WO1999028718A1

WO1999028718A1 - Fluid monitoring device

Info

Publication number: WO1999028718A1
Application number: PCT/US1998/025486
Authority: WO
Inventors: Daniel Dobrick; Michael T. Peterson; Robert Chinnock
Original assignee: Fluoroware, Inc.
Priority date: 1997-12-02
Filing date: 1998-12-02
Publication date: 1999-06-10
Also published as: WO1999028718B1

Abstract

A pressure transducer (10) comprising an injection molding fluoropolymer and a pressure gauge.

Description

FLUID MONITORING DEVICE

This is a utility application based on U.S. Provisional

Patent Application 60/067,256, filed December 2, 1997.

BACKGROUND OF THE INVENTION

This invention relates to pressure sensors. More particularly, the invention relates to devices suitable for measuring pressures in fluid circuits containing highly caustic fluids.

Fluids utilized in the semiconductor industry such as hydrofluoric acid, sulfuric acid, and ammonium., hydroxide a_^re highly caustic and may react to metals conventionally utilized in fluid flow circuits and pressure sensors. Even metals considered to be inert, such as stainless steel, are not suitable for use in such applications. Fluoropolymer plastics such as PFA and PTFE, due to their highly inert characteristics relative to these fluids, are ideal for the fluid flow courses and other ancillary devices such as associated fittings, valves, filters, etc., in the semiconductor industry.

Due to the dangerous nature of the fluids used in the semiconductor industry, it is vital that they be properly contained. Leakage of these fluids can produce an extremely hazardous condition for workers and equipment. Liquid transport systems used to carry these fluids to various semiconductor wafer processing equipment have sensing devices that are generally sealed using o-rings or other mechanical seals. These seals are inherently susceptible to leakage due to the existence of leakage paths through which the fluids may travel during thermal expansion and contraction of the seals and the surrounding materials.

Pressure sensors for use in fluid flow circuits may generally be classified as 1) dead-end or single port devices and 2) in-line or dual port devices. In industries such as the pharmaceutical industry and semiconductor processing industry, it is very important to minimize the quiescent or dead spots in fluid flow circuits. These quiescent areas can operate as a collection area for contaminants, such as particles or bacteria. Additionally, these quiescent regions can introduce air bubbles into the flow stream which can have a negative impact on the processing of semiconductor wafers. Furthermore, such quiescent areas can be hard to access making them difficult to clean.

Flow through in-line sensors essentially eliminate or minimize quiescent areas. These sensors utilize strain gauges on the exterior of stainless steel tubing to measure the expansion of the tubing and thus the interior pressure of the fluid in the tubing. See U.S. Patent No. 5,024,099 assigned to Setra which is hereby incorporated by reference which also illustrates circuitry associated with such pressure sensors. Due to the use of metal these sensors are not acceptable m the semiconductor processing industry.

Known in-line pressure transducer modules suitable in semiconductor processing applications utilize a transducer body of a fluoropolymer plastic with a longitudinal bore defining a fluid duct with an inlet on one end and an outlet on the opposite end. A transverse cavity extends into the longitudinal bore. See U.S. Patent No. 5,693,887, which is hereby incorporated by reference. A separate diaphragm is fitted into the cavity on a shoulder in the body and is sealed by O-rings. A pressure sensor is positioned adjacent the diaphragm opposite the fluid duct thus isolating the sensor from the caustic fluid in the fluid duct. These types of transducer modules still have the problem of the area below the diaphragm creating a dead-end or quiescent region. Additionally, the sealing of the diaphragm with O-rings creates a potential leakage path. Moreover the configuration with the cavity extending into the longitudinal bore does not provide a smooth fluid pathway and the flow-interrupting structure in itself creates a pressure drop.

