Composition and control principle of industrial automation control system
发布时间：2022-04-28
There are various types of control systems in industrial production process, such as simple control system, complex control system, etc. each control system includes control variables, controlled variables and corresponding control laws. Controlled variables are process variables that need to be controlled, such as outlet pressure and outlet temperature of heat exchanger pump. In order to make the controlled variable consistent with the expected set value, a control method is needed, such as steam flow, pump bypass flow, etc. The reason why the controlled variable deviates from the set value is the interference in the production process, such as the fluctuation of steam pressure, the change of pump speed, etc. generally, the variable used for regulation is called the control variable.
A simple control system consists of detection elements and transmitters, controllers, actuators and controlled objects.
Detection elements and transmitters are mainly used to detect controlled variables and convert detection signals into standard signals. For example, thermal resistors convert temperature changes into resistance changes, and temperature transmitters convert resistance signals into standard air pressure or current and voltage signals.
The controller compares the standard signal output from the detection and transmission link with the set value signal to obtain the deviation signal. The deviation signal is calculated according to a certain control law, and the calculation output is sent to the actuator. The controller can be realized by analog instruments or digital controllers composed of microprocessors, such as PID control function modules used in DCS and FCS.
The actuator is in the final position of the control loop, so it is also the final element. The actuator is used to receive the output signal of the controller and control the change of the control variable. In most industrial production process control applications, the actuator adopts regulating valve. In recent years, with the application of variable speed regulation technology, some control systems and actuators are composed of frequency converters and corresponding motors.
Control principle:
When the load of the production process changes or the operating conditions change, through the detection and transmission of the detection elements and transmitters, the controlled variables of the process are sent to the controller, and the output after the control law calculation is sent to the actuator to change the corresponding fluid flow in the process, so that the controlled variables are consistent with the set value. It can be seen that the function of detection elements and transmitters is similar to that of human eyes, the function of controllers is similar to that of human brain, and the function of actuators is similar to that of human hands and feet. The quality of a control system is affected by the components of the control system, which mainly depends on the weak links in the components of the control system.
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