Abstract:
A digital flow control assembly for controlling the volumetric flow rate of fluids includes a fluid flow conduit, a plurality of serially-arranged flow nodes positioned along a length of the fluid flow conduit, and a device for generating a signal. The device for generating a signal is used to adjust one or more of the plurality of serially-arranged flow nodes to maintain a desired volumetric flow rate of fluid in the fluid flow conduit. A method for controlling the volumetric flow rate of fluids includes providing a fluid flow conduit, providing a plurality of serially-arranged flow nodes positioned along a length of the fluid flow conduit, and providing a feedback signal to adjust one or more of the plurality of serially-arranged flow nodes to maintain a desired volumetric flow rate of fluid in the fluid flow conduit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/751,120, filed Dec. 15, 2005, the entirety of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This description relates to controlling the volumetric flow rate of fluids. 
     BACKGROUND 
     The control and management of fluids, and particularly liquids, is a practice and requirement of nearly every aspect of present day technology. As a result, a large number of liquid flow rate control devices have been devised and are in widespread use. 
     Particular volumetric flow rate control devices are point control devices having structure that limits and alters liquid flow rate as a function of a single or discrete point or location of restriction. Of these types, orifice plates, needle valves, ball valves, and plug valves are all widely used fixed or adjustable flow orifice devices. Each of these devices typically has a single fixed location or point of restriction which serves to entirely or principally define the pressure drop (the differential pressure between the pressure measured at the flow input and the pressure measured at the flow output) across the device. With a given motive force applied to the liquid (by, for example, a pump, gravity, or a pressurized vessel), this restriction causes flow at the liquid output to be reduced when compared to flow produced under the same conditions in the absence of the device. 
     For the purposes of this disclosure, a flow control device is a discrete device, made to the purpose of defining, establishing, limiting, or varying the liquid volumetric rate of flow through it, and which allows variable or adjustable liquid volumetric flow rate as a function of its structure and a physical or geometric change within the device. 
     The term “flow control” can be defined as a structure or device having the intended purpose of altering, establishing or defining the volumetric flow rate of a liquid. The term “control” can be defined as a volumetric liquid flow rate defining device which is manually adjusted and invariant in its flow rate control characteristics or structure unless manually altered or adjusted. Thus, a flow rate control may be thought of as a passive volumetric liquid flow control device which is not automatically adjustable or automatically interactive with or reactive to changing conditions. The term “flow controller” can be defined as a structure or device having the intended purpose of altering, establishing or defining the volumetric flow rate of a liquid. The term “controller” can be defined as a volumetric liquid flow rate defining device that can be automatically controlled and adjusted in its flow rate control characteristics, in response to some externally derived signal, command, time, or event. Thus, a flow controller may be thought of as an active, interactive, or dynamic volumetric liquid flow control device. In instances where the distinction between a flow rate control and a flow rate controller are unimportant, either may be referred to as a flow rate control device. 
     SUMMARY 
     According to one general aspect, a digital flow control assembly for controlling the volumetric flow rate of fluids includes a fluid flow conduit, multiple serially-arranged flow nodes positioned along a length of the fluid flow conduit, and a device for generating a signal used to adjust one or more of the serially-arranged flow nodes to maintain a desired volumetric flow rate of fluid in the fluid flow conduit. 
     Implementations of this aspect may include one or more of the following features. For example, the serially-arranged flow nodes may sum to define a total flow resistance through the fluid flow conduit. The flow resistance of each flow node may be added in a manner equivalent to discrete electrical resistances. 
     Each of the flow nodes may be discretely mechanically adjustable, ranging from a minimum flow setting to a maximum flow setting. Each mechanical adjustment of each flow node may be equipped with a Vernier scale dial readout or a digital readout of flow position. 
     The flow nodes also may be commonly mechanically adjustable, ranging from a minimum flow setting to a maximum flow setting. The mechanical adjustment common to all flow nodes may be provided with a Vernier scale dial readout or a digital readout of all commonly adjusted flow positions. 
     In addition, each of the flow nodes may define a flow, and the flow of each flow node may be fixed and nonadjustable. Each of the flow nodes may be discretely actuated to allow electronically controlled adjustment of the flow of each flow node from a minimum flow setting to a maximum flow setting, or all of the flow nodes may be commonly actuated to allow electronically controlled adjustment of the flow rate through the digital flow control assembly, ranging from a minimum flow setting to a maximum flow setting. A rate of fluid flow through the digital flow control assembly may be incrementally altered by at least sixty percent of the total flow range value of the device in twenty milliseconds or less. A previously defined flow rate within the flow range of the digital flow control assembly may be reproduced to within two tenths of one percent of a defined value under steady state inflow and outflow pressure conditions. 
     Furthermore, a second digital flow control assembly may be placed in series flow with the digital flow control assembly to increase the possible flow regulation resolution by the equivalent total number of nodes in series flow divided by the number of nodes in the digital flow control assembly. Some of the serially-arranged flow nodes may serve as a flow control valve in its fully closed position. The fully closed position of each flow node serving as a flow control valve may be encoded. When some of the flow nodes serve as a flow control valve, the flow rate through the assembly may allow the device to define a liquid batch or dose. Two or more flow nodes serving as control valves may provide redundant valving as a function of their series-arranged structure. 