A need exists for a fluoropolymer pressure transducer module which is an in-line sensor, which does not have any quiescent or dead regions, which has a minimal number of wetted components, which has a minimal number of potential leakage paths, and which has no significant pressure drop associated with the transducer flow structure. A further need exists for a fluoropolymer pressure transducer module which is a dead-end sensor, which has a minimal number of wetted components and a minimal number of potential leakage paths.

SUMMARY OF THE INVENTION

A pressure-sensitive fitting or pressure transducer comprising an injection molded fluoropolymer body and a pressure gauge. The body comprises integral thick and thin wall portions which define an open interior region that is open to the fluid circuit being monitored and a pressure gauge receptacle portion. The open interior region may be of the flow-through version having an inlet and an outlet, or it may be of the dead-end version having only an inlet. The thin wall portion is molded or machined as part of the pressure sensor body thereby eliminating the need for O-rings, and eliminating the potential fluid leakage pathways associated with conventional fluoropolymer modules with diaphragm and/or O-ring assemblies. The thin wall portion may be molded into the body eliminating machining. The thin wall portion acts as a deflectable diaphragm whose deflection corresponds with the pressure in the open interior region. The pressure gauge receptacle has a sensor cavity, which is partially defined by an exterior surface of the diaphragm.

The pressure gauge is contained within the pressure gauge receptacle and is configured to measure the pressure within the open interior region using a pressure sensor. The sensor is positioned within the sensor cavity and configured to measure a physical characteristic within the sensor cavity that relates to the deflection of the diaphragm and, therefore, the pressure within the open interior region. The sensor electronically communicates with electrical conditioning circuitry to produce an output signal which corresponds with the pressure within the open interior.

An object of an embodiment of the invention is the straight uninterrupted and smooth fluid flow course through the pressure transducer. This results in no additional pressure drop other than what would occur in tubing having the same inside diameter. Additionally, quiescent or dead regions are eliminated in the transducer.

An object of an embodiment of the invention is that there is only one wetted surface within the pressure transducer. That is, the portion of the pressure transducer contacted by the fluid is one piece and is integrally molded. This eliminates potential fluid leakage paths between assembled components .

Yet another object of an embodiment of the invention is that the utilization of a pressure transducer body with an integral thin wall portion for obtaining the pressure reading minimizes manufacturing expense and provides a high level of reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a pressure sensing transducer according to an embodiment of the invention.

FIG. 2 is a cross-sectional view taken in the longitudinal direction of a pressure transducer according to an embodiment of the invention.

FIG. 3 is a cross-sectional view of a pressure transducer, according to an embodiment of the invention, taken in the direction transverse to that of FIG. 2.

FIG. 4 is a detailed cross-sectional view of the pressure sensor unit according to an embodiment of the invention.

FIG. 5 is a perspective view of the pressure sensor unit according to an embodiment of the invention.

FIG. 6 is a cross-sectional view of the integral diaphragm and pressure sensor in a dead-end version of the invention.

FIG. 7 is a front plan view of the pressure transducer according to an embodiment of the invention.

FIG. 8 is an exploded perspective view of the pressure transducer according to an embodiment of the invention. FIG. 9 is a cross-sectional view taken in the longitudinal direction of the pressure transducer according to an embodiment of the invention.

FIG. 10 is a schematic illustrating a fluid flow circuit.

DETAILED SPECIFICATION

Referring to the figures, the pressure monitoring devices according to the invention are shown and are generally indicated with the numeral 10. The device 10 is comprised principally of molded fluoropolymer body 20 and pressure gauge portion 50. As shown in FIG. 10, the device may be configured as an in-line transducer 12 of a dead-end transducer 14.

