CA1205916A - Monitor for determining an unknown property of a gas or vapor sample - Google Patents

Abstract

"MONITOR FOR DETERMINING AN UNKNOWN
PROPERTY OF A GAS OR VAPOR SAMPLE"

ABSTRACT

Monitor apparatus for determining an unknown property of gases and vaporized liquids which is capable of use both in the laboratory and the field. The primary sensing device is a fluidic oscillator through which a sample of gas is passed. Heating values, density, and water content can be determined.

Description

"MONITOR FOR DETERMINI ~ fi PROPERTY OF A GAS OR VAPOR SAMPLE

BACKGROUND OF THE INVENTION
This invention relates to the determination of the characteristics of substances in gaseou~ form, and more specifi-cally to determination of heating value, or heat of combustion, density, and humidity or moisture content of a gas or vaporized liquid.

HEATING YALUE
Fuels in liquid or gaseous farm are burned to produce heat for a plethora of applications. These fuels may vary in composition from primarily single carbon hydrocarbons to hydrocarbons having many carbon atoms arranged in branched chain or ring structures or may be mixtures of many hydrocarbons. Often a fuel contains compounds which are inert with respect to normal combustion. It is useful to know the heating value of a fuel, that is, the amount of heat which a certain quantit~ of a fuel will produce when i~ is burned under a certain set of conditions. While the heating values of most pure substances caoable of being used as fue7s are readily available in the literature, that a myriad number of mixtures of compounds are used as fuels results in a continuing need for making heating value determinations. Apparatus and methods for determining ; heating values are used both in laboratories and in industrial operations outside the laboratory. It is often desirable to monitor heating value of a flowing stream on a corltinuous basis. Following are several exemplary applications for heating value m3nitoring.
Since the value of a fuel depends in large part upon the amount of heat ~t is capabl~ of producing, it is more appropriate to set fuel price in accordance with heating value and quantity~ rather than quantity alone. Natural gas ia a prime example9 today it is almost always sold on ~he basis of dollars per thousand ~TU instead ~s~

of the previously used basis of dollars per SCF. This is primarily $he result of ~he price increases of recent years. Imprecision in the number of BTU's transferred is now too expensive to tolerate.
Another factor necessitating transfer of custody on the basis of heat quantity is that natural gas heating values tend to vary more, as gases from different locations are pipelined around the country and gas is imported.
A gas stream which is a by-product of operation of a factory~ or plant, is often piped to a nearby plant to be burned as fuel. As in the above natural gas example, the payment made for the gas will probably be based on its heating value as well as the quantity burned. Average heatin~ value may be determined by periodic laboratory analysis or the heating value may be continu-cusly measured as the gas enters the user's plant. Further, heating values of the by-product gas must be determined, before its actual use begins, for reasons other than pricing~ Design and control of the burner, furnace, and other equipment involved in handling and burning the gas depends in part on the range of heating values which can be expected. Heatin~ value of a by-product gas would normally vary over a fairly large range, compared to natural gases, and the average heating value would be different from that ~f natural gases.
In certain manufacturing processes~ t2mperature and/or furnace atmosphere ~ust be maintained in a relatively narrow range in order to assure product quality. Changes in heating value of the fuel supplied to the furnace may necessitate corrective action to avoid an excursion from the acceptable range. An increase in heating value of a fuel indicates that more oxygen is required to combine with it. Where a ~urnace atmosphere is required to be rich ~sg~

in oxygen, an increase in rate of oxygen depletion in the ~urnace caused by an increased heating value may create quality problems.
The solution is often to increase oxygen flow as soon as an increase in heating value is detected by a heating value monitor and thereby avoid significant depletion.
Fuel savings can be reali7ed by using a heating value monitor in a combustîon zone control system. The amount of air supplied to the combustion zone can be adjusted by reference to the heating value monitor so that the excess air quantity is small, thus saving fuel used for heating unneeded air and so that use of extra fuel as a result of incomplete combustion is avoided.
There are many applications, such as mentioned above, where an apparatus and method for determining heating value on an instantaneous and cont,nuoùs basis is required. The most usual method of determining heating value in a laboratory is by use of a calorimeter in which the fuel is burned under precisely controlled oonditions and rise in temperature of a water bath heated by the burned fuel îS measureda While accurate, this method is time-consuming and cannQt be adapted to provide a eontinuous read-out of heating value for a continuous flow o~ sample to the calorimeter.
Also, as mentioned above, there are many applica$ions where a series of laboratory determinations of heating value need to be made quickly and not necessarily with the accura~y of a primary standard.
The instant ~nvention is expected to be significant in meeting these applications~
For purposes of comparison to the present invention, a continous reading on-line calorimeter device available from Fluid Data, Inc. of Merrick, New York is described. In this instrument, variations in heat produced by a test burner are of~set by adjustment of air flow to the burner, in a null balance fashion, and air flow rate is related to heating value. A sample of gas is piped from a stream to be tested to the test burner and gas flow rate is held constant. The flame heats a thermal expansion element whose movement adjusts air flow to the burner through a mechanical and pneumatic linkage. Air flow is independently measured by means of an orifice meter and displayed on a scale which is marked in terms of heating value.
Several recently issued patents show the interest in methods for determining heating value. In U.S. Patent 4,337,654, a fixed amount of gas is burned with a ~easured ~uantity of air and hydrogen or oxygen supplied by an electrolytic cell. The amount of hydrogen or oxygen added is controlled by an oxyg n sensor and related to the heating value of the gas burned. U.S. Patent 4,355,533 describes a method of determining heating value where information developed by use o~ a gas chromatograph is correlated with heating value. U.S. Patent Nos. 4932g,873 and 4,329,874 describe another calorimeter in which gas is oxidized~
A recent article by Yan Rossum which points up the need ~or the present invention can b~ found in Oil and Gas Journal of January 3, 1983 (p~ 71, Part 1) and January 10, 1983 ~p. 85, Part 2).
For background information on diFferent gases and liquids used as fuels and on combustion, reference may be made to the Fuels section of Perry's Chemical Engineers Handbook9 published by McGraw-Hil1, and in particular to p~geS 9-1 to 9~33 of the fourth edition.

