Pressure type flow control system with flow monitoring

Abstract

A pressure type flow control system with flow monitoring includes an inlet side passage, a control valve comprising a pressure-type flow control unit connected downstream of the inlet side passage, a thermal-type flow sensor connected downstream of the control valve, an orifice installed on a fluid passage connected downstream of the thermal-type flow sensor, a temperature sensor provided near the fluid passage between the control valve and orifice, a pressure sensor provided for the fluid passage between the control valve and orifice, an outlet side passage connected to the orifice, and a control unit comprising a pressure-type flow rate arithmetic and control unit to which a pressure signal from the pressure sensor and a temperature signal from the temperature sensor are input, and which computes a flow rate value of fluid flowing through the orifice, and outputs a control signal to a valve drive unit of the control valve.

Claims

1. A pressure type flow control system with flow monitoring comprising: (a) an inlet side passage for fluid; (b) a control valve comprising a pressure type flow control unit that is connected to a downstream side of the inlet side passage; (c) a thermal type flow sensor that is connected to a downstream side of the control valve; (d) an orifice that is installed on a fluid passage communicatively connected to a downstream side of the thermal type flow sensor; (e) a temperature sensor provided near the fluid passage between the control valve and the orifice; (f) a first pressure sensor provided to determine pressure of the fluid passage between the control valve and the orifice; (g) an outlet side passage that is communicatively connected to the orifice; (h) a second pressure sensor provided to determine pressure of the outlet side passage on a downstream side of the orifice; and (i) a first control unit comprising 1 a pressure type flow rate arithmetic and control unit to which pressure signals from the first pressure sensor and the second pressure sensor are input, and to which a temperature signal from the temperature sensor is input, and the pressure type flow rate arithmetic and control unit monitors critical expansion conditions for a fluid flowing through the orifice and computes a flow rate value Q of the fluid flowing through the orifice, and the pressure type flow rate arithmetic and control unit outputs a control signal Pd to a valve drive unit that brings the control valve into an opening or closing action in a direction in which a difference between the computed flow rate value and a set flow rate value is decreased; and 2 a flow sensor control unit to which a flow rate signal from the thermal type flow sensor is input, and the flow sensor control unit computes a first flow rate of the fluid flowing through the orifice according to the flow rate signal, to indicate an actual flow rate of the fluid flowing through the orifice, wherein the control valve, the thermal type flow sensor, the orifice, the first pressure sensor, the temperature sensor, the inlet side passage, the outlet side passage, and the second pressure sensor are integrally assembled in one body, and the fluid passage is integrally formed in the one body, and wherein the one body is formed by integrally assembling a first main body block, a second main body block, a third main body block, and a fourth main body block so as to be interconnected, and, respectively, the control valve is installed on a top surface side of the first main body block, a laminar flow element is installed on an internal left side surface of the third main body block, the orifice is installed on an internal right side surface of the third main body block, the first pressure sensor 5 is installed on a bottom surface side of the third main body block, a sensor circuit of the thermal type flow sensor is installed on a top surface side of the third main body block and the second pressure sensor is installed on a top surface side of the fourth main body block, and fluid passages communicatively connected to the respective first, second, third and fourth main body blocks are formed in the one body.

2. The pressure type flow control system with flow monitoring according to claim 1, wherein the first control unit performs an alarm indication when the fluid flowing through the orifice is out of the critical expansion conditions.

3. A pressure type flow control system with flow monitoring comprising: (a) an inlet side passage for fluid; (b) a control valve comprising a pressure type flow control unit that is connected to a downstream side of the inlet side passage; (c) a thermal type flow sensor that is connected to a downstream side of the control valve; (d) an orifice that is installed on a fluid passage communicatively connected to a downstream side of the thermal type flow sensor; (e) a temperature sensor provided near the fluid passage between the control valve and the orifice; (f) a first pressure sensor provided to determine pressure of the fluid passage between the control valve and the orifice; (g) an outlet side passage that is communicatively connected to the orifice; (h) a second pressure sensor provided to determine pressure of the outlet side passage on a downstream side of the orifice; and (i) a first control unit comprising 1 a pressure type flow rate arithmetic and control unit to which pressure signals from the first pressure sensor and the second pressure sensor are input, and to which a temperature signal from the temperature sensor is input, and the pressure type flow rate arithmetic and control unit monitors critical expansion conditions for a fluid flowing through the orifice and computes a flow rate value Q of the fluid flowing through the orifice, and the pressure type flow rate arithmetic and control unit outputs a control signal Pd to a valve drive unit that brings the control valve into an opening or closing action in a direction in which a difference between the computed flow rate value and a set flow rate value is decreased; and 2 a flow sensor control unit to which a flow rate signal from the thermal type flow sensor is input, and the flow sensor control unit computes a first flow rate of the fluid flowing through the orifice according to the flow rate signal, to indicate an actual flow rate of the fluid flowing through the orifice, wherein the flow sensor control unit comprises a monitoring flow rate output correction circuit that corrects a monitoring flow rate B.sub.2 computed on the basis of the flow rate signal from the thermal type flow sensor that is provided for the flow sensor control unit, and the monitoring flow rate output correction circuit corrects the monitoring flow rate B.sub.2 to be B.sub.2=B.sub.2C.Math.P/t, wherein C is a conversion factor, by use of a gradient P/t of fluid control pressure, and the monitoring flow rate output correction circuit outputs the corrected monitoring flow rate output B.sub.2 as a first monitoring flow rate.

