JP4852654B2 - Pressure flow control device - Google Patents

Description

  The present invention relates to a pressure-type flow rate control apparatus mainly used in semiconductor manufacturing equipment, chemical plants, and the like. More specifically, a pressure sensor for measuring fluid pressure is constituted by a resistance element, and at the same time, this resistance element is measured for fluid temperature. The present invention relates to a pressure type flow rate control device used as a temperature sensor for an automobile.

  In semiconductor manufacturing facilities, chemical plants, and the like, there are many cases where a plurality of gases serving as raw materials are supplied at a predetermined flow rate, and the raw material gases are chemically reacted in a reaction furnace to generate a target gas. In such a case, if the supply flow rate of the source gas is not accurate, excess or deficiency in the chemical reaction occurs, and the source gas remains in the target gas. In particular, if the source gas is flammable, there is a risk of explosion.

  Conventionally, in order to accurately control the gas flow rate, an orifice is arranged in the pipe, and a flow rate method having the highest possible accuracy as a theoretical flow rate passing through the orifice has been selected. In particular, in consideration of the incompressibility of the gas flow, a method of controlling the flow rate by setting the flow velocity of the gas flow passing through the orifice in the sonic region is used.

In this flow rate control method, when the pressure ratio P ₂ / P ₁ between the upstream pressure P ₁ and the downstream pressure P ₂ of the orifice is made smaller than a critical value of about 0.5, the flow velocity of the gas passing through the orifice becomes the sonic velocity. Thus, the property that the theoretical flow rate expression is expressed by Qc = KP ₁ with high accuracy in this sound velocity region is used. Here, it is known that the proportionality coefficient K depends on the type of fluid and the fluid temperature.

To control the orifice passing flow rate by this theory flow type, it is necessary to accurately measure the fluid temperature T on the upstream side pressure P ₁ and the upstream side of the orifice. Upstream pressure P ₁ is the pressure receiving by the diaphragm, are measured by the resistance element via the pressure transmission medium. On the other hand, the fluid temperature T is measured by placing a thermistor separately in a valve device incorporating an orifice.

JP-A-8-338546 JP 2000-322130 A

  As described above, the upstream pressure acts in direct contact with the diaphragm and is measured by the resistance element, which is a pressure sensor, via the pressure transmission medium, so that the fluid pressure can be accurately measured. On the other hand, the thermistor, which is a temperature sensor, is not in direct contact with the fluid, but is disposed in the vicinity of the orifice in the valve device described above. Since the fluid continuously passes through the orifice, it is considered that the temperature near the orifice reaches a thermal equilibrium state with the fluid and the temperature is equal, and the thermistor placed near the orifice can accurately reproduce the fluid temperature. Because it was thought.

However, since the valve device is generally made of metal, the thermal conductivity is extremely high. The heat drawn from the fluid at the orifice location is rapidly transferred to the outer surface of the valve device, and even at a temperature slightly away from the orifice due to this temperature gradient, it is not the same as the fluid temperature. Since the thermistor has a finite geometric dimension, even if the thermistor is placed near the orifice, the measured temperature is considered to deviate slightly from the fluid temperature. Therefore, the thermistor temperature when computing the flow rate of the fluid temperature, the first cause of inducing errors in the calculated flow rate by Qc = KP _1.

Further, the upstream pressure P ₁ and the fluid temperature T used for the calculation of Qc = KP ₁ are theoretically the pressure and temperature at the same point of the upstream fluid. This can be understood from the fact that the pressure P and the temperature T at the same point are used in the process of deriving the flow rate equation Qc = KP ₁ .

  However, in the conventional pressure type flow rate control device, as described above, the fluid pressure is measured by the resistance element, and the fluid temperature is measured by the thermistor arranged separately. Even if the resistance element and the thermistor are minimized, the measurement points for pressure and temperature are inevitably different because they are separate bodies. In the actual situation where both have a finite size and the mounting positions are different, the pressure and temperature measurement positions are somewhat separated, which causes a second error in the flow rate equation.

