US2404993A

US2404993A - Gas analyzer

Info

Publication number: US2404993A
Application number: US314899A
Authority: US
Inventors: Alan P Sullivan
Original assignee: Cities Service Oil Co
Current assignee: Cities Service Oil Co
Priority date: 1940-01-22
Filing date: 1940-01-22
Publication date: 1946-07-30
Anticipated expiration: 1963-07-30

Description

July 30, 1946. A. P. SULLWAN GAS ANALYZER Filed Jan. 22, 1940 "w ENTOR All/4N f. JULLlV/l/V avg ATTORNEY Patented July 30, 1946 GAS ANALYZER Alan P. Sullivan, Elizabeth, N. J., assignor to Cities Service Oil Company, New York, N. Y., a corporation of Pennsylvania Application January 22, 1940, Serial No. 314,899

3 Claims. 1

This invention relates to gas analyzers, and more particularly to an apparatus adapted to give accurate and sensitive measurements of the oxygen and combustible content of a gas in either low percentages or relatively high percentages of oxygen and combustibles.

The invention is particularly adapted for the analyses of exhaust gases, such as domestic and industrial furnace exhaust gases, Diesel and gasoline engine exhaust gases; and for other types of gases, such as mine gases and atmospheres in which the percentage of the combustibles and oxygen is not very large.

The apparatus of this invention is an improvement on and a continuation in part of the apparatus described in the Patent No. 2,273,981, issued February 24, 1942, to John D. Morgan and Alan P. Sullivan.

In the apparatus of the above patent, the gas to be analyzed is ignited in a combustion chamber by means of a platinum or platinum-alloy catalyst wire, which forms one leg of a Wheatstone bridge. The heat of combustion of the gas raises the temperature of the catalytic leg of the Wheatstone bridge, thus increasing its resistance proportionally to the amount of combustibles or oxygen in the gas. This change in the amount of resistance is indicated on a galvanometer connected across the Wheatstone bridge circuit.

The most efficient operatin temperature range for the catalyst wire in a gas analyzer of this type has been found to be from l400 to 1600 F.

If a platinum or platinum-alloy catalyst wire is operated below 1400 F. for the ignition of exhaust gases, such as exhaust gases from an internal combustion engine which contain partial oxidation products of hydrocarbons, the catalyst will lose its activity in a very short time due to poisoning. In other types of gases burned below 1400" F. the ignition is irregular and not dependable, due to incomplete combustion and formation of partial oxidation products.

The loss of activity of the catalyst wire due to poisoning above 1400 F. has been eliminated by the manner of assemblage and treatment of the catalyst as described in Patent 2,273,981.

When a platinum or platinum-alloy catalyst wire i operated above 1600 F., its life is considerably shortened due to the vaporization of the wire.

Such an apparatus, as described in the Patent No. 2,273,981, has been found to give accurate and sensitive analyses of a gas in the range of the percentage of oxygen and combustibles for which it was designed; but it is not suitably adapted to 2. give sensitive analyses of gases whose oxygen and combustible content varies over a wider percentage range. This lack of sensitivity of a single range apparatus for analyses in wide percentage ranges results from the necessity of the operation of the catalyst wire in a temperature range of 1400" to 1600 F. in order to insure long life, accuracy, and sensitivity to the catalyst wire.

The primary object of the invention is to provide a simple, accurate, and sensitive gas analyzer which can be used for measuring the oxygen and combustible content of gases in either a range of high or low percentages of oxygen and combustibles; and yet maintaining the temperature of the catalyst wire in the most effioient opcrating temperature range of 1400 to 1600 F.

Another object of the invention is to provide a gas analyzing apparatus which is adapted to be used as an indicating means for adjusting domestic furnaces, industrial furnaces, Diesel engines, and gasoline engines to the highest degree of opcrating efficiency.

The present invention is particularly adapted for analyses of gases exhausted from steam boiler furnaces, metallurgical furnaces, and internal combustion engines, particularly gasoline engines and Diesel engines. The exhaust gases from a gasoline engine rarely have free oxygen content, but all the other gases from the diiTerent types of furnaces and engines usually have both oxygen as well as combustible constituents. The apparatus is therefore well adapted for analyzing gases having both oxygen and combustible content, as the sample taken into the apparatus is divided and each part analyzed simultaneously.

The apparatus is so designed that a very short lag exists between the time that the sample is taken into the apparatus and the time that the analyses are determined. Therefore, this apparatus may be used for accurately controlling combustion in all types of furnaces and internal combustion engines.