5~

DENSITY

It is important to know the density of a gas in many industries, in particular, in the area of pe~roleum and petrochemical processing. A typical application is a mass flow meter, where volu-metric flow rate is combined with the density of the flowing stream to produce mass flow rate. One seeking to measure density, particu-larly on a continuous on-line basis, has a limited choice o~ apparatus.
- One commercially available density meter utilizes an oscillating element in the fluid whose density is measured. Qscillation is caused by an electromagnetic field~ The frequency of oscillation depends on the density of the fluid. The sensin~ element is contained in a housing havlng one-inch flanges for installation in a pipeline. A
standard reference, Process Instruments and Controls Handbook, 2nd - ed., 1974~ edited by Considine, lists only three techniques for measur-ing density, none o~ which are well suited for use outside the lS laboratory. The listed methods ~p. 6 152~ are as f~llows~
In a gas specific gravity balance, a tall column of gas is measured by a floating bottom fitted to the gas containment vessel.
A mechan~cal linkage displays movement of the bottom on a scale. A
buoyancy gas balance consists of a vessel containing a displacer 2Q mounted on a balance beam and with a manometer connected to it.
Displacer balance is established with the vessel filled with air and then filled with gas, the pressure required to do so being noted from the manometer in both cases. The pressure ratio is the density :~L2~?S~

of the gas relative to air. In a viscous drag density instrument, an air stream and a s~ream of the gas under test are passed through separate identical chambers, each containing a rotating impeller.
The two streams are acted upon by the rotating impellers and in turn each acts upon a non-rotating impeller mounted in the opposite end of the chamber. The non-rotating impellers are coupled together by alinkage and measure the relati~e drag shown by the tendency of the impellers to rotate, which ~s a function of relative density.

HUMIDITY
This inYention also relates to determination of humldity, or moisture content, of a gas or vaporized liquld. It ls pr~marily useful for analyzing Qases where the moisture content is large and there is a smdll difference between the molecular weight of water and the average molecular weight of the other components of the gas ~rwhere there is a large difference between the molecular weight of water and the average mNlecular we~ght of the other components.
There are a variety of methods for measur~ng water con tent, each of whlch involves at least one significant dlsadvantage which disqualif~es it for use in certain applications. Thus the cholce of a method must be made in light of the appl~cation. A sur-vey of methods and apparatus can be found in Process Instruments and Controls Handbook~ edited by ConsidineD 2nd ed., MoGraw-Hill, 19749 p. 10-3 and following. The applications for which the instant inven-tlon is suited will beco~e apparent upon reading this specification, as will the gap in the area of humidity measurement which is filled by the instant invention.

5~

STATEMENT OF ART

In an article in Oil and Gas Journal of April 5, 1982 entitled "Acoustic Measurement for Gas BTU Content", Watson and White suggest a method and apparatus which utilize the dependence of sound speed and BTU content on molecular weight and which utiliz2 some of the same basic scientific principles as this inYention. LeRoy and Gorland have explored the use of a fluidic oscillator as a molecular weight sensor of gases and reported their work in an article entitled "Molecular Weight Sensor" published in Instruments and Control Systems of January, 1971, ~nd in National Aeronautics and Space Administration Technical Memoranda TMX-527~0 (circa 1~70) and TMX-1939 (January 1970). In Fossil Ener~ C Briefs~ NOY~ 1g81, prepared ~or the U.S. Dept. of Energy by Jet Propulsion Laboratory of California Institute of Technology, Sutton of The Garrett Corp., referred to the use of a f1u1d~c oscillator to measure gas composltions, mass flow and the heating value of natural gas.
In a paper ~ntitled "Thermal Energy Measurem~nts", presented at the 55th International School of Hydrocarbon Measurement in 1980 at the Universi~y of Oklahoma~ ~. A. Fox of Consolidated Gas Supply Corp. of Clarksburg, West Virginia, suggests that specific gravity methods may be used for determining heating values. The use of a fluidic oscillator in measuring composition in a methanol-water system is discussed in an article on page 407 of In 9. Chem.
Fundam., Vol. 11, No. 3, 1972. U.S. Patent No. 3,273~377 (Testerman) shows the use of two fluidic oscillators in analyzing fluid streams.
A fluidic device for measuring the rativ by volume of two known gases is disclosed in U.S. Patent No. 3~554,004 (Rauch et al~ In U.5.
Patent No. 4,1509561, Zupanick claims a method of Jetermining the l~C5~6 constituent gas proportions of a gas mixture which u~ilizes a fluidic oscillator.
In National Aeronautics and Space Administration Technical Memorandum TMX~1269 (August 1966)~ Prokopius reports on the use of a fluidic oscillator in a humidity sensor developed for studying a hydrogen-oxygen fuel cell system. In NASA TMX-3068 (June 1974~, Riddlebaugh describes investi~ations into the use of a fluidic oscillator in measuring fuel-air ratios in hydrocarbon combustion processes. NASA Report No. L0341 (April 16~ 1976), written by Roe and Wright of McDonnell Douglas under Contract No. NAS 10-8764 at the Kennedy Space Center, reports on work done to develop a fluidic oscillator as a detector for hydrogen leaks from liguid hydrogen transfer systems. U.S. Patent No. 3,~56,068 (Villarroel et al.) deals with a device using two fluidic oscillators to determine the lS percen~ concentration of a particular gas relatiYe to a carri2r gas.
Previously cited U.S. Patent Nos. ~337D654 (Austin et al.), 4,329,873 (Maeda), 4,323,874 ~Maeda), and 4,355~533 (Muldoon), disclose methods of determining heating value. The previously cited artic1e in the Oil and Gas Journal (January ~ and 10, 1983~ presents a survey of methods used in EuropeO

BRIEF SUMMARY OF THE INVENTION

It is an object of this invention to provide methods and apparatus for determining unknown properties of gases and liqulds, which are capable of use both in the laboratory and in the field. Also, it is an object that such apparatus be relatively inexpensive9 have a minimum of moving mechanical parts, and be compact9 so as to faoilitate transportation and installation. It is a further object ~ 2~S ~ 6 of this invention that such methods and apparatus have high accuracy and reliability while providing resul~s essen~ially instantaneously.
In one of its broad embodiments, the invention comprises (a) a fluidic oscillator; (b) means for establishing flow of the sample through said oscillator (c3 means for measuring or control1-ing the pressure at which the sample passes through said oscillator and for providing a signal representative of the pressure when pressure is not controlled in a preYiously established range; (d) means for measuring the temperature of the sample at said osc;llator and for providing a signal representative of the temperature; (e) means for measuring the frequency of osc~llation at said oscillator and for providing a signal representative of the frequency; (f) computing means for read-ing said signals and for calculating the unknown property of the sample using equatlons and data stored in said computing means and data supplied by said means for providing a pressure signal when pressure is not con-trolled in a previously estabtished range; and, (g) means for communicating information contained in said computing means.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of a fluidic oscillator.
Figure 2 is a schematic diagram of an embodiment of the in~en-tion comprising a heating value monitor wherein the heating value of yas flo~.~ing in a pipeline is measured on a continuous basis and d;splayed in a remote location.
Figure 3 is a schematic diagram of an embodiment of the inven-tion comprising a density monitor wherein the density of gas flowing in a pipeline is measured on a continuous basis and displayed in a remote location.

~5~6 Figure 4 ls a schematic diagram o~ an embodiment of the invention comprising a humidity monitor using two oscillators in parallel wherein the moisture content of gas flowing in a pipeline is measured on a continuous basis and displayed in a remote location.
Figure 5 is an expansion9 in block diagram form, of the portions of Figures 2, 3 and 4 labelled electronics.