  Therefore, the temperature measuring device of the pressure type flow control device according to the present invention directly measures the fluid temperature at the same position as the position where the fluid pressure is measured, thereby satisfying the theoretical request of the flow type and passing through the orifice. It aims at controlling the flow rate of the fluid to be performed with high accuracy. In order to achieve this object, the present invention comprises the following group of inventions.

The present invention provides an orifice for flow rate control, a control valve provided on the upstream side piping of the orifice, a pressure sensor provided on a downstream side of the control valve to detect a fluid pressure P ₁ on the upstream side of the orifice, upstream of the orifice Sensor for detecting the fluid temperature T on the side, correction of the fluid pressure P ₁ based on the temperature T, and a flow rate through the orifice of the fluid according to the calculation formula Q _C = KP ₁ (where K is a proportional constant, P ₁ is the fluid pressure) And a control circuit for correcting the calculation of the flow rate through the orifice based on the fluid temperature T and outputting a control signal to the control valve based on the corrected flow rate calculation value. In a pressure type flow rate control device for controlling the flow rate of fluid through an orifice by controlling opening and closing of a control valve according to a control signal, the pressure is controlled. The sensor and the temperature sensor are connected to a constant current power source between the input terminals of the bridge circuit having four sides formed by four resistors formed on the pressure receiving surface, and the fluid pressure is detected by a voltage change between the output terminals. One pressure temperature sensor that simultaneously detects a temperature and a pressure configured to detect a fluid temperature by a voltage change between input terminals, and the control circuit includes the pressure input through a fixed amplifier circuit and an A / D converter This performing correction corresponding to the fluid temperature T and converts the fluid pressure P ₁ by the span correction means using the data of the memory means to the output voltage V _P corresponding to the pressure P ₁ of the temperature sensor, the pressure P ₁ When a zero pressure drift voltage is generated in the pressure temperature sensor when the pressure is zero, the zero point drift to be corrected corresponding to the fluid temperature T by the zero point correction means using the data of the memory means. Calculates the shift voltage V _O, output the negative value of the zero drift voltage V _O which is the arithmetic to the offset pin of the fixed amplifiers for amplifying the output voltage V _P of the pressure P ₁ via the D / A converter temperature a drift correction means and the output voltage V _T corresponding to the temperature T of the pressure temperature sensor input through a fixed amplifier circuit and a / D converter for converting the fluid temperature T, the temperature drift of the converted fluid temperature T A temperature conversion means for outputting to the correction means, a gas temperature correction means for correcting the temperature of the proportionality constant K of the flow rate calculation formula corresponding to the fluid temperature T from the temperature conversion means, and a calculated flow rate after the correction a comparator circuit for outputting to the control valve the difference between Q _C and the set flow rate Q _S as a control signal, a pressure type flow rate control apparatus characterized by being configured from.
Further, it is desirable that the resistance forming the pressure temperature sensor is a resistance element in which the resistance is diffused on the silicon substrate.

  According to the present invention, the resistance element alone can be used as a pressure sensor and a temperature sensor based on the novel discovery of the present inventors that the resistance element can simultaneously measure fluid pressure and fluid temperature. Therefore, if this resistance element is used as a pressure sensor on the upstream side under critical expansion conditions where the velocity of the fluid passing through the orifice becomes a sonic velocity state, a temperature sensor that has been conventionally required becomes unnecessary, and the same fluid is used. Since one point of pressure and temperature can be measured at the same time, the circuit configuration can be simplified and the flow control performance can be improved, which contributes to the cost reduction of the entire apparatus.

In the present invention, in the temperature drift correcting means 60 of the control circuit, the zero point correcting means 62 and the span correcting means 62 correct the span output drift of the zero point output drift voltage V _O and the pressure voltage VP corresponding to the fluid temperature T. Is performed while utilizing the data in the memory means 64 and the proportional constant K of the flow rate calculation formula corresponding to the fluid temperature T is corrected by the gas temperature correction means 68. It is possible to perform highly accurate pressure type flow rate control.

