US2582647A

US2582647A - Method and means for indicating changes in the composition of a gas

Info

Publication number: US2582647A
Application number: US69226A
Authority: US
Inventors: Thomas D Morgan
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1949-01-04
Filing date: 1949-01-04
Publication date: 1952-01-15
Anticipated expiration: 1969-01-15

Description

Jan. 15, 1952 T. D. MORGAN 2,582,647 METHOD AND MEANS FOR INDICATING CHANGES IN THE COMPOSITION OF A GAS Filed Jan. 4, 1949 l I 1142 l||||||||| 44 INVENTOR.

A 7' TORNEVS Patented Jan. 15, 1 952 METHOD AND MEANS FOR INDICATIN CHANGES IN THE COMPOSITION OF AGAS Thomas D. Morgan, Bartlesville, kla., assignor to l'hillips Petroleum Company, a corporation oi Delaware Application January 4, 1949, Serial No. 69,226

13 Claims.

This invention relates to a method of determining changes in the composition ot a gas and apparatus for carrying out the method. In one specific aspect it relates to determining diflerences in composition of a gas by changes in the ionization of the gas as determined by the amount of current carried by positive ions in said 88. In another specific aspect it relates $0 bombarding molecules of gas by low speed electrons to iorm positive ions. conducting a current through said positive ions and measuring the amount of said current.

Claims relating to a specific means for regulating the gas pressure in a chamber comprising evacuating means, gas supply means, conduit means, pressure regulating valve means, and a restricted orifice for controlling gas flow in the conduit have been made the sub ect matter of my copending divisional application, Serial No. 240,244, filed August 3, 1951.

It has been observed that the sum of the ions in a mass spectrum varies from one gas to another. -This sum is proportional to the total number of positive ions formed when a gas is bombarded by low speed electrons.

Many complicated means have been proposed in prior art for determining when the composition of a gas, such as a stream of gaseous product coming from a process in a plant. changes in composition, in order to monitor the process by indicating that the process is continuing as planned. When the composition of the gas varies, the process involved is not operating properly, and changes are made to restore the operation to normal. Prior art devices testing the stream of gas generally have relied on analysis of the gas by means of spectro-graphic analysis, chemical analysis, analysis by mass spectrometer, or some other relatively complicated and slow form of analysis.

The present invention gets away from such complicated and expensive means of analysis by relying on the simple fact that each gas forms a diiferent number of positive ions when bombarded under the same conditions by low speed electrons. The present invention also avoids indicating false changes in the composition of the gas caused by irregular thermal cracking of the original gas into other gases by contact with the filament from which the low speed electrons are being supplied. This is avoided by means of a novel arrangement of the filament, grids and plate so that the gas entering the test apparatus is subjected to low speed electron bombardment and the current is set up in the positive ions 01 the gas between a first grid and the plate before the gas passes through said first grid into contact with the heated filament. The gas which has contacted the heated filament and become thermally cracked is removed from the system from 2 the other side of the grid from the gas which is conducting the indicating current.

One ob ect of my invention is to provide an improved method of detecting and indicating dinerences in the composition of a gas.

Another object is to provide improved apparatus for carrying out such a method.

Another object is to provide such a method and apparatus in which the positive ions conducting the current are bombarded by low speed electrons without coming in contact with any heated element which would change their composition by thermal cracking or the like.

Another object is to provide an improved method and means of detecting a difierence in the composition of the gas by measuring an ionization current in said gas in an improved ionization tube.

Another object of the invention is to detect and indicate changes in the tube of a, gas stream and thereby to qualitatively determine the gas ,3 causing the deviation from the indication given by a gas or standard composition.

Another object is to indicate changes in the composition of a gas to provide a monitor which indicates when changes in a process of producing a gas should be made.

With a pure gas an object of the invention is to give an indication of the presence of impurities in said gas.

With binary mixtures of gases an object of the invention is to analyze the mixture to determine the exact percentage of each gas present.

With mixtures 01 known gases an ob ect of the inventionis to analyze the mixture to determine the exact percentage of each gas present.