     The digital flow control assembly may also include a common actuator for controlling the flow of the flow nodes, and the common actuator may be encoded to provide discrete position registrations, or to provide digital or analog readout of the entire range of flow adjustment. The assembly may further include one or more discrete actuators for controlling the flow of the flow nodes, and the discrete actuators may be encoded to provide discrete position registrations or to provide digital or analog readout of the entire range of flow adjustment of the node. The serially-arranged flow nodes may define a variable internodal spacing between consecutive nodes to minimize liquid flow turbulence within a given flow rate range. The fluid flow conduit and flow nodes may be constructed of rigid materials, or of a deformable or flexible conduit. 
     Moreover, the flow nodes may be variably spaced in order to accommodate flow system layout or spacing constraints. Multiple fixed or manually adjustable flow control nodes may be combined with discretely automatically adjustable or commonly automatically adjustable flow control nodes within the same assembly. Each of the flow nodes may be discretely adjusted to a mechanically defined high flow opening and to a mechanically defined low flow opening, with all flow control nodes discretely and simultaneously shifted between the two flow positions. Each of the flow nodes may be commonly adjustable to a mechanically-defined low flow opening and to a mechanically-defined high flow opening, with all flow control nodes commonly and simultaneously shifted between the two flow positions. Flow of fluid through the assembly may be adjusted based upon at least one externally derived process signal, such as temperature, pressure, pH, or conductivity. 
     The digital flow control assembly may also include an inflow pressure sensor for measuring pressure just prior to entry of fluid into the digital flow control assembly, and an outflow pressure sensor for measuring pressure at a point just beyond the digital flow control assembly. Correspondingly, the inflow and outflow pressure sensors may allow for measurement of the volumetric flow rate through the assembly. The assembly may automatically adjust itself to a desired volumetric flow rate within an adjustable flow range of the assembly. One or more of the flow nodes may be coarsely adjustable for purposes of establishing a flow rate through the assembly to within about ten percent of the desired value, and the remainder of the flow nodes may be finely adjusted in order to adjust the coarse flow rate to within about one percent or less of the desired value. A gas saturated liquid at a defined temperature range may be flow-rate controlled over a dynamic range of at least 8:1, without dissolved gas substantially leaving solution as a function of flow through the assembly. 
     One or more of the serially-arranged flow nodes may be mechanically or automatically adjusted to achieve linearization of flow rate across a variable flow range of the assembly. The serially-arranged flow nodes may be configured in a parallel configuration to provide for parallel fluid pathways. The spacing between the serially-arranged flow nodes may be sufficient to provide an internal fluid flow wake structure that includes fluid separation and recirculation zones downstream of the flow nodes, and substantial reattachment of the fluid to an inner wall of the conduit, before a subsequent node is approached. The device for generating the signal may be a fluid flowmeter. 
     At least two of the flow nodes may be simultaneously adjustable and at least two of the plurality of flow nodes may be independently adjustable to provide a desired fluid flow restriction through the assembly. In addition, one or more of the flow nodes may be independently adjustable and the remainder of the flow nodes may be simultaneously adjustable to provide a desired fluid flow restriction through the assembly. 
     According to another general aspect, a method for controlling the volumetric flow rate of fluids includes providing a fluid flow conduit, providing multiple serially-arranged flow nodes positioned along a length of the fluid flow conduit, and providing a feedback signal to adjust the serially-arranged flow nodes to maintain a desired volumetric flow rate of fluid in the fluid flow conduit. 
     Implementations of this aspect may include one or more of the following features. For example, adjusting the flow nodes may include discretely or commonly mechanically adjusting the flow nodes, ranging from a minimum flow setting to a maximum flow setting. Adjusting the flow nodes also may include discretely or commonly actuating the flow nodes, using electronically controlled adjustment of each flow aperture of each flow node from a minimum flow setting to a maximum flow setting. 
     The method may also include providing a second digital flow control assembly placed in series flow with the digital flow control assembly to increase the possible flow regulation resolution by the equivalent total number of nodes in series flow divided by the number of nodes in the digital flow control assembly. The method may further include providing a common actuator for controlling the flow aperture of the serially-arranged flow nodes, as well as encoding the common actuator to provide discrete position registrations, or to provide digital or analog readout of the entire range of flow aperture adjustment. In addition, the method may include providing one or more discrete actuators for controlling the flow aperture of the flow nodes, as well as encoding the discrete actuators to provide discrete position registrations, or to provide digital or analog readout of the entire range of flow adjustment of the node. 
     Furthermore, the method may include providing an inflow pressure sensor for measuring pressure just prior to entry of fluid into a digital flow control assembly, and providing an outflow pressure sensor for measuring pressure at a point just beyond the digital flow control assembly. Correspondingly, the inflow and outflow pressure sensors may allow for measurement of the volumetric flow rate through the assembly. Adjusting the flow nodes may include coarsely adjusting some of the flow nodes for purposes of establishing a flow rate through the assembly to within about ten percent of the desired value, as well as finely adjusting the remainder of the flow nodes in order to adjust the coarse flow rate to within about one percent or less of the desired value. Adjusting the flow nodes may also include mechanically or automatically adjusting some of the flow nodes to achieve linearization of flow rate across a variable flow range of the assembly. 
