Abstract:
A fluid pressure regulator and method of operating the same particularly adapted for use in alternating flow and no flow modes as in the batchwise delivery of pressurized gases used in semiconductor manufacture. Such pressure regulator and method include a controlled differential pressure setting capability which provides for the application of a differential pressure setting force independently of a main pressure setting force. As a result, operation of the pressure regulator may be controlled to obviate pressure creep at the regulator outlet.

Description:
RELATED CASES 
     The present application claims priority to U.S. Provisional Application Ser. No. 60/133,295, filed May 10, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates broadly to fluid pressure regulators and methods of operating the same, and more particularly to a pressure regulator having a controlled differential pressure setting capability providing improved response when utilized, for example, in batchwise gas delivery applications such as may be found in the semiconductor processing industry. 
     Fluid pressure regulators are used in a variety of fluid transfer applications involving the delivery or other transport of pressurized process gases or the like. Within these applications, pressure regulators are provided to deliver a flow of a pressurized gas or other fluid at a regulated outlet pressure, and to maintain that pressure at a set value generally independent of the gas flow rate. For that purpose, the pressure regulator is supplied at its inlet port by a source of fluid which typically is at a pressure substantially higher than the desired outlet pressure. The desired outlet pressure is set and the regulator automatically actuates an internal valve to adjusts the size of a variable passage between its inlet and outlet ports to minimize the offset between the actual outlet pressure and the set pressure. 
     As is detailed more fully in commonly-assigned U.S. Pat. Nos. 5,787,925; 5,762,086; 5,755,428; 5,732,736; 5,458,001; 5,230,359; 4,702,277; and 4,257,450, pressure regulators of the type herein involved conventionally are operated on a force balance principle. In this regard, an internal diaphragm assembly of the regulator is subjected to forces acting in opposite directions. These forces include a first force acting in a first direction and related to the pressure setting, typically developed by the manual compression of a coil or other spring, a second force acting in a second direction opposite the first direction and developed by the outlet pressure as applied to the effective area of the diaphragm exposed to that pressure. Under standard operating conditions, the first force of the pressure setting is held constant such that any variation in the inlet or outlet pressure effects a proportional change in the second, opposing force being applied to the diaphragm. The imbalance thereby created between these opposing first and second forces cause the diaphragm to deflect. This deflection is transmitted directly to the valve which cooperates with an associated valve seat to vary the open area of an orifice or other fluid passage defined between the valve and the seat and, as a result, the fluid flow from the inlet of the regulator to its outlet. 
     For example, a step change increase in outlet flow rate generally will tend to decrease the outlet pressure and, proportionally, the second, opposing force being applied to the diaphragm by the outlet pressure. The force imbalance thereby developed is translated to the valve element via the deflection of the diaphragm. Such deflection urges the valve element to move in a direction which increases the area of the fluid flow orifice defined between the element and its associated valve seat. This increase, in turn, effects a corresponding increase in the fluid flow rate through the regulator which ultimately balances at steady state condition wherein the decrease in the outlet pressure is modulated. 
     Conversely, for a step change decrease in the outlet flow rate, the flow imbalance thereby developed would have the effect of urging the valve element in an opposite direction to decrease the area of its fluid flow orifice and, proportionately, the flow rate. A new balance thus is effected in which the outlet pressure is marginally increased as compared to outlet flow prior to the step change decrease. 
     The above-described automatic operation illustrates that some change in outlet pressure is required to accommodate a change in outlet flow. The purpose of pressure regulation therefore is to minimize the change in outlet pressure for a given range of flow variation. In addition to outlet pressure, the response of a pressure regulator must accommodate the effect of inlet pressure changes on the regulated outlet pressure, and also the effect as the flow rate approaches zero. The latter is expressed as the ability of the pressure regulator to close under a no-flow condition. 
     Regarding the effects of inlet pressure changes, the inlet pressure applied to the area of the valve passage develops a force which, as aforementioned, acts in the opposite direction as that of the pressure setting force. For example, a decrease in inlet pressure results in a proportionate decrease in the force transmitted to the diaphragm assembly, with the force balance being restored by a corresponding increase in outlet pressure. Sequentially, the decrease in inlet pressure decreases the force opposing the pressure setting force which, in turn, causes the diaphragm assembly to increase the valve opening. With the flow across the valve thereby being increased, the outlet pressure is increased to a new value which again restores the force balance. As conventionally operated at inlet pressures of 30-500 psi, pressure regulators of the type herein involved typically exhibit about a 1 psi increase or, as the case may be, decrease in outlet pressure for each 100 psi change in inlet pressure. 
