Source: http://www.freepatentsonline.com/9010369.html
Timestamp: 2019-02-19 21:23:28
Document Index: 545839302

Matched Legal Cases: ['Application No. 2005', 'art; 5', 'art\n5', 'art\n34', 'art\n35', 'art\n36', 'art\n40', 'art, 2', 'art, 5', 'art 1', 'art 4', 'art 1', 'arts 34', 'arts 34', 'art 1', 'art 36', 'art 38', 'art 39', 'art 39', 'art 38', 'art 36', 'art 36']

Flow rate range variable type flow rate control apparatus - Fujikin Incorporated
United States Patent 9010369
A pressure type flow rate control apparatus is provided wherein flow rate of fluid passing through an orifice is computed as Qc=KP1 (where K is a proportionality constant) or as Qc=KP2m (P1−P2)n (where K is a proportionality constant, m and n constants) by using orifice upstream side pressure P1 and/or orifice downstream side pressure P2. A fluid passage between the downstream side of a control valve and a fluid supply pipe of the pressure type flow rate control apparatus comprises at least 2 fluid passages in parallel, and orifices having different flow rate characteristics are provided for each of these fluid passages, wherein fluid in a small flow quantity area flows to one orifice for flow control of fluid in the small flow quantity area, while fluid in a large flow quantity area flows to the other orifice for flow control of fluid in the large flow quantity area.
Saito, Masahito (Tokyo, JP)
Hino, Shoichi (Tokyo, JP)
Shimazu, Tsuyoshi (Miyagi, JP)
Miura, Kazuyuki (Miyagi, JP)
Sugita, Katsuyuki (Osaka, JP)
Hirose, Takashi (Osaka, JP)
Shinohara, Tsutomu (Osaka, JP)
Imai, Tomokazu (Osaka, JP)
Yoshida, Toshihide (Osaka, JP)
Tanaka, Hisashi (Osaka, JP)
13/763178
National University Corporation Tohoku University (Miyagi, JP)
137/601.01, 137/601.13
G05D7/06; G01F1/36; G01F1/684; G01F5/00; G01F7/00
137/599.06, 137/599.07, 137/487, 137/488, 137/601.01, 137/601.13, 137/601.14
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6997202 Gas storage and dispensing system for variable conductance dispensing of gas at constant flow rate 2006-02-14 Olander 137/2
6591851 Seal-gas valve device 2003-07-15 Palten et al. 137/12
6539968 Fluid flow controller and method of operation 2003-04-01 White et al.
6422264 Parallel divided flow-type fluid supply apparatus, and fluid-switchable pressure-type flow control method and fluid-switchable pressure-type flow control system for the same fluid supply apparatus 2002-07-23 Ohmi et al.
6314992 Fluid-switchable flow rate control system 2001-11-13 Ohmi et al.
5938425 Method and device for control of the flame size of gas-fired cooking or baking appliances 1999-08-17 Damrath et al. 431/62
5875817 Digital gas metering system using tri-stable and bi-stable solenoids 1999-03-02 Carter 137/599.06
5816285 Pressure type flow rate control apparatus 1998-10-06 Ohmi et al.
5735787 Centrifugal separator with flow regulator and method 1998-04-07 Lorey 494/5
5669408 Pressure type flow rate control apparatus 1997-09-23 Nishino et al.
5645866 Pressure controlling and/or regulating device for a fluid medium, in particular air or gas 1997-07-08 Eckardt et al. 425/130
