US1979976A

US1979976A - Gas detector

Info

Publication number: US1979976A
Application number: US610853A
Authority: US
Inventors: Abraham L Marshall
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1932-05-12
Filing date: 1932-05-12
Publication date: 1934-11-06
Anticipated expiration: 1951-11-06
Also published as: GB397815A

Description

Nov. 6, 1934. MARSHALL 1,979,976

GAS PETECTOR Filed May 12, 1932 I'll!!!llillllllllllpllla'11,!"arllllllilllrlllli Invenso'm Abraham L. Morshall,

His Atcov'neg.

Patented Nov. 6, 1934 ums s'r 1,979,976 Gas DETECTOR Abraham L. Marshall,

signer to General Electric tion of New York Schenectady, N. Y., as- Company, a cometa- Application May 12, 1932, Serial No. 610,853

3 Claims.

My invention relates to gas detectors and concerns particularly devices responsive to the presence in air or other gaseous mixtures of combustible or inflammable gases.

Disasters result from time to time in consequence of the unnoticed accumulation of infiammable, poisonous, or otherwise obnoxious gases in mines, sewers, the locality of gas mains and the like. Even where such gases are present in insufi'icient quantities to give rise to? explosions, the physiological effects on persons breathing the air containing such gases may be injurious or even fatal. In mines, for example, owing to insufficient ventilation or other causes, there is a danger that the percentage of fire damp or marsh gas present may gradually rise to an amount dangerous to the occupants of the mine without their becoming aware of the peril. In such cases, it is important to provide gas-detecting means which will not merely give an alarm when the danger becomes acute, but which is sufiiciently sensitive to respond as soon as the percentage of obnoxious gas present approaches a limiting safe value, thereby warning the occupants or setting in operation fans or other preventive meansin ample time.

Various devices are known for indicating the presence of obnoxious gases. Difficulty is experienced, however, in obtaining a device sufiiciently sensitive. Among these devices there is a device comprising a porous vessel containing an electrical filament and connected to a device which indicates differences in pressure between the interior of the vessel and the atmosphere surrounding it. The porous vessel is placed in the mine, the atmosphere of which is to be tested and the air in the mine diffuses through the porous walls into the vessel. A current is sent through the electrical filament and the heat ignites the fire damp or other inflammable gases in the vessel. The fire damp burns to carbon dioxide and water vapor but the water vapor condenses, causing the pressure within the vessel to fall, thereby indicating the presence of the fire damp.

Owing to the-heat supplied by the electrical filament, however,-the temperature of the interior of the vessel soon rises to an extent that the condensation of the water vapor formed is either reduced or prevented. Consequently, the sensitivity is greatly diminished and the calibration changes with the length of time the device is in use.

It is an object of my invention to provide a gas-responsive device of the porous vessel and igniter type having increased sensitivity and a relatively uniform calibration.

It is another object of my invention to provide 'a simple, reliable, easily constructed and maintained safety device for indicating and controlling the presence of relatively small quan tities of fire damp and other combustible gases in the atmosphere of mines or other places.

It is a further object of my invention to provide a device responsive to the presence of relatively small quantities of combustible gases in gaseous mixtures.

In accordance with my invention in its preferred form, I provide a container having porous walls and containing an electrical filament or other suitable means for igniting combustible gases contained in air or other gaseous mixtures difiusing into the container. Suitable pressure-responsive means are provided which serve'to give an indication, operate an alarm or set in operation other apparatus when the pressure within the container falls in response to the presence of combustible gases in the atmosphere surrounding the container as a result of the combustion of these gases and the reduced volume of the products of combustion. In order to increase the sensitivity of the device, I provide means for insuring the reduction in volume by condensation, absorption or some other manner of even minute quantities of some of the products of combustion, particularly water vapor, as soon as they are formed. This may be accomplished either by cooling the interior of the container sufiiciently to raise the humidity or by humidifying the atmosphere surrounding the container so that the mixtureof gases within the container is substantially saturated with water vapor. Consequently any additional water vapor formed will be condensed upon formation and water soluble gases will be absorbed.

The features of my invention which I believe to be novel and patentable will be pointed out in the claims appended hereto. My invention itself however will be best understood by referring to the following description taken in connection with the accompanying drawing in which Fig. 1 represents one arrangement which may be utilized for obtaining a gas-responsive device of high sensitivity, and Figs. 2 and 3 represent modified arrangements for carrying out my invention.

Referring now more in detail to the drawing in which like reference characters refer to like parts throughout, in the form of my invention illustrated in Fig. l, I provide an outer container 11 and suitable means such as a pump 12 for passing air or gaseous mixtures to be tested through the container 11, entering the container at the inlet 13 and leaving it at the outlet 14. The outer container 11 surrounds an inner container 15 having porous Walls 16 permitting the difiusion of air and gas into the interior of the inner container 15.

