WO2020102958A1

WO2020102958A1 - Metering pump control system capable of accurately controlling flow rate

Info

Publication number: WO2020102958A1
Application number: PCT/CN2018/116314
Authority: WO
Inventors: 韩正奇
Original assignee: 中芳特纤股份有限公司
Priority date: 2018-11-20
Filing date: 2018-11-20
Publication date: 2020-05-28

Abstract

A metering pump control system capable of accurately controlling the flow rate. The metering pump flow rate control system comprises: a metering pump (1), a buffer (6), a flow rate meter (9), a controller (10), and a frequency converter (2). An instantaneous flow rate outputted from the metering pump (1) is accurately obtained by means of the filtering of the buffer tank (6) and a software filtering algorithm. The controller (10) calculates the instantaneous flow rate and a set flow rate by means of a PID algorithm to control an output frequency of the frequency converter (2), thereby adjusting the output flow rate of the metering pump (1). The present flow rate control system has high precision and high efficiency, and may be widely applied in fields that require the accurate and fast control of the flow rate of a metering pump.

Description

A metering pump control system capable of accurately controlling flow

Technical field

The invention relates to the technical field of metering equipment, in particular to a metering pump control system capable of accurately controlling flow.

Background technique

The metering pump is a special volume pump that can meet the requirements of various strict technological processes. The flow rate can be adjusted steplessly within the range of 0-100%. It is used to transport liquids (especially corrosive liquids). It is widely used in the quantitative and proportional dosing of fluids in petroleum, chemical, water treatment, food, pharmaceutical, environmental protection, medical equipment and other industries (referred to as fluid constant dosing), and has become the heart and engine of the process industry.

In existing metering pump applications, there are usually two control schemes to achieve the purpose of controlling flow. The first one is to adjust the flow of liquid by manually rotating the flow adjustment handle. The second method is to adjust the flow rate of the metering pump by adjusting the frequency converter. However, because the metering pump is a positive displacement pump, and the flow rate fluctuates in a sinusoidal curve, the accurate flow rate output by the metering pump cannot be obtained in real time. As a result, the above two flow adjustment methods have certain blindness, which greatly reduces the accuracy of the metering pump. Especially in the field of chemical fiber and fine chemical industry, if the flow rate needs to be changed frequently during use, the traditional control method has a long operation time, low flow control accuracy, and a large cumulative error, which cannot meet the process requirements.

Summary of the invention

In view of the shortcomings in the application of existing metering pumps, the present invention proposes a metering pump control system that can accurately control the flow rate. The flow control system has high precision and high efficiency, and can be widely used in the field that requires precise and rapid control of the metering pump flow rate. .

In order to achieve fast and accurate control of the metering pump flow, the metering pump flow control system proposed by the present invention includes:

1) Metering pump, used to transport fluid materials and control the flow rate of output fluid materials through the speed;

2) Buffer, used to clip the smooth wave to the pulsating flow output by the metering pump;

3) Flowmeter, used to detect the output instantaneous flow, and transmit the flow to the controller as a 4-20ma current signal;

4) The controller is used to collect flow signals in real time and process the flow signals, compare the set flow and actual flow, and control the output of the inverter through a software algorithm;

5) The frequency converter controls the speed of the metering pump by receiving the speed signal output by the controller, which has achieved the purpose of controlling the fluid flow;

The buffer described in the present invention mainly plays the role of physical filtering. The capacity of the buffer tank must be more than 10 times the capacity of the metering pump to obtain a better filtering effect. The nitrogen inlet, outlet and a gas pressure gauge are installed on the top of the buffer tank, and the liquid material inlet is installed on the side of the buffer tank, the height is 60% -70% Left and right, the outlet is installed at the bottom of the buffer.

Fluid material flows in through the upper part of the buffer and flows out at the bottom. The pressure sensor installed on the top of the buffer tank is used to detect the nitrogen pressure in the buffer tank. When the nitrogen pressure in the tank is insufficient, the nitrogen is supplied through the nitrogen input valve. When the nitrogen pressure in the tank is too high, the nitrogen is released through the nitrogen output valve.