Fundamentally, the apparatus of this invention provides for the simultaneous measurements of the combustible content, the oxygen content, and the temperature of the gas to be analyzed; keeping the catalyst wire temperature in the range of 1400 to 1600 F. and nevertheless obtaining sensitive measurements regardless of the amount of oxygen and combustibles in the gas.

In the operation of the gas analyzer, the gas sample is divided into two parts. Hydrogen is added to one part, and the mixture of hydrogen and sample gas is conveyed to the oxygen analyzing chamber to be analyzed to determine its oxygen content. Air is added to the other part, and the mixture of air and sample gas is conveyed to the combustible nalyzing chamber to be analyzed to determine its combustible content. An electrically heated catalytic combustion Wire, suspended in each of the analyzing chambers, ignites the gaseous mixture passing through the chamber; and the resulting heat of combustion increases the resistance of the catalyst wire proportionally to the amount of oxygen or combustibles in the gaseous mixture. The catalyst wire in each analyzer forms a leg of a Wheatstone bridge circuit, and the increased resistance of each catalyst wire is measured directly in percentage of oxygen or combustibles on a millivoltmeter connected across each Wh'eatstone bridge circuit.

In analyzing a gas for its oxygen content, the apparatus may be designed to operate in any of two percentage ranges. The ranges selected for the preferred form are: to 4% oxygenlow range, and 0% to 20% oxygen-high range. To operate the analyzer in the low range, the apparatus is adjusted in such a way that the volume of hydrogen added to the gas is decreased to approximately one-fifth the volume added when operating in the high range; and the amount of the mixture of gas and hydrogen burned by the catalyst wire is approximately five times that amount burned when operating in the high range. These adjustments are accomplished by the operation of a multipole switch, which is electrically connected to an electrolytic hydrogen generator, and mechanically connected to a bafiie located in the combustion chamber. By turning the switch to the low range position, a resistance is connected into the electrolytic hydrogen generator circuit order to decrease the generation of hydrogen, and the bafiie in the combustion chamber is moved out of the path of flow of the gas mixture to the catalyst wire, such that more gas mixture will be ignited by the catalyst wire. By these adjustments, the catalyst wire will operate in the same temperature range for both the high and low percentage ranges.

In analyzing a. gas for its combustible content, the apparatus may be designedto operate in any of two percentage ranges. The ranges selected for the preferred form are, 0% to 4% combustibles-low range, and 0% to 20% combustibleshigh range. When operating the analyzer in the low range, the apparatus is adjusted such that a mixture of live parts sample gas and one part air is ignited by the catalyst wire. When operating in the high range, the apparatus is adjusted such that a mixture of one part sample gas and five parts air is ignited by the catalyst wire. The adjustment of the mixture ratio is performed by use of a switch which is mechanically connected to a movable valve in the proportioning pump. The proportioning pump has two suction ports, one of which draws in five volumes of gas while the other port draws in one volume of gas. When the switch is turned to the low range position, the movable valve is adjusted to connect the five volume suction port to the sample gas inlet, and the one volume suction port to the air inlet. In the high ringe position, the five volume suction port is connected to the air inlet and the single volume suction port is connected to the sample gas inlet. The catalyst wire will operate in the same temperature range for both the high range and low range analysis positions.

The invention which has been broadly explained will now be specifically described in connection with the accompanying drawing, which illustrates a flow and wiring diagram of the preferred form of the invention.

Referring to the drawing, a continuous sample of the gas to be analyzed is withdrawn from pipe I, which pipe may be the stack of a furnace or the exhaust pipe of a combustion engine. This sample is conveyed through conduit 2 to a gas filter 3, where suspended liquid and solid material, such as water and dust, are removed from the gas by a cotton filter contained therein.

This cleaned and dried gas sample is conducted through conduit 4 to a valve 5. With valve 5 in the position illustrated, the gas passes through passage 0 into conduit 1, through which it passe" to suction port 8 of the rotary sliding vane pump 9.

The pump 9 rotates at a constant speed in a counterclockwise direction, having one suction port 8, and two discharge ports to and M. The function of pump 8 is to discharge a constant flow of gas at port ll regardless of variation in the pressure of the gas entering the pump.

