Transcript Intoduction to Automation System

EJ501
PROGRAMMABLE LOGIC
CONTROLLER (PLC) AND
AUTOMATION
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UNIT 1
INTRODUCTION TO AUTOMATION SYSTEM
Objective ;
1.
Understand automation system
a. Understand type of automation
b. Comparison type of automation
2.
Understand relays, contactors, electromechanical timer and
electromechanical counter (symbol, building diagram,
operation and application examples)
a. Develop simple logical control/ automation sequence
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INTRODUCTION TO AUTOMATION SYSTEM
Automation System
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Automation is the use of control systems and information
technologies to reduce the need for human work in the production of
goods and services.
In the scope of industrialization, automation is a step beyond
mechanization.
Whereas mechanization provided human operators with machinery
to assist them with the muscular requirements of work, automation
greatly decreases the need for human sensory and mental
requirements as well
Type of Automation system :
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fixed/ hardwired automation
programmable automation
flexible automation
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Fixed/ Hardwired Automation
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Custom-engineering, special – purpose equipment to automate a fixed
sequence of operations.
High production rates, inflexible product design
Programmable Automation
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Equipment designed to accommodate a specific class of product changes.
Batch production, medium volume
Flexible Automation
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Design to manufactured a variety of product or parts
Low production rates, varying product design and demand
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Comparison Types of Automation
Automation
When to consider
Advantages
Disadvantages
Fixed
High demand volume, long
product life cycle

maximum efficiency
 low unit cost

Programmable
Batch production, products
with the different options

flexibility to deal with
changes in product
 low unit cost for large
batches

Flexible
Low production rates, varying
demand, short product life
cycles

flexibility to deal with
design variations
 customized product

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large initial investment
 inflexibility
new product requires
long set up time
 high unit cost relative
to fixed automation
large initial investment
 high unit cost relative
to fixed or
programmable
automation
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INTRODUCTION TO AUTOMATION SYSTEM
Relays
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Define
A relay is usually an electromechanical device that is actuated by an electrical
current. The current flowing in one circuit causes the opening or closing of another
circuit. Relays are like remote control switches and are used in many applications
because of their relative simplicity, long life, and proven high reliability. Relays are
used in a wide variety of applications throughout industry, such as in telephone
exchanges, digital computers and automation systems. Highly sophisticated relays are
utilized to protect electric power systems against trouble and power blackouts as well
as to regulate and control the generation and distribution of power. In the home, relays
are used in refrigerators, washing machines and dishwashers, and heating and airconditioning controls
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Symbol
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Building Diagram
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Relay
Diagram
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Bottom View
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How does a relay work?
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All relays contain a sensing unit, the electric coil, which is powered by AC or DC
current. When the applied current or voltage exceeds a threshold value, the coil
activates the armature, which operates either to close the open contacts or to
open the closed contacts. When a power is supplied to the coil, it generates a
magnetic force that actuates the switch mechanism. The magnetic force is, in
effect, relaying the action from one circuit to another. The first circuit is called the
control circuit; the second is called the load circuit.
There are three (3) basic functions of a relay:
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On/Off Control: Example: Air conditioning control, used to limit and control a “high power”
load, such as a compressor.
Limit Control: Example: Motor Speed Control, used to disconnect a motor if it runs slower or
faster than the desired speed.
Logic Operation: Example: Test Equipment, used to connect the instrument to a number of
testing points on the device under test.
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Operation
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When no voltage is applied to pin 1, there is no current flow through the
coil. No current means no magnetic field is developed, and the switch is
open. When voltage is supplied to pin 1, current flow though the coil
creates the magnetic field needed to close the switch allowing continuity
between pins 2 and 4.
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• Type of Relay / Application Examples
This is a Single Pole Single Throw (SPST) relay. Current will
only flow through the contacts when the relay coil is energized.
This is a Single Pole Double Throw (SPDT) relay. Current will
flow between the movable contact and one fixed contact when the
coil is DEenergized and between the movable contact and the
alternate fixed contact when the relay coil is energized. The most
commonly used relay in car audio, the Bosch relay, is a SPDT
relay.
This is a Double Pole Single Throw (DPST) relay. When the
relay coil is energized, two separate and electrically isolated sets
of contacts are pulled down to make contact with their stationary
counterparts. There is no complete circuit path when the relay is
DEenergized.
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• Type of Relay / Application Examples
This relay is a Double Pole Double Throw (DPDT) relay.
It operates like the SPDT relay but has twice as many
contacts. There are two completely isolated sets of
contacts.
This is a 4 Pole Double Throw (4PDT) relay. It
operates like the SPDT relay but it has 4 sets of
isolated contacts.
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Figure : Relay Contact Configuration
Single Pole – relay have 1 common
Double Pole – relay have 2 common
Single Throw – relay have NC or NO
Double Throw – relay have NC and NO
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Pin no 1 – Common
Pin no 2 – NC
Pin no 3 – NO
Figure : Wiring of relay
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Contactors
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Define
Contactors are used to indicate an open or closed path of current flow.
Contacts are shown as normally open (NO) or normally closed (NC).
Contacts shown by this symbol require another device to actuate them.
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Symbol
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Building Diagram
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Operation
Normally Open Contact
Normally Open Contact
In the following illustration the circuit
is first shown in the de-energized
state. The contacts are shown in their
normally open (NO) state. When the
relay is energized, the contacts
close, completing the path of current
and illuminating the light. The
contacts have been highlighted to
indicate they are now closed.
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Operation
Normally Close Contact
In the following illustration the
contacts are shown as normally
closed
(NC),
meaning
the
contacts is closed when the relay
is de-energized. A complete path
of current exists and the light is
on. When the relay is energized,
the contacts open turning the light
off.
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Normally Close Contact
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Electromechanical Timer
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Define
Electromechanical timers are used to start or stop a machine or other device
at preset or delayed intervals. They consist of both electrical and mechanical
components, and often feature an electric motor that drives one or more
gears. They typically accept electric or electronic inputs to operate a
mechanical output such as rotating wheels or knobs.
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Symbol Electromechanical Timer
Contact symbols determine the time of timer
action:On-delay action - TR energized, contacts
change state after set time interval
Off-delay action - TR de-energized,
contacts change state after set time interval
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Electromechanical Counter

Define
Electromechanical counters are used to detect, totalize, and indicate a
sequence of events. They typically accept electric or electronic inputs to
operate mechanical outputs such as rotating wheels or knobs. These
devices may count UP and/or DOWN, support multiple functions, and
provide reset capabilities.
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Symbol Electromechanical Counter
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Simple Logical Control/ Automation Sequence
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Contactor
Relay
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3ph Starter/1ph Motor
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