PLC & Pneumatic System

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Student Name Arjun Pratap Singh

Discipline Mechatronic Engineering

Module Name PLC & Pneumatic System

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Table of Contents

1 Introduction 3

2 Objective 6

3 PSIM Simulator

3.1 The Silo Simulator 7

3.2 The Batch Mix Lab Utilizing PLC Counters 13

4 Rotational Position System with DC Motor and Encoder

4.1 Connection Diagram 23

4.2 Ladder Logic Diagram 24

5 Pneumatic Palletizing and Punching System Design

5.1 3D Pneumatic Automation System Design 28

5.2 Component Selection 29

5.3 Implementation of Pneumatic Automation System

Using Pure Pneumatic Control 31

5.4 Implementation of Pneumatic Automation System

Using Electro Pneumatic Control 32

6 Discussion and conclusion 37

7 References 38

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Introduction

Programmable logic controllers are used in industry in many areas of automation and technology

as well as for control and regulation tasks. A PLC is a device with specialized input and output

interfaces. These interfaces (sensors and actuators) regulate, controls and monitors

manufacturing processes. Because the machines are getting more and more complicated,

industries won't be able to do without PLC programs. It is even possible to program and control

PLCs via data radio communication or radio relay system. It is also possible to write PLC

programs, implement error detection and correct errors via remote maintenance.

Programmable logic controllers are used for automation, monitoring and regulation of

technical processes. Here are few examples where programmable controllers can be used:

Control of an escalator

Control of a conveyor system

Control for filling a silo

Control of a bottling plant

Control of a traffic light system

Control of parking deck

Control of an automatic welding system

PLC were invented to do away with the hardwire logic, which was usually done using

number of sequential relays to control a machines operation. Below are few of the advantages of

using PLC’s:

Simplified Changes (changes in operation and circuit can be done easily by use of

programming)

Material and Space is saved (as number of relays aren’t use for control)

Duplications of Programs (program can be copied from one place to another without

trouble)

Comments and Documentation Possible (for easier understanding of the logic used)

Saving Time (less installation time, less cabling and parallel programming)

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Remote Maintenance and Diagnosis (easily monitored and controlled from remote

location)

Lower Energy Consumption

The PLC mainly consists of a CPU, memory areas, and appropriate circuits to receive

input/output data. It is possible to consider the PLC to be a box full of hundreds or thousands of

separate relays, counters, timers and data storage locations. They don’t exist physically but rather

they are simulated and can be considered software counters, timers, etc. These internal relays are

simulated through bit locations in registers.

(Inside PLC) (Available from http://www.plcs.net/chapters/parts3.htm)

(PLC Operation) (Available from http://www.plcs.net/chapters/howworks4.htm)

Below the researcher has explained the basic PLC instructions briefly:

The load (LD) instruction is a normally open contact. It is sometimes also called examine

if on. (XIO) (as in examine the input to see if it’s physically on). The symbol for a load

instruction is shown below.

http://www.plcs.net/chapters/howworks4.htm

http://www.plcs.net/chapters/parts3.htm

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(Available from http://www.plcs.net)

The Load bar instruction is a normally closed contact. It is sometimes also called Load

not or examine if closed. (XIC) (as in examine the input to see if it’s physically closed)

the symbol for a load bar instruction is shown below.


The Out instruction is sometimes also called an Output Energize instruction. The output

instruction is like a relay coil. Its symbol looks as shown below.


The latch instruction is often called a SET or OTL (output latch) once on will remain on

forever. The unlatch instruction is often called a RES (reset), OUT (output unlatch) or

RST (reset) once off will remain off forever. The diagram below shows how to use them

in a program.


http://www.plcs.net/




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Above researcher has shown and explained the basic instructions in PLC, more advanced

instruction include counters, timers, one shots, master controls, shift registers, getting and

moving data and math instructions.

For the given assignment, in the first part researcher has used PSIM software to control

the silo simulator and batch mixer, in the second part researchers have used rslogix 500 software

along with OMRON PLC to control dc motor rotational position aided by encoder and for the

last past researchers have used automation studio software to design an pneumatic automatic

system.

Pneumatic systems mainly comprise of pneumatic actuators which act due to change in

pressure of air. Pneumatic cylinder and valves are there to control and regulate air which is the

acting force; various mechanical works are done by the air pressure. In this assignment

researchers have designed a pneumatic system whose actions are controlled using PLC’s ladder

logic.

