U.S. patent application number 10/196071 was filed with the patent office on 2002-12-05 for fluid flow controlling.
This patent application is currently assigned to Mott Metallurgical Corporation. Invention is credited to Balazy, Richard D., Cowan, Cathy L., Eisenmann, Mark R., Frink, Kenneth E., Kulha, Edward.
Application Number | 20020179150 10/196071 |
Document ID | / |
Family ID | 22612565 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020179150 |
Kind Code |
A1 |
Balazy, Richard D. ; et
al. |
December 5, 2002 |
Fluid flow controlling
Abstract
A method and system for controlling the rate of fluid flow. A
flow restrictor having known pressure drop and flow rate
characteristics provided in a passage through which the fluid,
preferably a gas, flows. An upstream pressure sensor determines the
pressure of fluid in the flow passage upstream of the flow
restrictor. A downstream pressure sensor determines the pressure of
fluid in the flow passage downstream of said flow restrictor. A
pressure regulator adjusts the pressure of fluid upstream or
downstream of the flow restrictor based on the pressure drop across
the flow restrictor so that the actual pressure drop across the
flow restrictor closely corresponds to the pressure drop associated
with a desired rate of fluid flow.
Inventors: |
Balazy, Richard D.;
(Terryville, CT) ; Cowan, Cathy L.; (Canton,
CT) ; Eisenmann, Mark R.; (Burlington, CT) ;
Frink, Kenneth E.; (Prospect, CT) ; Kulha,
Edward; (Canton Center, CT) |
Correspondence
Address: |
HALE AND DORR, LLP
60 STATE STREET
BOSTON
MA
02109
|
Assignee: |
Mott Metallurgical
Corporation
Farmington
CT
|
Family ID: |
22612565 |
Appl. No.: |
10/196071 |
Filed: |
July 15, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10196071 |
Jul 15, 2002 |
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10002556 |
Nov 1, 2001 |
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10002556 |
Nov 1, 2001 |
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09722937 |
Nov 27, 2000 |
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6422256 |
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09722937 |
Nov 27, 2000 |
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09168697 |
Oct 8, 1998 |
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6152162 |
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Current U.S.
Class: |
137/487.5 |
Current CPC
Class: |
Y10T 137/2562 20150401;
Y10T 137/7759 20150401; G05D 7/0635 20130101; Y10T 137/0379
20150401; Y10T 137/7761 20150401 |
Class at
Publication: |
137/487.5 |
International
Class: |
F16K 031/12 |
Claims
What is claimed is:
1. A gas system comprising: an inlet; an outlet; a flow passage
between the inlet and the outlet including at least two flow
passage portions which are oriented in an orientation different
from the orientation of the inlet and outlet; a shutoff valve
positioned in the flow passage and being movable in the orientation
of at least one of the flow passage portions; and an integrated
metal media contained in the flow passage and substantially filling
a cylindrical section of the flow passage.
2. The gas system of claim 1 wherein the metal media is a sintered
metal.
3. The gas system of claim 1 wherein the metal media is a
filter.
4. The gas system of claim 1 wherein the inlet and the outlet are
substantially parallel.
5. The gas system of claim 1 wherein the inlet and the outlet are
substantially aligned.
6. The gas system of claim 1 wherein one of the flow passage
portions is substantially perpendicular to the inlet and the
outlet.
7. The gas system of claim 1 wherein the at least two flow passage
portions are substantially perpendicular to the inlet and the
outlet.
8. The gas system of claim 1 wherein the shutoff valve is in
substantial alignment with the flow passage.
9. The gas system of claim 1 further comprising a pressure sensor
in fluid communication with the flow passage.
10. The gas system of claim 1 wherein the shutoff valve is disposed
in one of the flow passage portions and the valve is adjustable
between a first position in which it permits flow through said flow
passage portion and a second position in which it blocks flow
through said first passage portion.
11. The gas system of claim 1 wherein the shutoff valve comprises:
a valve member; a valve actuator for controlling movement of the
valve member between an open position and a closed position; and a
biasing member for biasing the valve actuator toward an open
position or a closed position.
12. The gas system of claim 11 wherein the biasing member is a
spring.
13. The gas system of claim 11 wherein the biasing member is a
diaphragm.
14. The gas system of claim 11 wherein the biasing member is a
bellows.
15. A gas system comprising a module having: an inlet; an outlet; a
flow passage between the inlet and the outlet; a first cross
passage extending from a portion of the flow passage to a top
portion of the module; a second cross passage extending from a top
portion of the module and intersecting the flow passage; and an
integrated metal media contained in the flow passage and
substantially filling a cylindrical section of the flow
passage.
