Non-contaminating pressure transducer module

Abstract

A non-contaminating pressure transducer module having an isolation member is disclosed. The isolation member isolates a pressure sensor within the transducer module from exposure to ultra high purity fluids flowing through a conduit in the module without significantly affecting the accuracy of the pressure measurement. The transducer module may be positioned within a fluid flow circuit carrying corrosive materials, wherein the pressure transducer module produces a control signal proportional to either a gauge pressure or an absolute pressure of the fluid flow circuit. The pressure transducer module of the present invention also avoids the introduction of particulate, unwanted ions, or vapors into the flow circuit.

Description

The present application is a Continuation-In-Part of application Ser. No. 08/538,478 filed on Oct. 3, 1995, now U.S. Pat. No. 5,693,887, and entitled "PRESSURE TRANSDUCER MODULE HAVING NON-CONTAMINATING BODY AND ISOLATION MEMBER".

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates generally to non-contaminating pressure transducer modules, and more particularly relates to a pressure transducer module that effectively operates within Ultra High Purity (UHP) processing equipment that utilize UHP chemicals and require UHP conditions. The pressure transducer module of the present invention provides a continuous measurement of the pressure within a fluid flow circuit of the UHP processing equipment without contaminating the fluid within the circuit. An isolation member and a diameter of the isolation member substantially larger than the thickness of the flexible member 34 as shown in the figures. The isolation member is positioned in intimate contact and adjoins the pressure sensor. An isolation member having a thickness greater than 0.040 inches affects the accuracy of the pressure measurement. Also, an isolation member thinner than 0.001 inches is difficult to manufacture and an undesirable amount of fluid may permeate back and forth through such a thin member. The upper surface 36 of the isolation member may be abraded so as to create a pattern of grooves or channels. When the abraded upper surface 36 of the member is pressed against the base 38 of the pressure sensor 40 (see also FIG. 4), any air pockets that might otherwise have formed between the sensor base 38 and the member are relieved, allowing more intimate contact between the member and the pressure sensor 40. The flange 552 of the spacer 50 and the o-ring 54 are dimensioned to allow a slight gap between the sensor 40, o-ring 54, and spacer 50. The inner surface of the spacer 50 may also have a pattern of grooves or channels formed thereon, thereby creating a passage for the relieved air to escape into a central region of the cavity.

Referring again to FIGS. 3 and 4, the pressure sensor 40 is positioned on top of and pressed against the flexible member 34. The pressure sensor may be of a capacitance, piezoresistive, or piezoelectric type known to those skilled in the art. The base 38 of the pressure sensor is in direct contact with the member and may be either in pressure contact with or bonded to the member by an adhesive, thermal welding or by other known means.

In one embodiment generally shown in FIG. 6, an alumina ceramic pressure sensor is comprised of a thin, generally compliant ceramic sheet 42 having an insulating spacer ring 44 sandwiched between a thicker, non-compliant ceramic sheet 46. The first thin ceramic sheet or diaphragm is approximately 0.005 to 0.050 inches in thickness with a typical thickness of 0.020 inches. The thicker ceramic sheet has a thickness range between 0.100 to 0.500 inches. The spacer may be constructed of a suitable material such as a glass, ceramic, braze, or polymer, glass being preferred. The opposed faces of ceramic disks 42 and 46 are metalized by metals such as gold, nickel or chrome to create plates of a capacitor. A similar capacitive pressure transducer is described by Bell et al. in U.S. Patent 4,177,496 (the '496 patent). Those skilled in the art will appreciate that a sapphire pressure sensor or other capacitive pressure transducers similar to that described in the '496 patent may be implemented into the present invention. Referring again to FIG. 4, an electronic circuit module 48 is positioned above the ceramic pressure sensor 40 and is electrically coupled to the conductive surfaces of the ceramic pressure sensor. The electronic circuit module 48 is also connected by suitable leads or conducting wires (not shown) to interval contacts of the connector 22 (FIG. 1). In the preferred embodiment the electrical connector 22 is made of a chemically inert material and preferably may be of a type available from Pneumatico, part number po3rsd-00004-24.