Objectives

For the given assignment the researchers are put with 3 main objectives, first objective is

creating ladder logic control for silo simulator and batch mixing which has to be achieved

individually, the second objective is creating ladder logic control and use OMRON PLC to

control dc motor’s rotational position which has to be achieved in a group and the last objective

is designing a pneumatic automation system which is controlled using ladder logic, which has

also to be achieved in a group.

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Part 1: PSIM Simulator (Individual)

The Silo Simulator

(Flow Chart for SILO Simulator) (Constructed using MS Word)

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(The Silo Simulator at Start) (Available from PSIM Simulator)

(The Silo Simulator at Standby Mode) (Available from PSIM Simulator)

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(The Silo Simulator at Run Mode) (Available from PSIM Simulator)

(The Silo Simulator at Full Mode) (Available from PSIM Simulator)

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(Toggle Table, the process is repeated 3 times on 4 th time the box is filled but is not cleared by

the conveyer belt) (Available from PSIM Simulator)

(Ladder Logic 1 for the SILO Simulator) (Available from PSIM Simulator)

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(Ladder Logic 2 for the SILO Simulator) (Available from PSIM Simulator)

RUNG INSTRUCTION

1 When switch F2 is switched on or level sensor has detected high level and full light is on and count

has not reached 4 latch the motor to run

2 When switch F1 is pressed or photo switch detects box and full light isn’t on unlatch the motor to

stop

3 When motor is running on the run light

4 When photo switch detects box latch the solenoid valve to open

5 When full light is on and motor is running or when count is over unlatch the solenoid valve to close

6 When run light is on unlatch the solenoid valve

7 When level sensor detects high level on the full light

8 When photo switch doesn’t’ detect anything unlatch or off full light

9 When photo switch detects box on standby light

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10 Whenever full light is switched on increases the counter by 1

11 When switch F3 is pressed reset the counter, thus resetting the process

Above, researcher has shown the screen shots of the silo simulator in action, below which he has

shown the ladder logic developed by him to control the silo simulator along with the flow chart

for easier and better understanding and below which he has explained each rung of the ladder

logic. The process of silo simulator has be designed as asked by the assignment which is, system

should be started once the start switch (F2) is pressed, which means the conveyer should run and

run light should be on, the system should stop or pause when stop switch (F1) is pressed, all the

processes are to be halted and standby light should be on. The box should stop when right edge

of the box is sensed by the photo sensor or switch (stop the conveyer when sensed), after which

the standby light should come on and solenoid valve should open and pour the liquid into the

box. While this process is going on, when level sensor detects the high level, the full light should

come on and the solenoid valve should close and the conveyer should restart again. This process

has to be repeated 3 times, but the researcher designed the system in such a way that the box will

be filled 4 times but the box will be cleared of the system only 3 times. For deeper technical

understanding, the researcher urges reader to go through the rungs operation above in the ladder

logic.

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The Batch Mix Lab Utilizing PLC Counter

(Flow Chart for Batch Mixer) (Constructed using MS Word)

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(The Batch Mix Lab at Start) (Available from PSIM Simulator)

(At Run Mode, P1 working) (Available from PSIM Simulator)

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(At Run Mode, P2 working and P1 stop) (Available from PSIM Simulator)

(At Full Mode, Hi – Level ON, Mixer ON and Heater ON) (Available from PSIM Simulator)

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(At Standby Mode) (Available from PSIM Simulator)

(Heater OFF desired temperature reached, Mixer on 4 sec) (Available from PSIM Simulator)

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(At Run Mode, P2 Stop, P1 Stop and P3 Working) (Available from PSIM Simulator)

(At Run Mode P3 Stop, Low Level OFF and P1 Working) (Available from PSIM Simulator)

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(Ladder Logic 1 for the Batch Mix Lab) (Available from PSIM Simulator)


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RUNG INSTRUCTIONS

1 When switch F2 is pressed the system starts and run light is on

2 When switch F1 is pressed the system stops or pauses and run light is off

3 When flow valve 2 is activated pump P2 can pump 30 liters of liquid into vessel

4 When flow valve 1 is activated and low level sensor is on pump P1 can pump 30 liters of liquid into vessel

5 When run light is on, P2 is off and value through flow valve 1 is less than 29 liters latch on P1

6 When value through flow valve 1 is greater than or equal to 28 or run light is off stop or unlatch P1

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7 When run light is on, P1 is off, quantity through flow valve FL2 is less than 29 and quantity through flow valve P1 is 28, latch or start pump P2

