Abstract:
A planar manifold that integrates all the control pneumatics, electronic pressure controls (EPC), and injector inlet onto a single plate, therefore eliminating numerous seals, fittings and transfer tubing between these devices. The planar manifold utilizes plates of specific geometry that minimizes heat transfer between the heated components and the unheated components in the planar manifold, while maintains the mechanical rigidity to support the attached components during shock and vibration. The planar manifold not only improves the reliability and manufacturability of micro gas chromatographs, but also lowers the cost of production.

Description:
FIELD OF INVENTION 
     The present invention relates generally to miniaturized planar device for liquid and gas phase analysis. More specifically, the invention relates to a planar manifold that integrates heated inlets with unheated pneumatics on the same plate. 
     BACKGROUND OF THE INVENTION 
     A gas chromatograph (GC) is an analytical instrument that takes a gaseous sample (or converts a sample to the gaseous state if necessary), and separates the sample into individual compounds, allowing the identification and quantification of those compounds. The principal components of a typical gas chromatograph are the following: an injector that converts sample components into gases (if necessary) and moves a representative sample of the mixture onto the head of a separation column in a narrow band; a separation column that separates the sample mixture into its individual components as these components are swept through the column by an inert carrier gas, the separation being based on differential interactions between the components of the sample mixture and an immobilized liquid or solid material within the column; a detector that detects and measures components as they exit the separation column; and a data display. 
     Typical modern GC instruments are configured with a heated-block “flash evaporator” type injector, a long capillary tube column, an oven housing the column to maintain and to change the column&#39;s temperature in a predictable and reproducible fashion, a flame ionization detector (or other type of detector), and a computer with dedicated hardware/software to process the data collected. Conventional GC units are typically about the size of a large microwave oven (50-100 kg), require 2 to 3 kilowatts of power and considerable air conditioning. 
     Micro GCs are portable GC systems that are light, rugged and fast. Micro GCs use only utilities (compressed gas and electricity) that are readily available in the field. The micro GCs, smaller than a briefcase, have been widely used not only in field applications, such as custody transfer, well logging, environmental screening, and storage tank analysis, but also in laboratories because micro GCs require minimal laboratory space and operate at high speed with minimal consumption of utilities (compressed gases, air conditioning, etc.). 
     An important part of a GC system is the accurate control of fluid flow, which is typically achieved with an extensive and complex array of channels, tubing, fittings and the like in a conventional GC. U.S. Pat. No. 5,686,657, herein incorporated by reference, discloses a method to reduce external connections between fluid-handling devices by use of a single planar manifold for the provision of a plurality of flow paths. The fluid-handling devices that connect to the planar manifold are preferably constructed to be surface-mounted, which has been found to offer reliable, fluid-tight connection without the complexity and difficulty of conventional pneumatic connections. The number and complexity of external connections, which would otherwise undesirably increase the volume of the flow system, are also decreased. Another advantage is that the reliability of the pneumatic connections is improved. 
     A further advantage of the planar manifold technology is that multiple fluid-handling functional devices may be coordinated and assembled in a small volume. Multiple pneumatic channels can be integrated in a planar manifold, which is itself quite compact and amenable to construction in a variety of shapes and configurations. For example, it is contemplated that a planar manifold may be constructed in an irregular shape, such as a curved, bent, or multiple-angled configuration, so as to conform to an irregularly-shaped, compact volume. 
     A diffusion bonding method is one of the preferred methods to manufacture planar manifolds. In the diffusion bonding method, bonding members to be bonded to each other are held in close contact with each other, and pressed to a degree so that the bonding members are bonded by the diffusion of atoms which takes place in the interface between the bonded surfaces. Since the bonding members are actually “melted” into each other under the bonding conditions, diffusion bonding provides satisfactory bonding strength, air-tightness, and pressure resistance that are required in a pressured fluid-handling system. 
     Diffusion bonded planar manifolds have been used to perform gas supply functions that relate to injector inlets or detectors in conventional GCs, such as the Agilent 6890 Plus GC system. FIG. 1 shows a block diagram of a prior art GC unit  10 . This typical GC unit  10  comprises a computer  12 , a controller  14 , an injector inlet  16 , a detector  18 , a column  20 , an oven  22 , a column heater  28 , and a plurality of planar manifolds  24  and  26 . 