Another object is to provide an improved gas ionization tube which is rugged, simple in composition, is not efiected by products of thermal cracking, and which is relatively cheap and easy to operate.

Another object is to provide a suitable means of supplying gas to such a tube at a regulated pressure. I

Numerous other objects and advantages will be apparent upon reading the accompanying specification claims and drawings.

Figure 1 is an elevational view with parts in cross section of an ionization tube and means to supply the same with a stream of gas to be tested embodying the present invention, along with a wiring diagram for the same.

Figure 2 is an elevational view of a similar system employing the same type of ionization tube but having amodified system for supplying gas.

In Figure 1 a device tor indicating changes in the composition of a gas by ionization currents generally designated as 3 is attached to a pipe 4 containing a flowing stream of gas which passes out through pipe 6. A small amount of this gas is constantly being drawn into instrument 3 through pipe 1 under the control of a constant pressure regulating valve 8 which is designed to maintain the pressure in space 9 at a substantially constant pressure.

Also connected to apparatus 3 is an exhaust pipe II by which the interior of 3 is exhausted to a substantially constant pressure of approximately 10- mm. of mercury by means of any suitable vacuum pump l2. Vacuum pump I2 is regulated by constant pressure regulator l3 which may be of any usual type, regulator l3 being controlled as shown by the dotted lines between the pressure regulator l3 and tube Vacuum pump |2 discharges through line l4 to the atmosphere. In many installations with various types of vacuum pumps l2, it has been found that one pump alone does not provide a constant enough vacuum and it is customary to use separate pumps (not shown) in series in pipe H with pump |2. For example, pump l2 could be a VMF-20 oil diffusion pump and downstream in line l4 (not shown) and connected in series therewith a VMF-5 oil diffusion pump and then a Welch duo seal force pump. Also in line H before entering pump l2 an ice trap (not shown) may be provided. Chambers containing desiccant (not shown) could supplement the ice trap if the gas being tested contains water vapor. As such elaborations on vacuum pump |2 are well known in the art of evacuatin vessels it is not believed desirable to confuse the invention by elaborating on the type of vacuum pump system used at l2, it being understood that any suitable system known to the prior art for producing a vacuum in the neighborhood of mm. of mercury which can be regulated to give a relatively constant pressure in tube II is satisfactory in the practice of the present invention.

The pressure in the space 9 is of course considerably higher than 10- mm. of mercury because it is difilcult to find a regulating valve 8 which is accurate at such a pressure, however any system known to the prior art for getting the pressure in line 4 down to the desired pressure in space is may be employed. I prefer however to employ a restricted orifice H in a thickened portion l8 of tube 1 so that the pressure in space 9 may be in the neighborhood of 2 mm. of mercury while that in space l6 and space H is approximately 10- mm. of mercury.

While other shapes of apparatus may be employed provided the principle of operation is the same, it is preferred to use as the ionization tube IQ of apparatus 3 a cylindrical tube preferably made of glass. A plate 2| is provided inside the tube, which plate should have a considerable extent and preferably extends entirely around the tube to serve as the ion collector plate. I find the best way of forming this plate is to vaporize and deposit platinum on the glass surface of tube l9. Metallic plate 2| is connected to wire 22. A source of negative electrons is provided and is shown in the form of a naked tungsten metal filament 23; Other metal filaments may be employed provided they are not poisoned by gases. Obviously other types of heated cathodes may be employed, for example the filament 23 may be sheathed in a porcelain tube (not shown which porcelain tube is heated to incandescence and this porcelain tube may have metallic substances such as tungsten metal deposited thereon. However it is not believed necessary to go into detail on the electron emissive cathode 23 as such cathodes are well known in the electron art and any type producing slow electrons is satisfactory. By slow electron I mean an electron having a velocity within the ranges understood by those skilled in the art which upon being accelerated by grid 24 would be suitable for causing the formation of positive ions in the gas in the pressure of 10'- mm. of mercury. I have chosen a pressure of the ma nitude of about 10- mm. of mercury because at that pressure positive ions are more easily and more uniformly formed by electron bombardment, but those skilled in the art can easily predict the amount this pressure can be changed without departing from the present invention, for as long as the same type of operation occurs the process is unchanged and the present invention is being employed.