4. The pressure type flow control system with flow monitoring according to claim 3, wherein the monitoring flow rate output correction circuit comprises a differentiating circuit that receives as input a controlled flow rate output A.sub.2 from the pressure type flow control unit, an amplifying circuit that amplifies an output value from the differentiating circuit, a shaping circuit that shapes an output from the amplifying circuit, and a correction circuit that subtracts an input from the shaping circuit from the monitoring flow rate output B.sub.2 from the thermal type flow monitoring unit in order to output the corrected monitoring flow rate output B.sub.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a configuration of a pressure type flow control system with flow monitoring utilizing an orifice according to an embodiment of the present invention.

(2) FIG. 2 is a schematic diagram of a configuration showing another example of the pressure type flow control system with flow monitoring.

(3) FIG. 3 is a schematic diagram of a configuration showing yet another example of the pressure type flow control system with flow monitoring.

(4) FIG. 4 is an explanatory diagram of a configuration of a thermal type flow sensor.

(5) FIG. 5 is an explanatory diagram of the principle of operation of the thermal type flow sensor.

(6) FIG. 6 is a first conception diagram of the pressure type flow control system with flow monitoring, which is conceived by the inventors of the invention of the present application.

(7) FIG. 7 is a second conception diagram of the pressure type flow control system with flow monitoring, which is conceived by the inventors of the invention of the present application.

(8) FIG. 8 shows curves of the step response characteristics of the thermal type flow sensor (in the case of a set flow rate of 20%).

(9) FIG. 9 shows curves of the step response characteristics of the thermal type flow sensor (in the case of a set flow rate of 50%).

(10) FIG. 10 shows curves of the step response characteristics of the thermal type flow sensor (in the case of a set flow rate of 100%).

(11) FIG. 11 shows curves of the monitoring flow rate accuracy characteristics of the thermal type flow sensor (in the case of a set flow rate of 100% to 97%).

(12) FIG. 12 shows curves of the monitoring flow rate accuracy characteristics of the thermal type flow sensor (in the case of a set flow rate of 20.0% to 19.4%).

(13) FIG. 13 shows curves of the supply pressure fluctuating characteristics of the thermal type flow sensor (in the case of a set flow rate of 50%).

(14) FIG. 14 shows curves of the repetitive reproducibility characteristics of the thermal type flow sensor (in the case of a set flow rate of 100%).

(15) FIG. 15 shows curves of the repetitive reproducibility characteristics of the thermal type flow sensor (in the case of a set flow rate of 20%).

(16) FIG. 16 is a configuration diagram of a pressure type flow control system using an orifice.

(17) FIG. 17 is an explanatory diagram of a configuration of a mass flow control system according to a first embodiment of Japanese Patent No. 4137666.

(18) FIG. 18 is an explanatory diagram of a configuration of a mass flow control system according to a second embodiment of Japanese Patent No. 4137666.

(19) FIG. 19 shows an example of response characteristics of the pressure type flow control system with flow monitoring at a flow rate volume of 2000 SCCM, and shows a flow rate set value A.sub.1 in the case where the flow rate setting is set from 0% to 50, and back to 0%, a flow rate output A.sub.2, and a monitoring flow rate output B.sub.2 of the thermal type flow sensor.

(20) FIG. 20 shows an example of response characteristics of the pressure type flow control system with flow monitoring at a flow rate volume of 100 SCCM, and shows the case where the flow rate setting is set to 0% to 50%.

(21) FIG. 21 are schematic diagrams showing a structure of the pressure type flow control system with flow monitoring, wherein FIG. 21(a) is a longitudinal sectional front view thereof, FIG. 21(b) is a left side view thereof, FIG. 21(c) is a plan view thereof, and FIG. 21(d) is a bottom view thereof.

(22) FIG. 22 is a schematic block configuration diagram of a monitoring flow rate output correction circuit of the thermal type flow sensor.

(23) FIG. 23 shows an example of response characteristics of the system using the monitoring flow rate output correction circuit H in the case where a flow rate volume is 100 SCCM and N.sub.2 gas supply pressure is 300 kPaG (0%.fwdarw.20%.fwdarw.0% and 20%.fwdarw.40%.fwdarw.20%).

(24) FIG. 24 shows response characteristics at 40%.fwdarw.60%.fwdarw.40% and 60%.fwdarw.80%.fwdarw.60% in the system of FIG. 23.

(25) FIG. 25 shows response characteristics at 80%.fwdarw.100%.fwdarw.80% and 0%.fwdarw.100%.fwdarw.0% in the system of FIG. 23.