It is a block diagram of the flow control by the pressure type flow control device using a critical condition. It is a principal part section perspective view of pressure temperature sensor 10 consisting of a resistance element. FIG. 3 is an equivalent circuit diagram of the resistance element shown in FIG. 2. It is an experimental apparatus figure for the pressure characteristic of the pressure temperature sensor 10 and a temperature characteristic measurement. It is a bridge voltage-temperature characteristic figure of three types of pressure temperature sensors. It is a bridge voltage-pressure characteristic figure in the same temperature of three types of pressure temperature sensors. It is a detailed block block diagram of the control system of the pressure type flow control apparatus of this invention. It is a block diagram of the flow control of the pressure type flow control device using the non-critical expansion condition according to the present invention. It is a block diagram of the flow control by the improved pressure type flow control device using the non-critical expansion condition according to the present invention.

  As a result of intensive studies to simultaneously measure the fluid pressure and the fluid temperature at the same position in the fluid, the present inventors stopped arranging the pressure sensor and the temperature sensor separately, and the pressure sensor was simultaneously used as a temperature sensor. The present invention has been conceived with the idea that it cannot be used.

  The present inventors have conventionally used a resistance element as a pressure sensor when controlling the flow rate of fluid. This resistance element utilizes the property that the resistance changes when pressure is applied. Generally, four resistors are formed on a silicon substrate, and the four resistors are four Wheatstone bridges. Is configured.

  The principle of this pressure sensor is as follows. A constant current flows through the resistor by a constant current power source connected between the input terminals of the Wheatstone bridge. When the pressure is applied, the resistance value of the resistor changes. Therefore, the voltage between the output terminals of the bridge changes, and the fluid pressure can be measured by the voltage between the output terminals.

  In order to use this pressure sensor as a temperature sensor at the same time, the present inventors paid attention to the input terminal of the Wheatstone bridge. Although a constant current power source is connected between the input terminals, but no voltage power source is connected, the voltage between the input terminals naturally changes according to the resistance change.

  As a result of measuring the voltage between the input terminals while changing the temperature, the present inventors have found that the voltage changes over a wide range with respect to the temperature change. In addition, when only the pressure was changed while keeping the temperature constant, the voltage between the input terminals hardly changed or showed only a change within the error range allowed by the device of the present invention.

  From the above results, it was proved that the fluid temperature can be measured by the voltage between the input terminals of the resistance element. Therefore, hereinafter, the voltage between the input terminals is also referred to as a bridge voltage, and is used exclusively for fluid temperature measurement. Further, since the voltage between the output terminals is used for measuring the fluid pressure as before, this resistance element is a pressure sensor and a temperature sensor that function to the same point of the fluid, and is collectively referred to as a pressure temperature sensor. You can also.

  Embodiments of a pressure type flow rate control device according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a configuration diagram of flow rate control by a pressure type flow rate control device using critical expansion conditions. Since the pressure type flow rate control device 2 is based on the assumption that the supplied fluid is in a critical expansion condition, that is, the velocity of the fluid flowing out from the orifice 4 is a sonic velocity, the flow rate is represented by Qc = KP _1. The

  The pressure type flow rate control device 2 includes an orifice 4 having an orifice hole 4a, an upstream pipe 6, a downstream pipe 8, an upstream pressure temperature sensor 10, a control circuit 16, a valve drive unit 20, and a control valve 22. Has been placed.

  The pressure temperature sensor 10 is composed of a resistance element, and detects the upstream fluid pressure with the voltage between the output terminals of the Wheatstone bridge, as described later, and the same point in the fluid with the voltage between the input terminals (also called the bridge voltage). The fluid temperature is configured to be detected.

  The control circuit 16 is mainly composed of an electronic circuit, a microcomputer, and a built-in program. However, the control circuit 16 may be composed only of an electronic circuit, or may be composed of an electronic circuit and a personal computer. The control circuit 16 includes an electronic circuit system such as an amplifier circuit and an A / D converter (not shown), a flow rate calculation unit 17 that calculates a flow rate Qc based on an experimental flow rate equation, and a flow rate setting unit 18 that instructs a set flow rate Qs to flow. And a comparing means 19 for calculating a flow rate difference ΔQ (= Qs−Qc) between the calculated flow rate Qc and the set flow rate Qs. The flow rate difference ΔQ may be calculated by Qc−Qs.