8 When value through flow valve 2 is greater than or equal to 28 or run light is off stop or unlatch P2

9 When values through flow valve 1 and 2 are equal to 28 switch on or latch the full light

10 When run light is on, high level sensor is on, full light is on, temperature is less than or equal to 30 degrees and pump P3 is closed switch on or latch the heater

11 When run light is on, high level sensor is on, full light is on, temperature is less than or equal to 30 degrees and pump P3 is closed switch on or latch the mixer

12 When temperature equals 30 degrees , make the fictitious output on or latch it

13 When low level sensor is off, make the fictitious output off or unlatch it

14 When the fictitious output is on or run light off unlatch or off the heater

15 When the heater is off, fictitious output is on and mixer is on, start the retentive timer till it reaches 4 seconds mark

16 Once the timer has reached 4 seconds and P3 is off or run light is off unlatch or switch off the mixer

17 When the run light is on, heater is off, pumps 1 & 2 are off and mixer is off, on or latch the pump P3

18 When low level sensor is off or run light is off unlatch or off the pump P3

19 When low level sensor is off reset the flow meter valve FL1

20 When low level sensor is off reset the flow meter valve FL2

21 When low level is off, pump P3 is off, P1 is off then reset timer T1

22 When high level sensor is off unlatch or off the full light

23 When mixer is on start the retentive timer T2 to calculate the operation time for mixer

24 When heater is on start the retentive timer T3 to calculate the operation time for heater

25 When the run light is off standby light is on

26 When flow meter valve FL3 is on the counter C3 is switched on by which it means it counts the value of output through the pump P3.

Above, researcher has shown the screen shots of the batch mixer lab utilizing PLC counter in

action, below which he has shown the ladder logic developed by him to control the batch mixer

lab along with the flow chart for easier understanding and below which he has explained each

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rung of the ladder logic. The process of batch mixer lab has be designed as asked by the

assignment which is, the system should start as soon as switch S2 is pressed, once that happens

the run light should come on and pump P1 should start pumping the liquid into the vessel while

pump P2 is still off. The amount of quantity through P1 is controlled by the researcher, which is

exactly half the volume of the vessel, once the vessel is filled half, the P1 stops and P2 takes over

pumping the liquid into the vessel. As, soon as the high level sensor over the vessel detects that

vessel is full, the full light comes on and the P1 and P2 stop functioning, while at same time the

heater is switched on to get the temperature of the liquid in the vessel to the set point. As soon as

the temperature sensor detects the temperature has reached the desired value, the heater switches

off. All this while since the full light came on the mixer has been turning, even when heater was

on. Now once the desired temperature is reached, the heater switches of immediately but the

mixer runs for extra 4 seconds before switching off. Once those 4 seconds are over pump P3

opens up and starts to drain the liquid in the vessel to some other place, once the volume of the

liquid is virtually none in the vessel, the low level sensor detects (switching off) it, and causes

the P3 to be closed and P1 to start pumping the liquid into the vessel again. This process is

continuous, it won’t stop until someone presses the switch S1, which cause the system to halt or

stop completely by switching off the run light and switching on the standby light. For deeper

technical understanding readers are urged to go through the rungs operation above in the ladder

logic.

(This parts ladder logic was done by the researcher after discussing with some classmates

and researching a lot on internet as system wasn’t working perfectly after number of tries)

Part 2: Rotational position system with DC motor and Encoder (Group)

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The figure below shows rotational position system with DC motor and Encoder. OMRON PLC

programmed using rslogix 500 is used to control DC motor and Encoder. The programming

sequence desired is as following:

1. The DC motor must have 3 different positions by using 3 different switches.

2. The encoder is used to detect the positions.

3. The DC motor must be able to rotate CCW and CW 2 switches.

4. The system must also have a single start and stop switch.

(Rotational position system with DC motor and Encoder) (Available from the Lecturer)

Connection Diagram

(Connection diagram of Rotational Position System) (Available from Soh Boon Heng)

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10A enhanced DC motor driver MD10B is connected between DC motor and PLC, to protect

PLC from back EMF generated from the motor and also to control the motors speed and

direction parameters.