DETAILED DESCRIPTION OF THE INVENTION
A device known as a fluidic oscillator is used in this invention. ~his is one nf a class of deYices which are utilized in the field of fluidics. A fluidiç oscillator may have any of a number o~ different configura~ions in addition to that depicted in FIGURE 1. The publications men~ioned under the heading "Statement of Art" describe fluidic oscillators and their governing principles in detail and therefore it is unnecessary to present herein more than the follow~ng simple description.
A fluidic oscillator may be described as a set of passageways, in a solid b10ck of material, which are configured in particular manner. If the passa~eways are centered in the block and the block is cut ~n half in the appropriate place, a view of the cut surface would appear as the schematic diagr~ of FIGURE 1.
Referring to FIGURE 1, a gas stream enters the inlet~ flows through ; nozzle 109, and "attaches" itself to one of two stre~m attachment walls 105 and 106 in accordance with the principle known as the Coanda effect. 6as flows through either exit passage lOJ or exit passage 103, depending on whether the stre~m is attaehed to wall 105 or wall 106. Exit passages 1~7 and 108 can be cons~dcred as extending to the outside of the block of materîal in a direction perpendicular to the plane in ~hich ~he other passages lie.
Consider a gas stream which attaches to wall 105 and flows through exit passage 107. A pressure pulse is produced that passes through delay line 104. The pressure pulse ~mpinges on ~he gas s~ream a~
the outleg of nozzle 109, forcing it to "attach" to wall 106 and fl3w through exlt passage 108. A putse passing through delay line 103 then causes the stream to switch back to wall 105. It is in $his manner that an oscillation is e tabtished. The frequency of the oscillation is a function of the pressure propagativn time through the delay tine and time lag involYed in the s~ream switching from one attachment wall to the other. For a delay line of given length, the pressure propagation time is a ~unction of the characteristics of the gas, as shown in the above mentioned publications and also by the equations which are presented herein.
The frequency of oscillation can be sensed by a pressure sensor or microphone located in one of the passages, such as shown by sensing port 102. A differential sensing device connec~ed ~o both passages can also be used. Sensing port 101 is shown to indicate one potential location for a tempera~ure sensor.
The invention can be most easily described by initial r~ference to F~gures 2, 3~ 4 and S, wh~ch represent particular embod~ments of the invention. R~ference will also be made to a particular proto-type heating value monitor which was fabrioated and tested. Referring to Fi3ures 2, 3 and 4, gas is flowing through pipeline 50. A sample flow loop 51 is formed by means of conduit, surh ~s 3/4-inch diameter pipe, connected to pipeline 50 upstream and downstream of pressure drop element 53. The purpose of pressure drop element 53 is`to cause a loss of pressure in pipeline 50 which is the same as the pressure drop in ~low loop S1 when a sufficient 2mount of gas is passing thrcugh flo~ loop 51~ 6as flow through flow loop ~1 is suffioient when gas composition at sample point 54 is sub~tanti211y the same as that in pipeline 50 at any yiven instank. Normally pressure drop el~ent 53 is ~ device present ~n the pipeline for a primary purpose unrelated to taking a s~mplez ~or example9 a control valve. A
suff~cient length ~f pipeline ~0 can serve as pr~ssure drop element 53 or an orifice plate oan be installed in pipeline 50 to serve the purpose. Valves 52 are used to isolate flow loop 51 from pip~line ~0.

~Z~59~6 With regard to Figure 3 only, pressure and temperature of the gas flowingin pipeline 50 are provided by pressure ~ransm;tter 75 and temperature transmitter 76. These are located close to pipeline 50, so that differences in pressure and temperature between their loca-tions and pipeline 50 are not significant. Pipeline 50 is covered with thermal insulation of a type commonly used on pipelines. The loca-tion shown in Fi~ure 3 has the advantage of allowir.g the density moni-tor to be a self~contained package. However, If the pressure and tempera-ture differences are significant, transmi~ters 75 and 76 can be located directly on pipeline 50. The measured pressure and temperature are referred to hereln as Tl and Pl.
Figure 4 represents one alternative embodiment of the present invention wherein it is desired to determine the moisture oontent of a ~as sample. Flow of a gas sample is provided in parallel through first fluidic oscillator 56 and second fluidic oscillator 78 with means for adjusting the water content of a portion of the sample before it passes through the seoond oscillator 78.
In all three embodiments as depicted in Figures 2, 3 and 4, sample lines 5~ carry samples of gas from sample points 54 to fluidic oscillators 5S. Sample line 77 branches off to supply a sample ofgas to fluidic oscillator 78 in the embodi~ent of Fi~ure 4. Filters 57 are provided to remove particles which might be present in the sample, so ~at the narrow passages of fluidic oscillators 56 and 78 or other flow paths will not become plugged. Pressure regulators 58~ of the self-con-

2~ tained type with an in~egral gauge, are prov~ded so that gas flvwing through oscillators 56 and that flowing through osci11ator 78 is at a substantially constant pressure. The frequency of oscillation at the osoillators may vary w;th pressure, depending on the particular oscillators used and the actual pressure at the osci11ators. As will be seen, frequencies are correlated with humidity ~oisture content and density9 so var~ation ~L2~S~6 for any other rcason is unacceptable. Any pressure regulating means capable of maintaining flnw through the oscillators at a substantially constant value may be used. Under certain circumstancesl sufficient pressure regulation will exist by v;rtue of system configuration and pressure level, so that no separate pressure regulation device is needed.
Orifices 60 are provided for the purpose, in conjunction with pressure regulators 58, of maintaining a constant flow of gas through each oscillator. Pressure gauges 59 indicate the pressures lC downstream of orifices 60. Normally it is not necessary to installorifices 60, as the sample lines or the inlet ports of the oscillators serve the same purpose. Conduits 71 (Figures 2, 3, 4) and 79 (Figure 4) carry the samples away from oscillators 56 (Figu~e 2, 3, 4) and 78 (Figure 4), to the atmosphere in a location where discharge of the gas will cause no harm ar to a process vessel where it can be utilized. However, the quantity of gas is suffi-ciently small that it may not be economical to do more than discharge it to the atmosphere. Pressure transmitters 61 are switch devices which provide signals for actuation of alarms if the pressures do not remain in previously established ranges. Thus oommunication that inaccurate results may be obtalned is accomplished. With reference to Figure 4 onlyg ~ryer 80 is provided to remove substantially all water from th~ gas which passes through oscillator 78. There are many commercially available devices to accomplish this. A typical device contains two beds of a desiccant material so that gas to be desiccated passes through one bed while ?5 the other bed is being regenerated by applied heat.
Obtaining a representative sample stream fram a pipeline, providing it to the inlet port of a fluidic oscillator, removing it ~rom the outlet port of the oscillator, and maintaining a substan-tially constant pressure drop across the ~scillator can be accom-plished by a variety of different means and methods for each given ~ 6 set of conditions, such as desired flow rate through the oscillator and pipeline pressure. These means and methods, which can be applied as alternatives to those shown in Figures 2, 3 and 4, are well known to those skilled in the art.
A fluidic oscillator can be designed and fabricated upon reference to the literature, such as that mentioned under the heading "Statement of Art" or may be purchased. In test work applicable to this invention, an oscillator supplied by &arrett Pneumatic Systems Division af Phoenix, Arizona was used. This oscillator is of a di~ferent configuration than that shown in FIGURE 1 in that the "loops" formed by delay lines 10~ and 104 are open such that the "loops" define cav;ties and in that there is only one exit passage.
Drawings of this configuration can be found in the cited references.
The flow rate through ~his oscillator when testing natural gas is approximately 250 em3/min when upstream pressure is approximately 20 psig and the oscillator is vented directly to atmosphere. A f10w rate range of 200 to 500 cm3~min is considered to be reasonable for cummercial use and sufficient to provide aeceptable humidity results.
Te~perature transmitters 67 ~Figures 2, 3, 4) and 8l (Figure 4) pro-vide the temperature of the gas at each oscillator. Any of the well known means of sensing temperature may be used, such as a the~mister, thermocouple, or solidstate semiconductor sensor. The sensor may be located in a passage of the oscillator, such as shown in FI~URE 1 ~sensing port 101), or in the sample line or conduit ad3acent to the oscillator. Microphones 66 (Figures 2, 3, 4) and 82 (Figure 4) sense the frequency of oscillation at each oscillator~ A microphone is located in a position to sense when the gas stream a~taches itself to one o~ the walls, such as the position shown in FIGURE 1 (sensing port 102). There are a wide variety of ~ 9~Lt~

