Liquid additive injection device and control method

Abstract

The invention relates to the technical field of liquid additive injection in the resin production process, in particular to a liquid additive injection device and a control method. The inlet end of the vacuum generator is connected with a pressure reducing valve, and the outlet end of the vacuum generator is connected with the top of a glass metering tube; a capacitive liquid level transmitter is mounted on the outer side of the glass metering tube, a capacitive liquid level switch is mounted on the upper limit, and the lower end is connected with a ball valve through a conduit; the ball valve is mounted below the glass metering tube and connected through the guide tube; the three diaphragm electromagnetic switch valves are respectively positioned between the glass metering tube and the peristaltic pump, between the glass metering tube and the material tank, and between the material tank and the peristaltic pump; a low alarm switch is arranged at the bottom of the material tank; an inlet of the peristaltic pump is connected with outlets of the first diaphragm solenoid valve and the third diaphragm solenoid valve, and an outlet is communicated with the slurry tank through a silica gel hose. The device can be automatically started and stopped according to the actual proportioning amount of slurry, and the adding amount of the peristaltic pump can be adjusted.

Description

Technical Field

[0001] The invention relates to the technical field of adding liquid additives in a resin production process, and in particular to a liquid additive injection device and a control method. Background Art

[0002] In the process of preparing slurry for resin production, a small amount of a liquid additive needs to be added to the slurry. During the process of adding additives, fluctuations in the amount will cause abnormalities in the subsequent esterification reaction, so the additives require very high precision during the addition process, especially the control of the amount of addition should be controlled to 10g ± 2g per hour. The traditional method is to improve the accuracy by adding a glass metering tube to the front end of the peristaltic pump, manually injecting a certain amount of additives into the metering tube, and recording the height of the liquid level drop in the metering tube every hour, and then replenishing the additive every three hours and recording the value. When the slurry stops batching or the slurry batching amount is changed, it is necessary to manually stop the peristaltic pump or adjust the peristaltic pump speed to change the amount added. Due to frequent operations and human errors, the peristaltic pump pumping volume cannot be guaranteed, and the instability of other equipment on site will cause uneven addition of additives and untimely adjustment of equipment operation, causing production fluctuations. Summary of the invention

[0003] (1) Technical issues to be solved

[0004] The embodiment of the present invention provides a liquid additive injection device and a control method, which solves the problems of uneven liquid additive injection and operation errors in traditional manual operation through automation and intelligent control, so as to ensure the stability and accuracy of the production process.

[0005] (2) Technical solution

[0006] In a first aspect, an embodiment of the present invention provides a liquid additive injection device, the device comprising:

[0007] A vacuum generator, the inlet end of which is connected to a pressure reducing valve, and the outlet end of which is sealed and connected to the top of a glass metering tube;

[0008] The glass metering tube is a glass container with capacity scale marks, with a capacitive level transmitter installed on the outside, a capacitive level switch installed on the upper limit, and a ball valve connected to the lower end through a conduit;

[0009] A ball valve is installed below the glass metering tube and connected via a conduit;

[0010] There are three diaphragm electromagnetic switch valves, including a first diaphragm electromagnetic switch valve, a second diaphragm electromagnetic switch valve and a third diaphragm electromagnetic switch valve. The first diaphragm electromagnetic switch valve is located on the connecting conduit between the glass metering tube and the peristaltic pump, and is used for adding additives; the second diaphragm electromagnetic switch valve is located on the connecting conduit between the glass metering tube and the material tank, and is used for automatic material suction; the third diaphragm electromagnetic switch valve is located on the conduit between the material tank and the peristaltic pump, and is used for automatic material suction without affecting the peristaltic pump injecting additives into the slurry tank;

[0011] Material tank, with a low alarm switch installed at the bottom;

[0012] The peristaltic pump has an inlet connected to the outlets of the first diaphragm solenoid valve and the third diaphragm solenoid valve through a silicone hose, and an outlet connected to the slurry tank through a silicone hose.

[0013] Furthermore, the capacitive liquid level transmitter is installed on the outside of the glass measuring tube in a flexible external mounting manner, and the transmission signal is 4-20mA, and the corresponding range matches the capacity scale of the glass measuring tube.

[0014] Furthermore, the capacitive liquid level switch is installed within the upper limit of the measuring range of the glass measuring tube.

[0015] Furthermore, the peristaltic pump has an RS485 communication interface.