  On the upstream side of the pressure type flow control device 2, a gas tank 24 containing a high pressure gas, a regulator 26 for adjusting the gas pressure of the high pressure gas appropriately, and supplying this gas to the control valve 22 from a supply side pipe 27. A valve 28 is connected.

Further, on the downstream side of the pressure type flow rate control device 2, a control side pipe 29 for flowing a flow-controlled gas, a valve 30 for supplying this gas to the chamber 32, and a vacuum pump 34 are connected. Chamber 32 is a reaction chamber for generating in the reaction chamber to produce the desired gas from a raw material gas to be supplied, for example, from the source gas of H ₂ and O ₂ in H _{2 O} water vapor.

  Next, the control operation of the pressure type flow control device 2 will be described. On the upstream side, a gas having a predetermined pressure is supplied to the supply side pipe 27, and the supply flow rate to the upstream side pipe 6 is controlled by a control valve 22 that is controlled to be opened and closed by the valve drive unit 20. At the same time, the downstream pipe 8 is set to a low pressure by the vacuum pump 34 on the downstream side.

In the exhaust gas by the vacuum pump 34, the downstream side pressure P ₂ in the downstream pipe 8 is considerably smaller set than the upstream pressure P _1, at least P _{2 /} P 1 _<0.5 the critical expansion conditions are always satisfied Therefore, the gas velocity flowing out from the orifice hole 4a is a sonic velocity. Accordingly, the flow rate through the orifice 4 is represented by Qc = KP _1.

The upstream pressure P ₁ is measured by the pressure temperature sensor 10. In order to perform accurate pressure measurement, the gas pressure is directly received by a diaphragm having excellent corrosion resistance, and the pressure is measured by the sensor portion of the pressure temperature sensor 10 via a pressure transmission medium. In addition, the sensor portion is designed to be extremely small so as not to disturb the gas flow. Therefore, the sensor portion is equal to the gas temperature T.

  FIG. 2 is a cross-sectional perspective view of a main part of the pressure temperature sensor 10 made of a resistance element. A glass pedestal 37 is disposed on a header 35 having lead pins 36, 36, and a silicon substrate 38 supported at both ends by leg portions 38 a, 38 a is fixed on the glass pedestal 37. A gap-like space 39 is formed on the lower surface of the silicon substrate 38, and a through hole 41 is continuously drilled in the space 39.

  Four resistors 41a, 41b, 41c, and 41d are formed on the upper surface of the silicon substrate 38 by a thermal diffusion method. This resistance has the property that when a stress is applied to the surface, the electrical resistance changes in accordance with the stress. Therefore, when a constant current is passed, the voltage changes according to the stress, and pressure measurement is possible by this voltage change.

  The gas pressure (fluid pressure) is received by a diaphragm (not shown) to generate pressure P in the pressure transmission medium (fluid), the pressure P generated in the pressure transmission medium presses the upper surface of the silicon substrate 38, and the pressure P is resistance. Acts on 41a-41d. On the other hand, when the space 39 is evacuated, the silicon substrate 38 is deformed only by the fluid pressure P, so that the absolute pressure of the fluid acts on the silicon substrate 38 and functions as an absolute pressure sensor. When the through hole 41 is open to the atmosphere, the differential pressure between the fluid pressure P and the atmospheric pressure causes the silicon substrate 38 to be deformed, so that the gauge pressure of the fluid acts on the silicon substrate 38 and functions as a gauge pressure sensor. .

  FIG. 3 is an equivalent circuit diagram of the resistance element shown in FIG. The resistors 41a, 41b, 41c, and 41d constitute four sides of the Wheatstone bridge. Input terminals 42a and 42b are connected to one of the diagonal points C and D, and a constant current power source 43 is connected between the input terminals. Yes. The other diagonal points A and B are connected to output terminals 44a and 44b.

The resistance values of the four resistors 41a, 41b, 41c, and 41d change upon receiving the pressure P. A constant current I is passed from the constant current source 43 in the arrow direction, the potential difference between AB is changed by resistance change, the voltage V _P which corresponds to the fluid pressure between the output terminals 44a · 44b occurs. In this specification, referred to as the output terminal voltage of the voltage V _P, also referred to as pressure voltage in the sense of the detected voltage of the fluid pressure.