5269334 Fluid flow control system 1993-12-14 Eastman 137/12
5069252 Orifice system intermediate interface 1991-12-03 Kendrick et al.
4979639 Beverage dispenser control valve and ratio control method therefor 1990-12-25 Hoover et al. 222/1
4633911 Orifice plate seal 1987-01-06 Lohn
4518011 Control valve unit for the cylinder of a fluid actuator 1985-05-21 Stoll 137/596.17
4478246 Method and apparatus for proportioning of fuel usage by a fluid fueled apparatus 1984-10-23 Sherrod 137/557
4431020 Flow-control system having a wide range of flow-rate control 1984-02-14 Kowalski
4313465 Method and control device for dosing flow media 1982-02-02 Holzem et al. 137/599.07
4089007 Digital flow pressure regulator 1978-05-09 Perry et al. 347/6
3999572 Fluid flow instrumentality 1976-12-28 Mohr 137/599.07
3963043 Pressure sensing method and apparatus for gases 1976-06-15 Cota et al. 137/487.5
3831845 FLUID DELIVERY SYSTEM 1974-08-27 Pacht 239/76
3830256 FLUID MIXING 1974-08-20 Cox 137/599.04
3827457 FLUID PRESSURE SYSTEM FOR CONVERTING DIGITAL SIGNALS TO ANALOG SIGNALS 1974-08-06 Vutz et al. 137/599.07
3411669 Beverage dispenser regulation and the like 1968-11-19 Puster
3375845 Fluid flow device 1968-04-02 Behm 137/110
3081942 Digital-to-analog control system 1963-03-19 Maclay 341/151
2229903 Metering valve 1941-01-28 Schmohl et al. 137/599.05
1938460 N/A 1933-12-05 Muff
JP3033566 February, 1991
JP06004139 January, 1994
JP08087335 April, 1996
JP8338546 December, 1996
JP09330128 December, 1997
JP10055218 February, 1998
JP11125398 May, 1999
JP11265215 September, 1999
JP11265216 September, 1999
JP2000020135A 2000-01-21 FLOW RATE CONTROLLER
JP2000322130A 2000-11-24 METHOD FOR VARIABLE FLUID FLOW RATE CONTROL BY FLOW FACTOR AND ITS DEVICE
JP200066732 September, 2001
JP2003195948A 2003-07-11 IMPROVED PRESSURE TYPE FLOW CONTROL DEVICE
JP2004510225A 2004-04-02
JP2004199109A 2004-07-15 FLOW CONTROL METHOD FOR FLUID USING PRESSURE-TYPE FLOW CONTROLLER
JP2004243333A 2004-09-02 WELDING APPARATUS AND WELDING METHOD
JP2004278614A 2004-10-07 WAFER TYPE ORIFICE TRAP
JP2005115501A 2005-04-28 CHAMBER INTERNAL PRESSURE CONTROLLER AND INTERNAL PRESSURE CONTROLLED CHAMBER
JP2005149075A 2005-06-09 FLUID CONTROLLER
JP2005180527A 2005-07-07 LEAK VALVE
JP2000066732A 2000-03-03
JPH1055218A 1998-02-24
JPH09330128A 1997-12-22
JPH11265216A 1999-09-28
JPH11125398A 1999-05-11
WO2002025391A1 2002-03-28
JPH11265215A 1999-09-28
JPH0887335A 1996-04-02
JPH0333566A 1991-02-13
JPH064139A 1994-01-14
International Search Report issued in corresponding application No. PCT/JP2006/31295, dated Sep. 6, 2006, mailed Sep. 19, 2006.
International Search Report and Written Opinion completed Jul. 11, 2006 and mailed Jul. 25, 2006 in related international application No. PCT/JP2006/309368.
http://www.weisz.com/information/tablas%20tecnicas—pdf/Steel—grades—equivalence—table.pdf, downloaded Sep. 20, 2012.
Office Action issued on Jun. 25, 2012 in co-pending related U.S. Appl. No. 11/913,271.
This is a Divisional Application of U.S. Ser. No. 11/913,277, filed Feb. 16, 2010, which is a National Phase Application in the United States of International Patent Application No. PCT/JP2006/312952 filed Jun. 22, 2006, which claims priority on Japanese Patent Application No. 2005-185845, filed Jun. 27, 2005. The entire disclosures of the above patent applications are hereby incorporated by reference.
