阅读说明：本技术 质量流量控制器以及波动抑制方法 (Mass flow controller and fluctuation suppression method ) 是由 柳川雄成 长谷部亘 于 2021-05-25 设计创作，主要内容包括：本发明的质量流量控制器以及波动抑制方法将PID常数与仪表装配环境相匹配而抑制波动,该质量流量控制器具备：阀门驱动电路(9),其将与操作量相应的驱动电流输出到阀门(3)；PID控制部(4),其将流量设定值和流量测量值作为输入而算出操作量；存储部(5),其针对每个流量设定值存储PID常数；PID常数设定部(6),其当流量设定值已变更时,从存储部获取与变更后的流量设定值对应的PID常数,并将其设定于PID控制部；波动检测部(7),其判定流量测量值是否发生波动；以及PID常数变更部(8),其当检测出波动时,变更设定于PID控制部的PID常数,将存储在存储部的PID常数中的、与当前的流量设定值对应的PID常数更新为在PID控制部中设定的变更后的值。(The mass flow controller and the fluctuation suppression method of the present invention suppress fluctuation by matching PID constants with an instrument assembly environment, and the mass flow controller includes: a valve drive circuit (9) that outputs a drive current corresponding to the operation amount to the valve (3); a PID control unit (4) that calculates an operation amount using the flow rate set value and the flow rate measured value as inputs; a storage unit (5) that stores a PID constant for each flow rate set value; a PID constant setting unit (6) which, when the flow rate set value has been changed, acquires a PID constant corresponding to the changed flow rate set value from the storage unit and sets the PID constant in the PID control unit; a fluctuation detection unit (7) that determines whether or not the flow rate measurement value fluctuates; and a PID constant changing unit (8) that changes the PID constants set in the PID control unit when the fluctuation is detected, and updates the PID constant corresponding to the current flow rate set value among the PID constants stored in the storage unit to the changed value set in the PID control unit.)

1. A mass flow controller is characterized by comprising:

a flow rate sensor configured to measure a flow rate of a fluid flowing through the flow path;

a valve for controlling the flow of the fluid;

a PID control unit configured to calculate an operation amount for each control cycle by using a flow rate set value and a flow rate measurement value obtained by the flow rate sensor as inputs;

a valve drive circuit configured to output a drive current corresponding to the operation amount to the valve;

a storage unit configured to store a PID constant for each of the flow rate set values;

a PID constant setting unit configured to acquire, when the flow rate set value has been changed, a PID constant corresponding to the changed flow rate set value from the storage unit and set the PID constant in the PID control unit;

a fluctuation detection unit configured to determine whether or not the flow rate measurement value fluctuates; and

and a PID constant changing unit that changes the PID constant set in the PID control unit when the fluctuation of the flow rate measurement value is detected by the fluctuation detection unit, and updates the PID constant corresponding to the current flow rate setting value among the PID constants stored in the storage unit to the changed value set in the PID control unit.

2. A mass flow controller according to claim 1,

when the fluctuation detection unit detects the fluctuation of the flow rate measurement value, the PID constant modification unit increases the proportional coefficient of the PID constant set in the PID control unit by a predetermined modification amount.

3. A mass flow controller according to claim 1,

when the fluctuation detection unit detects the fluctuation of the flow rate measurement value, the PID constant change unit decreases the integration time of the PID constant set in the PID control unit by a predetermined change amount.

4. A mass flow controller according to any one of claims 1 to 3,

the storage unit stores a PID constant for each divided range of the flow rate set value,

when the flow rate set value has been changed, the PID constant setting unit acquires a PID constant corresponding to a range including the changed flow rate set value from the storage unit and sets the PID constant in the PID control unit,

the PID constant changing unit updates a PID constant corresponding to a range including the current flow rate set value among PID constants stored in the storage unit to a changed value set in the PID control unit.

