JP2008286812A - Differential flow meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a differential flow meter, having such a simple structure as to lower the cost of production, which can highly accurately measure flow rates with an error E of not more than (1%SP) over a wide flow rate range of 100% to 1% in real time and in an in-line state. <P>SOLUTION: The differential flow meter that measures a flow rate range of 100% to 10% of the maximum flow rate and a differential flow meter that measures a flow rate range of 10% to 1% of the maximum flow rate are combined. Fluid to be measured is selectively supplied to either of the differential flow meters through a switching valve in accordance with the flow rate ranges. This makes it possible to highly accurately measure flow rates over a wide flow rate range. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an improvement of a differential pressure type flow meter and a differential pressure type flow control device (hereinafter referred to as a differential pressure type flow meter, etc.) used in semiconductor manufacturing equipment, chemical plants, food manufacturing plants, etc., so-called in-line state. In addition, the flow rate of fluid in a critical state or non-critical state can be measured or controlled in real time with high accuracy even in a small flow rate region under vacuum. The present invention relates to a differential pressure type flow meter having a simple structure.

  Traditionally, semiconductor manufacturing facilities and chemical plants have used mass flow type flowmeters (thermal mass flowmeters), build-up type flowmeters, differential pressure type flowmeters, etc. for flow measurement and control of process gases and raw material gases. Has been used a lot.

  However, thermal mass flowmeters, etc. have low responsiveness, low measurement accuracy at low flow rates, many troubles during operation, limited types of controlled gas, and pressure fluctuation effects There are many disadvantages such as being easily affected.

  Similarly, build-up type flow meters, etc. have difficulty in real-time flow measurement or flow control, cannot be used in-line, have restrictions on the pressure of the controlled gas, and require a separate line for measurement. There are problems such as to do.

On the other hand, a differential pressure type flow meter using an orifice and a pressure gauge has almost no restrictions depending on the type of gas to be controlled, can be used in an in-line state, and can perform real-time flow measurement or flow control. It has an excellent utility.
Japanese Patent Publication No.59-19365 Japanese Patent Publication No.59-19366 However, this type of differential pressure type flow meter and the like uses a flow rate calculation formula derived from Bernoulli's theorem based on the premise that the fluid is incompressible, and various types thereof are used. Since the fluid flow rate is calculated by adding the above correction, when the pressure change of the fluid is large (that is, when the approximation that the fluid is incompressible is broken), the measurement accuracy and control of the flow rate There is a problem that a significant decrease in accuracy is inevitable, and as a result, highly accurate flow rate measurement or flow rate control cannot be performed.

Furthermore, forced as to solve the difficulties such as the difference pressure flowmeter, critical conditions the fluid passing through the orifice, i.e. such that the fluid velocity is sonic orifice upstream side pressure P ₁ and the orifice downstream side pressure P ₂ Pressure type flowmeters and the like that calculate the flow rate Q of the fluid with the theoretical formula Q = KP ₁ under this critical condition have been developed and disclosed (JP-A-10-55218, etc.) .

However, even in the pressure-flow meter or the like, results in the fluid small flow rate region and becomes (i.e., an orifice upstream side pressure P ₁ and downstream pressure P ₂ and a state in which close) non-critical condition appears, the flow rate as a result A large error is included in the measured value Q or the flow control value Q.

That is, a conventional differential pressure type flow meter (or pressure type flow meter), etc. uses a flow rate calculation formula derived from Bernoulli's theorem assuming that the fluid is incompressible, and is non-critical before the fluid reaches the speed of sound. Under the condition (non-sonic region), the downstream flow rate Q is obtained by Qc = SC (P ₂ (P ₁ -P ₂ )) ^1/2 / T ^{1/2 and} the critical condition after reaching the sound velocity ( In the sound velocity region), the calculation is performed by Qc = SCP ₁ / T ^1/2 . Here, T is the absolute temperature of the fluid when passing through the orifice, S is the sectional area of the orifice hole, and C is a proportional coefficient.

The critical condition for fluid velocity reaches the speed of sound is given by the critical value _{r c} of the pressure ratio _P 2 / _{P 1,} the critical value _{r c,} using a specific heat ratio n of the _{gas, P} 2 _/ P 1 = rc = (2 / (n + 1)) It is _calculated | required by ^{n / (n-1)} .

Further, the specific heat ratio n is given by n = Cp / Cv, where Cp is a constant pressure specific heat and Cv is a constant volume specific heat. In the diatomic molecular gas, n = 7/5 = 1.4 and r _c = 0.53. Further, in the case of the non-linear triatomic molecular gas, n = 8/6 = 1.33, and r _c = 0.54.

By the way, in order to improve the problems of the above-mentioned conventional differential pressure type flow meter (or pressure type flow meter), the inventors of the present application previously derived a conventional theory in which a fluid used under non-critical conditions was derived as incompressible. Comparing the calculated flow rate value by the flow rate equation Q with the actual flow rate measurement value, and calculating a plurality of parameters from the previous theoretical flow rate equation Qc = SC / T ^1/2 (P ₂ (P ₁ −P ₂ )) ^1/2 The experimental flow rate equation Qc ′ = SC / T ^1/2 · P ₂ ^m (P ₁ −P ₂ ) ⁿ = KP ₂ ^m (P ₁ −P ₂ ) ⁿ is derived, and the calculated flow rate by this experimental flow rate equation Qc ′ By determining the parameters m and n so that the values match the measured values, we proposed an experimental flow rate equation Qc ′ that can be better adapted to a compressible fluid, and published this as Japanese Patent Application No. 2001-399433. ing.

