Loop and Logic Diagrams and P&ID’s

This has recently been discussed at length on LinkedIn  on the ISA – International Society of Automation group under the title "Does control logic belong on P&IDs?"

Among the comments are
....Adding logic functions to a P&ID clutters it, is prone to add further unnecessary revisions to the P&ID every time a logic is changed ...
...agree that the complexity that we can configure into the DCS, PLc, and SIS cannot be represented adequately on the P&IDs...
...No, detail logic does not belong to PIDs. A PID is a construction document, as such it must show:
1-Hardwired input to logic interlock, complex loop or DCS/SIS
2-Hardwired output from logic interlock, complex loop or DCS/SIS to Final Control Element FCE
3-Identification of logic interlock, complex loop or DCS/SIS. Separate documents are generated for interlocks and complex loops...

So, how much can reasonably be shown on the P&ID depends on the type of process and previous practise but at the end of the day there are nearly always extra diagrams, typically with a cross reference on the P&ID. This blog post provides an explanation of how you can use ControlDraw to draw all those extra diagrams and relate them to the P&ID's
Top level diagram contains an object for each P&ID and child pages then provide a graphical list of the relevant loop and logic diagrams which are then diagrams under each object.
Here is a diagram that explains this (click to see full size)

This can even be extended to cover such things as State based control Matrices and Cause and Effect Matrices
Note - if you have a list of the P&ID's (which is normal) you can copy the list to create the P&ID Overview diagrams using Paste Special as Rows. And you can create all the P&ID Overview diagrams with a couple of clicks from the Group Menu >Create/Link Child diagrams.

A free peer reviewed automation design model for your process!

ControlDraw Ltd proposes to carry out and show online the development of functional requirement of a readers process.

Readers will define the process that will be used.

Readers will contribute by helping to choose which reader’s process we start with, and by reviewing the documents as they develop. This will be done using LinkedIn Groups

The Process
This could be a portion of a process plant, say a couple of process units.It may be batch or continuous
Ideally this will be one that is real and is soon to be automated. Even if you have already started – you might like to use the exercise to compare your own design.


Source information
Please send ,in the first place, a brief (but not too brief) description of your process. You must also be able to supply P&ID’s no more than 3. As this process will be carried out publicly you must accept that anything you send will be published online.

This will of course use ControlDraw, but others (especially those that promote their own methodologies) are invited to do the same using their normal documentation system.

Here is an overview of the plan