Portable Trace Moisture Generator For Calibration Of Moisture Analyzers

Abstract

An improved calibrator for moisture analyzers is provided. A flow of clean dry carrier gas into two streams, one of which passes through an improved saturator bomb, wherein it is completely saturated with water, and then this saturated stream is mixed with the other dry stream to provide a controlled wet stream for calibration. A capillary restrictor is used to control one of the streams. The invention utilizes a simple mathematical relationship for water concentration, means to vary each of the parameters in the relationship independently of the others, and means to simply determine values for the parameters, whichever are varied during a calibration.

Description

This invention pertains to method and apparatus for producing a stream of two gases containing a known concentration of one gas in the second gas. More in particular, the invention discloses an improved apparatus for generating a stream of a gas or other substance containing precisely known quantities of another substance, usually water, for use in calibrating other instruments, such as moisture analyzers.

In its most general sense, the invention can be used anywhere it is desired to produce a mixed fluid stream which consists of two fluids and which contains known concentrations of one of the fluids in the other fluid. One important element of the invention is that some of the carrier fluid is caused to become saturated, at some controlled temperature and pressure, with the second fluid. The saturated and non-saturated fluids are mixed together while gaseous. In the environment of the moisture analyzer described below, the carrier fluid is usually nitrogen and the second fluid is water. However, since the invention is not so limited, the term "saturated" shall be understood to mean: "being the most concentrated solution that can remain in the presence of an excess of the dissolved substance". The word "solution" in the above definition shall be understood to mean: "an act or the process by which a solid, liquid, or gaseous substance is homogeneously mixed with a liquid or sometimes a gas or a solid, or the mixture so formed". These definitions were taken from a standard dictionary, "Webster's Seventh New Collegiate Dictionary", published by G & C Merriam Co., copyright 1965. However, as will be appreciated from a reading of the detailed description below, the invention is most practically used and achieves all of its versatile capability in mixing two gases together. It will be understood that the substances must be gaseous when mixing takes place, and that they must mix rather than form a solution or otherwise combine, but that other substances, such as water which is normally liquid, can be used so long as they will gasify under the temperature and pressure conditions imposed. The invention provides means to adjust the temperature and pressure conditions in order to cause such gasification.

More particularly, in regard to calibrating moisture analyzers, the invention uses a stream of carrier gas which has been previously dried and cleaned. The initial dry flow is divided into two streams, one of which is kept in the dry state, and the second of which is completely saturated with water. The two streams are recombined, in varying proportions, to thus produce a flow containing known concentrations of water in the carrier gas. In other situations, generally, the carrier must be initially free of the other substance.

The invention provides several advantages over the best moisture calibrators heretofore available. The device of the invention is portable, where as prior devices were fixed in one place. Another advantage is that the invention is highly versatile in several if its facets, that is, it can supply a wide range of total volume flows, and it can supply, within its various total flows, a wide range of moisture concentrations. Another advantage is that no physical weighing is ever done. The various concentrations are achieved in accordance with a very simple pressure, temperature and volume relationship. In prior devices it was often necessary to weigh some flow or substance somewhere in the system, and this weighing introduced another source of inaccuracy and of human error. The invention has versatility in still another aspect, that is, moisture concentration in the carrier gas can be varied in several different ways, and this feature cooperates with several others in achieving the advantages of the invention.

In regard to the advantage of portability, the invention provides a compact instrument and a separate water saturator bomb which is removably attached to the instrument. The bomb is very simple in construction and provides the advantage of a long useful life between regenerations. Regeneration of the bomb is a simple procedure. The user need only supply a constant temperature bath for the bomb, which may be simply a bucket of ice water, or atmospheric air, or the like, and a source of clean and dry carrier gas, which may be simply a commercially available cylinder of nitrogen, hydrogen, air, or other gas, and suitable dryers. Thus, the invention provides an inexpensive, simple and highly reliable instrument which may be brought to the various analyzers to be serviced, thus assuring users of more reliable analyzer operation while reducing the cost of calibrating.

