Liquid Transfer Automation - Part 4

In this post we look at the procedural side of transfers. Starting with Recipes
In S88 a General Recipe "expresses equipment and site independent processing requirements" As such it really has nothing to say about transfers, not least because it is possible that different plants may be able provide the equipment in different ways. For example one Unit in one plant may be able to do what 2 units are needed for in another

Much the same can apply to a Site Recipe

It is when we come to the Master Recipe that transfers become important because this level of recipe must address the actual equipment in the plant in its Procedures

So here's a transfer in a Master Recipe procedure, with Send (Transfer Out) And Receive (Transfer In) phases running simultaneously

PFC showing Transfer from one unit to the next

And it is the Control Recipe that must actually perform the transfer, by invoking transfer phases in the units between which the transfer is happening
You will note that the diagram shows a Synch line connecting the Source (transfer out) and destination (transfer in) phases. This represents the data flow between sender and receiver.
Please note that these communications should be directly between the two units and should work entirely in the equipment phases,
The next post will cover this in more detail.

S88 Phase Programming for DeltaV

With Emerson’s DeltaV and some other systems an S88 Phase is constructed around their version of the S88 “State transition diagram for example states for procedural elements.”

The Emerson structure uses Sequential Function Charts for each of the major state changes, such as that the Running SFC that goes between  Idle and Complete. In addition a Fail Monitor evaluates conditions that cause the phase to go into the Holding state.

The diagram below shows an overview of this.

Now, there are other and in my opinion better ways of constructing the phases. For example a Phase could just have one SFC, but with Running Holding, Aborting, Stopping And Restarting logic all handled within the same SFC.

Actually it is quite possible to do that even using the Emerson structure, if you don’t slavishly follow the Emerson examples.