Regarding the disorder in the control of intermittent operation steps
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I would like to ask control experts: in batch production, there are dozens of steps for a reaction vessel, from feeding materials to carrying out the reaction, to allowing it to mature, and then to discharging the product. Control is achieved through step-by-step programming using a PLC. If an error occurs in the PLC, could it happen that a certain step is executed simultaneously while other steps are still in progress? For example, when performing step 15, is step 5 mistakenly started and executed at the same time? Or can step 5 only be advanced or delayed between step 4 or step 6?
I don’t know what mistake you’re referring to; what exactly is the issue – is it a problem with the PLC system itself? Or something else – in theory, a situation like yours shouldn’t occur; the sequential control is carried out based on certain conditions
If programming is not done well, it might skip steps
Are you working in fine chemical engineering? Is it possible to control the injection of the control valve through a PLC?
Intermittent operation is common in fine chemical industry. In basic chemical manufacturing as well, some steps are carried out in a batch manner or under time-controlled conditions. Isn’t it just the regeneration of the brine purification resin tower in caustic soda production? The regeneration of many catalysts is also controlled chronologically.
This depends on the level of programming skill involved. PLCs use cyclic scanning of programs; if the 15 steps are not divided into 15 subroutines but are instead placed within the same program block, then the scanning will start from step 1 in every scanning cycle. If the interlock conditions are not properly set up, for example, if an action in step 15 causes the conditions for step 5 to be met, then both steps’ programs will be executed.