     In other aspects, a fluid volumetric flow rate control device may include an integrated series arranged plurality of flow restrictive elements which sum to define a total flow resistance. An aperture in the plurality of flow restrictive elements may be larger in square area than the aperture of a flow rate equivalent single point liquid flow rate control device. A liquid flow rate control device may be arranged such that, as the number of flow restrictive elements is increased, the differential pressure drop required across each element to establish a particular flow rate is decreased. 
     A liquid flow rate control device may include a flow restrictive element that can be a controllable flow node. 
     Each discretely controllable flow node may be a digital node. More generally, a liquid flow rate control device, referred to as a digital flow rate control, may include a number of flow nodes that defines the digital base number. For example, 10 nodes yield a base  10  digital flow rate control device. 
     In a digital flow rate control device, discretely defining a flow orifice dimension for each flow node may allow a digital linear control of liquid flow rate in which the number of steps of linear control range is equivalent to the number of nodes. 
     In a digital flow rate control device, each integrated flow node may be discretely mechanically adjustable ranging from a minimum flow orifice setting to a maximum flow orifice setting. Two or more of the integrated flow nodes may be commonly mechanically adjustable ranging from a minimum flow orifice setting to a maximum flow orifice setting. 
     In a digital flow rate control device, the flow orifice of each integrated flow node may be defined and fixed and nonadjustable. 
     In a digital flow rate control device, each integrated flow node may be discretely actuated to allow electronically controlled adjustment of each flow orifice ranging from a minimum flow setting to a maximum flow setting. Two or more of the integrated flow nodes may be commonly actuated to allow electronically controlled adjustment of the flow rate through the device ranging from a minimum flow setting to a maximum flow setting. 
     In particular digital flow rate control devices, the rate of flow through the device can be incrementally altered by at least sixty percent of the total flow range value of the device in twenty milliseconds or less. In such devices, any previously defined flow rate within the flow range of the device can be reproduced to within two tenths of one percent of the defined value under steady state inflow and outflow pressure conditions. 
     In another aspect, a digital flow rate control device includes one or more devices placed in series flow with a first device, thus increasing possible flow regulation resolution by the equivalent of the total number of nodes in series flow divided by the number of nodes in the first device. The flow resistance of each series flow node in an integrated device can be added in a manner equivalent to discrete electrical resistances. 
     In a digital flow rate control device, one or more of the adjustable series flow nodes can serve as a flow control valve in its fully closed or occluded position. For example, a digital flow rate control device may include multiple (two or more) flow nodes serving also as control valves to provide redundant valving as a function of their series arranged structure. 
     In another aspect, a digital flow rate control device may include a common actuator that controls the flow orifice of all integrated nodes and may be encoded to provide one or more discrete position registrations or to provide digital or analog readout of the entire range of flow orifice adjustment. 
     In another aspect, a digital flow rate control device may include discrete actuators associated with each integrated flow node that may be encoded to provide one or more discrete position registrations or to provide digital or analog readout of the entire range of flow orifice adjustment of the node. 
     In another aspect, a digital flow rate control device may include mechanical adjustment of each integrated flow node that is equipped with a Vernier scale dial readout or a digital readout of flow orifice position, or a mechanical adjustment common to all flow nodes that is provided with a Vernier scale dial readout or a digital readout of all commonly adjusted flow orifices. The individual mechanical adjustment for each flow node also may be encoded for flow orifice position, as may be a mechanical adjustment common to all flow nodes. 
     In a digital flow rate control device, the fully flow occluded or closed position of any integrated flow node also may serve as a control valve and may be discretely and particularly encoded. 
     A digital flow rate control device may be flow rate adjustable under all conditions of flow and pressure for which a particular device is suited or rated. 
     In a digital flow rate control device, inter-nodal spacing can be varied and optimized to minimize liquid flow turbulence within a given flow rate range. 
     In a digital flow rate control device, the liquid flow pathway and flow control nodes may be constructed of suitable rigid materials. The liquid flow pathway and flow control nodes may be defined by a deformable or flexible conduit or flow tube or hose. Both rigid flow pathway and flexible flow pathway arrangements may be constructed to meet sanitary standards. 
     In a digital flow rate control device, the integrated flow control nodes can be variably separated in order to accommodate flow system layout or spacing constraints. 
     In a digital flow rate control device, a plurality of fixed orifice or manually adjustable orifice flow control nodes may be combined with a plurality of discretely automatically adjustable or commonly automatically adjustable flow control nodes within the same device. Each of the integrated flow control nodes may be discretely adjusted to a mechanically defined high flow orifice opening and to a mechanically defined low flow orifice opening, with all flow control nodes being discretely and simultaneously shifted between the two orifice flow positions. Each of the integrated flow control nodes may be commonly adjustable to a mechanically defined low flow orifice opening and to a mechanically defined high flow orifice opening, with all flow control nodes commonly and simultaneously shifted between the two orifice flow positions. 
     In a digital flow rate control device, flow through the device can be adjusted, altered, or maintained based upon one or more externally derived process signals such as temperature, pressure, pH, conductivity, and the like. 