5. A ripple suppression method, comprising:

a step 1 of referring to a storage unit in which PID constants are stored for each flow rate set value when the flow rate set value has been changed, acquiring a PID constant corresponding to the changed flow rate set value from the storage unit, and setting the PID constant in a PID control unit;

a step 2 of receiving the flow rate set value and a flow rate measurement value of the fluid to be controlled, and calculating an operation amount for each control cycle by the PID control unit;

a 3 rd step of outputting the operation amount to a valve drive circuit that drives a valve for controlling a flow rate of the fluid;

step 4, judging whether the flow measurement value fluctuates or not; and

and a 5 th step of, when the fluctuation of the flow rate measurement value is detected, changing the PID constants set in the PID control unit, and updating the PID constant corresponding to the current flow rate setting value among the PID constants stored in the storage unit to the changed value set in the PID control unit.

6. The fluctuation suppressing method according to claim 5,

in the step 5, when the fluctuation of the flow rate measurement value is detected, the proportional coefficient in the PID constant set in the PID control unit is increased by a predetermined change amount.

7. The fluctuation suppressing method according to claim 5,

in the step 5, when the fluctuation of the flow rate measurement value is detected, the integration time in the PID constant set in the PID control unit is reduced by a predetermined change amount.

8. The fluctuation suppressing method according to any one of claims 5 to 7,

the storage unit stores a PID constant for each divided range of the flow rate set value,

the step 1 comprises the following steps: when the flow rate set value has been changed, a PID constant corresponding to a range including the changed flow rate set value is acquired from the storage unit and set in the PID control unit,

the 5 th step comprises the following steps: and updating a PID constant corresponding to a range including the current flow rate set value among the PID constants stored in the storage unit to a changed value set in the PID control unit.

Technical Field

The present invention relates to a mass flow controller.

Background

In the past, mass flow controllers that control the flow of a fluid have been commercialized. When the flow rate is controlled by a mass flow controller, the flow rate may not be a fixed value and may fluctuate. In particular, in a mass flow controller using a direct-acting solenoid valve, fluctuation in flow rate is likely to occur in a meter in which pressure loss on the 2 nd side (downstream side) is large.

In a conventional mass flow controller, when a ripple is detected, a coefficient used for PID calculation is changed to a coefficient for reducing the ripple (see patent document 1).

However, the technique disclosed in patent document 1 has a problem that it is difficult to match the meter mounting environment of the mass flow controller because it is necessary to determine a coefficient for reducing the fluctuation in advance. In the technique disclosed in patent document 1, a value obtained by reducing the proportionality coefficient Kp from a normal value is used as a coefficient for reducing fluctuation. However, if the proportional coefficient Kp is made small, the fluctuation that occurs when the pressure loss on the 2 nd side is large and the pressure fluctuates greatly during control may not be suppressed. In such a case, it is necessary to perform a process (for example, thickening a piping system on the 2 nd side) of reconsidering the instrument mounting environment of the mass flow controller.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 6220699

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a mass flow controller and a fluctuation suppression method that can match a PID constant with an instrument installation environment and suppress fluctuations even when a pressure loss on the 2 nd side is large and a differential pressure greatly fluctuates during control.

Means for solving the problems

The mass flow controller of the present invention is characterized by comprising: a flow rate sensor configured to measure a flow rate of a fluid flowing through the flow path; a valve for controlling the flow of the fluid; a PID control unit configured to calculate an operation amount for each control cycle by using a flow rate set value and a flow rate measurement value obtained by the flow rate sensor as inputs; a valve drive circuit configured to output a drive current corresponding to the operation amount to the valve; a storage unit configured to store a PID constant for each of the flow rate set values; a PID constant setting unit configured to acquire, when the flow rate set value has been changed, a PID constant corresponding to the changed flow rate set value from the storage unit and set the PID constant in the PID control unit; a fluctuation detection unit configured to determine whether or not a fluctuation occurs in the flow rate measurement value; and a PID constant changing unit that changes a PID constant set in the PID control unit when the fluctuation of the flow rate measurement value is detected by the fluctuation detecting unit, and updates a PID constant corresponding to the current flow rate setting value among the PID constants stored in the storage unit to the changed value set in the PID control unit.

