Abstract:
A method for monitoring a filter installed in a fluid system. The steps include providing a reference region in the fluid system, the region including a chamber having a known volume and releasing a fluid from the chamber configured to flow through the reference region. The method further includes measuring pressure and temperature values at predetermined locations at predetermined time intervals and determining filter permeability values in response to measured pressure and temperature values. The method further includes comparing the filter permeability values to predetermined filter permeability values.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application is related to application Ser. No. ______, Attorney Docket No. 22026-0016, filed contemporaneously with this Application on Sep. 28, 2007, entitled ” NON-CLOGGING FLOW RESTRICTION FOR PRESSURE BASED FLOW CONTROL DEVICES” assigned to the assignee of the present invention and which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to fluid flow systems and, more particularly, to monitoring performance of components of fluid flow systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Many industrial applications require monitoring of fluid flows. In addition, the fluid flow streams may contain contaminants, such as particulate matter that may be removed from the flow streams by filtration. Over time, filters can clog, often requiring shut-down of plant critical analyzer equipment in order to replace the filters. 
         [0004]    Thus, there is a need for determining when filter replacement is required, and further, a framework for predicting when tests for determining possible filter replacement should be conducted. 
       SUMMARY OF THE INVENTION 
       [0005]    For laminar or porous flow through a permeable membrane or porous element such as a filter, the flow is governed by Darcy&#39;s law as shown for Equation 1. 
         [0000]    
       
         
           
             
               
                 
                   
                     Q 
                     . 
                   
                   = 
                   
                     
                       
                          
                         V 
                       
                       
                          
                         t 
                       
                     
                     = 
                     
                       κ 
                        
                       
                         
                           π 
                            
                           
                               
                           
                            
                           
                             d 
                             2 
                           
                            
                           Δ 
                            
                           
                               
                           
                            
                           P 
                         
                         
                           4 
                            
                           η 
                            
                           
                               
                           
                            
                           L 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   1 
                   ] 
                 
               
             
           
         
       
     
         [0006]    Equation 2 shows the circumstance when a first pressure gauge (P 1 ) and a differential pressure sensor (ΔP) are employed in the Darcy&#39;s law equation, while Equation 3 represents shows the circumstance when first and second pressure gauges (P 1 , P 2 ) or absolute pressure sensors are employed in the Darcy&#39;s law equation. 
         [0000]    
       
         
           
             
               
                 
                   
                     Q 
                     . 
                   
                   = 
                   
                     
                       
                          
                         V 
                       
                       
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                         t 
                       
                     
                     = 
                     
                       κ 
                        
                       
                         
                           π 
                            
                           
                               
                           
                            
                           
                             
                               d 
                               2 
                             
                              
                             
                               ( 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 P 
                               
                               ) 
                             
                           
                         
                         
                           4 
                            
                           η 
                            
                           
                               
                           
                            
                           L 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   2 
                   ] 
                 
               
             
             
               
                 
                   
                     Q 
                     . 
                   
                   = 
                   
                     
                       
                          
                         V 
                       
                       
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                         t 
                       
                     
                     = 
                     
                       κ 
                        
                       
                         
                           π 
                            
                           
                               
                           
                            
                           
                             
                               d 
                               2 
                             
                              
                             
                               ( 
                               
                                 
                                   P 
                                   1 
                                 
                                 - 
                                 
                                   P 
                                   2 
                                 
                               
                               ) 
                             
                           
                         
                         
                           4 
                            
                           η 
                            
                           
                               
                           
                            
                           L 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   3 
                   ] 
                 
               
             
           
         
       
     
         [0007]    By substitution of fluid density (ρ) as shown in Equation 4 from the ideal gas law equation having non-ideal compressibility, Equations 5 and 6 (for liquid flows) are obtained. 
         [0000]    
       
         
           
             
               
                 
                   ρ 
                   = 
                   
                     P 
                     
                       RTZ 
                        
                       
                         ( 
                         
                           P 
                           , 
                           T 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   4 
                   ] 
                 
               
             
             
               
                 
                   
                     m 
                     . 
                   