The above and other advantages of the invention will be pointed out or will become evident in the following detailed description and claims, and in the accompanying drawing also forming a part of the disclosure, in which:

FIG. 1 is a schematic drawing of an analyzer embodying the invention;

FIG. 1a is a view similar to part of FIG. 1 showing a modified form of the invention; and

FIGS. 2, 3 and 4 are front, left side, and right side views, respectively, of an instrument embodying the invention which has been built and successfully experimentally used.

Referring now in detail to the drawing, reference numeral 10 generally designates a preferred form of the apparatus of the invention. The dotted line box in FIG. 1 indicates the main instrument housing, but a saturator bomb 12, physically separate from the main instrument housing, is also part of the invention. Where a line crosses dotted line box 10 in FIG. 1, that is an indication that some other outside connection may be made. Accordingly, a fitting 14 on the instrument 10 is used to connect a line 16 to any suitable user supplied source of dried carrier gas. Most commonly the source will comprise a cylinder of nitrogen and a suitable dryer such as a molecular sieve type or chemical absorbent type, or the like. Line 16 includes a micron size filter 18 and a pressure gauge 20. The filter is provided as insurance that no particles enter the system. After gauge 20, line 16 branches into a pair of lines 22 and 24. Line 24 includes a pressure regulator 26, an on/off valve 28, and terminates at a mixing chamber 30. Line 22 includes an on/off valve 32 and ends at a fitting 34. Dry gas from the user's source is delivered via fitting 34 and a line 36 to the saturator bomb.

The invention requires means to saturate one fluid with the second fluid, and means to hold the saturating means at some constant temperature. In the moisture analyzer being described, the constant temperature is usually 0.degree. C., or ambient room temperature, because of the ease of obtaining and holding these two temperatures. The bomb 12 shown in the drawing is the preferred form of apparatus for achieving this end, but it will be understood that other forms, such as a bubble chamber, a packed column, or the like, could be used, Bomb 12 comprises a body 38 see FIG. 2, to which is screwed a cap 40 in an air and water tight manner. Within the body 38 there is provided a clean sponge 42, see FIG. 1 and means such as springs 44, to hold the sponge located intermediate the ends of the assembled bomb. The sponge may be of the ordinary plastic variety such as is used in the home, and is formed with a small hole through its center through which the line 36 is forced for a tight fit. Line 36 delivers dry gas to the space in the bomb to the right of the sponge. The dry gas is then driven through the wet sponge, and a line 46 delivers the now water saturated carrier gas to a fitting 48 on the instrument. The pressure drop across the sponge is less than the inherent instrument error of the components, and is therefore ignored. The bomb 12 is made ready for use by simply removing the cap 40, filling the body 38, with the sponge 42 located therein, with water, and then pouring out the excess water and reassembling the cap and lines. For periodic reconditioning, water can be simply run through the disconnected lines 36 and 46. Calculations have shown that in typical usage the amount of water in the sponge will be sufficient for 100's of calibrations of typical moisture analyzers in the 0-100 PPM range. To assure no failure at this point, it is a simple matter to infrequently and routinely, once every few months for example, refill the sponge with water. When the instrument is not being used, to prevent evaporation, the lines 36 and 46 are preferably capped by means of a protecting loop 50 on the fittings 34 and 48.

Internally, a line 52 extends from fitting 48 to, in sequence, an on/off valve 54, a pressure regulator 56, a pressure gauge 58, a capillary tube 60, a three-way atmospheric vent valve 62, and terminates within mixing chamber 30. In accordance with good fluid handling practice, the lines 24 and 52 are preferably arranged in chamber 30 in the manner shown in the drawing to prevent vortexing and other undesirable effects, and to achieve proper mixing. A vent line 61 connects to the third leg of three-way valve 62 and terminates at a fitting 63.

After mixing, the combined saturated and dry flows in the mixing chamber 30 are carried away in and are delivered by a line 64, which contains a pressure gauge 66, and ends at a three-way valve 68. The second leg of valve 68 is connected to a line 70 which contains a needle valve 72 and terminates at a fitting 74. The third leg of three-way valve 68 is connected by a branching line 76 to a pair of needle valves 78 and 80. A line 82 connects valve 78 to a fitting 84. A line 86, containing a rotometer 88, connects valve 80 to a fitting 90. Suitable lines connect one or both of the fittings 84 and 90 to the instrument or analyzer to be calibrated, the selection depending upon the requirements of the particular calibration as will appear in detail in the Operation section below.

