PATENT ABSTRACT
A device comprising a pressure monitor and a control means that receives a signal representing measured pressure at the pressure monitor and controls the controllable elements of a fluid system is utilized to monitor a fluid system for error conditions, to optimize operations and to diagnose the fluid system. By following a testing protocol that selectively enables parts of the system, the control means narrows the list of possible failing components. Comparing the measured pressure against normal pressures allows the device to identify error conditions. Determining the volume of fluid being transported and controlling the duration of the flow optimizes operation of the fluid system.

PATENT DESCRIPTION
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application No. 60/550,415, filed Mar. 5, 2004. The contents of these applications are incorporated herein by reference. 
    
    
     STATEMENT ON FEDERALLY SPONSORED RESEARCH 
     N/A 
     FIELD OF THE INVENTION 
     The present invention relates to fluid movement systems and in particular to improved operation and maintenance of such systems utilizing a pressure monitor. 
     BACKGROUND OF THE INVENTION 
     In one form of liquid chromatography sample injection, the fluid path for handling the sample is pressurized. Such pressurization improves the sample movement speed by limiting the risk of vaporization of the sample. In order to control the degree of pressurization in such a system, a pressure gauge is typically installed in line with the pressure source. This pressure gauge is typically used in a feedback mode to control the generated pressure. 
     The increased pressure increases the likelihood of leakage at each of the multiple connection points that comprise the fluid path(s). Leaks may occur due to wear internal to a component, when a component is replaced due to faulty installation and also due to failures in joints at unexpected areas. For fluid movement systems that have small diameters, the volume of fluid leaking may be large enough to distort performance and yet small enough that it evaporates or is in some other way rendered invisible to inspection. 
     A system controller can use the output of the pressure gauge to tell that there is fluid leakage in the system when there is a greater than normal pressure drop in the system. However, this technique does not help to isolate the source of the leak. Certain techniques may limit the search area for the leak rather than eliminate leak target areas. 
     Previous systems have been able to determine that there is a leak in the system, but have not been able to identify the location of the leak nor identify points without leaks. Therefore, repair operations have typically involved disconnecting all connections, replacing many active components and essentially rebuilding the fluid movement system when a leak became too severe. Because of the extent of the repair activities, lesser leaks were allowed to remain until the system could be brought down for the major replacement operation. 
     Many pressurized injection systems require a cleaning cycle between successive usage cycles. In order to assure adequate cleaning, a set volume of cleaning fluid must pass through the system. In order to lessen the need for user interaction, the systems are set up for the extremes of operation. Since viscous liquids will take longer to flow through the system in a cleaning cycle, sufficient time is allocated for the most viscous fluid anticipated to execute the cleaning cycle. For all other fluids, some part of this time is wasted. If the viscosity of the fluid were known, the operation of the cleaning cycle could be tailored to optimize the fluid path cleaning cycle. 
     Diagnostics for fluid systems would allow inefficient and/or failing components to be identified. One set of information available is the expected pressure and pressure decay within a fluid system. If the actual pressures experienced by the system can be measured, comparisons can be conducted against the expected values. 
     Repairing a leak involves first finding it. Identifying the leakage point is beneficial because the repair time is minimized. Another time when checking for leaks is important is when a component is replaced and reconnected with the fluid system. 
     SUMMARY OF THE INVENTION 
     A device for monitoring pressure in a fluid system comprises a pressure monitor for placement in communication with a fluid in the fluid system and a control means for receiving a signal representative of the measured pressure and comparing that measured pressure to a reference. The pressure monitor generates the signal representative of the measured pressure and the control means generates an error message or performs an action if a difference between the measured pressure and the reference exceeds a predetermined value. One fluid system well adapted to this monitoring is an autosampler for a liquid chromatography system. 
     In one embodiment, a fluid system is comprised of a controllable pressure source, at least one fluid path section having first and second ends and at least one fluid connection means. The fluid system is filled with fluid and monitored by the device for monitoring pressure. The controllable pressure source creates a source pressure on the fluid in response to a pressure command signal from the control means. The fluid connection means has a plurality of ports for interconnection with the system and is capable of assuming a first position where fluid flows between at least a first port and the second port and a second position in which fluid does not flow between any of the first ports and the second port. The system is interconnected with one port of the fluid connection means connected to an end of the fluid path section and the controllable pressure sources connected to the second end of the fluid path section. The fluid connection means is responsive to a connect command signal to assume the first position and a disconnect command signal to assume the second position. The monitoring device is placed in communication with the fluid in the fluid path section. The monitoring device sends the signal representing the measured pressure to the control device for comparison with the known source pressure. The control means generates an error message if a difference between the measured pressure and the source pressure exceeds a predetermined value. 
