US 3779069 A
A gas chromatograph for analyzing specimens from a chemical-process line is triggered by a pneumatic sawtooth generator. The output signal is delivered to the recorder directly and through control, regulating and computing elements, all operating with pneumatic, rather than electrical, signals. The process regulator is likewise of the pneumatic type.
Description (OCR text may contain errors)
United States Patent 1191 1111 3,779,069 Berthold Dec. 18, 1973 [5 CHROMATOGRAPHIC APPARATUS/AND 3,326,237 6/1967 Friclg 137/6254 METHOD 3,177,138 4/1965 Larrison..... 73/23.1 X 3,057,184 10/1962 Spracklen 73/23.]  Inventor: unt r th l r n s h, 3,106,087 10/1963 Kindred 73/231 Germany 3,212,323 10/1965 Thompson et a1 73/23.1
 Assignee: Veb Petrochemisches'Kombinat OTHER PUBLICATIONS Schwedt,Schwedt, Germany Industrial Applications'"-Chemical Eng. Progress-  Filed: Jam 4, 1971 Vol. 56, N0. 9, pp. 54-57, Sept. 1960  Appl. No.: 103,786 Primary Examiner-Charles A. Ruehl Art K 1F. R v  Foreign Application Priority Data army at 055 Jan. 5, 1970 Germany .......WP 421/144 788  ABSTRACT 0 1 v A gas chromatograph for analyzing specimens from a 52 vs. C]. 73/231, 137/624. 14 chemical-process line is triggered y a Pneumatic 51 1m. (:1. 60111 31/08 tooth generator The Output Signal is delivered to the  Field. of Search 73/23, 23.1; recorder directly and through control, regulating and 235 201 M 201 37 24 14;251 1 3 computing elements, all operating with pneumatic, rather than electrical, signals. The process regulator is 56 R f n Cited likewise of the pneumatic type.
UNITED STATES PATENTS 13 Claims, 19 Drawing Figures 2 951.361 9/1960 Fuller 73/23.] u g 4 DETECTOR AHE- scrcr/pueu.
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Gijnfer Berfhold INVENTOR. Z5 \CONI'EOLLEE I PATENTEU DEC 1 8 I975 SHEET 3 OF 4 INPUT FIG. 3
ENABLING INPUT. SIGNAL OUT/ 071f:
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INVENTOR. Gunter Berfhold FIG. 5A
CHROMATOGRAPHIC APPARATUS AND METHOD FIELD OF THE INVENTION My present invention relates to a chromatographic apparatus and method and, more particularly, to a method of and apparatus for controlling, evaluating and plotting chromatograms obtained from gas chromatography, especially for the control of a process followed by gas chromatographic analysis of a stream derived from the process.
BACKGROUND OF THE INVENTION Gas chromatographic analysis has been used heretofore for a variety of purposes which may be generally described as analysis and process control purposes. In accordance with the principles of gas chromatography, separation of the components of a gas mixture is carried out by passing the same through a chromatographic column whereby the components of the mixture are distributed between two phases, i.e., the solid phase or the porous packing of the column, also referred to as the stationary phase, and the moving or gas phase which may include a carrier gas sweeping the components and the mixture through or along the sta tionary bed. The column is maintained at a constant temperature and a substantially constant flow of the gas mixture, entrained by the carrier gas, is passed through the column.
Since the adsorption characteristics of each component of the mixture differ from those of the other components, the components are retained by the stationary phase to different degrees. The effective speeds of the several components of the mixture through the stationary phase or column thus differ.
The column length is selected such that, when the components emerge from the stationary phase, they ap pear as individual bands separated by zones of the carrier gas. The definition" of the column or its resolving power is a measure of the ability of the column to separate the distinct components into discrete bands. In practice, however, some components may be so alike in adsorption characteristics and effective velocities as to prevent sharp boundaries from forming between the bands. Hence, when the composition of the effluent is sensed by a detecting device capable of indicating the presence of the components qualitatively and quantitatively, the result is a signal having a number of peaks corresponding to the succession of components.
In process control, a gas or vapor stream is drawn from the end or any intermediate point of interest of a process line and is analyzed by gas chromatography, the results of such analysis being constituted as a feedback signal for controlling a process variable, e.g., an operating parameter such as temperature or pressure, or the amount or concentration of a particular reactant.
The principles of such control are fully described in Gas Chromatography, Reinhold Publishing Co., New York, 1959. To the extent that the present invention provides for a chromotographic apparatus of conventional type, therefore, it is to be understood that the intent is to describe a chromatographic system as set forth in this work. Conventional elements of the gas chromatograph include, of course, the source of the gas, the pressure-regulating means, the column, thermostatic devices and temperature control arrangements, the source of carrier gas, a differential detector and a gas-flow-regulating or sampling system.