1. A flow rate range variable type flow rate control apparatus comprising: (a) a pressure type flow rate control apparatus that operates to control flow rate Qc of fluid passing through an orifice according to the relationship Qc=KP1 when a critical condition between P1 and P2 is present, where K is a proportionality constant, or the pressure type flow rate control apparatus operates to control the flow rate Qc through the orifice according to the relationship Qc=KP2m (P1−P2)n when the critical condition between P1 and P2 is not present, where K is the proportionality constant, and m and n are constants, wherein P1 is an orifice upstream side pressure and P2 is an orifice downstream side pressure; and (b) a first fluid passage disposed between a downstream side of a control valve and a fluid supply pipe of the pressure type flow rate control apparatus, wherein the first fluid passage includes an orifice for effecting flow control of fluid flowing in a small flow quantity range and an orifice for effecting flow control of fluid flowing in a medium flow quantity range, wherein the orifices for effecting small and medium flow quantity are in series and located between the downstream side of the control valve and the fluid supply pipe, wherein a first switching valve is parallel to the orifice for effecting flow control of fluid flowing in the small flow quantity range, wherein a second switching valve and an orifice for effecting flow control of fluid flowing in a large flow quantity range are provided in series with one another and are parallel to the orifice for effecting flow control in the medium flow quantity range, such that when the first switching valve is open and the second switching valve is closed then fluid is made to flow through the orifice for effecting flow control of fluid flowing in the medium flow quantity range and thence to the fluid supply pipe, and wherein the first and second switching valves are operably connected so that when the first switching valve and the second switching valve are open then a part of fluid flowing from the first switching valve is made to flow through the orifices for effecting flow control of fluid flowing in the medium flow quantity range and a rest of fluid flowing from the first switching valve is made to flow through the second switching valve and thence through the orifices for effecting flow control of fluid flowing in the large flow quantity range, and then respective fluid flows are fed to the fluid supply pipe, wherein the first and second switching valves are operably connected so that using only the first and second switching valves, fluid flow is controlled in three flow quantity ranges: the small flow quantity range, the medium flow quantity range, and the large flow quantity range.
2. A flow rate range variable type flow rate control apparatus as claimed in claim 1, wherein fluid flowing through the orifice for effecting flow control of fluid flowing in a small flow quantity range is fluid under the critical condition.
3. A flow rate range variable type flow rate control apparatus as claimed in claim 1, wherein when the first and second switch valves are both closed then fluid flow is directed into the orifice for effecting flow control of fluid flowing in the small flow quantity range and thence to the fluid supply pipe via the orifice for medium flow quantity.
In FIG. 7(a) and FIG. 7(b), 3 designates an orifice upstream side pipe; 4 designates a valve driving part; 5 designates an orifice downstream side pipe; 9 designates a valve; 15 designates a flow rate conversion circuit; 10, 11, 22, 28 designate amplifiers; 7 designates a temperature detector; 17, 18, 29 designate A/D converters; 19 designates a temperature correction circuit; 20, 30 designate computation circuits; 21 designates a comparison circuit; Qc designates a computation flow rate signal; Qf designates a switching computation flow rate signal; Qe designates a flow rate setting signal; Qo designates a flow rate output signal; Qy designates a flow rate control signal; P1 designates orifice upstream side gas pressure; P2 designates orifice downstream side gas pressure; and k designates a flow rate conversion rate. The afore-mentioned pressure type flow rate control apparatus FCS shown in FIG. 7(a) is mainly used either in the case where the ratio P2/P1 of the orifice upstream side gas pressure P1 and the orifice downstream side gas pressure P2 is equal to the critical value of a fluid, or in the case where the ratio P2/P1 is lower than the critical value (that is, when a gas flow is constantly under the critical state). The gas flow rate Qc passing through the orifice 8 is given by Qc=KP1 (where K is a proportionality constant).
The afore-mentioned pressure type flow rate control apparatus FCS shown in FIG. 7(b) is mainly used for the flow rate control of gases that will be in the flow condition in both the critical and non-critical states. The flow rate of a gas passing through an orifice is given, in this case, by Qc=KP2m(P1−P2)n (where K is a proportionality constant, m and n are constants).
With the afore-mentioned pressure type flow rate control apparatus in FIG. 7(a) and FIG. 7(b), the setting value of the flow rate is given by a voltage value as Qe, the flow rate setting signal. For example, suppose that the pressure control range 0˜3 (kgf/cm2 abs) of the upstream side pressure P1 is expressed by the voltage range 0˜5V, then Qe=5V (full scale value) becomes equivalent to the flow rate Qc=KP1 at the pressure P1 of 3 (kgf/cm2 abs). For instance, when the conversion rate k of the flow rate conversion circuit 15 is set at 1, a switching computation flow rate signal Qf (Qf=kQc) becomes 5V if the flow rate setting signal Qe=5V is inputted; thus, a control valve 2 is operated for opening and closing until the upstream side pressure P1 becomes 3 (kgf/cm2 abs) in order to allow the gas of flow rate Qc=KP1, corresponding to P1=3 (kgf/cm2 abs), to flow through the orifice 8.