This is accomplished by the use of the atmospheric discharge port iii, which is located a little more than 45 in the direction of rotation past the point of maximum clearance between the rotor and the inner peripheral surface of the pump housing. As the gas passes this atmospheric discharge port ill at varying pressure, it is brought to atmospheric pressure, and any gas in excess passes out through the passage of port l0. The gas is compressed between the atmospheric discharge port I0 and the sample discharge port II, such that a constant uniform flow of gas is exhausted from the pump into conduit !2, regardless of any variation in the pressure of the gas entering the pump 9 at suction port 8.

The sample gas pumped into conduit i2 is conveyed therein to aperture M of oxygen analyzing chamber [3. The sample gas is analyzed in chamber l3 for its oxygen content by igniting a mixture of sample gas with hydrogen. The amount of hydrogen added to the sample gas is in slight excess of the amount of hydrogen required to react with the oxygen of a gas sample.

The hydrogen for the oxygen analysis is gen-- erated at a constant rate by an electrolytic hydrogen generator l5, which generator has an anode I6 separated from a cathode i? by an asbestos diaphragm l8; all of said parts being immersed in an electrolytic solution, such as a solution of sodium hydroxide. The hydrogen generated at cathode I! passes through conduit I9 to valve 5, through which it flows by means of a peripheral groove 20 into a conduit 2!. The hydrogen flowing through conduit 2| enters conduit l2, mixes with the sample gas flowing therein, and the mixture enters aperture I4 of the oxygen analyzing chamber I3.

In the oxygen analyzing chamber IS a catalytic ignition wire 22 is supported on one of the posts 23, which posts are surrounded by an impervious metallic cylindrical shield 24. A movable baflle 25 is supported over the shield 24, said baffle 25 having a central bore 26, and four openings 21 leading to the bore 26 from the side of the bafile.

The mixture of sample gas and hydrogen entering the oxygen analyzing chamber I 3 by the aperture 14, passes upwardly around the outside of the impervious shield 24. With the baflie 25 in the position illustrated, part of the mixture of sample gas and hydrogen passes into the shield 24 by diffusion and convection currents to be ignited by the catalyst wire 22 contained therein.

The remainder of the gas-hydrogen mixture along with the products of combustion pass upwardly out of the oxygen analyzing chamber |3 by way of the bore 26 of the baffle 25.

If the baflle is lowered to rest on the top of the shield 24, the air-hydrogen mixture after entering the oxygen analyzing chamber l3 passes through the side openings 21 into the bafile 25 and down through the bore 26 into the shield 24. Much less gas mixture enters shield 24 to be ignited by catalyst wire 22 when baffle 25 is lowered on shield 24. The area of accessibility of the gas to enter shield 24 by way of the bore 26 is much less than the area of accessibility of the gas to enter the shield unobstructed by baflle 25.

The mixture of hydrogen and sample gas is burned on the surface of the catalyst wire 22 which is electrically heated. The combustion of the mixture will generate more or less heat in accordance with the amount of oxygen present in the gas sample. This heat varies the resistance of the catalyst wire 22, and a measure of this resistance is used for determining quantitatively the amount of oxygen in the sample. The catalyst wire 22 forms one leg of a Wheatstone bridge, which bridge is used for measuring the resistance of the catalyst wire 22. A direct current is used in the Wheatstone bridge, and in the electrolytic hydrogen generator l5. All of the electrical current used in the apparatus is derived from a single source.

An electric current is introduced into the wires 28 from a power source, the current being controlled by a switch 29. The current is conducted by wires 23 to transformer 30, where the voltage is reduced to approximately twelve volts. The secondary transformer current is conducted by Wires 3| to full wave rectifier 32, which has a ballast lamp 33, such as an amperite, in series with the circuit.

A rectified D. C. current, leaving rectifier 32 at approximately 8 volts is conducted by line 34 to a Wheatstone bridge 35, then through the bridge 35 to a Wheatstone bridge 36. The current leaves bridge 36 through line 31, passing through a 0.2 ohm resistance 38, and thence through line 39 to the cathode ll of hydrogen generator l5. The current passing through the electrolytic solution of the hydrogen generator l5 leaves the generator at anode l6, and is conducted by line 40 back to rectifier 32.