Laboratory analyses make use of a simplified gas chromatograph in which the results may be plotted, while process-control systems employing gas chromatography additionally require means for sensing the peaks or any particular peak, means responsive to one or more peaks for producing an input altering a process parameter, calculating and control elements responding not only to the peak detected and plotted, but also to the tendency of the output curve, i.e., to the slope thereof, for providing control signals in accordance with proportional-control, proportional-integral control, and integrating means or planimetric-analysis means. The evaluation of the plot can be carried out manually in a time-consuming and expensive manner or automatically by conventional computing elements in the form of a digital output. For the most part, conventional plotting devices are electrical, electronic or electromechanical, involving electrical, electronic or electromechanical computing elements and may make use of planimetric measurements derived by similar automatic means. The output of such circuitry is applied to electrical, electronic or electromechanical controllers.
Not only are the circuits of the above-described systems complex and expensive, but in substantially all cases they involve contacts and other switching devices which are sensitive to corrosive gases and dust which is generally present in abundance at the plant. While efforts have been made to hermetically seal systems of the aforedescribed type because of the danger of explosion by sparking where explosive gases are used or eval uated, these techniques have not succeeded in overcoming the disadvantages of the electronic, electrical and electromechanical devices used heretofore. In practice, a high failure rate has been observed in part as a result of oxidation of contacts and electrical failure and, in part, because of corrosive mechanical and chemical attack upon the components. As a result, loss. of control of the process and the production of poorquality products is commonplace. It is not a satisfactory answer to provide nitrogen blankets, for example, explosion-proof housings or the like since these protective measures themselves may fail and open the door to the dangers set forth above.
OBJECTS OF THE INVENTION It is the principal object of the present invention to provide an improved gas chromatographic method and apparatus which will avoid the aforedescribed disadvantages and provide accurate and reliable results for process control.
Another object of the invention is to provide a method of controlling a chemical process involving a gas stream which is safe and reliable and makes use of relatively inexpensive components.
Still another object of the invention is the provision of an apparatus for controlling a chemical process and having a safe reliable system responsive to a gas chromatograph.
Another object of the invention is to provide a method of and an apparatus for gas chromatographic control of a chemical process which uses components of low cost and high reliability, which is not sensitive to corrosive and explosive gases, which cannot generate ignition signals, and which can carry out all of the mathematical functions required of such a control system.
Another object of the invention is found in the provision of a method of and an apparatus for the control of a gas chromatographic process and the plotting of its chromatogram, whereby the control system is of low cost and requires minimum monitoring, repair and replacement cost, which is completely secure against explosion and which is accurate and permits the operation of control devices from the outputs of the system.
SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, with a fully pneumatic control system for a gas chromatograph having a sampling member, a column through which the sample is passed, and a detector member responsive quantitatively and qualitatively to the bands of the mixture emerging from the column. The control system, which is fully pneumatic, as noted earlier, comprises a pneumatic sawtooth generator for triggering the gas chromatograph and providing a clock signal in the form of pressure pulses, and a gating network connected between this pneumatic clock and the pneumatic plotter for controlling the delivery of the signal to be plotted to the latter.
More specifically, the control of the gas chromatograph and the plotting apparatus, according to the invention, comprises the pneumatic clock or timer which includes integrating means, gate means, relay means and switch means for generating a pneumatic signal in the form of a sawtooth, the latter signal being applied to a plurality of pneumatic switching stages performing the requisite control functions. One pneumatic-switch stage or means is employed, in accordance with the present invention, for triggering of a pneumatic sampling means or the aforementioned sampling member via a pneumatic actuator so that the sample gas at predetermined intervals is introduced via the carrier-gas stream into the chromatographic column.
According to another feature of this invention, a further pneumatic switch stage or means controls the plotter, while this or similar stages provide for storage of the detected signal of the component of interest, provide a null correction for the recorder and connect various mathematical operating elements including a pneumatic summer or adder or a pneumatic multiplier into the system. Additional switch signals can be provided for, for example, functional interchange of the columns whereby, upon depletion of one of the columns, the input and output conduits are connected to another column. Such switchover or functional interchange may also be used where higher resolution stationary phases are required for particular gases.