Between the electron source 23 and the positive collection plate 2| I prefer a positive charged grid generally designated as 24. Grid 24 is preferably composed of two elements, the first bein a helical wire 26 suitable for degassing the metallic parts of tube l9 as will be explained later and a gauze wire cylinder 21 maintained at the same potential by wire 28. Tube 21 extends entirely around filament 23 but to avoid confusion, has not been drawn except where it is in section, as drawing all of the wires in cylinder 21 in back of filament 23 would make it almost impossible to see filament 23.

While the particular mode of supporting grid 21 is immaterial I prefer to imbed the lower end in an annular glass boss 29 formed in the wall of tube l9 and the upper end of 21 is similarly imbedded in the lower end of tube 3| which forms an extension of tube II. It will be obvious that gas coming from l6 passes in space 32 between plate 2| and grid 21 before passing through grid 21 and out tube 3| and tube II, and it will also be obvious that any of the gas which contacts heated filament 23 and is thermally cracked thereby will pass up tube 3| without reaching plate 2|.

The Wiring diagram will now be explained. In order to have a reference point let us say that wire 33 is at an intermediate potential. Filament 23 is at the same potential at the top of the filament but there is a difference of about the magnitude of 5 volts provided by battery 34 and rheostat 36 between the ends of the filament which are connected to

wires

31 and 38. Most of the current from battery 34 is forced to go through

wires

31 and 38 by relatively high resistances 39 and 4|, which however allow wire 33 to be at the same average potential as filament 23.

Plate 2| is preferably maintained at a lower potential than filament 23, but this is not essential as long as plate 2| is at a considerably lower potential than grid 21 in order that positive ions created in the space between grid 21 and plate 2| will be urged toward plate 2| by electrostatic forces and will conduct a current thereby to plate 2|. As shown in the drawing it is preferred to provide a battery 42 which will keep plate 2| about 12 volts or so below the potential oi filament 23 and about or volts below the potential of grid 21.

In the process of maintaining plate 2| at this potential it is necessary for current to flow from battery 42 through a milliammeter 43 to wire 22 because a current is being conducted by positive electrons between grid 21 and plate 2 I. Milliamthis current.

especially filament 23. grid 26 and grid 21.

The main source of difference in potential between plate 21 and grids 26 and 21 is battery 44, which is connected through instrument 46 with wire 41 leading to grid 26 and through wire 28 to grid 21. Battery 44 is preferably controlled by rheostat 45 to maintain a constant grid to filament current. Battery 44 is preferably in the neighborhood of 75 volts and in combination with battery 42 provides about 8'! volts potential drop between grid 21 andplate 2|. During normal operation milliammeter 46 indicates a filament to grid current of about milliamperes.

After relatively long continued use, and after any time the vacuum in tube l3 has been broken and air or other gas under substantially atmospheric pressure has been in space 32, I- have found that gas becomes occluded in the metal part: thereupon becomes desirable to drive oil this occluded gas because such gas tends to reduce the accuracy of the readings. For this purpose a wire 46 is connected to helical filament 26 and through battery 46, switch Ii and

wires

62 and 41 to the other end of grid 26. When switch 6| is closed, grid 26 is heated up by a suitable current from battery 43. I prefer battery 46 to be about 6 volts and pass a current of 4 or 5 amperes through grid 26.

It should be realized that while for illustrative purposes specific voltages, potentials and the like have been given that the invention is not limited thereby or thereto as any electronic engineer can modify these voltages and other electrical relationships within suitable ranges and still practice the present invention.

In Figure2, tube I3 is exactly the same as in Figure 1 and therefore is given the same reference numerals. The same is true of

wires

22, 41. 46 and

milliammeters

43 and 46 and the electrical circuit between said milliammeters and said tube. Pump l2, regulator l3 and exhaust pipe l4 are also the same and so are pipes 4. 6, 1 and regulator 8.