     In a digital flow rate control device, flow rate through the device, when calibrated, can allow the device, with one or more nodes having control valve functions, to define a liquid batch or dose. 
     A digital flow rate control device can be combined with a separate and discrete liquid flow meter such that the digital flow controller alters flow rate based upon a flow rate signal from the flow meter, with the combined elements forming a flow rate regulator. 
     In another aspect, a digital flow rate controller can be combined with an inflow pressure sensor and an outflow pressure sensor integrated into the controller structure, thereby forming an integrated self-contained and self-regulating flow rate regulator. 
     In a digital flow rate controller, an electronic controller can be integrated into or attached to the structure of the liquid flow rate controller itself. The electronic controller also can be separate or remote or removed from the liquid flow rate controller itself. 
     In a digital flow rate controller, the electronic controller can store, for on demand use, various flow controller flow rate configurations. The electronic controller can monitor flow actuator conditions and positions and integrated pressure sensors (where present) and alarm in the event a set of defined parameters is exceeded. Liquid flow rate characteristics and performance may be graphically portrayed based upon empirically and experimentally derived flow data. 
     In a flow rate control device, some of the plurality of integrated flow nodes may be coarsely adjusted for purposes of establishing a flow rate through the device to within ten percent of the desired value, and the remainder of the plurality of integrated flow nodes may be finely adjusted in order to adjust the coarse flow rate to within one percent or better of the desired value. 
     A flow rate regulator can automatically tune or adjust itself (auto tune) to a desired volumetric liquid flow rate within the adjustable flow range of the device. 
     In a digital flow rate control device, a gas saturated liquid at a defined temperature range can be flow rate controlled over a dynamic range of at least 8:1 without dissolved gas leaving solution as a function of flow through the digital flow rate control device. 
     In a digital flow rate control device, two or more individual flow rate control nodes with fixed orifices, mechanically adjustable orifices, or automatically adjustable orifices may be assembled one to the next to form an integrated digital flow rate control device. 
     In a digital flow rate control device, linearization of flow rate across the variable flow range of the device can be manually or automatically accomplished within and utilizing only the series sequential flow nodes incorporated into the structure of the device. 
     In a flow rate control device, a flow meter may be incorporated and integrated into the structure of a digital series flow restricting node flow controller, thus forming a self-contained and self-regulating digital flow rate regulator. 
     The details of one or more implementations of the device and method are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a single actuator digital flow controller associated with an electronic controller. 
         FIGS. 2A and 2B  show rigid formed tube digital flow controls. 
         FIG. 3  shows a parallel arrangement of a digital flow control devices with control valves addressing the flow pathways. 
         FIG. 4  shows a discrete modular digital flow control assembly. 
         FIG. 5  shows a rigid structure provided with a fixed flow rate digital control. 
         FIGS. 6A and 6B  show a cross section of a discrete modular node series digital flow controller with a single unit being shown in  FIG. 6A  and a series of assembled units being shown in  FIG. 6B . 
         FIGS. 7A and 7B  show a discrete manual modular node digital flow controller. 
         FIGS. 8A and 8B  show a cross section of discrete modular node series digital flow controllers provided with encoding sensors with a single unit being shown in  FIG. 8A  and a series of assembled units being shown in  FIG. 8B . 
         FIG. 9  shows a linearized flow range through separate flow orifice adjustment of each discrete flow node. 
         FIGS. 10A and 10B  show a symmetrical, dual anvil, digital flow controller. 
         FIG. 11  shows an asymmetrical digital flow controller acting upon a flexible tube. 
         FIGS. 12A and 12B  show a side elevational view ( FIG. 12A ) and a top plan view ( FIG. 12B ) of a series of digital flow rate controllers acting upon nodes of a common flexible tube, which series have a common manual actuator. 
         FIGS. 13A and 13B  show a digital flow control assembly where a plurality of nodes formed in a flexible tube are controlled by volumetric flow-rate adjustment fasteners. 
         FIGS. 14A and 14B  show a variable digital flow control which can be moved between a minimum flow geometry as shown in  FIG. 14A  and a maximum flow geometry as shown in  FIG. 14B . 
         FIGS. 15A and 15B  show two views of a series flow node digital flow rate controller with an integrated differential pressure flow meter forming a flow regulator. 
         FIGS. 16A and 16B  are views similar to those of  FIGS. 15A and 15B  but showing a manually actuated digital flow control. 
         FIG. 17  shows a digital flow control with an integrated turbine flow meter forming a flow regulator. 
         FIGS. 18-45 , in the various flow plots, show the empirical behavior of various arrangements. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a digital fluid flow rate control device  100  controls flow through a flexible tube  105 . The tube  105  extends between a fixed node plate  110  and a moveable node plate  115 , each of which includes multiple flow restriction nodes  120 . As the plate  115  moves toward the plate  110 , the nodes  120  compress the flexible tube  105 . Non-occlusion stops  125  are positioned between the plates  110  and  115  to prevent the plates from coming so close together that the nodes pinch the tube  105  to the extent that flow is stopped altogether. The movable plate  115  moves on tracks  130  that extend from opposite ends of the fixed plate  110 . 
