Liquid flow rate control system

Abstract

A liquid flow rate control system includes: a liquid flow rate control unit that controls a liquid flow rate and has a diaphragm; an on / off valve provided downstream of the liquid flow rate control unit; a liquid flow meter that measures the flow rate of the liquid; and a control device that compares an actual liquid flow rate with a target liquid flow rate to control an opening degree of the diaphragm and opening and closing of the opening / closing valve, and starts control when the opening / closing valve is in a closed state, in which the liquid flow rate control unit includes: a constant pressure regulator that controls the opening degree of the diaphragm; and an electropneumatic regulator that controls the pressure of the liquid supplied to the constant pressure regulator, the control device pre-prepares and applies an amount of current based on the target liquid flow rate to the electropneumatic regulator to pre-prepare to open the diaphragm, and when the current is pre-prepared and applied to the electropneumatic regulator, controls the pressure of the liquid supplied to the constant pressure regulator. A current corresponding to 95% to 100% less than the magnitude of the current to be applied for the target liquid flow rate is applied.

Description

Technical Field

[0001] The present disclosure relates to a liquid flow rate control system, and in particular to a liquid flow rate control system capable of controlling the liquid flow rate with high precision while being manufactured at a low production cost. Background Art

[0002] This section provides background information related to the present disclosure which is not necessarily prior art.

[0003] A liquid flow rate control system is a system configured to deliver (or supply) a target liquid flow rate and change the liquid flow rate, and generally includes a liquid flow meter, a liquid flow rate control valve, and a control device for controlling the operation of the liquid flow meter and the liquid flow rate control valve.

[0004] As an example, the operation of the liquid flow rate control system is performed in a method in which a control device controls the opening of a liquid flow rate control valve by comparing a liquid flow rate sensed by a liquid flow rate meter with a target liquid flow rate.

[0005] Liquid flow rate control systems are used in industries such as automotive, semiconductor, factory, chemical, and biological fields, and the accuracy of liquid flow rate control required by industry advancement continues to increase.

[0006] To this end, various studies have been conducted on each of a liquid flow meter, a liquid flow rate control valve, and a control device constituting a liquid flow rate control system, but as the accuracy increases, the system price increases, which acts as a great burden throughout the industry.

[0007] Particularly, among the components of the liquid flow rate control system, an electric valve using a stepping motor is used as the liquid flow rate control valve, which has very good accuracy but is very expensive and is the biggest cause of the increase in system price.

[0008] In addition, since the electric valve using the stepping motor does not have a separate liquid flow rate correction function, there is a problem that when a pressure change occurs at the input stage, the liquid flow rate oscillates at the output stage.

[0009] Such oscillations in the liquid flow rate may cause damage, such as causing unexpected alarms in liquid flow rate monitoring equipment or shutting down the process.

[0010] Therefore, there is a need to develop a technology for preventing liquid flow rate oscillation.

[0011] On the other hand, in the liquid flow rate control system, there is an example of using an on / off valve. However, in the case of control by an on / off valve, when the liquid flow rate control starts, it takes a little time to open and control the valve up to the target liquid flow rate in the closed state.

[0012] Therefore, in the initial liquid flow rate control, there is a problem that a liquid flow rate less than a target liquid flow rate is discharged, and reaches the target liquid flow rate value after a predetermined time, thereby affecting the process.

[0013] On the other hand, in various industrial fields, a liquid flow rate control system for controlling a liquid flow rate when a target liquid flow rate varies with time is required, and the demand for precise liquid flow rate control of such a liquid flow rate control system is gradually increasing. Summary of the invention

[0014] An object of the present disclosure is to provide a liquid flow rate control system that can prevent oscillation of the liquid flow rate at an output stage due to pressure changes at an input stage.

[0015] Another object of the present disclosure is to provide a liquid flow rate control system that can minimize the difference between an actual liquid flow rate and a target liquid flow rate at an initial stage of liquid flow rate control.