In the case where the pressure range to control is switched to 0˜2 (kgf/cm2 abs), and the pressure range is expressed by a flow rate setting signal Qe of 0˜5(V) (that is, when a full scale value 5V gives 2 (kgf/cm2 abs)), the afore-mentioned flow rate conversion rate k is set at 2/3. As a result, if a flow rate setting signal Qe=5(V) is inputted, the switching computation flow rate signal Qf becomes Qf=5×2/3(V) because of the relationship Qf=kQc. And thus, the control valve 2 is operated for opening and closing until the upstream side pressure P1 becomes 3×2/3=2 (kgf/cm2 abs).
In other words, the full scale flow rate is converted so that Qe=5V expresses a flow rate Qc=KP1 equivalent to P1=2 (kgf/cm2 abs). Under a critical condition, the flow rate Qc of a gas passing through the orifice 8 is given by the afore-mentioned equation Qc=KP1. However, when the type of gas whose flow rate is to be controlled changes, then the afore-mentioned proportionality constant K also changes if the same orifice 8 is in use.
It is also same, in principle, with the afore-mentioned pressure type flow rate control apparatus in FIG. 7(b). The flow rate Qc of a gas passing through the orifice 8 is given by Qc=KP2m (P1−P2)n (where K is a proportionality constant, and m and n are constants). When the type of gas changes, the afore-mentioned proportionality constant K also changes.
With a pressure type flow rate control apparatus, especially with an apparatus that employs the method with which computation control is performed as a flow rate Qc=KP1 under the critical state as shown in FIG. 7(a), the flow rate control range becomes gradually narrower as the orifice secondary side pressure P2 (that is, a chamber and the like to which a gas is supplied) rises. The reason for this is that because the orifice primary side pressure P1 is controlled at a certain pressure value complying with a flow rate setting value, it is inevitable that the correction range of the orifice primary side pressure P1, that is, the control range of a flow rate Qc by means of P1, becomes narrower as the orifice secondary side pressure P2 rises under the conditions in which P2/P1 satisfies the critical expansion conditions.
Also, to overcome difficulties with the afore-mentioned invention, the present invention, in accordance with a second embodiment, is basically constituted with a pressure type flow rate control apparatus wherein a flow rate of fluid passing through an orifice 8 is computed as Qc=KP1 (where K is a proportionality constant), or as Qc=KP2m (P1−P2)n (where K is a proportionality constant, m and n constants), by using an orifice upstream side pressure P1 and/or an orifice downstream side pressure P2, and a fluid passage between the downstream side of a control valve and a fluid supply pipe of the pressure type flow rate control apparatus is made to be more than at least 2 fluid passages in parallel, wherein orifices having different flow rate characteristics are provided with the afore-mentioned fluid passages arranged in parallel. In accordance with the second embodiment, the afore-mentioned fluid flowing in the small flow quantity range is made to flow to one orifice for the flow control of the fluid flowing in the small flow quantity range, and the fluid flowing in the large flow quantity range is made to flow to the other orifice for the flow control of the fluid flowing in the large flow quantity range.
Furthermore, to overcome difficulties with the afore-mentioned invention, the present invention, in accordance with a sixth embodiment, is basically constituted so that a thermal type mass flow rate control apparatus comprises a flow rate control valve; a laminar flow element device part; a flow rate sensor part; and the like, wherein temperature changes in proportion to a mass flow rate of a fluid are detected at the flow rate sensor part, and fluid with a certain set flow rate is made to flow out by means of opening/closing a flow rate control valve based on the detected temperature; a fluid passage to the flow rate control valve is made to be more than at least 2 fluid passages arranged in parallel, wherein each of the afore-mentioned parallel passages are provided with both laminar flow elements with different coarseness and flow rate sensors, wherein the afore-mentioned fluid in flowing the small flow quantity range is made to flow to one laminar flow element for flow rate control of fluid flowing in the small flow quantity range, while the afore-mentioned fluid flowing in the large flow quantity range is made to flow to the other laminar flow element for flow rate control of fluid flowing in the large flow quantity range.