     In a preferred embodiment, the control means is further for sending a connect command signal and a disconnect command signal to the at least one fluid connection means for controlling the connection means to assume the first and second positions. In addition, the control means is further for sending a pressure command signal to the controllable pressure source to cause the controllable pressure source to generate a source pressure. 
     Preferably, the fluid system has one of the fluid connection means in the second position, creating a closed fluid system. Then the control means monitors the measured pressure in the closed fluid system over time to detect a degradation of the measured pressure, which is indicative of a lack of fluid sealing integrity. 
     Preferably, the controllable pressure source is a syringe, preferably a metering syringe, positionable by the pressure command signals to create the source pressure on the fluid. Further, at least one fluid connection means is preferably a multiport valve having at least a first port and a second port. In the first position, fluid flows between the first port and the second port. In a preferred embodiment, the fluid system is a liquid chromatography system and more particularly, a liquid chromatography sample injector system. In operation, the control means sends a pressure command signal to the controllable pressure source to create a predetermined source pressure and reports an error if the measured pressure does not reach a predetermined value within a specified period of time. 
     In a preferred embodiment, the control means has a library of entries that comprise command signals to be sent, time between sending the command signals and taking readings and normal measured pressure values. The control means transmits the command signals for one entry and compares a set of received measured pressures to the normal measured pressure values. Differences that exceed a preset threshold cause a report to be sent. 
     In one embodiment, a fluid system that is to be monitored for errors is comprised of a monitored fluid path section having a first end and a second end and first and second fluid subsystems connected to the first and second ends respectively. Each fluid subsystem comprises at least one fluid path section, at least one fluid connection means and at least one controllable pressure source. The fluid path sections in the fluid subsystems have a section first end and a section second end. The fluid connection means have a plurality of ports for interconnection. At least one of the ports is connected to a fluid path section end for forming the fluid subsystem. The fluid connection means are responsive to a connect command signal to assume a first position wherein fluid flows between at least two of the ports and responsive to a disconnect command signal to assume a second position in which fluid does not flow between any of the plurality of ports. The controllable pressure source is connectable to the at least one section second end. The controllable pressure source is responsive to a pressure command signal to create a source pressure on fluid in the fluid subsystem. The first fluid subsystem is connected to the first end of the monitored fluid path section and the second fluid subsystem is connected to the second end of the monitored fluid path section. The pressure monitor is in communication with the monitored fluid path section. The control means looks for leakage in the system by monitoring the measured pressure over time, looking for a degradation that would be indicative of a leak. 
     The control means controls the pressure and configuration of the fluid system while monitoring the measured pressure. The control means executes a set of instructions that specify connect and disconnect command signals that define a configuration and pressure command signals for setting the source pressure. The instructions further specify the normal measured pressure for each entry so that actual measured pressure can be compared to the normal pressure. Degradations in the monitored measured pressure are indicative of reduced fluid integrity of the fluid system configuration. 
     When trying to find leaks, the control means issues at least one connect command signal and at least one disconnect command signal to form a first closed fluid circuit in the fluid system. The control means then pressurizes the first closed fluid circuit using the controllable pressure source and monitors the pressure. If the pressure becomes established in the circuit and remains stable, the control means concludes that the components and interconnections making up the first closed fluid circuit likely are not leaking. The control means can then expand the length of subsequent closed fluid circuits and incrementally add to the list of non-leaking components and interconnections. It should be understood that each of the fluid connection means can be composed of an interconnection of fluid connection means. 
     When the monitoring device can control the configuration of the fluid system by selectively isolating parts of the fluid system from the rest using the fluid connection means, successive fluidic integrity tests on different parts of the fluid system lead to isolation of a leaking component. By starting with a subsystem of the fluid system with few components, and verifying that there are no leaks in that part, the control means has a basis for comparison as further components are added. Each successive subsystem incorporates some previously tested components and some untested parts, allowing the control means to identify likely leaking components. 
     The device is preferably used to determine a parameter of a fluid in the fluid system. The control means that has been provided with reference information based on the diameters of the fluid path components, the length of a reference flow path and the friction factor of the reference flow path, can use that information with the measured pressure of the fluid moving past the monitor point at a known flow rate to determine the viscosity of the fluid. The viscosity can further be used to calculate the flow rate that can be used in the wash cycle without exceeding a predetermined parameter of the system. 
