of the chimney 10 and may be associated with appropriate bracket means for holding the device in the vertical position shown. Both of the caps 11 and 13 may be circular in shape to correspond to the circular cross section of the chimney 10.

The first cap 11 at the lower end of the chimney 10 underlies a multi-layer fine mesh Davy screen 14 which extends across the open lower end of the chimney 10 and spans the gas inlet ports 12. At the upper end of the chimney 10, a plurality of gas outlet ports 15 are formed in the vertical wall thereof, and they may be configured in the shape of slots. Surrounding the upper end portion of the chimney around these outlet ports 15 and below the second cap 13 is a retaining collar 16 which holds a second multilayer fine mesh Davy screen 17 in place. The screen 17 is thus disposed across the outlet ports 15. There can be no access to or exit from the interior of the chimney 10 except through the Davy screens 14 and 17, and hence any combustion of gases within the chimney 10 cannot spread outwardly into the atmosphere around the detecting device.

Mounted within the chimney 10 adjacent the lower end thereof on a suitable bracket 18 is a socket 19 into which an incandescent lamp 20 is inserted projecting downwardly into close proximity with and immediately above the inlet ports 12. The lamp 20 may be of the automotive type which produces about ten watts of energy as heat, preferably a metal filament type. At the upper portion of the chimney 10 are primary and secondary platinum filaments 21 and 22 respectively (shown schematically) which depend from the underside of the cap 13 and which are surrounded by respective cylindrical shields 23 and 24. The shield 23 has an open lower end 25 and vent apertures 26 at its upper end to allow gases rising in the chimney 10 to contact the: primary filament 21. The shield 24, however, has no openings and encloses the secondary filament 22 so that it is not exposed to the gases in the chimney 10. It is the purpose of the secondary filament 22 to provide a reference by which changes in ambient temperature do not affect the combustible gas sensing function of the primary filament 21. An electrical connector 27 is attached to the upper side of the cap 13 and is associated with conductors 28 leading to a power source.

In FIG. 2, the circuitry of the electrical components of the detecting device is shown. The primary and secondary filaments 21 and 22 are arranged in a bridge with resistors R and R so that an increase in the resistance of the primary filament 21 due to exposure to combustible gases causes current to flow through and activate a suitable alarm unit 29. Increases in the resistance of both filaments 21 and 22 due to changes in ambient temperature are equal and will not activate the alarm unit 29. The bridge circuit containing the filaments 21 and 22 is connected in series with the lamp 20 by the conductors 28 leading from the power source, the purpose being to reduce the voltage applied across the filaments to an acceptable value and at the same time provide a relatively constant current source when the input voltage varies.

In operation, this detecting device is mounted vertically in the area where combustible gases may form. The circuit means of the device are connected to the power source so that the platinum filaments 21 and 22 glow with a red heat and the lamp 20 is lighted and emits heat. The disposition of the heat-emitting lamp 20 at the lower end of the upright chimney causes convection currents to rise upwardly in the chimney and forces a draft which draws environmental gases into the inlet ports 12. These gases pass through the Davy screen 14 and proceed upwardly past the lamp toward the upper end of the chimney. Most of the gases in this current flow proceed out of the chimney 10 directly through the outlet ports 15. However, some of the gases enter the lower end of the shield 23 and pass in contact over the primary filament 21 before exiting from the shield 23 through its vent apertures 26. Thereafter, that portion of the gas proceeds with the remainder to the outlet ports 15, and all of the gases pass through the Davy screen 17 before leaving the device.

If any of the gases passing through the chimney 10 in this fashion are combustible, they react with the primary platinum filament 21 and increase its electric resistance. This change in resistance is in turn sensed to actuate the alarm unit 29. If any limited burning of the gas is produced within the chimney 10 it is safely contained by the Davy screens at the inlet and outlet ports and cannot spread the combustion to the inlet and outlet ports and cannot spread the combustion to the atmosphere surrounding the device.