The electronic circuit module 48 develops a control signal proportional to the measured pressure within the flow circuit using analog information received from the pressure sensor 40 related to changes in its capacitance due to deformation of member 42 by the fluid pressure acting on it. The electronic circuit may also adjust the signal proportional to the measured pressure as the temperature within the flow circuit changes by including a thermistor or like component therein.

In FIGS. 3 and 4, a cup shaped spacer member 50 is disposed above the pressure sensor 40 so as to exert,a force on the upper surface of the pressure sensor 40, holding the sensor flat against the member 34. The spacer 50 further has a circumferential flange 52 (FIG. 4) which transfers a force against the member 34 and lip 32 of the cavity. An o-ring 54 may be positioned between the flange 52 of the spacer and the isolation member, wherein through its elastomeric properties, the force may be transferred from the spacer member 50 against the isolation member to clamp it against the annular cavity lip 32. A threaded hold down ring 56 is rotated in mating relation with the inner threads of the cavity of the housing or body 14, thereby engaging the spacer member 50 and forcing it against the pressure sensor 40 and isolation member 34.

In order to reduce dead space, the distance "d" (FIG. 4) that the flexible isolation member is displaced from the lumen of the bore 28 should be kept to a minimum. The decrease in dead space reduces the chance of accumulation of debris and contamination. The decrease in dead space also reduces or eliminates the chance of air bubbles being trapped in the dead space and then suddenly released back into the flow circuit. The release of these air bubbles from the dead space has a negative impact on the semiconductor processing. The inner diameter of the lumen "D" should be equal to or exceed 2*(d). Ideally, the dimension, d, will be far less than the dimension, D, in measurement.

FIG. 7 shows an alternate embodiment wherein the spacer member 50 has rounded edges as at 58. The rounded edges help focus the force of the spacer 50 against the flexible isolation member 34 and the lip 32 of the cavity. This arrangement also eliminates the need for the o-ring 54. However, o-ring 54 may be positioned between the isolation member and the lip 32 (see FIG. 13). The flange 52 of the spacer 50 and the o-ring 54 are dimensioned to allow a slight gap between the sensor 40, o-ring 54, and spacer 50. The inner surface of the spacer 50 may also have a pattern of grooves or channels formed thereon, thereby creating a passage for the relieved air to escape. Further, a spacer 50' may have a bore extending through a center section, thereby extending the passage into the cavity of the housing.

FIG. 8 illustrates another preferred embodiment wherein the lip 32' of the cavity is stepped. The o-ring 54, when compressed by the spacer member 50, is made to conform to the shape of the step and pushes or forces the flexible isolation member 34, causing it to bend and mold to the shape of the stepped lip 32 to provide a seal against ingress of fluid. In yet another embodiment, the o-ring 54 may be positioned between the isolation member and the lip 32' (see FIG. 15).

FIG. 9 illustrates another preferred embodiment having the end of the spacer member flange 52 rounded, wherein the flange is forced against the o-ring 54 which, in turn, forces the o-ring against the flexible isolation member 34.

FIG. 10 illustrates yet another preferred embodiment wherein the o-ring seal 54' is contained within an annular groove or recess 60 formed within the lip 32'. The flexible isolation member 34 is forced against the o-ring 54', sealing the edges of the lip 32' thereby preventing the fluid of the flow circuit from leaking into the cavity of the housing. This shield arrangement is preferred in circumstances where the fluid flow pressure is less than the atmospheric pressure. In such a circumstance, the shield arrangement eliminates the possibility of the o-ring being drawn into the fluid flow circuit.

FIG. 11 illustrates yet another embodiment wherein an annular ridge 62 is formed along the surface of the lip 32. When the isolation member is compressed against the lip, the isolation member conforms to the shape of the ridge. In this manner, an effective seal is formed between the member sheet and the housing lip.

