Introduction about Piping Instrument

Symbol shape

The P&ID will use symbols and circles to represent each instrument and how they are inter-connected in the process.

Depending on Instrument Location: The presence or absence of a line determines the location of the physical device. For example no line means the instrument is installed in the field near the process.

Depending if it is Shared Displays/Shared Control : Some instruments are part of a Distributed Control System (DCS) where a specific controller or indicator can be selected from many others but shown in one location (like a terminal screen) : then there is a a square around the main symbol 

Symbol number

Tag “numbers” are letters and numbers placed within or near the instrument to identify the type and function of the device.

Based on Standard ANSI/ISA S5.1 and ISO 14617-6, the P&ID is used for the identification of measurements within the process. The identifications consist of up to 5 letters. The first identification letter is for the measured value, the second is a modifier, 3rd indicates passive/readout function, 4th - active/output function, and the 5th is the function modifier.

Connexion representation

These symbols are used to identify how the instruments in the process connect to each other and what type of signal is being used. (electrical, pneumatic, data, etc)

Instrument package

It sould be able to connect a pack of instruments each others if they are part of the same I&C loop by drawing only one I&C line connexion to the first instrument of the block 

On field Level Multifunction gauge (LT) is connected Shared instruments in control panel : Level Indicator (LI) and a Level Alarm Low (LAL) and a Level Alarm High (LAH) and a Level Switch Low (LSL) that are  physically integrated into a common device

Level Indicator is transmiting Data information to another shared Level indicator  that do the Average computation with other values from other Level indicators 

Very interesting article about P&ID:

http://www.aiche.org/chenected/series/how-interpret-piping-and-instrumentation-diagrams

Instrument in PFD or P&ID

Data organisation

needed output

• ICLoop line members 
• ICLoop extremities or Associated Equipment / process line
• Instrument functions/measure & connection type
• Instrument location