     Preferably, the device is used with fluid system to optimize a fluid path wash cycle. In an embodiment of a fluid path wash cycle using the device, one controllable pressure source comprises a first wash syringe containing a first wash fluid. A first fluid connection means is used to connect the first wash syringe to the fluid path to be flushed. After sending connect and disconnect command signals to the necessary fluid connection means for configuring the system for flushing, including creating the fluid path to be flushed, the control means connects the first wash syringe through the appropriate connection means. The control means monitors the measured pressure as the first wash syringe starts delivering wash fluid. When the measured pressure equals a first wash pressure that was calculated based on the viscosity of the fluid, the control means stabilizes the flow rate of fluid being delivered. Thereafter, the control means allows the precise volume of wash fluid needed to effect a complete wash to flow through the system in a timely manner. This washing mechanism saves time over systems that flow wash fluid based on a worst case viscosity. For systems that require two levels of washing, the controllable pressure source comprises a first and a second wash syringe filled respectively with a first wash fluid and a second wash fluid. Further the connection means is able to select between the first and second wash syringes. After washing with the first fluid, the control means repeats the process with the second wash syringe until a predetermined volume of second wash fluid has been pushed through the fluid system to be cleaned. 
     Methods of performing operations on a fluid system are built around the device for measuring pressure. In a method of monitoring pressure, the fluid system is comprised of at least one fluid path section having a first end and a second end and at least one controllable pressure source connected to the first end of the at least one fluid path section. Each controllable pressure source is responsive to a pressure command signal to create a source pressure in the at least one fluid path section. The fluid system is connected so that it forms a fluid path filled with a fluid. The method comprises providing the device comprising a pressure monitor for placement in communication with the fluid in a first path section and a control means. The pressure monitor generates a signal representative of a measured pressure that is received by the control means. The control means sends signals to the fluid system. The pressure monitor is placed in communication with the fluid in the fluid path. The control means issues a pressure command signal to the controllable pressure source to cause it to generate the source pressure in one fluid path section. The control means compares the measured pressure to the source pressure, and generates an error message if the difference between the measured pressure and the source pressure exceeds a predetermined value. 
     Preferably, the method determines whether the pressure in a pressurized system is established within a specified time after a source pressure is applied. In addition, a method to determines whether a decay in the pressure falls within prescribed limits. The fluid system further comprises at least one fluid connection means having a plurality of ports for interconnecting with the at least one controllable pressure source and the at least one fluid path section. The fluid connection means is capable of assuming at least a first position wherein fluid flows between at least two of the plurality of ports in response to a connect command signal and a second position in which no fluid flows in response to a disconnect command signal. A preferred fluid connection means is a multiport valve. 
     A preferred system comprises a first fluid connection means having at least a first port and a second port, a second fluid connection means having at least a first port and a second port, a first fluid path section and at least one controllable pressure source. A controllable pressure source is connected to the first port of the first fluid connection means and the second port of the first fluid connection means is connected to a first end of the first fluid path section. The second end of the first fluid path section is connected to the first port of a second connection means. The method further comprises sending at least one connect command signal to the first fluid connection means to place the first connection means in the first, open position. And sending at least one disconnect command signal to the second fluid connection means to place the second fluid connection means in the second, closed, position. This arrangement of fluid connection means creates a closed system that should maintain an applied pressure. The control means sends a pressure command signal to the controllable pressure source to generate a predetermined source pressure. The control means compares the measured pressure to the predetermined source pressure and reports an establishment error if the difference is greater than a first allowed amount. If no establishment error occurs, the method preferably further waits a predetermined length of time and compares the current measured pressure to the predetermined source pressure. If the decay in pressure is greater than a second allowed amount, a leak error is reported. 
     The method above is preferably extended to deal with more complex fluid systems. The control means is provided with a library of entries comprising sets of command signals for controlling connection means and pressure sources and sets of normal pressure values and allowable pressure decay rates. The control means selects one entry, issues the command signals from that entry and compares the measured pressures to the normal pressure values. The control means reports significant differences. Preferably, the method has the control means issue connect, disconnect and pressure command signals to the fluid system and identify degradations in the measured pressure indicative of reduced fluid integrity. 
     The method is adaptable to other configurations. For instance, when a second controllable pressure source is connected to the second port of the second fluid connection means, the method has further steps. The control means sends at least one connect command signal and disconnect command signal to the first and second fluid connection means to place the first fluid connection means in the second position and the second fluid connection means in a different first position where fluid flows between the first fluid path and the second controllable pressure source. The control means sends at least one pressure command signal to the second controllable pressure source to set the source pressure. The control means monitors the signal from the pressure monitor and identifies additional non-leaking components based on the stability of the measured pressure over time. When a third controllable pressure source is connected to a third port of the second fluid connection means, the method is extended similarly to identify further non-leaking components. 