16. The gas system of claim 15 wherein the first cross passage and
the second cross passage are substantially parallel.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The application is a continuation of now pending U.S. patent
application Ser. No. 10/002,556 filed Nov. 1, 2001 which is
continuation of U.S. patent application Ser. No. 09/722,937, filed
Nov. 27, 2000 which is a divisional of U.S. patent application Ser.
No. 09/168,697 filed Oct. 8, 1998 which issued as U.S. patent Ser.
No. 6,152,162 on Nov. 28, 2000.
FIELD OF THE INVENTION
[0002] This invention relates to fluid flow controlling and, more
particularly, to systems and methods for controlling gas flow.
BACKGROUND OF THE INVENTION
[0003] There are many industrial and other applications in which it
is necessary to measure and control the flow rate of fluids,
particularly gases. Typically, gas flow is measured and controlled
using volumetric flow devices such as turbine meters, rotometers,
thermal mass flow rate control devices, or sonic gas velocity
orifices.
[0004] The need for precision control is particularly acute in the
semiconductor industry. Computer chip manufacturing requires exact
control of various process fluids and gases, including but not
limited to hydrogen, silane, helium, nitrogen, oxygen and argon.
The current "stat of the art" in the semiconductor industry
utilizes a sophisticated gas delivery system, often referred to as
a gas panel incorporating "gas sticks", which includes a mass flow
controller, a pressure transducer, a filter, control vales and a
pressure regulator, all connected in series. The flow control
portion of these systems have high initial and maintenance costs,
require frequent calibration and service to avoid inaccuracies
caused by electronic drift and span, and may result in inaccurate
flow rates when very high or very flow rates are required.
[0005] In situations in which repeatability is more important than
absolute accuracy, precision calibrated orifices have been used to
provide a constant calibrated gas flow relative to gas supply
pressure; if multiple fixed flow rates are needed, a number of
orifices may be connected in parallel with each other with a
switching mechanism for selecting the appropriate orifice. However,
the use of such orifices is normally limited to applications that
require one or more constant, non-variable gas flows. Even in fixed
flow applications where their use is otherwise satisfactory, such
orifices require high gas velocities which cause excessive
turbulence, erosion therefore and flow instability, and are subject
to plugging.
[0006] Precision porous sintered metal flow restrictors, (e.g., of
the type manufactured and sold by Mott Corporation, the assignee of
the present application and which have hundreds of interconnected
through-pores or passages arranged both in parallel and series with
each other) are also used to provide a specified down-stream flow
relative to the applied upstream pressure. Such flow restrictors
are less susceptible to plugging, clogging and wear than are
conventional orifices, operate at relatively low flow velocities,
and provide a smooth and constant down-stream flow. Like orifices,
however, their use has been limited to applications that require an
essentially constant and non-variable flow.
[0007] There remains a need for a system that, like a thermal mass
flow controller, is capable of precisely measuring and controlling
fluid flow over a range of flow rates and pressures, but that is
more accurate over a wide range of flow rates, is less expensive,
and that requires significantly less calibration, servicing and
maintenance and is less susceptible to electronic drift and
span.
SUMMARY OF THE INVENTION
[0008] The present invention features a method and system for
controlling the rate of fluid, and particularly gas, flow which
uses pressure regulation rather than a control valve. A flow
restrictor having known pressure drop-flow rate characteristics is
provided in a passage through which the fluid flows, the pressure
drop across the flow restrictor is determined, and the pressure
drop of the fluid flowing through flow restrictor is adjusted so
that the actual pressure drop across the flow restrictor will
closely correspond to the pressure drop associated with a desired
flow rate.
[0009] In preferred embodiments a pressure regulator adjusts the
pressure of gas upstream or downstream of the flow restrictor based
on the pressure drop across the flow restrictor and with reference
to data defining the pressure drop-flow rate characteristics of the
flow restrictor, so that the actual pressure drop will closely
correspond to the pressure drop associated with a desired rate of
gas flow.
[0010] In particularly preferred embodiments, the flow restrictor
comprises a porous sintered metal element, an upstream pressure
sensor determines and provides data indicative of the pressure of
gas in the flow passage upstream of the flow restrictor, a
downstream pressure sensor determines and provides data indicative
the pressure of gas in the flow passage downstream of the flow
restrictor, the data from the sensors is compared with data
indicative of the desired rate of gas flow and the known data
representing the pressure drop-flow rate characteristics of the
flow restrictor, and the system controls a pressure regulator (and
hence gas pressure) on the basis of the comparison.