Referring to the other drawings, as an indication of the compactness of the invention and not as a limitation, the main apparatus 10 shown was built in a cabinet having approximate external dimensions of 15 inches high, 9 inches wide and 7 inches deep. A carrying handle 92 was provided for convenience. The bomb 12 was made of stainless steel tubing and measured about 11 inches long, 2 inches inside diameter, and 2 1/8 inches outside diameter. The instrument weighs about 28 pounds and the bomb about 6 pounds.

In regard to constructional details, the capillary 60 is critical. For general use a capillary made of stainless steel having a length of about 9 feet with an about 0.010 inch inside diameter has been successfully used. Other lengths and/or capillary diameters may be needed for other flows, and/or concentrations. In certain applications it may be desirable to use glass for the capillary, despite the disadvantage of possible breakage, because glass may be needed when handling certain highly corrosive fluids. Virtually all of the other conduits are one-eighth inch outside diameter grade 316 stainless steel tubing with a 0.012 inch wall thickness. The valves, pressure regulators and gauges are all standard items for the pressures used, with the exception, possibly, of needle valves 78 and 80 which must function as both needle valves and on/off valves. For this reason it may be desirable to use both a separate needle valve and a separate on/off valve in lieu of each of the items 78 and 80 shown in FIG. 1. Also, needle valve 72 is preferably of fine multi-turn construction because fine adjustment is often required of it in use. Similarly, it may be desirable to use a test meter in lieu of gauge 20 for improved accuracy.

The user may supply any suitable container C to house the bomb 12, such as an ordinary bucket, and this container may be filled with ice and water when a 0.degree. C. saturation temperature is to be used. Under other circumstances, the bomb could be housed in any other sort of a bath, including ambient air, to hold it at any desired temperature at or below ambient temperature. If the particular fluids being handled require high temperature, the entire apparatus could be housed in a modified oven.

OPERATION

The theory of and various modes of operation of the invention tie together. They can probably be best understood by means of the following three equations. Logically, the final output water concentration, parts of water per million parts of total flow, is equal to the parts of water per million parts of saturated wet gas, times the wet flow rate, divided by the total flow rate. The conversion factor of 10.sup.6 is used to convert the parts per part relationship to parts per million parts or PPM units. The above can be expressed as Equation I as follows:

It is fact of nature that a given volume of a gas can hold a certain amount of water at any given temperature, with only a slight deviation at elevated pressures in accordance with the Clausius-Clapeyron equation.

Thus, the wet gas water concentration term is equal to the partial pressure of water divided by the pressure in the system and this term in Equation I expands out as follows:

Combining Equations I and II the following results:

with the following definitions:

Conc. water is the concentration of water in the total diluted gas flow and is in PPM. P.sub. water is the vapor pressure of water at the temperature of the bath. Units given in PSI. P.sub. total is the pressure at the water saturator as read by the gauge 20 after the dryer. Units given in PSIA (absolute). Wet flow is the flow going through the restrictor and is found using the technique described below. Units given in milliliters/minute. Total flow is the flow measured at the analyzer exit and at the by-pass exit. 10.sup.6 is the conversion factor for PPm units.

From Equation III it can be seen that the concentration of water delivered by the invention to the device being serviced is dependent on the four terms on the right hand side. The invention provides means to vary each of these four parameters independently of the other three, and it is this ability which is instrumental in giving the invention its great versatility. The water vapor term P.sub.water is changed by simply changing the bath temperature of the bomb 12. The system pressure P.sub.total is changed by adjustment within the user supplied gas supply system as read on gauge 20. For example, all other factors being constant, a change in bath temperature, the P.sub.water term, from 32.degree. F. to a typical room temperature of 70.degree. F. will increase the water concentration by about 300 percent. Similarly, a change in system supply pressure, the P.sub.total term, from 100 PSIG to 10 PSIG, which are two typical pressures used, will cause an increase in PPM water concentration of about 500 percent.

