PROCESS AND

INSTRUMENTATION

DIAGRAM (P&ID)

1

CHAPTER 1

INTRODUCTION

• Process control employs a standard set of symbols and

definitions to represent a plant and its associated control

systems.

• This standard was developed and approved by a

collaboration between the American National Standards

Institute (ANSI) and the Instrumentation, Systems and

Automation (ISA) Society.

• The P&ID depicts the entire plant and associated control

system.

• This includes plant operating units, product flow lines,

measurement and control signal lines, sensors,

controllers and final control elements.

2

INTRODUCTION

• A complete control loop includes instrumentation for

measurement and control of a process variable.

• The complete loop includes the process, the process

measuring device, the controller and the process

adjusting device.

3

THE IDENTIFICATION

FORMAT

• Each loop on P&ID used ISA symbols to show the

particular devices that perform certain functions.

• The first letter of tag number is correspond to the

measured process variables.

• The succeeding letters in the tag number describe the

function of the elements in the loop such as T for transmit,

I for indicate, R for record, and or C for control.

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INSTRUMENTATION

IDENTIFICATION LETTERS

Table A.1. Fraser (2001).Process measurement and control 5

TYPICAL TAG NUMBER

• TIC-103 Temperature Indicate Control (loop number) 103

• Where

• TXX-103 identifies the loop by first letter and number

and IC in place of XX identifies the functions by succeeding

letter.

• Hyphens are optional

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INSTRUMENT LINE SYMBOLS

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Figure A.1. Fraser (2001).Process measurement and control

EXAMPLE LIQUID FLOW AND

LEVEL CONTROL LOOPS

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EXAMPLE LIQUID FLOW AND

LEVEL CONTROL LOOPS

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EXAMPLE LIQUID FLOW AND

LEVEL CONTROL LOOPS

• Flow loop F-212 includes both flow element and flow

transmitter.

• Level loop needs only the level transmitter.

• The P&ID shows all the instrument functions so that the

detailed drawings will reflect the complete loop and so

that any engineering cost estimates will be complete.

• The dotted line coming from the flow and level measuring

sensors to their controllers represent the electrical

feedback signal.

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GENERAL INSTRUMENTS OR

FUNCTIONS

• The ballons, rectangles, hexagons, and diamonds are

used to denote the instrumentation.

• A line through a symbol means it is accessible to an

operator, such as being in a panel in the control room.

• No lines means that the instrument is located in the field

and is not accessible to the operator.

• A dashed line means that the device is inaccessible by

virtue of being located within other equipment, such as

behind the panel of a control room.

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GENERAL INSTRUMENTS OR

FUNCTIONS

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