sensors which can be used, ~or example, a piezoceramic transducer, in which pressure induces a voltage change, or a piezo-resistance transducer, in which pressure induoes a resistance change. Used in test work applicable to this invention was a Series EA 1934 micro-phone supplied by Knowles Electronics of Franklin Park, Ill.
Signals from miorophones 66 and 82, temperature transmit-ters 67 and 81, and pressure transmitters 61 are processed by equip-ment denoted field electronics 68 and control room electronics 69.
Field electronics are located adjacent to the oscillators while control room electronics are in a central control room some distance away from the oscillators. This equipment processes the signals to obtain humidities of the gas and performs other functions wh~ch will be described herein. Display unit 70 receives signals from control room electronics 69 and communicates humidities of the sample gas and other information in human-readable form. It may be, for example, a liquid crystal ~isplay. The information may be communicated to other equipment, such as a strip chart recorder for making a permanent reccrd or a computer for further manipulation.
Two containers of oalibration gas, 64 and 653 are provided to check that ~he monitor is operating properly. Normally one of the calibration gases has prop~r~ies in the lower part of the range of values expected of the gas flowing in pipeline 50 and one has p~operties in the hlgher part o~ that range. The monitor ~s placed in the appropr~ate cal~bration mode by means of one of lnput switches 18 ~Fl~ure 5). By mani-pulating valves 63s 72 and 73, the calibration g~ses are allowed to flow, in turn, , through calibration conduit 62 and sample line 55 to oscillator 56.
The monitor may be arranged so that properties of the calibration gases are displayed and a human technician must, if necessary, adjust the monitor to the known calibra~ion gas property values, or - `~

3~2 ~
may be arranged so that the monitor is capable of adjusting itself.
For example, the mon~tor could re-calculate the values of constants stored in it which are used in calculating sample humidlties or densities or heating values. Periodic calibratiorl must be accomplished to check for malfunctions and changes which might take place in the apparatus such as electronic drift, corrosion, and substances accumulating in the apparatus.
Since the pressure and temperature of the calibration gases will vaPy as conditions such as ambient temperature change, the calibration gas densities calsula~ed by the monitor must be adjusted to a pressure and t~mperature at which the calibration gas densities are known. For example, if pressure transmitter 61 measures a pressure of 20 psig (140 kPa gauge) and temperature transmitter 67 measures a tempera-ture of 30F (--1.1C~ when cal~bration gas from container 64 is flow~ng and the density of container ~4 gas is known to be 0.0448 lb/f~3 ~0.718 kg/m3) at 0C and 1 atmosphere ~101 kPa gauge~, the density conmunicated by the monitor must be at 0C and 1.0 atmosphere (101 kPa).
If the commun~cated density ~s significan~ly different from 0.0448 ~
(0.718 kg/m3), the monitor is not operating properly. Adjustment of a density value frDm one pressure and tempera~ure to another is easily accomplished by means of the equat~on of state presented herein.
The monitor may be arranged so -1 ~

~ -that densities of the calibration gases are displayed and a human technician must, if necessary, adjust the monitor to the known calibration gas densities, or may be arranged so that the monitor is capable of adjusting itself. For example, as was done in the prototype device, the monitor could re-calculate the values of con-stants stored in it which are used in calculat~ng sample densities.
The procedure just described does not accomplish calibration of pressure transmitter 7~ and temperature transmltter 7S (see F~gure 3). These items can be calibrated separately by standard means. If desired, the calibration gases can be introduced into flow loop 51 upstream of these items in order to include them in the calibration. It is also possible to compare a value determined by the monitor to the density of a calibration gas by manual means. Pressure~ temp2rature, ~nd density could be sommunicated by the monitor and an operator 1~ could refer to a standard chart or tables to compare the communicated results to the actual dçnsity of the calibration gas. Another method ~s to provide apparatus in line 55 to adjust pressure and temperature of calibration gas entering the oscillator to particular pre-established values. However~ this me~hod would be used only in rare circumstances, since it is less costly to manipulate numbers than to manipulate the physic~l condition of the calibration gases.

-18- .

~2~59~ -Partial calibrations, or operation checks, can be accomplished in a number of different ways. Use of a calibration gas can be combined with operation checks accomplished electronically.
A totally electronic operational check can be made. For example,means for generating appropriate oscillating tones can be provided at mlcrophones 66 (Figures 2,3-4? and 82 (Figure 4) so that new values of Kl and K2 can be calculated. Of course, this procedure checks only the electronics and not the oscillator. In another simple check, tuning forks are used to generate tones at microphones 66 and 82 and the synthetic "value" resulting from the tone inputs is compared to the expected proper value in computing means. Qperational checks can be performed by switchingflow from one oscillator to ~he other in ~he embod~men~ of Figure 4.
Temperature changes can be used to perform operational checks. This can be doneby using heating means, such as electrical resistance coils, to heat gas flowing into the oscillators and comparing v~lues of properties for heated and unheated gas. If the gas used in the check is from a changing process source, provision must be made to prevent changes during the checking period. This can be accomplished by providing a container to collect a sufficient quantity of gas to do th~ check or recycling gas ~rom the outlet of the oscillators back through the system 6iven a particular objective to be accomplished, other checks will become apparent.