FCS pressure type flow rate control apparatus
MFC thermal type mass flow rate control apparatus
3 orifice primary side pipe
4 driving part
5 fluid supply pipe
8a orifice for a small flow quantity
8b orifice for a medium flow quantity
8c orifice for a large flow quantity
32 No. 1 switching electro-magnetic valve
33 No. 2 switching electro-magnetic valve
34 No. 1 switching valve
34a valve driving part
34b proximity sensor
35 No. 2 switching valve
35a valve driving part
35b proximity sensor
36 control part
36a bridge circuit
37 flow rate control valve
38, 38a, 38b laminar flow element bypasses
39 flow rate sensor part
40a, 40b fluid passages
41, 42 switching valves
FIG. 1 is a block diagram of a flow rate range variable type flow rate control apparatus according to one embodiment of the present invention. In FIG. 1, 1 designates a control part, 2 designates a control valve, 3 designates an orifice upstream side (primary side) pipe, 4 designates a valve driving part, 5 designates a fluid supply pipe, 6 designates a pressure sensor, 8a designates an orifice for a small flow quantity, 8b designates an orifice for a medium flow quantity, 8c designates an orifice for a large flow quantity, 32, 33 designate switching electro-magnetic valves, and 34, 35 designate switching valves. The control part 1, the control valve 2, the valve driving part 4, the pressure sensor 6, and the like, of the afore-mentioned pressure type flow rate control apparatus have been disclosed. With respect to the control part, there are provided flow rate input/output signals (i.e., an input signal of a set flow rate, an output signal of a controlled flow rate·DC 0-5V), terminals Qe, Qo, a power supply terminal (⊥DC 15V) E, and input terminals SL, SM, SS for providing a controlled flow rate switching command signal.
A first fluid passage 50p is disposed between the downstream side of the control valve 2 and the fluid supply pipe 5.
The afore-mentioned switching electro-magnetic valves 32, 33, which have been disclosed, are air operation type electro-magnetic valves. When switching signals C1, C2 are inputted from the control part 1 so that switching electro-magnetic valves 32, 33 start working and a driving gas (0.4˜0.7 MPa) Gc is supplied. Thus, the driving gas Gc is supplied to valve driving parts 34a, 35a of the switching valves, and the switching valves 34, 35 start operating for opening and closing. Furthermore, operation of both switching valves 34, 35 is detected by proximity switches 34b, 35b installed on the valve driving parts 34a, 35a, and a corresponding signal is inputted to the control part 1. With present embodiments of the invention, for each switching valve 34, 35 a pneumatically operated normally closed type valve has been employed.
More specifically, in the case that the maximum flow rate to be controlled is, for example, 2000 SCCM (Standard Cubic Centimeters per Minute), an orifice for the maximum flow rate of 20 SCCM is employed as the orifice 8a for small flow quantity, an orifice for the maximum flow rate of 200 SCCM is employed as the orifice 8b for medium flow quantity, and an orifice for the maximum flow quantity of 1780 SCCM is employed as the orifice 8c for large flow quantity, respectively. Namely, in the case that flow rate is controlled for a small flow quantity less than 20 SCCM, the switching signal Ss is inputted to the control part, the driving gas Gc is sent to the No. 2 switching valve 35 by releasing No. 2 electro-magnetic switching valve 33, and the No. 2 switching valve 35 is released (while the No. 1 switching valve 34 is maintained in a state of closing). As a result, fluid flows to pipe 5 through pipe 3, orifice 8a for small flow quantity, pipe 5b, valve 35, orifice 8c for large flow quantity, pipe 5c and pipe 5d, orifice 8b for medium flow quantity, and pipe 5f, and thus the flow rate QL of the fluid being controlled as Q=KLP1 (where KL is a constant specific to the orifice 8a for small flow quantity). Also, the flow rate characteristics of the apparatus of FIG. 1, in this case, are shown by curve A in FIG. 2. As shown, flow rate control can be performed accurately with an error of less than ±1% set point over the flow rate range of 2˜20 SCCM.
In the case wherein the flow rate to be controlled is 200 SCCM (i.e., for approximately medium flow quantity), the No. 1 switching valve 34 is switched to the state of opening (i.e., opened) and the No. 2 switching valve 35 is switched to the state of closing (i.e., closed), and fluid is made to flow to orifice 8b for medium flow quantity through pipe 3, pipe 5a, valve 34, pipe 5b and pipe 3 again, and through orifice 8a for small flow quantity. Thus, in this case, the flow rate QM of the fluid being controlled as Q=KMP1 (where KM is a constant specific to the orifice 8b for medium flow quantity). The flow rate characteristics in this case are shown by curve B shown in FIG. 2. As shown, flow rate control can be performed accurately with an error of less than ±1% of the set point over the flow rate range of 20˜200 SCCM.
