1) The document provides examples of ladder logic diagrams for various industrial automation processes and systems, as presented by Dr. Sebastian George to students in a PLCs and Industrial Automation course. 2) Six examples are given of ladder logic diagrams that control motors, heating and stirring processes, and a box packaging system based on inputs like push buttons, limit switches, and temperature sensors. 3) For each example, the inputs, outputs, and purpose of the automation process are described, and the corresponding ladder logic diagram is displayed and explained.

1. Sanjivani College of Engineering, Kopargaon
Department of Electronics & Telecommunication Engineering
(An Autonomous Institute)
Affiliated to Savitribai Phule Pune University
Accredited ‘A’ Grade by NAAC
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Subject: PLCs and Industrial Automation (ET8204)
UNIT-4
Topic: Exercise # 4
Dr. Sebastian George
Professor, E&Tc Department

2. Develop a PLC Ladder diagram for a motor with the following:
• Physically NO Start button
• Physically NC Stop button
• Thermal overload limit switch opens on high temperature
• Green light when running
• Red light for thermal overload.
Dr. Sebastian George E&Tc Department 2
Ladder Diagram Example #1

3. Inputs Outputs
START: I:0/10 Motor : O:0/0
STOP : I:0/11 Green light: O:0/1
Thermal overload Red light : O:0/2
Limit switch : I:0/0
START switch is NO. The STOP switch, though physically NC, is interpreted as
NO in the programmed ladder. The temperature limit switch is also interpreted
as NO.
B3/12 is Bit No. 12 of binary file. The bit is used for temporary storage of Rung
output status.
Dr. Sebastian George E&Tc Department 3
I/O Assignment

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Ladder Diagram

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Example # 2
A bidirectional movable arm is shown in the figure. Develop a
ladder diagram to control it as per the following conditions:
START push button is physically NO and STOP push button is physically
NC. When the system is turned ON, the motor should rotate continuously,
alternating between in the counter clockwise and clockwise directions, as
the movable arm touches two limit switches, RLS and LLS. Both the limit
switches are physically NC.

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Example # 2

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I/O Assignment
Inputs Outputs
START : I:0/10 CW: O:0/0
STOP: I:0/11 CCW:O:0/1
LLS:I:0/0
RLS:I:0/1

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Ladder Diagram

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Example # 3
Draw a ladder diagram for a two motor system having the
following conditions:
• START push button starts Motor 1
• After 10 seconds, Motor 2 is ON
• STOP push button stops Motor 1&2
START is physically NO and STOP is physically NC

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I/O Assignment
Inputs Outputs
START : I:0/10 Motor 1 : O:0/0
STOP: I:0/11 Motor 2: O:0/1
In addition, Timer T4:0 is also there in the ladder program. It is
ON Delay Timer

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Ladder Diagram

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Example #4
Draw a ladder diagram for a 2 motor system having the
following:
The START push button starts both motors 1 &2
STOP push button stops motor 1 first and after 15 seconds, stops
motor 2

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I/O Assignment
START is physically NO and STOP is physically NC. Timer T4:1 is
an OFF Delay Timer.
Inputs Outputs
START : I:0/10 Motor 1 :O:0/0
STOP: I:0/11 Motor 2: O:0/1

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Ladder Diagram

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Example #5
Prepare the ladder diagram for the control problem shown in
the figure. The global objective is to heat the liquid toa specified
temperature and keep it there for 30 minutes.
The event sequence is :
1. Fill the tank
2. Heat and stir the liquid for 30 minutes
3. Empty the tank
4. Repeat from Step 1

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Example #5

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I/O Assignment
START push button is physically NO and STOP is physically NC. Level
limit switches and Temperature limit switch open on crossing the
limits. Timer T4:0 is ON Delay Timer.
Inputs Outputs
START : I:0/10 VIN : O:0/0
STOP : I:0/11 VOUT : O:0/1
LUP : I:0/0 H: O:0/2
LE :I:0/1 Stir : O:0/3
Temp: I:0/2

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Ladder Diagram

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Example # 6
Draw the ladder diagram for a box packaging system having five
boxes stacked at a time and then bound with a wrapper.
Box present signal : I:0/0
Wrapper machine relay :O:0/0
Timer T4:1 is an ON Delay Timer and C5:1 is an UP counter

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Ladder Diagram

21. Prof.N.I.Bhopale ,Department of E&Tc Engineering 21
Thank You!