Thursday, 12 November 2009

Equipment Modules in Equipment Modules

As you all know S88 Part 1 supports Equipment Modules in Equipment Modules as indicated by this in the latest draft update.

I cannot at this moment think of one and nobody has ever shown me a real case that justifies it – if you know different Please Let Me Know. (You can comment here or email us.)
What I have seen is Equipment modules containing some sequential logic. But these are not phases that really perform Process Actions as phases should – I don’t rate sending a set point or prompting an operator as a Process Action by the way.
(I have also seen Common Resources implemented and Equipment modules and then containing equipment modules, but in those cases the Common resources were more like Units.)
Whenever I first review an S88 functional specification I look for this by the way. (If the functional specification is a ControlDraw model it takes about 10 seconds with Word it can take hours).
It is very rare, and always arguable.
Now, I think S88 would be greatly simplified and the implementations improved if the ability to have Equipment Modules in Equipment Modules was removed.
Of course you can do that yourselves when you do an S88 modularisation and without straying from the standard – and I highly recommend that you do.


Peter van den Berg said...

I also don't know any example of equipment modules containing an equipment module. There is no need using this possibility. By the way, I teach my students also to avoid control modules within control modules...

Francis said...

Great Peter
But I strongly agree with Control Modules in Control Modules. Even a PID Loop has a Measuring Module, the Functional one that does the PID and an Effector such as a control valve, all of which are type of Control Module.
Then there are higher level control modules that allow a group of valves, say a manifold, for example to be run as one object with one set of states. And there are many more examples.

Anonymous said...

I have created an enhanced module within an EM, initially calling it a Control Module, but later converting it to an EM for easier programming, by request of the programming team. This was very simple to do using CD.

Voila an EM in an EM. (Although the concept of an EM within an EM can be discarded, as using Control Modules within Control Modules is easily substitutable for this functionality)

Francis, try looking at the centrifuge in the PDL model!

I agree with Francis about using the concept of Control modules within control modules, as this can simplify repeatable sequences within an EM, and create more flexible & simpler designs.