Suitable means are provided to cause the combustion of the combustible gases within the inner container 15 or the chemical union of some of the gases contained therein. This means may take any desired form such as a heating means, a catalytic agent or any other means serving to ignite the gasesor serving to promote chemical combinations. Preferably, the means for causing the combustion of the gases takes the form of electrical filament 17 supplied with current from a suitable source such as a battery 18. In order that the filament 17 may be operated at a sufficiently hi h temperature to.

ignite the gases without undue heating of the apparatus, it is desirable that a relatively fine filament composed of platinum or other suitable material be employed. If desired, the filament 17 may be employed in conjunction with a catalytic agent, such as platinum black or the like, thereby permitting operation at a lower temperature. The combustion of gases, such as fire damp, causes the formation of water vapor which tends to condense, thereby producing a partial vacuum within the inner container 15. A manometer or other suitable pressure-responsive means may be connected to the interior of the inner container 15 in order to measure or give a response to partial vacuums created within the inner container by the combustion of gases and the condensation of products of combustion. For the sake of illustration I have shown a pressure-responsive means 19 taking the form of a contact-making vacuum gauge, but it will be understood thatI am not limited to this exact form of pressure-responsive device.

In order to promote the condensation of Water vapor and the condensation or absorption of' certain other products of combustion, means are provided for maintaining a relatively high humidity within the inner container 15. This may be accomplished either by humidifying the air or gaseous mixtures permitted to diffuseinto the inner container 15 or by cooling the space within the inner container to a temperature close to the dew point. In order to humidify the gaseous mixture which surrounds the innercontainer 15, a quantity of Water 20 is provided in the lower portion of the outer container 11. A reservoir 21 connected to the container 11 by means of tubing 22 may be employed if desired to provide a convenient means of replenishing the supply of water when necessary. The gaseous mixture entering through the inlet 13 would be humidified to some extent merely by passing through the water 20, but preferably a porous plate 23 composed, for example, of alundum of the type used in apparatus for aerating sewage, is interposed between the inlet '13 and the portion of the container 11 containing the water 20. Suitable means, such as gaskets 24 and clamps 25,are utilized for fastening the porous plate 23 to the bottom 23' of the outer container 11 and making a joint between the plate 23 and the bottom 23. The gaseous mixture is forced to pass through the numerous pores of the plate 23, thereby breaking up the air stream or the stream of gaseous mixture into numerous small bubbles which rise through the Water 20 and insure the absorption of sufficient water to substantially saturate the air or gaseous mixtures.

The inner container 15 may be constructed in any desired manner but I have found that a satisfactory construction is to employ a cylinder 16 of unglazed porcelain or other suitable material permitting the diifusion of air and gases therethrough and to clamp the porous cylinder 16 between the metal top and

bottom pieces

26 and 27. Since the pieces 26 and 2'? are composed of metal, which is a relatively good conductor of heat, some of the heat produced by the filament 17 is conducted by the

pieces

26 and 27 and dissipated by radiation. The cooling effect may be enhanced if desired by providing cooling fins on the metal portions of the inner container 15. Positive cooling means may also be employed such as the cooling coils 28 through which water may be circulated by means not shown. Although I have shown means both for humidifying the gaseous mixtures surrounding the inner container and for cooling the inner portions of the container, it will be understood that it is ordinarily not necessary to employ both humidifying and cooling means to insure sufiicient humidity in the inner portion oithe container 15. One or the other means, or means of both types may be employed, depending upon the conditions under which the apparatus operates.

The

bolts

29 and 29 serve not only as electrical conductors but also as supporting means for holding the

parts

26 and 27 together and attachv ing, the inner container 15 to the top piece 30 of the outer container 11. Links 31 and 32 provide electrical connections from the

bolts

29 and 29 to the bolts 33 and 3a to which the electrical filament 17 is attached. An electrical circuit is 1;.

formed from battery 18 through conductor 35, bolt 29, link 31, bolt 33, electrical filament 1'], bolt 34, link 32, bolt 29 and conductor 36, back to battery 18. Suitable bushings 3'7 are provided for insulating the conducting members I.

from other metallic portions of the apparatus.

The form of pressure-responsive means here illustrated comprises a pair of

circular diaphragms

38 and 39 sealed at their circumferences and supported by a tube 40 by means of which cooperates with a stationary contact 44.

When a partial vacuum is created within the interior of the inner container 15 the diaphragm 39 approaches diaphragm 38 and causes the contact 43 to move against the contact 44, there by closing the circuit through battery 45 and The apparatus the winding of contactor 46. may be arranged to control the operation of other apparatus, to set in operation alarm devices or may be arranged in any other suitable manner as will be Well understood by those skilled in the art to provide indications or desired responses to the presence of combustible gas in the inner container 15. Although I have shown a specific type or" pressure-responsive means, it will be understood that my invention is not limited to this exact arrangement.

Although the principal use of the apparatus is for the detection of fire damp or methane in mines and similar locations, it may be utilized for the detection of other poisonous or explosive gases as well. The operation of the device depends upon the fact that the gases to be testedare combustible or inflammable, but it so happens that most of the poisonous gases to which workers may be subjected without being aware thereof are combustible gases. Such gases usually contain hydrogen. In case of fire damp or marsh gas the COIllbLlS-ilOIl takes place according to the equation CH4+ 202=CO2 21-120.