[0016] Yet another object of the present disclosure is to provide a liquid flow rate control system that can minimize the difference between a target liquid flow rate and an actual liquid flow rate that varies with time.

[0017] This section provides a summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0018] In order to solve this problem, according to any one of the aspects used to describe the various aspects of the present disclosure, a liquid flow rate control system is provided, which may include: a liquid flow rate control unit, which controls the liquid flow rate by controlling the opening of a diaphragm, and has the diaphragm set in a pre-prepared open state with an initial set amount; an on / off valve, which is set downstream of the liquid flow rate control unit; a liquid flow meter, which measures the flow rate of the liquid flowing into the liquid flow rate control unit; and a control device, which compares the actual liquid flow rate measured by the liquid flow meter with the target liquid flow rate to control the liquid flow rate control unit. The opening of the diaphragm and the opening and closing of the on / off valve are controlled, and the control is started when the on / off valve is in a closed state, wherein the liquid flow rate control unit includes: a constant pressure regulator, which controls the opening of the diaphragm by the pressure of the supplied liquid; an electro-pneumatic regulator, which controls the pressure of the liquid supplied to the constant pressure regulator, and the control device can pre-apply an electric current based on the amount of the target liquid flow rate to the electro-pneumatic regulator to pre-prepare to open the diaphragm, and when the current is pre-applied to the electro-pneumatic regulator, a current corresponding to 95% to 100% of the magnitude of the current to be applied for the target liquid flow rate can be applied.

[0019] According to one aspect of the present disclosure, in the liquid flow rate control system, the amount of current prepared to be applied to the electro-pneumatic regulator may be continuously fluctuated so as to eject 95% to 98% relative to the target liquid flow rate.

[0020] According to one aspect of the present disclosure, in the liquid flow rate control system, the liquid flow rate control system may further include: a high-order control unit, which inputs target liquid flow rate information from the outside and applies the input target liquid flow rate information to the control device.

[0021] According to one aspect of the present disclosure, in the liquid flow rate control system, the target liquid flow rate information may be a first set liquid flow rate Q1, a second set liquid flow rate Q2 different from the first set liquid flow rate Q1, and a time interval T required when the first set liquid flow rate Q1 is changed to the second set liquid flow rate Q2, and the control device may control the liquid flow rate control unit by comparing the controlled liquid flow rate Qa changed according to the time interval Ta calculated and set based on the first set liquid flow rate Q1, the second set liquid flow rate Q2 and the time interval T with the liquid flow rate measured by the liquid flow meter.

[0022] According to one aspect of the present disclosure, in the liquid flow rate control system, the control liquid flow rate Qa can fluctuate at a fluctuating liquid flow rate Qs set at each time interval Ta, and the fluctuating liquid flow rate Qs is set by using the first set liquid flow rate Q1 as an initial value, and after the time interval T, the control liquid flow rate Qa can be determined as the second set liquid flow rate Q2.

[0023] According to one aspect of the present disclosure, in the liquid flow rate control system, the set fluctuating liquid flow rate Qs can be obtained by the following steps: calculating the liquid flow rate fluctuation amount (Qc=Q2-Q1) and the number of times the liquid flow rate is controlled to change (Tc=T / Ta, Ta is the control fluctuation period), and calculating the set fluctuating liquid flow rate Qs by dividing the liquid flow rate fluctuation amount (Qc=Q2-Q1) by the number of times the liquid flow rate is controlled to change (Qc / Tc).

[0024] According to one aspect of the present disclosure, in the liquid flow rate control system, the target liquid flow rate information may be at least three set liquid flow rates (Q1, Q2 and Qn, n is an integer of n≥3) and at least two time intervals (T1 and Tm, T=n-1) required to be changed in sequence, and the control device may control the liquid flow rate control unit 201, which compares the controlled liquid flow rate Qa changed according to the set time interval Ta with the liquid flow rate measured by the liquid flow meter, and the set time interval Ta is calculated based on at least two time intervals and each of the two set liquid flow rates associated with the time interval.