In order to use this resistance element also for fluid temperature measurement, the present inventors paid attention to the other diagonal points C and D. Since the constant current I causes a potential difference between the points CD, and this potential difference can be detected between the input terminals 42a and 42b, it is also referred to as an input terminal voltage or a bridge voltage. The inventors have predicted that this bridge voltage V _T will vary considerably with fluid temperature.

FIG. 4 is an experimental apparatus diagram for measuring pressure characteristics and temperature characteristics of the pressure temperature sensor 10. A pressure type flow rate control device 2 loaded with a pressure temperature sensor 10 made of a resistance element is disposed in the thermostatic chamber CT, and a reference pressure generator PG and a vacuum pump DP are connected to the piping system PS via valves V ₁ and V _2. It is connected to the.

First, close the valve _{V 1,} by opening the valve _{V 2,} vacuum piping system PS by a vacuum pump DP, i.e. the internal pressure is set to 0 (kPa · abs). In this state, the pressure temperature sensor 10 is operated for each temperature while changing the internal temperature of the thermostatic chamber CT from 25 ° C. to 100 ° C. No. 1, no. 2 and no. The bridge voltage V _T was measured for each temperature with the absolute pressure zero for the three types of pressure temperature sensors 3.

FIG. 5 is a bridge voltage-temperature characteristic diagram of three types of pressure temperature sensors. This characteristic diagram is obtained in a vacuum state where the absolute pressure is zero, the horizontal axis indicates the temperature T (° C.), and the vertical axis indicates the bridge voltage V _T (V).

The three types of pressure temperature sensors 10 are no. 1, no. 2 and no. 3, the temperature of the thermostatic chamber CT was changed from 25 ° C. to 100 ° C. The dependency of the bridge voltage V _T (V) on the temperature T (° C.) is as follows. 1 is a solid line. 2 is a chain line and No.2. 3 is indicated by a broken line and is substantially a straight line.

No. 1, no. 2 and no. 3, the bridge voltage V _T at 25 ° C. was 7.295 V, 7.380 V and 7.271 V, and the bridge voltage V _T at 100 ° C. was 8.966 V, 9.076 V and 8.925 V. The difference in individuality between pressure and temperature sensors is about 0.15 V at the same temperature, but the linearity of each sensor is extremely high.

Temperature differential 75 ° C. from 25 ° C. to 100 ° C., the amount of change of the bridge voltage _{V T} is the 2.228V (No.1), 2.205V (No.2 ) and 2.261V (No.3) . Therefore, the variation of the bridge voltage _{V T} per 1 ℃ is, 22.28mV (No.1), it can be seen quite large and 22.05mV (No.2) and 22.61mV (No.3). Since the bridge voltage V _T changes by about 20 mV with a change of 1 ° C., it is shown that the temperature T can be measured by the bridge voltage V _T.

FIG. 6 is a bridge voltage-pressure characteristic diagram at the same temperature of three types of pressure temperature sensors. Or bridge voltage V _T of the pressure temperature sensor 10 is how much change the pressure was measured. If the bridge voltage is almost independent of pressure, it is demonstrated that the bridge voltage V _T can be used for temperature measurement.

FIG. 6 shows two experimental results when the temperature is maintained at 25 ° C. and when the temperature is maintained at 100 ° C. Both the case of changing the pressure P to 0~700 (kPa · abs), bridge voltage _{V T} was measured.

When the pressure P is changed from 0 to 700 (kPa · abs) at 25 ° C., the bridge voltage V _T becomes 7.295 V → 7.285 V (No. 1), 7.271 V → 7.261 V (No. 2) and The voltage changed from 7.380 V to 7.370 V (No. 3). Accordingly, the pressure change of 700 (kPa · abs), the variation of the bridge voltage _{V T} in all three kinds of pressure temperature sensor showed only very small changes and -10 mV.