Between regulator 6 and restricted orifice l1 however a different form of apparatus has been inserted in order to regulate the pressure in tube l9 to a pressure in the neighborhood of 10- mm. of mercury. Regulator 6 discharges into pipe 53 at a constant pressure. A clock 64 drives a valve operating mechanism 66. This valve operating mechanism 66 first opens valve 61 by a means of solenoid valve operator 66. Valve 63 is closed. Valve 51 is reclosed and then valve 63 is opened by solenoid 6| controlled by clock 64 whereupon the gas in tube 62 expands from its pressure of several mm. of mercury and passes through pipe 63 into storage chamber to provide a source of gas. Valve 63 is then closed. Gas from 64 leaks uniformly through orifice l1 into tube I9 where the operation becomes the same as in Figure 1.

When intermittent operation is desired valve 65A is actuated along with valve 61 to open flow through pipe 65B by closing switch "D so that solenoids 65C and 66 are in parallel and operate in unison. While 62 fills through valve 61,

parts

63 and 64 are rapidly evacuated through pipe 653 by pump l2.

While the size of orifice l1 may be varied considerably I have obtained satisfactory results by making this orifice by punching a hole about 20 microns in diameter in a 0.0003" platinum plate with a sharpened needle and mounting the plate in the glass tube (not shown), or by forming a fine hole in the glass as shown.

Operation The operation of Figure 1 will now be described. Vacuum pump I2 is started up and the pressure in space 32 of tube It is lowered to somewhere in the neighborhood of 10- mm. of mercury. Switch ii is then closed a suitable length of time, say about 15 minutes, during which time grid 26 becomes incandescent driving any occluded gases, out of itself, out of filament 23, out of grid 21 and plate 2|. As fast as these occluded gases are driven on they are removed through pipe by vacuum pump l2, switch 5| is then opened and pump 12 continues to pump. out tube l9, grid 26 cools down and the system comes into a relatively stable state in a few minutes.

In this relatively stable state a relatively uniform representative sample of gas from pipe 4 is passing through regulator 6, through orifice l1, through space 32 between plate 2| and grid 21. through the meshes of grid 21 and on out through pipes 3| and II to vacuum pump l2.

Filament 23 is heated by battery 34 and is emitting slow electrons. A certain constant proportion of these slow electrons are accelerated by, attracted to and collide with positively charged grids 26 and 21, but a relatively con- ,stant number of electrons pass through grid 21 out into space 32 where they collide with gas molecules forming positive ions in the process of such collisions. At the selected predetermined uniform pressure, such as 10- mm. of mercury, the number of positive ions formed varies with the type of gas molecules struck by the electrons, while a certain constant proportion of these electrons are attracted by and fall back into grid 21. Therefore for any constant pressure in space 32 there is a definite number of positive ions formed per second depending on the composition of the gas in the space.

These positive ions in space 32 are in an electrostatic field because grid 21 is charged at a higher potential (preferably about to volts higher) than plate 2 I. The force of this electrostatic field moves the positive ions steadily over to plate 2| and because of this ion current the battery 42 is caused to supply an equivalent current through milliammeter 43 where it is indicated. Milliammeter 43 can be a recording milliammeter if desired, and in fact can be used to control machinery (not shown) which exists in the prior art, which can be so operated, by which the milliammeter 43 can control the process (not shown) producing the gas in pipe 4. However I prefer to merely indicate the change in the composition of gas, and then have someone investigate why this change is taking place and make suitable adjustments to restore the former composition of gas in pipe 4. Modern electronic controls are quite sensitive and can be operated by milliammeters, or by low level currents.

While milliammeter 43 is indicating the rate of ionization of the gas, milliammeter 46 is merely indicating the grid to filament current in tube I9 and should read a steady value in order to provide accurate operation of the device. Any desired steady grid to filament current can be maintained by adjusting rheostat 46 from time to time. While this can be done manually, it obviously is preferable to substitute one of the many constant current controls now on the market, as such an automatic electronic current control circuit (not shown) can do a better job of regulating the current in wire 41 to about 5 7 milliamperes than manual operation of rheostat I.