[0025] According to an exemplary embodiment of the present disclosure, since the diaphragm is set in a pre-open state or is pre-opened by a control device before starting liquid flow rate control, liquid flow rate oscillation can be prevented and the difference between the actual output flow rate and the target flow rate in the initial stage of liquid flow rate control can be minimized.

[0026] According to an exemplary embodiment of the present disclosure, the difference between a target liquid flow rate that fluctuates with time and an actual liquid flow rate to be controlled may be minimized.

[0027] According to an exemplary embodiment of the present disclosure, even when the time change rate of the fluctuating target liquid flow rate varies with time, the difference between the target liquid flow rate and the actual flow rate of the liquid to be controlled can be minimized.

[0028] According to an exemplary embodiment of the present disclosure, instead of using an electric valve using an expensive stepping motor, it is advantageous to control the liquid flow rate with high precision while adopting a constant pressure regulator. In addition, it is advantageous to reduce manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other aspects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0030] Figure 1 is a diagram conceptually illustrating a liquid flow rate control system according to an exemplary embodiment of the present disclosure;

[0031] Figure 2 It is shown Figure 1 A diagram showing the construction of a liquid flow rate control system;

[0032] Figure 3 is a diagram conceptually illustrating a liquid flow rate control system according to another exemplary embodiment of the present disclosure; and

[0033] Figure 4 It is shown Figure 3 Graph of the flow rate control results of the liquid flow rate control system. DETAILED DESCRIPTION

[0034] Exemplary embodiments of implementing a liquid flow rate control system according to the present disclosure will now be described in detail with reference to the accompanying drawings.

[0035] However, it cannot be said that the exemplary embodiments of the inherent technical spirit of the present disclosure are limited to the exemplary embodiments described below, and the technical spirit disclosed includes a scope that can be easily proposed by a person skilled in the art by replacing or changing the exemplary embodiments described below based on the inherent technical spirit of the present disclosure.

[0036] Furthermore, since the terms used hereinafter are selected for ease of description, the terms are not limited to dictionary meanings and should be appropriately interpreted as meanings consistent with the technical spirit of the present disclosure in order to grasp the inherent technical spirit of the present disclosure.

[0037] Figure 1 is a diagram conceptually illustrating a liquid flow rate control system according to an exemplary embodiment of the present disclosure, and Figure 2 It is shown Figure 1 Diagram of the construction of a liquid flow rate control system.

[0038] Reference Figure 1 and Figure 2 , a liquid flow rate control system 100 according to an exemplary embodiment of the present disclosure includes a liquid flow rate control unit 101 , an on / off valve 113 , a liquid flow rate meter 130 , and a control device 140 .

[0039] In addition, according to the exemplary embodiment of the present disclosure, the liquid flow rate control system 100 also includes a high-level control unit 150, which inputs necessary information of the control operation of the control device 140 from the outside and provides the information to the control device 140 or processes the information input from the outside and provides the processed information to the control device 140.

[0040] The liquid flow rate control unit 101 controls the liquid flow rate by controlling the opening degree of a diaphragm (not shown), and the diaphragm is set in a pre-open state with an initial setting amount.

[0041] Here, the liquid flow rate control unit 101 opens the diaphragm to be pre-opened by an amount less than 95% to 100% compared to the target liquid flow rate which becomes the control reference, and the liquid flow rate control unit 101 identifies the interval for stably maintaining the liquid flow rate whenever the injection process is performed so as to always maintain the pre-opened state less than 95% to 100%.

[0042] Furthermore, the liquid flow rate control unit 101 is controlled by the control device 140 so that the diaphragm can be opened less than 95% to 100% in the pre-open state based on an interval for stably maintaining the flow of liquid.

[0043] Furthermore, the liquid flow rate control unit 101 includes a constant pressure regulator 110 that controls the opening degree of the diaphragm by the pressure of the supplied liquid, and an electro-pneumatic regulator 120 that controls the pressure of the fluid supplied to the constant pressure regulator 110 .