In the experimental flow rate equation Qc ′, the proportionality constant K is given by SC / T ^1/2 and is calculated from the material conditions of the gas flow and the absolute temperature T. Also, _{P 1} is an orifice upstream side pressure, _{P 2} represents an orifice downstream side pressure, the unit is kPaA (kilopascal absolute pressure). Furthermore, in the region where the measurement flow rate range is 10 to 30 sccm (flow rate in cc / min in the standard state), the parameters m and n are set to m = 0.47152 and n = 0.49492. Heading.

  The values of the two parameters m and n depend on the flow rate range to be measured and the gas type. The values of m = 0.47152 and n = 0.49492 are in the region where the flow rate is 10 to 30 sccm. However, when the flow rate range is 10 to 100 sccm or 100 to 1000 sccm, the values of m and n deviate from these values.

  FIG. 13 is a configuration diagram of an improved pressure type flow rate control device using the experimental flow rate type Qc ′, which was previously disclosed as Japanese Patent Application No. 2001-399433 by the inventors of the present application. Although the apparatus of FIG. 13 is configured as a flow rate control device, it can be easily understood that a differential pressure type flow meter can be obtained by omitting the control valve 21, the valve drive unit 22, and the flow rate comparison unit 23e. .

In FIG. 13, 20 is an orifice, 21 is a control valve, 22 is a valve drive unit, 23 is a control circuit, 23a is a pressure ratio calculation unit, 23b is a pressure ratio calculation unit, 23c is a flow rate calculation unit, and 23d is a flow rate calculation. parts, 23e are flow comparison section, P ₁ is an orifice upstream side fluid pressure detector, P ₂ is an orifice downstream fluid pressure detector, T is the fluid temperature detector, Qs is a flow rate set value signal, Delta] Q is the flow rate difference signal, Qc ′ is a flow rate calculation value.

In this apparatus, first, the pressure ratio P ₂ / P ₁ is calculated from the detected upstream pressure P ₁ and downstream pressure P ₂ (23a), and it is always determined whether the fluid is in a critical condition or a non-critical condition. (23b) The flow rate calculation is performed using the flow rate equation Qc = KP ₁ in the critical condition (23c), and the non-critical condition using the experimental flow rate equation Qc ′ = KP ₂ ^m (P ₁ −P ₂ ) ^n. .

As described above, the critical value rc is given by (2 / (n + 1))) ^{n / (n-1)} (where n is the specific heat ratio of the gas), and in the diatomic molecular gas, rc = 0. .53, for a non-linear triatomic molecular gas, r _c = 0.54 and r _c = approx. 0.5.

  Further, in the flow rate comparison unit 23a, the flow rate difference ΔQ between the set flow rate Qs and the calculated flow rate Qc is calculated, the valve drive unit 22 is operated so that the flow rate difference ΔQ becomes zero, and the control valve 21 is controlled to open and close. However, when used as a flow meter, the flow rate comparing unit 23e, the control valve 21, and the valve driving unit 22 are not necessary as described above.

Curve A in FIG. 14 shows the flow measurement or flow control characteristics using the improved pressure flow meter of FIG. 11, and curve B shows the pressure flow meter using Qc = KP ₁ under the previous critical conditions. Flow measurement or flow control characteristics are shown respectively. As is apparent from FIG. 14, the improved pressure type flow meter of FIG. 13 uses the critical condition flow rate equation Qc = KP ₁ under the critical condition and the non-critical condition experimental flow equation under the non-critical condition. Since Qc ′ = KP ₂ ^m (P ₁ −P ₂ ) ⁿ is used, an accurate flow rate Q proportional to the set flow rate can be calculated, and the linearity of the flow rate Q with respect to the set% is as shown by a curve A in FIG. Therefore, even in a region where the flow rate is low, it is possible to perform flow rate measurement and flow rate control with relatively high accuracy.

  The improved pressure type flow meter and the like shown in FIG. 13 has a relatively high precision flow rate as long as it is up to about 10% of the maximum flow rate as shown by the curve A in FIG. Measurement or flow rate control can be performed, and excellent practical utility is achieved.

  However, if the flow rate region is a small flow rate region of about 10% or less of the maximum flow rate, there is a problem that practical flow measurement and flow control accuracy cannot be obtained in practice.

Further, in the improved pressure-type flow meter, etc., the pressure P ₂ downstream side of an orifice is about 200Torr following vacuum, measured relative to the reference set flow rate error Error (% SP or% FS) is relatively large, practical There is a difficulty that various problems occur.

The present invention is intended to solve the above-mentioned problems in the improved pressure type flow meter and the like previously developed by the present inventors. From the maximum flow rate (100%) to about 1% of the maximum flow rate. over a wide flow rate range of the degree with high precision flow measurement or flow control can, even in a case where the pressure P ₂ downstream side of the orifice is such that variations thereto and a vacuum error obtained in advance by actual measurement By storing data in a storage device and correcting the flow rate calculation value with reference to this correction data, highly accurate flow rate measurement or flow rate control can be performed, and the structure is simple and can be manufactured at low cost. A differential pressure type flow meter or the like is provided.

  The invention of claim 1 is a combination of a differential pressure type flow meter that measures a flow rate range of 100 to 10% of the maximum flow rate and a differential pressure flow meter that measures a flow rate range of 10% to 1% of the maximum flow rate. The basic configuration of the invention is to perform highly accurate flow rate measurement over a wide flow rate range by switching and supplying the fluid to be supplied to each differential pressure flow meter with a switching valve according to each flow rate range. is there.