Further, when the pressure P is changed from 0 to 700 (kPa · abs) at 100 ° C., the bridge voltage V _T becomes 8.966 V → 8.956 V (No. 1), 8.925 V → 8.915 V (No. 2). ) And 9.076V → 9.067V (No. 3). Accordingly, the pressure change of 700 (kPa · abs), the variation of the bridge voltage _{V T} of the three pressure temperature sensor of -10 mV, -10 mV and -9mV next, although the difference of individuality of sensor appears, above As with, it showed only very small changes.

In summary, the pressure change of 700 (kPa · abs), at 25 ° C. -10mV, changes in bridge voltage _{V T} of the 100 ° C. to about -10mV observed. Since the bridge voltage V _T changes by about 2 V with respect to a temperature change of 75 ° C., 10 mV is only 0.5%.

Discuss some more errors. If the actual working pressure of the gas fluid is 350 (kPa · abs), the fluctuation of the bridge voltage V _T is 10 mV / 2 = 5 mV. No. Since one pressure temperature sensor changes by 22.28 mV per 1 ° C., the above 5 mV only gives a temperature error of 0.224 ° C. from 5 / 22.8.

  This temperature error of 0.224 ° C. gives only an error of 0.04% by the required calculation in the gas temperature correction. If the zero point temperature drift as a pressure sensor is 0.1% per 1 ° C., an error of 0.1% × 0.224 = about 0.02% is induced with respect to a temperature error of 0.224 ° C. Accordingly, the temperature error of 0.224 ° C. only induces an error of 0.04% + 0.02% = 0.06% to 0.06%. Since the error of the pressure type flow rate control device is designed to be 1% or less, for example, the error of 0.06% is only a level that is buried in the overall error.

Therefore, a pressure temperature sensor using a resistance element can simultaneously measure pressure and temperature without correlation, and can function as a temperature sensor as well as a pressure sensor. Thus, the performed temperature measurement in, as described above, the output terminal voltage of the resistance element performs pressure measurement in (pressure voltage) V _P, the voltage between the input terminals, namely _(also referred to as temperature voltage) bridge voltage V _T, It can be said that the resistance element is a suitable element to be called a pressure temperature sensor.

FIG. 7 is a detailed block diagram of the control system of the pressure type flow rate control apparatus of the present invention. Pressure temperature sensor 10 described above for measuring the fluid temperature T on the upstream side pressure P ₁ and the same point of the fluid at the same time. This pressure voltage (voltage between the output terminals) V _P corresponding to the pressure P ₁ of the pressure temperature sensor 10 is amplified by the fixed amplifier circuit 45 and the variable amplifier circuit 47, it is inputted to the CPU51 via the A / D converter 48 It is converted to the pressure _{P 1.} Further, the upstream pressure P ₁ is displayed outside through the variable amplifier circuit 46.

The pressure temperature sensor 10 is composed of a resistance element, and may output a pressure voltage V ₀ even when the pressure is zero, and this V _{0 is referred} to as a zero point drift voltage. In this case, the voltage −V ₀ is output to the offset terminal 45a via the offset D / A converter 49, and the zero point drift is forcibly set to zero.

On the other hand, the pressure temperature sensor 10 outputs a bridge voltage V _T corresponding to the fluid temperature T, and outputs the bridge voltage V _T to the CPU 51 via the fixed amplifier 56 and the A / D converter 58. This bridge voltage V _T is converted into a fluid temperature T by the temperature converting means 50.

  This fluid temperature T is input to the temperature drift correction means 60 and the gas temperature correction means 68. In the temperature drift correction means 60, the zero point correction means 62 and the span correction means 66 perform correction corresponding to the fluid temperature T while utilizing the data in the memory means 64. In the gas temperature correction means 68, the proportional coefficient K of the calculated flow rate Qc is corrected using the fluid temperature T.

In this way, the accurate upstream pressure P ₁ and proportionality constant K are calculated, and the calculated flow rate Qc is calculated from these data as Qc = KP ₁ . The calculated flow rate Qc is output via the D / A converter 72 and the fixed amplifier circuit 74 and displayed on an external display device (not shown).

  The set flow rate Qs input as the target flow rate from the flow rate setting means 18 is input to the comparison means 19 via the fixed amplifier circuit 76 and the A / D converter 78. On the other hand, the calculated flow rate Qc is input from the gas temperature correction unit 68 to the comparison unit 19, and the flow rate difference ΔQ is calculated as ΔQ = Qc−Qs and output to the valve drive unit 20.