(26) FIG. 26 is a line graph showing flow control characteristics with respect to a N.sub.2 gas of the pressure type flow control system with flow monitoring at a flow rate volume of 2000 SCCM in which the monitoring flow rate output correction circuit H is provided.

(27) FIG. 27 shows flow control characteristics in the case where the gas type is an O.sub.2 gas in the pressure type flow control system with flow monitoring, and corrected flow control characteristics in consideration of a conversion factor (C. F.) of the gas type.

(28) FIG. 28 shows flow control characteristics in the case where the gas type is an Ar gas, and corrected flow control characteristics in consideration of a conversion factor (C. F.) of the gas type.

(29) FIG. 29 is a process flowchart for initial value memory of a thermal type flow sensor flow rate output with respect to a live gas.

(30) FIG. 30(a) is a briefing diagram of an initial value memory process for a thermal type flow sensor flow rate output with respect to a live gas in FIG. 29.

(31) FIG. 30(b) is a briefing diagram of a checking process for a thermal type flow sensor flow rate output.

DETAILED DESCRIPTION OF THE INVENTION

Detailed Description of the Preferred Embodiments

(32) Hereinafter, an embodiment of the present invention will be described with reference to the drawings included with this disclosure. FIG. 1 is a schematic diagram of a configuration according to an embodiment of a pressure type flow control system with flow monitoring 1 according to the present invention. The pressure type flow control system 1 with flow monitoring is composed of a pressure type flow control unit 1a and a thermal type flow monitoring unit 1b.

(33) Furthermore, the pressure type flow control unit 1a is composed of a control valve 3, a temperature sensor 4, a pressure sensor 5, an orifice 6, and a pressure type flow rate arithmetic and control unit 7a forming a component of a control unit 7.

(34) Moreover, the thermal type flow monitoring unit 1b is composed of a thermal type flow sensor 2 and a flow sensor control unit 7b forming another component of the control unit 7.

(35) The pressure type flow control unit 1a is, as described above, composed of the control valve 3, the temperature sensor 4, the pressure sensor 5, the orifice 6, the pressure type flow rate arithmetic and control unit 7a, and the like. A flow rate setting signal is output from an input terminal 7a.sub.1, and a flow rate output signal of a fluid flowing through the orifice, which has been computed by the pressure type flow control unit 1a, is output from an output terminal 7a.sub.2.

(36) The pressure type flow control unit 1a itself, which uses the orifice 6, is a publicly-known technique as evident by Japanese Patent No. 3291161, and as evident by U.S. Pat. No. 5,791,369 that is incorporated herein by reference, and the like, and computes a flow rate of a fluid flowing through the orifice 6 under the critical expansion conditions on the basis of pressure detected by the pressure detection sensor 5, with the pressure type flow rate arithmetic and control unit 7a, and outputs a control signal Pd proportional to a difference between the set flow rate signal input from the input terminal 7a.sub.1 and the computed flow rate signal to a valve drive unit 3a of the control valve 3.

(37) Because the configurations of the pressure type flow control unit 1a and the flow rate arithmetic and control unit 7a thereof are substantially the same as those described in FIG. 16, detailed descriptions thereof are omitted here. Furthermore, as a matter of course, various types of ancillary mechanisms such as the publicly-known zero-point adjustment mechanism and flow rate anomaly detection mechanism, and a gaseous species conversion mechanism (F. F. value conversion mechanism), are provided in the pressure type flow control unit 1a. Moreover, in FIG. 1, reference symbol 8 denotes an inlet side passage, reference symbol 9 denotes an outlet side passage, and reference symbol 10 denotes a fluid passage in the device main body.

(38) The thermal type flow monitoring unit 1b composing the pressure type flow control system 1 with flow monitoring is composed of the thermal type flow sensor 2 and the flow sensor control unit 7b, and an input terminal 7b.sub.1 and an output terminal 7b.sub.2 are respectively provided for the flow sensor control unit 7b. Then, a setting signal within a flow rate range to be monitored is input from the input terminal 7b.sub.1, and a monitoring flow rate signal (i.e., a real flow rate signal) detected by the thermal type flow sensor 2 is output from the output terminal 7b.sub.2. In addition, as a matter of course, ancillary mechanisms such as a gaseous species conversion mechanism (C. F. value conversion mechanism) are provided in the thermal type flow monitoring unit 1b as well.

(39) Furthermore, although not shown in FIG. 1, as a matter of course, input and output of the monitoring flow rate signal and a computed flow rate signal are appropriately carried out between the flow sensor control unit 7b and the pressure type flow rate arithmetic and control unit 7a, and a difference between them both and a level of the difference may be monitored, or a warning may be issued in the case where the difference between the monitoring flow rate signal and the computed flow rate signal exceeds a given value.

(40) FIG. 2 shows another example of the pressure type flow control system 1 with flow monitoring, which is configured to detect fluid pressure between the control valve 3 and the thermal type flow sensor 2 with the pressure sensor 5. In addition, other configurations and operations of the pressure type flow control system 1 with flow monitoring are completely the same as those in the case of FIG. 1.

