What is the meaning of process control system classification of automatic control systems

In a dynamic process, how can the temperature and liquid level be maintained at the required values?

If the properties of raw materials change, how can the manufactured products always maintain high quality?

For a dangerous situation, how long does it take to respond?

The above-mentioned production control problems are the basic problems that an automatic control system engineer needs to master.

How to implement a production process is very interesting. In the following chapters, we will learn to design system devices that can ensure safe production and product quality.

First, let's study what is a control system?

Can I drive if I don’t look outside the windshield?

What must be provided when designing a car?

If you don't need a steering wheel, can you have a better design?

How to keep the room warm?

What are the dynamic characteristics of temperature?

What must be provided when designing a room?

Can you have a better design if you don't need to heat the mechanism?

Through the above two examples, we know that there are three basic parts of the sensor, controller, and actuator in the control system! They are used to simulate the functions of human eyes, brain, and hands.

Can these three parts constitute an automatic control system?

In an automatic control system, in addition to the above three parts of automatic equipment, it is necessary to have the production equipment to be controlled to form an automatic control system.

The production equipment to be controlled is called: the controlled object. The controlled objects in chemical production include: various towers, reactors, heat exchangers, various pumps, containers, pipelines, etc.

The automatic control system is composed of a closed loop circuit consisting of measuring elements and transmitters, automatic adjustment controllers, actuators (regulating valves), and controlled objects.

Why is control necessary?

One word: disturbance!

The controlled variables of the automatic control system in the production process are systems with such variables as temperature, pressure, flow, liquid level, and composition.

The purpose of process control: increase production output, increase the income of high-quality products, reduce energy consumption, reduce pollution, reduce production risks, improve production safety, extend equipment life, improve operability, and reduce labor.

The current process control system is as follows:

(1) Controlled parameters (also known as system output): process parameters that are required to be stable in the controlled process;

(2) Control parameter (also known as manipulated variable control medium): the amount of material or energy that keeps the controlled parameter at the desired value;

(3) Interference amount: in addition to the controlled parameter, various factors that act on the controlled process and cause the controlled parameter to change;

(4) Set value: the set value (desired value) corresponding to the controlled parameter;

(5) Feedback value: the actual measured value of the controlled parameter after measurement and transmission;

(6) Deviation: the difference between the set value and the feedback value;

(7) Control function: the output value of the controller.

1. According to the controlled variables, it is classified into: temperature, pressure, flow, liquid level and other control systems.

2. According to the control law adopted by the controller, it is classified into: proportional, proportional integral, proportional integral derivative and other control systems.

3. According to whether the given value of the controlled variable changes, it is classified into: fixed value, follow-up and program control system.

Fixed value control system: In production, the function of the control system is to keep the controlled variable unchanged at the given production index. For example, the level control and temperature control described above.

Follow-up control system: In production, the function of the control system is to make the controlled variable follow the change of the given value accurately and quickly. For example, in the ratio system in chemical production, the flow rate of fluid A and fluid B maintain a certain ratio; when the flow rate of fluid B changes, the flow rate of fluid A can change quickly and accurately. Another example is the radar system and the antenna receiving system.

Program control system: In production, the given value of the control system is a variable and known function of time; that is, the controlled variable changes according to a certain time program. This type of system is commonly used in intermittent production processes. The application of computer technology provides good technical conditions for program control.

In the production process control, we hope that the production equipment meets the requirements of safety, environmental protection, equipment protection, smooth operation , product quality, profit, monitoring and diagnosis.