Instrument loop diagrams are an important document of instrumentation and control design. These are used both at construction time and later troubleshoot because they show the complete loop on one sheet (or two at maximum).

Some of the importanat information which is put on ILDs are:

The instruments in the loop

The field junction box along with the termination strip no of each instruemnt

The core/pair size of the JBs cables to and from

The Marshaling cabinet strip no

The slot, rack and cabinet no to which the cable terminates

The loop no to which the instrument belongs

Now lets see what are the source documents which are needed for preparations of ILDs.

First of all we should have the master index list of all the instruments whci are in the system or plant.

From the index and using the P&ID  I/O list is developed from which we know how many cables and instruments are total in all the closed loops in the system.

Then the JBs and their termination information is extracted from cable schedule.

to be continued…