An assembly of electronics devices for processing signals from the transmitters and microphones (variables) and providing signals to the display unit can be fabricated from standard components by one skilled in the art. FIGURE 5 shows one such design in simplified ~orm. Line 19 indicates which items are located in the field and which are located in the control room. For ease of understanding, Figure 5 is drawn for the cases in which only one oscillator is used. It can easily be seen that certain items would need to be duplicated so data relat~ng to two osc~llators can be provided to the computing means.
lQ Though the following description mentions only oscillators 56 and associ-ated items, operation of osc~llator 7~ (Figure 4~ and associated items is the same as for oscillators 56. A signal from microphone 66 is provided to amplifier 1, passed through filter 2~ and converted to a square wave pulse 1n square wave shaper 3. The output of square wave shaper 3 is provided to counter 6 by means of transmitter 4 and receiver 5. Counter 6 counts the number of cycles occurring in oscillator 5b in a unit of time, thus generating frequency information.
The signals from pressure transmitter 61 and temperature transmitter 67 are selected one at a time by analog switching device 7 and sent 2Q sequentially to analog-to-digital converter 89 where they are converted to digital form. Serial input/output devioe 9 converts the output of analog~to-digital converter 8 to a serial pulse train, ; which is provided by means of transmitter 10 and receiver 11 toserial input/output device 12, located in the control room.
Memory device 1~, a random access memory chip (RAM), is used to store the variables. A progr~m ~or control G~ the electronics devices and performing computations is st~red in memory -59~ E;

device 14, a programmable read-only memory chip (PROM). Constants needed for the computation are storecl in memory device 16, an electronically erasable programnable read-only memory chip (EEPROM).
Central processing unit 13 performs the necessary computations and provides output signals to display unit 70 (Figures 2, 3,4). Input switches 18 are used to provide human input to the electronic components. These are rotary click-stop switches which can be set to any digit from O to 9. One of the switches is the mode switch and the others are used to enter numerical values. The position of the mode switch "instructs" the apparatus what to do. In the calculate mode, the apparatus displays the humidity of a sample. When the mode switch is placed in the "constant load" position, numeric~l values of constants can be ~anually set on the other switches and loaded into the system by depressing a button. Another position of the mode switch allows values of variables to be displayed in sequence on display 70. When it is desired to calibrate the apparatus, still other positions are used~ Additional positions are used as required.
Parallel input/output device 17 provides a means of transmitting inFormation from input switches 18 and also controlling counter 6.
It will be clear to one skilled in the art that certain of the electronic devices may be collectively referred to as a computer or computing means or may be contained within a computer or computing means.
The basic equation used in the practice of this invention which describes the operation of a fluidic osçillator is KlGT
M = _ ~ K2 , where M = molecular weight of the gas flowing through oscillator, G = specific heat ratio of the gas flowing through oscillator, T = temperature of the gas flowing through oscillator, F = frequency of oscillator output signal, and K1 and K2 = constants.
The quantity G can be provided as a constant stored in computer memory or can be calculated by means o~ a correlation, such as the equation 6 = K3 ~ K4M + KsM2 ~ ~6M3 , where K3, K4, Ks and K6 are constants.
The computer is programmed to solve these equations for each oscillator, using values of F and T provided as described above, and values of constants which exist in computer memory. lt can be ; readily seen that these molecular weights can be used to obtain the moisture content of the sample by ~eans of the equations Ms = Xw Mw + Xb Mb and Xw + Xb ~ l , where X = weight fraction, Xw = X of water present in the s~mple, Xb = X of all components of the s~mple other than water9 Ms = M of the sample ~efore water content adjustment, Mb - M of the sample components other than water ~average), and Mw = M of water.
M~ is calculated by means of the bas k equation applied to data ~rom oscillator 56 ~nd Mb is derived from data ~rom oscillator 78 in the same manner. Thus there are two equations and two unknowns9 so Xw ean be calculated in ~he computer.

-~2-. The heating value of the gas can be calculated by use of an equation such as H ~ C1M ~ C2 , where Cl and C2 are constants and H ~ heating value.
The computer is programmed to solve these equations to obtain H, using values of F and T provided as described above, and values of constants which exist in computer memory.

The density of the gas can be calculated by use of the equation D _ m = MPI , where V ZRT

D = density, m = mass, V = volume, Pl - pressure at the point of density measurement~
Tl = temperature at the point of density measurement, ~ = compressibil~ty factor, and R ~ universal gas constant.

This equation is derived from the familiar equation of state m PV - ZnRT = Z - RT 9 where : M

n - number o~ moles. Z can be easily expressed by means of equations which depend on M and data available in the l~terature, as explained herein.

9~

The computer is programmed to solve these equations to obtain D, using values o~ F, T, Tl, and Pl provided as described : above, and values of constants which exist in computer memory.
The equation for G used in the prototype unit was S developed by a standard curve-fitting method usiny values of G
available in the literature h r gases such as methane, ethane, etc.
As can be appreciated by those skilled in the art, there are other ways to develop and express G and to store it in the computer.
The most appropriate method is dependent on the particular applica-tion.
An approach to developing a basic oscillator equation on a theoretical basls is as follows. Reference is made to Figure 1 as -~4-an exanple. A pressure pulse which passes through delay linP 103 or 104, described above, travels at the local speed of sound, u.
Denoting the length of each delay line as L, the time required for the pulse to traverse a delay line is L/u. The time for a oomplete oycle of oscillation includes that required for a pulse to travel through each delay line. An equation for the local speed of sound is ~ GgRT ~ l/2 u = _ ) , where M

u = speed of snund, g = gravitational constant, and R = universal gas constant.
Thus the time required for the pulse to traverse the two delay lines is 2 L/u or f GgRT ~ l/2 2 L / ~ _ J

As explained above9 the total time for a cyc7~ of oscillation also depends on switching time, the time required for switohing of the stream from one attachment wall to another, or the period between arrival o~ a pulse propagated through a delay llne at nazzle 109 and the start of a pulse through the oth2r delay line. Switching time oan be expressed as inversely propor~io~al ~o w, ~hat is as ~2~5i9~

~ GgRr ~ I/2 constant / ~ J
\ M

Since L is a constant for any given oscillator and the inverse of time is frequency, t~e following equation can be wri~ten /GgRT~1/2 ~GgRT~1/2 F = ~ - ) / cons~ant ~ ~ ~ / 2 L