                   = 
                   
                     
                       
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                         m 
                       
                       
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                     = 
                     
                       
                         ρ 
                          
                         
                             
                         
                          
                         
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                       = 
                       
                         κ 
                          
                         
                           
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                              
                             
                                 
                             
                              
                             
                               d 
                               2 
                             
                              
                             
                               M 
                               w 
                             
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                              
                             
                               PP 
                               1 
                             
                           
                           
                             4 
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                             η 
                              
                             
                                 
                             
                              
                             
                               LRTZ 
                                
                               
                                 ( 
                                 
                                   P 
                                   , 
                                   T 
                                 
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                   [ 
                   5 
                   ] 
                 
               
             
             
               
                 
                   
                     m 
                     . 
                   
                   = 
                   
                     
                       
                          
                         m 
                       
                       
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                     = 
                     
                       
                         ρ 
                          
                         
                             
                         
                          
                         
                           Q 
                           . 
                         
                       
                       = 
                       
                         ρκ 
                          
                         
                           
                             π 
                              
                             
                                 
                             
                              
                             
                               
                                 d 
                                 2 
                               
                                
                               
                                 ( 
                                 
                                   
                                     P 
                                     1 
                                   
                                   - 
                                   
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                                     2 
                                   
                                 
                                 ) 
                               
                             
                           
                           
                             4 
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                             L 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   6 
                   ] 
                 
               
             
           
         
       
     
         [0008]    Filter permeability (κ) can then be calculated as shown in Equation 7 (using volumetric flow) and Equation 8 (using mass flow for gases). 
         [0000]    
       
         
           
             
               
                 
                   κ 
                   = 
                   
                     
                       
                         4 
                          
                         η 
                          
                         
                             
                         
                          
                         L 
                          
                         
                             
                         
                          
                         
                           Q 
                           . 
                         
                       
                       
                         π 
                          
                         
                             
                         
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                           d 
                           2 
                         
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                          
                         
                             
                         
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                         P 
                       
                     
                     = 
                     
                       
                         
                           4 
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                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   7 
                   ] 
                 
               
             
             
               
                 
                   κ 
                   = 
                   
                     
                       
                         4 
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                         η 
                          
                         
                             
                         
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                          
                         
                             
                         
                          
                         
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                           . 
                         
                       
                       
                         π 
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                           d 
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                             LRTZ 
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                             1 
                           
                         
                       
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                         ( 
                         
                           
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                             m 
                           
                           
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                             t 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   8 
                   ] 
                 
               
             
           
         
       
     
         [0009]    Once filter permeability is known from an initial state calculation of mass flow or volumetric flow (by measuring pressure drop over time in a fixed volume), the fluid viscosity (η) can be calculated as shown in Equation 9 (using volumetric flow) and Equation 10 (using mass flow for gases). 
         [0000]    
       
         
           
             
               
                 
                   η 
                   = 
                   
                     κ 
                      
                     
                       
                         π 
                          
                         
                             
                         
                          
                         
                           d 
                           2 
                         
                          
                         Δ 
                          
                         
                             
                         
                          
                         P 
                       
                       
                         4 
                          
                         L 
                          
                         
                             
                         
                          
                         
                           Q 
                           . 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   9 
                   ] 
                 
               
             
             
               
                 
                   η 
                   = 
                   
                     κρ 
                      
                     
                       
                         π 
                          
                         
                             
                         
                          
                         
                           d 
                           2 
                         
                          
                         Δ 
                          
                         
                             
                         
                          
                         P 
                       
                       
                         4 
                          
                         L 
                          
                         
                             
                         
                          
                         
                           m 
                           . 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   10 
                   ] 
                 
               
             
           
         
       
       
         
           
             Where: 
             d=Hydraulic diameter or flow passage diameter of porous restriction or laminar element 
             A=Hydraulic area or flow passage area 
             ΔA=Pressure differential across restriction (P upstream -P downstream ) 
             L=Length over which the pressure drop occurs 
             η=Fluid absolute viscosity 
             ρ=fluid density (either gas or liquid) 
             M w =Molecular weight of the gas 
             κ=Material permeability (for porous media) 
             V=volume 
             t=time
           {dot over (Q)}=volumetric flow rate (volume per unit time)   dt=time differential   dV=volume change rate   Z(P,T)=Non-ideal gas compressibility (function of pressure and temp.)   
         