According to a second aspect of the invention, in the invention of claim 1, each differential pressure type flow meter, orifice, the fluid pressure P ₁ upstream side of the orifice detector and, the detector fluid pressure P ₂ downstream side of the orifice A differential pressure type flow meter comprising: a fluid temperature T detector on the upstream side of the orifice; and a control calculation circuit for calculating the fluid flow rate Q using the detected pressures P ₁ and P ₂ and the detected temperature T from each detector. And Q = C ₁ · P ₁ / √T · ((P ₂ / P ₁ ) ^m − (P ₂ / P ₁ ) ⁿ ) ^1/2 (where C ₁ is a proportional constant, m And n are constants).

The invention according to claim 3, in the invention of claim 1, each differential pressure type flow meter, orifice, the fluid pressure P ₁ upstream side of the orifice detector and, the detector fluid pressure P ₂ downstream side of the orifice A differential pressure type flow meter comprising: a fluid temperature T detector on the upstream side of the orifice; and a control calculation circuit for calculating the fluid flow rate Q using the detected pressures P ₁ and P ₂ and the detected temperature T from each detector. In addition, the fluid flow rate Q is set to Q = C ₁ · P ₁ / √T · ((P ₂ / P ₁ ) ^m − (P ₂ / P ₁ ) ⁿ ) ^1/2 (however, C ₁ is a proportional constant, m and n are correction data storing the relationship between the flow rate calculation circuit for calculating a constant), the variation of the orifice downstream side pressure P ₂ obtained in advance by actual measurement and the flow rate error error of the fluid flow rate Q Memory circuit and correction data for the calculated fluid flow rate Q A flow rate correction computation circuit for correcting the correction data from憶回path provided, the configuration to correct the fluid flow rate Q which is calculated in accordance with the variation of the orifice downstream side pressure P _2, and outputs a flow rate value Q 'after the correction This is the basic configuration of the invention.

The invention of claim 4 includes a fluid inlet a, a fluid outlet b, a mounting hole 17a of the first switching valve 10, a mounting hole 17b of the second switching valve 11, a mounting hole 18a of the fluid pressure detector 2 upstream of the orifice, and an orifice. A valve body 12 provided with a mounting hole 18b of the downstream fluid pressure detector 3 and a mounting hole of the fluid temperature detector 4 upstream of the orifice, a fluid inlet a formed in the valve body 12, and the first switching valve. Fluid passages 16a, 16b, and 16e that directly connect the bottom surface of the mounting hole 17a, the mounting hole 18a of the fluid pressure detector 2 upstream of the orifice, and the bottom surface of the mounting hole 17b of the second switching valve 11, and the first switching valve. A fluid passage 16f communicating the bottom surface of the mounting hole 17a and the bottom surface of the mounting hole 17b of the second switching valve 11, the bottom surface of the mounting hole 17b of the second switching valve 11, and the mounting hole of the fluid pressure detector 3 on the downstream side of the orifice. 18 A fluid passage 16c communicating with the bottom surface of the fluid, a fluid passage 16d communicating with the bottom surface of the mounting hole 18b of the fluid pressure detector 3 on the downstream side of the orifice and the fluid outlet b, and an orifice fixed to the mounting holes 18a and 18b. A fluid pressure detector 2 on the upstream side, a fluid pressure detector 3 on the downstream side of the orifice, a fluid temperature detector 4 on the upstream side of the orifice, a first switching valve 10 for opening and closing between the fluid passage 16e and the fluid passage 16f, The second switching valve 11 that opens and closes between the fluid passage 16b and the fluid passage 16c, the small-flow orifice 1 'interposed in the middle of the fluid passage 16f, and the fluid passage 16a or the fluid passage 16b. 'and the two pressure detectors 2 and 3 of the sensed pressure P ₁ · P ₂ and temperature detector 4 detects the temperature small flow rate orifice 1 by T' orifice 1 'for a large flow rate and high flow orifice '' The fluid flow _{Q Q = C 1 · P 1} / √T · that flows _- from the ^{_{((P 2 / P 1)}} m (P 2 / P 1) n) control calculation circuit for calculating a ^1/2 The first switching valve 10 is closed and the second switching valve 11 is opened, and the flow rate range of 10% to 1% of the maximum flow rate is the first flow rate range of 100 to 10% of the maximum flow rate. The basic configuration of the invention is to perform measurement with the first switching valve 10 opened and the second switching valve 11 closed.

  According to a fifth aspect of the present invention, in the invention of the fourth aspect, the pressure detector 2 upstream of the orifice, the pressure detector 3 downstream of the orifice, and the temperature detector 4 upstream of the orifice are connected to a differential pressure flow meter. It is intended to be shared with others.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a basic configuration of a first embodiment of a differential pressure type flow meter according to the present invention. The differential pressure type flow meter includes an orifice 1, an absolute pressure type pressure detector 2 upstream of the orifice, and an upstream side of the orifice. It comprises an absolute pressure type pressure detector 3, an absolute gas temperature detector 4 upstream of the orifice, a control arithmetic circuit 5, an output terminal 6, an input terminal 7, and the like. In addition, 8 is a gas supply apparatus, 9 is a gas using apparatus (chamber).

In the differential pressure type flow meter of the present invention, the flow rate Q of the gas passing through the orifice 1 under the differential pressure condition (that is, non-critical condition) is the following (1) in the control arithmetic circuit 5. Calculation is performed using the experimental flow rate equation, and the calculated value is output from the output terminal 6 to the outside. Q = C ₁ · P ₁ / √T · ((P ₂ / P ₁ ) ^m − (P ₂ / P ₁ ) ⁿ ) ^1/2 ·· (1)
The above experimental flow rate equation Q is newly proposed by the present inventor based on the following flow rate calculation equation (2) based on the conventional continuity equation.