In addition, in the case wherein the flow rate to be controlled is 2000 SCCM (i.e., the maximum flow rate), both switching valves 34, 35 are released through the mediation of both switching electro-magnetic valves 32, 33, and fluid is supplied to pipe 5 through pipe 3, pipe 5a, valve 34, valve 35, the orifice 8c for large flow quantity, pipe 5c and the orifice 8a for small flow quantity, the orifice 8b for medium flow quantity, and pipe 5f. In this case, the flow rate of the fluid is controlled mainly by orifice 8c for large flow quantity as a flow rate QM=KMP1 (where KM is a constant specific to an orifice 8c for large flow quantity). However, strictly speaking, the flow rate of pipe 5 is controlled as the sum of the flow rate QM=KMP1 passing through orifice 8b for medium flow quantity and the flow rate QL=KLP1 passing through orifice 8c for large flow quantity. Also, in this case, flow rate characteristics are shown by curve C shown in FIG. 2. As shown, the flow rate QL can be controlled accurately with an error of less than ±1% of the set point over the flow rate range of 200˜2000 SCCM.
FIG. 3 shows another embodiment of the present invention, wherein flow rate control is appropriately performed by employing an orifice 8a for small flow quantity and an orifice 8c for large flow quantity. For example, in the case that flow rate control for a maximum flow rate of 2000 SCCM is performed, the apparatus is constructed so that a flow rate up to 200 SCCM is controlled by the orifice 8a for small flow quantity and a flow rate up to 2000 SCCM is controlled by the orifice 8c for large flow quantity. Specifically, in the case that a flow rate of up to 200 SCCM is controlled, the switching valve 34 is maintained in a state of closing (i.e., closed), and the flow rate QS of a fluid passing through the orifice 8a for small flow quantity is controlled as QS=KSP1 (where KS is a constant specific to the orifice 8a). By using the orifice 8a for small flow quantity, the flow rate can be controlled accurately with an error of less than ±1% set point over the flow rate range of 20 SCCM˜2000 SCCM. Curve D in FIG. 4 shows the flow rate control characteristics for the embodiment shown in FIG. 3. In the case that the pressure in pipe 5 on the orifice downstream side is less than 100 Torr, it has been verified that the error can be reduced to less than ±1% of the set point with a flow rate of 20 SCCM.
In accordance with the afore-mentioned flow rate control apparatus shown in FIG. 3, if the orifice downstream pressure exceeds 100 Torr, or if the flow rate QS of the fluid is found to be less than 20 SCCM although the orifice downstream side pressure is less than 100 Torr, then it becomes difficult to maintain the flow rate control error to be less than ±1% of the set point. Accordingly, in such a case, the flow rate range of less than 20 SCCM is controlled in the manner of a so-called pulse control as shown in FIG. 4. Pulse control mentioned herein is a control method wherein fluid is made to flow into pipe 3 in a pulse form by performing the opening and closing of a control valve 2 on the orifice upstream side by using pulse signals so that the flow rate of a fluid passing through the orifice 8a for small flow quantity can be controlled with comparatively high accuracy by means of adjusting the number of pulse signals opening and closing the control valve 2. On the other hand, to control the flow rate of fluid of less than 2000 SCCM, the switching valve 34 is released through the mediation of the switching electro-magnetic valve 32. Thus, the fluid is made to flow to pipe 5 through pipe 5a, switching valve 34, orifice 8c for large flow quantity, orifice 8a for small flow quantity, and pipe 5g. In particular, the flow rate of fluid flowing into pipe 5 is the sum of the flow rate QC=KCP1 passing through orifice 8c for large flow quantity (where KC is a constant specific to orifice 8c for large flow quantity) and the flow rate QS=KSP1 passing through orifice 8a for small flow quantity (where KS is a constant specific to orifice 8a for small flow quantity). The curvature of flow rate characteristics is as shown by curve E in FIG. 4.
As described above, in accordance with the first two embodiments of the present invention, the accuracy of flow rate control with an error of less than ±1% set point becomes possible over a wide flow rate control range of, for example, 2 SCCM˜2000 SCCM, by means of appropriately combining orifice 8c for large flow quantity and orifice 8a for small flow quantity (or orifice 8c for large flow quantity, orifice 8b for medium flow quantity and orifice 8a for small flow quantity). A swift switching operation is required, however, to change the flow rate of a gas when the flow rate control is performed using orifice 8a for small flow quantity. In such a case, with the present invention, the pressure drop time for a pipe on the orifice secondary side can be easily shortened by installing bypass passages (5a, 34, 8c, 5c) in parallel with the flow passage in which orifice 8a is disposed, and releasing the bypass passages.
