introduction to instrumentation and control engineering

branch of physics which deals with the

measuring, monitoring and controlling

variables in a process industry.

INSTRUMENTATION

device that measures, monitors and control

process variables.

INSTRUMENT

“It is a collection of instruments, devices,

hardware or functions or their application

for the purpose of measuring,

monitoring or controlling an industrial

process or machine, or any combination of

these.”

Instrumentation

“It is device used for direct or indirect

measurement, monitoring, and/or control

of a variable including indicators,

controllers, and other devices such as

annunciators, switches and pushbuttons.”

INSTRUMENT

Instrument Society of America

ISA

Instrumentation, Systems &Automation Society

ISAS

International Society for Automation

ISA

Philippine Instrumentation and Control Society

PICS

Scientific Apparatus Manufacturers Association

SAMA

Purpose of Instrumentation and Control

• Quality Control

• Conservation of Energy and Raw Materials

• Safety

• Savings in Installation

• Material Balance & Product Accounting

• Coordination of Process Variables

• Research & Development

• Enterprise Management

HEART OF AUTOMATION

Instrumentation

Classification of Instruments

• Critical

• Non-critical

• Reference Only

Classification of Instruments - An instrument which, if not conforming to specification, could potentially compromise product or process quality and safety.

Critical

Classification of Instruments - An instrument whose function is not critical to product or process quality, but whose function is more of an operational significance.

Non-critical

Classification of Instruments - An instrument whose function is not critical to product quality, not significant to equipment operation, and not used for making quality decisions.

Reference Only

in process industries it refers to the

regulation, command or direction of all

aspects of the process.

CONTROL

2 Types of Control

• Manual Control

• Automatic Control

refers to the methods of changing or

refining raw materials to create end

products.

PROCESS

the regulation or manipulation of variables

influencing the conduct of a process in such a way

as to obtain a product of desired quality and

quantity in an efficient manner.

PROCESS CONTROL

an arrangement, set or collection of physical

components connected or related in such a

manner as to form and/or act as an entire

unit.

SYSTEM

an arrangement of physical components

connected or related in such a manner as to

command, direct or regulate itself or

another system.

CONTROL SYSTEM

an arrangement of two or more

instruments connected together to

perform a unified task.

INSTRUMENTATION SYSTEM

a process management system designed

to maintain a process variable at a

desired set point.

CONTROL LOOP

2 Types of Control Loop

• Closed Control Loop

• Open Control Loop

exists when a process variable

is measured, compared to a setpoint and action is

taken to correct any deviation from setpoint.

Closed Control Loop

exist when the process variable

is not compared, and action is taken not in response

to on the condition of the process variable.

Open Control Loop

a value for a process variable that is desired

to be maintained.

Setpoint

history - Fly-ball governor by Boulton &Watt

1789

history - Level Control System

by Greeks

Technological Development

• 1798-1920> Mechanical Technology

• 1920-1965> Pneumatics Technology

• 1930-1940> Electrical Technology

• 1950-present> Electronics Technology

• 1970-present> Microprocessor Technology

• 1980-present> Software Technology

ELEMENTS of the INSTRUMENT LOOP

• Process

• Measuring Element

• Receiving Element

• Final Control Element

Any operations or sequence of operations

involving a change of energy, state,

composition, dimension or other properties

that may be defined with respect to a

datum/data.

Process

any variable property of a process

Process Variable

any input variable that seats the

desired value of the measured variable.

Set point (SP)

outputs signal generated in

response to a change of a process

variable.

Controller Output

a process variable linked to

the controller output that is used to

influence the measured variable.

Manipulated variable

MAJOR PROCESS VARIABLE

• PRESSURE

• LEVEL

• FLOW

• TEMPERATURE

MINOR PROCESS VARIABLE

• ANALYSIS

• POSITION

• SPEED

• VIBRATION

A combination of two or more instruments or

control functions arranged so that signal pass

from one to another for the purpose of

measurement and/or control of a process

variables.

Instrumentation &Control Loop or Instrument Loop

The regulation or manipulation of variables

influencing the conduct of a process in

such a way as to obtain a product of

desired quality and quantity in an

efficient manner.

Process Control

The determination of the

magnitude of a variable (VALUE)

Measurement

The determination of the

existence or the presence of a variable.

Detection

Basic Function of Analog Measuring Devices

Basic Characteristics of a Measuring Element

• Output represents the input faithfully.

• Linear input/output relationship.

• No effect of Temperature & others.

The limit or extent of variation. The lower

limit is called LRV & the upper limit is called URV.

RANGE

The number of units between

two limits, the LRV and URV.

SPAN (of a range)

Standard Instrumentation Signals

• Analog Signal

• Digital Signal

a signal that has no discrete

positions or states and changes value.

Analog Signal

a signal that generates or uses

binary digit signals to represent continuous values or

discrete states.

Digital Signal

Pneumatic or Air Pressure

• English = 3 to 15psi

• Metric = 0.2 to 1.0 bars (or Kg/cm^2)

Electrical or Electronic

• Current = 4 to 20 mA dc

• Voltage = 1 to 5 V dc

Computerized

• Smart Transmission

• Fieldbus Transmission

TYPES OF MEASURING ELEMENTS

Analog Output (Numerical Information)

• Sensor

• Transmitter

• Transducer

Discrete Output

• Process Switch

The part of Instrument loop or instrument that

first senses the value of a process variable, and

that assumes a corresponding, predetermined,

and intelligible state or output.