The Wheatstone bridge 35 is employed in determining the oxygen content of the gas. One of its legs is the catalytic wire 22, which ignites the mixture of sample gas and hydrogen in the combustion chamber l3. When the gas burns, it heats the catalyst wire, increasing its resistance, and thus unbalancing the bridge. A millivoltmeter 4| is connected across the bridge 35, and any unbalancing of the bridge 36 causes a current to flow to the millivoltmeter 4|, through the multipole switch 42. The multipole switch 42 is used in connection with the analyzer for the purpose of selecting the range of operation of the analyzer. There are two percentage ranges: 0 to 4% oxygen or low range, and 0 to 20% oxygen or high range.

The switch 42 is a triple-pole, triple-throw switch, having a movable shaft 43 with an adjusting lever 44 at one end and a cam 45 at the other end. Three contact blades 46, 41 and 48 are fixed on the shaft 43, and arranged for each blade to connect two contact points at each position of the switch. Several of the contact points are internally connected together; thus contact point 49 is connected to contact point 50, contact points 5|, 52 and 53 are connected together; contact points 54, 55 and 56 are connected together; contact point 5! is connected to contact point 58; and contact points 59, 60 and 6| are connected together. The cam 45 connected to the switch shaft 43, when turned, raises and lowers the baffle 25 in the oxygen analyzing chamber |3 by means of linkage 61.

The Wheatston bridge 36 shown in the illustration is composed of an active catalytic platinum-alloy wire 22, a wire 69 of the same material and having substantially the same resistance, and two gold plated platinum-alloy inactive wires 68 and Ti], each of which has the same resistance. The catalyst wire 22 and one of the gold plated wires 68 are mounted upon the posts 23 in. the oxygen analyzing chamber l3, and when air alone is passeed through chamber I3, the bridge 33 should be balanced with no current flowing through the millivoltmeter 4| connected across the bridge 35.

When a gas sample mixed with hydrogen is passed through combustion chamber l3, it will be ignited by catalyst Wire 22, whose resistance will be increased due to the temperature rise. The increase in resistance will unbalance the bridge 36 and a current will flow to the millivoltmeter 4!. With the multipole switch 42 in the low-range position, as illustrated, the meter current flows through line H to contact point 49, thence through the internal connections and switch blade 46 of the switch 42, and out of the switch at contact point 5|, to flow through line 12 to the meter 4|. The current leaves the meter 4| to flow through the line 13 to contact point 54, then through the connections and switch blade 41 of switch 42, leaving at contact point 64 through line H to Wheatstone bridge 33. A resistance 15 is placed in the line 74 for the purpose of calibrating the meter to give direct readings on its scale in percentage oxygen of the gas being analyzed.

Since the amount of hydrogen added to the sample gas is decreased during the operation of the analyzer in the low-range, a resistance 16 is placed in parallel with the hydrogen generator Hi. The circuit of the hydrogen generator, the rectifier, and the bridges for low-range operation may be described as follows: rectified D. C. current leaves rectifier 32 by line 34, passes through bridge 35, through bridge 35, leaving by line 31, then through the 0.2 ohm resistance 38. G ne part of the current goes to hydrogen genorator 15 by line 39, then to the rectifier 32 by line 40; the other part of the current goes by line H to contact point 6 i, then through the internal connections and switch blade 48 of switch 42, out at contact point 58, and thence through line 18, through the 1.3 ohm adjusted resistance 16 to the rectifier 32.

When analyzing a gas having more than 4% oxygen, the switch 42 is turned counterclockwise, from the position of the switch illustrated. By turning the switch 42 to this high-range position, the flow of hydrogen from the generator I5 is increased, and the flow of sample gas and hydrogen mixture to the catalyst wire 22 is decreased.

By thus turning the switch 42, 90 counterclockwise, the cam 45 lowers the baffle 25 down upon the shield and as a result, the gas and hydrogen mixture will have to enter the baffle 25 through side holes 21, and go down through bore 26 to be burned by catalyst wire 22. The

- tact point 66.

central bore 23 is designed to permit approximately only one-fifth as much gas and hydrogen mixture to reach the catalyst wire 22 when the baiile is lowered, as will reach the wire when the baffie is raised.

The circuit for the rectifier, the bridges and the hydrogen cell for the high range position of the switch may be outlined as follows: the current leaves rectifier 32 by line 34, goes through bridge 35, through bridge 36, through line 31, to con- The current goes through switch blade 48 and the internal connections of the switch 42, out of the switch at point 3|, through line I1, through line 39, thus cutting out both the 0.2 ohm resistance 38, and the 1.3 ohm resistance I6. The current then flows through line 39, goes through the hydrogen cell I out through line 49 back to the rectifier 32. By cutting out resistance 38 and 19 the generation of hydrogen will be increased approximately five times.