The flowmeter of the present invention requires that the length of the upstream straight pipe section of the flowmeter should be at least 5 times the pipe diameter, and the length of the downstream straight pipe section should be at least 3 times the pipe diameter. The process tube and the sensor must be concentric, and the coaxial deviation is not greater than 0.05DN. (DN refers to the diameter of the pipe)

During the use of the buffer, the metering pump needs to be turned on first to allow a certain amount of material to be stored in the buffer tank. The height of the material liquid level is higher than the entrance of the buffer tank and does not exceed 80% of the height of the buffer tank.

In the control system described in the present invention, after receiving the flow signal of the flowmeter, software filtering must be performed first, and the filtering algorithm may use sliding filtering or average filtering.

The filtered flow signal is accumulated in the timing period T to obtain the cumulative flow Q. When the timing period ends, the average instantaneous flow F = Q / T is calculated. At the end of the timing period, the accumulated flow Q is cleaned at the same time, and the flow is accumulated in the next timing period.

The average instantaneous flow rate F and the set flow rate F _s are processed by the PID algorithm to obtain an output value, and this output value is converted into a frequency signal of the frequency converter and output to the frequency converter, and the flow rate of the metering pump is controlled by controlling the speed of the frequency converter.

BRIEF DESCRIPTION

Figure 1 is a block diagram of the system of the present invention;

The serial numbers in the system block diagram of Figure 1 are: 1) Metering pump, 2) Frequency converter, 3) Nitrogen input valve, 4) Pressure sensor, 5) Nitrogen output valve, 6) Buffer tank, 7) Nitrogen pipeline, 8) Fluid Material pipeline, 9) flowmeter, 10) controller

2 is a control flow in the controller of the present invention;

detailed description

The invention discloses a metering pump control system capable of accurately controlling the flow rate. The following implementation example will be described in conjunction with FIGS. 1 and 2.

The equipment used in this implementation example is as follows:

The metering pump, as shown in (1) in Figure 1, uses a plunger metering pump with a working flow of 200L / h and a motor using a 1.1kw variable frequency motor;

The buffer, as shown in (6) in Figure 1, has a capacity of 2L;

The flowmeter, as shown in (9) in Figure 1, uses an electromagnetic flowmeter with a range of 400L / h and an output signal of 4-20ma (4ma corresponds to 0L / h and 20ma corresponds to 400L / h);

The controller, as shown in (10) in Figure 1, uses a Siemens S7-300 controller, which is installed with a 4-20ma analog input module and a 4-20ma analog output module.

The frequency converter, as shown in (2) in Figure 1, uses Siemens MM440 frequency converter with a power of 1.5kw.

First, install the pipeline according to Figure 1. Connect the output of the metering pump to the input of the buffer tank, and the output of the buffer tank to the input of the electromagnetic flowmeter. Install a pressure gauge, nitrogen input valve, and nitrogen output valve on the top of the buffer tank . In order to ensure the stable flow when installing the electromagnetic flowmeter, the length of the upstream straight pipe section of the flowmeter should be at least 5 times the pipe diameter, and the length of the downstream straight pipe section should be at least 3 times the pipe diameter. The process tube and the sensor must be concentric, and the coaxial deviation is not greater than 0.05DN. (DN refers to the diameter of the pipe)

Then, make electrical connections according to Figure 1, connect the input signals of the flowmeter and pressure transmitter to the analog input module of the controller, and connect the analog signal of the analog output module of the controller to the analog input terminal of the inverter . Then connect the inverter to the motor.

After starting the whole system, first manually turn on the metering pump to allow the buffer tank to store a certain amount of material. The height of the liquid level of the material is required to be higher than the inlet of the buffer tank and not exceed 80% of the height of the buffer tank.

Then open the nitrogen input valve and nitrogen input method, adjust the pressure in the buffer tank, and observe the flow curve of the electromagnetic flowmeter. When the flow fluctuation is minimum, note the pressure value on the pressure transmitter at this time, and close the nitrogen input valve and Output valve.