           
         
       
     
         [0025]    The present invention relates to a method for monitoring a filter installed in a fluid system. The steps include providing a reference region in the fluid system, the region including a chamber having a known volume and releasing a fluid from the chamber configured to flow through the reference region. The method further includes measuring pressure and temperature values at predetermined locations at predetermined time intervals and determining filter permeability values in response to measured pressure and temperature values. The method further includes comparing the filter permeability values to predetermined filter permeability values. The present invention further relates to a method of obtaining a viscosity value for a fluid in a fluid system. The method includes providing a reference region in the fluid system, the region including a chamber having a known volume and releasing a fluid from the chamber configured to flow through the reference region. The method further includes measuring pressure and temperature values at predetermined locations at predetermined time intervals and determining a difference in pressure values at each of the chamber and the reference region at predetermined time intervals. The method further includes determining a filter permeability value from the measured pressure and temperature values and the calculated difference in pressure values and determining at least one of a mass flow rate and a volumetric flow rate of the fluid from at least one of the measured pressure and temperature values and the calculated difference in pressure values, and from a separate device. The method further includes determining a fluid viscosity value, wherein the filter permeability value remains substantially unchanged between the predetermined time intervals. 
         [0026]    The present invention further relates to a method of obtaining a viscosity value for a fluid in a fluid system. The method includes providing a reference region in the fluid system, the region including a chamber having a known volume and releasing a fluid from the chamber configured to flow through the reference region. The method further includes measuring pressure and temperature values at predetermined locations at predetermined time intervals and determining a difference in pressure values at each of the chamber and the reference region at predetermined time intervals. The method further includes determining a filter permeability value from the measured pressure and temperature values and the calculated difference in pressure values. The method further includes determining at least one of a mass flow rate and a volumetric flow rate of the fluid from at least one of the measured pressure and temperature values and the calculated difference in pressure values, and from a separate device. The method further includes determining a fluid viscosity value, wherein the filter permeability value remains substantially unchanged between the predetermined time intervals. 
         [0027]    The present invention still further relates to a fluid system. The fluid system includes a reference region including a chamber having a known volume and a filter. The fluid system includes pressure and temperature sensors disposed at predetermined locations along the reference region. Upon selective release of a fluid from the chamber configured to flow through the reference region and measurement of pressure and temperature values by the pressure and temperature sensors at predetermined time intervals, filter permeability values are calculable. 
         [0028]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a schematic view of an embodiment of a portion of a fluid system of the present disclosure. 
           [0030]      FIGS. 2-3  are schematic views of alternate embodiments of a portion of a fluid system of the present disclosure. 
           [0031]      FIG. 4  is a graphical representation of a filter life cycle of the present disclosure. 
           [0032]      FIGS. 5-10  are graphical representations of different operating scenarios encountered by a fluid system of the present disclosure. 
       
    
    