Solving the equation ~or M and making 9~ L, and R a part of the constant, the equation becomes constant x 6T
M = 2 : : F
: If the above constant is designated as Kl, and K2 is added to the right-hand side~ the basic equation presented above is obtairled~ It : has been found necessary to ~dd the constant K2 to the equation in order to accurately describe the oscillator. It is not possible to use a purely theoretical equation, in part as a result o~ the imper-fections o~ hardware and measuring equipment, For example, no two fluidic oscillators will perform in an ident~cal manner. In ~ par-ticular oscillator, which was used in a natural gas applic~tisn, K1 and K2 were empirirally established by flowing gases such as methane, ~thane, propane, butane, and pentane through the mon~tor. The values of Kl ~nd K2 thus established were 7.53B x 10~ and 1.~8, respectively, 2~ This calibration procedure mus~ be followed for each ~onitor which is ~abrica~ed, using gases similar to ~he gas for which the monitor is ts be used. However, only two calibr~tion gases are required to define K 1 ~nd K2.
_?6_ ~ S 9 ~ ~i The compressibility fac~or, Z, from the equation of state to calculate density, is a measure of the deviation of the sample gas from ideality and is added to ~he expression commonly known as the ideal gas law in order to make the ideal gas law applicable to real gases. Since compressibility factors are covered by a vast quantity of literature wllich includes a number of different methods of computing them, there is no need to explain the basic theory herein. For further information and references to the litera~ure, .

refer to Basic Prin~ples and Calculations in Chem~cal En~ineerinq, 2nd edition, 1967, Prentice-Hall, Inc.9 by Himmelblaul p. 149 and following. Also useful are Chemical Process PrinciEles, 2nd edition, 1954~ John Wiley & Sons, by Hougen et al, p. ~7, and Perry's Chemical Engineers' Handbook, 4th edition, McGraw-Hill, p. 4-49.
In the prototype device, Z is calculated by means of the equation Z~
Z
S~

where S = (I ~ 3.444 x 105 P1 loO~062 M ) 1 T13.82 M between 16 and 21.75, or S ~ 9.16 x 105 P1 ~0.041 M ~ 1/2 .
T13-82~ J

M between 21O76 and ?7,55, and ~B = 0.999287 ~ 9.25222 x 10-5 M - 1.06605 x 10-5 M2, where Z~ = 7 at partieular base conditions, S - supercompressibility factor, P1 ~ psig, and T1 ~ R.
The equations ~or S are empirically derived. These and the equation for Z can be found in Princi~les_and Prac~ices of Flow Meter ~2~S91f~
Engineerin~, 9th edition9 1967, by Spink, published by Foxboro Co.
and Plimpton Pre~s of Norwood, Massachusetts. The expressi~n for ZB
was derived by ~eans of correlating values of Z~ for gases of different molecular weights. This was done by converting values o~
base temperatures and pressures for various gases~ using critical temperatures and pressures ubkained from the literature, to reduced pressure and temperature and then using charts prepared by Nelson and Obert to obtain Zg.
The equation for heating value presented above can be found in Report No~ 5 of the Transmission Measurement Committee of the American Gas Association (Arlington, Virginia, Catalog No. XQ 0776).
When H is expressed in BTU per standard cubic feet o~ gas, C1 =
54.257 and C2 = 144. If it is desired to express H in BTU per pound of fuel gas9 Report No. 5 indicates that Cl and C2 assume different values and l/M is substituted for M. Of course, it is possible to use other correlations for calculating H of natural gas ~n the practic~ ~f this invention. And a ~ifferent correlation is needed for determining H of substances other than hydrocarbons having one to approximately six carbon atoms. This correlation would likely be developed by empirical methods.
It is possible to present information derived from the practice of this invention in several different forms. For example, H may be provided in metric units by appropriately programming the computer or the Wobbe Index of the sample gas may be presentedO
Wobbe Index is a parameter used in ~he yas industry. One method ~f expressing ~t is Wobbe Index = kH / M1/2 , where k - the square root of the ~olecular weight of air.
The samp1e gas may contain compounds which are non-combust-ible. The concentrations and mo1ecular weights of these compounds must be provided to the eomputer in order to produce an accurate heating Yalue~ This may be done by means of an analyzer through -29~

`;
~2~5~

which the sample gas ~s passed and which is arra~ged to automatical~y provide appropriate signals to the computer, A variety of analyzer apparatus is available for use, such as a gas chromatograph.
Alternatively, average values of concen~rations and molecular S weights of the non-combustible components may be manually entered into the computer. For example, natural gas often contains carbon dioxide and nitrogen and their concentrations do not vary greatly from hour to hour. It will often be satisfactory to analy~e for these once a day and enter values by use of the input switches mentioned above. The eguation ~or H must be modified to account for these constituents which add to the volwme of gas buk not the heating value. For example, if there are two ron-combustible constituents whose concentrations are expressed by Yolume fractions Xl and X2 and having molecular weights M1 and M2~ the equation 1~ presented above becomes ~1 (M - XlMl - X2M;~) -Il s , _ + C? (1 - Xl - X2) 1 - Xl - X2 ~

The derivation of this and similar forms is easily accomplished by algebraic manipulation.
In some appl ka~ions it ~ay be desirable to provide to the computer concen~rations and ~olecular weights of combustible constitu ents in the same manner as non~combustible const~tuents in order to improve ~ccuracy. The equation used to calculate H can easily be modified for these applications. An example is the measurement of heating value of off-gas from a hydrogen-producing hydrogen recycle process, such as catalytic reforming or dehydrsgenation~ For -3~-. _ , ~a 2~ 9 background in this area, U.S. Patent No. 3,974,~64 (Baiek et al.) may be consulted. ThP o~f-gas is often used in whole or part as a fuel. It is comprised of both hydrogen and various hydrocarbon com-pounds. Since the heating value of hydrogen is not accurately reprç-sented by many correlations used for hydrocarbons~ it can be seen that use of exact hydrogen concentrations and a correlation for hydrocarbons yields greater accuracy than use of a correlation which accounts for both hydrogen and hydrocarbons. Also, because hydrogen roncentration in hydro-gen recycle processes is often meas~red for other purposes, the improve-ment in accuracy may be available without purchase of another analyzer.
Use of a heating value monitor in control of a combustion zone may be highly desirable or necessary to ~chi2ve acceptabl2 control. Consider a process in which temperature in a ~urnace must be mnintained in a relatively narrow range. A typic~l control arrangement is to ~easure furnace temperature and adjust fuel flow to maintain it constant. When the amount of heat absorbed by the process incre~ses, the temperature drops and more fuel is burned to increase temperature to the proper Yalue. Also, changes in fuel heating value will cause furnace temperature changes for wh~ch the control system must compensate. Since the performance of 2 control system degrades as the number of factors for which it must compensate increases, it is desirable to eliminate fluctuations in temperature resulting from ohanges in fuel heating value. This can be ~ccomplished by m~asuring fuel flow and heating value~ establishing a signal representative of their produ~t, and adjusting fuel flow by reference to this product. The product is representative of rate of heat flow to the process. The rate of hea~ flow is adjusted ~ith reference to process temperature. Expressing the system in terms of standard ~S91~