[0011] Fluid flow controllers embodying the invention comprise a
fluid flow passage in which such a flow restrictor is positioned,
and pressure sensors for determining the pressure of fluid flowing
in the flow passage positioned both upstream and down stream of the
flow restrictor. A pressure regulator responsive to the sensors
adjusts the pressure of the fluid either upstream or downstream of
the flow restrictor to provide a desired pressure drop across the
flow restrictors.
[0012] Preferred gas flow controllers have a pair of gas flow
passages connected in parallel between the inlet to and outlet from
the controller, the flow restrictor is positioned in one of the
flow passages, and a valve opens and closes one of the flow
passages to gas flow.
[0013] Some preferred systems are of modular construction and
include a plurality of stacked rectilinear modules. Typically one
of the modules defines a by-pass flow passage and includes a
control valve, others of the modules define a passage including the
flow restrictor, and an ultra-high efficiency gas filter may be
mounted in series with the flow restrictor. An electronics module
including a memory storing data representing the pressure drop-flow
rate characteristics of the flow restrictor receives signals from
pressure sensors and outputs a signal for controlling an upstream
pressure regulator.
[0014] Other objects, features and advantages of the present
invention will appear from the following detailed description of
preferred embodiments thereof, taken in connection with the
drawings.
DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a schematic illustration, partially in section, of
a flow control system embodying the present invention.
[0016] FIG. 2 is a graphical representation of the relationship
between gas flow and pressure drop in the system of FIG. 1.
[0017] FIGS. 3, 4, 5 and 6 are schematic illustrations, partially
in section, of other flow control systems embodying the present
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] FIG. 1 shows a flow control system, generally designated 10,
including a gas flow control module 12 connected in series between
an upstream pressure sensor 14 and a downstream pressure sensor 16.
In an alternative design, pressure sensors 14 and 16 are not part
of gas flow control module 12 but are mounted in close proximity to
inlet 22 and outlet 24, respectively. Gas from a source 18 flows
into system 10 through a pressure regulator 20. The pressure
regulator is adjustable to control the pressure of the gas flowing
into the gas flow control module 12.
[0019] Flow control module 12 has an inlet 22, an outlet 24, a flow
passage 26 extending between the inlet and outlet, and a porous
sintered metal flow restrictor 28 mounted in the flow passage 26. A
shutoff valve 30 is also provided in the flow passage. As shown,
shutoff valve 30 includes a valve actuator 32 (e.g., a solenoid or
driven pneumatic actuator) which controls the movement of a valve
member 34 between a full open position in which the head of the
valve member is spaced from a valve seat 36, and a closed position
(not shown) in which the head of the valve member sits on the valve
seat 36 and closes the flow passage. In the illustrated embodiment,
the valve member 34 is biased (e.g., by helical spring 38, or,
alternatively, by a diaphragm or bellows type mechanism) towards
its closed position, so that the valve 30 will automatically close
in the event of failure of power to actuator 32, designated as
"normally closed" valves can also be designed to operate as
"normally open" in the event of a power failure.
[0020] Flow restrictor 28 includes a porous sintered metal element
or porous sintered metal encapsulated assembly, secured in and
spanning the entire width of the flow passage 26. In the
illustrated embodiment, the flow restrictor 28 is mounted adjacent
to the outlet 24 of flow control module 12. The position of the
flow restrictor 28 within the flow passage 26 is not critical;
alternatively the flow restrictor could be placed, for example,
adjacent inlet 22 or in one of the short flow passage portions 26a,
26b closely upstream of or downstream from valve seat 36.
[0021] It is well known that the rate of fluid, e.g., gas or
liquid, flow through a porous sintered metal element depends on the
pressures upstream of and downstream from the element; the greater
the pressure drop across the porous clement the greater the rate of
flow through the element. Thus, the rate of flow through an element
can be increased by raising the pressure drop, and can be decreased
by lowering it. Conventionally, the flow rate and pressure drop are
varied by adjusting upstream pressure.