     The precise relationship between inlet pressure decrease and outlet pressure increase is determined by the ratio of the effective areas of the valve passage and the diaphragm. For a more detailed analysis of this effect, reference may be had to the present inventor&#39;s prior U.S. Pat. No. 5,230,359, entitled “Supply Pressure Compensated Fluid Pressure Regulator And Method.” 
     Particularly for applications involving the batchwise delivery of a process gas at the point of use, there has been an expressed interest in providing for a fast start-up at the beginning of each delivery cycle. Such a start-up may be achieved when the outlet pressure of the regulator is controlled to stabilize quickly at a steady-state value as the gas flow is increased from no flow prior to the commencement of a delivery cycle, to a given delivery flow rate. 
     The semiconductor industry, for example, utilizes the batchwise delivery of process gases in the manufacture of integrated circuit (IC) chips or dies. In the general mass production of semiconductor devices, hundreds of identical “integrated” circuit (IC) trace patterns are photolithographically imaged over several layers on a single semiconductor wafer which, in turn, is cut into hundreds of identical dies or chips. Within each of the die layers, the circuit traces are deposited from a metallizing process gas such as tungsten hexafluoride (WF 6 ), and are isolated from the next layer by an insulating material deposited from another process gas. The process gases typically are delivered in discrete flow cycles or “batches” from pressurized supplies, thereby requiring delivery systems of a type which may be operated in alternate flow and no-flow modes. 
     A representative delivery system of such type is shown at  10  in the schematic of FIG.  1 . Referring then to FIG. 1, delivery system  10  may be seen to conventionally include, in series, a gas supply  12 , a pneumatic isolation valve,  14 , a pressure regulator,  16 , a pressure transducer,  18 , a manual valve,  20 , a mass flow controller,  22 , and a pneumatic on/off valve,  24 . Fluid flow through system  10  is in the direction reference by arrow  30 . 
     Prior to the initiation of a delivery cycle, system  10  is in a start-up/stand-by or “no-flow” operational mode wherein pneumatic valve  24  is commanded closed, manual valve  20  is set open, and mass flow controller  22  is set to zero. At the initiation of “flow” or delivery operational mode, pneumatic valve  24  is commanded to open and the mass flow controller  22  is set to control flow at a desired rate. Thereupon, at the termination of the flow mode, the pneumatic valve  24  is commanded closed and the setting of the mass flow controller  22  is returned to zero. At all times during both operational modes, the pressure regulator  16  remains set at a desired regulated pressure with supply or inlet pressure being provided to the inlet  32  of the regulator and with outlet or delivery pressure being provided from the outlet  34  of the regulator to mass flow controller  22 . 
     Indeed, within fluid systems such as system  10 , there is a particular need to maintain a generally constant gas pressure notwithstanding the gas flow rate demand which varies between the operational modes of the system from low or no flow to a relatively high flow. In this regard, the flow regulating devices employed in these systems, such as mass flow controller  22 , generally are highly accurate if a stable gas pressure can be maintained at the inlet of the device. However, the large pressure drops associated with changes in the flow demands of the delivery system often make it difficult to maintain a stable gas pressure and, accordingly, to assure the accuracy of the flow regulating device. Ultimately, the defect rate and yield of the process may be deleteriously affected. 
     Moreover, it has been observed in connection with the conventional operation of system  10  that the outlet pressure of regulator  22  begins to decrease as soon as flow is initiated in the delivery mode, and continues to decreases until it reaches a value corresponding to the setting of the regulator. The pressure decrease comprises two components, namely, a “creep” component and a “droop” component. The effect of each of these components may be appreciated with reference to FIG. 2 wherein a flow curve for a representative pressure regulator of the type herein involved is plotted at  40  as a function of outlet pressure (P o ) versus the log of flow rate (R) for a given inlet pressure. As the flow rate increases from about 50 to 1,0000 cc/min in the direction referenced by arrow  42 , the droop component is expressed as a pressure drop which is proportional to the flow rate. The creep component, in turn, is expressed as a pressure drop as the flow rate increases from zero to a small value of about 20-50 cc/min or, alternatively, as a pressure increase in the direction referenced by arrow  44  as the flow is decreased from 20-50 cc/min to zero. 