The operation of Figure 2 is very similar except for the means of lowering the pressure from line 4 down to that necessary in tube i8. In many plant operations the pressure in line 4 is too high to permit a single stage reduction of pressure by regulator 8, so in Figure 2 the pressure having been made constant by regulator 8 in pipe 53, a definite volume in pipe 82p: this gas under the pressure in pipe 63 is collected in pipe 62 by opening valve 51 and closing the same and then this gas is passed to storage vessel 64 at a low pressure by opening valve 59 and closing the same. The gas in vessel 64 is at a substantially uniform pressure during the

cycles employing valves

51 and 59 and by the time this gas passes through orifice l1 into chamber 19 it is at a substantially constant reduced pressure as desired. 1

It should be noted that after the gas passes through positively charged grid 21, contacts heated filament 23 and is thereby cracked to form a difierent gas, that any positive ions formed in this different gas by electrons emitted from filament 23 cannot get through grid 21 because they are repelled by the positive charge on the grid, and therefore they must pass up tube 3| and be exhausted by pump l2. Therefore it does not matter that filament 23 changes the composition of the gas by cracking because grid 21 protects the instrument from any variation in measurements due to the same. Other irregularities in ionization of the gas, such as thermal cracking and formation of ions on the surface of the filament itself, make the complete removal of gas passing close to the filament essential in order to achieve a high degree of accuracy.

EXAMPLE The readings of milliammeter 43 will vary from instrument to instrument, the relative readings will be different for the difierent gases and about of the order set forth in the following table. This table is made at a constant pressure of 10- mm. of mercury. Obviously all comparative tests should be made at the same constant pressure, as varying the pressure varies the amount of ionization. This selected constant pressure can be chosen from a quite wide range of pressures however, but preferably is chosen from the best range of operation, which runs from 10- mm. to 10- mm. of mercury, and I prefer the neighborhood of 10- mm. of mercury as the best range to operate it. Once the pressure is selected it is maintained constant as closely as it is possible to do so.

Table It should be obvious that if only butene-l and butadiene are present in tube 4 that a reading 8 intermediate 2.60 and 1.26 will be given at milliammeter 43. By tests of known amounts of these gases a calibration table can be prepared from which the reading can be translated into .definite percentages of each component. Other similar uses are obvious with more than two gases where only one gas varies. Other uses are suggested to those skilled in the art by this example.

While I have shown and described a certain arrangement of parts for carrying out the process of my invention and have described certain specific processes, these have been for purpose of illustration and obviously my inventionis not limited thereto but instead is as defined in the following claims.

Having described my invention, I claim:

1. The process of indicating a change in the composition of a gas which comprises passing a sample of the gas at a constant low pressure through a zone where it is subjected to a bombardment of slow electrons to form a first group of positive ions at a rate dependent upon the composition of the gas, collecting said first group of positive ions on a .negatively charged plate, measuring the electric current resulting therefrom, and protecting said first group of positive ions from contamination with a second group of positive ions formed from such portions of said gas as come in contact with the source of such electrons and crack thereon by repelling said second group of positive ions with a positively charged screen.

2. A gas analyzer comprising in combination a chamber, means for takin a sample of a stream of gas, means for reducing and keepin the pressure of saidsample at a constant value and passing itinto said chamber, an exhaust conduit connected to said chamber, means to exhaust said exhaust conduit and thereby exhaust said chamber, a cathode in said chamber, means to heat said cathode so it will emit electrons, a screen surrounding said cathode .and connected to the walls of said exhaust conduit and said chamber so as to isolate said cathode and said exhaust conduit from the rest of said chamber. a positive ion collecting element in said chamber on the other side of said screen from said cathode, means to heat said cathode, screen and element to drive out any gases occluded therein, means to maintain said screen positive relative to said cathode and means to maintain said element negative relative to said screen.

3. A gas analyzer comprising in combination a chamber, means for taking a sample of a stream of gas, means for reducing and keeping the pressure of said sample at a constant value and passing it into said chamber, an exhaust conduit connected to said chamber, means to exhaust said exhaust conduit and thereby exhaust said chamber, a cathode in said chamber, means to heat said cathode so it will emit electrons, a screen surrounding said cathode and connected to the walls of said exhaust conduit and said chamber so as to isolate said cathode and said exhaust conduit from the rest of said chamber, a positive ion collecting element in said chamber on the other side of said screen from said cathode, means to maintain said screen positive relative to said cathode and means to maintain said element negative relativeto said screen.