Still another feature of this invention provides that a pneumatic detector is employed in the gas chromatograph or an electrical or electronic detector is connected via an electricalpressure transducer or converter to a pneumatic gating element or stage and, when a suitable enabling pulse is applied to the latter, to the storage member or stage. The gating stage may be triggered through a pneumatic switch stage, and a pneumatic differentiator (differential stage) to pass the signal at a predetermined time.
When the component has attained a predetermined value, the differentiator closes the gate so that the cornponent amplitude is applied pneumatically to the storage or memory stage. Upon conclusion of the chromatogram, at a predetermined instant, a relay stage applies the stored component amplitude through a second gate to the second storage stage and the signal in the latter to a summer or adder which, at the same time, receives a stored null or reference signal. In the summer, the null-point or zero-point signal is subtracted from the pressure signal representing the component amplitude so that only an absolute value of the level of the measured component appears at the output of the summing stage. The indicating means coupled to the latter can provide the level in terms of percent or in absolute quantities and can plot the magnitude as a function of time.
In many cases, it is desirable to plot or indicate the tendency of the magnitude, i.e., to follow the change in magnitude when, for example, process control of the proportional-integral (P-I) type or process-integraldifierential (PID) type is required. The output signal of the summer, in this case, is subjected to further mathematical processing. Even these processing elements, however, are of a pneumatic character. Also integrating devices may provide planimetric or area analysis of the region under the chromatographic curve.
The advantages of the present system include complete security against explosion even at the most explosive atmosphere since each element is purely pneumatic. While in the specific system described below, various pneumatic elements have been set forth, it will be understood that, in most cases, the elements may be combined into compact units or may be replaced by conventional fluidics controls. The entire system is free from the danger of failure due to contact damage. When the system is operated at low pressures of, say, 0 to 500 mm H O (water column), preferably 0 to mm H O, high precision and speed is obtained because compressibility factors are minimized and rapid changing of the storage elements is obtained.
Finally, since the system is continuously flushed with air, the latter forming a signaling medium, corrosive fluids cannot attack the essential parts.
DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIG. 1 is a circuit diagram of the pneumatic control and plotting system for a gas chromatograph as used in conjunction with a process line;
FIG. 2 is a block diagram of portions of the system for use in plotting the slope of the characteristic of the gas chromatograph;
FIG. 3 is a diagrammatic cross-sectional view of an AND gate for use in the system of FIG. 1 or FIG. 2;
FIG. 3A is a diagram graphing the output pressure along the ordinate against time along the abscissa for the pneumatic circuit element of FIG. 3;
FIG. 4 is a diagrammatic cross-sectional view of a pressure amplifier for use in the pneumatic system of FIG. 1 or 2;
FIG. 4A is a diagram graphing the relationship between the input pressure plotted along the ordinate against the output pressure plotted along the abscissa for the device of FIG. 4;
FIG. 5 is an axial cross-sectional view, in diagrammatic form, of a pneumatic threshold switch or relay for use in the system of FIG. '1;
FIG. 5A is a graph showing an ideal relationship between the pressure output plotted along the ordinate and against time plotted along the abscissa for the device of FIG. 5;
FIG. 6 is a diagram of a pneumatic integrator for use in the system of FIG. 1;
FIG. 6A is a diagram graphing the output pressure, plotted along the ordinate vs. time as plotted along the abscissa for the device of FIG. 6;
FIG. 7 is a diagrammatic axial cross-sectional view of a pneumatic relay for use in the system of FIG. 1 or FIG. 2;
FIG. 7A is a pressure vs. time plot illustrating ideal operation of the device of FIG. 7;
FIG. 8 is an axial cross-sectional view through a pneumatic differentiator according to the present invention;
FIG. 8A is a graph of the output pressure, plotted along the ordinate against time, plotted along the abscissa for the differentiator;
FIG. 9 is a diagrammatic axial cross-sectional view through a pneumatic adder or summer for use in the system of FIG. 1;
FIG. is a cross-sectional view diagrammatically illustrating a pressure multiplier as employed in the system of FIG. 2;
FIG. 11 is an axial cross-sectional view of a monoflop pneumatic trigger according to the invention;
FIG. 11A is a graph of the output pressure vs. time illustrating the pulse produced by the monoflop; and
FIG. 12 is a diagrammatic axial cross-sectional view of a pneumatic signal inverter as employed in the system of FIG. 2.
SPECIFIC DESCRIPTION OVERALL PNEUMATIC CIRCUIT OF FIG. 1
In FIG. 1, I have shown a gas chromatographic system, for use in controlling a process line, which comprises a pneumatic closer or sampling system 1 to which the sample gas mixture and the carrying gas is fed at la and which permits the sample to pass at constant velocity through the pneumatic chromatographic column 1b which is constituted as described in GAS CHROMA- TOGRAPHY, cited earlier.