(41) FIG. 3 shows yet another example of the pressure type flow control system 1 with flow monitoring, and a pressure sensor 17 is separately installed on the downstream side of the orifice 6, which makes it possible to monitor whether or not the fluid flowing through the orifice 6 is under the critical expansion conditions, to issue an alarm, or to perform flow control by use of differential pressure between the pressure sensor 5 and the pressure sensor 17.

(42) The thermal type flow monitoring unit 1b is composed of the thermal type flow sensor 2 and the flow sensor control unit 7b, and FIG. 4 and FIG. 5 show an outline of the configuration thereof. That is, as shown in FIG. 4, the thermal type flow sensor 2 has a laminar flow element (a bypass pipe group) 2d and a sensor pipe 2e, which bypasses the laminar flow element 2d, and a gas fluid of a small quantity compared to the laminar flow element 2d is made to flow through the sensor pipe 2e at a constant ratio. Furthermore, a pair of resistance wires R1 and R4 for control, which are series-connected, are rolled around the sensor pipe 2e to output a flow rate signal 2c indicating a mass flow rate value that is monitored by a sensor circuit 2b connected to the resistance wires R1 and R4.

(43) The flow rate signal 2c is introduced into the flow sensor control unit 7b composed of, for example, a microcomputer or the like, to determine a real flow rate of a currently flowing fluid on the basis of the flow rate signal 2c.

(44) FIG. 5 shows a basic structure of the sensor circuit 2b of the thermal type flow sensor 2, and the series-connected circuits of two standard resistors R2 and R3 are connected in parallel to the series-connection of the resistance wires R1 and R4 described above, so as to form a bridge circuit. A constant current source is connected to this bridge circuit, and a connecting point between the resistance wires R1 and R4 and a connecting point between the standard resistors R2 and R3 are connected to the input side, to provide a differential circuit, that is configured to determine a potential difference between the two connecting points, to output this potential difference as the flow rate signal 2c.

(45) In addition, because the thermal type flow sensor 2 and the flow sensor control unit 7b themselves are publicly known devices, detailed descriptions thereof are omitted here. Furthermore, in the present embodiment, a thermal type flow sensor mounted in the FCS-T1000 series manufactured by Fujikin Incorporated is used as the thermal type flow monitoring unit 1b.

(46) FIG. 21 includes schematic diagrams showing a structure of the pressure type flow control system 1 with flow monitoring according to the present invention. In particular, FIG. 21(a) is a longitudinal sectional view thereof, FIG. 21(b) is a left side view thereof, FIG. 21(c) is a plan view thereof, and FIG. 21(d) is a bottom view thereof.

(47) The pressure type flow control system 1 with flow monitoring composed of the pressure type flow control unit 1a and the thermal type flow monitoring unit 1b shown in FIG. 1 and FIG. 21 is formed of the body 30 and the control unit 7, and the control valve 3, the thermal type flow sensor 2, the temperature sensor 4, the pressure sensor 5, and the orifice 6, and the like, which are assembled in the body 30, and further, the control unit 7 is formed of the pressure type flow control unit 7a and the flow sensor control unit 7b.

(48) The body 30 is formed of the first main body block 30a, the second main body block 30b, the third main body block 30c, and the fourth main body block 30d, and the first main body block 30a, the third main body block 30c, and the fourth main body block 30d are fixedly interconnected with four fixation bolts 34. Furthermore, the second main body block 30b is fixed to the first main body block 30a with two fixation bolts 35.

(49) Moreover, respectively, the laminar flow element 2d of the thermal type flow sensor 2 is fixedly installed on the internal left side surface of the third main body block 30c, the pressure sensor 5 is fixedly installed on the bottom surface of the third main body block 30c, the pressure sensor 17 is fixedly installed on the top surface side of the fourth main body block 30d, the sensor circuit 2b of the thermal type flow sensor 2 and the control unit 7 are fixedly installed on the top surface side of the third main body block 30c, the drive unit 3a of the control valve 3 is fixedly installed on the top surface side of the first main body block 30a, the prefilter 29 is fixedly installed between the first main body block 30a and the second main body block 30b, and the orifice 6 is fixedly installed in the third main body block 30c.

(50) In the same way, respectively, the inlet side passage 8 is formed in the first main body block 30a, the fluid passage 10 is formed in the first main body block 30a and the third main body block 30c, and the outlet side passage 9 is formed in the fourth main body block 30d and, in particular, the inner diameters and the lengths of the fluid passage 10 are selected so as to keep the internal volumes to the minimum necessary. Furthermore, a housing hole 2e for the sensor pipe 2e and a housing hole 4a for the temperature sensor 4 are respectively drilled in the third main body block 30c. In addition, although not shown in FIG. 21, as a matter of course, the respective main body blocks 30a to 30d, and the respective main body blocks and the laminar flow element 2d and the orifice 6, are interconnected to each other in an airtight manner via sealing materials.