       [0033]    Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Referring now to the drawings,  FIG. 1  shows a schematic view of a portion of a fluid system  10 , such as for use in fluid flow metering or flow control device  11 . Flow control device  11  includes a housing  14  containing various measuring components and a control panel  12 , although the measuring components may be exterior of housing  14 . Measuring components include, but are not limited to temperature sensors  19 ,  21  and pressure sensors  18 ,  20 , and may also include mass sensors (not shown) or sensors to measure other fluid parameters. In one embodiment, flow control device  11  is secured to a manifold  16  to which is also secured a filter housing  44  and a manifold  42  for filtering pressurized fluid flow through flow control device  11 . 
         [0035]    In one embodiment, pressure and/or temperature sensors may be combined into a single device. 
         [0036]    As used herein, the term “measuring pressure” in the context of measuring pressure at each of two locations, is intended to include a pressure measurement at a first location and a differential pressure measurement between the first and second locations. 
         [0037]    As further shown in  FIG. 1 , a pressurized fluid  32  from a pressurized fluid source, such as a chamber  76  of known volume, is directed through a passageway  34  formed in manifold  16  upon the opening of a valve  67 . Pressure sensor  18  is immediately adjacent to and in fluid communication with pressurized fluid  32  via passageway  36  bridging passageway  34  and sensor  18 . Similarly, one leg of differential pressure sensor  20  is in fluid communication with pressurized fluid  32  via passageway  38  bridging passageway  34  and pressure sensor  20 . In one embodiment, a bypass outlet  54  is in fluid communication with passageway  34  to further direct pressurized fluid  32 , if desired. Pressurized fluid  32  is further directed through passageway  34  and then passageway  40  before flowing into filter housing  44  and then through filter element or filter  46  to remove particulates entrained in pressurized fluid  32 . 
         [0038]    After passing through filter  46 , pressurized fluid  32  becomes filtered fluid  58 . Upon passing through filter  46 , filtered fluid  58  is then directed through passageway  48 . The other leg of differential pressure sensor  20  is in fluid communication with filtered fluid  58  via passageway  50  bridging passageway  48  and differential pressure sensor  20  so that differential pressure sensor  20  measures the difference in pressure between pressurized fluid  32  and filtered fluid  58 . In one embodiment, a bypass outlet  56  is in fluid communication with passageway  48  to further direct filtered fluid  58 , if desired. Filtered fluid  58  is further directed through passageway  52  in fluid communication with passageway  48 , which fluid referred to as pressurized fluid  60 . For ease of description and convenience, the pressure value or magnitude as sensed by pressure sensor  18  is referred to as P 1  and the pressure value or magnitude as sensed by the one leg of pressure sensor  20  in communication with passageway  50 , which is pressurized fluid  60 , is P 2 . The pressure value P 2  refers to the backpressure downstream in fluid system  10 . It is to be understood that while pressurized fluid  32  (P 1 ) is shown in  FIG. 1  upstream of filter  46  and pressurized fluid  60  (P 2 ), and that the pressure value or magnitude of pressurized fluid  32  (P 1 ) is greater than the pressure value or magnitude of pressurized fluid  60  (P 2 ), both the pressure magnitudes and thus, directions of travel of the pressurized fluids, may be reversed. 
         [0039]    As further shown in  FIG. 1 , flow control device  11  operates as follows. After valve  67  is opened, pressure values or magnitudes of pressurized fluid  32  (P 1 ) from chamber  76  are sensed or measured by pressure sensor  18  at predetermined time intervals, while differential pressure values or magnitudes between pressurized fluid  32  (P 1 ) and pressurized fluid  60  (P 2 ) are substantially simultaneously sensed or measured. For convenience, this differential pressure corresponding to locations of pressurized fluids  32 ,  60  disposed on opposite sides of filter  46  is referred to in  FIGS. 5-9  as ΔP. Similarly, temperature values corresponding to positions in close proximity of pressurized fluids  32  (P 1 ),  60  (P 2 ), if required, are sensed or measured by temperature sensors  19 ,  21  (T 1 , T 2 ) at predetermined time intervals substantially simultaneously as the pressurized fluid measurements. 
         [0040]    Once the temperature/pressure measurements are performed, the pressure sensors  18 ,  20  and temperature sensors  19 ,  21  transmit signals corresponding to those measurements to an amplifier/converter  22  to amplify and/or convert the signals from analog to digital form, if required. In one embodiment, signals  25  from other devices (not shown) permitting mass flow measurement, such as precision mass measurement devices or a mass spectrometer, may be transmitted to amplifier/converter  22  to amplify and/or convert the signals  25  from analog to digital form, if required. 