The column has a porous-adsorbent packing and is thermostatically controlled in the usual manner. The effluent emerges at 10 after passing through a detector 2 which is responsive to the nature of each component band and to the quantity thereof to produce an output which is delivered to the amplifier 4. The amplifier 4 may be a pneumatic amplifier of the character to be described in connection with FIG. 4, but may also be an electrical/pressure transducer of any conventional type designed to convert the electrical output of a conventional chromatographic detector into a pressure-signal analog. A typical transducer of this type may include the nozzle-flapper system described at pages 36 7 ff. of MECHANICAL DESIGN AND SYSTEMS HAND- BOOK, McGraw Hill Book Co., N.Y.. 1964, wherein the flapper is controlled by the electrical output of an electrical amplifier, the latter being energized by the output of the detector. A pressure amplifier 3 is connected with the pneumatic actuator which constitutes the sampling device 1.
The system of the present invention comprises a pneumatic-sawtooth generator for controlling the plotter and the chromatographic apparatus, the generator comprising a pneumatic integrator 5 which is fed with air at a predetermined pressure as represented at 5a. The output of the integrator 5 is applied to one input of a pneumatic AND gate 6, the output of which is vented to the atmosphere at 6a while an enabling input is delivered via a pneumatic-threshold switching element 7 responsive to the buildup of a pressure signal at a pneumatic relay 8, the input of which is the integrator 5 mentioned earlier.
The relay output provides the sawtooth in the form of a linear pressure rise, followed by a sharp pressure drop as will be apparent hereinafter. The sawtooth is delivered to a pneumatic switching element 9 which, at the desired moment, triggers the pressure amplifier 3 via a line 9a. The output of relay 8 is, moreover, ap plied to pneumatic switches 10, 12 and 13 controlling the plotter and to the pressure recorder 23 which scribes a plot of the input pressure vs. time constituting the chromatogram.
The pneumatic switch 10 and the pneumatic switch 12 are connected to the rate-controlling input of a pneumatic differentiator 11, the other input of which derives from the amplifier 4 and thus receives the actual measurement signal, the output of the differentiator provides, via line 11a, the enabling input for a gate 15. The pneumatic switch 13 is connected to a monoflop trigger-pulse generator 14, hereinafter referred to as a pneumatic monoflop, the output pulse of which constitutes the enabling inputs of pneumatic AND gates 18 and 20 via lines 14a and. 14b.
The measured pressure signal is applied by line 4a to one input of the gate 15 and is delivered by the output of the latter to a storage element 16, e.g., a pressure accumulator (see FLUID POWER, US. Government Printing Office, Washington, D.C., I966). The output of the storage device is appliedto a pneumatic relay 17 and thence to the input to gate 18. The output of this gate is applied through a storage element 19 to the summer or adder 22 operating in accordance with pneumatic principles. Another portion of the measurement signal is branched at 4b from the line 4a connected with the recorder 23 and is applied to one input of the pneumatic gate 20 and delivered by the latter, upon receipt of an enabling signal, to the storage element 21. Theoutput of the summer 22 constitutes the control signal which is delivered via line 22a, on the one hand, to the recorder 24 and, on the other hand, to the process controller 25. The latter may be any of the process controllers described at pages 22 51 to 22 -106 of Perrys Chemical-Engineers Handbook, McGraw-Hill Book Co., New York, 1963.
The block 5 of the sawtooth generator or pneumatic clock is an integrator to which a constant signal level is fed, e.g., in the form of a constant rate of flow of air, and provides an integrated output in the form of a linear increase in pressure with time. The system may be constituted as described in connection with FIG. 6, as a storage element provided with a pneumatic resistance, e.g., a nozzle or an orifice forming a constriction. The output signal, in terms of the increasing pressure, moreover, need not be linear, but may have an exponential characteristic. The integrated output is applied to thegate 6 and, when the latter is triggered, is vented to the atmosphere to bring the output pressure to zero and re-establish the cycling buildup of pressure along the ramp of the sawtooth and decline of pressure along the steep flank thereof. The gate 6 is normally blocked in the absence of an enabling input as applied by the relay 8. The relay '8 has, as its function, elimination of spurious signals as may result from minor pressure variations produced by operation of the pneumatic switching devices downstream of the timer and the storage tendencies of such devices.