analog control apparatus9 a temperature controller receiYing a signal representativè of furnace temperature would supply the set pointj in cascade fashion, to a controller which receives a signal representa-tive of the heat content of the fuel and adjusts the fuel flow control valve.
A heating value ~onitor may be applied to improve fuel economy. Consider a combustion ~one where fuel ~low is adjusted to maintain a constant zone temperature. Combustion air flo~ rate is normally established by measuring fuel flow and combining a signal representatiYe of fuel flow with a previously established ratio value to obtain a signal used ~o adjust air rate. This control method is incapable of responding to changes in fuel hea~ing valu , so normal practice is to set up the system so that excess air is supplied to the combustion zone. Fxces5 air is that quantity o~ ~ir which is not needed to combine with the fuel~ It is desirable to keep excess air at a minimum as the amount of fuel used to heat it represents a total loss. As the fuel heating value increases, more combustion a~r is required. If insufficient combustion air is supplied~ fuel i~ wasted as a result of incomplete combustion. A signal representa-tive of fuel gas heating value can be used to ad~ust air ~low rate9usually by means of adjusting the ra~io value, SQ tha~ the excess ~ir quantity is small, thus saving fuel for heat~ng unnPeded air and avoiding use of extra fuel.
In the simple examples above, reference is made to objectives of close contrQl, or control in a narrow range~ and control to improve fuel economy. Of course, these objectives are not mutually exclusive. Control systenls can be designed to achieve both objectives by adjusting both ~uel and air flows. Th~se systems 5~

may utilize standard analog control instrumentation or more sophisticated apparatus, such as that incorporatin~ digital computing devices. Further, there are other objec~ives, such as mentioned herein~ which may need to be achieved in control of a 5 particular combustion ~one. While it is not possible to present herein all of the variations in objeotives and methods of achieving same, the usefulness of the present invention in doing so will be seen by those skilled in the art upon consideration of particular situations.
FIGURE 2 shows an embodiment of the invention where a continuous flow of sample through the occillator is established in order to obtain a continuous heating value for gas flowing in a process pipeline. An embodiment of the invention for use in a 1aboratory would not require the flow loop shown in FIGURE 2.
Sample can be collected in an evacuated pressure-resistant container~
commonly called a sample bomb, which is then connected to sample line 55. ~n applications where ~he heating values of liquids are to be determined, a means for vaporizing the liqu~ds is required. This can be accomplished; for example, by use of electric resistance heat-ing elements surrounding a portion o~ conduit through which thesample passes. The term "gas" is frequently used hereinp it should be understood to include vapors result~ng from fuels whioh are lnitially in liquid form. For example~ it may be desired to deter-mine the heating value of a sample of No. 2 fuel oil, whioh ~s liquid at normal ambient temperatures.
,.

In a relatively simple embodiment of the invention, the sample loop shown in Figure 3 omitted~ Sample is collected in an evacuated pressure-resistant oontainer, which is then connected to sample line 55, either upstream or downstream of filter 57. The density communicated by the apparatus is that at the temperature and the pressure measured by pressure transmitter 61 and temperature transmitter 67. There is no need to divide the electronics into two packages at two different locations. This embodiment might be used in a laboratory. It might be desired to add to this embodiment the feature that the apparatus is oapable of calculating a density value for sample gas at pressures anJ temperatures different from those measured by transmitters 61 and 67 and which are proYided to the apparatus as follows. A tempPrature and a pressure can be manually entered into the apparatus by means such as input switches 18 or l~ they can be provided by apparatus which measures kemperature and pressure at some point of interest and transmits appropriate signals to the oomputing ~eans of the i m ention.
F~ure 3 shows a more complQx embodiment of the invention where a continuous flow of sample through the oscillator (at temperature T~ is established in order to obtain a con~inuous density value for gas flowing ~n a process pipeline (at temperature ~ ~q~S 9 T1 and press~re P1). In thls embodiment, the apparatus is arranged to provide a density representative of the sample gas at a point upstream of the pressure controllinq means represented by item 58 of Fiyure 3 further arranged so that the upstream point is representative of the main stream from which the sample is taken.
As noted earlier~ a variation in the pressure at which gas passes throu~h the oscillator may affeot the accuracy of ~he monitor.
This is true even though the pressure is a variable used in calculating density; that is, a oalculated density value may be in~orrect i~ the presswre value used in the calculation is correct but outside a particular range. Thereforeg it is desirable to monitor the pressure and communicate any departure ~r~m a previously established range.
This can be aocomplished by seYeral means, including adding a primary sersor9 suoh as a pressure switoh, in ~he appropria~e location9 such as line 55 nf Figure 3, or adding the appropriate means in the elec-tronics portion of the apparatus to utilize the pressure signal provided for use ~n the equation, suoh as the signal transmitted by pressure transmitter 61 of Figure 3. This monitoring provision is not depicted in Figure 3.
The presen~ invention may be embod1ed in apparatus ~or determining the mass flow rate of gas in a pipeline~ This can be donP by combinirg apparatus such as that shown in Figure 3 with apparatus for measuring the volumetr~c flow rate of the gas in the ~ pipelire and multiplying density times volumetric flow rate in apparatus such as the computing means of Fi5ure 3. Xf the apparatus for measuriny volumetric flow rate comprlses a calibrated obstruction to flow, such ~s an orifice plate, and means to measure the pressure drop across the obstruotion, such as a differ2ntial pressure cell, -3~-~L2~59~

the pressure drop can be provided to the computing means for calcula-tion of mass flow rate instead of calculating the volumetric rate outside the computing means.
An alterna~ive to the use of dryer sn of Figure 4 is to use apparatus to saturate the sample portion passing through oscillator 7&~ This apparatus is readily available. For example, saturating apparatus may comprise a small chamber into which a fine spray of water is introduced through a nozzle. After gas pas~es through this saturating chamber, it is passed through another çhamber for removal of any water droplets which might exîst in the stream. The equations used in practicing this embodiment of the invention are similar to those presented above. An example is as follows. For the oscillator through which sample is flowing before adjustment of water content Ms ~ XwMw ~ ~bMb and Xw + X~ = 1.
For the oscillator through which saturated sample is flowing Ma ~ XaWMw ~ XabMb and ~aw + Xab = 1.
Previously undefined terms are Ma = M of sample after satura~ion, Xaw = X of water in sample ~ter saturation, Xab = X of all components of the sample other than water after saturation.
It can be seen that there are five unknowns and only four equations~
so that it is necessary to know one morP quantity whPn practicing this embodimen~ o~ the invention than when using drying apparatus as described ~bove. However, ~his informatlon is of~en available.