[0016] Furthermore, the inlet of the pressure reducing valve is connected to a gas source through a conduit.

[0017] In a second aspect, a control method of the liquid additive injection device according to the first aspect is provided, the control method comprising:

[0018] Step 1: Add liquid additives to the material tank to make the low-level switch at the bottom have no alarm state;

[0019] Step 2: The controller controls the peristaltic pump to start and adjust the speed according to the process slurry amount, opens the third diaphragm electromagnetic switch valve on the connecting conduit between the material tank and the peristaltic pump, and the peristaltic pump injects the additive into the slurry tank at the output speed;

[0020] Step 3: Open the second diaphragm electromagnetic switch valve on the connecting conduit between the glass measuring tube and the material tank at the same time, the vacuum generator is energized to generate negative pressure, and the liquid additive in the material tank is extracted into the glass measuring tube;

[0021] Step 4: When the liquid level reaches the position of the capacitive liquid level switch, the vacuum generator loses power, so that the glass measuring tube remains at normal pressure;

[0022] Step 5: close the second diaphragm electromagnetic switch valve on the connecting conduit between the glass metering tube and the material tank, and close the third diaphragm electromagnetic switch valve on the connecting conduit between the material tank and the peristaltic pump, open the first diaphragm electromagnetic switch valve on the connecting conduit between the glass metering tube and the peristaltic pump, and the peristaltic pump continues to inject the additive into the slurry tank at the output speed;

[0023] Step 6: The real-time liquid level change is directly measured by the capacitive liquid level transmitter. The processor reads the liquid level change measured by the capacitive liquid level transmitter in real time and converts it into volume flow rate, compares it with the peristaltic pump speed, and corrects the peristaltic pump speed through PID regulation.

[0024] Step 7, the processor reads the value of the capacitive liquid level transmitter with a scanning cycle of one minute. When the read value is △h, the corresponding actual amount is the flow rate per minute, which is used as the PID correction value of the peristaltic pump flow control;

[0025] Step 8: When the liquid level of the glass measuring tube drops to zero, close the first diaphragm electromagnetic switch valve between the glass measuring tube and the peristaltic pump, and repeat steps 3 to 7.

[0026] Furthermore, the capacitive liquid level transmitter is installed on the outer side of the glass metering tube, and its zero point position corresponds to the zero point of the glass metering tube, and its full scale corresponds to the full scale of the glass metering tube.

[0027] Furthermore, the vacuum generator is connected to the gas source through a pressure reducing valve, and negative pressure is generated and normal pressure is restored by controlling the power on and off of the vacuum generator.

[0028] Furthermore, the peristaltic pump communicates with the controller via RS485 communication, and the controller is used to control the start, stop and speed adjustment of the peristaltic pump.

[0029] Furthermore, the capacitive liquid level switch is installed on the upper part of the glass measuring tube, and is used to detect when the liquid level reaches the high alarm position and send a signal to stop the vacuum generator; a low alarm switch is installed at the bottom of the material tank, and an alarm signal for replenishing additives is sent when the additive level is lower than the alarm line.

[0030] (3) Beneficial effects

[0031] Compared with the prior art, the liquid additive injection device and control method provided by the present invention realizes accurate metering and automatic adjustment of additives by adopting an integrated automatic control system. The device uses a capacitive liquid level transmitter in conjunction with a central processing unit to automatically monitor and adjust the rotation speed of the peristaltic pump to ensure that the hourly additive injection amount is maintained within a strict control range (10g±2g). In addition, through an automatic replenishment system and real-time data analysis, the method reduces the need for manual operation and corresponding errors, while improving production efficiency and system safety. The automatic start-stop function and PID feedback adjustment mechanism further ensure the accuracy of the amount added, thereby effectively solving the problems of uneven additive injection and operational errors, and ensuring the stability and accuracy of the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 It is a schematic diagram of the overall structure of a liquid additive injection device according to an embodiment of the present invention.

[0034] Figure 2 It is a process flow chart of a method for controlling injection of a liquid additive according to an embodiment of the present invention.