Body 20 may appropriately be of PFA or PVDF and comprises thick wall portion 22 and thin wall portion 24 as depicted in FIGS. 2, 3, and 9. Thick and thin wall portions 22 and 24 are integrally molded and define open interior 28 to constrain fluid having a pressure which is to be monitored. The open interior is preferably a circular bore although other smooth walleα configurations such as an oval are also included within the scope of the invention. Thin wall portion 24 has a predetermined minimal thickness, preferably .020 inches, and is configured to be a deflectable diaphragm whose deflection corresponds with the pressure within open interior 28. The balance of body 20 is comprised of thick wall portion 22 which has a pressure gauge receptacle 52 for receiving pressure gauge portion 50. Fluid is prevented from leaking into pressure gauge receptacle 52 due to the integral relationship of the thin wall portion or diaphragm 24 with the thick wall portion 22 of body 20. Threaded portions 40 may be provided on body 20 where needed. Sensor cavity or sensor region 54 positioned within pressure gauge receptacle 52 is partially defined by exterior surface 25 of diaphragm 24. Although sensor cavity 54 is principally formed by way of the molding of body 20, final machining may be performed to precisely control the thickness of diaphragm 24. Surface 56, partially formed by exterior surface 25 of deflectable diaphragm 24, of sensor cavity 54 is depicted in FIGS. 2, 3 and 9 as being flat. However, surface 56 could take on other shapes such as a pedestal, a partial pedestal, or a curved surface that could follow the curvature of fluid flow course 26.

Fittings or connectors 30 are used to connect tubing to pressure transducer 10. The fittings 30 as illustrated are conventional flared end fittings generally comprising flared cap 32, nose portion 33, and threaded portion 40. Such fittings 30 are well known to those in the art and are available under the FLARETEK® brand name from Fluoroware, Inc., 102 Jonathan Boulevard North, Chaska, Minnesota 55318. Other means for connecting tubing to pressure transducer 10 could be substituted for fittings 30 such as welding the tubing to inlet 36 and outlet 34 or using other types of fittings or methods known to those skilled in the art.

Pressure gauge 50, shown in FIGS. 2, 3 and 9, is configured to monitor a characteristic within sensor cavity 54 that correlates with the deflection of diaphragm 24, and produce an output signal that is representative of said characteristic. Therefore, the pressure within open interior 28 may be directly determined from said output signal. The output signal may be processed by an external processor to take into account various factors that may affect the accuracy of the output signal's relation to the pressure within open interior 28.

One embodiment of pressure transducer 10 is in-line pressure transducer 12 shown in FIGS. 1-3. Body 20 of pressure transducer 12 allows fluids to flow unimpeded between inlet 36 and outlet 34 along fluid flow course 26. As shown m FIG. 3, fluid flow course may be is circular and does not have any structural anomalies or features as a result of the adjacent pressure gauge portion 50 or the integral diapnragm 24. No quiescent areas are present in fluid flow course 26 that could result in the collection of contaminants, the production of air bubbles to the flowing fluid, or the reduction in pressure. Note that inlet 36 and outlet 34 are identified for the sake of explanation and the flow direction could also be reversed. In other words, the orientation of the device is bidirectional. Base portion 38 is used to secure pressure transducer 12 to a stable surface.

A second embodiment of pressure transducer 10 is αead-end pressure transducer 14 shown in FIGS. 6-9. Body 20 of pressure transducer 14 allows fluid 59 to access open interior 28 through inlet 36. As with pressure transducer 12, tuomg is connected to inlet 36 by way of fitting 30.

Pressure transducer 14 determines the pressure within open interior 28 through the monitoring of diaphragm 24 as discussed above. Diaphragm 24 is depicted as being positioned opposite inlet 36. It is apparent that the diaphragm 24 could be positioned otherwise. For example, pressure transducer 12 could be modified by capping outlet 34 to create a dead-end pressure transducer 14 where diaphragm 24 is not positioned opposite inlet 36. Referring to FIGS. 2, 3, 8 and 9 pressure gauge portion 50 can be viewed in detail (wiring omitted) . Pressure gauge portion 50 generally comprises pressure sensor unit 60, electrical circuitry 94 configured as a circuit board, and switchcraft connector 96. Pressure sensor unit 60 is generally configured to measure a measurable characteristic within pressure sensor region or cavity 54 that corresponds to the pressure within open interior 28. It is envisioned that the characteristic could be: the strain on exterior surface 25 of diaphragm 24; the pressure within sensor cavity 54; the displacement of diaphragm 24; or any other measurable characteristics that would correspond to the pressure within open interior 28.