Seven (7) inputs pins or ports have been used on the PLC’s input card, they are as following:

I: 000 (Output of infrared channel fiber optics sensor – working as an encoder)

I: 001 (Switch to control the direction of rotation – CW/ON or CCW/OFF)

I: 002 (Switch to stop dc motor at position 1 defined by the researchers)



I: 005 (Switch to reset the counter)

I: 006 (Switch to Start/Stop the dc motor)

Three (3) output pins or ports have been used on the PLC’s output card, they are as following:

O: 105 (Connected to PWM pin of MD10B to control the dc motors speed)

O: 106 (Connected to DIR pin of MD10B to control the direction of dc motor)

O: 107 (Connected to RUN pin of MD10B to control the direction of dc motor)

Programming (Ladder Logic)

(Rung 1) (Constructed on rslogix 500)

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In rung 1, 3 switches are connected to reversible counter or bi – directional counter

(up/down). When I: 001 is ON the dc motor moves in forward direction, while I: 000 aides in

increasing the counter while in forward direction (the fiber optic sensors output goes high when

white color is detected and low when black is detected. Researchers painted a black plus sign on

circular white sheet, which was attached to the rotating shaft of the dc motor). This function

reverses when I: 001 is OFF. The final switch in this rung is I: 005 which is there to reset the

counter, but hasn’t been used or shown in demonstration as, the starting position of the dc motor

has already been identified and recorded by the counter, if counter is to be reset, the a new

starting position would be set, as where the dc shaft is positioned currently.

(Rung 2, 3, 4) (Constructed on rslogix 500)

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Rungs 2, 3 and 4 work in similar manner. That is 3 positioning switches are connected in

series, any one of them is supposed to be ON while other 2 OFF. For example, in rung 2, switch

number I: 002 is ON while others are OFF. Thus, the comparator to which switches are attached

will compute if the number of counts by the counter is equal to the condition specified by rung 2,

for this case the value is 3. So, when count value in the counter gets to 3, then according to rung

2, the motor (Q: 104) will stop at the position where, P_EQ value becomes equal to counter

value specified by the rung and Q: 101 (function) will go true or be ON. For rungs 3 and 4 the

values are 6 counts and 9 counts.

(Rung 5 to 10) (Constructed on rslogix 500)

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Rung 5 is controlling the start and stop of the dc motor. As, can be seen switch I: 006 is

attached to this rung, thus when the switched is pressed the dc motor stops in its tracks and

doesn’t move or when the dc motor reaches its position as defined by the positioning switches, it

stops completely.

Rung 6, 7 and 8 are to generate PWM signals. In rung 6, after DC motor is activated,

timer T0023 is started and will run for 10ms. This period is also known as on period of PWM

signal. In rung 7, when timer T0023 reaches 10ms, second timer T0024 is activated for 300ms.

Back in rung 6, when timer T0024 is activated, timer T0023 is deactivated. This 300ms period is

known as off period of PWM signal. In these rungs the PWM is being created by switching on

the dc motor for some time then switching it off for some time. Rung 8 is just controlling the

output to the MD10B, at one time O: 105 it high and at other its low, thus creating ON/OFF or

High/Low effect required for PWM. Speed of dc motor can be varied by changing the time

intervals.

Rungs 9 and 10 are used to control the directions of the dc motor, when switch I: 001 is

pressed in one direction dc motor rotates in one direction as DIR pin goes high and the RUN pin

goes low, and when switch I: 001 is pressed in other direction dc motor rotates in other direction

as now DIR pin goes low and RUN pin goes high. This characteristic or functioning of MD10B

can be seen in its datasheet or manual.

(Practical of Rotational Position System with DC motor and Encoder)

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Part 3: Pneumatic Automation System Design (Group)

3D Pneumatic Automation System Design (Working)

(3D design of Pneumatic Palletizing and Punching System) (Constructed using Autodesk

Inventor, 2010)

The above pneumatic automation system is used for palletizing and punching metal plates. This

can be used in manufacturing industry where punching metal plates for holes and placing them in

stack manually is tiresome and slow. Thus, in the design researchers use 4 electro pneumatic

cylinders (can be controlled by PLC). For starting or initial configuration, the cylinders are

positioned such that the whole system is to top upper left corner (X Axis not extended, Y Axis

not extended, Z Axis not extended and 4th Cylinder not extended). The metal sheet is put onto the

base of the system, which may be done manually or using some other automated means. Once

it’s put there, the 3rd cylinder (Z Axis) extends down; this cylinder has punching tool attached to

it, after punching the 3rd cylinder retracts back to original position, after which 1st cylinder (X

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Axis) extends, and 3rd cylinder (Z Axis) extends, punches hole and retracts, after which the 2nd

cylinder (Y Axis) extends and the 3rd cylinder punches holes, after which the 2nd cylinder (X

Axis) retracts and 3rd cylinder punches holes, At last the 2nd Cylinder retracts to get the

configuration of the system to initial.