The integration magnitude is applied via the relay 8 to the pneumatic switch 7 which is of the threshold type as described hereinafter with reference to FIGS. and 5A, for example. The switch 7 is provided to trigger the gate 6 with a signal upon the attainment of an adjustable magnitude of the integration signal. The gate 6 is switched over from its blocked condition, as represented in FIG. 1, to a conductive condition whereby the integrated pressure signal is brought to zero by venting to the atmosphere. Consequently, the switch 7 closes the gate 6 and integration in unit 5 begins anew. Hence the pneumatic output signal at the relay 8 is in the form of a sawtooth. The sawtooth signal is used to trigger the various switching elements for operation of the gas chromatograph and the plotting device respectively.
The sawtooth is, of course, applied to the pneumatic switch 9 which generates a pulse for the automatic sampling of the process line to feed a precise volume of the specimen to the chromatographic column. The signal derived from the pneumatic switch 9 is applied to a pressure amplifier 3 (see FIG. 4) and the amplified signal is applied, in turn, to the pneumatic dosing device 1. Hence with each pulse of the sawtooth, a sampling is carried out. I may adjust the switch 9 so that sampling is effected once for each of a number of sawtooth pulses if so desired.
The switch element 10 is so adjusted that, upon initiation of the measurement of the component peak which is to be plotted, a pressure signal is applied as a control level to the differential element 11. In addition, the detector signal, derived from the amplifier 4, is applied as a pneumatic input to the differential element 11 as well. The increase of the signal associated with the measured component provides in the differential unit 11 a pneumatic pressure signal which falls upon the attainment of the component peak. At this peak, a signal is triggered by the differential element 11 which triggers the gate to connect the line 4a at which the peak signal is maintained to the storage element 16 in which this peak level is stored. In order to prevent the following components from triggering the differentiator, a second switch element 12 is provided and is set to respond to the decline in the magnitude associated with the component to be measured (the peak of which was stored) to block the auxiliary input to the differentiator 11. When all of the components have been evaluated and the chromatogram reaches a zero value, the pneumatic switch 13 is triggered to operate the monostable pneumatic pulse generator 14 (monoflop) to produce a short output pulse (see FIG. 11) which briefly opens the gates 18 and 20.
The gate 18 drains a signal from the storage unit 16, representing the peak magnitude of the component to be measured, via the relay 17 to a second storage element l9 and, via the latter, to the adder 22 (see FIG.
9). At the same time, the gate 20 applies the chromatograph signal which has fallen to its null level, to the storage element 21 and I hence to the adder 22. The adder 22 performs an algebraic summing of the component peak magnitude and the null value of the chromatogram and hence provides an output signal representing the true component level. This output signal may be represented in percent or can be transformed into a tendency measurement and is recorded at 24, the signal being also used to control the process line via the quality-control regulator 25. Recorder 23, of course, discloses the entire chromatogram while recorder 24 registers only the peak levels of the components of interest as is apparent from FIG. 1.
One or more of the components of the sample can be measured or controlled and, for each component to be measured, we provide a switch system 10, 12, 13 and the associated storage units.
PLANIMETRIC SYSTEM (FIG. 2)
In FIG. 2 I have shown an area or planimetric plotting system using the principles of the present invention. This system may be employed for the measurement of components which have quantitative values in the form of a time variation of a pneumatic signal which must be integrated over the area of the plotted curve. The gas chromatographic signal is provided by line 4a while the output of the pneumatic clock is delivered via the line 8a as in the system of FIG. 1.
In this embodiment, the clock signal is applied to a pneumatic switch 26, the output of which triggers a pneumatic switch 27 and is then applied through an inverter 28 (FIG. 12) to a pneumatic monostable trigger 29 (FIG. 11). The output of the pneumatic switch 26 is also delivered to the pneumatic mono-flop 30 which releases a signal designed to trigger the AND gate 20 briefly into a conductive state, the AND gate 20 being connected with a storage element 21 previously described.
The output of the pneumatic switch 27 is applied to the AND gate 35 which connects the chromatographinput line 44 with an integrator 36 and thence with an AND gate 37 in series with the storage element 38 producing one of the input signals to a multiplier 34 (see FIG. 10). The multiplier 34 receives a signal from the storage unit 19 upon triggering of the AND gate 18 by the monoflop 29. The AND gate 15 is provided as described earlier between the chromatograph output line 4a and the storage element 19 in series with the gate 18. In this embodiment, however, an integrator 33 is provided between the gates 15 and 18. Pneumatic switches 31 and 32 are provided to trigger the AND gate 15. Integrators 33 and 36 are provided with auxiliary inputs from the storage element 21.