Valve drive section 20, the flow rate difference and closes adjust the valve opening of the control valve 22 to the ΔQ to zero, the upstream pressure P ₁ is controlled by the opening and closing. As a result, ΔQ becomes zero, and the calculated flow rate Qc is automatically controlled so as to coincide with the set flow rate Qs.

  In the present invention, the surprising discovery that a resistance element conventionally used as a pressure sensor also functions as a temperature sensor opens the way to use one resistance element as a pressure temperature sensor. Therefore, as can be seen from the block diagram, the pressure and temperature can be measured with one pressure temperature sensor, and the circuit configuration can be simplified and the cost can be reduced at the same time.

  FIG. 8 is a configuration diagram of a pressure type flow rate control device using non-critical expansion conditions according to the present invention. This pressure type flow control device 2 is premised on the case where the fluid to be supplied is in a non-critical expansion condition, that is, the fluid velocity of the fluid flowing out from the orifice 4 is lower than the sonic velocity.

When the fluid is in a non-critical expansion condition, one of the theoretical flow equations for the flow rate through the orifice is derived from Bernoulli's theorem that holds for incompressible fluids, and Q = KP ₂ ^1/2 (P ₁ −P ₂ ) ^1/2 . However, it is assumed that the fluid temperature does not change before and after passing through the orifice. In FIG. 8, this theoretical flow rate equation is used to control the gas flow rate.

This flow rate formula, the orifice throughput Q is calculated using both the upstream pressure P ₁ and downstream pressure P _2. However, since either the upstream side or the downstream side may be used for the fluid temperature T, the pressure temperature sensor 10 of the present invention is disposed on the upstream side, and only the pressure sensor 12 is disposed on the downstream side. Accordingly, the upstream pressure P ₁ and the fluid temperature T are measured by the pressure temperature sensor 10, the downstream pressure P ₂ is always measured by the pressure sensor 12, and the calculated flow rate Qc is calculated as Qc = KP ₂ ^1/2 (P ₁ −P ₂ ) Calculate by ^1/2 .

The difference from FIG. 1 is that the electronic circuitry and software system to enter the downstream pressure P ₂ to the control circuit 16 and measured by the pressure sensor 12 is added. Since the function and effect are substantially the same as those in FIG. 1, the details thereof are omitted.

  FIG. 9 is a configuration diagram of the flow rate control by the improved pressure type flow rate control device using the non-critical expansion condition according to the present invention. This pressure type flow rate control device 2 is based on the premise that the supplied fluid is in a non-critical expansion condition, but uses an improved theoretical flow rate equation.

Since an actual gas fluid has expandability and compressibility, Bernoulli's theorem based on incompressibility can only be established approximately. Therefore, the flow rate expression represented by Qc = KP ₂ ^1/2 (P ₁ −P ₂ ) ^1/2 is only an approximate expression. The inventors of the present invention have studied a flow rate formula that can improve the approximate formula and reproduce the actual flow rate with high accuracy.

As the improved flow _type, it was decided to use _{^{Qc = KP 2 m (P 1}} -P 2) n. Conventionally, two parameters m and n are used as indices, and m and n are derived by fitting the actual flow rate with this flow rate equation. By using these parameters m and n, the actual flow rate could be reproduced with high accuracy.

  In this embodiment, the flow rate calculation means 17 is configured using an improved flow rate equation, and except this point, it is exactly the same as the embodiment shown in FIG. That is, the pressure temperature sensor 10 according to the present invention is disposed on the upstream side, and the pressure sensor 12 is disposed on the downstream side. Other configurations and operational effects are the same as in FIG.

  The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications, design changes, and the like are included in the technical scope without departing from the technical idea of the present invention.