SENSOR

Integral part of loop that first senses the value of a

process variable that assumes a corresponding

predetermined state and generates an output signal

indictive of or proportional to the process variable.

SENSOR

A device that senses a process variable through

the medium of a sensor and has an output

whose steady-state value varies only as a

predetermined function of the process variable.

TRANSMITTER

A general form of a device that receives information in

the form of one or more physical quantities, modifies

the information and/or its form, if required, and

produces a resultant output signal.

TRANSDUCER

can be primary element,

transmitter, relay, converter or other device. Because this term is not specific,

its use for specific applications is not recommended.

TRANSDUCER

a device that translates a mechanical signal

into an electrical signal.

TRANSDUCER

Transducers and transmitters are

virtually the same thing, the main

difference is

the kind of electrical signal each sends.

• A transducer sends a signal in volts (V) or millivolt (mV)

• a transmitter sends a signal in milliamps (mA).

TRANSMITTER

• Expensive

• Very Accurate

• Very rugged

• Repairable

• Adjustable range

• Standard signal output

TRANSDUCER

• Low cost, cheap

• Not so accurate

• Not rugged

• Not Repairable

• Fixed Range

• Different outputs by the manufacturer

a device that converts one type of signal into

another type of signal. (current into voltage,

analog to digital)

Converter

a device that converts a reading from one

sensor or transducer into a standard and

transmits that signal to a monitor or

controller.

Transmitter

Methods of Measurement

• Direct Method

• Inferential Method

the process variable is directly measured in units that

represent the basic nature of that variable.

Direct Method

is the measurement of a process variable indirectly by

using another variable.

Inferential Method

Types of Measurement

• Single Point Type

• Continuous Type

• the measurement depends on a fixed value of the process variable.

• the reading is indicated either as high or low

Single Point Type

is the measurement of a process variable indirectly by

using another variable.

Continuous Type

refers to the capability of the

instrument to measure a variable.

Instrument Range

refers to the set of values within the

instrument measuring range where the scaled output;

4-20 mA, 3-15 psior 1-5 V is set duringcalibration.

Calibration Range

It is the distance (or difference) between the upper range

value (URV)and lower range value (LRV).

Instrument Span

the highest value of the measured

process variable that the output of a transmitter is currently

configured to measure.

Upper Range Value (URV)

the lowest value of the measured process

variable that the analog output of a transmitter is currently

configured to measure.

Lower Range Value (LRV)

refers to a true-or-false condition.

“discrete” variable or measurement

one that is only

able to indicate whether the measured variable is above or below a

specified setpoint.

discrete sensor

typically take the form of “switches”, built to

trip when the measured quantity either exceeds or falls below a

specified value. These devices are less sophisticated than so-called

continuous sensors capable of reporting an analog value, but they

are quite useful in industry.

discrete sensor

status its electrical

contacts are in under a condition of minimum physical stimulus.

“normal” status for a switch

Electrical switch contacts are typically classified as either, referring to the open or closed statusof the contacts under “normal” conditions.

normally-open or normally closed,

an electrical switch actuated by a person’s hand

motion. This may takeaform of toggle, pushbutton or rotary.

Hand Switches

detects the physical motion ofan objectby direct contact

with that object. it will be in its “normal” status when it is not in

contact with anything.

Limit Switches

detects the proximity (closeness) of an object. By

definition, these switches are non-contact sensors, using magnetic, electric

oroptical means tosense the proximityofobjects.

Proximity Switches

detects the presence of fluid pressure. it is often use diaphragms or bellows as the pressure sensing elements, the motion of which actuatesone or more switch contacts.

Pressure Switches

detects the level of liquid or solid (granules or powder) in

a vessel. it is often use floats as the level-sensing element, the

motion of which actuatesoneor more switch contacts.

Level Switches

detects the temperature of an object. switches often use bimetallic strips as the temperature-sensing element.

Temperature Switches

detects the flow of some fluid through pipe. switches often use “paddles” as the flow-sensing element, the motion of which actuatesoneor more switch contacts.

Flow Switches

the fluid

equivalent of an electrical

switch: a device that either

allows unimpeded flow or acts

to prevent flow altogether.

on/off valve

Valve styles commonly

used for on/off service include

• ball

• plug

• butterfly

• gate

• globe.

Known as the controller and is the brain of

the control system

Controlling Element

Performs appropriate functions for

maintaining the desired level (set point) of

parameters to restore quality and rate of

production.

Controlling Element

device that receives data from a

measurement instrument , compares that

data to a programmed setpoint, and, if

necessary, signals a control element to

take corrective action.

Controller

Common examples of controller:

• Programmable Logic Controller (PLC)

• Distributed Control System (DCS)

usually

computers connected to a set of input/output (I/O)

devices. The computers are programmed to respond to

inputs by sending outputs to maintain all processes at

setpoint.

Programmable Logic Controller (PLC)

are controllers that, in addition to performing control

functions , provide readings of the status of the process,

maintain databases amd advance man-machine-

interface.

Distributed Control System (DCS)

The part of the control system that acts to

physically change the manipulated

variable.

Final Control Element

Typically used to increase or decrease

fluid flow.

Final Control Element

the part of a final control device that causes

a physical change in the final control device

when signalled to do so.

Actuator

manipulate the flow rate of gas or liquid;

whereas, the control switches manipulate the

electrical energy entering a system.

Control Valves

Instrument applications:

• Factory automation instruments

• Plant safety or safeguarding instruments

• Product Quality monitoring/control instruments

• Environmental condition monitoring /control instruments.

• Process variable measurement and control instruments.