The important role of SFC language in realizing sequential control
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Colleagues, in a recent project we used the ECS700 DCS along with SFC for sequence control, and it was found that the central control DCS can now achieve performance that is essentially on par with Siemens’ SFC for sequence control. It is very user-friendly, allowing clear visibility of the execution conditions and steps for each sequence step. I recommend everyone to use it.
The important role of the SFC (Sequential Function Chart) language in implementing sequential control lies in its ability to visually represent each step of the process flow as well as the transition conditions, which facilitates monitoring and management by operators and enhances the efficiency and reliability of the control system. .
The programming language for central control systems seems to be leaning towards Siemens’ approach
This post was last edited by Xin Chang Xiao Xu on 2024-5-30 at 16:55. I create text blocks representing each step directly within a program segment; in these text blocks for each step, I specify the actions to be performed as well as the conditions under which a transition should occur. When such conditions are met, the variable representing that step is assigned the value of the next step. The enable terminal of each step’s text function block is determined jointly by RUN and whether the step value is the current generation. As in the text block of Step 3, if the step variable is equal to 3 and RUN is set to ON, then the program contained in the text block of Step 3 is executed. In this way, when the pause button is pressed, RUN turns off and all programs cease to execute; this is also utilized in emergency responses. Once a danger occurs, the program sets RUN to OFF and then executes the emergency procedure. In each step of the procedure, there is a variable that changes depending on the status of that step, in order to alter the color of the various graphical buttons. For example, at the start of the feeding step, if there is no nitrogen displacement, the feeding button is gray; if the color variable is 1, after the conversion is completed, the value of this color variable is set to 2, and the feeding button turns green.
That’s absolutely correct, but the utilization rate is currently low; many peers are not familiar with this configuration. We need to transform into engineers with expertise in both processes and control.
SFC prepares the framework for you; what you have here is CFC, which is executed during each cycle. By sequential control, it means that things are carried out in order and then nothing else is done. So some jumping and such are very convenient.
Hollyland is more similar to Siemens, but the panels of SFC sequential control are of poor quality and not as intuitive and user-friendly as those of central control systems.
Actually, with this implementation of mine, it’s possible to understand how SFC works – by using a variable (a step variable) to enable jumping between different states. Because it is a text-based functional block, it possesses characteristics similar to the ST language, which gives it greater flexibility; as a result, the conditions for transition can be as complex as desired. During the reaction step, it is possible to check whether the fans and mixing motors are operating, whether there is sufficient airflow, and whether the oxygen level exceeds the specified limits; based on these checks, different response procedures can be carried out. If any limit is exceeded, the process moves on to the accident response step. You think it would also be convenient to add a jump step. N ones will work too.
SFC thinks ahead for you, allowing engineers to focus on steps, logic, and the integration of continuous control