Documents for instrumentation

Instrumentation documents:

• Process Flow Diagrams (PFDs)
• Process and Instrument diagrams (P&IDs)
• Loop diagrams (“loop sheets”)
• Functional diagrams

Process Flow Diagrams (PFDs)

The interconnections of process vessels, pipes, and flow paths of process fluids.The proper form of diagram to represent the “big picture” of a process are called a process flow diagram. Individual instruments are sparsely represented in a PFD, because the focus of the diagram is the process itself.

Process and Instrument diagrams (P&IDs)

Process and instrument diagrams (P&IDs) lie somewhere in the middle between process flow diagrams and loop diagrams. A P&ID shows the layout of all relevant process vessels, pipes, and machinery, but with instruments superimposed on the diagram showing what gets measured and what gets controlled.

 The following should be shown on the P&ID:

• Mechanical Equipment
• Equipment Numbering
• Presentation on the P&ID
• Valves
• Hand valves
• Control valves
• Piping
• Pipe numbering
• Nozzles & Flanges
• Equipment & instrument numbering systems

Loop diagrams (“loop sheets”)

The interconnections of individual instruments, including all the wire numbers, terminal numbers, cable types, instrument calibration ranges, etc. The proper form of diagram for this level of fine detail is called a loop diagram. Here, the process vessels and piping are sparsely represented, because the focus of the diagram is the instruments themselves.

Functional diagrams

            Functional diagrams are used for an entirely different purpose: to document the strategy of a control system. In a functional diagram, emphasis is placed on the algorithms used to control a process, as opposed to piping, wiring, or instrument connections. These diagrams are commonly found within the power generation industry, but are sometimes used in other industries as well.