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.
For the representation of such instruments, equipments an standard are followed to define their various types. These are symbolised by specific standard symbols for the identification of different types, are termed as instrumentation symbols. Here Process equipment symbols are not part of this standard, but are included only to illustrate applications of instrumentation symbols. The standard is suitable for use whenever any reference to an instrument or to a control system function is required for the purposes of symbolization and identification. The standard is suitable for use in the chemical, petroleum, power generation, air conditioning, metal refining, and numerous other process industries.
‘American National Standards’ are most widely used and followed by the process industries for the Instrumentation symbols, identification and preparing P&IDs. We will cover all type of symbols, identifications in such format-
ü Instrumentation Identification Letters
ü Instrument line symbols
ü General instrument or function symbols (defining mounting)
ü Control valve body symbols, damper symbols
ü Actuator symbols
ü Symbols for self-actuated regulators, valves, and other devices
ü Symbols for actuator action in event of actuator power failure
ü Primary element symbols (Level & Flow)
ü Equipments Symbols