         [0041]    After the various signals, e.g., P 1 , ΔP, T 1 , T 2 , are transmitted from amplifier/converter  22  to microprocessor  24 , and saved in a storage device  26 , such as an EEPROM, various calculations are performed as is known in the art, such as volumetric fluid flow from chamber  76  over time versus differential pressure, for example by application of Equation  7  to yield a filter permeability constant (e.g., see K i  of  FIG. 4 ). Once the filter permeability constant value K is calculated, it may be stored and/or compared to previously stored filter permeability constant values in storage device  26 . In one embodiment, a time reference corresponding to each calculated filter permeability constant value K is saved and compared in order to determine when subsequent filter permeability calculations should be performed, based on historical data. That is, over time, filter permeability values K, i.e., the slopes of the curves shown in  FIG. 4 , decrease.  FIG. 4 , which is a graphical representation of the life cycle of a filter, further shows an operational region  72  and a “replacement recommended” region  74 . For example, filter permeability curve K i  corresponds to an initial filter permeability curve, such as when the filter is new and substantially unclogged or uncontaminated with particulates. A significant portion of the filter permeability curve K i  is contained in the operational region  72  of  FIG. 4 . However, a significant portion of the filter permeability curve K3 i.e., the third calibration of the filter, is contained in the replacement recommended region  74 , and is near the end of its operating life. Due to the accumulation of data in storage device  26 , trends relating to filter life are identified, seeking a balance between minimizing the number of filter monitoring cycles, which can result in shut-down of portions of fluid system  10 , and probability of operating filters in a replacement recommended region  74 , or filter failure. 
         [0042]    It is appreciated that electrical power required to operate components of flow control device may be provided by an electrical power source  30 , which includes, but is not limited to, a power grid, batteries or other sources. Additionally, in one embodiment, a transceiver  28  may receive and exchange information such as from a digital bus, which may be transmitted over power lines or other wired or wireless devices and/or techniques. 
         [0043]    In order to minimize or eliminate shut-down of a portion of fluid system  10  while a filter  46  is being replaced, flow control device  11  may include multiple modules  78  (only one shown in  FIG. 1 ). In one embodiment, multiple modules  78  are disposed in a parallel flow arrangement, such that one module  78  may be maintained in fluid communication with the fluid system  10  while the other modules  78  are selectably isolated, such as by use of valving arrangements (not shown) to replace filters  46  or to perform a filter monitoring cycle without disturbing operation of the fluid system. In one embodiment, module  78  includes a filter housing  44  (and filter  46 ), manifolds  16 ,  42  and corresponding sensors  18 ,  19 ,  20 ,  21 , although the sensors may have multiple leads, with the leads corresponding to the operating module remaining on-line being active. Therefore, in another embodiment of module  78 , the only components include a filter housing  44  (and filter  46 ), associated manifolds  16 ,  42  and sensor leads. 
         [0044]    As shown in  FIG. 2 , which is otherwise similar to  FIG. 1 , filter housing  44  abuts and is in fluid communication with pressure sensors  18 ,  20 . As a result, manifolds  16 ,  42  from  FIG. 1  are not required. A removable cap  66  abuts filter housing  44  and filter  46  and is in fluid communication with both filter  46  and one leg of differential pressure sensor  20  by virtue of tee passageway  64 . Upon removal of cap  66 , filter  46  can be replaced. Pressurized fluid  32  (P 1 ) is provided directly into filter housing  44 , the volume between filter  46  and the inner surfaces of filter housing  44  defining a chamber  176  being a known volume in one embodiment. An optional bypass  62  can be used to evacuate pressurized fluid  32  in fluid housing  44 . 
         [0045]    It is to be understood that the filter permeability K decreases over time in response to becoming gradually more clogged, and must therefore be monitored, as the equations must account for the change in filter permeability to provide accurate information. 
         [0046]      FIG. 3  shows the arrangement of  FIG. 2  with a valve  68  disposed upstream of opening  45  and a valve  70  disposed downstream of cap  66  and there being a known volume between filter  46  and the inner surfaces of filter housing  44  (chamber  76 ). 
         [0047]    The following steps are followed to monitor or re-calibrate the filter permeability K as follows.
       1) Valve  68  is opened and valve  70  is closed, until a maximum, stable pressure value is achieved therebetween.   2) Valve  68  is closed and valve  70  opened, permitting pressurized fluid in chamber  176  to become filtered fluid  58  flowing through filter  46  until the differential pressure measured by differential pressure sensor  20  is substantially zero. At predetermined time intervals, pressure values as measured by pressure sensor  18  and differential pressure sensor  20  are stored in storage device  26 .   3) The rate at which the volume of chamber  176  is depressurized can be measured by virtue of the multiple pressure sensor  18  readings taken at predetermined time intervals. By dividing the volume of chamber  176  by the time of depressurization, yields average volumetric flow rate, Equation 2 can be calculated.   4) The average volume flow rate is dividing by the average change in pressure over time to yield a new filter permeability value (K), which is stored in storage device  26 .   5) Valves  68 ,  70  are reopened, with the flow control device returning to measuring flow and with multiple pressure readings taken at predetermined time intervals across the filter, checking for anomalies, as will be discussed in conjunction with  FIGS. 5-9  below, and for trending data.       
 