[0022] For any particular element, the precise relationship between
flow rate and pressure drop depends, not only on the element
itself, but also on the viscosity, density (if gas), and overall
pressure of the particular fluid flowing through the element. For
any particular fluid and pressure, the relationship between flow
rate and pressure drop can be determined empirically to a high
degree of accuracy (e.g., using precision volume meters and
pressure gauges which are traceable to standards of the National
Institute of Standards and Technology). The relationship between
pressure drop and fluid flow of a typical porous sintered metal
flow restrictor is shown in FIG. 2. The data in FIG. 2 illustrates
the flow characteristics, for hydrogen, helium, nitrogen, air,
oxygen and argon, of a standard process control Mott Flow
Restrictor that is nominally rated to deliver 100 SCCM (standard
cubic centimeters per minute) of nitrogen at an inlet pressure of
30 PSIG and an outlet to atmospheric pressure, i.e., when the
pressure drop across the flow restrictor is 30 PSI. As shown in
FIG. 2, at any given pressure drop the flow of hydrogen and helium
will be greater than, and the flow of air, oxygen and argon will be
less than, that of nitrogen. The flow rate of any of these gases
increases, non-linearly, with increasing pressure drops; for
example, when the pressure differential across the flow restrictor
is 20 PSI, the flow rate of nitrogen through the flow restrictor
having the characteristics are illustrated in FIG. 2 is about 60
SCCM, at a 30 PSI pressure differential it is 100 SCCM, and at 40
PSI it is about 160 SCCM. It is also evident and well-known that,
for any particular pressure drop, the amount of gas flowing through
the flow restrictor depends on the overall pressure level. For
example, for a given flow restrictor, the rate of gas flow (e.g.,
volume measured in standard cubic feet or liters per unit of time
in minutes) through the restrictor at an inlet pressure of 100 PSIG
and an outlet pressure of 70 PSIG will be greater than the rate of
flow when the inlet pressure is 30 PSIG and the outlet is at
atmospheric pressure.
[0023] The data that defines the pressure drop-flow rate
characteristics of a particular flow restrictor for one or more
fluids is referred to as the flow restrictors Flow Rate Control
Data. As a practical matter, it is desirable that the design of,
and the procedures used in the manufacture of, flow restrictors
used in the present invention be well-defined so that the Flow Rate
Control Data for different flow restrictors of the same design,
overall size and configuration will be consistent.
[0024] To control the rate of fluid flow through the system of FIG.
1, the pressures upstream and downstream of the flow restrictor 28
are monitored using pressure sensors 14, 16, the difference between
the upstream and downstream pressures is determined, and the
pressure of fluid flowing from pressure regulator 20 adjusted
(either upwardly or downwardly, as required) so that the measured
pressure drop across die flow restrictor 28 corresponds to the
pressure drop required to produce the desired flow. Again using the
exemplary data from FIG. 2, if the flow restrictor 28 of FIG. 1 has
the Flow Rate Control Data illustrated in FIG. 2, pressure
regulator 20 would be adjusted to provide a pressure drop of 20 PSI
across flow restrictor 28 to atmosphere to produce a nitrogen flow
of 60 SCCM, to provide a pressure drop of 30 PSI to atmosphere to
produce a nitrogen flow of 100 SCCM, and to provide a pressure drop
of 40 PSI to atmosphere to produce a nitrogen flow of 160 SCCM.
[0025] In many circumstances, the pressure downstream of flow
restrictor 28 will be greater than atmospheric pressure and the
pressure drop across the flow restrictor thus will be somewhat less
than, rather than the same as, the outlet pressure of regulator 20.
If, however, the outlet of the fluid flow manager 12 is
sufficiently open so that the pressure downstream of flow
restrictor 28 is substantially equal to atmospheric pressure, the
pressure drop across the flow restrictor 28 will be substantially
equal to the gage pressure indicated by inlet pressure sensor 14
(and also to the outlet pressure of regulator 20). In these
circumstances it is possible in some applications not to have or
utilize a downstream pressure sensor 16, and to control flow
through the flow control system 10 simply by increasing the
upstream pressure and assuming that the upstream gage pressure is
equal to the pressure drop across flow restrictor 28. In general,
however, at the same differential pressure, higher system inlet and
outlet pressures will result in increased flow through the
restrictor.