After the process is over, 4 holes have been punched through the metal sheets at 4

different corners of rectangular sheet of metal. For, be able to put a new sheet on the base, the 4 th

cylinder extends and pushes out the punched metal sheets from the base after which it retracts

back to original position.

Components Selection

The components for this pneumatic automation system were selected from FESTO as they are

the leading suppliers of electrical automation and pneumatic technology. Researchers could

easily find components to choose from, for the pneumatic automation system design from their

website. The part file and assembly file for Autodesk inventor (3D design) has been imported

from the website itself. All components specification, like piston diameter, rod length, and stroke

length, follows standards set by FESTO.

Actuators chosen for the system are the double-acting cylinders which are directly

controlled by 4-way directional valves. Double – acting cylinders extend or retract by changing

the pressure of the compressed air. To control these cylinders researchers use 4-way directional

valves, they have two inputs (pressurized air) and two outputs (exhaust). For extension of the

actuator (cylinder) pressurized air is given to one of the inputs of the valve, and to retract

vacuum is created by letting pressurized air out (exhaust) through one of the outputs of the valve.

Below researcher have shown the specification of the pneumatic actuator (Cylinder)

chosen for the pneumatic automation system from FESTO:

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(Specifications for Standard cylinder DSNU-25-200-PPS –559257) (Available from

http://www.festo.com)

http://www.festo.com/

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Implementation of Pneumatic Automation System using Pure Pneumatic Control

(Part 1 for Fully Pneumatic Control) (Constructed using Automation Studio)



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The components used above system are the double acting pneumatic cylinder, 3/2 normally

closed valve with roller and spring returns (acts as touch sensor), 5/2 valve (14) is used to control

pressure in or out of double acting cylinder. Sequential logic step modules are used to allow the

cylinder to be extended or retracted, following a certain sequence. Start switch and stop switch is

applied to control the operation of system.

From the figure above (Part 3 for fully pneumatic control), at first, once the start switch is

pressed, the process starts, the sequential logic starts from 1. Cylinder C is extended until roller

C1 is touches by the shaft of cylinder C. When it reaches C1, sequential logic jumps to 2. The

similar process is repeated until sequential logic reaches 8. These sequences will move the object

to 4 different positions for punching (4 corners), and remove the metal sheet after the processes

finish. If the slider start switch is not toggle off, the whole process will be repeated again, if it is

turned off, the process stops at sequential logic 8. Emergency switch can be used to stop the

whole process at any point of time (cuts of the supply).

Implementation of Pneumatic Automation System using Electro Pneumatic Control

(Pistons used for the Electro Pneumatic Control) (Constructed using Automation Studio)

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(PLC Ladder Logic for 1st, 2nd and 3rd table) (Constructed using Automation Studio)

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(PLC Ladder Logic using 4th, 5th and 6th table) (Constructed using Automation Studio)

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From the figures above, 1st table is for drilling process, punching holes at initial position and then

retracting it drill actuator back, 2nd table if for the drilling process at position 2, 3rd table is for

drilling process at position 3 and the 4th table is for drilling process at position 4. The positions

defined are the 4 corners of the metal sheet. The drilling process or the ladder logic at the initial

position has been explained in brief, other tables are very similar to the 1st table, except that there

are new positions to move to along X, Y and Z axis. 5th table is to get back to the initial position

and the last table or the 6th table is to push the metal sheet out of the system’s base.