[0044] The on / off valve 113 is provided downstream of the liquid flow rate control unit 101 , and serves to selectively block the flow from the liquid flow rate control unit 101 to the outside.

[0045] The liquid flow rate meter 130 measures the flow rate of the liquid flowing into the liquid flow rate control unit 101 .

[0046] The control device 140 compares the actual liquid flow rate measured by the liquid flow meter 130 with the target liquid flow rate as a control reference to control the opening degree of the diaphragm of the liquid flow rate control unit 101 and the opening / closing of the on / off valve 113 .

[0047] Here, the control device 140 is configured to start control when the on / off valve 113 is in a closed state.

[0048] The constant pressure regulator 110 is configured so that the liquid flow rate is controlled according to the opening / closing rate of a diaphragm (not shown), and the opening / closing rate of the diaphragm (not shown) is controlled by the pressure of air supplied from an electro-pneumatic regulator 120 described below.

[0049] The liquid flow meter 130 is arranged upstream of the constant pressure regulator 110 in the flow direction to measure the liquid flow rate, and the type of the liquid flow meter 130 is irrelevant, but preferably, the liquid flow meter 130 is set to an ultrasonic liquid flow meter 130, which can minimize the measurement error of the liquid flow rate caused by the liquid flow meter.

[0050] The electro-pneumatic regulator 120 , which supplies air to the constant pressure regulator 110 to open / close a diaphragm provided in the constant pressure regulator 110 , is provided to control the pressure of the supplied air to control the opening degree of the diaphragm.

[0051] Here, the pressure of the supplied air is set to be controlled based on the difference between a target liquid flow rate input from the outside through a high-level control unit 150 described later and the liquid flow rate sensed by the liquid flow meter 130 .

[0052] On the other hand, the electro-pneumatic regulator 120 preferably has a heat exchange device to prevent the temperature of the air from rising so that the air density remains constant. In this case, the heat exchange device can be set as a cooling pipe in which heat exchange is performed by contact with the air passing through the inside of the electro-pneumatic regulator 120.

[0053] The control device 140 controls the difference between the liquid flow rate information sensed by the liquid flow meter 130 and the target liquid flow rate within the error range through feedback control.

[0054] Specifically, after receiving the target liquid flow rate input from the outside through the high-level control unit 150 described later, and after receiving the liquid flow rate information sensed by the liquid flow meter 130 and comparing the sizes of the two liquid flow rates, an electrical signal is applied to the electro-pneumatic regulator 120 based on the difference between the sizes.

[0055] The electro-pneumatic regulator 120 to which the electric signal is applied supplies air of a pressure proportional to the magnitude of the electric signal to the constant pressure regulator 110 to control the opening degree of the diaphragm.

[0056] In an exemplary embodiment of the present disclosure, since the diaphragm is set in a pre-prepared open state with an initial set amount or is controlled by the control device 140 in a pre-prepared open state, control of the opening by the electric pneumatic regulator 120 can be provided so that the opening decreases as the air pressure increases, and the opening increases as the air pressure decreases.

[0057] As a result, the liquid flow rate is changed, and the changed liquid flow rate measured by the liquid flow meter 130 and the liquid target flow rate are compared again, and the above control operation is repeated so that the difference between the liquid flow rate information input from the liquid flow meter 130 and the target liquid flow rate is controlled within the error range.

[0058] Meanwhile, in the exemplary embodiment of the present disclosure, the on / off valve 113 allows the initial injection liquid flow rate to quickly reach the target liquid flow rate.

[0059] Specifically, after the liquid flow rate ejected by the constant pressure regulator 110 approaches the target liquid flow rate, the on / off valve 113 is switched to an open state so that the target liquid flow rate can be supplied through the liquid flow rate control system 100 .

[0060] However, in this case, it takes a considerable time (about 3 seconds) for the liquid flow rate ejected by the constant pressure regulator 110 to approach the target liquid flow rate, and a configuration to improve this point is required.