         [0053]    It is to be understood that in one embodiment of flow control device  11  where the filter  46  is not substantially contaminated or clogged and fluid viscosity is sufficiently low, such as less than about 100 centipoise and exhibiting Newtonian behavior, i.e., substantially devoid of shear thinning or thickening, the flow control device  11  can obtain an inferential value of the viscosity of the fluid. 
         [0054]      FIG. 3  shows the arrangement of  FIG. 2  with a valve  68  disposed upstream of opening  45  and a valve  70  disposed downstream of cap  66  and there being a known volume between filter  46  and the inner surfaces of filter housing  44  (chamber  76 ). The following steps are followed to measure fluid viscosity η.
       1) Valve  68  is opened and valve  70  is closed, until a maximum, stable pressure value is achieved therebetween.   2) Valve  68  is closed and valve  70  opened, permitting pressurized fluid in chamber  176  to become filtered fluid  58  flowing through filter  46  until the differential pressure measured by differential pressure sensor  20  is substantially zero. At predetermined time intervals, pressure values as measured by pressure sensor  18  and differential pressure sensor  20  are stored in storage device  26 .   3) The rate at which the volume of chamber  176  is depressurized can be quantified by virtue of the multiple pressure sensor  18  readings taken at predetermined time intervals. Dividing the volume of chamber  176  by the time of depressurization yields average volumetric flow rate {dot over (Q)}.   4) The average volume flow rate is then divided by the average change in pressure over time to yield a new filter permeability value K, which is stored in storage device  26 .         
         [0059]    Since filter permeability K is originally calculated with a known fluid, deviation of differential pressure ΔP may be an indication of a change in fluid viscosity η. If filter permeability K is assumed to be substantially constant, repeating numbered steps 1)-3) above can be used to calculate fluid viscosity η, versus filter permeability K. 
         [0060]      FIGS. 5-9  correspond to various scenarios flow control device  11  can encounter during operation. For example, as shown in  FIG. 5 , P 1  stays substantially constant, but ΔP increases and backpressure P 2  decreases. In response, a possible action is to obtain backpressure from another sensor monitoring P 2 , if possible. If P 2  continues to decrease below a predetermined critical level, the control panel notifies the operator, such as by a low backpressure message. For example, this scenario may be indicative of a process upset on the return line, a leak in the fluid system, or some other fluid system upset. 
         [0061]    As shown in  FIG. 6 , P 1  stays substantially constant, but ΔP decreases and backpressure P 2  increases. In response, a possible action is to obtain backpressure from another sensor monitoring P 2 , if possible. If P 2  continues to increase above a predetermined critical level, the control panel notifies the operator, such as by a low backpressure message. For example, this scenario may be indicative of a clogged sample return line for bypass filters or a clogged/malfunctioning device/passage downstream. 
         [0062]    As shown in  FIG. 7 , P 1  increases, but P 2  remains substantially constant and ΔP backpressure increases. It is then assumed that the filter permeability K has decreased, i.e., the filter is clogging. In response, once calculated filter permeability decreases past a predetermined amount, the control panel notifies the operator, such as with a filter replacement message. 
         [0063]    As shown in  FIG. 8 , P 1  decreases, but P 2  remains substantially the same and ΔP backpressure decreases. It is then assumed that there is a low flow condition or obstruction upstream of the filter or a system leak. In response to a sufficient ΔP backpressure decrease in combination with P 1  decrease, the control panel notifies the operator, such as with a low flow condition message. 
         [0064]    As shown in  FIG. 9 , P 1  increases, but P 2  decreases and ΔP backpressure increases. It is then assumed that there are pressure regulation creep problems, or filter clogging with a simultaneous decrease in outlet pressure. In response to a sufficient ΔP backpressure increase in combination with P 1  increase and P 2  decrease, the control panel notifies the operator, such as with a general system error message. 
         [0065]    As shown in  FIG. 10 , P 1  decreases, P 2  increases and ΔP backpressure increases. This scenario could mean that a valve or restriction upstream caused interruption in inlet flow and a backflow condition in the system. This condition would normally be transient, as P 1  and P 2  would equalize and ΔP would equilibrate, unless a sufficient amount of particulate clogged the valve from the backside and effectively plugged the filter thereby allowing backpressure to remain higher than inlet pressure. In response to this condition, the control panel notifies the operator, such as with a general system error message. 
         [0066]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.