     A flow rate adjustment actuator  135  is secured to an actuator thrust plate  140  through an arm  145 . The actuator  135  moves the arm  145  to cause the plate  140  to push against the plate  115  and cause the plate  115  to compress the tube  105 . When the actuator  135  releases or withdraws the arm  145 , fluid pressure in the tube  105  causes the tube  105  to expand, which, in turn, pushes away the plate  115 . The actuator  135  is mounted on a backer plate  150  that is secured to the rails  130 . 
     A position feedback device  155  is mounted on the actuator  135  to monitor the position of the arm  145  and thereby monitor the position of the plates  140  and  115 , and the corresponding amount by which the tube  105  is compressed. 
     An electronic controller  160  receives an output signal of the feedback device  155  and generates a control signal to control the actuator  135 . The controller  160  includes actuator driver control electronics  165 , flow controller position control electronics  170 , and a primary processor  175 . In addition to the feedback signal, the controller  160  includes variable inputs including measurements of one or more of pressure, flow, temperature, chemistry, level and compound variables. The controller  160  may generate compiled data and feedback to external controls. 
     In this arrangement, a single actuator acts upon series integrated flow limiting nodes formed from a flexible tube. This device can be linearized in terms of its flow rate control curve using a digital feedback actuator, and the flow nodes can also serve as redundant sequential control valves in some cases. Particularly when paired with a fast-acting linear actuator, this arrangement can alter flow very quickly, on the order of less than 50 milliseconds to move from lowest to highest flow or the reverse. 
     More generally, a flow rate control device includes fixed or adjustable flow limiting and flow restricting nodes, with each node having an orifice and two or more nodes being incorporated into a single structure or assembly such that the fluid, most particularly liquids, must flow through each flow node in its movement from an infeed port of the device to an outfeed port of the device. Because each node is discrete in terms of its pressure dropping role, but is integrated into a whole, the device is referred to as a digital flow rate control or controller. 
     The term digital also refers to the form and mode of control of the rate of liquid flow through the devices. The flow nodes can be fixed, defined and nonadjustable. More commonly, however, the nodes are either manually or automatically adjustable, either individually and independently from one another, or by a common adjustment mechanism. Thus, in this context, digital refers to a discrete and adjustable flow node location or address, and in still another context, to the nature of the automatic controls such that each node can be electronically adjustable using a digitally controlled actuator or using an actuator in conjunction with a digital feedback device or system. 
     Successive pressure drops in a liquid flow pathway can sum to define a desired liquid flow rate through the pathway. The merits of using multiple series arranged flow restricting nodes instead of one are found in the mathematics of the operation of an adjustable liquid flow control, as well as the physical consequences (and benefits) of such an arrangement. 
     The performance of multiple nodes can be illustrated by considering a simplified model as a valid analogy. First, consider a 100 ohm potentiometer variable resistor with a center wiper such that its effective resistance can be varied from zero to its full 100 ohm value. The resistance element has an overall tolerance of 1.0 percent, or a worst case variation of 1 ohm. Now, consider 10 center wiper potentiometers, each of 10 ohms resistance, series connected, each with an overall tolerance of 1.0 percent. Each potentiometer in this case has a tolerance of 0.10 ohms and they sum to a 1.0 ohm worst case variation of the summed 100 ohms. 
     In this comparison it is given that either system can be adjusted to deliver a total resistance to current flow within zero to 100 ohms and each to a certain accuracy of set point. 
     The chances of the single 100 ohm resistor being below 100 ohms in value is nearly one in two. The other possibility is that it is above 100 ohms in value (the probability of it being exactly 100 ohms being so extremely small as to be irrelevant). The chances of each 10 ohm resistor being above or below the exact value are the same as with the larger value resistor, but it is far more likely that the net total resistance will more closely approximate the ideal 100 ohm value since some of the ten will be above 10 ohms while others will be below. Thus, in this analogy, the inherent accuracy of the ten element system is improved. 
     Now compare the instance where a particular resistance value is sought with the single 100 ohm potentiometer and it is adjusted to within 2.0 percent error of total span of target value, and the case where each of the ten 10 ohm potentiometers is adjusted to within 2.0 percent of its span to sum to the particular resistance value sought. Since 10×0.02×10 is 2.0 and 100×0.02 is 2.0, there appears to be no difference in the two systems. However, there is one crucial difference, that results from problems in accurately adjusting a single point system. In the single point approach, there is only one adjustment that my be right or wrong. In the ten element system, however, things are more forgiving. 
     Consider adjusting the 100 ohm unit to within 3.0 percent of span of the desired value instead of the target of 2.0 percent. Then consider the error effect of setting one of the ten series units to 3.0 percent and the rest to the correct 2.0 percent. In the single unit case the actual error is 3.0 percent. In the series units case the actual error is 2.10 percent. If three of the series units are badly adjusted to a 3.0 percent error, the cumulative error across the ten devices is 2.3 percent. If five of the ten units are badly adjusted to 3.0 percent error, the cumulative error across the ten devices is 2.5 percent. If nine of the ten units are badly adjusted to 3.0 percent error, the cumulative error across the ten devices is 2.9 percent, and still better than achieved with the single element device. 