[0061] To this end, in the exemplary embodiment of the present disclosure, as described above, the on / off valve 113 is provided such that the diaphragm is prepared to be opened by a set amount in a closed state, or is controlled by the control device 140 .

[0062] For example, in the closed state, the on / off valve 113 is controlled to prepare to apply current to the electro-pneumatic regulator 120. The applied current corresponds to 95% to 100% less than the current magnitude applied to eject the target liquid flow rate. Therefore, the diaphragm is prepared to be opened by a set amount.

[0063] Thus, since the constant pressure regulator 110 is prepared to be opened by a set amount when the on / off valve 113 is in a closed state, the initial injection liquid flow rate can quickly reach the target liquid flow rate according to the experiment of the inventor. As a result, the inventor of the present disclosure confirmed through experiments that the liquid flow rate injection within 1% of the target liquid flow rate was achieved in about 1.5 seconds.

[0064] However, when the on / off valve 113 is in the closed state, the constant pressure regulator 110 should be prepared to open 95% to 98% of the set amount, and this changes with the hysteresis of the process facility.

[0065] As a method for solving this problem, the initial liquid flow rate flows when the on / off valve 113 is in an open state, and the initial liquid flow rate is checked in a state where the constant pressure regulator 110 is prepared for the opening duration Tb after the open state.

[0066] In this case, the difference between the initial liquid flow rate Qb and the control liquid flow rate Qa is checked, and the initially applied electric signal of the electro-pneumatic regulator 120 is changed so as to change the preliminarily opened state of the constant pressure regulator 110 according to the difference.

[0067] As a method of checking the difference between the initial liquid flow rate Qb and the control liquid flow rate Qa, the initial liquid flow rate is checked in a state where the constant pressure regulator 110 is set to 95% to 98% and the external environment (temperature and pressure) is stable. However, in this case, it is preferable to set a reference for identifying the initial liquid flow rate after completing the H / W operation of the components operating in the liquid flow rate control system 100.

[0068] After checking the difference between the initial liquid flow rate and the control liquid flow rate, the initial liquid flow rate is corrected by adjusting the amount of current applied to the electro-pneumatic regulator 120 according to the difference.

[0069] In the exemplary embodiment of the present disclosure, the electric signal applied from the control device 140 to the electro-pneumatic regulator 120 is preferably set as an analog current signal of 4 to 20 mA.

[0070] Compared with control using a voltage signal, control using a current signal has an advantage of being less affected by external noise.

[0071] On the other hand, the 4 to 20 mA current control signal has the advantage of being compatible with analog control standards.

[0072] The high-level control unit 150 inputs a target liquid flow rate from the outside (eg, a processing facility operator), and applies the input target liquid flow rate to the control device 140 .

[0073] The high-level control unit 150 performs the function of inputting various setting values ​​for the operation of the treatment facility except the target liquid flow rate and controlling the entire treatment facility. Information transmission between the high-level control unit 150 and the control device 140 is performed by communication.

[0074] According to the liquid flow rate control system 100 according to the exemplary embodiment of the present disclosure described above, the valve for controlling the liquid flow rate is provided with the low-cost constant pressure regulator 110 in addition to the expensive electric valve. In addition, the liquid flow rate passing through the constant pressure regulator 110 is controlled by the pressure of the air supplied from the electric pneumatic regulator 120. Therefore, the on / off valve 113 can prevent a sudden pressure fluctuation on the outlet side, and thus can prevent flow rate oscillation.

[0075] Furthermore, since the diaphragm is set in a pre-opened state or pre-opened by the control device before the start of liquid flow rate control, the difference between the actual output liquid flow rate and the target liquid flow rate at the initial stage of liquid flow rate control can be minimized.

[0076] Figure 3 is a diagram conceptually illustrating a liquid flow rate control system according to another exemplary embodiment of the present disclosure, Figure 4 It is shown Figure 3Graph of the flow rate control results of the liquid flow rate control system.

