PFD:Process flow diagram.PFD gives an overview of the plant process.PFD is a simplified version of P&ID.

Symbols,circles and lines are used to represent instrument and their interconnection.For identifying instruments and pipe lines tag numbers are used.For reading P&ID(Piping & instrument diagarm) one must be familiar with standard instrument symbols and standard identification letter.

Instrument Location:The presence or absence of a line determines the location of the physical device.Some instruments are a part of a distributed control system where a specific controller or indicator can be selected from many others but shown in one location.

Piping and connection symbols:These symbols are used to identify how the instruments in the process connect to each other.And what type of singnal is being used.