     This analogy holds up in the case of the multi-node digital flow control device, and is empirically demonstrable. Further, in practice, the set point accuracy advantage is magnified by the understanding that each flow resistance node in the multi-point system is larger in dimension for a given flow rate than the single orifice of the single point system. Thus, with an adjustment apparatus of the same physical resolution in each case, the inherent resolution of adjustment of each node in the multi-node system must be inherently greater, both at a given node and, even more importantly, across all nodes. By example, if each adjustment apparatus has  100  increments, the total resolution of a 10 node system is one part in 1000, while the single node system is total resolution of the one part in 100. 
     Referring to  FIGS. 2A and 2B , digital flow controls  200  and  205  disclosed herein can be of fixed and invariant flow characteristics based upon forming the integrated flow nodes from a rigid material such as a metal tube.  FIG. 2A  illustrates a rigid tube  200  having circumferential nodes  210 , while  FIG. 2B  illustrates a rigid tube  205  having nodes  215  on a single side. This simple control may be employed in a liquid flow system with narrow or predictable variations in flow pressure and/or where predictable variations in flow rate with flow pressure changes are tolerable. Changing the net effective flow allowed by the device requires altering the flow pressure applied to its infeed, which may be readily accomplished since the pressure to flow relationship of these devices is proportionate and free of discontinuities. Additional devices can be added in series to reduce flow (termed a series-series arrangement) or the device can be replaced with one of overall matching dimensions but with differently dimensioned flow orifices. Another important variant is to place these differing devices in parallel with a suitable control valve (manual or automatic) on each parallel branch, allowing different pre-defined flow rates to be valved in and out of the flow pathway. Such an arrangement is illustrated by the system  300  of  FIG. 3 , which includes four flow controls  305  connected in parallel, with flow into each flow control  305  being permitted or prevented by a corresponding valve  310 . 
       FIG. 4  shows a nonadjustable flow control  400  that employs modular flow nodes  405  of desired flow orifice dimensions stacked inside of a flow tube  410  with inter-nodal spacers  415 . The flow control  400  also includes an inflow fitting  420  extending from a flange  425 , an outflow fitting  430  extending from a flange  435 , and an expansion spacer tube  440 . The flow control  400  is flow rate modified by changing out some or all of the nodes for others with different orifice dimensions. The inter-nodal spacers provide intervening reduced turbulence zones and may or may not be required depending upon liquid characteristics. This flow control may also be flow rate modified by adding modular flow nodes in lieu of the expansion spacer tube shown, as well as by deleting nodes. 
       FIG. 5  shows a fixed flow rate  500  that includes spherical flow restricting nodes  505  spaced apart in a flow tube  510  and supported on a coaxial support rod  515 . The circumferential space between the circumference of each ball and the inner wall of the tube form a flow reducing node. The dimension of the space constitutes the degree of flow reduction and is an annular shaped flow orifice. The spherical nodes  505  are separated by internodal spacers  520  and arranged such that flow entering through an inflow port  525  passes by each of the nodes  505  before entering through an outflow port  530 . 
       FIGS. 6A and 6B  depict still another fixed orifice modular node device  600  where the nodes  600  are physically discrete until assembled and integrated together into a multi-node series arrangement  605 . As shown in  FIGS. 7A and 7B , a similar flow control device  700  can include a manually-adjustable control knob  705  that can be manipulated to extend or retract a post  710  into the flow path. As shown in  FIG. 7B , multiple devices  700  may be connected in series to create a multi-node flow control  715 . 
     As shown in  FIGS. 8A and 8B , another flow control device  800  may include an automatic actuator  805  and an encoding sensor  810  at each node. Each of these actuators may be hydraulic, magneto rheological, thermal, pneumatic, magnetic, solenoid, or motor operated (motors of all types being usable), and any other actuator types suitable to rapid precise motion may also be used. As shown in  FIG. 8B , devices  800  may be connected in series to form a multi-node flow control  815 . 
     The use of individual actuators allows the maximum flexibility in flow rate control formatting, including combining some nodes for range ability (coarse adjustment) and some for fine increment adjustment. Essentially, the pattern of use and adjustment is constrained only by the versatility of the actuators and their controlling software. The use of individual actuators also allows a straightforward control format for following external flow command signals where the number of nodes responsive to a given signal type constrains and limits the absolute magnitude of the flow change possible. This format also allows multiple signals to be segregated to a discrete flow node or nodes, allowing an unusually flexible flow rate control device scaled to and responsive to mixed or multiple control signals. 
     The use of discrete automatic actuators also allows a fast digital system to be embodied where flow nodes are fully engaged or fully disengaged into or out of the flow pathway of the flow controller. This use format may be more precisely termed ultrafast in that flow can be altered by any given flow node in twenty one-thousandths of a second or less (20 milliseconds) such that the device is useful for applications such as missile control systems, super critical liquid process environments, and signal tracking systems. The bar graph  900  of  FIG. 9  illustrates the general form of control possible with this “all digital” control format. The graph shows a ten node system and the relative flow rate control pattern possible with this methodology. Although flow rate through these devices is relatively linear in basic form, full linearization as shown in the bar graph is possible with simple discrete definition and calibration at each flow node. 
       FIGS. 10A and 10B  show a flow controller  1000  in which individual actuators  1005  control flow nodes  1010  comprising periodic restrictions of a flexible tube  1015 . 