In the 1 configuration example of the mass flow controller according to the present invention, the PID constant changing unit increases the proportional coefficient of the PID constant set in the PID control unit by a predetermined change amount when the fluctuation of the flow rate measurement value is detected by the fluctuation detecting unit.

In the 1 configuration example of the mass flow controller according to the present invention, the PID constant changing unit is characterized in that, when the fluctuation detection unit detects the fluctuation of the flow rate measurement value, the integration time of the PID constant set in the PID control unit is reduced by a predetermined change amount.

In addition, in 1 configuration example of the mass flow controller according to the present invention, the storage unit stores PID constants for each divided range of the specified flow rate value; a PID constant setting unit that acquires, when the flow rate set value has been changed, a PID constant corresponding to a range including the changed flow rate set value from the storage unit and sets the PID constant in the PID control unit; and a PID constant changing unit that updates a PID constant corresponding to a range including the current flow rate set value among the PID constants stored in the storage unit to a changed value set in the PID control unit.

Further, a ripple suppressing method according to the present invention includes: a step 1 of referring to a storage unit in which PID constants are stored for each flow rate set value when the flow rate set value has been changed, acquiring a PID constant corresponding to the changed flow rate set value from the storage unit, and setting the PID constant in the PID control unit; a step 2 of receiving the flow rate set value and a flow rate set value of the fluid to be controlled, and calculating an operation amount for each control cycle by the PID control unit; a 3 rd step of outputting the operation amount to a valve drive circuit that drives a valve for controlling a flow rate of the fluid; step 4, judging whether the flow measurement value fluctuates or not; and a 5 th step of, when the fluctuation of the flow rate measurement value is detected, changing the PID constants set in the PID control unit, and updating the PID constant corresponding to the current flow rate setting value among the PID constants stored in the storage unit to the changed value set in the PID control unit.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, since the PID constants set in the PID control unit are automatically changed when the flow rate measurement value fluctuates, the PID constants can be matched with the meter installation environment of the mass flow controller, and the fluctuation can be suppressed even when the pressure loss on the 2 nd side of the mass flow controller is large and the differential pressure on the 1 st side and the 2 nd side greatly fluctuates during control.

Drawings

Fig. 1 is a diagram showing 1 example of the P-Q characteristics.

Fig. 2 is a diagram showing another example of the P-Q characteristic.

Fig. 3 is a diagram showing another example of the P-Q characteristic.

Fig. 4 is a diagram showing the manipulated variable MV and the flow rate Q in the case where the flow rate control is performed at a low flow rate in an environment where a throttle valve is provided on the 2 nd side of the mass flow controller.

Fig. 5 is a diagram showing the manipulated variable MV and the flow rate Q in the case where the PID constant is changed in the environment where the throttle valve is provided on the 2 nd side of the mass flow controller.

Fig. 6 is a diagram showing the manipulated variable MV and the flow rate Q in the case where the PID constant is changed in the environment where the throttle valve is provided on the 2 nd side of the mass flow controller. .

Fig. 7 is a graph showing the manipulated variable MV at the time of rise in fig. 4 to 6.

Fig. 8 is a block diagram showing the structure of a mass flow controller according to an embodiment of the present invention.

Fig. 9 is a flowchart illustrating the operation of the PID control unit, the PID constant setting unit, the fluctuation detection unit, and the PID constant changing unit of the mass flow controller according to the embodiment of the present invention.

Fig. 10 is a block diagram showing an example of the configuration of a computer that implements a mass flow controller according to an embodiment of the present invention.