If a gas is passed through the analyzer when switch 42 is in the high-range position, the meter current flow from the bridge 36 to the millivoltmeter 4|, due to unbalancing of the bridge, will go through line II to contact point 49. This current flows through the switch blade 46 to contact point 5|, and out through line 12 to the millivoltmeter 4|. The current leaves the millivoltmeter 4| by line I3, going to contact point 54, through blade 41 to contact point 63. The current leaves the contact point 63 through line 8! to return to bridge 35. The current passes through high-range calibrating resistance 79, in the line 8|. The calibrating resistance I9 is used in order that a direct reading of the percentage of oxygen in the gas to be analyzed can be read directly on a meter scale of the millivcltmeter 4|.

By turning the switch 90 clockwise from the position illustrated the apparatus will be adjusted to give temperature readings on the millivoltmeter 4! of the temperature of the gas withdrawn from the pipe I. The temperaure of the sample gas is important when the apparatus is used in conjunction with adiusting furnaces for their maximum operating efiiciency. A thermocouple 82 is inserted in pipe I near the opening of conduit 2. A lead 83 is connected to contact point 65, and a lead 84 is connected to contact point 62.

When the switch 42 is in position for measuring the gas temperature, the current of the thermocouple goes through line 83 to contact point 55. through switch blade 41 and the switch connections, and out through contact point 54 through line 13 to the millivoltmeter 4|. The current leaves the millivoltmeter 4| through line 12 going to contact point 5|, then through switch blade 46 and the switch connections and out through contact point 62, through lead 84 to thermocouple 82.

The millivoltmeter 4| has three scales upon its face; a high-range percentage oxygen scale; a low-range percentage oxygen scale; and a temperature scale.

Part of the sample gas is mixed with air, ignited by a catalyst wire of a Wheatstone bridge, and the percentage of combustibles in the gas is directly indicated on a millivoltmeter connected across the Wheatstone bridge. The source of the sample gas is from the atmospheric discharge port ID of the sample pump 9. The sample gas discharged at port I0 is at atmospheric pressure, and part is drawn through the pump passage 85 of the sample pump 9 to a range changing valve 86 located in pump 81.

The pump 8i is a proportional mixing pump which has two suction ports 88 and 89, and one discharge port 99. The suction ports are so located with respect to the periphery of the housing, that suction port 88 draws in five volumes of a gas while suction port 89 draws in only one volume of gas. The ports have passages leading to the seat of the movable valve 86, and the openings in the valve seat are 90 apart on the periphery.

The range changing valve 88 has two axial passageways leading from the ends of the valve, one of which, passage 9|, is open to the air and the other, passage 92, opens into passage of pump 9. With the valve 86 in the valve seat of the pump 3? in the position illustrated, sample gas from passage 85 will be drawn through valve passage 92 to port 83 by way of the port passage. Air will be drawn through valve passage 9| to port 89 through the port passage. The mixture discharged at port 30 will consist of five parts sample gas and one part air.

If the valve 86 is turned clockwise from the position illustrated, then the sample gas from passage 85 is drawn through valve passage 9| into port 89, and air is drawn through valve passage 9| to port 88, such that the mixture discharged through port 98 is one part sample gas and five parts air.

The mixture of air and sample gas discharged at a constant rate at port 99, passes through conduit 93 to the aperture 94 of a combustible analyzing chamber 95. The combustible analyzing chamber 95 is constructed similarly to the oxygen analyzing chamber I3 except it has no bafile. A catalyst wire 96 is mounted on one of the posts 91 which are enclosed in an impervious cylindrica1 shield 93. The gas mixture entering the aperture 94 passes upwardly around the outside of the shield 98, part of which passes down into the shield 98 by diffusion and convection currents to be ignited by the catalyst wire 96. The remainder of the gas mixture, along with the products of combustion of the part of gas mixture ignited, pass out of analyzing chamber 95 by means of a hole 93 in the top of said chamber.

The catalyst wire 96 forms one leg of the Wheatstone bridge 35, through which passes the rectified D, C. current from rectifier 32 as previously described. When gas is passed through the analyzing chamber 95, and ignited by the catalyst wire 95, the temperature of the wire is raised, thus increasing its resistance. The change in resistance of one leg of bridge 35 unbalances the bridge causing a current to flow through switch Iill to millivoltmeter I90 connected across the bridge 35.