Furthermore, in accordance with the two embodiments of the present invention described above, because the apparatus is constructed so that the flow rate control of fluid is performed under a critical condition, the computed flow rate Q can be converted to the flow rate of a gas in use by making use of a so-called flow factor F.F. even when a type of gas flowing is changed. Thus, it is possible that excellent properties of the pressure type flow rate control apparatus may be fully utilized. However, accuracy of flow rate control in a state outside of the critical condition of the fluid, wherein a pressure type flow rate control apparatus used in the first two embodiments of the present invention is employed, is shown in FIG. 5 wherein an orifice secondary side pressure P2 is made a parameter. For example, as shown by curve F, in the case of P2=100 Torr, the error exceeds −1% F.S. at a point wherein the flow rate to be controlled reaches approximately 5% of a rated set flow rate. As a result, as shown by curve D (20 SCCM˜200 SCCM with orifice 8a for small flow quantity) in FIG. 4, the flow rate control can be performed surely and accurately with an error of less than ±1% of the set point between 20 SCCM˜200 SCCM. However, when the flow rate to be controlled is less than 20 SCCM, it becomes difficult in practice to lower the error of less than 1% F.S. to the point of the approximate flow rate 5% (200 SCCM×5%=10 SCCM) of the set flow rate because when the flow rate to be controlled becomes less than 20 SCCM, the apparatus falls out of a critical condition at a time wherein the orifice secondary side pressure P2 is 100 Torr. Accordingly, as shown in FIG. 4, in the case of a small flow quantity area (10 SCCM˜20 SCCM) of 5%˜10% of the set flow rate, a pulse control method can be employed. (Of course, there is no need to employ the method when an error of less than 0.1% F.S. (when a full scale of the orifice for large flow quantity is used as the standard) can be maintained.)
FIG. 6 shows yet another embodiment of the present invention wherein a so-called thermal type mass flow rate control apparatus MFC is employed in a flow rate control apparatus. As shown in FIG. 6, the thermal type mass flow rate control apparatus comprises a control part 36, a flow rate control valve 37, a laminar flow element bypass part 38, a flow rate sensor part 39, a switching valve 41, 42, and the like. Temperature changes in proportion to a mass flow rate of a fluid are detected with a flow rate sensor part 39, and fluid of a certain set flow rate is made to flow out by controlling the flow rate control valve 37 for opening and closing based on the detected temperature. A thermal type mass flow rate control apparatus MFC itself has been disclosed. Therefore, a detail description of such is omitted here.
In FIG. 6, 36a designates a bridge circuit, 36b designates an amplification circuit, 36c designates a correction circuit, 36d designates a comparison circuit, 36e designates a valve driving circuit and 36f designates an actuator. In accordance with this embodiment of the present invention, two passages 40a, 40b are separately installed as a bypass passage of a laminar flow bypass part 38, and switching valves 41, 42 are provided on the passages 40a, 40b, respectively. In particular, a coarse laminar element 38a is provided on one fluid passage 40a of the bypass passage, which is used for flow rate control of a fluid with a medium flow quantity, while the coarser laminar element 38b is provided on the other fluid passage 40b of the bypass passage, which is used for flow rate control of fluid with a large flow quantity. Specifically, the switching valve 41 and the switching valve 42 are made to open when controlling flow rate of fluid with a large flow quantity. On the other hand, the switching valve 42 and the switching valve 41 are made to close in order to control flow rate of fluid with a small flow quantity, and the amplification level of the amplification circuit 36b of the control part 36 is switched to a level suitable for detecting a small flow quantity. Furthermore, the switching valve 41 is made to close and the switching valve 42 is made to open in order to control the flow rate of fluid with a medium flow quantity, and the amplification level and the like of the afore-mentioned amplification circuit 36b is switched to a level suitable for detecting medium flow quantity. Accordingly, a highly accurate flow rate control becomes possible over three flow rate ranges of large, medium and small flow quantities by using one set of thermal type mass flow rate control apparatus MFC wherein the afore-mentioned switching valves 41, 42 are switched, and the amplification level of the control part 36 and the like are also switched.
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