What are these Common Resources?
If more than one unit can acquire or request the services of a single resource, the resource is
designated as a common resource. Common resources are often present with complex batch
processes. Common resources are often implemented as either equipment modules or control
modules. A common resource may be either exclusive-use or shared-use.
That definition is pretty good for me, but there is still disagreement, and to a degree I think that they are the bits where the original S88 parties could not agree. For example, some give the example of Storage Tanks, but in an alternative perspective (not just mine) Storage Tanks are Units.
Another good example is transfer systems. Surely these are common resources?
Actually some of the best batch implementations I have seen treat them as units. They call them X units, but as far as controlling them they are exactly the same as 'normal' Units, including having Equipment Procedural Elements.
The viewpoint once described to me was that if contains even part of the batch it then it is a unit.
Something like steam supply or other utilities are for sure common resources aren't they?
Can a resource be a Unit and a Common Resource?
So, is there any prospect of the revised part 1 coming up with an improved wording that will stop the divergent interpretations, of things like storage tanks, transfer systems?
Of course, the definition that CR's may be made as equipment modules implies that they can have EPE's, and take part in recipes.
To be continued
Comments and musings about Control Systems and the ISA 88 standard, primarily Part 1 and Part 5, from a real control engineer, who wears a suit rarely - but sometimes!
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1 comment:
"Can a resource be a Unit and a Common Resource?
So, is there any prospect of the revised part 1 coming up with an improved wording that will stop the divergent interpretations, of things like storage tanks, transfer systems?"
Yes. Sort-of.
An example is the sterile transfer of material from Reactor A to Reactor B through common resource (X-Unit, as it were) C.
Let us assume that the line must be sterilised prior to transfer, and is currently dirty.
To sterilise the entire path, the Outlet EM of Reactor A, together with the Inlet EM of Reactor B, together with the Common Resource C must be acquired (by a SIP recipe, for example), in order to perform a controlled SIP. The path can then be kept in a sterile state, and released from the SIP recipe immediately prior to product transfer.
Thus, the Outlet EM of reactor A, and the Inlet EM of reactor B can be 'owned' (acquired) by the common resource (SIP recipe) or by the unit itself.
By your definition, these EMs would be common resources. I am not sure I agree with that, as their primary function is with the parent unit (Reactor), plus all the problems which would be associated with P&IDs, tagging etc.
What about the concept of expanding and shrinking Units? How would this fit in with the concepts of common resources?
Cheers!
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