ISA Symbols and Loop Diagrams

P& ID SYMBOLS

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Piping and Instrumentation Diagrams or simply P&IDs are the

“schematics” used in the field of instrumentation and control

(Automation).

The P&ID is used to by field techs, engineers, and operators to better

understand the process and how the instrumentation is inter

connected.

Most industries have standardized the symbols according to the ISA

Standard S5.1 Instrumentation Symbol Specification.

Piping & Instrumentation Drawing (original)

Process & Instrumentation Diagram (also used)

Process Flow Diagram – PFD (simplified version of the P&ID)

P&IDs

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Using pictorial diagrams may be

informative however it is not practical

or CAD friendly especially in a multi-

loop process.

Temperature Process The P&ID will use symbols and

circles to represent each

instrument and how they are inter-

connected in the process.

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The pneumatic signal from the positioner (or I/P if a positioner is not used)

applies directly to the actuator. For this control valve, the air enters above the

diaphragm and pushes against spring pressure to close the valve. The valve

fully closes when the plug seats tightly against the seat ring.

As air pressure decreases, the spring pressure causes the diaphragm, stem,

and plug to move upward, opening the valve. This means a loss of pressure

would cause the valve to open. This is a fail-open valve (AF)

Pneumatic Control Valve

SECCION 5.2

TEXTO GUIA

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The figure below shows the setup for a bench calibration of an I/P transducer. The air

supply connected to the input must be in accordance with manufacturer's specification

(typically between 20-100 psig). The pressure standard connects to the air outlet, and a

mA simulator connects to the current input.

Once the setup is established, apply the mA inputs for each desired test point, such as

4.0, 8.0, 12.0, 16.0, and 20.0 mA. Record the corresponding outlet pressure at each test

point. For a 4-20 mA input = 3-15 psig output I/P, the corresponding outputs would be 3.0,

6.0, 9.0, 12.0, and 15.0 psig.

Some facilities adjust the 0% test point so a slightly higher mA input results in the 0%

output. For example, 4.10 mA may result in a 3.0 psig output. This ensures the valve is in

the closed state with a controller output of 4.0 mA.

I/P transducter calibration

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Intercambiador de Calor m(t) , mA

Para abrir una válvula cerrada en falla

se requiere energía y por esto se conocen

como válvulas de “aire para abrir” (AO)

Tag “numbers” are letters and numbers placed within or near

the instrument to identify the type and function of the device.

Tag Numbers

Tag Descriptors

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Flow Control Valve Norma ISA-S5-1

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ZSH

E elemento primario

G visor

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Pneumatic/Hydrulic Simbols The P&ID mixes pneumatic / hydraulic elements, electrical elements

and instruments on the same diagram

Valve Symbols

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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.

Tag Numbers

The instrument is mounted

in the field near the process

(close to the operator)

The instrument is mounted

in the control room

(accessible to the operator)

The instrument is mounted

out of sight (not accessible

to the operator)

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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)

Shared Displays/Shared Control

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Summary of instrument type & location

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Piping and Connection Symbols

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)

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A PFD shows less detail than a P&ID and is used

Only to understand how the process works.

Process Flow Diagram - PFD

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Basic Column Control System

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Tarea

Identifique cada uno de los símbolos y Explique el funcionamiento de

los sistemas de control representados en las diapositivas 22 & 23

Repita el ejercicio con otra planta de un grado de dificultad igual o superior

NO OLVIDE LA REFERENCIA BIBLIOGRAFICA

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Anexar la norma ISA –S5-1 Solo en le CD