4. In a gas analyzer an evacuated chamber, and means to regulate the pressure in said chamber comprisin vacuum pump means for evacuating said chamber to a predetermined pressure, and means supplying gas to maintain said pressure comprising a source of said gas at greater than atmospheric pressure, a conduit connecting said source and said chamber, a constant pressure regulating valve in said conduit receiving gas from said source and passing it under reduced pressure through said conduit, and a restricted orifice controlling flow from said conduit into said evacuated chamber, said chamber having a cen tral depending exhaust duct and an inlet duct disposed to discharge against said exhaust duct, a screen sealed to and completely surrounding said exhaust duct and forming said chamber into two portions isolated by said screen, a cathode on the exhaust duct side of said screen, and a film of deposited metal on the walls of said chamber on the inlet side of said screen.

5. An ionization tube comprising in combination a glass chamber having a central depending exhaust duct and a radial inlet duct disposed to discharge against the side of said exhaust duct,

-a gauze screen sealed to and completely surrounding said exhaust duct and forming said chamber into two portions isolated by said screen, a cathode and screen heating means on the exhaust duct side of said screen, and a film of deposited platinum metal on the walls of said chamber on the inlet side of said screen.

6. An ionization tube comprising in combination a glass chamber havinga central depending exhaust duct and an inlet duct disposed to discharge against the side of said exhaust duct, a screen sealed to and completely surrounding said exhaust duct and forming said chamber into two portions isolated by said screen, a cathode and screen heating means on the exhaust duct side of said screen, and a film of deposited platinum metal on the walls of said chamber on the inlet side of said screen.

7. 'An ionization tube comprising in combination a glass chamber having a central depending exhaust duct and a radial inlet duct disposed to discharge against the side of said exhaust duct, a gauze screen sealed to and completely surroundingsaid exhaust duct and forming said chamber into two portions isolated by said screen, a cathode on the exhaust duct side of said screen, and a film of deposited platinum metal on the walls of said chamber on the inlet side of said screen.

8. An ionization tube comprising in combination a chamber having a central depending exhaust duct and a radial inlet duct disposed to discharge against said exhaust duct, a gauze screen sealed to and completely surrounding said exhaust duct and forming said chamber into two portions isolated by said screen, a cathode and screen heating means on the exhaust duct side of said screen, and a film of deposited metal on the walls of said chamber on the inlet side of said screen.

9. An ionization tube comprising in combination a chamber having a central depending exhaust duct and an inlet duct disposed to discharge against said exhaust duct, a screen sealed to and completely surrounding said exhaust duct and forming said chamber into two portions isolated by said screen, a cathode on the. exhaust duct side of said screen, and a film of deposited metal on the walls of said chamber on the inlet side of said screen.

10. The method of determining the varying percentage of one gas in an otherwise substantially constant gas mixture,- comprising forming positive ions in said gas mixture by subjecting said gas to electrons thermally ejected from a hot cathode, and measuringthe current conducted by said ions at a given potential, and repelling positive ions of said gas cracked by contact with the cathode back toward the cathode and evacuating the same before they can conduct said current.

11. An ionization tube comprising in combination a chamber having an exhaust duct and an inlet duct, an accelerator screen in said chamber completely separating said ducts, a cathode in said chamber on the exhaust duct side of said screen, apositive ion collecting element in said chamber on the inlet duct side of said screen, and means to heat said cathode.

12. An ionization system comprising an ionization tube comprising in combination a chamber having an exhaust duct and an inlet duct, a vacuum pump disposed to draw gas from said exhaust duct, means to supply predetermined amounts of gas to said inlet duct, an accelerator screen in said chamber completely separating said ducts, a cathode in said chamber on the exhaust duct side of said screen, a positive ion collecting elementin said chamber on the inlet duct side of said screen, and means to heat said cathode.