Detailed Description

[ P-Q characteristics ]

The P-Q characteristic, i.e., the relationship between the differential pressure P between the pressure on the 1 st side (upstream side) and the pressure on the 2 nd side (downstream side) of the mass flow controller and the flow rate Q of the fluid, can be modeled as follows.

Q＝CP₁(P₀/P₁< 1/2 case (1).)

C＝－K₀P+K₁M－F ···(3)

P＝P₁－P₀ ···(4)

In the formulae (1) to (4), C is a valve capacity coefficient, P₁Is the pressure of the fluid on the 1 st side, P₀Is the pressure of the fluid on the 2 nd side, M is the valve control quantity, K₀Is the opening coefficient, K, with respect to pressure₁Is an opening degree coefficient, F (═ K), relative to a control amount₀P’+K₁M ') is a value obtained from the valve control amount M ' and the differential pressure P ' at the time when the flow rate starts to flow.

When the fluid is a gas and the 2 nd atmosphere is open, the flow rate Q is as follows (P)₀＝0、P＝P₁)。

Q＝－K₀{(P－m/2)²－m^2/4} ···(5)

m＝(K₁M－F)/K₀ ···(6)

Fig. 1 is a diagram showing an example of P-Q characteristics obtained from equations (5) and (6) under the condition that the fluid is a gas and the atmosphere is opened 2 times. Pressure P on the 1 st side when the 2 nd side atmosphere is open₁The flow rate Q is easily overshot in the case of m/2 or more, but it is preferable to make the valve m as large as possible. Pressure P on the 1 st side₁The reason why the flow rate Q is easily overshot when m/2 or more is that if the valve opening is increased to increase the flow rate Q, the flow rate Q increases and the differential pressure P momentarily decreases, so that the flow rate Q further increases, and apparently, the flow rate Q behaves in a smaller (higher sensitivity) ratio band.

Fig. 2 and 3 are diagrams showing examples of P-Q characteristics examined by using a mass flow controller under the condition that the fluid is a gas and 2 times the atmosphere is open. Fig. 2 shows a case where the valve diameter is 6mm, and fig. 3 shows a case where the valve diameter is 12 mm. In the examples of fig. 2 and 3, the opening degree of the valve is kept constant, and the pressure P on the 1 st side is shown₁Flow rate Q in case of fluctuations. Up1, up2 in FIGS. 2 and 3 show the let-down pressure P₁The P-Q characteristics when changing from a small value to a large value are shown by down1 and down2 as the pressure P₁P-Q characteristics when changing from a large value to a small value. On the horizontal axis in FIGS. 2 and 3, the pressure P is measured₁The values of 10kPa, 20kPa, 50kPa, 100kPa, 150kPa, 200kPa, 250kPa, 300kPa, and 350kPa are described as 1, 2, 3, 4, 5, 6, 7, 8, and 9, respectively. FIGS. 2 and 3 show the pressure P₁The absolute value of the flow rate Q in the direction of change changes, but the pressure and overall tendency to reach the maximum flow rate does not change.

If the pressure P of the 1 st side₁When the pressure becomes larger than 150kPa (5 on the horizontal axis in FIGS. 2 and 3), the flow rate Q is accompanied by the pressure P₁Is increased and decreased. Therefore, if the valve is opened sharply at 300kPa (8 on the horizontal axis in fig. 2 and 3), for example, although the flow rate Q increases, the pressure P on the 1 st side increases₁Decreases and thus the flow Q further increases. In order to avoidSuch a phenomenon requires that the flow rate Q has a characteristic of monotonically increasing with respect to the use differential pressure.

[ wave stabilization ]

As a factor of the fluctuation of the flow rate Q, in an environment where there is a throttle valve on the 2 nd side of the mass flow controller or the differential pressure P dynamically changes according to the flow rate Q, in addition to the case where there is a problem in the standard setting of the simple PID (the proportionality coefficient Kp is too large and the integration time Ti is too small), there is a high possibility that the fluctuation occurs by using the standard PID constant due to the problem of the P-Q characteristic described so far. Such fluctuations can be suppressed by changing the PID constant.