[0035] In the figure:

[0036] 1. Gas source; 2. Pressure reducing valve; 3. Vacuum generator; 4. Glass metering tube; 5. Material tank; 6. Capacitive liquid level switch; 7. Capacitive liquid level transmitter; 8. Ball valve; 9. Slurry tank; 10. Peristaltic pump; 11. First three-way pipe; 12. First diaphragm solenoid switch valve; 13. Second three-way valve; 14. Second diaphragm solenoid switch valve; 15. Third three-way pipe; 16. Third diaphragm solenoid switch valve; 17. Material tank discharge valve; 18. Low alarm switch. DETAILED DESCRIPTION

[0037] The following is a further detailed description of the embodiments of the present invention in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the described embodiments, and covers any modification, replacement and improvement of parts, components and connection modes without departing from the spirit of the present invention.

[0038] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0039] Figure 1 is a schematic diagram of the overall structure of a liquid additive injection device according to an embodiment of the present invention. Figure 1 As shown, the equipment includes a vacuum generator 3 connected to an air source 1 and a pressure reducing valve 2, the air source 1 is connected to the inlet of the pressure reducing valve 2, the outlet of the pressure reducing valve 2 is connected to the inlet of the vacuum generator 3, the outlet end of the vacuum generator 3 is connected to the top port of a glass metering tube 4, the glass metering tube 4 is a glass container with a capacity scale mark, a capacitive liquid level transmitter 7 is installed on the outside, a capacitive liquid level switch 6 is provided at the upper limit, the lower end is connected to a ball valve 8 through a conduit, and the outlet of the ball valve 8 is connected to the A end of the second three-way pipe 13.

[0040] The device also includes three diaphragm electromagnetic switch valves, namely a first diaphragm electromagnetic switch valve 12, a second diaphragm electromagnetic switch valve 14 and a third diaphragm electromagnetic switch valve 16. The B end of the second three-way pipe 13 is connected to the first diaphragm electromagnetic switch valve 12, and the C end of the second three-way pipe 13 is connected to the outlet of the second diaphragm electromagnetic switch valve 14; the inlet of the second diaphragm electromagnetic switch valve 14 is connected to the B end of the third three-way pipe 15, and the A end of the third three-way pipe 15 is connected to the outlet of the material tank discharge valve 17, and the inlet of the material tank discharge valve 17 is connected to the bottom of the material tank 5, the C end of the third three-way pipe 15 is connected to the inlet of the third diaphragm electromagnetic switch valve 16, and the outlet of the third diaphragm electromagnetic switch valve 16 is connected to the A end of the first three-way pipe 11, the C end of the first three-way pipe 11 is connected to the peristaltic pump 10, and the A end of the first three-way pipe 11 is connected to the outlet of the first diaphragm electromagnetic switch valve 12.

[0041] The low alarm switch 18 is installed at the lower side of the material tank 5. The capacitive level transmitter 7 is installed on the outer side of the glass metering tube 4, and its zero point position corresponds to the zero point of the glass metering tube 4, and the full scale of the capacitive level transmitter 7 corresponds to the full scale of the glass metering tube 4. The capacitive level switch 6 is installed on the upper side of the glass metering tube 4 and is installed within the upper limit position of the range of the glass metering tube 4. The central controller reads the high alarm signal of the capacitive level switch 6 on the glass metering tube 4, the signal of the capacitive level transmitter 7, the alarm signal of the material tank 5 and the speed of the peristaltic pump 10 in real time.

[0042] When it is put into use for the first time, first open the ball valve 8 and the material tank discharge valve 17. At this time, the peristaltic pump 10 is in a stopped state, and the first diaphragm electromagnetic switch valve 12, the second diaphragm electromagnetic switch valve 14 and the third diaphragm electromagnetic switch valve 16 are all closed. The system detects that the low alarm switch 18 of the material tank 5 sends a low alarm signal, and the capacitive liquid level transmitter 7 displays zero, indicating that additives need to be added.

[0043] A certain amount of liquid additive is manually added to the material tank 5 until the low alarm switch 18 of the material tank 5 no longer sends a low alarm signal. After receiving the system ratio signal, the processor issues an instruction to start the peristaltic pump 10 and adjust the speed of the peristaltic pump 10. Next, the third diaphragm electromagnetic switch valve 16 between the material tank 5 and the peristaltic pump 10 is opened, and the second diaphragm electromagnetic switch valve 14 between the glass metering tube 4 and the material tank 5 is opened at the same time. After a delay of 2 seconds, the vacuum generator 3 is started to generate negative pressure to draw the additive in the material tank 5 into the glass metering tube 4. At this time, the peristaltic pump 10 delivers the additive normally.