     The “creep” of a pressure regulator therefore is defined as its ability to maintain a constant outlet pressure as the flow is decreased from a small value to a no-flow condition. In this regard, the internal valve of any pressure regulator cannot, as a result of cold flow or other deformation of the seating materials, make an absolutely fluid-tight seal in the zero flow condition. The outlet pressure of the regulator therefore is observed to increase slowly over time. The rate of increase is generally non-linear and decreases over time, i.e., it may take 30 seconds for the outlet pressure to increase by 1 psi, 3 minutes to increase by 2 psi and 30 minutes to increase by 3 psi. 
     The effect of creep upon the operation of a fluid system, such as system  10  of FIG. 1, is to increase the response time of the system to reach steady-state flow as the outlet pressure must decrease from a higher, creep-induced no-flow value, to a lower, operating or setpoint value determined by the regulator setting. The time necessary for the outlet pressure to reach the setpoint value of the regulator is a function of the flow rate and fluid volume between the regulator  16  and the mass flow controller  22 . For example, a decrease of 2 psi, i.e., from 17 psi to a standard operating pressure of 15 psi, may require about 0.3 sec for a typical fluid volume of 8 cc and a flow rate of 200 cc/min. However, at lower flow rates, i.e., 20-50 cc/min, the response time may become significant, i.e., 1-3 sec, and even may be considered unacceptable as a response of less than 1 sec generally is desired. 
     A separate, but similarly important consideration is the manner in which the outlet pressure approaches a steady-state condition in response to a step change in flow rate. That is, if the outlet pressure response is not linear, but rather is oscillatory with some overshoot and recovery, it may not be possible to establish a steady state flow to the mass flow controller within the desired 1 sec interval. In this regard, the operation of mass flow controllers is known to be adversely affected by a pressure reversal as may be caused by a pressure overshoot. The greater the outlet pressure decrease from the creep-induced no-flow valve to the operating setpoint increases the potential for a pressure overshoot. 
     In view of the foregoing, it will be appreciated that further improvements in the design of pressure regulators for process gas delivery and other bath processes would be particularly well-received by the semiconductor manufacturing industry. Especially desired would be a regulator which provides a rapid response with no pressure overshoot from a no-flow to a flow condition of the fluid circuit, and thus economizes the use of process gases for higher yields per batch. 
     SUMMARY OF THE INVENTION 
     The present invention is directed broadly to a fluid pressure regulator construction and method of operating the same. More particularly, the invention is directed to a diaphragm-type regulator construction and method affording a controlled differential pressure setting capability providing improved response when utilized, for example, in fluid systems for the batchwise delivery of pressurized gases as may be found in the semiconductor processing industry, as well as in other applications having flow and no-flow operational modes. Such capability allows for a differential pressure setting force to be applied to the diaphragm of the regulator independently of the main pressure setting force. As a result, the regulator of the present invention may be operated in a manner which obviates or at least minimizes the effect of creep on the outlet pressure for a more rapid approach to steady-flow without pressure overshoot or other system de-stabilizing hysteresis effects. 
     In accordance with the precepts of the present invention, the regulator thereof is operated within a fluid system in a conventional manner except that the outlet pressure setting is determined by both a main pressure setting force, which may be manually adjustable, and an separate, differential force, which may be controlled pneumatically or by another pressure signal. In this regard, the main pressure setting force is adjusted such that the outlet flow is regulated at an outlet pressure which is incrementally less than the outlet pressure specified for the mass flow controller or other flow component of the fluid system. At about the start of the operation of the system in a flow mode, the differential force is applied to the diaphragm in the same direction as the main pressure setting force so that the fluid flow is regulated in the flow mode of the system at an outlet pressure which is about the specified outlet pressure. Thereafter, the application of the differential force is terminated at about the end of the operation of the system in the flow mode, i.e., the beginning of the no-flow mode. In this way, an ersatz creep effect is mimicked such that, over time, the outlet pressure is maintained in the no flow mode of the system at a value which is about equal to, or only marginally greater than, the specified value. Accordingly, upon the differential force being re-applied and system flow being initiated, steady-state operation may be rapidly approached with only a marginal “droop” decrease in outlet pressure as the flow rate is increased and, as a result, substantially no pressure overshoot. Therefore, when utilized, for example, in the manufacture of semiconductors, the regulator and method of the present invention economizes the use of process gases for higher yields per batch. 