An example of changing the PID constant to become stable will be described below. Fig. 4 is a diagram showing the manipulated variable MV and the flow rate Q in the case where the flow rate control is performed at a low flow rate in an environment where a throttle valve is provided on the 2 nd side of the mass flow controller. Here, the flow rate Q is represented by a normalized value in which a predetermined maximum value FS (full scale) is 100%. The unit of time on the horizontal axis is 5 msec. In the example of fig. 4, the flow rate set value at time 0msec is changed from 0 to 5% FS, the flow rate set value SP and the flow rate Q are input, and the manipulated variable MV calculated by a standard PID constant PID is output to the valve by a PWM (Pulse Width Modulation) signal. Pressure P of the 1 st side₁Is 300 kPa. Regarding the PID constants, the proportional coefficient Kp is set to 0.02, and the integration time Ti is set to 4.

As can be seen from fig. 4, the flow rate Q fluctuates when set at a low flow rate and a standard PID. Fig. 5 is a diagram showing the manipulated variable MV and the flow rate Q when the proportional coefficient Kp is increased from 0.02 to 0.05 under the same conditions as in fig. 4. Fig. 6 is a diagram showing the manipulated variable MV and the flow rate Q in the case where the integration time Ti is reduced from 4 to 2 under the same conditions as in fig. 4. As is clear from fig. 5 and 6, if the proportional coefficient Kp is increased or the integration time Ti is decreased, the fluctuation of the flow rate Q is subsided.

If the manipulated variable MV is compared between the case where the flow rate Q fluctuates and the case where it does not fluctuate, as shown in fig. 7, the behavior of the flow rate Q is extremely different although the manipulated variable MV is almost the same at the rise of the flow rate set value SP. In the example of fig. 7, the manipulated variable MV in the example of fig. 4 is MV0, the manipulated variable MV in the example of fig. 5 is MV1, and the manipulated variable MV in the example of fig. 6 is MV 2.

Although the manipulated variables MV are almost the same, the flow rate Q behaves differently, and the following (I) and (II) are conceivable.

(I) When the proportionality coefficient Kp is large, the differential pressure P fluctuates greatly, and therefore the operation region moves from an unstable region (region on the right side of m/2 in fig. 1) in which the flow rate Q decreases with respect to an increase in the differential pressure P to a stable region (region on the left side of m/2 in fig. 1) in which the flow rate Q increases with respect to an increase in the differential pressure P, and the flow rate control operation is performed in the stable region, and therefore, the operation becomes stable.

(II) when the proportional coefficient Kp is small, the operating region becomes an unstable region in which the flow rate Q decreases with respect to an increase in the differential pressure P, and therefore the flow rate Q fluctuates.

Therefore, as a countermeasure against the fluctuation in the case where the pressure loss on the 2 nd side is large and the differential pressure P greatly fluctuates during control, the control may be performed in a stable region by increasing the proportional coefficient Kp or by decreasing the integration time Ti.

[ examples ]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 8 is a block diagram showing the structure of a mass flow controller according to an embodiment of the present invention. The mass flow controller is provided with: a flow path main body 1 made of, for example, resin; a sensor package 2 attached to the flow path body 1; a proportional solenoid valve 3 for controlling the flow rate of the fluid; a PID control unit 4 that receives the flow rate set value SP and the flow rate measured value Q as inputs and calculates an operation amount MV for each control cycle; a storage unit 5 that stores a PID constant for each flow rate set value SP; a PID constant setting unit 6 that, when the flow rate set value SP has been changed, acquires a PID constant corresponding to the changed flow rate set value SP from the storage unit 5 and sets the PID constant in the PID control unit 4; a fluctuation detection unit 7 that determines whether or not the flow rate measurement value Q fluctuates; a PID constant changing unit 8 that changes the PID constants set in the PID control unit 4 when the fluctuation of the flow rate measurement value Q is detected by the fluctuation detecting unit 7, and updates the PID constant corresponding to the current flow rate setting value SP among the PID constants stored in the storage unit 5 to the changed value set in the PID control unit 4; and a valve drive circuit 9 for driving the proportional solenoid valve 3.