2 is a pressure flow control device, 4 is an orifice, 4a is an orifice hole, 6 is an upstream pipe, 8 is a downstream pipe, 10 is an upstream pressure temperature sensor, 12 is a downstream pressure sensor, and 16 is a control circuit. , 17 is a flow rate calculation means, 18 is a flow rate setting means, 19 is a comparison means, 20 is a valve drive unit, 22 is a control valve, 24 is a gas tank, 26 is a regulator, 27 is a supply side pipe, 28 is a valve, and 29 is a control Side piping, 30 is a valve, 32 is a chamber, 34 is a vacuum pump, 35 is a header, 36 is a lead pin, 37 is a glass base, 38 is a silicon substrate, 38a is a leg, 39 is a space, 41a to 41d are resistors, 42a and 42b are input terminals, 43 is a constant current power source, 44a and 44b are output terminals, 45 is a fixed amplifier circuit, 45a is an offset terminal, 46 is a variable amplifier circuit, 47 is Variable amplifier circuit, 48 A / D converter, 49 D / A converter for offset, 50 Temperature conversion means, 51 CPU, 56 fixed amplifier circuit, 58 A / D converter, 60 temperature drift Correction means, 62 is zero point correction means, 64 is memory means, 66 is span correction means, 68 is gas temperature correction means, 72 is a D / A converter, 74 is a fixed amplifier circuit, 76 is a fixed amplifier circuit, and 78 is A / D converter, CT is a thermostat, _{P 1} is the pressure upstream, _{P 2} is the downstream pressure, PG is a reference pressure generator, Qc is calculated flow rate, Qs is set flow rate, Delta] Q is the flow rate difference, _{V 0} is Zero point output drift voltage, V ₁ and V ₂ are valves, _VP is a pressure voltage, and _VT is a bridge voltage (temperature voltage).

Claims (2)

An orifice for flow rate control, a control valve provided on the upstream side piping of the orifice, a pressure sensor for detecting the fluid pressure P ₁ on the upstream side of the orifice provided on the downstream side of the control valve, the fluid temperature of the upstream side of the orifice A temperature sensor for detecting T, correction of the fluid pressure P ₁ based on the temperature T, and calculation of the flow rate of fluid through the orifice by an arithmetic expression Q _C = KP ₁ (where K is a proportional constant, P ₁ is fluid pressure) And a control circuit for correcting the calculation of the flow rate through the orifice by the fluid temperature T and outputting a control signal to the control valve based on the corrected flow rate calculation value, and is controlled by the control signal from the control circuit. In a pressure type flow rate control device for controlling the flow rate of fluid through an orifice by controlling opening and closing of a valve, the pressure sensor and The degree sensor is connected to a constant current power source between the input terminals of the bridge circuit having four sides formed by four resistors formed on the pressure receiving surface, and the fluid pressure is detected by a voltage change between the output terminals. A pressure temperature sensor configured to simultaneously detect a temperature and a pressure configured to detect a fluid temperature by a voltage change between them, and the control circuit is configured to input the pressure temperature sensor through a fixed amplifier circuit and an A / D converter with this by performing correction corresponding to the fluid temperature T by span correction means using the data of the memory means to the output voltage V _P corresponding to the pressure P ₁ is converted into fluid pressure P ₁ of the pressure P ₁ is zero the pressure temperature sensor zero point drift voltage when the zero drift voltage occurs to be corrected corresponding to the fluid temperature T by the zero point correcting means using the data in the memory means of the pressure V during Calculated and a temperature drift correcting means for outputting a negative value of the zero drift voltage V _O which is the arithmetic to the offset pin of the fixed amplifiers for amplifying the output voltage V _P of the pressure P ₁ via the D / A converter The output voltage V _T corresponding to the temperature T of the pressure temperature sensor input through the fixed amplifier circuit and the A / D converter is converted into the fluid temperature T, and the converted fluid temperature T is output to the temperature drift correcting means. setting the temperature converting unit, and the gas temperature correction means in response to the fluid temperature T from the temperature conversion means performs a temperature correction of the proportional constant K of the flow rate calculation equation, the calculated flow rate Q _C after corrected to the pressure type flow rate control apparatus for a comparison circuit for outputting to the control valve the difference between the flow rate Q _S as a control signal, that was formed from the features.   2. The pressure type flow rate control device according to claim 1, wherein the resistance forming the temperature pressure sensor is a resistance element in which resistance is diffused and formed on a silicon substrate.

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