Prior to the development of a component peak, the switch 26 and monoflop 30 trigger a brief pulse at the gate 20 which registers a null-point signal of the chromatogram in the storage element 21 and thus enables the null-point correction to be applied to the integrators 33 and 36. Via the gate 35 which is triggered by the pneumatic switches 26 and 27, the successive component peaks are applied to the integration unit 36 and are there stored in the form of a pressure level representing the integrated peaks.
Switches 31 and 32 trigger the gate 15 to deliver the desired-component peak signal to the integrator 33. Upon conclusion of the chromatogram, the switches 26 and 27, via the inverter 28, trigger the monoflop 29 to release a short-duration signal which operates the gates 18 and 37 and applies the integrated values via the storage elements 19 and 38 to the multiplier 38. The multiplier establishes the ratio (x IOU/x where x, is the value of the component of interest, and x is the sum of the magnitudes for all of the components. The output of the multiplier is then the concentration, in percent, of the component or interest of represents the direction of change of this magnitude. As in the system of FIG. 1, the output signal is recorded and used to control the process variables.
PNEUMATIC ELEMENTS The pneumatic elements illustrated in block form in FIGS. 1 and 2 may be any of the conventional pneumatic amplifiers, gates, differentiators, integrators, adders, storage units or accumulators, relays and multipliers known in the art in connection with fluid calculating and computing devices and may also be of the fluidics'type operating in part in accordance with Coanda principles. In FIGS. 3 12, however, we have shown devices which may be used for the purposes of the present invention in order to enable those skilled in the art to make and practice the invention with ease. Attention is directed to pages 417 ff. of SERVOMECHANISM PRACTICE, McGraw-Hill Book Company N.Y., 1960, which discuss pneumatic devices such as amplifiers and relays as well as t electrical/pneumatic interfaces between electrical devices such as the detector 2 and the member 4. Relays and the like are also described in MECHANICAL DESIGN AND SYSTEMS HAND- BOOK, McGraw-Hill Book Company, N.Y., 1964, at chapter 36.
In FIG. 3, I have shown an AND gate for use in the detent 46 and is shiftable to unblock the outlet port 47 and to disconnect the same from a vent 48 when the pressure of the input signal, as applied at 49, is provided in conjunction with the enabling signal at 45. Hence, as can be seen from FIG. 3A, the input signal may be applied at t, but is insufficient alone to displace the detent but, upon application of the enabling signal P, at time t the valve body is displaced to open port 47 and generate the output signal P The gate of FIG. 3 can, of course, be used as the elements 6, l5, 18, 20, 35 and 37 of FIGS. 1 and 2.
In FIGS. 4 and 4A, I have shown a pressure amplifier of the type illustrated at 3 in FIG. 1, the amplifier comprising a stepped housing 50 defining a large-diameter chamber 51 and a small-diameter chamber 52 in axial alignment therewith. The input signal P, is applied as a pressure at inlet 53 to the large-diameter chamber while the output signal is received as a pressure P, at the port 54. A stepped piston 55 is shiftable in the housing and has a large-diameter head 56 of area A,, and a body 57 of cross-sectional area A: exposed to the pressure in chamber 52. Since P, X A, P, X A,, the relationship between the input pressure and the output pressure is represented by the equation P,= (A /A P,,, the ratio A /A, being the gain of the amplifier and also the slope of the input-pressure/output-pressure characteristic (see FIG. 4A). The system of FIG. 4 is utilized where the pressure delivered by the switch may be in- 10 sufficient to operate a pneumatic actuator such as the sampling device.
FIGS. 5 and 5A represent, in diagrammatic form, a threshold switch having a switching hysteresis, such that the actuating path is represented at I in FIG. 5A while the restoration path is represented at 11. It should be noted in connection with the characteristic curves of this element and the other elements described, that the graphs show idealized operating parameters for illustrative purposes. In practice, the various portions of the graphs may have curvature and nonlinearity, time constants, etc. without affecting basic principles of the invention.
The device of FIG. 5 may comprise a housing 60 having an inlet port 61 at which the input signal P, is applied to a chamber 62 on one side: of an orifice 63. The opposing chamber 64 is connected by a port 65 to the device actuated by this switch and the output signal P, 7
appears at this port. A valve member 66 is displaceable in the orifice to seat on opposite sides thereof and is held in each of its extreme positions by a spring member 67 which is shifted through a dead-center position. In the orifice, a pressure accumulator 68 is connected to the system. As P, builds up to the left-hand sideof the valve member 66, therefore, the pressure reaches a point, at t, which suffices to displace the valve member against the force of a spring 68 which is adjustable by a screw 69, to close the connection between the input port 61 and the accumulator 68, while opening the connection between the accumulator and the outlet port 65. The accumulator thus discharges at the level P, through the port 65. When the pressure falls at time t" to a level sufficient to permit the spring 68 to overcome the retaining force of spring 67, the valve is restored to its original position. The switching threshold can of course be adjusted by the spring 69. The device of FIG. 5 is used as indicated at 7 in FIG. 1.