FIG. 12 shows yet another embodiment wherein the lip has a multiple step wherein the o-ring 54 is positioned on the lower step below the isolation member 34. An additional annular sealing ring 64 having an external groove 66 for receiving an o-ring 68 and an internal groove 70 for receiving an o-ring 72 provides an additional seal between the housing 14 and the pressure sensor 40. The additional annular sealing ring 64 is shown as being positioned between a top step 74, and the first spacer ring 76. The spacer member 50 is in direct contact with both the first spacer ring 76 and the pressure sensor 40. In this manner, the interior of the housing is sealed from the fluid circuit independently of the seal created between the member 34 and the pressure sensor 40. A drain channel 78 extends through the housing 14 to an external surface. The drain channel 78 is positioned between the top step 74 and the lower step to which the seal 54 is in contact. If fluid from the flow circuit leaks past o-ring 54, the drain channel 78 allows this fluid to drain out of the housing without contaminating or affecting the sensor 40 or regressing back into the flow circuit. The drain channel 78 also provides a visual indicator to the user that fluids have permeated, leaked, or otherwise made it past the first seal or o-ring 54. This visual indication is commonly referred to in the industry as a leak indicator.

When the o-ring 54 is positioned on the fluid flow circuit side (see FIGS. 10 and 12-15), the o-ring must be manufactured from a chemically inert material. An elastomeric perfluorocarbon such as KALREZ available from duPont Nemours, Inc., is suitable for this purpose. Other materials such as CHEMRAZ, an elastomeric PTFE available from Greene, Tweed & Co., Inc. is equally suitable.

Referring now to FIGS. 16 and 17 another embodiment of the pressure transducer module 10 is shown. The module generally includes a housing or body 80, flared pressure fitting 82 (only a portion of which is shown) and a cover or cap 84. An electrical connecting member 86 of known construction may be removably attached to the cover 84. The flared pressure fitting 82 serves as an inlet to the transducer body 80 and is of known construction. FIG. 17 shows a pressure sensor 88, spacer ring 90, hold down ring 92, sealing spacer 94, sealing members 96-98, and isolation member 100 positioned within the cavity 120 of the housing 80. Those skilled in the art will appreciate that housing 80, cover 84, spacer ring 90, hold down ring 92, sealing spacer 94, and isolation member 100 may be manufactured from the same chemically inert material including fully fluorinated fluorocarbon polymers (including PFA, PTFE, and FEP), partially fluorinated fluorocarbon polymers (including ETFE, CTFE, ECTFE, and PVDF), and high performance engineering thermoplastics (including PEEK). The sealing members may be manufactured from suitable chemically inert polymers including elastomeric perfluorocarbons (including elastomeric polytetrafluoroethylene).

A drain or vent 102 extends from an outer surface of the housing 80 into the that portion of cavity 120 between sealing members 96 and 98 (chamber 121). The vent may include an internally threaded bore adapted for receiving a tubing member (not shown) used to isolate and direct fluids from the vent 102. Further, the vent may include a sensor 89 of known suitable construction coupled to the integrated circuit 106, wherein the sensor 89 transmits a signal when predetermined fluids flow past or in contact with the sensor 89 in the vent 102. An integrated circuit 106 is electrically coupled to the sensor 88 via electrical wires 104. Electrical wires 108 electrically couple the integrated circuit 106 to the connecting member 86. Those skilled in the art will appreciate that a pigtail cable with a corrosion resistant outer sheath may extend from the connecting member 86. Further, the outer 84 may include internal threading (see FIG. 3) to thereby engage the cover to the housing 80.