     In a preferred embodiment, the regulator of the present invention is provided to be responsive to a pneumatic or other pressure signal to apply the differential force. In this regard, the regulator includes a separate compressible spring member, which may be a spring coil, coupled in force transmitting communication with the diaphragm. For compressing the coil to apply the differential force on the diaphragm, a piston member is received within said regulator as operably coupled to the compressible member. The piston member is displaceable responsive to the pressure signal along a longitudinal axis of the regulator from a normally-biased first position to a second position effecting the compression of the compressible member to apply the differential force on the diaphragm. Advantageously, the signal may be controlled to be supplied to both the regulator and a pneumatic valve of the fluid system such that the application of the differential force is initiated at the same time as the flow mode of the system. 
     The present invention, accordingly, comprises the apparatus and method possessing the construction, combination of elements, and arrangement of parts and steps which are exemplified in the detailed disclosure to follow. Advantages of the invention includes a pressure regulator and method for operating the same which minimizes pressure creep when utilized in fluid systems operated in alternate flow and no-flow modes for faster pressure response and steady-state operation. Additional advantages include a regulator construction which is generally robust and economical to manufacture, and which eliminates the need for multiple stages, electronic controls, or additional valves and components heretofore necessary for more stable operation. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein: 
     FIG. 1 is schematic diagram of an representative fluid circuit as may be used in conjunction with the present invention for delivering a regulated, batchwise flow of a pressurized process gas from a supply to a semiconductor manufacturing tool; 
     FIG. 2 is a typical flow curve at a given inlet or supply pressure for a diaphragm-type pressure regulator, the curve being shown as a logarithmic plot of the regulator outlet or delivery pressure versus flow rate; 
     FIG. 3 is a cross-sectional view of an representative embodiment of a diaphragm-type pressure regulator according to the present invention including a manually adjustable main pressure setting assembly and a pneumatically-controllable differential pressure setting assembly which is actuable to apply a differential force on the regulator diaphragm independent of the main pressure setting force; 
     FIG. 4 is a magnified view of the regulator of FIG. 3 showing the manual main pressure setting adjustment thereof in enhanced detail; and 
     FIG. 5 is a representative pressure response of a regulator operated according to the present invention with a controlled differential pressure setting, the response being shown as the regulator outlet pressure traced as a cyclic function of time and as compared to the response of a regulator which is conventionally operated at a constant pressure setting. 
    
    
     The drawings will be described further in connection with the following Detailed Description of the Invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain terminology may be employed in the following description for convenience rather than for any limiting purpose. For example, the terms “forward,” “rearward,” “right,” “left,” “upper,” and “lower” designate directions in the drawings to which reference is made, with the terms “inward,” “inner,” or “inboard” and “outward,” “outer,” or “outboard” referring, respectively, to directions toward and away from the center of the referenced element, the terms “radial” and “axial” referring, respectively, to directions or planes perpendicular and parallel to the longitudinal central axis of the referenced element, and the terms “downstream” and “upstream” referring, respectively, to locations relative to the fluid flow. Terminology of similar import other than the words specifically mentioned above likewise is to be considered as being used for purposes of convenience rather than in any limiting sense. 
     For the purposes of the discourse to follow, the precepts of the pressure regulator, and the controlled differential pressure setting operation thereof, of the invention herein involved are described in connection with the utilization of such regulator within a fluid system, such as the delivery circuit shown in FIG. 1, wherein a pressurized gas is delivered batchwise from a supply. It will be appreciated, however, that aspects of the present invention may find application in other fluid systems operable in alternating flow and no-flow modes. Use within those such other applications therefore should be considered to be expressly within the scope of the present invention. 