Another way of obtaining changes in water concentration is by making changes in the "total flow" term in Equation III. This is accomplished by changing the flow in branching line 76. From FIG. 1 it can be seen that the flow out of the branches of line 76 are controlled by the two needle valves 78 and 80. Changing one or both of these needle valve settings will change total flow accordingly. For a reason which will be explained in more detail below, changes in total flow so obtained are usually made up entirely by dry gas from line 24. Thus, increasing total flow will cause a decrease in water concentration and, conversely, a decrease in total flow by manipulation of valve 78 and/or 80 will cause an increase in water concentration.

Another facet of the versatility of the invention is provided by the structure above, i.e., the apparatus starting from line 76 and to the right thereof on FIG. 1. This versatility concerns the ability to bypass and vent varying portions of the combined wet and dry flow in line 64. In use, fitting 84, called "flow 2", is connected to the instrument being serviced and "flow 1" out of fitting 90 is connected to a suitable vent. By manipulating the two valves 78 and 80, any desired portion of the total flow from the mixing chamber can be vented, and the amount so vented and not taken by the instrument being serviced determined by the reading on rotometer 88. Thus, the total flow term in Equation III is given a numerical value by adding together the flow out of fitting 90 as read on rotometer 88, and the flow out of fitting 84 as read by the appropriate components on the instrument being serviced. This versatility is important, for example, where the instrument being serviced is small and/or requires an extremely small volume flow rate. The calibrator of the invention can thus be operated at a higher flow rate comfortably within its operating range, and any desired fraction, including a very large portion, vented out of fitting 90. Thus, the small flow used for calibration accurately contains the desired water concentration.

Another adjustment of water concentration, the fourth mode of operation, which is often used during the making of a calibration, is provided by making changes in the wet flow term in Equation III, i.e., the flow in line 52 from the capillary to the mixing chamber.

This last mode of operation will be explained in conjunction with an overall explanation of the manner of operation of all modes, since there are several preliminary steps which are common. First, the bomb 12, properly loaded with water, is allowed to stabilize at the bath temperature. For example, this may be simply accomplished by permitting the bomb to stabilize in an ice bath for several hours or overnight. The wet and dry portions of the apparatus of the invention must be conditioned prior to use. This is accomplished by opening valves 28 and 32, adjusting regulators 26 and 56 to some desired relatively low pressure to efficiently condition the system, and moving three-way valve 62 to divert the wet flow to atmosphere. Three-way valve 68 is operated to direct the dry flow through lines 76, 82 and 86 and out to both the instrument and atmosphere to condition all lines and the instrument. This procedure may be simultaneously allowed to continue overnight prior to further calibration to assure that the dry portion, including the instrument to be serviced, is dry and that the wet system, between line 46 and valve 62, is purged of dry gas. The zero water concentration calibration point is, of course, automatically obtained after conditioning is complete and before three-way vent valve 62 is operated to supply wet gas to the flow feeding the instrument via fitting 84. The analyzer can be conditioned together with the calibrator of the invention, and in any case, the analyzer must be equilibrated before calibration proceeds.

After conditioning is complete, some system pressure from the user's supply system is selected and registered on gauge 20, thus determining the "P.sub.total " term, and valves 78 and 80 adjusted to some setting, thus determining the "Total Flow" term in Equation III. Regulator 26 is operated to produce some operating pressure on its downstream side and in mixing chamber 30. At the same time a value for the "P.sub.water " term is determined since a bath temperature was previously selected, see Equation II. After vent line 61 is shut off by valve 62, and because all lines are large with respect to capillary 60, the pressure in the entire system, from the output side of capillary 60 through mixing chamber 30, including the part of line 24 after regulator 26, and lines 64 and 76, is all controlled by the setting on pressure regulator 26. The invention utilizes the fact that capillary tube 60 is a highly stable, almost a fixed restrictor to flow passing therethrough. However, the restriction provided by a capillary is dependent on temperature, and therefore the calibrator should not be subjected to temperature changes during use. After valve 62 is operated, some mixture of dry and saturated gas is supplied to the instrument via the mixing chamber. Pressure regulator 56 will be in some initial position to supply some initial inlet pressure to the capillary 60, causing some initial saturated flow to the mixing chamber, which in turn causes some initial concentration of water to be supplied to the analyzer being serviced. The operator notes the capillary inlet pressure on gauge 58, and then manipulates regulator 56 to change the capillary inlet pressure. Because the capillary 60 is a very stable restrictor, the capillary outlet pressure will stay at the pressure determined by the setting on pressure regulator 26. If capillary inlet pressure were increased, then the pressure drop across the capillary will have been increased, and the water concentration will have increased at the expense of a decrease in the dry flow in line 24 because total flow stays constant. Conversely, if it is desired to decrease water concentration, the capillary inlet pressure will have been reduced by operation of regulator 56 thus causing the pressure drop across the capillary to decrease, which in turn causes wet flow to decrease while dry flow increases. In both cases, total flow remains unchanged and at the value determined by valves 78 and 80. Because total flow does not change any increase in wet flow is made up by a corresponding decrease in dry flow, and vice versa.

