Abstract:
The present invention is directed to a flow through pipet for sample measurement. The pipet of the invention has a body defining an interior space for receiving a fluid. The drain line is provided to drain fluid above a drain line inlet, thereby establishing a repeatable upper fluid level in the body. A dispense valve on the lower end of the body selectively permit dispensing of the fluid from the body. A restriction member may be located in the interior space of the body for defining a passageway. The drain line inlet may communicate with the passageway to establish a smaller surface area for an upper surface of the fluid, thereby minimizing a variance in the fluid level. A vent line vents gas from the measuring chamber during filling of a fluid. The pipet of the invention is particularly suitable for use in an automated system due to the top fill feature, which eliminates the need for cycling back and forth between a fill vessel and a dispense vessel. Additionally, the invention is suitable for use in an automated system utilizing a multi-pipet assembly, wherein multiple pipets may be filled simultaneously or in any manner desired.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to a pipet used to measure a discrete amount of a fluid. More particularly, the invention relates to a flow through pipet, wherein a fluid is delivered to the pipet through a first end and a predetermined amount of fluid is dispensed through a second end. 
   2. Background 
   Pipets are used to extract, measure and transfer a pre-determined volume of a fluid. A typical pipet draws fluid by suction from a fluid source and then dispenses the fluid volume into a receiving vessel. Pipets are typically used in laboratory and clinical environments. A typical pipet includes a cylindrical vessel that is open at both ends and has a mark specifying a predefined volume and a means to apply pressure and suction to one end of the vessel. 
   In use, one end of the pipet is immersed in a source of fluid and suction is applied to the vessel at the other end. The operator adjusts the level of fluid in the vessel to a specified mark. Next, the pipet is positioned to access a receiving vessel and pressure or gravity forces the fluid out of the pipet into the receiving vessel. The pipet is then withdrawn from the receiving vessel and is relocated to prepare to intake the next volume of fluid from the same or another fluid source. 
   In addition to manual pipets, automated pipet systems have been developed. An example automated pipet system may include a syringe, a stepper motor, a three-way valve to select between intake and dispense functions, and equipment necessary to move the pipet vertically in and out of a fluid as well as equipment necessary to move the pipet horizontally from an intake location to a dispense location. Although a means to apply pressure and suction has been automated and the movement of the pipet in the x and y directions has been automated, typically the same basic design is used, wherein a cylindrical vessel is opened at both ends. Examples of typical “glass straw” pipet vessels may be found in U.S. Pat. Nos. 3,992,947, 4,476,095, 4,624,147, 5,090,255, 5,271,902, 5,679,575, 5,820,824, and 6,253,628. 
   A drawback with typical manual pipets and with typical automated pipets is that fluid is drawn into the pipet and dispensed from the pipet through the same orifice, which is usually located at the lower end of the pipet. Filling and dispensing of fluid from the same orifice in the pipet necessitates locating the pipet in a fluid source to fill the pipet and then relocating the pipet at a dispensing location every time it is desired to dispense a sample of fluid. Consequently, automated pipet systems require complex systems to relocate the pipet from the fluid source to the dispensing location. 
   A pipet is desirable that is capable of delivering a repeatable predetermined volume of fluid, wherein the pipet fills from the top and dispenses from the bottom, i.e., a flow through pipet. It is further desirable to provide a top fill pipet that does not trap air in the measuring chamber. Such a pipet could be provided in an automated pipetting system wherein the pipet would not have to be repositioned to a fill location after dispensing a fluid sample, thereby greatly simplifying an automated pipetting system. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a flow through pipet for fluid measurement. The pipet of the invention has a body defining an interior space for receiving a fluid. The drain line is provided to drain fluid in the interior space above a drain line inlet, thereby establishing a repeatable upper fluid level in the body. A dispense valve on the lower end of the body selectively permits dispensing of the fluid from the body. 
   A restriction member may be located in the interior space of the body for defining a passageway. The drain line inlet preferably communicates with the passageway. By locating the drain line inlet in the restriction member passageway, a smaller surface area of an upper surface of the fluid is exposed, thereby minimizing a variance in the fluid level. The drain line inlet establishes an upper end of a measuring chamber and also establishes a lower end of an overflow chamber. 