RUN

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INSTRUCTIONS

1 DRILL latch (S1) to start drilling, piston moves downwards

2 deactivated when BACK is activated, bring piston upwards and stop drilling

3 activate latch back when D2 and DRILL are ON ,D2 is the maximum position of actuator one

4 activates the input S2 when back is ON and drill done is OFF, indicates 1st process is over

6 activate the DRILL DONE latch when the drill arm has retracted back to its initial position D1

and that the back latch is ON

7 unlatch the DRILL latch and the BACK latch when the DRILL DONE latch is activated

8 the STEP1 latch is activated when the DRILLDONE is ON and the STEP2 and LATCHTO3 is

OFF (new position)

9 activate the S3 switch when STEP1 is ON and STEP2 is OFF, activating S3 will extend the

second actuator until STEP2 is ON

10 STEP2 is activated when STEP1 is still ON and D4 is activated which means the second

actuator has reached the maximum position D4. Thus STEP2 is activated which will disable the

8th and 9th rung

11 unlatch the DRILLDONE latch whenever the STEP2 latch is activated meaning that the

program must run the drill program again but this time in the second location of the metal piece

12 DRILL is latched when STEP2 is ON, BACK and DRILLDONE is OFF. This means that the

drill process is started from STEP2 but this rung must be disabled when the BACK and

DRILLDONE is ON so that the DRILLDONE from the 6th rung can unlatch the DRILL

13 activate the LATCHTO3 latch when the STEP2 latch is activated, the LATCHTO3 latch

indicates that the second piston has reached its designated position

14 STEP1 and STEP2 are unlatched when DRILL is ON to allow other latches such as STEP3 and

STEP4 to latch the DRILL in the next program without any conflicts15

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36 The 36th rung is responsible for activating the push piston

To start this whole process HIT IT switch needs to be pressed, once it’s pressed the

electro pneumatic automation system comes to life, the drilling process is done at initial position

(finish process – DRILL DONE), and then the process is repeated at 2nd, 3rd and 4th position.

After finishing drilling process at these positions the system comes back to original or initial

position and at last the metal sheet is pushed (PUSH) out of the base to make room for new one.

The process ends when one complete cycle is over. Below researcher has explained what does

the main terms used in the ladder logic means:

DRILL Go down and drill a hole

BACK Go up after drilling hole

DRILL DONE Drilling process at a particular position is completed

HIT IT Start the system

D(X) Various positions (4 corners)

STEP(X) Indicates piston (X) reached its desired position

LATCHT(0X) Piston reached its pos., program must be prepared for next process

PUSH Removes the metal sheet or piece

WITHDRAW Similar to BACK

FINISH Similar to DRILL DONE

(X) Positive Integer

Discussion and Conclusion

Researcher has achieved all the objectives defined above as, he constructed ladder logic using

PSIM simulator software to control SILO SIMULATOR which is or can be used for filling

bottles at bottling plant and to control BATCH MIXER which is used mix 2 or more substances

or cool down the temperature at large industries such as refineries (individual), after which

research and his group mates were able to control the rotational position of dc motor with the

help of OMRON PLC, MD10B motor driver, RSLOGIX 500 software to construct the ladder

logic for the control, and optic fiber sensor which acted as the encoder and at last researcher and

group mates were able to develop a pneumatic automation system which can be used for

palletizing and punching holes through metal sheets at positions defined, the design developed

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was test for fully pneumatic and electro pneumatic control separately. The controlling of the

electro pneumatic system was done using ladder logic (PLC) in AUTOMATION STUDIO

software, and the designing part was done in Autodesk Inventor 2010.

As, such researcher and his group mates did not face much trouble doing the assignment,

but there were some issues related to use of quadrature encoder as the outputs of the encoder

could not be properly read, unless programmed with a microcontroller and the other issue which

researchers came across was related to the automation studio software, same sequences weren’t

working at different steps, by which it means, if a sequence has been done at a particular step it

won’t be repeated at another step, as the researchers desired.

After doing this assignment researcher has gained massive knowledge which would be

really handy when he starts working. As, this assignment was focused on industrial automation,

the researcher learnt how to control things using PLC, which is popular in various industries for

control and monitoring operations.

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References

Cytron Technologies Sdn Bhd, 2008, [ONLINE] Available at:

http://www.cytron.com.my Accessed on 5 Sep 2011

Festo 2011 [ONLINE] Available at: http://www.festo.com [Accessed, 30th September

2011]

MikroElektronika: books: Introduction to PLC controllers. [ONLINE] Available at:

http://www.mikroe.com/old/books/plcbook/plcbook.htm [Accessed, 30th September

2011]

PLC Programming, EN 61131, IEC 61131. [ONLINE] Available at:

http://www.automation-course.com/plc-programming/ [Accessed, 30th September

October 2011]

http://www.automation-course.com/plc-programming/

http://www.mikroe.com/old/books/plcbook/plcbook.htm

http://www.festo.com/

http://www.cytron.com.my/

Documents

PLC & Pneumatic System