[0026] It will be appreciated that, using conventional powder
metallurgy processing techniques, porous sintered metal flow
restrictors can be made for a wide range of desired target flow
rates, e.g., within 2% of a desired target flow at outlet pressures
ranging from full vacuum to 100 or more PSI, by varying the size
and/or structure of the porous metal element. Porous sintered metal
flow restrictors can be individually calibrated to obtain tighter
flow tolerances, e.g., plus or minus 0.5% or better. For example,
if the target flow is 200 SCCM of a gas at a 30 PSI pressure drop,
this may be accomplished either or by using an element whose
configuration, size and porosity are such that it has the same Flow
Rate Control Data as the element that illustrated in FIG. 2 except
with twice the face area, or by making a thinner or more open
element. Similarly, a target flow of 100 SCCM at 20 PSI may be
accomplished using a thinner or more open element or by using an
element having the same Flow Rate Control Data but about 1.43
(100/70) times the face area, and a target flow of 50 SCCM at 30
PSI may be accomplished using a thicker or more closed element or
an element having half the face area. Flow restrictors having a
variety of different rated flows at different pressures are
commercially available.
[0027] FIG. 3 illustrates a flow control system, generally
designated 100, that is generally similar to the system of FIG. 1
except its valve controller controls by-pass flow rather than
providing shutoff capability. The location of the flow restrictor
in the FIG. 3 embodiment is more critical to the device's operation
than is the case with the FIG. 1 system. Portions of system 100
that correspond to portions of system 10 are identified using the
same reference number, with a "1" prefix added.
[0028] As shown, the system 100 of FIG. 3 includes a gas flow
control module 112 connected in series between an upstream sensor
114 and a downstream pressure sensor 116. As with the design of
FIG. 1, pressure sensors 114 and 116 may be mounted in close
proximity to inlet 122 and outlet 124, respectively, rather than
being part of module 112. Gas from source 118 flows into system 100
through a pressure regulator 120.
[0029] Gas flow control module 112 has an inlet 122, an outlet 124,
and a flow passage 126 extending between the inlet and outlet. As
shown, the central portion of flow passage 126 includes two
parallel-connected flow passage portions, designated 125 and 127. A
porous sintered metal flow restrictor 128 is mounted in flow
passage portion 125. A shutoff valve 130 is provided in flow
passage portion 127. As shown, shutoff valve 130 includes a valve
actuator 132 (e.g., a solenoid or pneumatic actuator) which
controls the movement of a valve member 134 between a fully open
position (not shown) in which the head of the valve member is
spaced from a valve seat 136 and a closed position (shown) in which
the head of the valve member sits on the valve seat 136 and closes
the flow passage portion 127. As will be evident, flow passage
portion 127 provides a by-pass flow in which flow from inlet 122
can pass, essentially unrestricted, to outlet 124 when valve 130 is
open. When, on the other hand, valve 130 is closed, all flow passes
through flow passage portion 125 and the flow restrictor 128
mounted therein.
[0030] When valve 130 is closed, the rate of gas flow through gas
flow control module 112 is controlled by monitoring pressure
sensors 114 and 116. In the embodiment of FIG. 1, and in the
normally preferred practice with the gas flow control module 112 of
FIG. 3, the pressure drop across the flow restrictor (as determined
by the upstream and downstream pressure sensors) is varied using a
pressure regulator 120 upstream of the upstream pressure sensor
114.
[0031] FIG. 3, however, also illustrates an alternative procedure.
In this alternative procedure, the upstream pressure regulator 120
may be omitted or replaced by a constraint outlet pressure drive, a
pressure flow regulator, e.g., an adjustable flow control valve
120a (shown in phantom in FIG. 3), may be mounted downstream of
pressure sensor 116. In this alternative procedure, the gas flow
from source 118 is not controlled by an upstream pressure regulator
such as regulator 120. This alternative, and as should be apparent,
the rate of gas flow through the gas flow control module 100 and
also the pressure of gas downstream of flow restrictor 128, may be
varied by opening and closing valve 120a. If, thus, the pressures
indicated by sensors 114, 116 show that the pressure drop across
flow restrictor 128 is less than that corresponding to the desired
rate of flow, the rate of gas flow through (and pressure drop
across) flow restrictor 128 may be increased by opening valve 120a.
Similarly, closing valve 120a will reduce both the rate of gas flow
through, and the pressure drop across, flow restrictor 128.
[0032] FIG. 4 illustrates a flow control system, generally
designated 200. Whereas systems 10 and 100 provided a single
controlled flow, system 200 provides two controlled flows and also
a by-pass flow. Portions of system 200 that correspond to portions
of system 10 are identified using the same reference number, with a
"2" prefix added; e.g., the gas flow control system 10 is
identified as gas flow control module 12, while that of system 200
is identified as gas flow control module 212.