The flow control scheme in the controller performs software filtering on the flow signal received from the flowmeter. The filtering algorithm can use sliding filtering or average filtering. The filtered flow signal is accumulated in the timing period T to obtain the cumulative flow Q. When the timing period ends, the average instantaneous flow F = Q / T is calculated. At the end of the timing period, the accumulated flow Q is cleaned at the same time, and the flow is accumulated in the next timing period. The average instantaneous flow rate F and the set flow rate F _s are processed by the PID algorithm to obtain an output value, and this output value is converted into a frequency signal of the frequency converter and output to the frequency converter, and the flow rate of the metering pump is controlled by controlling the speed of the frequency converter.

The controller detects and controls the pressure of the buffer tank at the same time. When the controller detects that the nitrogen pressure in the tank is insufficient, the nitrogen is supplemented through the nitrogen input valve. When the nitrogen pressure in the tank is too high, the nitrogen is released through the nitrogen output valve.

Claims

A metering pump control system capable of accurately controlling the flow rate for metering pump flow control, including:

Metering pump, used to transport fluid materials and control the flow rate of output fluid materials through speed;

Buffer, used to clip the smooth wave to the pulsating flow output by the metering pump;

Flow meter, used to detect the output instantaneous flow and transmit the flow signal to the controller;

The controller is used to collect flow signals in real time and process the flow signals, compare the set flow with the actual flow, and control the output of the inverter through a software algorithm;

The frequency converter controls the speed of the metering pump by receiving the speed signal output by the controller, which has achieved the purpose of controlling the fluid flow.
The metering pump control system capable of accurately controlling the flow rate according to claim 1, wherein the capacity of the buffer tank is greater than 10 times the capacity of the metering pump, and a nitrogen inlet valve, a nitrogen outlet valve and a gas pressure are installed on the top of the buffer tank In the transmitter, the liquid material inlet is installed on the side of the buffer tank with a height of about 60% -70%, and the outlet is installed on the bottom of the buffer. The liquid level of the material inside the buffer during operation is higher than the material inlet and does not exceed 80% of the height of the buffer tank.
The metering pump control system capable of accurately controlling the flow according to claim 1, characterized in that after the controller receives the flow signal of the flowmeter, it must first perform software filtering, and the filtering algorithm can use sliding filtering or average filtering. The filtered flow signal is accumulated in the timing period T to obtain the cumulative flow Q. When the timing period ends, the average instantaneous flow F = Q / T is calculated. At the end of the timing period, the cumulative flow Q is cleared at the same time, and the The flow is accumulated in a regular period, and the average instantaneous flow F and the set flow Fs are processed by the PID algorithm to obtain an output value, and this output value is converted into the frequency signal of the inverter and output to the inverter, which is controlled by controlling the inverter speed The role of metering pump flow.
The metering pump control system with accurate flow control according to claim 1, characterized in that the length of the upstream straight pipe section of the flowmeter should be at least 5 times the pipe diameter, and the length of the downstream straight pipe section should be at least 3 times the pipe diameter. The sensor must be concentric, and the coaxial deviation is not greater than 0.05DN.
A flow control method of a metering pump capable of accurately controlling the flow rate, which uses the metering pump control system of accurately controlling the flow rate according to claims 1-4, characterized in that:

S1: Start;

S2: read flow data;

S3: Perform software filtering on the flow data;

S4: Clear the accumulated flow value and start the timer;

S5: Start to calculate the cumulative flow;

S6: judge whether the timer is over, return to S5 if it is not over, continue to execute S7 and return to S4 to restart the calculation of the accumulated flow when the timer is over;

S7: Divide the cumulative flow obtained by S6 by the timer timing period to obtain the average instantaneous flow;

S8: PID processing the instantaneous flow obtained by S7;

S9: Convert the PID processing result into the inverter speed control signal to control the inverter speed;

S10: End.