[0044] When the liquid level reaches the high alarm position of the capacitive liquid level switch 6, the processor issues an instruction to close the vacuum generator 3 and stop extracting additives from the material tank 5 to the glass metering tube 4. The second diaphragm electromagnetic switch valve 14 and the third diaphragm electromagnetic switch valve 16 are closed, and the first diaphragm electromagnetic switch valve 12 between the glass metering tube 4 and the peristaltic pump 10 is opened. At this time, the peristaltic pump 10 continues to squeeze the hose to transport the additives in the glass metering tube 4 to the slurry tank 9.

[0045] The present invention realizes precise injection control of liquid additives by using a vacuum generator 3 connected to an air source 1 and a pressure reducing valve 2, and a structure including a plurality of diaphragm electromagnetic switch valves, a glass metering tube 4, a peristaltic pump 10 and a material tank 5. The device can read the status information of each sensor and switch in real time through a processor according to a system ratio signal, and automatically adjust the start, stop and speed of the peristaltic pump 10, thereby ensuring that the additive is accurately injected into the slurry tank 9 according to the set ratio.

[0046] As a preferred embodiment, the capacitive liquid level transmitter 7 is installed on the outside of the glass measuring tube 4 in a flexible external mounting manner, and the transmission signal is 4-20mA, and the corresponding range matches the capacity scale of the glass measuring tube 4.

[0047] As another preferred embodiment, the capacitive liquid level switch 6 is installed within the upper limit of the measuring range of the glass measuring tube 4 .

[0048] As another optional embodiment, the peristaltic pump 10 has an RS485 communication interface for communicating with the central controller.

[0049] It should be noted that the present invention effectively improves the accuracy and reliability of the additive injection process through an automated and intelligent control system. By configuring a glass metering tube 4 with a high-precision sensor, combined with the real-time data processing and PID adjustment function of the central processor, the system can automatically adjust the operating state and speed of the peristaltic pump 10 according to the actual slurry ratio requirements to ensure the continuous and uniform addition of additives. In addition, by using a combination of a diaphragm electromagnetic switch valve and a vacuum generator 3, the device can automatically complete the extraction and delivery of additives without human intervention, greatly reducing human operating errors and fluctuations in the production process, thereby ensuring the stability and efficiency of the entire production process.

[0050] like Figure 2 As shown, in a second aspect, the present invention further provides a method for controlling the injection of a liquid additive, the control method adopts the method of the first aspect as follows Figure 1 The liquid additive injection device shown includes the following steps 1 to 8:

[0051] Step 1, add liquid additive to the material tank 5 so that the low-alarm liquid level switch 18 at the bottom is in a non-alarm state; in this step 1, it is necessary to manually add a certain amount of liquid additive to the material tank 5 until a sufficient liquid level is reached so that the low-alarm liquid level switch 18 at the bottom is in a non-alarm state. This step ensures that there is enough additive in the material tank 5 for subsequent steps, which is a prerequisite for ensuring the normal operation of the system and the continuous supply of additives; in this step, the diaphragm electromagnetic switch valve (12, 14, 16) needs to be closed first.

[0052] Step 2: The controller controls the peristaltic pump 10 to start and adjust the speed according to the process slurry amount, opens the third diaphragm electromagnetic switch valve 16 on the connecting conduit between the material tank 5 and the peristaltic pump 10, and the peristaltic pump 10 injects the additive into the slurry tank 9 at the output speed; In this step 2, the controller first sets the start and speed of the peristaltic pump 10 according to the current process slurry amount to ensure that the additive is delivered to the slurry tank 9 at a predetermined rate and amount. Subsequently, the controller instructs to open the third diaphragm electromagnetic switch valve 16 connecting the material tank 5 and the peristaltic pump 10, so that the peristaltic pump 10 can extract the additive from the material tank 5 and accurately inject it into the slurry tank 9 at the set output speed.

[0053] Step 3, simultaneously open the second diaphragm electromagnetic switch valve 14 on the connecting conduit between the glass metering tube 4 and the material tank 5, the vacuum generator 3 is energized to generate negative pressure, and the liquid additive in the material tank 5 is extracted into the glass metering tube 4;

[0054] Step 4: When the liquid level reaches the position of the capacitive liquid level switch 6, the vacuum generator 3 loses power, so that the glass measuring tube 4 maintains a normal pressure state; in this step 4, when the liquid level of the liquid additive reaches the position of the set capacitive liquid level switch 6 in the glass measuring tube 4, the vacuum generator 3 automatically loses power and stops generating negative pressure. This operation restores the pressure in the glass measuring tube 4 to a normal pressure state, prevents excessive suction or backflow, and ensures the stability and accuracy of the liquid level.