     Referring then to the cross-sectional view of FIG. 3, wherein corresponding reference numbers are used to designate corresponding elements throughout the several views, a fluid pressure regulator in accordance with the present invention is shown generally at  50 . In basic construction, regulator  50  includes a housing, referenced at  52 , which may comprise a generally annular, upper cap portion,  54 , and a lower body portion,  56 . A associated nut,  58 , may be received over a flanged lower end,  60 , of the cap  54  for a threaded connection with an externally-threaded upper end,  62 , of body  56 . Cap and body portions  54  and  56  thereby may be engaged to define an internal chamber,  63 , within housing  52 . Upper and lower support plates,  64  and  65 , respectively, are clamped between the cap and body portions  54  and  56  for supporting other regulator components. Each of plates  64  and  65  are formed as having a central opening,  66  and  67 , respectively. Plate  65  further is formed as having a plurality of axially-extending through bores or channels, one of which is referenced at  68 , and is made to compressively engage a raised annular surface,  69 , of body  56  to effect a back-up seal against leakage of the gas or other fluid flowing through the regulator  50 . 
     Body portion  56  of housing  52  itself is formed as having an internal fluid passageway,  70 , which may be divided into generally L-shaped upstream and downstream portions  71   a  and  71   b,  each extending from an axial surface,  72 , of body  56 , to an upper radial surface,  73 , thereof. Fluid passageway  70  itself extends between an inlet,  74 , and an outlet,  75 , of the regulator for the flow of fluid therethrough in the direction referenced by arrows  76 . Within the fluid circuit  10  of FIG. 1, a high pressure flow of gas is supplied to regulator inlet  74  from supply  12 , and a regulated, lower pressure flow is delivered to mass flow controller  22  from regulator outlet  75 . In this regard, regulator inlet  74  may be coupled in fluid communication with supply  12  via valve  14 , with outlet  75  being coupled in fluid communication with mass flow controller  22  via valve  20 . Each of inlet  74  and outlet  75  accordingly may be configured, as is shown, as flanged tubing extensions,  76   a-b,  respectively, which may be brazed or otherwise joined to body portion  56 . For connection within the fluid  10 , extension  76   a  is shown as having an associated female fitting connector,  78 , with extension  76   b  being shown as having an associated male connector,  80 . 
     For controlling the flow of fluid through passageway  70 , chamber  63  houses a valving assembly including a poppet,  82 , and an associated valve seat,  84 , defined within passageway  70  such as by a disc which is supported over the upstream portion  71   a  of passageway  70  and clamped between the central opening  67  of lower support plate  65  and the opening of passageway portion  71   a  into the upper radial surface  73  body portion  56 . Valve seat  84 , is oriented relative to the flow direction  76  as having an upstream side,  86  and a downstream side,  88 , and includes an aperture,  90 , for admitting fluid pressure into a lower plenum,  92 , of chamber  63 , which plenum is defined partially by lower support plate  65 . Flow out of plenum  92  and into the downstream portion  71   b  of passageway  70  is accommodated via plate channels  69 . The disc for valve seat disc  84  preferably is formed of a plastic or other polymeric material, and most preferably of a fluoropolymer such as Kel-F® (3M, St. Paul., Minn.). 
     Poppet  82  is movable along a central longitudinal axis,  94 , of the regulator  50  between a first position (shown in FIG. 3) closing passageway  70  to fluid flow for the operation of fluid system  10  (FIG. 1) in its no-flow mode, and a variable second position throttling the fluid flow through passageway  70  for the operation of system  10  in its flow mode. For cooperation with valve seat  84 , poppet  82  is provided to extend along axis  94  from a lower head portion,  96 , disposed opposite the upstream side  86  of valve seat  84 , to an upper, elongate stem portion,  98 , which, in turn, extends through aperture  90  and lower plate opening  67  along axis  94  from a lower proximal end,  100 , connected to head portion  96 , to an upper distal end,  102 . Poppet head portion  96  is configured, such as the general conic shape shown, to annularly vary the relative size of aperture  90  and, accordingly, the flow rate through the regulator, when moved toward or away from valve seat  84  in the variable second poppet position. 