The calibration procedure continues in this manner, changing capillary inlet pressure using regulator 56, and recording the corresponding pressure readings on gauge 58, and the corresponding concentration readings on the instrument being serviced, until any desired number of calibration points have been so obtained. Having obtained sufficient calibration points, four points are usually adequate for most moisture analyzers, the operator need now only determine a numerical value for each wet flow used at each calibration point. Since the other three terms in Equation III have been constant therethrough, these numerical values for wet flow will be inserted in the Equation, and a simple multiplication performed to obtain the actual water concentration which was supplied at each point. These calculated water concentrations are then compared to the corresponding concentration readings registered on the instrument, and suitable corrections made, i.e., a calibration curve supplied for use with the instrument, or suitable adjustments made in the instrument. To determine the values of the wet flows used, the operator connects a bubble tube or other suitable flow measuring device to fitting 74, shuts off the dry gas by closing valve 28, operates valve 68 to divert all flow away from line 76 and into line 70, opens needle valve 72, and adjusts valve 56 to produce a pressure on gauge 58 equivalent to that pressure used in obtaining one calibration point. The system is now changed to a configuration wherein the wet gas flow only moves through the mixing chamber 30 and through line 64, and out to atmosphere via valve 68, line 70, valve 72 and the measuring device connected to fitting 74 wherein it is measured. Valve 72 is now operated to produce the same pressure in the mixing chamber and associated parts as was used in obtaining the calibration points. Thus, it can be seen that the restriction provided by needle valve 72 in this step simulates the total restriction that was on the system when the calibration points were taken, that is, the setting on valve 72 during the measurement of the wet flows reproduces the pressure on the outlet side of restrictor 60 that was present when the calibration point was taken. This simulation step is readily accomplished by simply observing gauge 66 and operating valve 72 until the same calibration pressure is shown on gauge 66. Now valve 56 is again operated so as to reproduce the series of calibration point pressures on gauge 58 which were previously recorded. Valve 72 is used to hold the constant pressure at gauge 66. At each restrictor inlet pressure the wet flow is measured by the device attached to fitting 74 and recorded for use in Equation III to calculate the actual concentrations that were supplied.

During all of these steps, the taking of the calibration points and the reproduction of the calibration point wet flows, it may be necessary to make very minor "trimming" type adjustments in the settings of regulator 26, and valves 78 and 80 to hold pressures constant, in order to accommodate for slight inaccuracies in the components.

As explained above, it can be seen that at no time is it necessary or even desirable to physically weigh any flow. The values of all parameters are determined by reproduction, by flow measurement, and by simple calculation, thus substituting an effectively zero instrument error for an otherwise substantial human error in making a calibration. At the same time, inexpensive, simple, and highly reliable standard items are used as components in building the apparatus of the invention, as opposed to many prior calibrators which need much more sophisticated, expensive, and more highly prone to error components, such as relatively large baths, and dual stage compressors.