(51) With the structure in which the plurality of main body blocks 30a to 30d are interconnected and combined to form the body 30 as described above, it is possible to considerably reduce the internal volumes of the fluid passage 10, and it is possible to compactly install the laminar flow element 2d, the pressure sensor 5, the orifice 6, and the like in the body 30. This structural configuration makes it possible to downsize the pressure type flow control system 1 with flow monitoring, and considerably reduce the level of transient overshoot of a sensing flow rate in the thermal type flow monitoring unit 1b.

(52) Transient overshoot of the monitoring flow rate (i.e., a flow rate output B.sub.2 from the thermal type flow sensor 2) shown in FIG. 19 and FIG. 20, and the like, is ascribed as a cause for generating a difference between the monitoring flow rate output B.sub.2 and the flow rate output A.sub.2 from the pressure type flow control unit 1a, which causes a decrease in the flow control accuracy and the responsive performance of the pressure type flow control system 1 provided with flow monitoring. Therefore, it is necessary to make an overshoot of the flow rate output B.sub.2 in the thermal type flow monitoring unit 1b (a flow rate output B.sub.2 from the thermal type flow sensor 2) as small as possible, in order to decrease the difference between the monitoring flow rate output B.sub.2 and the flow rate output A.sub.2 in the pressure type flow control unit 1a.

(53) Then, in accordance with the present invention, in order to decrease the difference between the monitoring flow rate output B.sub.2 caused by the overshoot in the fluid passage 10 of FIG. 1 and the flow rate output A.sub.2, a gradient P/t of control pressure in the fluid passage 10 when the overshoot is caused is detected according to the rate of change in the flow rate output A.sub.2 from the pressure type flow control unit 1a, and a detection value B.sub.2 as the flow rate output from the thermal type flow sensor 2 is corrected by use of the gradient P/t of the control pressure, thereby decreasing the difference between the flow rate output B.sub.2 from the thermal type flow monitoring unit 1b (the flow rate output B.sub.2 from the thermal type flow sensor 2) and the flow rate output A.sub.2 from the pressure type flow control unit 1a, to further improve the monitoring flow rate accuracy.

(54) Referring to FIG. 1, assuming that the flow rate of a fluid currently flowing in the fluid passage 10 in the system main body is F.sub.1, the fluid flow rate F.sub.1 becomes a fluid flow rate B.sub.2 to be detected by the thermal type flow sensor 2. Furthermore, assuming that the flow rate of the fluid flowing in the passage on a downstream side of the orifice 6 (i.e., the outlet side passage 9) is F.sub.2, the fluid flow rate F.sub.2 becomes a fluid controlled flow rate A.sub.2 in the pressure type flow control unit 1a.

(55) That is, because the controlled flow rate F.sub.2 of the pressure type flow control unit 1a is to be computed by F.sub.2=KP.sub.1 (K=a constant, P.sub.1=pressure on the upstream side of the orifice 6), the above-described difference between the flow rates F.sub.1F.sub.2 is proportional to the rate of increase in control pressure in the fluid passage 10 (i.e., the rate of increase in the flow rate output A.sub.2 from the pressure type flow control unit 1a).

(56) As a result, according to F.sub.1F.sub.2P/t, it is possible to express F.sub.2=F.sub.1C (P/t) (however, C is a factor for converting the rate (pace) of increase in control pressure into a flow rate) and, in principle, it is possible to convert the flow rate F.sub.1 to the flow rate F.sub.2 according to (P/t). In addition, in the case of a stationary state (that is, there is no increase in pressure in the fluid passage 10 and the control pressure is constant), P/t=0 and F.sub.1F.sub.2=0.

(57) FIG. 22 is a block configuration diagram of the monitoring flow rate output correction circuit H of the thermal type flow sensor 2 for correcting the monitoring flow rate B.sub.2 in the thermal type flow monitoring unit 1b. In FIG. 22, reference symbol 36 denotes an input terminal for the controlled flow rate output A.sub.2 from the pressure type flow control unit 1a, reference symbol 37 denotes an input terminal for the monitoring flow rate output B.sub.2 from the thermal type flow monitoring unit 1b, reference symbol 38 denotes an output terminal for the corrected monitoring flow rate output B.sub.2, reference symbol 39 denotes an input circuit, reference symbol 40 denotes a differentiating circuit, reference symbol 41 denotes an amplifying circuit, reference symbol 42 denotes a shaping circuit, and reference symbol 43 denotes a correction circuit.

(58) The controlled flow rate output A.sub.2 from the pressure type flow control unit 1a is input to the differentiating circuit 40 through the input circuit 39, and a rate of change in the controlled flow rate output A.sub.2, i.e., the pace of change P/t in control pressure P, is detected therein. Furthermore, a gradient (the rate of change) P/t of the control pressure P is input to the amplifying circuit 41, to be amplified (by amplification factor C) therein, and is thereafter shaped into a waveform matching the monitoring flow rate output B.sub.2 from the thermal type flow monitoring unit 1b input from the input terminal 37 so as to be, thereafter, input to the correction circuit 43 formed of a differential amplifier. Moreover, in the correction circuit 43, the corrected flow rate C.Math.P/t input from the shaping circuit 42 is subtracted from the monitoring flow rate output B.sub.2 from the thermal type flow sensor 2, and the corrected monitoring flow rate output B.sub.2 is output from the corrected output terminal 38.