It will be observed that as long as the substances, the formulas of which are given in the equation, retain their gaseous form and remain at the same temperature and pressure, the volume of the initial substances is the same as that of the products of combustion since each side of the equation contains 3 molecules of gas and since, in accordance with Avogadros hypothesis, under the same physical conditions, all gases occupy the same volume for a given number of molecules. However, the water vapor formed is condensed, as a result of the high humidity maintained in inner container 15, thereby reducing the number of gaseous molecules in the products of combustion and creating a partial vacuum within the inner container.

A similar chemical relationship exists in the case of any other obnoxious hydrocarbon gases since one of the products of combustion in each case is water vapor. However, the apparatus is obviously not limited to the detection of hydrogen or hydrocarbon gases in air. Although a chemical union between another substance and oxygen is the most general example of combustion, it will be understood that the term combustion also applies to the chemical union of substances with substances other than oxygen, and in using the term combustion or combustible in the claims appended hereto, I mean to include such chemical reactions as well as the burning of substances in oxygen or air. An example of burning in a substance other than oxygen is the chemical union of hydrogen and chlorine, a reaction which evolves heat and resembles the burning of hydrogen in oxygen. If the apparatus is utilized for detecting the presence of hydrogen and chlorine in a mixture of gases, it is obviously essential in this case also to maintain sufiicient humidity within the inner container 15 in order to insure the presence of condensed water in the inner container which serves to absorb the HCl produced so as to create a partial vacuum and cause the operation of the pressure-responsive apparatus.

Although I have shown a specific arrangement for humidifying the gaseous mixtures to be tested by my apparatus, it will be understood that I am not limited to the exact arrangement disclosed. Modified means, for example, for insuring a relatively high humidity within the inner container 15 are illustrated in Figs. 2 and 3. The specific modifications shown, however, are not my invention, but are described and claimed in the copending application of Fred L. Stone, filed May 12, 1932, Serial No. 616,881 and assigned to the same assignee as the present invention. In the modification illustrated in Fig. 2, the apparatus is suspended from a suitable support 17 and the container 15 is provided with a metal top 26 as shown in Fig. l, but the lower portion 48 is composed of a porous plate instead of a metal plate. In this arrangement the igniting filament 17 is supported from above by means of tapped rods 49 andv 50 which also serve as electrical conductors. A felt pad 51 is fastened below and in contact with the plate 48. A wick 52 is in con tact with the edges of the felt pad 51 and serves to raise water by capillary attraction from the body of water 26 in a suitable container which is not shown. Capillary attraction causes the felt pad 51 to be kept moistened and the pad in turn keeps the porous plate 48 saturated. Since the air or gaseous mixture within the con-' tainer 15 is in contact with the moist inner surface of the saturated plate 48, relatively high humidity is maintained within the container 15, thereby insuring the condensation of water vapor formed by combustion as explained in connection with Fig. 1.

A further modification is illustrated in Fig. 3 in which the porous plate forming the bottom of the container 15 takes the form of a cup 53 of unglazed porcelain or other suitable material projecting into a body of water 20 carried by a receptacle 54. The receptacle 54 communicates with reservoir 21 by means of a tube 22, and means are provided to guard against the receptacle 54 running dry. A float 55 carried by a rod 56 is provided in the reservoir 21 and when the level of water therein falls below a certain point, the projection 5'? carried by the rod 56 causes the mercury switch 58 to trip thereby closing the circuit through battery 59 and a suitable device such as an electric bell 60 serving to give a warning when the quantity of water in the reservoir 21 is exhausted.

In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

. What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. A device responsive to the presence of combustible gases in a mixture of gases, comprising a container having porous walls, means for surrounding said container with a mixture of gases to be tested, means for humidifying said mixture, said porous walls serving to permit difiusion of said mixture into said container, means within said container for causing the combustion of combustible gases therein, means for maintaining a relatively low temperature within said container, and means responsive to fall in pressure within said container resulting from combustion of gases therein.

2. A device responsive to the presence of combustible gases in a mixture of gases, comprising an outer container, an inner container having porous walls and located within the upper portion of said outer container, a quantity of water in the lower portion of said outer container, said outer container having an inlet in its lower portion and an outlet at its upper portion, a porous plate in the lower portion of said outer container separating the space near said inlet from the remaining space within said outer container, means for passing said mixture of gases to be tested into said outer container at said inlet through said porous plate into the water in the lower portion of said outer container into the upper portion of the outer container and out through said outlet, thereby humidifying said mixture of gases, the porous walls of said inner mixture into said container, means within said container for causing the combustion of combustible gases therein, means for humidifying the space within said container to facilitate the reduction in volume of products of combustion, means for maintaining a relatively low temperature within said container to further facilitate reduction in volume of products of combustion, and means responsive to fall of pressure within said container resulting from combustion of gases therein.

- ABRAHAM L. MARSHALL.