Instrumentation - ISA

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Nov 14, 2013 (3 years and 11 months ago)

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Instrumentation

Leo SaLemi

September 2008

What is it?

Definitions of Instrumentation from the Web:



The use of rods, screws, plates, hooks, wires,
bolts, etc. to correct and stabilize abnormalities
of the spine.


The art of composing, orchestrating, or
arranging for an instrumental ensemble.


An electrical or pneumatic device placed in the
field to provide measurement and/or control
capabilities for the system.

Objectives for this course

Learning the fundamentals of industrial
instrumentation


Terminology and Symbols


Measuring Means


Pressure, Temperature, Level, Flow


Controlling Means


Simple Closed Loop Control


PID Loop tuning


Resources

Text Book:

Industrial Control Electronics 3rd edition by Terry Bartelt,

Published by Thompson (Delmar Learning)

ISBN 1 4018 6292 6


ISA
(Instrumentation, Systems, and Automation Society)
The
I
nternational
S
ociety for
A
utomation

-

Setting the
Standard for Automation

www.isatoronto.org


Other web links:
see notes



Automation Technology

Instrumentation plays an important role in almost every
aspect of Automation Technology.



Industrial Automation


Manufacturing Automation


Process Automation


Building Automation


Everyone needs to measure and/or control something


and
that’s what instrumentation is all about.

Measurement

Things that are measured include:


Pressure
,
temperature
,
level
,
flow
, humidity, speed,
motion, position, weight, density, conductivity, pH,
light, quality, quantity, and more.


Devices that process or do the measuring are called:


Sensors, transducers, transmitters, indicators,
displays, recorders, data loggers, and data
acquisition systems.

Controllers

These are the devices that do the controlling:


Programmable Logic Controllers (PLCs)


Programmable Automation Controllers (PAC)


Distributed Control Systems (DCS)


Proportional, Integral, Derivative (PID)
Controllers


Supervisory Control and Data Acquisition
(SCADA)


Building Automation Controllers (BAC)


Energy Management Systems (EMS)


Control Elements

These are the devices the controller
operates:



Pneumatic valves, solenoid valves,
rotary valves, motors, switches, relays,
variable frequency drives.


Overview of Process Automation

The

process

is
“that portion of an automation
operation which use energy measurable by
some quality such as pressure, temperature,
level, flow, (and many others) to produce
changes in quality or quantity of some material
or energy.”

PROCESS

Some Quality or
Quantity

of the

Material or Energy

Input
Energy
or
Material

Desired

Result

Example of a Temperature Process

Heating Element

Water Bath

Temperature

The objective of this process is to maintain a constant water
bath temperature.

Temperature Process Terminology

Heating Element

Water Bath

Temperature

This is a Temperature Process

The measuring means is the thermometer. (Temperature Indicator
-

TI)

The process temperature is maintained at a desired point (Set Point


SP)

Steam (Control Agent) is used to vary the temperature by opening and
closing the control valve (Final Control Element)

Level Process


Oil Stock

Level Indicator

Oil Feed to
next
process


The control objective is to maintain a constant liquid level of oil
inside the tank (e.g. 100 gallons +/
-

20 gallons). The hand valve is
opened and closed as required to maintain the desired tank level.

Terminology used to describe the process



PROCESS:

Level


CONTROLLED VARIABLE:

Head pressure at bottom of tank


CONTROL POINT:

The level of oil in the tank (
S
et
P
oint = 100 gallons)


MEASURING MEANS:

Level Indicator (Head Pressure)


CONTROL AGENT:

Volume of oil stock


MANIPULATED VARIABLE:

Flow rate of oil (gpm)

Oil Stock

Level Indicator

Oil Feed to
next
process


Basic Model of a Process

The process is maintained at the desired point (SP)
by changing the FCE based on the value of the PV

Manipulated
Variable

Desired

Result

Control
Agent


PROCESS

(Temperature,
pressure, level, flow)

FINAL
CONTROL
ELELMENT

(valve)

Measuring
Means

(transmitter)

Process Variable (PV)

Controlled
Variable

Actuating
Input

pH, conductivity, humidity,
density, consistency, etc.

