ej501_unit-1

1EJ501

PROGRAMMABLE LOGIC CONTROLLER (PLC) AND

AUTOMATION

SBO/ PMM/ EJ501/ Jun2011 2

UNIT 1

INTRODUCTION TO AUTOMATION SYSTEM

Objective ;

1. Understand automation systema. Understand type of automationb. Comparison type of automation

2. Understand relays, contactors, electromechanical timer andelectromechanical counter (symbol, building diagram,operation and application examples)

a. Develop simple logical control/ automation sequence


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Automation System Automation is the use of control systems and information

technologies to reduce the need for human work in the production ofgoods and services.

In the scope of industrialization, automation is a step beyondmechanization.

Whereas mechanization provided human operators with machineryto assist them with the muscular requirements of work, automationgreatly decreases the need for human sensory and mentalrequirements as well

Type of Automation system : fixed/ hardwired automation programmable automation flexible automation


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Fixed/ Hardwired Automation Custom-engineering, special purpose equipment to automate a fixed

sequence of operations. High production rates, inflexible product design

Programmable Automation Equipment designed to accommodate a specific class of product changes. Batch production, medium volume

Flexible Automation 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

large initial investment inflexibility

Programmable Batch production, products with the different options

flexibility to deal with changes in product low unit cost for large batches

new product requires long set up time high unit cost relative to fixed automation

Flexible Low production rates, varying demand, short product life cycles

flexibility to deal with design variations customized product

large initial investment high unit cost relative to fixed or programmable automation


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Relays Define

A relay is usually an electromechanical device that is actuated by an electricalcurrent. The current flowing in one circuit causes the opening or closing of anothercircuit. Relays are like remote control switches and are used in many applicationsbecause of their relative simplicity, long life, and proven high reliability. Relays areused in a wide variety of applications throughout industry, such as in telephoneexchanges, digital computers and automation systems. Highly sophisticated relays areutilized to protect electric power systems against trouble and power blackouts as wellas to regulate and control the generation and distribution of power. In the home, relaysare used in refrigerators, washing machines and dishwashers, and heating and air-conditioning controls

Symbol


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Building Diagram


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Relay Diagram Bottom View


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How does a relay work? 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 coilactivates the armature, which operates either to close the open contacts or toopen the closed contacts. When a power is supplied to the coil, it generates amagnetic force that actuates the switch mechanism. The magnetic force is, ineffect, relaying the action from one circuit to another. The first circuit is called thecontrol circuit; the second is called the load circuit.

There are three (3) basic functions of a relay: 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

When no voltage is applied to pin 1, there is no current flow through thecoil. No current means no magnetic field is developed, and the switch isopen. When voltage is supplied to pin 1, current flow though the coilcreates the magnetic field needed to close the switch allowing continuitybetween pins 2 and 4.


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This is a Single Pole Single Throw (SPST) relay. Current willonly flow through the contacts when the relay coil is energized.

This is a Single Pole Double Throw (SPDT) relay. Current willflow between the movable contact and one fixed contact when thecoil is DEenergized and between the movable contact and thealternate fixed contact when the relay coil is energized. The mostcommonly used relay in car audio, the Bosch relay, is a SPDTrelay.

This is a Double Pole Single Throw (DPST) relay. When therelay coil is energized, two separate and electrically isolated setsof contacts are pulled down to make contact with their stationarycounterparts. There is no complete circuit path when the relay isDEenergized.

Type of Relay / Application Examples


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This relay is a Double Pole Double Throw (DPDT) relay.It operates like the SPDT relay but has twice as manycontacts. There are two completely isolated sets ofcontacts.

This is a 4 Pole Double Throw (4PDT) relay. Itoperates like the SPDT relay but it has 4 sets ofisolated contacts.

Type of Relay / Application Examples


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Figure : Relay Contact Configuration

Single Pole relay have 1 commonDouble Pole relay have 2 commonSingle Throw relay have NC or NODouble Throw relay have NC and NO


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Figure : Wiring of relay

Pin no 1 CommonPin no 2 NCPin no 3 NO


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Contactors 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.

Symbol


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Building Diagram


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Operation

Normally Open Contact

Normally Open Contact

In the following illustration the circuitis first shown in the de-energizedstate. The contacts are shown in theirnormally open (NO) state. When therelay is energized, the contactsclose, completing the path of currentand illuminating the light. Thecontacts have been highlighted toindicate they are now closed.


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Operation

Normally Close Contact

Normally Close Contact

In the following illustration thecontacts are shown as normallyclosed (NC), meaning thecontacts is closed when the relayis de-energized. A complete pathof current exists and the light ison. When the relay is energized,the contacts open turning the lightoff.


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Electromechanical Timer Define

Electromechanical timers are used to start or stop a machine or other deviceat preset or delayed intervals. They consist of both electrical and mechanicalcomponents, and often feature an electric motor that drives one or moregears. They typically accept electric or electronic inputs to operate amechanical output such as rotating wheels or knobs.


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Symbol Electromechanical Timer

Contact symbols determine the time of timeraction:-On-delay action - TR energized, contactschange state after set time intervalOff-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 asequence of events. They typically accept electric or electronic inputs tooperate mechanical outputs such as rotating wheels or knobs. Thesedevices may count UP and/or DOWN, support multiple functions, andprovide reset capabilities.


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Symbol Electromechanical Counter


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Simple Logical Control/ Automation Sequence


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Relay

Contactor


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3ph Starter/1ph Motor

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