   The flow through pipet may further include a vent line that communicates the overflow chamber with the measuring chamber, which allows trapped gas to escape from the measuring chamber during filling of a fluid. A fill valve may be provided in the interior space, wherein the fill valve defines an upper end of an overflow chamber and a lower end of a fill chamber. The fill valve selectively permits fluid to pass from the fill chamber to the overflow chamber. 
   A compressed gas line may be provided that is in communication with the overflow chamber for delivering compressed gas to the interior space. A junction for separating the body into an upper segment and a lower segment is provided so that the body can be disassembled, thereby permitting the attachment of a lower segment of a desired volume to be affixed to the upper segment. 
   In use, a fluid is delivered into a measuring chamber through an upper end of a pipet body to fill the measuring chamber with a fluid. Fluid in excess of a predetermined amount is drained out of the drain line. The draining of excess fluid establishes an upper fluid level in the measuring chamber so that a predetermined volume of sample fluid may be established in the measuring chamber. During delivery of the fluid into the measuring chamber, gas may be vented from the measuring chamber via a separate pathway simultaneous to the filling of the measuring chamber with fluid. 
   Fluid may be delivered into the measuring chamber through an upper end of the body from an attached supply source, which may be desirable in an automated process. Preferably, the filling and delivering steps are achieved without moving the body in an X or Y direction. Compressed gas may be delivered into the body above the sample chamber to force the fluid out of the body or the fluid may be delivered by gravity feed. 
   A better understanding of the present invention, its several aspects, and its advantages will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the attached drawings, wherein there is shown and described the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated for carrying out the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements retain the same numerical designation in the several figures. 
       FIG. 1  is a schematic view of a pipet of the invention for sample or reagent measuring; 
       FIG. 2  is a schematic view of a pipet of the invention having a remote fluid supply, a pump, and a recirculation line for recirculating excess fluid; 
       FIG. 3  is a schematic view of a pipet of the invention having a continuous supply source; 
       FIG. 4  is a schematic view of a pipet of the invention suitable for use with small volumes of fluid; 
       FIG. 5  is a schematic view of another embodiment of a pipet of the invention suitable for use with small volumes of fluid. 
       FIG. 6  is a schematic view of the pipet of the invention incorporated into a multi-pipet assembly. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Before explaining the present invention in detail, it is important to understand that the invention is not limited in its application to the details of the embodiments and steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation. 
   Referring now to  FIGS. 1-6  shown are embodiments of a flow through pipet designated generally  10 . Pipet  10  has a body  12 . Body  12  has an upper end  14 , a lower end  16  and defines an interior space  18 . Supplied fluid is delivered to interior space  18  through or proximate to upper end  14 . 
   In one embodiment, shown in  FIG. 2 , a fill line  20  is provided that communicates a remote fluid supply source  22  to interior space  18 . Remote fluid supply source  22  may be a supply pump reservoir or other fluid supply source. Fill line  20  preferably communicates with interior space  18  proximate upper end  14  of body  12 . A fill line valve  24  is preferably provided to control fluid flow from the fluid supply source  22 . 
   In another embodiment, shown in  FIG. 3 , the upper end  14  of body  12  communicates with a continuous supply source  26 . Examples of a continuous supply source  26  include a process pipe, tank or other source. As shown in  FIG. 3 , a measured volume of fluid may be collected from process pipe  28 . Still referring to  FIG. 3 , an isolation valve  30  is preferably provided to selectively allow supplied fluid into interior space  18  from the continuous supply source  26 . 
   Referring back to  FIGS. 1-3 , a restriction member  32  may be provided in interior space  18  of body  12 . Restriction member  32  has a lower surface  34 , which may be conically shaped. Restriction member  32  additionally has an upper surface  36  which is preferably conical to assist in directing fluid toward a reduced area passageway  38 . Reduced area passageway  38  is defined by inner walls  40  located between upper surface  36  and lower surface  34 . 
   Still referring to  FIGS. 1-3 , drain line  42  has a inlet  44  that communicates with passageway  38  in interior space  18 . When a restriction member  32  is used, drain line  42  preferably communicates with passageway  38 . Placing inlet  44  in passageway  38  is advantageous because passageway  38  has a reduced diameter as compared to a diameter of body  12 . The reduced diameter passageway  38  results in a reduced diameter of an upper surface of the fluid, thereby yielding a greater accuracy with respect to the fluid volume. A drain line valve  46  is provided to selectively open or close drain line  42 . 