Process equilibrium (balance) is when the input energy
maintains the output at a constant “desired” point.

Basic Model of a Process

The measuring means provides the standardized signal
that represents the condition of the process, i.e. is the
process at the desired point?

Manipulated
Variable

Desired

Result

Control
Agent


PROCESS

(Temperature,
pressure, level, flow)

FINAL
CONTROL
ELELMENT

(valve)

Measuring
Means

(transmitter)

Process Variable (PV)

Controlled
Variable

Actuating
Input

pH, conductivity, humidity,
density, consistency, etc.

Measuring Means


Pressure




Level




Flow




Temperature


pH


Humidity


Density


Speed


Thermocouples

RTDs / Thermistors

Filled Systems

Bi
-
metallic




Strain gauge

Piezo
-
electric

Capacitance

Bourdon Tube

Head meters

(orifice, venturi)

Coriolis, velocity,
Mass,

Mechanical Floats

Guided Wave

Weight (load cell)

Ultrasonic

Differential Pressure


Transmitters







Pressure Transmitter


Level Transmitter


Differential Pressure
Cell


Flow Transmitter


Temperature Transmitter



Pneumatic

3
-
15 PSI


Electrical


Current

4


20 mA

0


20 mA

10


50 mA


Voltage

0


5 V

1


5 V

0


10 V


Digital

ON/OFF

Field Bus

ModBus

ProfiBus

HART



Open Loop Control

Open loop (or manual control) is used when
very little change occurs in the Process
Variable (PV)

Manipulated
Variable

Desired

Result

Control
Agent


PROCESS

(Temperature,
pressure, level, flow)

FINAL
CONTROL
ELELMENT

(valve)

Measuring
Means

(transmitter)

Process Variable (PV)

Controlled
Variable

Actuating
Input

pH, conductivity, humidity,
density, consistency, etc.

Corrective action is provided by manual feedback

Closed Loop Control

Closed loop or feedback control provides a corrective action based
on the deviation between the PV and the SP

Automatic

Controller Output



(3
-
15 psi, 4
-
20mA etc)


CONTROLLING

MEANS

Manipulated
Variable

Desired

Result

Control
Agent


PROCESS

(Temperature,
pressure, level, flow)

FINAL
CONTROL
ELELMENT

(valve)

Measuring
Means

(transmitter)

Controller Input
(PV)


(3
-
15psi, 4
-
20mA etc)

Controlled
Variable

pH, conductivity,
humidity, density,
consistency, etc.

Manual

SP

Controlling Means

Controllers provide the required control
action to position the FCE at a point
necessary to maintain the PV at the
desired SP.


PID (single loop feedback controller)


DCS (distributed controllers)


PLC (programmable logic controllers)


Single Loop Feedback Control

1.
Measuring
Means

2.
Controlling
Means

3.
Final Control
Element

4.
Temperature
Process

Temperature Controller and
Recorder

Sensing

Bulb

Temperature
Transmitter

Pneumatic
Control Valve

Heat Exchanger

Steam

2

3

4

1

The TT provides the signal (PV) that represents the condition of the
process being controlled. The TIC compares the PV to the SP and opens
and closes the FCE to maintain the process at equilibrium.

Summary


Process automation makes use of instrumentation to
maintain the process at some desired condition.


Common instrumentation used in a process loop are the
measuring means (usually transmitters), the controlling
means (usually a PID controller), and the Final Control
Element (usually some type of valve)


The measuring means provides the feedback signal (PV)
used in the process loop. The controlling means
operates the FCE based on the difference between the
PV and the SP.


Process equilibrium is maintained when the difference
between the PV and SP is zero or constant (offset?)

NEXT?

What are
transmitters?

What is PID?

What are P&ID
symbols?

What types
of FCE are
there?

What am I
doing here?

How do I
measure?

Pressure
Level
Temperature
Flow

How do I
tune a loop?

What is
Integral
action?

What is a?

FIC

TT

LRC

PRV


Should I use
a 3
-
15 psi or
4
-
20 mA
valve?

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