     In order to perform a chromatographic separation of a given sample compound, a sample is injected with a pressurized carrier gas by means of the injector inlet  16 . The carrier gas supplied to inlet  16  is provided from a source  16 A through one or more inlet planar manifold(s)  24 , each of which serves in part to control and redirect a plurality of gas flows. The column  20  is positioned within the oven  22  which has an operating temperature of between room temperature and about 450° C. The carrier gas/sample combination passing through column  20  is exposed to a temperature profile resulting in part from the operation of the column heater  28  within oven  22 . During this profile of changing temperatures, the sample will separate into its components primarily due to differences in the interaction of each component with the column  20  at a given temperature. As the separated components exit the column  20 , the components are detected by the detector  18  which requires a plurality of detector gasses of appropriate types, such as air, hydrogen, and make-up gas. The detector gases are provided from respective sources  18 A through one or more detector planar manifold(s)  26 . The inlet planar manifolds  24  and detector planar manifolds  26  are placed in a GC manifold carrier  30 . Suitable fluid-handling devices, such as fittings, regulators, valves, sensors, and the like in the planar manifolds  24  and  26  may be passive (such as a termination fitting) or active and hence operated under the control of the computer  12  by way of control signals provided the controller  14 . 
     To avoid a “cold spot” or “condensing point”, the injector inlet  16  and detector  18  are both heated in their respective heated zones  17  and  19 . Since the various valves and electronic pressure controls (EPC) in the planar manifolds  24  and  26  are usually operated at room temperature, the GC manifold carrier  30  is located outside the oven  22  and is connected to the inlet  16  and the detectors  18  by stainless steel tubing  32 . Furthermore, all prior art designs use separated planar manifolds for injector inlet and detector gas supplies. 
     Up until now, micro GCs have not used diffusion bonded planar manifold technology. Instead, micro GCs use discrete stainless steel tubing, machined manifold blocks, o-ring seals, and press fit tapered unions with UV-glue to integrate the gas supply pneumatics and injector device together. Micro-GCs are currently designed to use iso-thermal ovens, and operate over a narrower temperature range of between room temperature to about 120° C. 
     SUMMARY OF THE INVENTION 
     Disclosed is a diffusion bonded planar manifold integrating a variety of fluid handling devices that require different operating temperatures onto a single plate. The diffusion bonded planar manifold comprises a high temperature zone for devices requiring high operating temperatures, a low temperature zone for devices requiring lower operating temperatures, and an insulating zone to separate the high temperature zone from the low temperature zone. The insulating zone is designed with such a geometry that heat transfer between the high temperature zone and the low temperature zone is minimized while the mechanical rigidity of the diffusion bonded planar manifold is maintained. 
     In a preferred embodiment, the high temperature zone is surrounded by a frame which limits heat transfer and provides convection barrier around the devices requiring high operating temperatures. 
     In another preferred embodiment, the low temperature zone is attached to a heat sink, i.e., a large piece of heat conductive material, that absorbs heat from the low temperature zone and helps to maintain the temperature in the low temperature zone within a desired range. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a prior art conventional GC. 
     FIG. 2 is a block diagram of an embodiment of the present invention. 
     FIG. 3 is a exploded view of a preferred embodiment of a diffusion bonded planar manifold assembly. 
     FIG. 4 is a side perspective view of an assembled diffusion bonded planar manifold assembly of FIG.  3 . 
     FIG. 5 is an inside view of the diffusion bonded planar manifold of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The diffusion bonded planar manifold will find useful application in a variety of analytical systems containing fluid handling functions operating at different temperatures. Gases are the preferred fluids according to the practice of the present invention, and therefore the following description will include a description of the arrangement, construction, and operation of certain pneumatic devices, and hence is particularly directed to the control of a plurality of gaseous streams in an inlet or detector in a gas chromatographic analytical system. However, for the purposes of the following description, the term “pneumatic” will also be considered to refer to all types of fluids. 
     FIG. 2 shows a block diagram of an embodiment. This embodiment provides a diffusion bonded planar manifold assembly  34  for a micro GC  100 . The micro GC  100  preferably includes an on board computer  12 ′, a controller printed circuit board (PCB)  14 ′, and a GC module  36 . The GC module  36  preferably includes a module PCB  15 , a diffusion bonded planar manifold assembly  34 , a detector  18 , a column  20 , an oven  22  and a column heater  28 . The diffusion bonded planar manifold assembly  34  preferably combines all the control pneumatics (not shown in FIG.  2 ), EPC (not shown in FIG.  2 ), an injector inlet  16  and an injector heater  38  into a single assembly, hence eliminating numerous seals and transfer tubing and improving the reliability and manufacturability of the micro GC  100 . Two gas sources  16 A and  18 B are provided. The inlet gas source  16 A provides one or more gases for the column  20 . The gas flow is divided by an injector die (not shown) within the diffusion bonded planar manifold assembly  34  into analytic and reference flows for the needs of the detector. The valve actuation gas source  18 B provides one or more gases to actuate pilot valves. An alternative might be to provide a single supply of gas to be divided by the diffusion bonded planar manifold into an appropriate number of gas streams. This embodiment incorporates the existing planar manifold uses of gas regulation with the new uses in the heated injector and sample stream realm. 