[0077] Reference Figure 3 and Figure 4 The liquid flow rate control system 200 according to another embodiment of the present disclosure is the same as the exemplary embodiment of the present disclosure described above in terms of configuration. However, there is a difference in the control operation of the control device 240, and due to this difference, when the target liquid flow rate changes over time, the liquid flow rate control is possible.

[0078] Therefore, the description of the liquid flow rate control unit 201, the on / off valve 213, and the liquid flow rate meter 230 is replaced by the previous description, and hereinafter, the control operation of the control device 240 will be described in detail.

[0079] The control device 240 receives the liquid flow rate measured by the liquid flow meter 230, and compares the received liquid flow rate with the control liquid flow rate Qa to control the opening of the liquid flow rate control unit 201. The control device 240 controls the liquid flow rate passing through the liquid flow rate control unit 201 to be consistent with the control liquid flow rate Qa within the error range through feedback control.

[0080] Furthermore, the control device 240 feedback controls the liquid flow rate passing through the liquid flow rate control unit 201 while controlling the liquid flow rate Qa by changing the fluctuating liquid flow rate Qs at each set time interval Ta.

[0081] The high-level control unit 250 inputs various data about the entire system (e.g., etching facility system) including the liquid flow rate control system 200 from the outside (e.g., system operator), transmits the input data to each control component (e.g., lower control system), and controls the smooth operation of the entire system. The high-level control unit 250 inputs the first set liquid flow rate Q1, the second set liquid flow rate Q2 different from the first set liquid flow rate Q1, and the time interval T at which the first set liquid flow rate Q1 changes to the second set liquid flow rate Q2 to transmit to the control device 240.

[0082] According to another embodiment of the present disclosure, it is sufficient that the high-level control unit 250 provides information about the first set liquid flow rate Q1 and the second set liquid flow rate Q2 and the time interval T as the target liquid flow rate information at the initial stage. In addition, the control device 240 uses the fluctuating liquid flow rate Qs for each set time interval Ta to change and control the control liquid flow rate Qa, so the transmission and reception of instructions and data between the high-level control unit 250 and the control device 240 is minimized to prevent time delay of control. Therefore, the liquid flow rate that fluctuates over time can be accurately controlled.

[0083] Specifically, the set fluctuating liquid flow rate Qs is obtained by the following steps: 1) calculating the liquid flow rate fluctuation amount (Qc=Q2-Q1) and the number of controlled liquid flow rate changes (Tc=T / Ta, Ta is the controlled fluctuation period), and 2) calculating the set fluctuating liquid flow rate Qs by dividing the liquid flow rate fluctuation amount Qc by the number of controlled liquid flow rate changes Tc (Qc / Tc).

[0084] Here, the control fluctuation period Ta is preferably 200 ms.

[0085] According to this, it is possible to minimize the liquid flow rate error due to the extension of the control fluctuation period Ta, and prevent the control time delay due to the increase in the amount of data to be transmitted and received when the control fluctuation period Ta is shortened.

[0086] In addition, since the liquid flow rate fluctuation amount Qc can have a positive value (when the liquid flow rate increases over time) or a negative value (when the liquid flow rate decreases over time), the liquid flow rate control of the control device 240 can be controlled so that the controlled liquid flow rate increases or decreases linearly over time without time delay.

[0087] refer to Figure 4 , it can be verified that during the time interval T, control of the liquid flow rate fluctuation is performed by linearly decreasing from the first set liquid flow rate Q1 of 800 mL / min to the second set liquid flow rate Q2 of 500 mL / min.

[0088] At the same time, according to another exemplary embodiment of the present disclosure, the target liquid flow rate information can be at least three set liquid flow rates (Q1, Q2 and Qn; n is an integer of n≥3) and at least two time intervals (T1 and Tm; T=n-1) required to be changed sequentially.

[0089] At this time, the control device 240 may be configured to control the liquid flow rate control unit 201, which compares the controlled liquid flow rate Qa changed according to the set time interval Ta calculated based on at least two time intervals and each of the two set liquid flow rates associated with the time intervals with the liquid flow rate measured by the liquid flow meter 230. Here, the control process for each of the single time intervals Tm is the same as described above.