(59) FIG. 23 to FIG. 25 show the results of response characteristics tests under the condition of N.sub.2 gas supply pressure of 300 kPaG of the pressure type flow control system 1 with flow monitoring at a flow rate volume of 100 SCCM, using the monitoring flow rate output correction circuit H shown in FIG. 22. In addition, in FIG. 23 to FIG. 25, reference symbol A.sub.1 denotes a set input of the pressure type flow control unit 1a, reference symbol A.sub.2 denotes a controlled flow rate output from the pressure type flow control unit 1a, reference symbol B.sub.2 denotes a monitoring flow rate output from the thermal type flow monitoring unit 1b, and reference symbol B.sub.2 denotes a corrected monitoring flow rate output from the thermal type flow monitoring unit 1b.

(60) As is clear from FIG. 23 to FIG. 25 as well, the controlled flow rate output A.sub.2 from the pressure type flow control unit 1a and the corrected monitoring flow rate output B.sub.2 of the monitoring flow rate output B.sub.2 from the thermal type flow monitoring unit 1b show the approximate response characteristics at the time both of starting-up and closing-down the system. In other words, by using the monitoring flow rate output correction circuit H according to the present invention, even when overshoot is caused in the monitoring flow rate output B.sub.2, it is possible to eliminate the influence of the overshoot with comparative ease, to obtain a highly accurate monitoring flow rate output B.sub.2 with high response characteristics.

(61) In the pressure type flow control system 1 with flow monitoring as well, when the gas type of the control fluid is changed, it is necessary to correct the flow control characteristics relating to a so-called conversion factor (C. F.) in the same way as in the case of a conventional pressure type flow control system. FIG. 26 to FIG. 28 show the relationship between the monitoring flow rate output B.sub.2 and the corrected monitoring flow rate output B.sub.2, and the set flow rate A.sub.1 of the pressure type flow control unit 1a, in the case where the gas type of the control fluid is changed in the pressure type flow control system 1 with flow monitoring at a flow rate volume of 2000 SCCM in which the monitoring flow rate output correction circuit H shown in FIG. 22 is provided. Furthermore, calibration of the flow rate is carried out with a N.sub.2 gas serving as a standard, and the gas supply pressure is set to 300 kPaG in each case.

(62) FIG. 26 shows the relationship between the corrected monitoring flow rate output B.sub.2 and the set flow rate A.sub.1 of the pressure type flow control unit 1a with N.sub.2 serving as a control fluid. As evident from FIG. 26, the set flow rate A.sub.1 and the monitoring flow rate output B.sub.2 correspond to one another in a relationship of 1:1.

(63) In contrast thereto, FIG. 27 and FIG. 28 show the case where the control fluid is O.sub.2 and Ar, respectively. As shown by FIG. 27, when the control fluid is O.sub.2 in the pressure type flow control system 1 with flow monitoring, in which calibration is carried out with N.sub.2 serving as a control fluid, and which has the flow characteristics shown in FIG. 26, the flow control characteristics become like the straight line O.sub.2. Therefore, in order to contrast the monitoring flow rate output B.sub.2 with the set flow rate A.sub.1 in 1:1, it is necessary to again correct the flow control characteristics for O.sub.2 to be like the straight line O.sub.2.

(64) In the same way in the case where the control fluid is Ar, because the flow control characteristics becomes like the straight line Ar, as shown in FIG. 28 where the control fluid is Ar, in order to contrast the monitoring flow rate B.sub.2 with the set flow rate A.sub.1 in 1:1, it is necessary to correct the flow characteristics Ar to be like the straight line Ar, in consideration of a conversion factor (C. F.) of the gas type between N.sub.2 and Ar.

(65) Next, an initial value memory of a thermal type flow sensor output before actual use of the pressure type flow control system 1, with flow monitoring, according to the present invention will be described. The pressure type flow control unit 1a and the thermal type flow monitoring unit 1b of the pressure type flow control system 1 with flow monitoring are the same as in the case of the conventional pressure type flow control system with respect to the fact that it is necessary to execute a so-called flow rate self-diagnosis at the time of actual use of the system 1, in order to check whether or not there is a difference between the monitoring flow rate and the real fluid flow rate.

(66) Therefore, in the pressure type flow control system 1 with flow monitoring of the present invention as well, in the case where this system 1 is attached to a gas supply system pipe, or the like, first, it is necessary to memorize the relationship between the set flow rate value and the flow rate output value of the thermal type flow monitoring unit 1b in an initial stage of supply of the live gas (hereinafter called a live gas monitoring flow rate output initial value memory). As a matter of course, it is necessary to convert a live gas flow rate output of the pressure type flow control unit 1a as well. However, because this is already publicly known, explicit descriptions of such a conversion are omitted here. However, such a conversion is disclosed by U.S. Pat. No. 5,669,408, and by U.S. Pat. No. 5,791,369, and by U.S. Pat. No. 5,816,285 and others, which are incorporated herein by reference for all it discloses.