尚、（２）式に於いて、δはガス密度、κはガスの比熱比、Ｐ_１はオリフィス上流側圧力、Ｐ_２はオリフィス下流側圧力、Ｔはガス温度、Ｒはガス定数、Ｓはオリフィス断面積であり、当該（２）式は公知のものである。

In equation (2), δ is the gas density, κ is the specific heat ratio of the gas, P ₁ is the pressure upstream of the orifice, P ₂ is the pressure downstream of the orifice, T is the gas temperature, R is the gas constant, and S is The cross-sectional area of the orifice, and the formula (2) is known.

In the equation (1) according to the present invention, Q is a volume flow rate (SCCM) converted to a standard state, C ₁ is a coefficient including the cross-sectional area S of the orifice 1, and P ₁ is an absolute pressure on the upstream side of the orifice ( Pa), _{P 2} is an orifice downstream of the absolute pressure (Pa), T is the absolute temperature of the orifice upstream side gas (K).

Further, m and n are constants determined by calculating κ = 1.40 of N ₂ gas from the equation (2), and in a flow meter having an orifice diameter φ of 2.0 mmφ and a maximum flow rate of 2000 sccm. In the formula (1), C ₁ = 2680, m = 1.4286, and n = 1.143.

Of course, the constants C ₁ , m, and n vary depending on the type of gas that can be measured, but in N ₂ gas, m = 1.4286 and n = 1.7143. Is known.

FIG. 2 is an actual measurement value showing the relationship between the set flow rate value (%) of the differential pressure type flow meter (100% set value 2000 sccm) of FIG. 1, the pressures P ₁ and P ₂ (Torr), and the error Error (% SP). Even if the gas pressures P ₁ and P ₂ are vacuums of 50 Torr or less, if the set flow rate is up to 10% (10% of maximum flow rate = 200 sccm), the flow rate error Error is the set flow rate value (%). Is extremely small (1% SP or less).

  However, when the set flow rate value is 10 (%) or less, the flow rate error Error is -1 (% SP) or more, which causes a problem in practical use of the flow rate measurement value.

FIG. 3 is a diagram showing the relationship between the orifice secondary side pressure P ₂ (Torr), the set flow rate (%), the error Error (% SP), and the secondary side piping conditions of the differential pressure type flow meter according to the present invention. 9a is when the set flow rate (%) is 100 sccm, 9b is 200 sccm, 9c is 400 sccm, 9d is 600 sccm, 9g is 1200 sccm, 9j is 1800 sccm, 9k is 2000 sccm (100% ) In each case. The maximum flow rate (100%) of the differential pressure type flow meter used is 2000 sccm.

  Also, in each set flow rate value (%), the square mark indicates that the outlet side of the differential pressure type flow meter remains on the piping (4.35 mmφ • 100 mm) as shown in FIG. The error error (% SP) when there is not, the diamond mark indicates the error Error (% SP) when a control valve with a Cv value of 0.3 is installed on the outlet side of the differential pressure flow meter, and the triangle mark indicates the Cv value The circles indicate error Error (% SP) when a control valve having a Cv value of 0.1 is provided and when a control valve having a Cv value of 0.1 is provided.

That is, as is clear from FIG. 3, when the working pressure is a vacuum (50 Torr or less), the piping conditions on the secondary side (downstream side of an orifice), that relationship of the pressure P ₂ and the flow rate Q greatly varies As a result, the error Error (% SP) changes.

Therefore, when adjusting the differential pressure flow meter, the flow rate error Error (% SP) when the secondary pipe resistance (conductance) is changed in advance is measured (4 conditions × 11 points in the case of FIG. 3). A correction coefficient for canceling out the error Error is obtained in advance. Then, by correcting the flow rate value Q calculated by the experimental flow rate equation (1) in the flow rate calculation circuit 5 by the correction coefficient, the secondary pressure P _{2 of the} differential pressure type flow meter under the vacuum condition is changed. Even in the case of a change, it is possible to perform a flow calculation with higher accuracy.

FIG. 4 shows a measurement circuit for obtaining the error correction coefficient shown in FIG. 3. A pressure type flow rate control device is used as the standard flow rate controller SF, and a control valve V is used to change the secondary side piping conditions. ₂ can be mounted freely, and the standard flow rate controller SF adjusts the supply gas flow rate (N ₂ (11 points in total) between the flow rate ranges of 100 sccm to 2000 sccm with a gap of 200 sccm. P ₁ , P ₂ , Q, and the pressure P ₂ downstream of the orifice at that time were measured.

Incidentally, the secondary conduit resistance (when connected by conduits differential pressure type flowmeter A direct internal diameter to a vacuum pump 4.35mmφ (about 100mm long)) If there is no control valve V _2, the control valve when the V ₂ Cv value were of 0.3, when the Cv value and that of 0.2 was adjusted by the four cases when the Cv value and that of 0.1.

  Moreover, the measurement flow volume set 11 points in total between 100 sccm-2000 sccm as above-mentioned.

  Further, the error Error (% SP) was calculated by (SF flow rate value−A flow rate value) / SF flow rate value × 100%.

The supply pressure P ₁ to the pressure type flow control device is about 300 kPaG, and the secondary side of the orifice of the differential pressure type flow meter A is evacuated by a vacuum exhaust pump Vp (300 l / min, maximum ultimate pressure 1.2 × 10 ⁻² Torr). A vacuum was drawn continuously.