     FIGS. 4 and 5  disclose pipets suitable for use with small volumes of fluid. Additionally, the pipets of  FIGS. 4 and 5  could be used with any volume of fluid when less precision is required. The pipets of  FIGS. 4 and 5  have no restriction members therein. Therefore, inlet  44  of drain line  42  communicates with interior space  18 . 
   Inlet  44  defines an upper end of a measuring chamber  54  in interior space  18 . Additionally, inlet  44  defines a lower end of an overflow chamber  56  in the interior space  18  (FIGS.  1 - 3 ). In all embodiments, drain line  42  defines a repeatable upper fluid level of the interior space  18  of pipet  10 . 
   In one embodiment, shown in  FIG. 2 , drain line  42  communicates with a pump  48 , which is used to draw excess fluid from interior space  18 . The excess fluid may then be pumped through recirculation line  49  back to remote fluid supply source  22  or discarded as desired. Still referring to  FIG. 2 , if a drain line pump  48  is used to suck excess fluid from the interior space  18 , then it is desirable to provide a pressure equalization line  50  with a pressure equalization valve  52  to allow gas to enter interior space  18  when drain line pump  48  is activated. 
   Referring now to FIGS.  1  and  3 - 5 , a fill valve  58  is located in body  12  to isolate a fluid supply from a measured fluid that is located in measuring chamber  54 . Fill valve  58  defines an upper end of overflow chamber  56  and defines a lower end of fill chamber  60  (FIGS.  1  and  3 - 5 ). Fill valve  58  selectively permits fluid to pass from fill chamber  60  to overflow chamber  56 . 
   Referring now to  FIGS. 1 ,  2  and  4 , a vent line  62  is provided that communicates the overflow chamber  56  with measuring chamber  54 . As shown in  FIGS. 1 ,  2  and  4 , vent line  62  is located in the interior space  18  of body  12 . It is desirable to provide a weather cap  64  ( FIGS. 1 ,  2  and  4 ) on an upper end of vent line  62  so that when fluids are delivered to interior space  18 , fluids are prevented from entering an upper end of the vent line  62 . 
   In other embodiments, as shown in  FIGS. 3 and 5 , vent line  62  communicates with an exterior of body  12 . In embodiments having an exterior vent line  62 , it may be desirable to provide a vent valve  66  (FIGS.  3  and  5 ). 
   A compressed gas line  68  may be provided for communicating a compressed gas source with interior space  18  (FIGS.  1 - 6 ). A compressed gas valve  70  may be provided to control access of compressed gas to the body  12 . Compressed gas may be useful in forcing fluids out of lower end of  16  the pipet  10 . However, compressed gas may be substituted by the use of gravity to dispense fluids from the body  12  with the pipet  10  of the invention. 
   A dispense valve  72  is provided on lower end  16  of body  12 . Dispense valve  72  allows for selective dispensing of a fluid from measuring chamber  54 . Dispense valve  72  may be any type of suitable valve known in the art. However, in a preferred embodiment, dispense valve  72  is pressure actuated. Additionally, dispense valve  72  may be manually actuated, electronically actuated, or actuated by other means. 
   A junction  74  may be provided so that body  12  is separatable into an upper segment  76  and a lower segment  78 . Upper segment  76  and lower segment  78  may be connected at junction  74  by threads, cooperating detents and protrusions, clips or other means. 
     FIG. 6  shows a multi-pipet assembly  80  having a fill line  20  that has multiple branches that communicate a remote fluid supply source  22  to interior space  18   a  and  18   b  of bodies  12   a  and  12   b , respectively. Although only two pipet bodies,  12   a  and  12   b , are shown for purposes of example, it should be noted that any number of pipet bodies  12   a ,  12   b ,  12   c  . . . may be incorporated into the multi-pipet assembly  80  of the invention. It should also be noted that like elements of multi-pipet assembly  80  to elements of embodiments shown in  FIGS. 1-5  have retained the same numerical designation in  FIG. 6 , with the exception that “a” or “b” has been appended to some of the numbers to designate to which of the pipet bodies  12   a, b  that the numeral designations refer. For example, in a manner similar to that of the embodiment of  FIG. 2 , drain line pump  48  draws excess fluid from interior space  18   a  and  18   b  through drain line branches  42   a  and  42   b . The excess fluid may then be directed through recirculation line  49  back to remote fluid supply source  22  or discarded as desired. A single pressure equalization line  50  and compressed gas line  68  may be provided, which are capable of acting upon interior spaces  18   a ,  18   b , etc., since interior spaces  18   a ,  18   b , etc. communicate with one another via passageway  82 . Alternatively, pressure equalization line  50  and compressed gas line  68  may provide individual branches for communicating with each of interior spaces  18   a ,  18   b , etc. 