The apparatus is designed to analyze gases in two different percentages of combustible ranges: 0 to 4% combustibles or low range, and 0 to 20% combustibles or high range. The switch IIJI is used for selecting the range of operation of the analyzer.

The switch I9I is a single-pole, double-throw switch having a shaft I82 with an adjusting lever I03 at one end and a disk I04 at the other end. The movable valve 86 is connected to disk I04 by the linkage I05, such that the valve 86 will move in the same direction as the lever I83. There are four contact points on the switch IUI, of which contact points I06 and I01 are connected together by connections in the 9. switch. A contact blade III is attached to the shaft I02, which blade connects contact point I06 to contact point I08 when the blade is in a vertical position, and connects contact point IN to contact point I09 when the blade is in a horizontal position.

The Wheatstone bridge 35 is composed of the platinum alloy catalyst wire 56, a wire of similar material III and of approximately the same resistance, and two nickel plated platinum-alloy wires H and H2, of equal resistance. The catalyst wire 90, along with the nickel plated wire H0 is mounted on posts 01 in the combustible analyzing chamber 95,

When the bridge 35 is in an unbalanced condition and the switch IOI is in the low-range position, as illustrated, meter current leaves the bridge 35 by the line I I3, and flows to the millivoltmeter I00. This current leaves the meter I00 by line 4, going to contact point [01, passing through the switch IOI, out at contact point I08 through line I I5 to the bridge 35. The low-range calibrating resistance H6 is placed in the line II5 i" order that direct readings of the percentage combustibles of the gas analyzed are indicated on a scale of millivoltmeter I00.

With the switch IOI in' the low-range position, the disk I04 holds the movable valve 85 in the position illustrated, such that five volumes of sample gas enter port 88 of the pump. 81, and one volume of air enters the port 89.

To operate the apparatus in the high-range, the switch IN is turned 90 clockwise from the position illustrated, and meter current will flow from the bridge 35, due to its unbalanced condition,

through line II3 to millivoltmeter I00. The current leaves millivoltmeter I00 through line H4, going to contact point I01, passing through switch blade Ill to contact point I09, and returning to bridge 35 by line H8. The high-range calibrating resistance I I9 is placed in the line I IS in order that direct readings of the percentage combustibles may be read from a scale of meter I00.

When the switch IOI is turned to the high range position, the movable valve 85 is also turned 90 clockwise from the position illustrated. In this position of the valve 86, one volume of sample gas is drawn into port 89 and five volumes of air are drawn into port 38 of pump 81, such that the air-gas mixture entering the analyzing chamber 95 in the high-range position will be in the ratio of five parts air to one part gas.

The millivoltmeter I00 has two scales upon its face: a high-range percentage combustible scale and a low-range percentage combustible scale.

nected directly across the power intake leads 28 This motor is a constant speed motor, and drives the interconnected pumps 9 and 81 at a constant rate so that the pumps operate to deliver a predetermined quantity of gas mixture for analysis at a uniform flow.

In order to obtain accurate analyses, the apparatus should be periodically checked to balance Wheatstone bridges 35 and 36, and to set the flow of hydrogen delivered by the hydrogen generator I5 to the oxygen analyzer. The valve 5 is adapted to be used in conjunction with other controls for making these adjustments, as the valve 5 controls the type of gas going to the sample pump 9 and connects the flow of hydrogen to the oxygen analyzing chamber l3.

The valve 5 can be turned to four different positions. The position illustrated being the read or sample gas analysis position; by

10 turning the valve 60 counterclockwise, it is in the check ratio of hydrogen to sample gas position; by turning the valve counterclockwise, it is in the check balance of Wheatstone bridges" position; and by turning the valve counterclockwise, it is in the "011 position.

The valve is turned to the off position when the apparatus is not in use. The upper section of the valve 5 shuts off any sample gas flow to the pump, and the lower section of the valve 5 connects the hydrogen generator I5 to the oxygen analyzing chamber I3.

When the valve 5 is turned to the check balance of Wheatstone bridges position, air alone is pumped through both analyzing chambers in order that the bridges can be electrically balanced by potentiometers I20 and I2I. When an electrical balance is reached, the millivoltmeters connected across the bridges should have a zero reading. In this position the upper section of valve 5 connects air inlet I22 through valve passage 8 to the tube 1 leading to sample pump 0. The lower section of the valve 5 shuts off the flow of hydrogen to the oxygen analyzing chamber I3 and vents the hydrogen through slot I25 of the valve 5 to a valve vent I23. A potentiometer I26 connected across Wheatstone bridge 35 is adjusted to balance the bridge 35, and a potentiometer I2i connected across the Wheatstone bridge 38 is adjusted to balance the bridge 36.