(67) The live gas monitoring flow rate output initial value memory of the thermal type flow monitoring unit 1b is carried out following the process flow as shown in FIG. 29. First, the relationship of the flow rate output B.sub.2 from the thermal type flow sensor 2 with the controlled flow rate A.sub.1 of the system 1 is checked by use of a N.sub.2 gas. Thereafter, the flow rate output B.sub.2 from the thermal type flow sensor 2 to be memorized, with respect to the controlled flow rate A.sub.1 in the case where a live gas is supplied, is checked.

(68) Referring to FIG. 29, first, after attachment to actual equipment (Step S.sub.1), a flow factor F. F. value of N.sub.2 is input to the pressure type flow control unit 1a (Step S.sub.2), to vacuum-exhaust the N.sub.2 gas in the pipe passage (Step S.sub.3). Thereafter, an automatic zero-point adjustment of the pressure sensor P.sub.1 (Step S.sub.4) and an automatic zero-point adjustment of the thermal type flow sensor 2 (Step S.sub.5) are performed, and the N.sub.2 gas is supplied to the inside of the pipe passage (Step S.sub.6), to perform the flow rate self-diagnosis for the N.sub.2 gas (Step S.sub.7). Moreover, the result of the flow rate self-diagnosis for the N.sub.2 gas is determined in Step S.sub.8, and when the result of the flow rate self-diagnosis is within a range of allowable values, the flow rate output B.sub.2 from the thermal type flow sensor 2 is checked in Step S.sub.9, and the flow rate output B.sub.2 with respect to the controlled flow rate A.sub.1 is checked in Step S.sub.10, and when a difference between them both is within the range of allowable values, the process flow with the N.sub.2 gas is terminated, so as to proceed to the process flow with a live gas in Step S.sub.12. Furthermore, in the case where the result of the self-diagnosis in Step S.sub.8 is out of the range of allowable values, it is judged that the system 1 is abnormal, which results in termination of the process flow in Step S.sub.11.

(69) When the process flow with the N.sub.2 gas is terminated, a flow factor F. F. value of the live gas is input to the pressure type flow control unit 1a (Step S.sub.12), and vacuuming of the inside of the pipe (Step S.sub.13), an automatic zero-point adjustment of the pressure sensor 5 (Step S.sub.14), and an automatic zero-point adjustment of the thermal type flow sensor 2 (Step S.sub.15) are performed. Thereafter, the live gas is supplied into the pipe passage (Step S.sub.16) to perform the initial value memorization in the flow rate self-diagnosis for the live gas in Step S.sub.17. The initial value memorization in Step S.sub.17 is performed by a memory unit 7c of the control unit 7 so that an initial value memory is obtained and memorized in the memory unit 7c as described above. In addition, the initial value memory is the result of a process for memorizing the pressure drop characteristics in an initial stage of supply in the case where a live gas is supplied, and furthermore, the flow rate self-diagnosis for the live gas in Step S.sub.19 is employed to check the pressure drop characteristics memorized in Step S.sub.17.

(70) It is judged whether or not a difference between the pressure drop characteristics at the initial value memorized and at the diagnosis is within a range of allowable values by the flow rate self-diagnosis for the live gas in Step S.sub.18 (Step S.sub.19). When the difference is within the range of allowable values, the initial value memorization of the flow rate output from the thermal type flow sensor 2 is carried out in Step S.sub.20, and next, the flow rate output B.sub.2 from the thermal type flow sensor 2 is checked in Step S.sub.21, and the corrected value B.sub.2 of the monitoring flow rate B.sub.2 from the thermal type flow sensor with respect to the controlled flow rate A.sub.2 is checked (Step S.sub.22). When the difference is within the range of allowable values, the initial value memory process of the thermal type flow sensor output with respect to the live gas is completed (Step S.sub.23). Furthermore, when the result of the flow rate self-diagnosis for the live gas in Step S.sub.19 is out of the range of allowable values, the process flow is discontinued because it is judged that the system 1 is abnormal (Step S.sub.24).

(71) The processing of the initial value memory of a thermal type flow sensor flow rate output in Step S.sub.20 is, specifically, as shown in FIG. 30(a), which ultimately results in memorization of the correction value by the memory unit 7c. Thus, as shown in FIG. 30(a), flow control is executed at respective flow rate set values A.sub.1, and a corrected value B.sub.2 is automatically calculated from an output value B.sub.2 from the thermal type flow sensor at each of the respective flow rate set values A.sub.1, until memorization of the final correction value (i.e., the correction value memory). In addition, latency times t at the respective flow rate set values A.sub.1 and the respective set values are memorized in the memory unit 7c of system 1 in advance of factory shipment. In the example of FIG. 30(a), the flow control set values A.sub.1 are set to 25%, 50%, 75% and 100%, and the latency time t is set to 10 seconds, and the monitoring flow rate B.sub.2 of the thermal type flow sensor 2 is measured, and its corrected value B.sub.2 is calculated to be memorized by the memory unit 7c.

