Interpretation of chain logic
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Gentlemen, if I get the sequential logic file of a device, how can I determine the conditions that trigger this sequence? In other words, the interlock logic generally consists of “or” and “and”; based on this alone, can I determine whether the interlock is triggered when just one of the conditions is met, or only when all conditions are met?
Is this interlock logic a textual description?
It depends on how your company handles it; we operate in a chain format, and there are many conditions where OR and AND don’t match.
The poster is wondering why sometimes it’s 0 interlock and other times it’s 1 interlock. When I first started working on the SIS project, I also faced many difficulties, as in previous DCS projects interlocks were based on the use of \"1\", that is, what is known as positive logic. When working on SIS, fault safety must be taken into account; therefore, \"0\" is used to trigger interlocks, and in this context 0 represents a fault condition. Invert logic is then applied, which means that the usage of AND and OR operations is reversed. My method for making judgments: 1. DCS typically uses 1 for interlock functions, while SIS usually uses 0 for such functions. 2. Observe the interlock condition: if the output is 1, it is positive logic; if the interlock condition outputs 0, it is negative logic. 3. Observe the bypass button: if 0 indicates bypass, and a value of 0 represents a normal condition, then it is positive logic ； If 1 is the bypass, and it is normal when 1 is set, then it is inverse logic. Of course, there’s also checking the output, etc., but the output is divided into electrical and field aspects, and the situation can vary from time to time. Examine more logical relationships; gradually understand the differences between AND and OR. Once you become familiar with them, it will become clear naturally.
In sequential logic, what comes before “OR” and “AND” are the sequential trigger conditions. “As long as one of the “OR” conditions is met, the chain reaction can proceed. “Perform the action only when all “AND” conditions are met. There are also the “Manual, Automatic” (in the trigger conditions) and “Activate, Deactivate” (for activating/deactivating in a cascade) buttons. Knowing the safety state the process is intended to achieve makes the logic easy to understand. There’s a post titled “How to understand chain logic diagrams?” ? ? http://bbs.hcbbs.com/thread-1060299-1-1.html (Source: Haichuan Chemical Industry Forum) Hope this can help you