I claim:

1. A gas detector device for detecting the amount of a combustible constituent contained within a potentially explosive mixture confined in a predetermined space, said device including the combination of:

a transducer housing having a passage therein;

an inlet port in said housing opening into the passage,

said inlet port being adapted to communicate with the space whereby a sample stream of said mixture may enter said housing and fiow through the passage therein;

an outlet port in said housing opening into the housing passage for exhausting the sample stream from the passage;

an electrically conductive filament positioned within the housing passage having a surface thereof exposed to at least a portion of the mixture in the sample stream flowing through the housing passage, said filament having an electrical resistance which is a function of its temperature, the surface of said filament being effective when heated into a predetermined temperature range to produce an exothermic reaction involving the combustible constituent whereby the instantaneous temperature of the filament is increased above the nominal temperature as a function of the reaction; an electrical current source being coupled to said filament or circulating an electric current through said filament and increasing the temperature thereof into said predetermined temperature range, said source including means for regulating the current through said filament whereby the nominal temperature is maintained substantially constant, said regulating means including a metal filament incandescent lamp disposed in the housing passage to heat the sample stream and cause it to circulate through the housing passage and past said filament, the lamp being electrically connected to said filament whereby the electrical resistance of the lamp varies so as to maintain the current in said filament substantially constant; and means responsive to changes in the resistance of said filament resulting from the temperature being increased above the nominal resistance by the reaction, said means being effective to indicate the combustible constituent. 2. The gas detection device as defined in claim 1 and further including heat absorbing means substantially disposed in said inlet port and said outlet port whereby said reaction cannot propagate beyond the housing passage.

3. The gas detection device as defined in claim 1 wherein the passage is in a substantially vertical direction and whereby it acts as a chimney and the heated mixture rises through the housing passage and past said filament.

4. The gas detection device as defined in claim 1 and further comprising:

heating means disposed in the housing passage upstream from said filament to preheat the mixture in the sample stream. before it reaches said filament; and

heat absorbing means disposed in said inlet port and said outlet port whereby the reaction cannot propagate beyond the housing passage.

5. A gas detector device for detecting the amount of a combustible constituent contained within a potentially explosive mixture confined in a predetermined space, said device including the combination of:

a transducer housing having a passage therein;

an inlet port and an outlet port in said housing opening into the passage in said transducer, said inlet port being adapted to communicate with the predeterined space whereby a sample stream of said mixture may enter said housing, flow through the passage therein, and exhaust through said outlet port;

first and second electrically conductive filaments having nominal electrical resistances which are functions of their temperatures;

mounting means positioning said filaments in the passages of said transducer adjacent each other whereby their temperature and the consequent nominal resistances are equilibrated;

said first filament having its surface intimately exposed to at least a portion of the mixture in the sample stream, the surface of said filament being effective when heated into a predetermined temperature range to produce an exothermic reaction involving the combustible constituent whereby the instantaneous temperature of the filament is increased above the nominal temperature as a function of the reaction;

said second filament having its surface separated from said mixture whereby its instantaneous temperature is maintained substantially equal to the nominal temperature and independent of the combustible constituent;

an electrical current source being coupled to said filaments for circulating an electric current through said filaments and increasing their nominal temperatures into said predetermined temperature range, said source including means for maintaining the current through said filament substantially constant where- 8. The gas detection device as defined in claim 5 and by the nominal temperatures are maintained subfurther comprising: stantially constant, said current source, including a heating means disposed in the housing passage up metal filament incandescent lamp disposed in the stream from said filament to preheat the mixture in housing passage to heat the sample stream and cause 5 the sample stream before it reaches the filament; and it to circulate through the passage and past the filaheat absorbing means being disposed in the inlet ports ment, the lamp being electrically connected to said and the outlet ports whereby the reaction is prefilament, whereby the electrical resistance of the lamp cluded from propagating beyond the passage. tends to stabilize the current flow through said filat; d 10 References Cited means responsive to the difference between the re- UNITED STATES PATENTS sistances of the filaments resulting from the reaction to indicate the presence of a combustible mixture. 1 g

6. The gas detection device as defined in claim 5 where- 2 A 5 Z l in the housing is positioned with the passage in a sub- 15 1 12/193 Jo at a stantially verical direction with the inlet port near the bottom and the outlet port near the top thereof, whereby MORRIS WOLK Pnmary Exammer the heat mixture rises through the housing passage and R- M- RE SE, Assistant Examiner passes the filament.

7. The gas detection device as defined in claim 5 and 20 further comprising heat absorbing means being disposed 7327 in said inlet port and said outlet port whereby said reaction is precluded from propagating beyond the housing passage.

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