[0055] Step 5, close the second diaphragm electromagnetic switch valve 14 on the connecting conduit between the glass metering tube 4 and the material tank 5, and close the third diaphragm electromagnetic switch valve 16 on the connecting conduit between the material tank 5 and the peristaltic pump 10, open the first diaphragm electromagnetic switch valve 12 on the connecting conduit between the glass metering tube 4 and the peristaltic pump 10, and the peristaltic pump 10 continues to inject the additive into the slurry tank 9 at the output speed; in this step 5, by accurately switching the diaphragm electromagnetic switch valves, the smooth flow and precise control of the additive are ensured, and the continuity and accuracy of the additive injection process are maintained.

[0056] Step 6. The real-time liquid level change is directly measured by the capacitive liquid level transmitter 7. The processor reads the liquid level change measured by the capacitive liquid level transmitter 7 in real time and converts it into a volume flow rate, compares it with the rotation speed of the peristaltic pump 10, and corrects the rotation speed of the peristaltic pump 10 through PID adjustment. In this step 6, the real-time liquid level change of the additive in the glass metering tube 4 is directly measured by the capacitive liquid level transmitter 7. The processor reads these liquid level data in real time and converts it into a volume flow rate. Then, the calculated volume flow rate is compared with the rotation speed of the peristaltic pump 10, and the rotation speed of the peristaltic pump 10 is adjusted and corrected through the PID (proportional-integral-differential) control algorithm to ensure that the injection amount of the additive remains within the set accuracy range. This step achieves high-precision control of the additive injection process through real-time monitoring and dynamic adjustment, ensuring the stability and accuracy of production. In this step, V=πr 2 △h, where V is the volume, r is the radius of the metering tube, and △h is the height of the liquid level change.

[0057] Step 7, the processor reads the value of the capacitive liquid level transmitter 7 with a scanning cycle of one minute. When the read value is △h, the corresponding actual amount is the flow rate per minute, which is used as the PID correction value of the peristaltic pump flow control;

[0058] Step 8: When the liquid level of the glass measuring tube 4 drops to zero, close the first diaphragm electromagnetic switch valve 12 between the glass measuring tube 4 and the peristaltic pump 10, and repeat steps 3 to 7.

[0059] In this embodiment, the vacuum generator 3 is connected to the gas source 1 through the pressure reducing valve 2, and the negative pressure is generated and restored to normal pressure by controlling the power on and off of the vacuum generator 3. The peristaltic pump 10 communicates with the controller through RS485 communication, and the controller is used to control the start, stop and speed adjustment of the peristaltic pump 10; the capacitive liquid level switch 6 is installed on the upper part of the glass metering tube 4, and is used to detect that the liquid level reaches the high alarm position and send a signal to stop the vacuum generator 3; the bottom of the material tank 5 is equipped with a low alarm switch 18, and when the additive liquid level is lower than the alarm line, an alarm signal for replenishing additives is sent.

[0060] It should be clear that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. For the embodiments of the method, the relevant parts can refer to the partial description of the device embodiment. The present invention is not limited to the specific steps and structures described above and shown in the figures. In addition, for the sake of brevity, a detailed description of known method technologies is omitted here.

[0061] The above is only an embodiment of the present application and is not limited to the present application. For those skilled in the art, the present application may have various changes and variations without departing from the scope of the present invention. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A liquid additive injection device, characterized in that: include: A vacuum generator, the inlet end of which is connected to a pressure reducing valve, and the outlet end of which is sealed and connected to the top of a glass metering tube; The glass metering tube is a glass container with capacity scale marks, with a capacitive level transmitter installed on the outside, a capacitive level switch installed on the upper limit, and a ball valve connected to the lower end through a conduit; A ball valve is installed below the glass metering tube and connected via a conduit; There are three diaphragm electromagnetic switch valves, including a first diaphragm electromagnetic switch valve, a second diaphragm electromagnetic switch valve and a third diaphragm electromagnetic switch valve. The first diaphragm electromagnetic switch valve is located on the connecting conduit between the glass metering tube and the peristaltic pump, and is used for adding additives; the second diaphragm electromagnetic switch valve is located on the connecting conduit between the glass metering tube and the material tank, and is used for automatic material suction; the third diaphragm electromagnetic switch valve is located on the conduit between the material tank and the peristaltic pump, and is used for automatic material suction without affecting the peristaltic pump injecting additives into the slurry tank; Material tank, with a low alarm switch installed at the bottom; The peristaltic pump has an inlet connected to the outlets of the first diaphragm solenoid valve and the third diaphragm solenoid valve through a silicone hose, and an outlet connected to the slurry tank through a silicone hose.