     For controlling the movement of poppet  82  along axis  94 , a diaphragm,  110 , is received within chamber  63  as disposed in fluid communication with passageway  70  to define a flexible upper wall of plenum  92 , and as coupled in force transmitting contact with poppet  82 . Diaphragm  110  is of a conventional single or multiple piece construction, and includes a circumferentially extending, generally flexible “membrane” portion,  112 , which may be formed of a thin, corrugated sheet of aluminum, steel, or other metal foil. Membrane portion  112  extends radially outwardly to an outer margin which defines the outer periphery of the diaphragm  110 , and which is clamped between upper and lower plates  64  and  65  for the mounting of diaphragm  110  within chamber  63 . In a two-piece construction of diaphragm  110 , membrane portion  112  is welded, bonded, or otherwise attached to a backup portion,  114 , which supports the membrane portion  112 , and which extends axially therefrom through the opening  66  of plate  64  in defining a cylindrical extension,  115 , including an internal central passage,  116 , and an external shoulder,  118 . Passage  116  is configured to receive the distal end  102  of poppet stem  98 , and may be internally threaded for engagement with an externally threaded portion,  120 , of stem  98 . So received in chamber  63 , diaphragm  110  is provided to be responsive to a fluid pressure force, which is proportional to the inlet pressure (P i ) and outlet fluid pressure (P o ) of the fluid flow to regulator  50  and is applied in the direction referenced at  122  to urge poppet  82  toward its first position closing passageway  70  to fluid flow. Atmospheric pressure (P a ) is admitted in chamber  63  on the upper side of diaphragm  110  via ports  124  and  126  formed, respectively, through cap  54  and nut  58 . 
     A main pressure setting assembly, reference generally at  127 , is actuable to applying a balancing force on diaphragm  110  in the direction referenced at  128  for opposing the fluid pressure force  122  and urging poppet  82  toward its second position opening passageway  70  to fluid flow. Such force  128  is developed at least in part by the adjustable compression of a main coil spring, shown in phantom at  130 , or other resilient member received within chamber  63 . In the illustrated embodiment of FIG. 3, spring  130  is disposed coaxially with axis  94  for compression intermediate diaphragm  110  and a manually-adjustable knob,  132 , which is translatable along axis  94 . For a compact design of regulator  50 , knob  132  is externally-threaded as at  134 , and is housed within cap  54  as threadably rotatably engaged with an internally threaded portion,  136 , thereof. As may be seen best with momentary reference to the magnified frontal view of main pressure setting assembly  127  shown in FIG. 4, cap  54  is provided as having a window,  140  (also shown in phantom in FIG.  3 ), through which a knurled portion,  142 , of knob  132  is provided to be hand accessible. 
     Returning to the cross-sectional view of FIG. 3, spring  130  may be seen to be received within chamber  63  as disposed intermediate an upper retainer,  150 , and a lower retainer,  152 . Upper spring retainer  150  is generally disc-shaped, and is disposed in abutting, force-transmitting contact with a thrust portion,  154 , of knob  132 . Lower spring retainer  152  is generally cylindrically-shaped, and is received coaxially over diaphragm back-up extension  115  as threadably engaged in force transmitting contact with an externally-threaded portion,  156 , thereof. Retainer  152  is fastened onto extension  115  with a nut,  160 , which may have an associated O-ring,  162 , over which the lower end of spring  130  may be friction fit for assisting the coaxial alignment of the spring with axis  94 . A compression ring,  164 , or other spacer may be received with retainer  162  over extension  115  for delimiting the travel of the retainer over the extension. 
     For applying an additional force on diaphragm  110  in the direction of arrow  122 , a wave spring or other compressible member, shown in phantom at  170 , is received coaxially over retainer  162 . Spring  170  is supported on upper support plate  64  for compression therebetween and a radially-outwardly extending flange portion,  172 , of retainer  152 . Such compression of spring  170  provides a biasing force for further urging poppet  82  toward its first position such that fluid passageway  70  is normally closed in the absence of a pressure setting force  128 . The movement of poppet  82  between its first and second positions may be damped with a compressible foam washer,  174 , which is received coaxially over diaphragm extension  115  for compression intermediate retainer  152  and plate  64 . The displacement of poppet  82  in its second position by the application of pressure setting force  128  is delimited by the abutting engagement of a lower stop surface,  176 , of retainer  152  with plate  64 . 