   In use, a fluid is delivered into measuring chamber  54  through an upper end  14  of body  12 . Fluid in excess of a desired amount drains out of drain line  42 . By draining fluid out of drain line  42 , an upper fluid level is established in interior space  18 . The upper fluid level defines a predetermined volume of fluid in measuring chamber  54 . The predetermined volume of fluid may then be dispensed out of lower end  16  of body  12  through dispense valve  72 . The dispense valve  72  may be electronically actuated, manually actuated or actuated by other methods. 
   In one embodiment, e.g., as shown in  FIGS. 1-3  and  6 , the surface area of the fluid may be restricted or reduced in size as compared to the dimensions of the interior space  18  by providing a restriction member  32 . For example, the drain line  42  may be located to communicate with an inner wall  40  of a restriction member  32 , thereby establishing an upper fluid level having a reduced or restricted surface area. Minimizing the surface area of the fluid surface minimizes measurement error of the pipet. 
   To prevent gas from being trapped in the measuring chamber  54 , a vent line  62  ( FIGS. 1-6 ) may be provided. By separating the vent line  62  from the passageway  38  ( FIGS. 1-3  and  6 ), gas may simultaneously escape from measuring chamber  54  while measuring chamber  54  is being filled with the fluid. 
   The delivery of fluid into interior space  18  may be accomplished via a fill line  20  (FIGS.  2  and  6 ), which delivers fluid to an area proximate upper end  14  of the body  12 . Additionally, fluid may be delivered directly into upper end  14  of body  12  via manual delivery or delivery from a remote fluid supply source  22  ( FIGS. 2 and 6 ) or a continuous supply source  26  (FIG.  3 ). 
   Referring back to  FIGS. 2 and 6 , it may be desirable to provide a pump  48  for sucking excess fluid from the interior space  18 . To minimize waste of the fluid, a recirculation line  49  may be provided to route excess fluid back to a remote fluid supply source  22  where the fluid can be reintroduced into the interior space  18  via fill line  20 . 
   Dispensing the predetermined volume of fluid may be achieved by gravity feed or, alternatively, by delivering compressed gas into the interior space  18  to force the fluid out of lower end  16  of body  12 . To deliver compressed gas to interior space  18 , compressed gas valve  70  is opened and gas is delivered through line  68  into interior space  18  at a location above the drain line  42 . 
   Referring now to  FIGS. 4 and 5 , for dispensing very small amounts of a predetermined volume of fluid, it may be unnecessary to provide a restriction member  32 , as shown in  FIGS. 1-3 , in the interior space  18  of the body  12 . However, it may still be desirable to provide a structure for venting gas from measuring chamber  54  when fluid is delivered to the measuring chamber  54 . In particular, for a very small diameter of body  12 , incoming fluid may not readily permit trapped gas to escape. Therefore, in one embodiment, vent line  62  may be provided within interior space  18 , where the vent line  62  has a lower opening at a location below the inlet  44  of drain line  42  and has an upper opening at a location above the inlet  44  of drain line  42 . Weather cap  64  is preferably provided above the vent line  62  of  FIG. 4  to prevent fluid from entering the upper opening of vent line  62 . In another embodiment, as shown in  FIG. 5 , the vent line  62  may be provided externally to the body  12 . A vent valve  66  may be provided on vent line  62 . 
   Referring back to  FIG. 3 , delivery from a continuous supply source  26  may be desirable to provide a sampling device for a process stream. In this embodiment, isolation valve  30  is selectively opened to admit fluid from process pipe  28 . The fluid then fills the fill chamber  60 . Fill valve  58  may then be opened to allow the fluid to pass from the fill chamber  60  through overflow chamber  56 , through passageway  38  and into measuring chamber  54 . As the fluid fills measuring chamber  54 , displaced gas is vented out through vent line  62 . In this embodiment, the vented gas is vented to an exterior of body  12  through vent line  62 . Once the fluid level in the measuring chamber  54  rises to the inlet  44  of level of the drain line  42 , any excess fluid is drained out of interior space  18 , e.g., any fluid rising into overflow chamber  56  will be drained out of interior space  18 , thereby establishing a maximum volume of fluid in the measuring chamber  54 . 
   If it is desired to use a pipet  10  having a fill valve  58 , a drain valve  46  on a drain line  42 , a gas valve  70  on a compressed gas line  68  and a dispense valve, then a prescribed sequence of opening and closing various valves  58 ,  46 ,  70  and  72  is desirable for operating the pipet. Below is an example sequence of valve operation. The valve operation may be varied without adversely effecting the accuracy and precision of the inventive pipet. 
   Description of Steps: 
   