The cavity 120 intersects with a bore 114 extending from an external surface of the housing into the housing 80. The pressure fitting 82 is coupled to the housing 80 in alignment with the bore 114 and in a well known manner. The cavity 120 forms a ledge 116 near the bore 114 to which the sensor 88 and isolation member 100 are engaged. A plug 110 positioned within a passage extending from an external surface of the housing into the bore 114. An annular groove 118 is formed in the ledge 116 (see FIG. 26) and provides an increased sealing surface between the ledge and sealing member 98 positioned therein. Another sealing member 96 is positioned between the pressure sensor 88 and an internal surface of the cavity 120, thereby providing a redundant seal or trap to prevent any minute amounts of fluids from flowing above the sensor 88 sidewalls and contaminating the integrated circuit 106 positioned above the sensor 88. The cavity wall adjacent the sealing member 96 may be beveled to provide a sealing surface between the sensor 88 and cavity 120. The sealing spacer 94 transfers a force from the spacer ring 90, thereby compressing the sealing member 96 against the beveled sidewall.

FIG. 18 shows the housing 80 modified to eliminate the need for a redundant sealing arrangement. A thin wall 122 is molded integral with the housing 80 and separates the cavity 120 from the bore 114. The thin wall 122 having a thickness between 0.005 and 0.040 inches acts as the isolation member 100. The thin wall must be molded thin enough to be flexible and allow the pressure sensor to effectively operate without interfering with an accurate measurement of pressure, however a thin wall 100 122 molded too thin (approximately less than 0.005 inches) will not effectively block fluids from permeating through the wall 100 122 and into the cavity 88. The drain channel or vent 102 extends from the external surface of the housing 80 into that portion of the cavity 120 that forms chamber 121. In the event fluids permeate through the thin wall 122, the fluid drains out the channel 102 and avoids contamination with the integrated circuit. Those skilled in the art will appreciate that the sealing members may be positioned within the cavity 120, as described above, for added preventative measures to avoid contaminating contact between the processing fluids and the integrated circuit 106.

FIG. 19 shows another modified embodiment of the housing 80, wherein the flexible member 100 extends up the sides of the sensor 88 such that both the bottom and sides of the sensor 88 engage the isolation member 100 against the internal sides of the housing 80 defined by the cavity 120. The sealing member 98 is formed into the ledge 116. Fluid flows through the opening formed by the ledge 116 and forces the isolation member 100 against the sensor 88. When the isolation member 100 is pressed against the sealing member or ridge 98, the flexible member tends to conform to the shape of the sealing member or ridge 98, thereby providing a sealing member between the housing and isolation member 100.

FIG. 20 shows another embodiment of the present invention. The isolation member 100 is not shown positioned between the ledge 116 and the sensor 88. Instead, a ceramic pressure sensor is shown having a layer of sapphire 124 bonded, engaged, formed or otherwise defining the lower surface of the sensor 88. The sapphire layer may be an additional layer to the ceramic sensor or may replace the lower layer 42 of the ceramic sensor (see FIG. 6). The sapphire layer 124 is chemically inert and highly resistive to the corrosive nature of the chemicals used in the UHP processing equipment. The sapphire layer 124 acts as the isolation member and seals against the sealing member 98.

FIG. 21 shows another embodiment wherein the isolation member 100 is tubular in nature, wherein a free end of the tube or isolation member 100 wraps around the lower end of the bore 114 opening such that the flared pressure fitting seals the free end of the tube against the housing 80. The fixed or terminal end 128 of the tube is closed and conforms to the shape of the opening between the cavity 120 and the bore 114. Fluid flows through the tube and forces the isolation member 100 against the sensor 88. Various known suitably chemically inert thermoplastic materials may be used to form the tube or isolation member 100, with fluoropolymers being preferred. The sealing and drain arrangement as described above may be utilized as shown to further isolate the integrated circuit 106 from any potentially damaging chemicals.