The integrator 5 of FIG. 1 or the integrators 33 and 36 of FIG. 2 can be constituted as illustrated in FIGS. 6 and 6A. Basically, the integrator comprises a storage element, e.g., an accumulator 70, and a pneumatic resistance as represented by a constriction 71 formed by a needle valve 72 which, of course, if adjustable. At the downstream side of the construction, there is provided a port 73 at which the output signal P, appears, while the upstream side of the orifice is provided with an inlet 74 at which the input signal appears. The input signal may be in the form of a source of fluid with a constant volume-rateof-flow. A check valve may be provided at 75 in the inlet lining by virtue of the constriction (pneumatic resistance) and the accumulator, the output pressure is a function of the input signal in accordance with ,the itsggl 19156225111} Rit ISidt as indicated in FTG. 6A, the slope of thecurve being adjustablevby variation of the construction.
In FIGS. 7 and 7A, we have shown a pneumatic switch which may be used at the locations represented at 9, l0, l2, 13, 27, 31, 32 in FIGS. 1 and 2, the switch 0 comprising a valve body forming a valve seat 81 for 65 output signal P at the time of this pulse at the outlet port 86 downstream of thevalve member. The pneumatic switch prevents pneumatic perturbations from producing undesired actuation of the various components and establishes the timing of the operation of the logic elements for each clock pulse.
FIG. 8 shows a differentiating component as, for example, provided at 11 in FIG. 1, this component comprising a housing 90 with an inlet 91 at which the input pressure P, to be differentiated is applied as the input signal. A diaphragm 92 separates the upstream portion of the chamber from the downstream portion which is connected to a source of pressure P: determining the differentiated output f (P see FIG. 8A, as develops at the conclusion of diflerentiation t... The output signal P, is derived from a bellows chamber 93 mounted upon the diaphragm. It follows that P, is a function of the time rate of change of the pressure P, with the level established by the pressure P In FIG. 9, I show a pneumatic adder for use as the element 22 in FIG. 1 and capable of developing a pressure output P, which is a function of P +P,, the two input pressures. The stepped housing 100 comprises a large-diameter chamber 101 in which the output signal P is obtained at a port 102, and a small-diameter chamber 103 to which the input pressure P, is applied at a port 104. The stepped piston 105 has a largediameter step 105a defining an annular chamber 106 which is effective behind the piston head 105a and receives the input signal P via a port 107. The smalldiameter step 105b is exposed to pressure in chamber 103. If chambers 103 and 106 have respective effective areas A and the effective area of the piston in chamber 101 is 2A, P, will be the algebraic sum of the pressures P and P FIG. shows a pneumatic multiplier in accordance with the present invention for use at 34 in the system of FIG. 2. Here the housing 110 is subdivided into a compartment 111 receiving the input pressure P via a port 112 and a chamber 113 communicating with a port 114 for delivering the output pressure P,,. The partition is a diaphragm system 115 carrying a valve member 1 16 co-operating with the orifice of a nozzle 1 17 by means of which the input pressure P, is delivered via a conduit 118. As P, increases, it tends to bias the valve member upwardly, thereby increasing P while an increase in P likewise acts upon the valve member in a similar direction. Hence the output pressure P, is a function of the product P P In FIG. 11, I show a monoflop for use, for example, as the elements 14, 30, etc. of FIGS. 1 and 2. In this device, the housing 120 receives a piston 121 having a small-diameter head 121a and a large-diameter head 121b exposed to pressure in a small chamber 122 and a large chamber 123, respectively. The piston is biased by an adjustable spring 124 against the input pressure which is applied to the chamber 122 via a port 125. The heads of the pistons form valves as will be described further below. The output pressure P, is derived at 126 from chamber 123. A throttle valve 127 bleeds fluid from chamber 123. With normal increase in the pressure P,, the piston moves to the right against the force of spring 124 until the pressure reaches a threshold level P, (FIG. 11A) whereupon the head 121a connects the chamber 122 with an intermediate chamber 128 to apply increased pressure to the head 121b at its lefthand side. The piston suddenly shifts to the right at a rate greater than that at which air is bled from the chamber 123, to produce. the pulse illustrated in FIG. 1 1A at the outlet 126. As soon as the head l21b clears the edge 129, however, the pressure behind the piston is relieved and the spring 124 returns the piston to its original position.