(72) Checking of the flow rate output B.sub.2 from the thermal type flow sensor 2 from the thermal type flow sensor when the live gas is supplied in Step S.sub.22 is performed in the same way. As shown in FIG. 30(b), flow control is executed at respective flow rate set values A.sub.1, and a thermal type flow sensor output B.sub.2 is measured after the elapse of a predetermined latency time, and a sensor flow rate output B.sub.2 that the output B.sub.2 is corrected is output, in order to compare it with the controlled flow rate A.sub.1. In addition, the respective set values A.sub.1 of the pressure type flow control unit, and their scores, latency times t, reference values for check and determination, and the like are memorized by the memory unit 7c of the system 1 in advance of factory shipment. FIG. 30(b) shows the case where the controlled flow rate set values A.sub.1 are set to 12%, 37%, 62% and 87% of the rating, and the latency time t is set to 10 seconds.

INDUSTRIAL APPLICABILITY

(73) The present invention is widely applicable not only to gas supplying facilities for semiconductor manufacturing equipment, but also to fluid supply circuits for chemical product manufacturing equipment, and the like, as long as the present invention controls a flow rate of a fluid under the critical expansion conditions. Generally, the present invention provides a pressure type flow control system with flow monitoring that is capable of easily and precisely, and appropriately, monitoring a real flow rate of a control fluid in real time while making full use of the excellent flow control characteristics obtained by a pressure type flow control system using an orifice, and by adding a simple configuration. Thus, broadly constructed, the present invention pertains to a pressure type flow control system with flow monitoring that is composed of an inlet side passage 8 for fluid, a control valve 3 composing a pressure type flow control unit 1a that is connected to a downstream side of the inlet side passage 8, a thermal type flow sensor 2 that is connected to a downstream side of the control valve 3, an orifice 6 that is installed along the way of a fluid passage 10 communicatively connected to a downstream side of the thermal type flow sensor 2, a temperature sensor 4 that is provided near the fluid passage 10 between the control valve 3 and the orifice 6, a pressure sensor 5 that is provided for the fluid passage 10 between the control valve 3 and the orifice 6, an outlet side passage 9 that is communicatively connected to the orifice 6, and a control unit 7 that is composed of a pressure type flow rate arithmetic and control unit 7a to which a pressure signal from the pressure sensor 5 and a temperature signal from the temperature sensor 4 are input, and which computes a flow rate value Q of a fluid flowing through the orifice 6, and outputs a control signal Pd for bringing the control valve 3 into an opening or closing action in a direction in which a difference between the computed flow rate value and a set flow rate value is decreased, to a valve drive unit 3a, and a flow sensor control unit 7b to which a flow rate signal 2c from the thermal type flow sensor 2 is input, and which computes a flow rate of the fluid flowing through the orifice 6 according to the flow rate signal 2c, to indicate the actual flow rate.

DESCRIPTION OF REFERENCE SYMBOLS

(74) 1: Pressure type flow control system with flow monitoring 1a: Pressure type flow control unit 1b: Thermal type flow monitoring unit 2: Thermal type flow sensor 2b: Sensor circuit 2d: Laminar flow element 2e: Sensor pipe 2e: Flow passage between sensor pipe and laminar flow element 3: Control valve 3a: Valve drive unit 4: Temperature sensor 4a: Housing hole for temperature sensor 5: Pressure sensor 6: Orifice 7: Control unit 7a: Pressure type flow rate arithmetic and control unit 7b: Flow sensor control unit 7a.sub.1: Input terminal 7a.sub.2: Output terminal 7b.sub.1: Input terminal 7b.sub.2: Output terminal 8: Inlet side passage 9: Outlet side passage 10: Fluid passage in device main body 11: Gas supply source 12: Pressure regulator 13: Purge valve 14: Input side pressure sensor 15: Data logger 16: Vacuum pump 17: Pressure sensor Pd: Control valve control signal Pc: Flow rate signal A.sub.1: Flow rate setting input A.sub.2: Flow rate output from pressure type flow control system B.sub.1: Output from thermal type flow sensor (FIG. 6: In the case of thermal type flow sensor on the primary side) B.sub.2: Output from thermal type flow sensor (FIG. 7: In the case of thermal type flow sensor on the secondary side) 30: Body 30a: First main body block 30b: Second main body block 30c: Third main body block 30d: Fourth main body block 31: Fluid inlet 32: Fluid outlet 33: Connector 34: Fixation bolt 35: Fixation bolt H: Monitoring flow rate output correction circuit 36: Input terminal for flow rate output A.sub.2 from pressure type flow control unit 37: Input terminal for monitoring flow rate output B.sub.2 from thermal type flow monitoring unit 38: Output terminal for corrected output B.sub.2 of monitoring flow rate 39: Input circuit 40: Differentiating circuit 41: Amplifying circuit 42: Shaping circuit 43: Correction circuit