     Each actuator  1005  includes an integral encoding sensor that monitors the position of the actuator. The controller  1000  is symmetrical, in that nodes  1010  are positioned opposite fixed nodes  1020 . The nodes and inter-nodal spacing combine to form well defined Laval shaped flow structures. With spacing of nodes appropriate to the flow rate range of use, flow through this device is relatively non-turbulent. In particular, this arrangement has been empirically shown to be useful in controlling the flow rate of gas saturated liquids. For example, one particular implementation is capable of varying the flow rate of beer over a dynamic range of greater than 8:1 without causing the dissolved CO2 to leave solution. This embodiment also has the particular advantage of being very sanitary in its construction, with its non-invasive flow tube. The tube used in the device can be of a particularly wide variety of chemistries, elastomers, and durometers because it need not be occluded but only restricted. Thus the over-folding or creasing of the tube when pinched to occlusion can be avoided in this device leading to greatly extended and generally indefinite service life. Nevertheless, any given node position can be restricted to occlusion, such that the flow controller  1000  can serve as a control valve. This capability is enhanced where multiple sequential nodes serve also as valves, in that a redundant valve structure is created. Also of note in this regard is the increased sealing pressure or differential pressure possible with these multiple in series valve structures. Also, the occlusive force that is required to seal against a given pressure can be shown to be reduced in this series valve structure. It is well understood that the greater the occlusive force applied to a pinch valve tube, the shorter the tube life. 
       FIG. 11  shows a flow controller  1100  that is asymmetrical and differs from the controller  1000  in that the fixes nodes  1020  are replaced with a flat plate  1105 . 
     As an alternative to individually adjusting the flow nodes, systems may adjust all of the flow nodes in unison. The flow rate control device  100  of  FIG. 1  provides one example of a system that operates in that way. 
       FIGS. 12A and 12B  show a flow control device  1200  that is similar to the device  100  of  FIG. 1  but differs in that the automatic actuator  135  has been replaced with a manual adjustment knob  1205  mounted on the backer plate  150 . The adjustment knob  1205  allows manual adjustments of all flow limiting nodes simultaneously. This simple flow rate adjustment methodology can be calibrated using a mechanical dial indicator, a mechanically incremented digital shaft position indicator, or by an electronic digital readout (“DRO”). 
       FIGS. 13A and 13B  show a flow control  1300  that employs symmetrical nodes  1305  to compress a flexible tube  1310 . The nodes  1305  are mounted on rails  1315 , with the spacing between the rails being controlled by adjustment fasteners  1320 . Non-occlusion stops  1325  prevent the rails from moving so close together that flow through the tube  1310  is occluded. 
       FIGS. 14A and 14B  show a variable flow controller  1400  having nodes  1405  that are arranged similarly to the nodes  505  of the flow control  500  of  FIG. 5 . In particular, the nodes  1405  are separated by internodal spacers  1410  and are mounted on a shaft  1415  that is coaxially positioned in a tube  1420 . The shaft extends through a shaft seal  1425  at the end of the tube where it is connected with an actuator  1430  having an associated position encoder  1435 . The actuator  1430  is configured to move the shaft between a first position (as shown in  FIG. 14A ) in which the nodes  1405  are aligned with annular rings  1435  on an interior surface of the tube  1420  and flow between an inflow port  1440  and an outflow port  1445  is minimized, and a second position (as shown in  FIG. 14B ) in which the nodes  1405  are positioned equidistant between neighboring rings  1435  and flow is maximized. Using the encoder  1435 , the actuator  1430  also is able to position the shaft in positions between those shown in  FIGS. 14A and 14B . 
     As shown, the range of motion to effect a large and essentially linear flow control range is comparatively small and thus allows a highly responsive and very fast-adjusting device. The physical shape of each flow node can be varied widely as appropriate to the velocities of the particular application. 
       FIGS. 15A and 15B  show a variable flow controller  1500  that differs from the flow controller  1400  by including an inflow pressure sensor  1505  at the inflow port  1440  and an outflow pressure sensor  1510  at the outflow port  1445 . By placing a pressure sensor on each side of a single flow restricting orifice and reading the pressure differential, volumetric flow rate may be determined. The integration and combination of these sensors into a digital series flow restricting node flow rate controller provides a highly efficient and capable fully integrated flow regulator solution. When combined with a digital flow controller as herein disclosed, the rational and useful range of differential pressure signals from the spaced apart sensors is greatly increased, often by a range of two or three times over conventional configurations. 
       FIGS. 16A and 16B  show a variable flow controller  1600  that differs from the flow controller  1400  in that the actuator  1430  is replaced with a manual actuator  1605  that extends through a threaded thrust plate  1610 . 
       FIG. 17  shows a variable flow controller  1700  that differs from the flow controller  1400  by including an integrated turbine flow meter  1705 . Inclusion of the liquid flow meter  1705  in the same liquid flow conduit as the digital flow controller permits the digital flow rate controller to function as a flow rate regulator in that it can actively hold and maintain a defined flow rate set point based upon a flow rate signal. This arrangement is particularly suited for this application because of its inherent relative linearity, its ability to be configured by adjustment, its comparatively fast speed of response, high predictability of response, essentially total lack of hysteresis or overshoot under flow adjustment, and lack of flow discontinuities in its flow rate curves, particularly at the extreme low end and extreme high end of useful flow range of a particular device. 