2. The liquid additive injection device according to claim 1, characterized in that: The capacitive liquid level transmitter is installed on the outside of the glass measuring tube in a flexible external mounting manner, and the transmission signal is 4-20mA, and the corresponding range matches the capacity scale of the glass measuring tube.

3. The liquid additive injection device according to claim 1, characterized in that: The capacitive liquid level switch is installed within the upper limit position of the measuring range of the glass measuring tube.

4. The liquid additive injection device according to claim 1, characterized in that: The peristaltic pump has an RS485 communication interface.

5. The liquid additive injection device according to claim 1, characterized in that: The inlet of the pressure reducing valve is connected to the gas source through a conduit.

6. A method for controlling the injection of a liquid additive, characterized in that: Using the liquid additive injection device according to any one of claims 1 to 5, the control method comprises the following steps: Step 1: Add liquid additives to the material tank to make the low-level switch at the bottom have no alarm state; Step 2: The controller controls the peristaltic pump to start and adjust the speed according to the process slurry amount, opens the third diaphragm electromagnetic switch valve on the connecting conduit between the material tank and the peristaltic pump, and the peristaltic pump injects the additive into the slurry tank at the output speed; Step 3: Open the second diaphragm electromagnetic switch valve on the connecting conduit between the glass measuring tube and the material tank at the same time, the vacuum generator is energized to generate negative pressure, and the liquid additive in the material tank is extracted into the glass measuring tube; Step 4: When the liquid level reaches the position of the capacitive liquid level switch, the vacuum generator loses power, so that the glass measuring tube remains at normal pressure; Step 5: close the second diaphragm electromagnetic switch valve on the connecting conduit between the glass metering tube and the material tank, and close the third diaphragm electromagnetic switch valve on the connecting conduit between the material tank and the peristaltic pump, open the first diaphragm electromagnetic switch valve on the connecting conduit between the glass metering tube and the peristaltic pump, and the peristaltic pump continues to inject the additive into the slurry tank at the output speed; Step 6: The real-time liquid level change is directly measured by the capacitive liquid level transmitter. The processor reads the liquid level change measured by the capacitive liquid level transmitter in real time and converts it into volume flow rate, compares it with the peristaltic pump speed, and corrects the peristaltic pump speed through PID regulation. Step 7, the processor reads the value of the capacitive liquid level transmitter with a scanning cycle of one minute. When the read value is △h, the corresponding actual amount is the flow rate per minute, which is used as the PID correction value of the peristaltic pump flow control; Step 8: When the liquid level of the glass measuring tube drops to zero, close the first diaphragm electromagnetic switch valve between the glass measuring tube and the peristaltic pump, and repeat steps 3 to 7.

7. The method for controlling the injection of liquid additive according to claim 6, characterized in that: The capacitive liquid level transmitter is installed on the outer side of the glass metering tube, and its zero point position corresponds to the zero point of the glass metering tube, and its full scale corresponds to the full scale of the glass metering tube.

8. The method for controlling the injection of liquid additive according to claim 6, characterized in that: The vacuum generator is connected to the gas source through a pressure reducing valve, and negative pressure is generated and normal pressure is restored by controlling the power on and off of the vacuum generator.

9. The method for controlling the injection of liquid additive according to claim 6, characterized in that: The peristaltic pump communicates with the controller via RS485 communication, and the controller is used to control the start, stop and speed adjustment of the peristaltic pump.

10. The method for controlling the injection of liquid additive according to claim 6, characterized in that: The capacitive liquid level switch is installed on the upper part of the glass metering tube, and is used to detect that the liquid level reaches the high alarm position and send a signal to stop the vacuum generator; the bottom of the material tank is equipped with a low alarm switch, and when the additive liquid level is lower than the alarm line, an alarm signal for replenishing additives is sent.

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