     Regulator  50  further includes a differential pressure setting assembly, referenced generally at  180 . In accordance with the precepts of the present invention, differential pressure setting assembly  180  is provided to be actuable independently of the main pressure setting assembly  127  to apply a differential force, such as via the compression of a second coil spring member,  181 , on diaphragm  110  in the direction of arrow  128  further urging poppet  82  toward a second position opening passageway  70  to fluid flow. In the illustrated embodiment of FIG. 3, differential pressure setting assembly  180  is actuable responsive to a pneumatic on/off control signal of a given input pressure (P s ) which, preferably, may be between about 40-60 psig to be at the same level which is conventionally employed in operating the pneumatic valves  14  and  24  of fluid system  10  of FIG.  1 . The signal to assembly  180 , as well as valves  14  and  24  of system  10 , may be provided under the common control of, for example, of a pneumatic 3-way valve (not shown). 
     The pressure control signal may be admitted to regulator  50  via a tubing or other fitting connection,  182 , having, for example, a female end,  184 , configured for a tubing or other connection to the above mentioned 3-way valve or other control signal source, and a male end,  186 , configured for a threaded connection with an adapter,  190 , of regulator housing  52 . Adapter  190 , in turn, has a male end,  192 , configured for a threaded connection with an internally threaded upper end,  194 , of cap  54 , and a female end,  196 , which, depending upon the sizing of fitting end  186 , may be coupled thereto via a bushing or other reducer,  198 . The female end  196  of adapter  190  further is configured as having a recess which extends to internal end wall,  200 , that defines a second chamber,  202 , within housing  52 . The adapter male end  192  further is configured as having an elongate guide portion,  204 , which is fitted within a generally cylindrical counter bore,  206 , of knob  132  to assist in guiding the knob along axis  94 . 
     For controlling the compression of second spring member  181 , a piston,  210 , having an associated O-ring or other seal or packing ring,  211 , is received within chamber  202  as displaceable intermediate lower end wall  200  and an upper end wall,  212 , of chamber  202 . Upper end wall  212  is defined, such as by a radially-inwardly extending internal shoulder portion of reducer  198 , about a common opening,  214 , of adapter  190  and reducer  198 , which opening  214  functions as a port the admission of the signal fluid pressure into chamber  202 . 
     Piston  210  is operably coupled to spring  181  via an elongate force transmitting member,  220 . Such member  220  extends along axis  94 , as received coaxially through a central bore,  222 , formed through each of adapter  190 , knob  132 , and spring retainer  150 , from an upper end,  224 , disposed in abutting contact with piston  220 , to a lower end,  226 , disposed in abutting contact with spring  181 . Spring  181  itself is disposed coaxially within main pressure setting spring  130  as mounted over diaphragm extension  115  for compression between the shoulder portion  118  thereof, and an inverted U-shaped retainer,  228 , interposed between spring  181  and the lower end  226  of elongate member  220 . 
     Within chamber  202 , piston  210  is actuable responsive to the control pressure signal as admitted through opening  214  and applied to an upper surface,  230 , of the piston. That is, piston  210  is displaceable along axis  94  from a normally-biased upper position to the lower position shown in FIG.  3 . For biasing piston in its upper position, a compressible spring coil,  232 , may be received within a recess,  234 , formed within a lower surface,  236 , of the piston for compression against adapter lower end wall  200 . In its lower position, piston  210  depresses elongate member  220  which, in turn, effects the compression of spring  181  to apply a differential force, which may be between about 3-4 psig, on diaphragm  110 . In this way, a controlled application of the differential force may be achieved independent of the application of the main pressure setting force. 
     The force applied by spring  181  is “differential” in that it may be applied as a step function to effect a proportionate change in the regulator outlet pressure without changing the main pressure setting. For example, with the main pressure setting  127  of regulator  50  being adjusted within a range of between about 0-30 psi, differential pressure setting assembly  180  is actuable by the control signal to increase the effective regulator setting by a nominal 3 psi. If desired, the pressure of the control signal may be adjusted to effect a generally proportional increase or decrease in the differential force. 