       FIG. 13  somewhat schematically shows another embodiment in which shaft mounted spheres are manually movable coaxially in relation to hemispherical-circumferential elements fitted periodically to the internal diameter of a suitable rigid flow containment cylinder. Each pair of these structures comprises a series integrated flow rate node and varying the relative position of the annular or doughnut shaped orifice formed between the paired elements of each node can vary flow rate in a nearly linear manner. 
     In the 48 flow plots depicted in  FIGS. 18 to 45 , the empirical behavior of various implementations of the device is extensively presented, with these data and graphs serving as the basis for further comments and analysis on the functional flow rate behavior of the device. The plots illustrated in  FIGS. 18-23  are examples of graphical plots of empirical flow data correlating flow rate expressed in fluid ounces per second against the flow node flow aperture diameter in fractional inches, defined as the compression gap or interval set consistently between each flow node defining an anvil pair (where an “anvil” is a structure that serves to define the flow node). The general form of the flow control used to gather this data is shown variously in  FIGS. 1 ,  11 , and  13 . Flexible flow conduit size and flow pressure were held constant, while anvil spacing was varied over a 2:1 range and anvil count was varied over a 2:1 range. 
       FIGS. 23A and 23B  summarize these flow relationships, which can be shown to be representative of results with a broad range of flexible tube sizes and flow pressures. Thus, the flow control devices can be empirically shown to produce an average change in flow of 13.75 percent at a constant flow conduit diameter, constant flow pressure, and setting of the flow nodes gap ranging from about 0.35 to about 0.44 of the uncompressed inside diameter of the tube (termed herein as the flow orifice ratio), when the flow node count range is varied over a range of 5 nodes to 10 nodes (2:1 range) and when the center-to-center spacing of the nodes is varied from 0.75 inches to 1.5 inches (2:1) range. The flow change is inverse in relationship to the spacing of the flow nodes. Thus, flow can be varied as specified merely by changing the flow nodes spacing. 
     Linearity of flow rate with a change in flow nodes flow aperture sizing is also summarized in  FIGS. 23A and 23B  over the same range of test conditions as defined above. Thus, over the flow node aperture range defined by anvil gapping of about 0.35 to about 0.44 of the uncompressed inside diameter of the flexible tube, linearity is within 2.5 percent or better across a flow range that varies at least 3.5 times from minimum flow to maximum flow. 
       FIGS. 32A ,  32 B,  33 A, and  33 B are flow curve examples that show that the linear operation of the multi-node devices can be subdivided into two separate zones based upon the relative degree of flow aperture or orifice restriction expressed as a ratio of flow anvil spacing to the uncompressed inside dimension of the flexible flow tube. Thus, in the example of  FIGS. 33A and 33B , at an illustrated 3:1 pressure range, a first linear range exists from an aperture ratio of 0.35 to 0.44. A second linear range extends from an orifice ratio of 0.60 to 0.87. Because of this dual zone linearity, a flow control capability is recognized in which a coarse adjustment control of flow rate and a fine adjustment control of flow rate are possible. Consider, in  FIGS. 33A and 33B , that adjustment in the first linear zone of the flow aperture ratio of 0.35 to 0.44 changes flow rate through the device by a factor of 4:1 in the case of the highest pressure operating curve shown. In the second linear zone, adjustment from a flow aperture ratio from 0.67 to 0.87 changes flow rate through the device by a ratio of 1.1:1. Thus, in the first zone, each 0.01 increment of aperture ratio change causes a flow change of 0.11 of the 4:1 range. In the second zone, each 0.01 increment of aperture ratio causes a flow change of 0.037 of the 1.1:1 range. Thus, the span and resolution of adjustment per increment of flow aperture ratio change are different in each case. This, in turn, allows the flow control device to be adjusted on a coarse and fine basis. 
     As another example of the coarse and fine adjustment, consider a unitized ten flow node element device in which five flow nodes are adjusted to approximately reach a desired flow within the first linear zone range. The remaining five node can then be used to adjust flow with significantly higher resolution in order to more precisely and more easily reach the exact desired flow rate value. This allows adjustments that are easier and faster to achieve and reduces the effects of setpoint undershoot and overshoot (manual or automatic) or a desired flow rate setpoint. This benefit can also be gained by using two separate devices in series flow, one operating in the high resolution zone, and one operating in the low resolution zone. 
       FIGS. 25 and 34  illustrate that a defined span of useful adjustment ranges, expressed as the flow orifice ratio span, increases as the number of series flow nodes in the flow control device increases. Thus, the resolution of flow adjustment per increment of flow rate change increases as the number of flow nodes increases. Therefore, by example in  FIG. 25 , a two flow nodes on one inch centers, the flow aperture ratio span to vary flow from two ounces per second to ten ounces per second is 0.21. At ten nodes on one inch centers and at the same flow pressure, the flow aperture ratio span to vary flow from over the same range is 0.27, which is an improvement over 28.5 percent. 
     A number of implementations of the control devices have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.