In FIG. 12, there is shown an inverter wherein an input pressure P, is applied to a port 131 of a stepped housing to shift the piston 132 to the left and thereby develop a negative pressure in the chamber 133 to which the outlet port 134 is connected. Hence the pressure P is proportional to (P and may equal it when the effective areas of the piston exposed to the input and output pressures are equal.
The improvement described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the invention except as limited by the appended claims.
1. A method of operating a gas chromatograph having a chromatographic column, sampling means for passing a sample of gas containing a plurality of components through said column and detector means for providing an output responsive to the presence of the respective components, said method comprising the steps of:
generating a timing chain of pressure pulses;
pneumatically triggering said sampling means with said pressure pulses;
transforming said output into a pressure magnitude;
pneumatically storing peaks of said pressure magnitude in the cadence of said pulses in the form of storage pressures; and
recording at least said storage pressures, said timing chain of pressure pulses being generated by repeatedly building up a pneumatic pressure level by integrating a pressure signal of constant value, sensing the buildup magnitude and venting the same to the atmosphere upon the buildup magnitude attaining a predetermined threshold level, thereby generating a pneumatic sawtooth sequel.
2. The method defined in claim 1, further comprising the step of pneumatically storing a pressure magnitude representing the zero level of the chromatogram developed by said detector means, and pneumatically adding said pressure magnitudes prior to recording of said storage pressures.
3. The method defined in claim 1, further comprising the step of pneumatically integrating said storage pressures prior to recording same.
4. The method defined in claim 3, further comprising the step of integrating the pressure magnitude corresponding to all of said components to produce a first stored integrated signal and integrating the pressure magnitude corresponding to a selected one of said components to produce a second stored signal, said stored signals being in the form of said storage pressures, and multiplicatively combining said stored signals to provide an output corresponding to the ratio of said one of said components to all of said components.
5. The method defined in claim 4, further comprising the step of storing a zero-point signal of the output of said detector means and modifying the stored signals in accordance with said zero-point signal.
6. The method defined in claim 1, further comprising the step of controlling a process line in response to said storage pressures.
7. An apparatus for the chromatographic analysis of a gas mixture consisting of a plurality of components, comprising:
gas-chromatographic means including a chromatographic column, pneumatically actuatable sampling means for passing quantities of said gas mixture through said column for resolution thereby into said components, and detector means responsive to said components for producing an output representing the passage of same;
a pneumatic timer for producing a train of pressure pulses;
indicating means responsive to said detector means for displaying said output;
pneumatic switch means responsive to said pressure pulses for operating said sampling means and said indicator means, said indicating means including a pressure recorder, said switch means including a storage element, a pneumatically actuatable gate connected between said detector means and said storage element and at least one pneumatic switch element responsive to a pressure pulse of said train for triggering said gate;
a differential element responsive to the rate of change of said output and connected between said switch element and said gate, said switch means including a further storage element responsive to a zero level of said output and a further gate connected between said further storage element and said detector means, a further switch element triggerable by said train of pressure pulses and a shortduration pneumatic pulse generator pneumatically energizable by said further switch element for triggering said further gate, and pneumatic adder means operatively connected to both said storage elements for producing a pneumatic output signal representing the algebraic sum of the signals stored in said storage elements.
8. The apparatus defined in claim 7 wherein said pneumatic timer comprises a pneumatic integrating element for building up a pneumatic pressure level, a pneumatically actuatable gate connected to said integrating element and triggerable for venting same to the atmosphere, thereby reducing said level to a low value, a threshold switch element connected to said integrating element for pneumatically triggering said gate upon said level reaching a predetermined threshold value, and a pneumatic relay connected between said integrating element and said switch means for applying said train to the latter in the form of a pneumatic sawtooth.
9. The apparatus defined in claim 7, further comprising a pneumatic integrating element connected between said gate and said storage element.
10. The apparatus defined in claim 9, further comprising another integrating element for integrally summing pressure magnitudes corresponding to all of said components, the first-mentioned integrating element producing a pressure output corresponding to the integrated magnitude of only one of said components, another gate connecting said other integrating element with said detector means, another storage element connected to the output of said other integrating element, and means multiplicativelycombining the pressure signals of the last-mentioned storage element and the peak-magnitude storage element.
11. The apparatus defined in claim 7, further comprising a second gate triggerable by said short-duration selected one of said components.