One embodiment of pressure sensor 60 is depicted in FIGS. 2, 3, 8 and 9. In this embodiment, pressure sensor unit 60 is configured to measure the strain on exterior surface 25 of diaphragm 24. A suitable pressure sensor, as well as technical information, is available from Bourns Pressure Products, 1200 Columbia Avenue, Riverside, California 925507. As shown in FIGS. 4 and 5, pressure sensor 60 has hollow center area 62 and utilizes ceramic base 102 formed of alumina oxide and sapphire diaphragm 104 upon which is applied strain gauge tracings 106 configured as a wheatstone bridge. The size of sapphire 104 is approximately .2 inches square. Strain gauge tracings 106 engage exterior surface 25 of deflectable diaphragm 24 and measure the strain on that surface which relates to the pressure within open interior 28. A signal corresponding to the strain on exterior surface 25 is transmitted through flex tape 80 to circuitry 78. Other types of known pressure sensors may also be used, such as capacitive or piezoelectric sensors. Pressure sensor 60 is retained within sensor cavity 54 and maintained against surface 56 with sensor retention portion 64 and washer retainer 70. Sensor unit 60 may be further secured to exterior surface 25 of diaphragm 24 by way of epoxy 108 or other suitable means. Seals 66 and 68, depicted as o-rings, protect the remainder of pressure gauge 50 from leakage caused by a breach of deflectable diaphragm 24. Flex tape 80 extends from ceramic base 102 to the electrical circuitry 78 and provides for electronic communication between the two elements.

Electrical circuitry 77 is on a circuit board 78 and is maintained in electrical communication with pressure sensor unit 60 via flex tape 80 as shown in FIGS. 4 and 9. The analog output of the pressure sensor is suitably conditioned by way of the circuitry 77 to provide an electrical signal indicating a pressure reading. Such conditioning circuits are well known in the art. Circuitry 77 may be connected by way of electrical wires (not shown) to switchcraft connector 96. Mating connector 98 allows for electric communication between electrical circuitry 78 and the equipment used to monitor the pressure gauge 50.

Additional elements of pressure gauge 50 include EMI shielding can 88, o-ring 86, set screw 82, filter 84, o-ring 90, and cap 74. EMI shielding can 88 is optional and may be used if necessary. Set screw 82 has two purposes. First, it can be removed to provide access to the potentiometers of circuitry 78 to calibrate pressure gauge 50. Second, it provides a means to purge the interior compartment of air to equalize the interior pressure to ambient conditions.

In one embodiment of the invention, pressure gauge 50 may produce an analog output signal in the form of a varying current. The range of the output signal is from a minimum of 4 mA to a maximum of 20 mA. If the pressure within open interior 28 is equal to ambient pressure, a zero pressure difference, the corresponding amplitude of the output signal current will be 4 mA. A 20 mA output corresponds to a maximum pressure difference. This maximum pressure difference may be, for example, either 60 or 100 psig depending on the pressure gauge unit. Pressure gauge 50 can be adjusted for temperature changes and flow rates by adjusting the potentiometers of circuitry 78 or by compensating circuitry known in the art.

Referring to FIG. 10, a simple fluid flow circuit is shown comprising a source 100 of a caustic fluid, a pump 100, PFA tubing 108, an in-line flow through pressure monitoring device 110, processing equipment 116, and a dead-end pressure monitoring device 120. The flow through device suitable signal lines 124, 126 may connect the devices to a monitoring station 130. Alternatively, a reach out display 132 may be positioned at the device 120.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof; and it is, therefore, desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.