     The method is applicable and provides additional information when an additional controllable pressure source is located at a different fluid connection means in the fluid circuit. In particular, when a second controllable pressure source is connected to a second port of the first fluid connection means, the control means interconnects the fluid circuit by sending connect command signals to the first fluid connection means to assume a first position in which fluid flows between the first fluid path and the second controllable pressure source. In addition, the control means sends disconnect command signals to the second fluid connection means to assume a second position blocking the fluid path. Then the control means sends a pressure command signal to the second controllable pressure source to pressurize the fluid path. By monitoring the signal from the pressure monitor, the control means identifies additional non-leaking components based on the stability of the measured pressure over time. Preferably, the first fluid connection means comprises an interconnection of a plurality of fluid connection means and the second fluid connection means comprises an interconnection of a plurality of fluid connection means. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above noted and other features of the invention will be better understood from the following detailed description, when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic of an implementation of the inventive device; 
         FIG. 2A  is a schematic of the device of  FIG. 1  in a fluid system; 
         FIG. 2B  is an illustration of the fluid system of  FIG. 2A  with command signals connected to components of the fluid system; 
         FIG. 3  is an illustration of a fluid system comprising two connected fluid subsystems being monitored by the device of  FIG. 1 ; 
         FIG. 4  is an illustration of the device of  FIG. 1  being used to optimize a fluid system wash cycle; 
         FIGS. 5A and 5B  illustrate a sequence of tests based on the fluid system of  FIG. 3 , wherein  FIG. 5A  illustrates a first configuration and  FIG. 5B  illustrates a second configuration; 
         FIG. 6A  illustrates a first test configuration of an example; 
         FIG. 6B  illustrates a second test configuration of an example; 
         FIG. 6C  illustrates a third test configuration of an example; 
         FIG. 6D  illustrates a fourth test configuration of an example; and 
         FIG. 6E  illustrates the failures identified by the tests of  FIGS. 6A-6D . 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the term “leak” refers to a hole, crack or opening through which fluid escapes in a manner not intended by the user. The leak may be totally internal. That is, the fluid escapes from an area of high pressure to an area of low pressure within the apparatus. Or, such leak may be external, allowing fluid to escape from the confines of the hydraulic circuit. Leaking fluids could represent a safety concern, the detection of which would be very useful. 
     As used herein, “pressure monitor” comprises any device for measuring pressure, including strain gauges and pressure transducers. The output of the pressure monitor, representing a measured pressure, may be an analog signal that is digitized before being input to a control means or may be a digitized representation of the measured pressure. 
     Fluid connection means are devices for closing, opening or directing fluid flow. In many cases a fluid connection means is a valve. Typical valves include mechanical check valves and active valves. Mechanical check valves are responsive to pressure. Active valves receive a signal that directs power means, such as motors, solenoids and the like, to open or close the valve. Cycling valves are capable of selectively opening and closing the flow of fluid from one or more sources or directing the flow to one or more destinations. 
     As used herein, the term “control means” means any processing entity that can receive information signals and send command signals. An embedded microprocessor with memory and an associated input/output section for signal handling is one implementation. Alternately, one of the central processors embedded in an instrument may act as the control means with the memory and input/output sections handling the instrument as well as the device functions. Other central processors, as are known to those skilled in the art, can serve as the control means. 
     A controllable pressure source is a device that can be commanded to exert a defined pressure on a fluid. Such a pressure source may establish a pressure in a closed fluid system. Alternately, the applied pressure will cause a flow rate in an open fluid system. One example of a controllable pressure source is a metering syringe wherein a motor is used to drive the syringe precisely. 
     As illustrated in  FIG. 1 , a device  10  for monitoring pressure in a fluid system  18  comprises a pressure monitor  12  for placement in communication with a fluid  16  in the fluid system  18  and a control means  14  for receiving a signal  20  representative of the measured pressure and comparing that measured pressure to a reference. The pressure monitor  12  generates the signal  20  representative of the measured pressure and the control means  14  generates an error message, and/or other signals  22  if a difference between the measured pressure and the reference exceeds a predetermined value. One fluid system well adapted to this monitoring is a an auto sampler for a liquid chromatography system. 
     Turning now to  FIG. 2A , a fluid system  18  is comprised of a controllable pressure source  30 , at least one fluid path section  32  having first and second ends  34 ,  36  and at least one fluid connection means  40 . The fluid system is filled with fluid  16  and monitored by the device  10  for monitoring pressure. The controllable pressure source  30  creates a source pressure on the fluid  16  in response to a pressure command signal  38  from the control means  14 . The fluid connection means  40  has a plurality of ports  42 ,  44 ,  46 ,  48  for interconnection with the system and is capable of assuming a first position (represented by the dotted line  50 ) where fluid flows between a first port  44 ,  46   48  and the second port  42  and a second position (not illustrated) in which fluid does not flow between any of the first ports  44 ,  46 ,  48  and the second port  42 . The system  18  is interconnected with one port  42  of the fluid connection means  40  connected to an end  34  of the fluid path section  32  and the controllable pressure source  30  connected to the second end  36  of the fluid path section  32 . The fluid connection means  40  is responsive to a connect command signal  52  to assume the first position and a disconnect command signal  54  to assume the second position. These signals may be implemented as separate levels on one signal line, encodings on a line, distinct signals or other means including a combination of the above implementations as is known to one skilled in the relevant art. The monitoring device  12  is placed in communication with the fluid  16  in the fluid path section  32  and sends the measured pressure signal  20  for comparing the measured pressure to the source pressure. The control means  14  does the comparison and generates an error message  22  if a difference between the measured pressure and the source pressure exceeds a predetermined value. 