For example, first, the control valve V ₂ is removed from the secondary side pipe line, and the secondary side pipe line is formed only with a straight stainless steel pipe having an inner diameter φ = 4.35 mm · L = 100 mm, and the pressure type flow control device SF When the supply flow rate was 1000 sccm, the measured value of the differential pressure type flow meter A was about 1000 sccm, the error E was zero, and the secondary pressure P ₂ at that time was about 18 Torr. Similarly, when the supply flow rate from the SF is 2000 sccm, the differential pressure type flow meter A reads 1920 sccm (error E is −4% SP), and the secondary pressure P ₂ at that time is about 29 Torr.

Similarly, if the conditions of the secondary side pipe are changed, the error E = −1% SP and P ₂ = 34.5 Torr when Cv = 0.3 even when the supply flow rate from SF is 2000 sccm (100%). When Cv = 0.2, the error E = −0.05% SP and P ₂ = 40.5 Torr. When Cv = 0.1, the error E = + 2% SP and P ₂ = 59.5 Torr.

By organizing the results of FIG. 3, a table indicating the association of the set flow rate value relative to (% SP), and variable orifice downstream side pressure P ₂ such as shown in the following table and the generated error Error (% SP) Can be obtained.

即ち、約１００Ｔｏｒｒ以下の真空状態下で使用する差圧式流量計に於いて、オリフィス２次側圧力Ｐ_２が何らかの事情で変動した際には、上記表１の補正データを用いて、差圧式流量計の現実の測定値を修正する。

That is, in a differential pressure type flow meter used in a vacuum state of about 100 Torr or less, when the orifice secondary side pressure P ₂ fluctuates for some reason, the differential pressure type flow rate is calculated using the correction data in Table 1 above. Correct the actual measurement of the meter.

For example, if a differential pressure type flow meter in use at 2000 sccm (100%) displays 2000 sccm as a measured value and the pressure P ₂ downstream of the orifice at that time is 60 Torr, the measured value (2000 sccm) is +2 % Error Error (% SP) is included, and correction of + 2% is performed to correct the measured value of 2000 sccm to 1960 sccm.

  FIG. 5 shows a basic configuration of the present invention in which the above correction means is adopted, and a correction data storage circuit 5b and a flow rate value control circuit 5 of the differential pressure type flow meter of FIG. 1 showing the first embodiment. The correction arithmetic circuit 5c is provided.

That is, the flow rate calculation circuit 5a flow rate value Q was calculated using the flow rate empirical formula Q, with reference to an orifice downstream side pressure P ₂ at that time correction data storage circuit 5b from the pressure P ₂ in the in error Error (% SP) is extracted to correct the error Error (% SP) from the flow rate calculation value Q, and the correction value calculation circuit 5c outputs a flow rate value Q 'close to the corrected direct value from the output terminal 6 to the outside. .

FIG. 6 shows a third embodiment of the present invention. In the differential pressure type flow meter of FIG. 5, when under a critical condition, the flow rate is calculated by the flow rate formula of Q = KP ₁ , and In the non-critical condition, the flow rate calculation is performed by the control calculation circuit 5 of FIG.

That is, as shown in FIG. 6, in the differential pressure type flow meter of the third embodiment, the control calculation circuit 5 of FIG. 5 includes a pressure ratio calculation circuit 5d, a critical condition determination circuit 5e, and a flow rate calculation under critical conditions. First, the ratio (γ) between the orifice upstream pressure P ₁ and the downstream pressure P ₂ is obtained, the pressure ratio γ is compared with the critical pressure ratio γc, and the critical condition is satisfied. Sometimes, Q = KP _{1 is used} to calculate the flow rate and output the calculated value.

When the flow rate is in a non-critical condition, the flow rate is calculated by the flow rate equation Q = C ₁ · P ₁ / √T · ((P ₂ / P ₁ ) ^m − (P ₂ / P ₁ ) ⁿ ) ^1/2. After the calculation value Q is corrected by the flow rate correction calculation circuit 5c, the corrected flow rate value Q 'is output from the output terminal 6.

  On the other hand, in the first to third embodiments, even if the experimental flow rate calculation formula Q is used or the flow rate calculation value Q is corrected Q ′, the error error of the flow rate measurement value can be practically used. The flow rate range is 100 to 10 (%), and the error error can be reduced to 1 even if correction is performed. It is difficult to keep it below (% SP).

  Therefore, in the fourth embodiment of the present invention, two sets of differential pressure type flow meters according to the first to third embodiments having different flow ranges are combined, and the two sets of differential pressure type flow meters are switched. As a result, the entire flow rate can be measured with a high accuracy with an error Error of 1 (% SP) or less over a wide flow rate range of 100 (%) to 1 (%).

  FIG. 7 is an overall configuration diagram of the differential pressure type flow meter according to the fourth embodiment. In FIG. 7, 10 is a first switching valve (NC type), and 11 is a second switching valve (NC type). , A is a gas inlet side, b is a gas outlet side, 1 ′ is a first orifice (for small flow rate), 1 ″ is a second orifice (large flow rate side), 5 ′ is a first control arithmetic circuit, 5 ″. Is a second control arithmetic circuit.

  That is, a differential pressure type flow meter on the small flow rate side (for example, a flow rate range of 10 to 100 sccm) by the first orifice 1 ′, the first control arithmetic circuit 5 ′, etc., and the second orifice 1 ″ and the second control arithmetic circuit 5 ”Etc. constitute a differential pressure type flow rate control device (for example, a flow rate range of 100 to 1000 sccm) on the large flow rate side, and a flow rate range of 1000 sccm (100%) to 10 sccm (1%) by both differential pressure type flow rate control devices. The flow rate can be measured with high accuracy with error Error of 1 (% SP) or less over a wide range.