     FIG. 3 depicts an exploded view of a preferred embodiment of a diffusion bonded planar manifold assembly  34  in the micro GC  100  of FIG.  2 . The diffusion bonded planar manifold assembly  34  preferably comprises a flow bracket  42 , one or more pressure sensors  44 , one or more pressure sensor clamps  66 , a front clamp  46 , a front gaskets  48  and a rear gasket  49 , a heated micro electronic machine system (MEMS) injector die  50  with injector outlets  54 , a heater cable  64 , a rear clamp  52 , one or more proportional pressure valves  56 , and a plurality of pilot valves  58 , and a diffusion bonded planar manifold  40  with an injector inlet fitting  62  and a plurality of manifold ports (not shown) for the attachment of the pressure sensors  44 , the MEMS injector die  50 , and the valves  56  and  58 . 
     Devices and components held between the front clamp  46  and the rear clamp  52  constitute a high temperature zone  202  on the left part of the diffusion bonded planar manifold  40  (i.e., the area for the attachment of the heated injector die  50 ), where the sample temperature is typically controlled to several degrees under an oven setpoint. Devices and components attached on the right part of the diffusion bonded planar manifold  40  constitute a low temperature zone  206  (i.e., the area for the attachment of the pilot valves  58  and the proportional pressure valves  56 ), where the temperature is usually near ambient. 
     FIG. 4 illustrates an assembled diffusion bonded planar manifold assembly  34 . The two pressure sensors  44  are preferably mounted to the flow bracket  42  through the pressure sensor clamps  66 . The diffusion bonded planar manifold  40  is preferably made of stainless steel and mounted to the flow bracket  42  on top of the pressure sensors  44 . The proportional valves  56  and the pilot valves  58  are preferably mounted on the opposite side of the diffusion bonded planar manifold  40  from the pressure sensor clamps  66 . The heated injector die  50  is preferably sandwiched between the front gasket  48  and the rear gasket  49 , and is preferably mounted to the diffusion bonded planar manifold  40  on the opposite side of the injector inlet fitting  62 . A heater (not shown) is located between the rear gasket  48  and the injector die  50 . The diffusion bonded planar manifold  40 , the heated MEMS injector die  50 , the heater, and the two gaskets  48  are preferably clamped together by the front clamp  46  and the rear clamp  52 . The precise alignment between the diffusion bonded planar manifold  40  and the attached fluid-handling devices are provided by a plurality of register pins and dowels (not shown). A number of O-rings (not shown in FIG. 4) built into the gasket create seals between the surface mounted fluid-handling devices and the diffusion bonded planar manifold  40 . 
     FIG. 5 shows a detailed view of the diffusion bonded planar manifold  40  of FIG.  3  and FIG.  4 . Based on the required operating temperature of the attached devices, the diffusion bonded planar manifold  40  is preferably divided into three zones: the high temperature zone  202 , the low temperature zone  206 , and a insulating zone  204  between the high temperature zone  202  and the low temperature zone  206 . The high temperature zone  202  preferably matches the geometry of the MEMS injector die  50 , and is uniformly heated to about 120°. The low temperature zone  206  preferably matches the required valve footprints for the proportional pressure valves  56  and the pilot valves  58 , which have a maximum operating temperature of 40°-60°. 
     To limit heat transfer out of the high temperature zone  202  to ambient or to the low temperature zone  206 , the high temperature zone  202  is preferably insulated in the front (i.e., the side facing the front clamp  46 ) and on the back (i.e., the side facing the rear clamp  52 ). In addition, the high temperature zone  202  is preferably surrounded by a frame  208  which limits heat transfer and provides a convection barrier around edges of the high temperature zone  202 . The frame  208  preferably defines one or more cavities  208 ′ that surround the high temperature zone  202 . 
     The heat transfer through the diffusion bonded planar manifold  40  is further minimized by the insulating zone  204 . The insulating zone  204  is designed to connect the high temperature zone  202  to the low temperature zone  206  with minimal material in order to limit heat transfer, while still providing a conduit for fluid flows and enough mechanical rigidity to support the MEMS injector die  50  during shock and vibration. The insulating zone  204  preferably defines one or more cavities  204 ′ that reduce heat transfer through the diffusion bonded planar manifold  40 . In addition, the low temperature zone  206  is preferably mounted on the flow bracket  42  that functions as a “heat sink” to absorb the excess heat from the low temperature zone  206 . The flow bracket  42  is preferably made of a heat conductive material, preferably aluminum. 
     While the invention has been described and illustrated with reference to specific embodiments, those skilled in the art will recognize that modification and variations may be made without departing from the principles of the invention as described herein above and set forth in the following claims.