     As illustrated in  FIG. 2B , the control means  14  is further for sending the connect command signal  52  and disconnect command signal  54  to the at least one fluid connection means  40  for controlling the connection means  40  to assume the first and second positions. In addition, the control means  14  is further for sending the pressure command signal  38  to the controllable pressure source  30  to cause the controllable pressure source  30  to generate the source pressure. 
     In an embodiment for testing for leakage, the fluid system has one of the at least one fluid connection means  40  in the second position, blocking fluid passage and creating a closed fluid system. Then, the control means  14  can monitor the measured pressure in the closed fluid system over time to detect a degradation of the measured pressure, which is indicative of a lack of fluid integrity. 
     Preferably, the controllable pressure source  30  is a syringe, preferably a metering syringe, positionable by the pressure command signal  38  to create the source pressure on the fluid  16 . Further, the at least one fluid connection means  40  is preferably a multiport valve having at least a first port and a second port. In the first position, fluid flows between the ports, and in the second position fluid does not flow between any of the ports. When the multiport valve has more than two ports, there may be more than one first position in that in a first first position fluid flows between ports A and B, while in a second first position fluid may flow between ports A and C (or C and D). In a preferred embodiment, the fluid system is a liquid chromatography system and more particularly, a liquid chromatography sample injector system. In operation, the control means  14  sends a pressure command signal  38  to the controllable pressure source  30  to create a predetermined source pressure and reports an error if the measured pressure does not reach a predetermined value within a specified period of time. 
     In a preferred embodiment, the control means  14  has a library of entries that comprise command signals  38 ,  52 ,  54  to be sent, time and normal measured pressure values. The control means  14  transmits the command signals  38 ,  52 ,  54  to specified fluid connection means and controllable pressure sources for one entry and compares received measured pressures to the normal measured pressure values. Differences that exceed a preset threshold cause a report to be sent. 
     In one embodiment illustrated in  FIG. 3 , a fluid system that is to be monitored for errors is comprised of a monitored fluid path section  60  having a first end  62  and a second end  64  and first and second fluid subsystems  70 ,  72  connected to the first and second ends  62 ,  64  respectively. Each fluid subsystem  70 ,  72  comprises at least one fluid path section  32 ,  32 ′, at least one fluid connection means  40 ,  40 ′,  40 ″,  40 ′″ and at least one controllable pressure source  30 ,  30 ′,  30 ″,  30 ′″. The fluid path sections  32 ,  32 ′ have a section first end  34 ,  34 ′ and a section second end  36 ,  36 ′. The fluid connection means  40 ,  40 ′,  40 ″,  40 ′″ have a plurality of ports, for instance ports  41 ′,  43 ′ and  45 ′ of fluid connection means  40 ′. These ports are for interconnecting the system. At least one of the ports  41 ′ is connected to a fluid path section end  36  for forming the fluid subsystem. The fluid connection means  40 ,  40 ′,  40 ″,  40 ′″ are responsive to connect command signals  52 ,  52 ′,  52 ″,  52 ′″ respectively to assume a first position wherein fluid flows between at least two of the ports and responsive to disconnect command signals  54 ,  54 ′,  54 ″,  54 ′″ respectively to assume a second position in which fluid does not flow between any of the plurality of ports. As illustrated in  FIG. 3 , each illustrated fluid connection means has three possible first positions—using fluid connection means  40  for example, connecting ports  41  and  43 ,  41  and  45  or  43  and  45 —as well the single second position wherein no fluid flows. A controllable pressure source  30 ,  30 ′,  30 ″,  30 ″ may be connected to the at least one section second end  34  directly (not shown) or through a fluid connection means. The controllable pressure sources  30 ,  30 ′,  30 ″,  30 ′″ are responsive to pressure command signals  38 ,  38 ′,  38 ″,  38 ′″ respectively to create a source pressure on fluid in the fluid subsystem. In the figure, each of the controllable pressure sources in connected to an end of the fluid path section  32 ,  32 ′ and/or to the monitored fluid path  60  through at least one connection means. The first fluid subsystem  70  is connected to the first end  62  of the monitored fluid path section  60  and the second fluid subsystem  72  connected to the second end  64  of the monitored fluid path section  60 . The pressure monitor  14  is in communication with the monitored fluid path section  60 . 