  FIG. 8 is a schematic cross-sectional view of the main part of a differential pressure type flow meter according to a fourth embodiment of the present invention. First and second control arithmetic circuits 5 ′, 5 ″, etc. forming both differential pressure type flow meters. Is omitted.

  In FIG. 8, 12 is a body, 13a and 13b are seals, 14a is a mounting bolt for the upstream upstream absolute pressure detector 2, 14b is a mounting bolt for the downstream downstream absolute pressure detector 3, 15a, Reference numeral 15b denotes a diaphragm valve mechanism, 10a, 11a driving cylinder.

  The body 12 is formed by assembling the gas inlet member 12a, the gas outlet member 12b, the first body member 12c, and the second body member 12d in an airtight manner, and is made of stainless steel.

  Further, mounting holes 17a and 17b of the first switching valve 10 and the second switching valve 11 are provided on the upper surface side of the block-shaped first body member 12c and the second body member 12d, and further, the orifice upstream is provided on the lower surface side thereof. Mounting holes 18a and 18b for the side pressure detector 2 and the orifice downstream pressure detector 3 are formed, respectively.

  Although not shown in FIG. 8, a mounting hole for the gas temperature detector 4 on the upstream side of the orifice is formed in the first body member 12c.

  Further, each body member 12c, 12d, etc. has a fluid inlet a, a bottom surface of the mounting hole 17a of the first switching valve 10, a bottom surface of the mounting hole 18a of the orifice upstream pressure detector 2, and a mounting hole of the second switching valve 11. The fluid passages 16a, 16b, and 16e that communicate with the bottom surface of 17b, the fluid passage 16f that communicates between the bottom surfaces of the mounting hole 17a and the mounting hole 17b, and the bottom surface of the mounting hole 17b and the bottom surface of the mounting hole 18b communicate with each other. The fluid passage 16c, the fluid passage 16d communicating the bottom surface of the mounting hole 18b, and the fluid outlet b are respectively formed.

  Further, the fluid passage 16 is provided with a small flow rate orifice 1 ′, and the fluid passage 16a (or 16b) is provided with a large flow rate orifice 1 ″. In the embodiment of FIG. The orifices 1 ′ and 1 ″ are arranged on the joint surfaces of the body members 12c and 12d.

  The valve seats communicating with the fluid passages 16e and 16b formed in the bottom surfaces of the mounting holes 17a and 17b are opened and closed by the valve mechanisms 15a and 15b of the first switching valve 10 and the second switching valve 11, respectively. By opening and closing, the passage 16e and the passage 16f and the passage 16c and the passage 16b are opened and closed.

  The passage 16c always communicates between the mounting holes 17b and 18b.

  7 and 8, first, when the measured flow rate is in a large flow rate range, the first switching valve 10 is closed, the second switching valve 11 is opened, and the gas flowing in from the gas inlet a is passed through the passage 16a, The gas flows out from the gas outlet b through the orifice 1 ″, the passage 16b, the passage 16c, and the passage 16d. Then, a flow rate calculation is performed by a second control calculation circuit 5 ″ (not shown), and the result is output to a necessary location.

  When the measured flow rate region decreases to 10% or less of the rated flow rate, the first switching valve 10 is opened and the second switching valve 11 is closed. As a result, the gas flow flows out from the gas outlet b through the passage 16a, the passage 16e, the small flow rate orifice 1 ', the passage 16f, the passage 16c, and the passage 16d. In the meantime, the flow rate calculation is performed by the first control calculation circuit 5 ′ and output to the necessary part is the same as in the measurement in the large flow rate region.

  Since the material of the body 12, the processing of the inner surface of the gas passage, the diaphragm valve mechanisms 15a and 15b, the pressure detectors 2 and 3, the temperature detector and the like are well known, the description thereof is omitted here.

  FIG. 9 shows a first embodiment of a differential pressure type flow rate control apparatus according to the present invention. A control valve 21 and a valve drive unit 22 are provided in the differential pressure type flow meter shown in FIG. Is provided with a flow rate comparison circuit 5g, which calculates the flow rate difference ΔQ between the set flow rate Qs input from the outside and the calculated flow rate Q calculated by the flow rate calculation circuit 5a, and controls the flow rate difference ΔQ to the valve drive unit 22. Input as a signal. As a result, the control valve 21 is operated in such a direction that the flow rate difference ΔQ becomes zero, and the gas flow rate Q flowing through the orifice 1 is controlled to the set flow rate Qs.

  FIG. 10 shows a second embodiment of the differential pressure type flow rate control device. The control valve 21 and the valve drive unit 22 are provided in the differential pressure type flow meter shown in FIG. 5g is provided.

  In the flow rate comparison circuit 5g, the flow rate difference ΔQ is calculated using the corrected flow rate Q ′ obtained by correcting the error in the calculation flow rate Q by the correction calculation circuit 5c, and the control valve 21 is set in the direction in which the flow rate difference ΔQ becomes zero. Is controlled to open and close.

  FIG. 11 shows a third embodiment of the differential pressure type flow rate control device. The differential pressure type flow meter shown in FIG. 6 is provided with a control valve 21 and a valve drive unit 22, and correction data is stored from the control arithmetic circuit 5. Except for the circuit 5b and the correction arithmetic circuit 5c, a flow rate comparison circuit 5g is provided instead.