[0033] As shown, gas flow control module 212 has a single inlet
222, and three outlets, designated 224a, 224b and 224c. A
conventional four-way valve 230 provides for flow from inlet 222 to
a selected one of the outlets, and also provides an "off" for
preventing any flow through flow manager 210. A manifold system
with four on/off control valves (not shown) could be used instead
of four-way valve. One porous sintered metal flow restrictor 228a
is mounted in the flow passage 226a leading to outlet 224a, and a
second porous sintered metal flow restrictor 228b is mounted in the
flow passage 226b that leads to outlet 224b. An upstream pressure
sensor 214 is provided between the inlet 222 to flow control module
212 and pressure regulator 220. Two downstream pressure sensors
216a, 216b are provided, one adjacent to each of outlets 224a,
224b, downstream of flow restrictors 228a and 228b. As will be
appreciated, pressure sensors 214 and 216a are used to measure the
pressure drop across flow restrictor 228a, and pressure sensors 214
and 216b are used to measure the pressure drop across flow
restrictor 228b. As also will be appreciated, flow restrictors 228a
and 228b may have different pressure-flow characteristics; for
example, flow restrictor 228a may be selected to provide 200 SCCM
at a 30 PSI pressure drop at a particular outlet pressure while
flow restrictor 228b is selected to provide 50 SCCM at either the
same or a different pressure drop at the same or a different outlet
pressure. Thus, depending on the position of valve 230, outlet 224a
may provide a controlled 200 SCCM output, outlet 224b may provide a
controlled 50 SCCM output, and the full output gas flow from
pressure regulator 220 may be obtained from outlet 224c. If a
controlled 200 SCCM output is required, valve 230 is set to direct
flow through outlet 224a and an operator (or the system
automatically) will monitor sensors 214 and 216a and adjust
pressure regulator 220 to maintain a 30 PSI pressure drop across
flow restrictor 228a. If, on the other hand, a controlled 50 SCCM
output is required, valve 230 directs flow through outlet 224b and
the operator monitors sensors 214 and 216b and adjusts pressure
regulator 220 to maintain the then-desired pressure drop across
flow restrictor 228b. It will be noted that, depending on the
particular flow restrictors and desired flows, the pressure of gas
output from regulator 220 may be very different when the controlled
flow is through flow restrictor 228a and outlet 224a than when the
flow is through flow restrictor 228b and outlet 224b.
[0034] FIG. 5 illustrates a fourth system, generally designated
300, embodying the present invention. As shown, system 300 is
modular construction and includes a gas flow control module 312
consisting of a top module 302 with a flow restrictor 328 therein
mounted on top of the bottom flow module 301. Bolts 303 hold the
two modules together, and seals 309 are provided where flow
passages extend from one module into the other. As before, portions
of system 300 corresponding to portions of previously discussed
systems are identified using the same reference numbers having the
same two last digits, with a "3" prefix added.
[0035] Top module 302 includes a through-drilled flow passage 326,
and two cross-passages designated 305 and 307. Cross passage 305
extends from the center of through passage 326 downwardly to the
top of module 301. Cross passage 307 extends diagonally from the
bottom of module 302 and intersects drilled passage 326 more
closely adjacent the outlet end 324 of passage 326. In module 301,
a generally u-shaped passage 323 communicates at one end with
cross-passage 305, and at its other end with second cross passage
307.
[0036] Flow restrictor 328 is mounted in the lower portion of
cross-passage 305, closely adjacent the top of module 301. A
three-way manual valve 330 is mounted at the intersection of
passages 326 and 305. In its fully closed position, valve 330
prevents through flow from inlet 322 to outlet 324, either directly
through passage 326 or through cross passages 305, 307. In a second
position, valve 330 closes passage 326 to through flow, but permits
flow from the inlet portion 326-i of passage 326, through cross
passage 305 and u-shaped passage 323, and then through cross
passage 307 and the downstream portion 326-o of passage 326 to
outlet 324. In its third position, valve 330 permits flow through
the drilled passage 326 while preventing flow through the cross
passages 305, 307 and the u-shaped passage 323 in module 301.
[0037] Alternatively, to valve 330 a manual on/off valve 332 (
shown in phantom in FIG. 5) may be mounted in passage 326 after the
intersection of passages 326 and 305 and before the intersection of
passage 307 and 326. Valve 332 divides flow passage 326 into two
sections, inlet flow passage 326-i and outlet passage 326-o. In its
fully closed position, valve 330 directs the gas flow from inlet
322 and flow passage 326-i, through flow passages 305 and 307, and
then through flow passage 326-o to outlet 324. In its fully open
position, valve 330 allows a bypass flow by permitting flow
directly through drilled passage 326, and also permits flow
(typically at a much lower rate of flow) through the cross passage
305 with restrictor 328, u-shaped passage 323 and passage 307 in
modules 301 and 302. An additional on/off valve (not shown) may
also be mounted in flow passage 326-i between pressure regulator
320 and the intersection of flow passages 326-I and 305 to provide
positive shut off capability.