When valve 5 is in the check ratio of hydrogen to sample gas position, air is pumped to both analyzers and hydrogen is supplied to oxygen analyzing chamber I3. In this position of valve 5, its upper section connects the air inlet I22 to the conduit I by valve passage 6, thus introducing air into the suction of the pump 9. The lower section of valve 5 connects hydrogen generator I5 to oxygen analyzing chamber I3. The ratio of hydrogen to sample gas in the gas mixture entering the oxygen analyzing chamber should be such that there is a slight excess of hydrogen over the amount needed to react with the maximum amount of oxygen encountered in either the high range or the low range. When the switch 42 is in the high-range position with the sample gas being air, the correct ratio of hydrogen to sample gas is obtained by adjusting the vent I26 until a maximum reading is indi cated on the high-range scale of millivoltmeter 4i connected across bridge 36. When the switch is in the low-range position and the sample gas pumped to the analyzer is air, the correct ratio oi hydrogen to sample gas is obtained by adjusting 3.1 the variable resistor I5 until a reading slightly in A motor I24 for operating the pumps is conexcess of 4% is obtained on the low-range scale of millivoltmeter 4I connected across bridge 35.

When the valve 5 is in the read position as illustrated, the sample gas is analyzed for its oxygen content in the oxygen analyzing chamber and its combustible content in the combustible analyzing chamber. The upper section of valve I2 connects the gas passage conduit 4 to the pump suction passage conduit I by the groove 6, and the lower section of valve 6 continues to introduce hydrogen from the hydrogen generator I5 to the oxygen analyzer I3.

The preferred form of the invention having been thus described, What is claimed as new is:

l. A gas analyzer for quantitatively measuring the oxygen content of a gas, comprising a combustion chamber, means for passing a continuous stream of gas to be analyzed at a uniform rate through the chamber, a metal shield mounted centrally within the chamber having imperforate base and side walls positioned in baffling relation to the stream of gas flowing through said chamber, a Wheatstone bridge electric circuit embodying a catalyst wire leg mounted within said shield and a galvanometer for measuring variations in electric conductivity of the catalyst, an apertured movably mounted closure for the top of the metal shield, and a switching mechanism controlling the galvanometer circuit for adjusting the sensitivity of the galvanometer, said switching mechanism and closure moving means being interconnected and arranged for simultaneous adjustment of the position of said closure and the sensitivity of said galvanometer.

2. In a multi-range gas analyzer adapted for analyzing gas quantitatively for a constituent of a gaseous mixture, a combustion chamber, means for positively delivering a continuous flowing stream of gas to be analyzed through a conduit to said chamber, means comprising a Wheatstone Bridge electric circuit including a catalyst wire leg mounted in said chamber for setting up combustion therein and a galvanometer for measuring any increase in temperature thereby developed, means connected with said conduit for supplying to the gas stream a continuous flowing stream of gas which is combustively reactant with said constituent of the gas, means connected with the supplying means for changing the relative volumes of gas and reactant gas in the mixture, and an electrical switching mechanism controlling the galvanometer circuit for adjusting the sensitivity of the galvanometer, said volume changing means and switching mechanism being connected together and so arranged that adjustment of the switching mechanism to actuate said sensitivity adjusting mechanism will simultaneously operate said volume changing means.

3. In a multi-range gas analyzer adapted for analyzing products of combustion quantitatively for oxygen content, a combustion chamber, means for delivering to said chamber a continuous flowing stream of the gas to be analyzed, a Wheatstone bridge electric circuit including a catalyst wire leg mounted in said chamber for setting up combustion therein, a galvanometer for measuring any increase in temperature thereby developed, an electrolytic hydrogen cell and connections arranged for adding to the gas stream flowing to the combustion chamber a continuously flowing stream of hydrogen, and means in the bridge circuit including electrical switches and calibrated resistances whereby to adjust the sensitivity of the galvanometer and the rate of supply of hydrogen by the hydrogen cell, said switches and the circuits of said resistances being interconnected and arranged for simultaneously actuating said sensitivity adjusting means and said hydrogen proportioning means for making analyses in different ranges.

ALAN P. SULLIVAN.