Claims

IN THE CLAIMS :

1. A pressure monitoring device formed of plastic for monitoring fluid pressure in a fluid circuit, the device comprising :

a) a plastic body portion having a non-pressure sensitive thick wall portion and an integral pressure- sensitive thin wall portion; the thick and thin wall portions defining an open interior extending between a first end and a second end and having a smooth interior surface; the device connectable with the fluid circuit at the first and second ends thereby exposing the open interior to the fluid circuit and allowing fluid to flow unimpeded from the fluid circuit through the open interior and back to the fluid circuit, the thin wall portion defining a pressure-sensitive deflectable diaphragm portion having an exterior surface, the deflection of the diaphragm portion correlating with the pressure withm the open interior and the fluid circuit; and

b) a pressure gauge portion positioned adjacent to the exterior surface of the diaphragm portion, the pressure gauge configured to monitor the deflection of the diaphragm portion whereby the pressure inside the fluid circuit can be monitored.

2. A pressure monitoring device for monitoring the pressure within a fluid circuit, the pressure monitoring device being formed of plastic and comprising integral thick and thin wall portions which define a smooth interior surface; the fitting device sealmgly connected to the fluid circuit thereby exposing the interior surface to the pressure of the fluid circuit; the thin wall portion being a pressure-sensitive deflectable diaphragm having an exterior surface, whereby the deflection of the diaphragm corresponds with the pressure within the fluid circuit.

3. The pressure monitoring device of claim 2, wherein the interior surface forms a seamless fluid flow course, and wherein tne fitting is connectable in-line with the fluid circuit, thereby providing an unimpeded course for fluid to flow.

4. The pressure monitoring device of claim 2, wherein the fitting is a dead-end fitting having a single opening to the fluid circuit which exposes the interior surface to the pressure within the fluid circuit.

5. The pressure monitoring device of claim 2 further comprising a pressure sensor region and a sensor positioned within the pressure sensor region, the sensor configured to detect a measurable physical characteristic which corresponds with the deflection of the diaphragm portion, whereby the pressure within the fluid circuit may be monitored by monitoring the measurable characteristic.

6. The pressure monitoring device of claim 5, wherein said sensing region is positioned proximate the exterior surface of the diaphragm, and wherein said exterior surface of the diaphragm expands as it deflects straining the exterior surface of the diaphragm, and wherein said measurable characteristic is the strain on said exterior surface.

7. A method for measuring the interior pressure of a fluid circuit comprising the steps of:

a) providing a pressure sensitive fitting having a cylindrical wall portion which defines a seamless fluid flow concourse, the cylindrical wall portion having a deflectable diaphragm portion which is thinner relative to the balance of the integral cylindrical wall portion, the deflection of the diaphragm portion corresponds to the interior pressure;

b) connecting the pressure sensitive fitting to the fluid circuit;

c) measuring a physical characteristic which corresponds to the deflection of the diaphragm;

d) determining the interior pressure using the measurement of the physical characteristic; and

e) producing an output signal corresponding to the interior pressure.

8. A method for measuring the interior pressure of a fluid circuit comprising the steps of:

a) providing a pressure sensitive fitting having an open interior, an inlet, and integral thick and thin wall portions, the thick and thin wall portions forming an interior surface, the thin wall portion being a deflectable diaphragm, the deflection of the diaphragm corresponding to the pressure within the open interior;

b) connecting the inlet of the pressure sensitive fitting to the fluid circuit, thereby exposing the open interior to the pressure within the fluid circuit;

e) producing an output signal corresponding to the interior pressure.

9. A method for manufacturing a pressure responsive device for use in caustic fluid flow circuits, the method comprising the steps of:

a) molding a body portion of an inert plastic molding, a thin wall diaphragm portion integral with a thick wall portion to define an open interior in a body portion; and b) placing a sensor adjacent the thin wall diaphragm portion to measure deflection of the thin wall diaphragm portion when open interior is pressurized with caustic fluid.