       
       0. Start with valves  46 ,  58 ,  70  and  72  closed. 
       1. Fluid is delivered through the fill valve  58 . The fluid flows through the passageway  38  through the restriction member  32  and into the measuring chamber  54 . 
       2. The drain valve  46  is opened and excess liquid drained out of the manifold. 
       3. The fill valve  58  is closed. 
       4. Gas valve  70  is opened briefly to ensure that excess liquid drains through the drain valve  46  and into drain line  42 . 
       5. The drain valve  46  is closed. 
       6. The compressed gas valve  70  is opened. The increased pressure inside interior space  18  activates a pressure actuated dispense valve  72  to allow the measured liquid within measuring chamber  54  to exit via the open dispense valve  72 . 
       7. The compressed gas valve  70  is closed. 
       8. The drain valve  46  is opened to relieve pressure. 
       9. Step 5 is repeated 
       10. Step 6 is repeated 
       11. Step 7 is repeated 
       12. Step 8 is repeated 
       13. Step 9 is repeated 
     
  
   Alternatively, step 9 could comprise “close drain valve  46 ” and steps 10-13 could be eliminated. Steps 10-13 are cautionary to ensure that all measured liquid has been discharged. 
   Steps for one method of operation are presented in the below Table. 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
             
             
                 
                 
                 
                 
               Dispense 
             
             
               Step 
               Fill Valve 58 
               Drain Valve 46 
               Gas Valve 70 
               Valve 72 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               0 
               Close 
               Close 
               Close 
               Close 
             
             
               1 
               Open 
               Close 
               Close 
               Close 
             
             
               2 
               Open 
               Open 
               Close 
               Close 
             
             
               3 
               Close 
               Open 
               Close 
               Close 
             
             
               4 
               Close 
               Open 
               Pulse 
               Close 
             
             
               5 
               Close 
               Close 
               Close 
               Close 
             
             
               6 
               Close 
               Close 
               Open 
               Open 
             
             
               7 
               Close 
               Close 
               Close 
               Close 
             
             
               8 
               Close 
               Open 
               Close 
               Close 
             
             
               9 
               Close 
               Close 
               Close 
               Close 
             
             
               10 
               Close 
               Close 
               Open 
               Open 
             
             
               11 
               Close 
               Close 
               Close 
               Close 
             
             
               12 
               Close 
               Open 
               Close 
               Close 
             
             
               13 
               Close 
               Close 
               Close 
               Close 
             
             
                 
             
           
        
       
     
   
   As described above, a novel pipet is taught for automatically and inexpensively extracting an aliquot of liquid from one source, measuring a predetermined volume of the liquid and transferring the volume of liquid to a different vessel. Benefits of the novel pipet include simplicity and therefore low expense to manufacture, ease of automation, minimization of the volume of liquid that must be used to rinse the apparatus, elimination of a need to reposition the pipet after liquid has been introduced into the pipet, elimination of expensive syringe pumps that are used in typical automated pipetting systems, elimination of the use of suction to fill the pipet with liquid, and use of gravity and overflow rather than a syringe pump to measure volume. 
   While the invention has been described with a certain degree of particularity, it is understood that the invention is not limited to the embodiment(s) set for herein for purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.