     Considering next the operation of regulator  50  of the invention as employed in a representative fluid circuit such as batchwise gas delivery circuit  10  of FIG. 1 (with regulator  50  of the invention being substituted therein for regulator  16 ), reference may be had additionally to FIG. 5 wherein a typical response of regulator  50  within such circuit is graphically portrayed at  250  as a plot of outlet pressure (P o ) versus time (t). For a given inlet fluid pressure, which may be between about 30-500 psi, and a specified outlet pressure setpoint of about 15 psi, the system is operated prior to time t 0  in a flow mode. In such mode, gas is delivered through regulator  50  at a steady-state flow rate of, for example, 200 cc/min, and a regulated outlet pressure of about 14.8 psi. Such pressure is effected under the control of the main pressure setting of the regulator  50  which is adjusted to a nominal pressure of 12 psi, and with signal pressure being supplied to the regulator to apply a differential pressure which is nominally 3 psi. Both the main and the differential pressure settings may be set at a lower flow rate of, for example, 50 scc/min. In this regard, it may be noted that the actual regulator outlet pressure at steady flow is about 0.2 psi less than the setpoint due to the effect of “droop” (see FIG. 2) as the flow rate is increased from low flow to its steady-state value. 
     At about time t 0 , corresponding to the termination of the flow mode, the mass flow controller  22  (FIG. 1) is commanded “off.” Shortly thereafter, i.e., 0.5 sec or less, pneumatic on/off valve  24  is actuated to close such that fluid flow decreases from the steady-state rate to zero. Generally simultaneously with the actuation of valve  24 , signal pressure is discontinued to regulator  50  to remove the differential pressure setting. In this regard, the operation of valve  24  and regulator  50  advantageously may be synchronized under the control of a common signal pressure. 
     With the differential pressure setting being removed, the setting of regulator  50  effectively is reduced to 12 psi. Inasmuch as the outlet pressure remains at the operating pressure of 14.8 psi, the regulator closes such that the outlet pressure is maintained substantially at 14.8 psi. Depending upon the length of the no-flow period and/or on the interval, typically about 0.5 sec, between when the no flow mode is initiated and when the control pressure signal is removed to effect the closing of the regulator, the outlet pressure may increase slightly, to perhaps 15 psi, over the period Δt 0 . It will be appreciated, however, that by virtue of the controlled differential pressure setting, no appreciable creep effect is evident even when the system is operated with very long intervals, i.e., 1 hour or more, between the flow modes. 
     Continuing then along trace  250 , at time t 1 , corresponding to the initiation of the next flow mode, the pressure signal is resumed to open valve  24  and to re-apply the differential force on the regulator. Shortly thereafter, the mass flow controller  22  is commanded to again control flow. In such operation, flow may be increased from zero to a steady-state value before any appreciable increase in the outlet pressure as a result of creep induced from the effective change in the regulator setting from 12 psi to 15 psi. Thus, as the flow rate increases, the outlet pressure decreases only about 0.2 psi to settle quickly at the operating pressure within a very short period Δt 1 , of about 0.5 sec or less. Importantly, as no overshoot or other oscillatory effects are observed, the transition from zero to steady-state flow is able to be established within 1 sec or less. 
     For purposes of comparison, the pressure trace of a regulator conventionally operated at a constant pressure setting of 15 psi is shown at  250 ′. At time t 0  and continuing over the period Δt 0 ′ which may be 100 sec or more, the outlet pressure of trace  250 ′ may be noticed to increase by about 2 psi from the operating pressure. As compared to the 0.2 psi increase for valve  50  of the invention, such increase is significant, as is the period Δt 1 ′ which may be 1.5 sec or more with some overshoot or other oscillatory effects being evident. 
     Thus, a unique and efficient fluid pressure regulator construction and method of operation are described which mitigate the effect of pressure creep and which, when employed in fluid systems operated in alternate flow and no-flow modes, allow faster pressure response and steady-state operation for improved process gas utilization or other system economy. 
     Unless otherwise specified, materials of construction are to be considered conventional for the uses involved. Such materials generally will be corrosion resistant and otherwise selected for compatibility with the fluid being transferred or for desired mechanical properties. 
     As it is anticipated that certain changes may be made in the present invention without departing from the precepts herein involved, it is intended that all matter contained in the foregoing description shall be interpreted in as illustrative rather than in a limiting sense. All references cited herein are expressly incorporated by reference.