     The control means  14  controls the pressure and configuration of the fluid system while monitoring the measured pressure. The control means executes a set of instructions that specify connect and disconnect command signals to be sent to define a configuration and pressure command signals for setting the source pressure. The instructions further specify the normal measured pressure for each entry, so that the actual measured pressure can be compared to the normal pressure. Degradations in the monitored measured pressure are indicative of reduced fluid integrity of the fluid system configuration. 
     As an illustration, the control means  14  sends connect and disconnect command signals to the subsystems to create a configuration with one connection means  40 ′ in one subsystem  70  in the second position (closed) and a second connection means  40 ″ in the other subsystem  72 , in the first position (open) so that the fluid is in a closed system comprised of the controllable pressure source  30 ″, connection means  40 , and monitored fluid path  60  and the termination at fluid connection means  40 ′. Then the control means  14  sends a pressure command signal  38 ″ to set the source pressure to a value. By monitoring the signal  20  from the pressure monitor  12  and noting whether the measured pressure remains stable over time, the control means  14  is able to identify non-leaking components. 
     When the monitoring device  10  can control the configuration of the fluid system by selectively isolating parts of the fluid system from the rest using the fluid connection means, successive fluidic integrity tests on different parts of the fluid system lead to isolation of the leaking component. By starting with a subsystem of the fluid system with few components, and verifying that there are no leaks in that part, the control means  14  has a basis for comparison as further components are added. Each successive subsystem incorporates some previously tested components and some untested parts, allowing the control means to identify likely leaking components. 
     The device is further preferably used to determine the viscosity of the fluid currently in the fluid system. Prior to this operation, the fluid system is calibrated to yield a viscosity calibration factor. Thereafter, when a fluid is flowed through the calibrated fluid path at a predetermined flow rate, the viscosity of the current fluid can be determined by multiplying the measured pressure by the viscosity calibration factor. In calibrating the fluid system, using equation (1) is used.
 
η= VΔPD   Ref   6 /64 CL   ref   Q   2   (1)
 
In equation (1), ΔP is the difference from source pressure at the measurement point, and, V, D ref , C, L ref  and Q are incorporated in a the viscosity calibration factor from the calibration run. (V is velocity, D ref  is the average diameter of the reference fluid path, C is a unit correcting factor, L ref  is the length of the reference fluid path, and Q is the flow rate used in the calibration run and measurement run).
 
     Preferably, the device  10  is further used with a fluid system to optimize a fluid path wash cycle. Using the configuration of components in  FIG. 4 , the fluid path to be washed  62  extends from fluid path section  84  to the fluid connection means  40 ″ that connects the controllable pressure source  30 ″, wherein here, the controllable pressure source  30 ″ is a first wash syringe containing a first wash fluid. The control means  14  executes a series of instructions that cause the control means  14  to send connect command signals  52 ,  52 ′,  52 ″ to fluid connection means  40 ,  40 ′,  40 ″ to interconnect the fluid path  62  as illustrated for flushing. The control means  14  may send disconnect command signals  54  to other fluid connections means (not shown) to eliminate fluid path sections that are not be washed. The control means  14 , having already determined the viscosity of the wash fluid, sets a first wash pressure. It then sends a first pressure command signal  38 ″ to the first wash syringe  30 ″ to push wash fluid into the fluid path  62 . The control means  14  monitors the measured pressure in fluid path section  60 , and increases the source pressure, until the measured pressure equals the first wash pressure. This pressure assures that the wash fluid is flowing at the correct rate and assures that the predetermined volume of first wash fluid is delivered in a timely manner. 
     For systems that require two levels of washing, a second controllable pressure source (not shown) functioning as a second wash syringe is filled with a second wash fluid and connected to port  43 ″. The first connection means  40 ″ selects between the first and second wash syringes. After washing with the first fluid, the control means  14  uses the first connection means  40 ″ to select the second wash syringe and sends a second pressure command signal to the second wash syringe until the measured pressure equals a predetermined second wash pressure. The control means  14  causes the second wash fluid to flow at the second wash pressure until a predetermined volume of second wash fluid has been provided. 