While the above exemplary explanation of the operation of the invention concerns itself with varying the wet flow term in Equation III, it will be appreciated by those skilled in the art that any of the other three parameters may be varied, either during a single calibration or from one calibration to another, and the effect of such other changes duly recorded and then properly reproduced when determining the values for the parameter which has been varied after all the calibration points are taken. For example, P.sub.water is changed by changing bath temperature, P.sub.total is changed by adjustment within the user supplied gas supply system, and Total Flow is changed by adjustment of needle valves 78 and/or 80.

As can now be appreciated, the constant restriction provided by capillary 60 is an important part of the invention. Different diameter and/or length capillaries can be used in different applications. However, the invention is not limited to use with a capillary, a relatively constant pressure restrictor means is all that is functionally required. A high quality needle valve, or a packed column, or other means, could be used in lieu of the capillary. Many other structural changes will be evident to those skilled in the art. For example, a suitable packed column could be substituted for both the saturator bomb and the capillary. Another modification, which might be useful in other circumstances and/or when dealing with other fluids, might be a separate source feeding the "wet" and "dry" paths, as described above. With such separation, different pressures could be used for each path, thereby permitting greater flexibility as to final concentrations produced. In such a form, another change might be to replace regulator 56 with a pressure intensifier or pump or the like, to thereby still further increase the pressure drop across the pressure restricting means 60. In the application described, as mentioned above, the pressure drop across the sponge 42 in the bomb 12 is small enough to be ignored. In other applications, at higher pressures, with other saturator configurations, or for other reasons, it may be desirable to relocate gauge 20 closer to the saturator, perhaps directly on the bomb. The disadvantage of such a change in the constructed form of the invention is that the bomb is handled considerably more than the main instrument thus increasing the possibility of damage to gauge 20. However, for calibrating moisture analyzers, the preferred form of the invention is that shown in the drawings.

Because moisture calibrators generally operate with relatively low water concentrations, the ratio of dry to wet saturated flow into the mixing chamber is usually high. This fortuitous circumstance enhances the ability of pressure regulator 26 to hold the entire system, between the capillary and the needle valves 78 and 80, at the constant pressure at which it is set. It will be understood by those skilled in the art that final water concentrations produced and dry to wet flows produced will depend upon the physical configurations of various parts, particularly capillary 60, and that changing the size and shapes of such components is another facet of the versatility of the invention. With the parts as shown and as described herein, experiments have produced a 5,000 PPM water in hydrogen concentration at a bath temperature of 22.degree. C. With no dry gas flow, valve 28 closed, a concentration in the range of 8,500 to 9,000 PPM can be obtained. If very high concentrations are required the capillary 60 can be replaced by a straight length of tubing and concentrations up to 20,000 PPM can be obtained.

In the event a situation should arise wherein very high concentrations, in the range of 15,000 to 20,000 PPM, are needed, the parts of the invention could be rearranged as shown in FIG. 1a to restrict the dry flow and permit unrestricted wet flow. This would be accomplished by replacing capillary 60 in line 52 with tubing, and placing a capillary 60a in line 24a between valve 28a and the mixing chamber 30a. In FIG. 1a the parts are indicated by the same reference numerals used in FIG. 1 followed by a. This modification has not been tested because such high water concentrations are not usually required in calibrating moisture analyzers.

Tests have shown that the instruments built in successfully testing the invention have capacities of total flow in the range of about 100 to about 1,500 ccs per minute. As an indication of other physical parameters, which are recited here to enhance the teaching and not as a limitation, the mixing chamber 30 was made of 316 stainless steel and had a capacity of about 20ccs, the saturator pressure on gauge 20 may be about 10 to 100 PSIG, the pressure in the mixing chamber has been tested in the range of about 5 PSIG to 10 PSIG, and amounts of total flow bypassed have been in the range of about 100 to almost 1,500 ccs per minute. The invention has been operated at 0.degree. C. and 20.degree. C., with the capillary described above, and wet flows from 5 to 70 ccs per minute have been used.

While the invention has been described in detail above, it is to be understood that this detailed description is by way of example only, and the protection granted is to be limited only within the spirit of the invention and the scope of the following claims.

