OT: S88 Implementation Question

I am looking for some guidance on how to change the current process implementation and still adhere to S88 guidlines. Since this is a late cahnge in functionality, i would like to keep changes to a minimum, if possible.

For the sake of this discussion, I'm simplifying the equipment a little. There is one vessel that we're calling a unit. There is another smaller vessel that supplies a liquid to the bigger vessel. This smaller vessel is also part of the unit. The samller vessel has an agitator that now needs to run all the time even when the unit as a whole is idle. If we make the agitation of this vessel a unit procedure, then we can't run another unit procedure at the same time. Currently, the smaller vessel agitation is a control module. I don't think I can run a control module on this smaller vessel without running a unit procedure too. I think my only course of action is to make this smaller vessel it's own unit. then i can run an agitation unit procedure on it without affecting the larger vessel. Does this sound right or have I missed something?

I could classify it as an "Equipment Module". You would have an agitation equipment module that can control your agitator control module. The equipment module has enough logic to allow it to be controlled as a "stand-alone" operation.

Your unit procedure(s) may need to send commands to initiate the equipment module pending the current state of the equipment module, however it should be able to be ran completely independent of any unit procedures or process sequencing.

Thanks for responding. So I would program the EM to use the agitation CM and it would run independently from any unit procedures. But the UPs could command the EM to shutoff the agitation EM when necessary. And this still would follow S88 guidelines?

You're still following S88 design guidelines, when you get into the nitty-gritty S-88 may not have a direct answer, so as long as you are applying the philosophy of it I don't see much issue.

Thanks for the help. I understand that S88 is a higher level structure with some interpretation needed. I am modifying my code accordingly. Thanks again.