     The device is used in a method of monitoring pressure in a fluid system. In  FIG. 2 , the fluid system  24  is comprised of at least one fluid path section  32  having a first end  36  and a second end  34  and at least one controllable pressure source  30  connected to the first end  36  of the at least one fluid path section  32 . Although  FIG. 2 , does not illustrate this, the connection between the at least one fluid path section  32  and the at least one controllable pressure source  30  may be through further components of the fluid system  24 . Each controllable pressure source  30  is responsive to a pressure command signal  38  to create a source pressure in the at least one fluid path section  32 . The fluid system  24  is connected so that it forms a fluid path filled with a fluid  16 . The method comprises providing a device  10  comprising a pressure monitor  12  for placement in communication with the fluid  16  in a first path section  32  and a control means  14 . The pressure monitor  12  generates a signal representative  20  of a measured pressure that is received by the control means  14 . The control means  14  sends signals  22  to the fluid system  24 . The pressure monitor  12  is placed in communication with the fluid  16  in the fluid path  32 . The control means  14  issues a pressure command signal  38  to the controllable pressure source  30  to cause it to generate the source pressure in one fluid path section  32 . The control means  14  compares the measured pressure to the source pressure, and generates an error message if the difference between the measured pressure and the source pressure exceeds a predetermined value. 
     Preferably, the method determines whether a pressurized system is established within a specified time after a source pressure is applied. The fluid system  24  further comprises at least one fluid connection means  40  having a plurality of ports  42 ,  44 ,  46 ,  48  for interconnecting with the at least one controllable pressure source  30  and the at least one fluid path section  32 . The fluid connection means  40  is capable of assuming at least a first position wherein fluid flows between at least two of the plurality of ports in response to a connect command signal  52  and a second position in which no fluid flows in response to a disconnect command signal  54 . A preferred fluid connection means is a multiport valve. 
     A preferred system, as shown in  FIG. 5A , comprises a first fluid connection means  140  having at least a first port  144  and a second port  142 , a second fluid connection means  140 ′ having at least a first port  144 ′ and a second port  142 ′, a first fluid path section  132  and a controllable pressure source  130 . The controllable pressure source  130  is connected to the first port  144  of the first fluid connection means  140  and the second port  142  of the first fluid connection means  140  is connected to a first end  134  of the first fluid path section  132 . The second end  136  of the first fluid path section  132  is connected to the first port  144 ′ of the second connection means  140 ′. The method further comprises sending at least one connect command signal  152  to the first fluid connection means  140  to place the first connection means  140  in the first, open position wherein fluid can flow between the first and second ports  144 ,  142 . And sending at least one disconnect command signal  154 ′ to the second fluid connection means  140 ′ to place the second fluid connection means  140 ′ in the second, closed, position. This arrangement of the fluid connection means  140 ,  140 ′ creates a closed system that, in the absence of leaks, should maintain an applied pressure. The control means  14  sends a pressure command signal  138  to the controllable pressure source  130  to generate a predetermined source pressure. The control means  14  compares the measured pressure to the predetermined source pressure and reports an establishment error if the difference is greater than a first allowed amount. If no establishment error occurs, the method preferably further waits a predetermined length of time and compares the current measured pressure to the predetermined source pressure again. If the decay in pressure is greater than a second allowed amount, a leak error is reported. 
     Further, as fluid systems with more components and potential paths are monitored, the method above is preferably extended to provide the control means  14  with a library of entries comprising sets of command signals, times and sets of normal pressure values. Each set of commands is sufficient to configure the fluid system. The times are for specifying the interval between sending the set of commands and comparing pressures. The control means  14  selects one entry, issues the command signals for that entry and compares the measured pressures to the normal pressure values after the time interval. The control means  14  reports significant differences. Preferably, the method has the control means  14  issue connect  152 , disconnect  154  and pressure command  138  signals to the fluid system and identify degradations in the measured pressure indicative of reduced fluid integrity. 
     In particular, after testing the fluid system as depicted in  FIG. 5A , the method is preferably applied to a fluid system, shown in  FIG. 5B , that is a variation on the tested system. The system comprises a first fluid path section  132  connected between a second port  144  of a first fluid connection means and a first port  142  of a second fluid connection  140 ′ means. The device  10  for monitoring measured pressure measures at the first fluid path  132 . A first controllable pressure source  130 ′ is connected to the second port  142 ′ of the second fluid connection means  140 ′. The sequence of steps in the method comprise sending disconnect command signals  154  from the control means  14  to the first fluid connection means  140  to cause it to assume the second position and connect command signals  152  to the second fluid connection means  140 ′ to assume a first position in which fluid flows between the first fluid path  132  and the first controllable pressure source  130 ′. The control means  14  then sends a pressure command signal  138 ′ to set the source pressure. Finally, the control means monitors the signal from the pressure monitor and identifies non-leaking components based on a stability of the measured pressure over time. If the second method indicates a leaking component, while the first method did not, the control means  14  can suggest that the components common to the two methods (port  142  of the first fluid connection means  140 , the fluid path section  132  and port  144 ′ of the second fluid connect ion means) are non-leaking. 