In fig. 8, 10 is a flow channel formed inside the flow channel main body 1, 11 is an opening on the inlet side of the flow channel 10, 12 is an opening on the outlet side of the flow channel 10, and 13 is a flow sensor mounted in the sensor package 2.

Fluid flows into the flow path 10 from the opening 11 and is discharged from the opening 12 through the proportional solenoid valve 3. At this time, the flow sensor 13 measures the flow rate Q of the fluid. The flow sensor 13 is mounted on the sensor package 2 and is attached to the flow path body 1 so as to be exposed to a fluid to be measured.

The characteristic action of the present embodiment will be described below. Fig. 9 is a flowchart illustrating the operations of the PID control unit 4, the PID constant setting unit 6, the fluctuation detection unit 7, and the PID constant changing unit 8.

When the flow rate set value SP is changed by, for example, an operator (yes in step S100 in fig. 9), the PID constant setting unit 6 sets a PID constant corresponding to the changed flow rate set value SP in the PID control unit 4 (step S101 in fig. 9). The storage unit 5 stores PID constants (a proportional coefficient Kp, an integral time Ti, and a derivative time Td) for each flow rate set value SP. More specifically, the entire range of the flow rate set value SP from 0% FS to 100% FS is divided into a plurality of ranges (for example, 10), and the PID constants are stored in the storage unit 5 for each of the divided ranges. The PID constant setting unit 6 acquires a PID constant corresponding to a range of the flow rate set value SP including the changed flow rate set value SP from the storage unit 5, and sets the PID constant in the PID control unit 4.

The PID control unit 4 acquires the flow rate measurement value Q from the flow rate sensor 13 (step S102 in fig. 9). Then, the PID control unit 4 receives the flow rate set value SP and the flow rate measurement value Q acquired in step S102 as inputs, and calculates the manipulated variable MV by performing PID calculation so that the flow rate measurement value Q coincides with the flow rate set value SP (step S103 in fig. 9). The equation of the PID calculation using the PID constant is shown in equation (7). e is the deviation of the flow set point SP from the flow measurement Q.

[ equation 1]

The PID control unit 4 outputs the calculated manipulated variable MV to the valve drive circuit 9 (step S104 in fig. 9). The valve drive circuit 9 outputs a valve drive current (electromagnetic current) I to the proportional solenoid valve 3 in accordance with the operation amount MV output from the PID control unit 4. In this way, the proportional solenoid valve 3 is controlled to have an opening degree corresponding to the operation amount MV.

On the other hand, the fluctuation detection unit 7 determines whether or not the flow rate measurement value Q fluctuates based on the flow rate measurement value Q and the flow rate set value SP (step S105 in fig. 9). For example, when there are three consecutive peak values of the flow rate measurement value Q at which the deviation e between the flow rate set value SP and the flow rate measurement value Q becomes equal to or greater than the absolute value | e | of SP-Q, the fluctuation detection unit 7 determines that fluctuation occurs in the flow rate measurement value Q. The steady determination reference value δ is smaller than the variation (deviation e) in the normal control, and is an index of the maximum deviation that should be maintained in the steady state. Note that the method of detecting the fluctuation is not limited to the above example, and details thereof are not repeated.

When the fluctuation of the flow rate measurement value Q is detected (yes in step S105), the PID constant changing unit 8 increases the proportional coefficient Kp of the PID constant set in the PID control unit 4 by a predetermined proportional coefficient change amount (step S106 in fig. 9).