13. An ionization system comprising an ionization'tube comprising in combination a chamber having an exhaust duct and an inlet duct, a vacuum pump disposed to draw gas from said exhaust duct, means to supply predetermined amounts of gas to said inlet duct, a screen in said chamber completely separating said ducts, a cathode in said chamber on the exhaust duct side of said screen, a positive ion collecting element in said chamber on the inlet duct side of said screen, means to maintain said screen positive relative to said cathode, means to maintain said element negative relative to said screen, and means to heat said cathode.

THOMAS D. MORGAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 674,840 Hoffman May 21, 1901 930,989 Richards Aug. 10, 1909 1,212,163 Tigerstedt Jan. 9, 1917 1,334,143 Dushman Mar. 16, 1920 1,421,720 Roberts July 4, 1922 2,127,229 McRae Aug. 16, 1938 2,149,045 Farnsworth Feb. 28, 1939 2,400,940 McCollum May 28, 1946 2,454,564 Nelson Nov. 23, 1948 2,455,437 Nagel et al. Dec. 7, 1948 2,468,261 Hillier Apr. 26, 1949 FOREIGN PATENTS Number Country Date 586,594 Great Britain May 20, 1941 OTHER REFERENCES Thermionic Vacuum Tube by Van Der Bill, pages 375, 376, 377.

General Electric Review, June 1946, pages38 to 42, article by Van Valkenberg.

Claims

1. THE PROCESS OF INDICATING A CHANGE IN THE COMPOSITION OF A GAS WHICH COMPRISES PASSING A SAMPLE OF THE GAS AT A CONSTANT LOW PRESSURE THROUGH A ZONE WHERE IT IS SUBJECTED TO A BOMBARDMENT OF SLOW ELECTRONS TO FORM A FIRST GROUP OF POSITIVE IONS AT A RATE DEPENDENT UPON THE COMPOSITION OF THE GAS, COLLECTING SAID FIRST GROUP OF POSITIVE IONS ON A NEGATIVELY CHARGED PLATE, MEASURING THE ELECTRIC CURRENT RESULTING THEREFROM, AND PROTECTING SAID FIRST GROUP OF POSITIVE IONS FROM CONTAMINATION WITH A SECOND GROUP OF POSITIVE IONS FORMED FROM SUCH PORTIONS OF SAID GAS AS COME IN CONTACT WITH THE SOURCE OF SUCH ELECTRONS AND CRACK THEREON BY REPELLING SAID SECOND GROUP OF POSITIVE IONS WITH A POSITIVELY CHARGED SCREEN.

4. IN A GAS ANALYZER AN EVACUATED CHAMBER, AND MEANS TO REGULATE THE PRESSURE IN SAID CHAMBER COMPRISING VACUUM PUMP MEANS FOR EVACUATING SAID CHAMBER TO A PREDETERMINED PRESSURE, AND MEANS SUPPLYING GAS TO MAINTAIN SAID PRESSURE COMPRISING A SOURCE OF SAID GAS AT GREATER THAN ATMOSPHERIC PRESSURE, A CONDUIT CONNECTING SAID SOURCE AND SAID CHAMBER, A CONSTANT PRESSURE REGULATING VALVE IN SAID CONDUIT RECEIVING GAS FROM SAID SOURCE AND PASSING IT UNDER REDUCED PRESSURE THROUGH SAID CONDUIT, AND A RESTRICTED ORIFICE CONTROLLING FLOW FROM SAID CONDUIT INTO SAID EVACUATED CHAMBER, SAID CHAMBER HAVING A CENTRAL DEPENDING EXHAUST DUCT AND AN INLET DUCT DISPOSED TO DISCHARGE AGAINST SAID EXHAUST DUCT, A SCREEN SEALED TO AND COMPLETELY SURROUNDING SAID EXHAUST DUCT AND FORMING SAID CHAMBER INTO TWO PORTIONS ISOLATED BY SAID SCREEN, A CATHODE ON THE EXHAUST DUCT SIDE OF SAID SCREEN, AND A FILM OF DEPOSITED METAL ON THE WALLS OF SAID CHAMBER ON THE INLET SIDE OF SAID SCREEN.