Claims

I claim:

1. A method of forming a mixture having a known concentration of a first fluid in a second fluid, comprising the steps of supplying a first flow of said second fluid to a mixing chamber, maintaining said mixing chamber at a first known pressure, supplying a second flow of said second fluid to saturating means containing said first fluid, maintaining said saturating means at a known temperature and a second known pressure whereby said second flow of said second fluid is saturated with the first fluid, flowing the saturated flow from said saturating means to said mixing chamber, flowing a selected one flow of said first flow of said second fluid and said saturated flow through pressure restrictor means prior to flowing said selected one flow into said mixing chamber, wherein said temeperature and said first and second pressures are selected for said first and second fluids so that said first and second fluids will mix in said mixing chamber in the gaseous state, restricting the mixed flow out of said mixing chamber to thereby control the volume of said mixed flow out of said mixing chamber, changing the pressure of said temperature one flow flowing to said pressure restrictor means to thereby control the amount of said selected one flow passing through said pressure restrictor means, whereby the amount of said selected one flow flowing into said mixing chamber is changed while the mixed flow flowing out of said mixing chamber remains unchanged, and determining the amounts of said selected one flow and of said mixed flow to thereby determine the concentrations of said first fluid in said second fluid.

2. The method of claim 1, wherein said selected one flow is said saturated flow.

3. The method of claim 2, wherein said first fluid is water and the concentration of water in said second fluid is determined according to the relationship:

where P.sub.water is the vapor pressure of water at said temperature of the saturating means; wet flow is the amount of the flow out of the saturating means; P.sub.total is said second pressure of said saturating means; and total flow is the amount of the mixed flow leaving the mixing chamber.

4. The method of claim 2, wherein said second known pressure in said saturating means is greater than said first known pressure in said mixing chamber.

5. The method of claim 2, wherein the mixed flow out of said mixing chamber is supplied to a device for calibrating the ability of said device to detect the concentration of said first fluid, and wherein the amount of the saturated flow generated is determined by simulating the effect of the device being calibrated, stopping said first flow of said second fluid, diverting the saturated flow only through the simulating means and to flow measuring means, reproducing the different changing pressures of said saturated flow going to said pressure restrictor means, and measuring the amount of the saturated flow at each of the different saturated flow pressures.

6. The method of claim 2, wherein said first fluid is water and said second fluid is a water insoluble substance which is gaseous at atmospheric temperature and pressure, and said saturating means saturates said second flow of said second fluid with water by forcing gaseous second fluid through a confined water soaked sponge.

7. The method of claim 1, wherein all of said second fluid is supplied from a single source and said first and second flows are produced by dividing the outflow of said single source into said first and second flows.

8. The method of claim 7, and removing any of said first fluid which may be in said second fluid before dividing said source outflow into said first and second flows.

9. The method of claim 1, wherein said first fluid is water and said second fluid is a water insoluble gas.

10. The method of claim 1, wherein said second fluid is nitrogen and said first fluid is water.

11. The method of claim 1, wherein said second fluid is hydrogen and said first fluid is water.

12. The method of claim 1, wherein said second fluid is air and said first fluid is water.

13. The method of claim 1, wherein the mixed flow out of said mixing chamber is supplied to a device for calibrating the ability of said device to detect the concentration of said first fluid.

14. The method of claim 13, bypassing a portion of said mixed flow away from said device, and determining the amount so bypassed in order to supply a small enough volume of the mixed first and second fluids suitable for used by said device and yet large enough to permit efficient generation of known concentrations of said first fluid in said second fluid, and wherein the amount of mixed flow generated is determined by determining the amount of the mixed flow taken by the device and the amount of the mixed flow bypassed and by the addition of said last mentioned two amounts.

15. The method of claim 1, said pressure restrictor means comprising a capillary tube formed of stainless steel, having a length of about 9 feet, and an inside diameter of about 0.010 inch.