     The method is adaptable to other configurations. For instance, when a second controllable pressure source (not shown) is connected to the second port of the second fluid connection means, the method has further steps. The control means sends at least one connect command signal and disconnect command signal to the first and second fluid connection means to place the first fluid connection means  140  in the second position and the second fluid connection  140 ′ means in an alternate first position. Now, fluid flows between the first fluid path  132  and the second controllable pressure source (not shown). The control means sends at least one pressure command signal to the second controllable pressure source to set the source pressure. The control means monitors the signal from the pressure monitor and identifies additional non-leaking components based on the stability of the measured pressure over time. When further controllable pressure sources are connected to a further ports of the first and second fluid connection means  140 ,  140 ′, the method is extended similarly to identify further non-leaking components. 
     Preferably, the first fluid connection means comprises an interconnection of more than one fluid connection means and the second fluid connection means comprises an interconnection of more than one fluid connection means. 
     The method is applicable and provides additional information when the controllable pressure source providing pressure is located at a different fluid connection point in the fluid circuit. In particular, when an additional controllable pressure source is connected to a previously unused port of a fluid connection means, the control means connects the fluid circuit by sending connection command signals to the that fluid connection means to assume a first position in which fluid flows between the monitored fluid path and the additional controllable pressure source. In addition, the control means sends disconnect command signals to some fluid connection means to assume a second position blocking the fluid path. Then the control means sends a pressure command signal to the additional controllable pressure source to pressurize the fluid path. By monitoring the signal from the pressure monitor, the control means identifies additional non-leaking components based on the stability of the measured pressure over time. 
     EXAMPLE 
     A sample injector for a liquid chromatography system is illustrated in  FIG. 6A . It comprises an injection mechanism comprised of a needle assembly  278  connected to a multiport valve and a metering syringe  210  and a wash mechanism comprising a pair of wash syringes  246 ,  264 , a washing manifold and switching mechanisms  240 ,  234 ,  256 ,  226 , and  208  to wash the fluid path between injections. A pressure monitor  212  that feeds readings to a control means (not shown) monitors the pressure between the metering syringe  210  and the multiport valve  200 . In testing the system to identify possible sources source of leaks, a sequence of four tests are performed. 
       FIG. 6A  illustrates the first test. Fluid path  201 , from the metering syringe  210 , through valve means  208  along fluid path section  204 , to multiport valve  200 , that is in the disconnect state, is pressurized by the metering syringe. Because multiport valve  200  is in the disconnect state, the fluid path  201  s closed and should hold a pressure. If the fluid path  201  does not maintain pressure the failure is likely one of: the metering syringe, pathway  203  through the valve  208  between the metering syringe  210  and the fluid path  204 , the fitting  206  at the interconnection of valve  208  and fluid path  204 , the fluid path  204 , the fittings  202  between the fluid path  204  or the multiport valve  200  in a disconnect state. If the fluid path  201  maintains pressure, the above components are likely sealing well and can be used as a basis for further tests. 
       FIG. 6B  illustrates a second test path  225  utilizing one of the wash syringes  246  to establish the pressure. This path uses the multiport valve  200  in the disconnect state, fluid path  204  and the fittings above as the known part of the fluid path. The switching mechanisms (valve means)  240 ,  234 ,  224  and  208 , fluid paths  235 ,  230 ,  22 , and the wash syringe  246  comprise the newly tested parts of the fluid path  225 . If this test reveals a leak, the likely leaking components or joints are along fluid path  225  after the fitting at junction  206  between the fluid path  204  and the valve  208 . 
       FIGS. 6C and 6D  illustrate two further tests that are performed on the system illustrated as part of the test sequence. Each of these tests incorporates further components in the fluid path. The test illustrated in  FIG. 6C  adds the untested components and connections between switching mechanism  226  port  224  and the second washing syringe  264 . In the test illustrated in  FIG. 6D , the needle assembly  278  is inserted in a wash block manifold  276  to allow the fluid path  275  to pass through the needle assembly  278 . This test requires that valve means  208  at the end of the measured fluid path section  204  seal the fluid path  275  when in the disconnect position. Further, the valve means  200  is utilized in one of the open positions, with fluid flowing between the ports as shown by connection  286 . A further test, would change the position of the injection valve means  200 , so that the seal on the sample loop  294  and the internal paths  290 ,  292  to the sample loop  294  were test. The results of the four tests illustrated in  FIGS. 6A-6D  are summarized in  FIG. 6E , where most likely failure points are highlighted. 
     A similar sequence of tests can be constructed for a known fluid system to minimize the uncertainty of leakage sources. 
     The numerous teachings of the present application will be described with particular reference to the presently preferred embodiments. However, it should be understood that these embodiments provide only a few examples of the advantageous uses of the teachings herein. In general, statements made in the specification of the present application do not necessarily delimit any of the various claimed inventions. It will be obvious to those skilled in the art that various modifications can be made without departing from the spirit and scope of this invention.