  That is, when the gas flow is under a critical condition, the calculated flow rate Q from the second flow rate calculation circuit 5f is used, and when the gas flow is under a non-critical condition, the calculated flow rate Q from the flow rate calculation circuit 5a is used. The flow rate difference ΔQ is calculated and the control valve 21 is controlled to be opened and closed in a direction that makes the flow rate difference ΔQ zero.

  FIG. 12 shows a fourth embodiment of the differential pressure type flow rate control device. The control valve 21 and the valve drive unit 22 are provided in the differential pressure type flow meter shown in FIG. It is set as the structure which provides 5g.

  That is, when the gas flow is under a critical condition, the calculated flow rate Q from the second flow rate calculation circuit 5f is used, and when the gas flow is under a non-critical condition, the calculated flow rate Q from the flow rate calculation circuit 5a is used. The flow rate difference ΔQ is calculated using the flow rate Q ′ from the correction calculation circuit 5c with the correction, and the opening / closing control of the control valve 21 is performed in such a direction as to make the flow rate difference ΔQ zero.

  The present invention greatly simplifies the structure of a differential pressure type flow meter and the like, and performs flow rate calculation using a new experimental flow rate calculation formula that can obtain a calculated flow rate value that matches the measured value with extremely high accuracy. Since it is configured, it can be manufactured at low cost, and can be used in an in-line form without being restricted by the mounting posture. In addition, the control flow rate is hardly affected by fluctuations in pressure, and it is highly accurate. Flow measurement or flow control can be performed in real time.

Further, in the present invention, since the control arithmetic circuit is provided with a correction data storage circuit for pressure fluctuation and a calculation flow correction circuit by this, even if pressure fluctuation occurs on the secondary side of the orifice, effect can be easily corrected, even in a condition of state pressure P ₂ is closer to the vacuum (50 Torr or less low pressure) of the orifice secondary side, a high precision without undergoing little effect on the pressure fluctuations Flow measurement or flow control can be performed.

  Further, in the present invention, the differential pressure type flow meter for small flow rate and the differential pressure type flow meter for large flow rate are organically integrated, so that both differential pressure flow meters are switched. By doing so, the error Error (% SP) is 1 (% SP) or less over a wide flow range from the rated flow rate (100%) to a small flow rate (1%) about 1% of the rated flow rate. Measurement can be performed continuously.

  Although the present invention is an inexpensive differential pressure type flow meter having a simple structure as described above, the flow rate of all kinds of gas can be measured over a wide range of flow rate even under a gas use condition of 100 Torr or less. Therefore, it has an excellent practical utility that it can measure or control the flow rate with high accuracy.

It is a basic lineblock diagram of a differential pressure type flow meter concerning a 1st embodiment of the present invention. It is a diagram which shows the error characteristic of the differential pressure type flow meter of FIG. In case an orifice downstream side pressure P ₂ is a vacuum, a graph showing the relationship between the "flow rate and the secondary side pressure and error" in the case of changing the secondary conduit resistance. FIG. 4 shows a measurement circuit used to obtain the data of FIG. It is a basic lineblock diagram of a differential pressure type flow meter concerning a 2nd embodiment of the present invention. It is a basic lineblock diagram of a differential pressure type flow meter concerning a 3rd embodiment of the present invention. It is a systematic diagram which shows the whole differential pressure type flow meter structure concerning 4th Embodiment of this invention. It is a cross-sectional schematic diagram of the principal part of the differential pressure type flow meter which concerns on 4th Embodiment of this invention. It is a basic lineblock diagram of a 1st embodiment of a differential pressure type flow control device concerning the present invention. It is a basic lineblock diagram of a 2nd embodiment of a differential pressure type flow control device concerning the present invention. It is a basic lineblock diagram of a 3rd embodiment of a differential pressure type flow control device concerning the present invention. It is a basic lineblock diagram of a 4th embodiment of a differential pressure type flow control device concerning the present invention. It is a block diagram of the improved pressure type flow control device disclosed previously. It is a diagram which shows the flow volume characteristic of the improved type pressure type flow control apparatus previously disclosed.

Explanation of symbols

Q is an experimental flow rate calculation formula, Q ′ is a corrected flow rate, Qs is a set flow rate, SF is a standard flow rate controller (pressure type flow rate control device), A is a differential pressure type flow meter, and V _{21 to} V ₂₃ are secondary side controls. Valve, VP is an evacuation pump, a is a gas inlet, b is a gas outlet, 1 is an orifice, 1 'is a small flow orifice, 1''is a large flow orifice, 2 is an absolute pressure type pressure detector upstream of the orifice 3 is an absolute pressure type pressure detector downstream of the orifice, 4 is a gas absolute temperature detector upstream of the orifice, 5 is a control calculation circuit, 5a is a flow rate calculation circuit, 5b is a correction data storage circuit, and 5c is a flow rate correction calculation circuit. 5d is a pressure ratio calculation circuit, 5e is a critical condition determination circuit, 5f is a second flow rate calculation circuit for calculating the flow rate under the critical condition, 5g is a comparison circuit between the set flow rate and the calculated flow rate, and 5 'is a first control calculation circuit. 5 ″ is the second control arithmetic circuit, and 6 is the flow output. Terminal, 7 power input terminal, 8 gas supply device, 9 gas use device (chamber), 10 first switching valve, 10a driving cylinder, 11 second switching valve, 11a driving cylinder, 12 body , 12a is a gas inlet member, 12b is a gas outlet member, 12c is a first body member, 12d is a second body member, 13a and 13b are seals, 14a and 14b are pressure sensor mounting bolts, and 15a and 15b are diaphragm valves. Mechanism, 16a to 16f are passages, 17a is a first switching valve mounting hole, 17b is a second switching valve mounting hole, 18a is an orifice upstream pressure detector mounting hole, and 18b is an orifice downstream pressure detector mounting. Hole, 21 is a control valve, 22 is a valve drive unit.