[0038] Manual pressure regulator 320 is mounted between valve 330
and the inlet to module 302. As in the previously discussed
embodiments, inlet pressure sensor 314 monitors the pressure of gas
upstream of valve 330 and flow restrictor 328, and downstream
pressure sensor 316 monitors the pressure of gas downstream of the
valve and flow restrictor.
[0039] In the embodiments of FIGS. 1, 3, 4 and 5, the pressure
sensors shown are conventional pressure gauges from which an
operator may visually determine the particular pressure and thus
obtain the data necessary to determine the pressure drop across the
relevant flow restrictor. Alternatively, conventional electronic
pressure sensors, which provide an analog or digital signal
representative of the particular pressure, may be used. Such
electronic pressure sensors may provide a printed or other visual
output. In automated systems, the pressure sensors provide pressure
signals to an automatic controller which in turn determines the
pressure drop(s) across die flow regulator(s) and controls a
pressure regulator as required to maintain the pressure drops that
produces the desired flow(s). Similar automated systems are
well-known in the art.
[0040] FIG. 6 illustrates a fifth gas flow control system embodying
the invention, generally designated 400, which also is of modular
construction but which additionally includes a gas flow manager
control system. Portions of system 400 which correspond to portions
of system 10 are identified using tie same reference numbers used
in connection with system 10, with the prefix "4" added.
[0041] As illustrated, system 400 includes six stacked blocks or
modules: bypass valve module 401, restrictor and pressure sensor
module 402, pressure control and sensor module 403, filter module
404, electronics module 405, and input/readout module 406. Each
module is generally rectilinear in shape, and the various modules
are stacked, one above (or in the case of modules 403 and 404, also
beside) another. Where flow passages extend from one block into
another, the passages are sealed by metal seals or O-rings, e.g.,
rings 409, at the juxtaposed faces of the adjacent blocks.
[0042] By-pass module 401 includes a through flow passage 421
having a gas inlet 422 at one end and a gas outlet 424 at the other
end, and also a pair of inlet and outlet flow passages 401-i,
401-o, each of which extends from through passage 421 upwardly to
the top face of module 401. A 3-way valve 430 is mounted in flow
passage 421 at its intersection with inlet flow passage 401-i. In
one position, valve 430 directs flow from inlet 422 directly to
outlet 424, in a second it directs the flow from inlet 422 into
inlet-flow passage 401-i, and in its third position the valve
closes off flow from inlet 422.
[0043] An alternative design replaces 3-way valve 430 with a shut
off valve 432 (shown in phantom in FIG. 6) located in passage 421
between inlet flow passage 401-i and outlet flow passage 401-o.
This alternative design allows flow through the inlet passages 422,
401-i, 402-i, 403-i, 404-i, through flow restrictor 428, and
through outlet passages 404-o, 402-o, 401-o and 424 when the valve
432 is fully closed. When fully open, valve 432 allows bypass flow
through the flow passage 421 and also, typically at a lesser rate
of flow, through the inlet passages 422, 401-i, 402-i, 403-i,
404-i, through flow restrictor 428, and through outlet passages
404-o, 402-o, 401-o and 424.
[0044] Restrictor and sensor module 402 is mounted on top of bypass
valve module 401. Module 402 is stepped in longitudinal cross
section; its thinner portion includes an inlet flow passage 402-i
communicating at its lower end with inlet flow passage 401-i of
module 401; and its thicker portion has an inlet flow passage
402-i, in which a porous sintered metal flow restrictor 428 is
mounted, extending downwardly from the top of module 402 and
communicating with an outlet flow passage 402-o that communicates
at its lower end with outlet passage 401-i of module 401. A
downstream pressure sensor 416 is positioned in a tapped cross-bore
that intersects the lower portion of inlet flow passage 402-i below
flow restrictor 428 in position to sense the pressure of gas
downstream of the flow restrictor.
[0045] Pressure regulator module 403 includes a through flow
passable 423 including an inlet flow passage portion 403-i
communicating at its lower end with passage 402-i of module 402 and
an outlet portion 403-o at tie other end of the module. A pressure
regulator 420 is mounted in inlet flow passage portion 403-i, and
an upstream pressure sensor 414 is provided in passage 423
downstream of pressure regulator 420.