-36- ~

~2~S9~l Ei Equations ~or other cases can easily be written.
~ igure 4 shows an embodimen~ of the invention when a oontinuous flow of sample through the oscillators is established in order to obt~in a continuous humidity value for gas flowing in a pipeline. An emb~diment of the invention for use in a laboratory would not require the sample loop shown in Figure 4. Sample could be collected ~n an evacuated pressure-resistant container, commonly called a sample bomb, which is then connected to sample line 55. In applications where the moisture csntents of liquids are to be deter-mined, a means for vaporizing the liquids is required. This can beaccomplished, for example, by use of electric resistance heating elements surrounding a portion o~ the conduit through Nhich the sample passes. The term "gas" is frequently used herein; ~t should be understood to include vapors resulting from substances which are initially in liquid form.
In the parallel flow arr~ngement shown in Figure 4, the sample is spllt into two portions and each portion is passed through a different oscillator. The water content of one of the portions is adjusted before passage thrcugh the oscillator and the humidity of 2n the sample is calculated by reference to di N erences in signals obtained from the transmitters associated with ~ach oscillator. An alternate flDw arrangement involves series flow, wherè the entire sample is passed thrnugh one oscillator and then through another.
The means for moisture adjustment is located such that ~he ~ample 2~ passes thrsugh the first oscillat~r, has 1~s moisture content ~djusted9 and then passes through the second oscillator. This can easily be Yisualized by altering F~gure 4-so that sample llne 77 connects to vent line 71 instead of sample line 55, thus the flow ~L~ S ~L 6 sequence would be oscillatdr 56 to dryer 80 to oscillator 78. In this embodiment of the invention, the moisture content o~ the sample is calcul~ted in the same manner, that is, by reference to the differences at each oscillator. However, it should ~e no~ed that when a continuous flow of sample is provided, a rapidly changing sample humidity could result in inaccuracies, since there is a time lag between measurement of a "particle" of sample in the first oscillator and measurement of the same moisture adjusted "particle"
in the second oscillator. Compensation for this time lag can easily be a~complished in the electronics portion of a monitQr to remove any inaccuracy. One of the methods of compensating inYolves simply placing the same time lag in the s~gnal path associated with the appropriate oscillator just before the signal differences are noted.
In another embodiment of the invention, only one oscillator is used. Means for adjusting thc water content of the sample are provided along with means for periodically bypassing the sample flow around the water content adjustment means. For example, if a dryer is used, the stream continuously passing through the oscillator alternately co~tains water and does not contain water. This san be : 20 easily visualized by altering Figure 4 to eliminate the sample line branch for oscillator 56, placing a three-way va1ve in sample line 77 just ahead of dryer 80~ and placing a length of conduit between the valve and sample line 77 just downs$ream o~ dryer B0; then the three-way valve ~s periodically cycled to route sample flow "around"
dryer 80. The moisture content o~ the s~mple is calculated by reference to differences in signals received from the transmitters associated ~ith the oscillator for each oondition; that is, when dried sample is flowing and when non-dried sample is flowingO The -~8-same time lag problem as noted above exists when the sample humidity is rapidly changing. Compensation can be accomplished in the same manner.
The use of the examples set forth herein are not intended as a limitation on the broad scope of the invention as set forth in the claims. It is also intended that further applications of the principles of the invention as would normally occur ta one skilled in the art to which the invention relates be included within the claims. Mixtures of gases not including water can be analy2ed by applications of the principles of this inven$ion. The term "gas"
is frequently used herein; it should be understood to include vapors.

, .

Claims (17)

CLAIMS:

1. Apparatus for determing an unknown property of a sample of gas comprising:
(a) a fluidic oscillator;
(b) means for establishing flow of the sample through said oscillator;
(c) means for measuring or controlling the pressure at which the sample passes through said oscillator and for providing a signal representative of the pressure when pressure is not controlled in a previously established range;
(d) means for measuring the temperature of the sample at said oscillator and for providing a signal representative of the temperature;
(e) means for measuring the frequency of oscillation at said oscillator and for providing a signal representative of the frequency;
(f) computing means for reading said signals and for cal-culating the unknown proprty of the sample using equations and data stored in said computing means and data supplied by said means for pro-viding temperature and frequency signals and by said means for provid-ing a pressure signal when pressure is not controlled in a previously established range; and, (g) means for communicating information contained in said computing means.

2. The apparatus of Claim 1 further comprising means for establishing a flow of one or more calibration gases, in sequence, through said oscillator and means for adjusting the apparatus so that the property calculated by the apparatus for the calibration gases is substantially identical to the known property of the calibra-gases.

3. The apparatus of Claim 1 further comprising means for establishing a continuous flow of sample through said oscillator.

4. The apparatus of Claim 1 further comprising a flow loop which is comprised of an inlet connection and an outlet connection communicating by means of a first conduit, wherein the inlet and outlet connections are connected to a process pipeline so that process fluid can flow continuously through the flow loop, and further comprising a second conduit through which the sample can flow continuously from the flow loop to the apparatus of Claim 1.

5. The apparatus of Claim 1 further comprising means for vaporizing a sample in liquid form to provide a gaseous sample.

6. The apparatus of Claim 1 further comprising means for monitoring the pressure of the sample flowing through said oscillator and communicating any departure of the pressure from a previously established pressure range.

7. The apparatus of Claim 1 wherein the unknown property is heating value and wherein component (c) is a means for controlling pressure of the sample in a previously established range.

8. The apparatus of Claim 1 wherein the unknown property is density and wherein component (c) is a means for measuring the pressure and for providing a pressure signal to said computing means.

9. The apparatus of Claim 8 further comprising means for providing values of pressure and temperature to said computing means and calculating a density value for sample gas at the provided values of pressure and temperature.

10. The apparatus of Claim 8 further comprising means for measuring and transmitting the pressure and temperature of the sample at a point upstream of said pressure controlling means to said com-puting means and calculating a density value for sample gas at said upstream point.

11. The apparatus of Claim 8 further characterized in that said upstream point is located such that the measured pressure and temperature are representative of the main stream from which the sample is taken.

12. The apparatus of Claim 1 wherein the unknown property is moisture content, wherein component (c) is a means for controlling pressure of the sample in a previously established range and wherein the apparatus includes means for adjusting the water of the gas sample before it passes through said oscillator and means for periodically by-passing flow of the sample around the water adjustment means and for providing a signal to said computing means that the water adjustment means is being by-passed.

13. The apparatus of Claim 1 wherein the unknown property is mGisture content, wherein component (c) is a means for controlling pressure of the sample in a previously established range and wherein the apparatus includes a second fluidic oscillator with means essentially identical to that of the fluidic oscillator of Claim 1 and means for adjusting the water content of the gas sample before it passes through said second oscillator.

14. The apparatus of Claim 13 further characterized in that said oscillators are arranged in series, so that the sample flows initially through said first oscillator and then through said second oscillator, and in that said means for adjusting water content act upon the sample before it passes through said second oscillator, but after it passes through said first oscillator.

15. The apparatus of Claim 13 further characterized in that said oscillators are arranged in parallel, such that a first portion of the sample passes through said first oscillator and a second portion of the sample passes through said second oscillator, and in that said means for adjusting water content act only upon the second portion.

16. The apparatus of claim 12 or 13 further characterized in that said means for adjusting water content removes substantially all water from gas passing through said means.

17. The apparatus of Claim 12 or 13 further characterized in that said means for adjusting water content substantially saturates gas passing through said means.