[0090] Thus, even when the time rate of change of the target flow rate of the fluctuating liquid varies with time, the difference between the target liquid flow rate and the actual liquid flow rate can be minimized and controlled.

[0091] While the present disclosure has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the disclosure as defined by the appended claims.

Claims

1. A liquid flow rate control system, comprising: a liquid flow rate control unit, the liquid flow rate control unit controlling the liquid flow rate by controlling the opening of the diaphragm, and having the diaphragm set in a pre-open state with an initial setting amount; an on / off valve, the on / off valve being disposed downstream of the liquid flow rate control unit; a liquid flow meter that measures a flow rate of liquid flowing into the liquid flow rate control unit; and a control device that compares the actual liquid flow rate measured by the liquid flow meter with a target liquid flow rate to control the opening degree of the diaphragm of the liquid flow rate control unit and the opening / closing of the on / off valve, and starts control when the on / off valve is in a closed state, Wherein, the liquid flow rate control unit comprises: a constant pressure regulator, wherein the constant pressure regulator controls the opening of the diaphragm by supplying a pressure of a liquid; an electropneumatic regulator that controls the pressure of the liquid supplied to the constant pressure regulator, The control device preliminarily applies an amount of current based on the target liquid flow rate to the electro-pneumatic regulator to preliminarily open the diaphragm, and When current is prepared to be applied to the electro-pneumatic regulator, a current corresponding to 95% to 100% less than a magnitude of current to be applied for the target liquid flow rate is applied.

2. The liquid flow rate control system according to claim 1, wherein: The amount of current applied to the electro-pneumatic regulator is prepared to continuously fluctuate so as to spray 95% to 98% relative to the target liquid flow rate.

3. The liquid flow rate control system according to claim 1, further comprising: A high-level control unit inputs target liquid flow rate information from the outside and applies the input target liquid flow rate information to the control device.

4. The liquid flow rate control system according to claim 3, wherein: The target liquid flow rate information is a first set liquid flow rate Q1, a second set liquid flow rate Q2 different from the first set liquid flow rate Q1, and a time interval T required when the first set liquid flow rate Q1 is changed to the second set liquid flow rate Q2, and The control device controls the liquid flow rate control unit by comparing the controlled liquid flow rate Qa changed according to the time interval Ta calculated and set based on the first set liquid flow rate Q1, the second set liquid flow rate Q2 and the time interval T with the liquid flow rate measured by the liquid flow meter.

5. The liquid flow rate control system according to claim 4, wherein: The control liquid flow rate Qa fluctuates at a fluctuating liquid flow rate Qs set at each time interval Ta, and the fluctuating liquid flow rate Qs is set by using the first set liquid flow rate Q1 as an initial value, and after the time interval T, the control liquid flow rate Qa is determined to be the second set liquid flow rate Q2.

6. The liquid flow rate control system according to claim 5, wherein: The set fluctuating liquid flow rate Qs is obtained by the following steps: Calculate the liquid flow rate fluctuation amount Qc=Q2-Q1 and the number of controlled liquid flow rate changes Tc=T / Ta, where Ta is the control fluctuation period, and The set fluctuating liquid flow rate Qs is calculated by dividing the liquid flow rate fluctuation amount Qc=Q2-Q1 by the control liquid flow rate change number Qc / Tc.

7. The liquid flow rate control system according to claim 3, wherein: The target liquid flow rate information is at least three set liquid flow rates Q1, Q2 and Qn and at least two time intervals T1 and Tm required to be changed in sequence, n is an integer of n≥3, T=n-1, and The control device controls the liquid flow rate control unit, and the liquid flow rate control unit compares the controlled liquid flow rate Qa changed according to the set time interval Ta and the liquid flow rate measured by the liquid flow meter, and the set time interval Ta is calculated based on at least two time intervals and each of the two set liquid flow rates associated with the time interval.

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