[0046] Filter module 404 includes an inlet flow passage 404-i
communicating with outlet passage flow portion 403-o of module 403,
and an outlet flow passage 404-o communicating with inlet passage
402-i of restrictor and sensor module 402. A cup-shaped, sintered
porous metal ultra-high efficiency (e.g., 9 log reduction) filter
440 is provided between inlet flow passage 404-i and outlet passage
404-o. Filter 440 is of the general type illustrated by U.S. Pat.
Nos. 5,114,447 and 5,487,771 and in co-pending application Ser. No.
08/895,605, all of which are hereby incorporated by reference. As
is known in the art, such 9 log filters are capable of removing
99.9999999% of the particles in an inlet process stream, determined
at the most penetrating particle size which is typically about 0.1
micrometer.
[0047] Electronics module 405 includes a memory section 450
containing the Flow Rate Control Data of restrictor 428, and a
comparator section 452 that receives data representative of the
inlet and outlet gas pressures sensed by pressure sensors 414 and
416 and data representative of the desired flow rate from, for
example, input/readout module 406, uses the Flow Rate Control Data
from memory section 450 to determine whether the actual flow rate
is the same (within any permitted tolerance) with the desired flow,
and (if required) outputs a signal to increase or decrease (as
required) the pressure output by pressure regulator 420.
[0048] Input/readout module 406 includes inputs (e.g., a keyboard
entry pad 454) for inputting the desired gas flow rate and,
optionally, other inputs such as the type of gas, process cycle
times and gas flow periods, so that an operator may visually
monitor the operation. Module 406 also includes outputs (e.g.,
digital displays 456) which show process or flow related data
including the real-time inlet and outlet pressures, the desired (or
set) flow rate, and the actual flow rate.
[0049] In operation, the empirically determined Flow Rate Control
Data for the flow restrictor 428 and the specified process gas
included in system 400 is loaded into the memory section of
electronics module 406 by the user or, if the flow restrictor is
that originally supplied, by the manufacturer of the system 400.
Gas inlet 422 is connected to a source of process gas 418 and gas
outlet 424 is connected to the inlet of the semiconductor
manufacturing operation that requires the process gas. The user
enters the desired flow rate, and perhaps other process data
depending on the particular system, into module 406 using keyboard
entry pad 454. A valve control sets 3-way valve 430 in the desired
(off, controlled flow, by-pass flow) position.
[0050] When valve 430 is set to direct flow in the controlled flow
mode, i.e., into system 400 through inlet 422, and then through
filter 440 and flow restrictor 428 to system outlet 424, upstream
and downstream sensors 414 and 416 measure the gas pressures
upstream and downstream of flow restrictor 428. The data from
sensors 414, 416, together with the desired flow rate data from
module 406, is sent to the electronics module 405. Electronics
module 405, in turn, continuously monitors the input data and
continuously adjusts (as required) pressure regulator 420 to insure
that the actual flow through the system precisely corresponds to
that desired.
Other Embodiments
[0051] The flow restrictor used in the above-described embodiments
is a porous sintered element of the type now being made and sold
by, among others, Mott Corporation. It will be appreciated that
other three-dimentional porous elements also may be used. For
example, porous metal flow restrictors are also manufactured by GKN
Sinter Metals (Terryville, Conn.), SSI Sintered Specialties
(Janesville, Wis.) and Chand Associates (Worcester, Mass.). Porous
sintered metal media such as those used by Pall Corp. and Millipore
Corporation for high efficiency gas filters could be used for flow
restrictors, particularly if additional processing were employed to
control the density and flow properties more accurately than is
typically required for filter applications. Other porous materials
such as ceramics and plastics, high density foams, and foam/powder
composites such as those disclosed in co-pending U.S. patent
application Ser. No. 09/074,957 filed May 8, 1998 (which is hereby
incorporated by reference) also could be employed as the porous
elements in flow restrictors. In the broadest sense, and as used in
this application, the term "flow restrictor" encompasses any
three-dimensional porous structure that defines a through-flow
matrix including a multiplicity of pores or passages through which
gas flows such that, for a particular gas and over a range of
pressures, the rate of gas flow through the structure depends on
the pressure drop across the structure and the pressure drop-flow
rate characteristics are well defined.
[0052] It will be further appreciated that the scope of the present
invention is not limited to the above-described embodiments, but
rather is defined by the appended claims; and that these claims
will encompass modifications of and improvements to what has been
described.
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