Claims (5)

  A differential pressure type flow meter that measures a flow rate range of 100 to 10% of the maximum flow rate and a differential pressure flow meter that measures a flow rate range of 10% to 1% of the maximum flow rate are combined, and the fluid to be measured is each flow rate described above. A differential pressure type flow meter that performs high-precision flow rate measurement over a wide flow rate range by switching and supplying the differential pressure flow meter to each differential pressure flow meter according to the range. Each differential pressure type flow meter includes an orifice, a detector for fluid pressure P ₁ upstream of the orifice, a detector for fluid pressure P ₂ downstream of the orifice, a detector for fluid temperature T upstream of the orifice, A differential pressure type flow meter comprising a control calculation circuit for calculating a fluid flow rate Q using detected pressures P ₁ and P ₂ and a detected temperature T from the detector, and the fluid flow rate Q is defined as Q = C ₁ · P ₁ / _{2. The} calculation according to claim 1, wherein calculation is performed by √T · ((P ₂ / P ₁ ) ^m − (P ₂ / P ₁ ) ⁿ ) ^1/2 (where C ₁ is a proportional constant, and m and n are constants). Differential pressure type flow meter. Each differential pressure type flow meter includes an orifice, a detector for fluid pressure P ₁ upstream of the orifice, a detector for fluid pressure P ₂ downstream of the orifice, a detector for fluid temperature T upstream of the orifice, A differential pressure type flow meter comprising a control arithmetic circuit for calculating a fluid flow rate Q using detected pressures P ₁ and P ₂ and a detected temperature T from the detector, and the fluid flow rate Q is supplied to the control arithmetic circuit as Q = C ₁ · P ₁ / √T · ((P ₂ / P ₁ ) ^m- (P ₂ / P ₁ ) ⁿ ) ^1/2 (where C ₁ is a proportional constant, m and n are constants) an arithmetic circuit, a correction data storage circuit that stores the relationship between the flow rate error error of the fluid flow rate Q and variable orifice downstream side pressure P ₂ obtained in advance by actual measurement, the fluid flow rate Q from the correction data storage circuit mentioned above calculation The flow to be corrected by the correction data And a correction calculation circuit is provided to correct the fluid flow rate Q which is calculated in accordance with the variation of the orifice downstream side pressure P _2, a differential pressure type according to claim 1 which were of configurations for outputting a flow rate value Q 'after the correction Flowmeter. Fluid inlet a, fluid outlet b, mounting hole 17a of the first switching valve 10, mounting hole 17b of the second switching valve 11, mounting hole 18a of the fluid pressure detector 2 upstream of the orifice, and fluid pressure detector downstream of the orifice 3, a valve body 12 provided with a mounting hole 18 b and a mounting hole for the fluid temperature detector 4 on the upstream side of the orifice, a fluid inlet a formed in the valve body 12, and a bottom surface of the mounting hole 17 a of the first switching valve 10. And fluid passages 16a, 16b, 16e directly passing through the mounting hole 18a of the fluid pressure detector 2 upstream of the orifice and the bottom surface of the mounting hole 17b of the second switching valve 11, and the bottom surface of the first switching valve mounting hole 17a The fluid passage 16f that communicates with the bottom surface of the mounting hole 17b of the second switching valve 11 communicates with the bottom surface of the mounting hole 17b of the second switching valve 11 and the bottom surface of the mounting hole 18b of the fluid pressure detector 3 on the downstream side of the orifice. A fluid passage 16c, a fluid passage 16d communicating with the bottom surface of the mounting hole 18b of the fluid pressure detector 3 on the downstream side of the orifice and the fluid outlet b, and a fluid pressure detection on the upstream side of the orifice fixed to the mounting holes 18a and 18b. 2 and the fluid pressure detector 3 downstream of the orifice, the fluid temperature detector 4 upstream of the orifice, the first switching valve 10 that opens and closes between the fluid passage 16e and the fluid passage 16f, the fluid passage 16b and the fluid The second switching valve 11 that opens and closes between the passages 16c, the small-flow orifice 1 'provided in the middle of the fluid passage 16f, and the large-flow orifice 1 provided in the fluid passage 16a or the fluid passage 16b. '', And the detected pressures P ₁ and P ₂ of the pressure detectors ₂ and 3 and the detected temperature T of the temperature detector 4, the fluid flow flowing through the small flow rate orifice 1 ′ and the large flow rate orifice 1 ″. And a control arithmetic circuit for calculating the quantity Q by Q = C ₁ · P ₁ / √T · ((P ₂ / P ₁ ) ^m − (P ₂ / P ₁ ) ⁿ ) ^1/2 The first switching valve 10 is closed and the second switching valve 11 is opened for the flow rate range of 100 to 10%, and the first switching valve 10 is opened for the flow rate range of 10% to 1% of the maximum flow rate. The differential pressure type flow meter is characterized in that the second switching valve 11 is closed and the measurement is performed.   The differential pressure type flow meter according to claim 4, wherein the pressure detector 2 on the upstream side of the orifice, the pressure detector 3 on the downstream side of the orifice, and the temperature detector 4 on the upstream side of the orifice are shared by both differential pressure flow meters. .

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