16. Apparatus for generating a mixture of fluids containing a known concentration of a first fluid in a second fluid comprising a mixing chamber, means for holding said mixing chamber at a first known pressure, means to flow second fluid to saturating means containing said first fluid to produce a stream of said second fluid saturated with said first fluid out of said saturating means, means for holding said saturating means at a known temperature and a second known pressure, pressure restrictor means for reducing the pressure of a stream flowing therethrough, means to flow a selected stream of second fluid or said saturated stream to said mixing chamber via said pressure restrictor means and to flow the other of second fluid or said saturated stream directly to said mixing chamber, wherein said temperature and said first and second pressures are selected for said first and second fluids so that said first and second fluids will mix in said mixing chamber in the gaseous state, means for restricting the mixed flow out of said mixing chamber to thereby control the amount of the mixed flow out of said mixing chamber, and means for determining the amounts of said selected stream and of said mixed flow to thereby determine the concentration of said first fluid in said second fluid.

17. The apparatus of claim 16, wherein said selected stream is said saturated stream.

18. The apparatus of claim 17, wherein said first fluid is water and the concentration of water in said second fluid is determined according to the relationship:

where P.sub.water is the vapor pressure of water at said temperature of the saturating means; wet flow is the amount of the flow out of the saturating means; P.sub.total is said second pressure of said saturating means; and total flow is the amount of the mixed flow leaving the mixing chamber.

19. The apparatus of claim 17, a source of said second fluid, said means to flow second fluid to said mixing chamber and to said saturating means comprising means to divide the outflow from said source, wherein said first fluid is water and said second fluid is a substance which is gaseous at atmospheric pressure and temperature, said source comprising a pressurized container of said second fluid, pressure regulator means to reduce said supply pressure to said first known pressure which is less than the supply pressure, and pressure regulator means to control the pressure of said saturated stream within a range more than said first known pressure and less than or equal to supply pressure.

20. The apparatus of claim 16, wherein the mixed flow out of said mixing chamber is supplied to a device for calibrating the ability of said device to detect the concentration of said first fluid, means for bypassing a portion of said mixed flow away from said device, and means for determining the amount so bypassed in order to supply a small enough volume of the mixed first and second fluids suitable for use by said device and yet large enough to permit efficient generation of known concentrations of said first fluid in said second fluid, and wherein the amount of mixed flow generated is determined by determining the amount of the mixed flow taken by the device and the amount of the mixed flow bypassed and by the addition of said last mentioned two amounts.

21. The apparatus of claim 20, said means for determining the amount of said mixed flow which is bypassed comprising a rotometer.

22. The apparatus of claim 17, wherein the mixed flow out of said mixing chamber is supplied to a device for calibrating the ability of said device to detect the concentration of said first fluid, means for diverting the mixed flow away from the device to be calibrated including means to simulate the restricting effect of said device, on/off valve means for shutting off the direct flow of first fluid to said mixing chamber, and means for measuring the saturated flow passing through said diverting means.

23. The apparatus of claim 22, said simulating means comprising needle valve means.

24. The apparatus of claim 22, said measuring means comprising a bubble tube.

25. The combination of claim 16, and means for changing the pressure of said selected stream flowing to said pressure restrictor means to thereby control the amount of said selected stream flowing through said pressure restrictor means.

26. The apparatus of claim 16, said pressure restrictor means comprising a capillary tube.

27. The apparatus of claim 16, a source of said second fluid, said means to flow second fluid to said mixing chamber and to said saturating means comprising means to divide the outflow from said source.

28. The apparatus of claim 27, and means for removing any of said first fluid which might be in said source outflow.

29. The apparatus of claim 28, said first fluid being water and said removing means comprising a molecular sieve.

30. The apparatus of claim 28, said first fluid being water and said removing means comprising a drier.

31. The apparatus of claim 16, said pressure restrictor means comprising a capillary tube formed of stainless steel, having a length of about 9 feet, and an inside diameter of about 0.010 inch.

32. The apparatus of claim 16, wherein said first fluid is water and said second fluid is a water insoluble substance which is gaseous at atmospheric temperature and pressure.

33. The apparatus of claim 32, said saturating means comprising a saturator bomb having a water soaked sponge located mediately the ends thereof, and means to flow said gaseous second fluid in one end of said bomb, through said sponge, and out the other end of said bomb to thereby produce said saturated stream.

34. The apparatus of claim 33, said means to hold said bomb at a known temperature comprising a container of ice water in which said bomb is located.

35. The apparatus of claim 33, said means to hold said bomb at a known temperature comprising ambient air.