Then, the PID-constant changing unit 8 updates the proportional coefficient Kp corresponding to the range of the flow rate set value SP including the current flow rate set value SP among the PID constants stored in the storage unit 5 to the value changed in step S106 (step S107 in fig. 9).

The processing in steps S106 and S107 may be performed only once when the fluctuation is first detected after the change of the flow rate set value SP.

The mass flow controller executes the processing of steps S100 to S107 for each control cycle until, for example, the operator instructs the end of the operation of the apparatus (yes in step S108 of fig. 9).

As described above, in the present embodiment, when the flow rate measurement value Q fluctuates, the proportional coefficient Kp set in the PID control unit 4 is automatically increased, so that the PID constant can be matched with the meter-mounting environment of the mass flow controller, and the fluctuation can be suppressed even when the pressure loss on the 2 nd side is large and the differential pressure P during control fluctuates greatly. If the fluctuation occurs after the change of the flow rate set value SP, the proportional coefficient Kp is changed again, and thus the proportional coefficient Kp is slowly changed to such an extent that the fluctuation does not occur.

In addition, in the present embodiment, the proportional coefficient Kp is increased when the fluctuation occurs, but it is also possible to decrease the integration time Ti. In this case, when the fluctuation of the flow rate measurement value Q is detected (yes in step S105), the PID constant changing unit 8 decreases the integration time Ti of the PID constant set in the PID control unit 4 by a predetermined integration time changing amount (step S106). Then, the PID-constant changing unit 8 updates the integration time Ti corresponding to the range of the flow rate set value SP including the current flow rate set value SP among the PID constants stored in the storage unit 5 to the value changed in step S106 (step S107).

In addition, there are various conventional methods for PID control, and there is also PID control using a model. However, the use of the model has problems as described below.

(A) Although the general-purpose method has a wide application range, the program is complicated and cannot be installed in an inexpensive CPU.

(B) Since the operation of adaptively estimating the model requires a long calculation time, it is not suitable for actual sites.

In the present invention, a simpler and more practical method is proposed for the purpose of coping with only specific factors that cause fluctuations. Specifically, the present invention proposes a simple and practical method for suppressing the hunting phenomenon caused by the fluctuation of the downstream-side pressure due to the flow rate in the case of meter mounting in which the pressure loss on the downstream side is large due to a problem point (a problem point in which the P-Q characteristic does not monotonically increase) in the direct-acting valve driving method using the electromagnetic valve. In the case of the pilot valve system, the problem in the case of using the solenoid valve does not occur, and the fluctuation due to the pressure fluctuation on the downstream side does not generally occur, so the present invention is not applicable. The present invention is effective for a mass flow controller having a P-Q characteristic in which a flow rate Q peaks due to a certain pressure, as shown in fig. 1.

In the mass flow controller of the present embodiment, at least the PID control Unit 4, the storage Unit 5, the PID constant setting Unit 6, the fluctuation detection Unit 7, and the PID constant change Unit 8 can be realized by a computer provided with a CPU (Central Processing Unit), a storage device, and an interface, and a program for controlling these hardware resources. The computer is configured as shown in fig. 10.

The computer includes a CPU200, a storage device 201, and an interface device (I/F) 202. The I/F202 is connected to the flow sensor 13, the valve drive circuit 9, and the like. In such a computer, a program for implementing the fluctuation suppressing method of the present invention is stored in the storage device 201. The CPU200 executes the processing explained in the present embodiment following the program stored in the storage device 201.

[ possibility of Industrial use ]

The present invention can be applied to a flow control system.

Description of the symbols

The flow channel comprises a flow channel body 1 …, a sensor package 2 …, a proportional solenoid valve 3 …, a PID control part 4 …, a storage part 5 …, a PID constant setting part 6 …, a fluctuation detection part 7 …, a PID constant changing part 8 …, a valve driving circuit 9 …, a flow channel 10 … and a flow sensor 13 ….