Referring to FIG. 22, the sapphire layer 124 may be incorporated into the sensor 88 as described above, wherein the face or lower surface of the sapphire layer engages the ledge 116. The ledge 116 includes multiple sealing members 130 and 132 that seal and engage against the face of the sapphire sensor. Those skilled in the art will appreciate that the sealing members 130 and 132 may be constructed of chemically inert elastomers or formed as ridges in the top surface of the ledge 116. Additionally, a combination of elastomers and ridges may be utilized as desired. In this manner a redundant seal may be formed on the face or lower surface of the sapphire layer 124. Of course, the sealing members may be utilized in any of the several embodiments wherein the sealing member 98 is positioned under the face or lower surface of the sensor 88. A drain channel 134 extends from an outer surface of the housing 80, through a portion of ledge 116 and into the cavity 120 between the two annular sealing members 98.

FIG. 23 shows another embodiment of the invention, wherein the isolation member 100 is a formed as a tubular member having open ends 136-138. Each end extends past and overlaps a corresponding end of the bore 114. The tubular member may be manufactured consistent with the above description of the tubular member utilized in the embodiment shown in FIG. 21. As fluid flows through the flow-through bore 114, the pressure forces the isolation member outward, engaging a portion of the isolation member 100 against the sensor 88.

FIG. 24 shows the housing 80 having an outer ring 140 engaging the housing proximate the intersection of the bore 114 and cavity 120. The outer ring is constructed of a suitable known material having a low co-efficient of expansion, ceramic for example, and restricts expansion of the housing 80 near the sealing members 96 and 98. Those skilled in the art will appreciate that the ceramic ring 140 may be utilized in any of the embodiments to control the expansion of the housing as desired.

FIGS. 25-27 show the isolation member 100 positioned above the sealing member 98. The sealing member 98 may be constructed of an annular elastomer (see FIGS. 25-26) or may be formed directly into the ledge 116 (see FIG. 27). FIG. 28 shows an annular groove 142 formed in the ledge 116. The isolation member conforms to the groove and an elastomer seal is shown positioned above the isolation member adjacent the groove 142. FIG. 29 shows another variation of the sealing member 98, wherein the opening formed by the ledge 116 and the adjacent edge of the sensor 88 are beveled. When the isolation member 100 is sandwiched between the ledge and sensor the beveled edge 144 forms the sealing member 98 therebetween.

FIG. 30 shows yet another preferred embodiment of the pressure sensor. The sensor 88 has an annular groove 146 formed on the lower surface thereof An annular ridge 148 conforming to the shape and size of the annular groove 146 extends up from the ledge 116. When the sensor 88 engages the ledge 116 the ridge 148 engages the groove 142 thereby sealing the lower surface of the sensor to the ledge 116. The lower surface of the sensor 88 may comprise a sapphire layer. Alternatively, an isolation member 100 may be positioned between the sensor 88 and ledge 116, wherein the isolation member is engaged between the groove 146 and ridge 148, thereby forming the sealing member 98.

Having described the constructional features of the present invention the mode of use will now be discussed. The user couples the pressure transducer module 10 into a UHP fluid flow circuit through pressure fittings. As fluid flows through the flow circuit, the pressure distorts the thin ceramic plate of the pressure sensor or as a function thereof, and thus changes the capacitance of the ceramic pressure sensor. The change in capacitance is related to the pressure within the flow circuit. This change in capacitance is detected by the electric circuit which, in turn, produces an analog signal proportional to the pressure. The gauge pressure or absolute pressure may equally be determined.

Those skilled in the art will recognize that the transducer output may be calibrated so that minimum output values are associated with minimum pressure and maximum output pressures are associated with maximum pressure. For example, a transducer intended to measure 0 to 100 psig (pounds per square inch gauge) can be calibrated to read 4 mA (milliamps) at 0 psig and 20 mA at 100 psig.

By providing the various embodiments of the chemically inert isolation member which engages the pressure sensor, the working fluid does not contact the surfaces of the sensor which could lead to contamination. The various sealing arrangements disclosed above insure that the working fluid does not enter the cavity of the housing and adversely affect the electronic circuitry even when the fluid flow conduit and therefore the housing area subjected to high temperatures.

This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different devices, and that various modifications, both as to the equipment details and operating procedures, can be accomplished without departing from the scope of the invention itself.