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Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
ME SEMESTER-II • EXAMINATION SUMMER 2018
Subject Code:2725407 Date: 23-05-0218
Subject Name: PROGRAMMABLE LOGIC CONTROLLERS AND APPLICATIONS
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1

Explain PLC based control system using suitable block diagram.
07

Using suitable diagrams, explain digital AC output module for PLC.
07
Q.2

Discuss the comparison between PLC based control systems and conventional relay based control systems.
07

Develop Instruction List and Functional Block Diagram programs for the following Boolean expression.
Y AC BC
07
OR

A 3 phase AC Induction Motor is to be controlled in forward and reverse directions using two push buttons by PLC. Draw and explain connections of the motor with PLC.
07
Q.3

Using timing diagram and suitable example, explain OFF delay timer instruction used in PLC programming.
07

Write Instruction List program for the following system.
There are two machines M1 and M2. Each machine has a separate start push button. There is one master stop push button. The system can be started only by starting of M1. While the system is running, start of one motor will stop the other running motor (that means only one motor will run at a time).When master stop push button is pressed, both the motors will stop.
07
OR
Q.3

Using suitable diagrams and example, explain down counter instruction used in PLC programming.
07

Develop and draw Functional Block Diagram program for the following:
Two input EX-OR gate and Two input EX-NOR gate.
07
Q.4

How the analog inputs and outputs are handled by PLC? Explain in detail.
07
2

The operation of a pneumatic plant is to be controlled by PLC. There are two pneumatic cylinders and inductive proximity sensors are given at both the ends of each cylinder to sense extraction and retraction of the cylinders. Initially both the cylinders will be in retracted condition. When normally open START pushbutton is pressed, after 5 seconds, first cylinder will start to extract and when extracted fully, second cylinder will start to extract and after 15 seconds. Furthermore, both the cylinders will require 2 seconds for extraction, but if by chance any of the cylinders takes more than 2 seconds for extraction, it indicates a fault in the system and in this condition both the cylinders should come in the retracted condition. If STOP (normally closed) is pressed at any time while the system is running, system should be reset i.e. both the cylinders will come in retracted condition.
07
OR
Q.4

Enlist different data comparison instructions in PLC and explain all of them in detail.
07

The operation of two indicating lamps is to be controlled by PLC. When START pushbutton is pressed lamp 1 will be turned ON and lamp 2 will remain in OFF condition. After 5 seconds lamp 1 will be turned OFF and lamp 2 will be turned ON. This ON and OFF process of both the lamps will continue.
But if CHANGE pushbutton is pressed, lamp 2 will be turned OFF after 3 seconds (if ON) and lamp 1 will be turned ON immediately. (The effect of CHANGE pushbutton will be there only if system was started by pressing START button initially)
When Stop pushbutton is pressed both the lamps will turned OFF.
Design PLC ladder logic diagram.
07
Q.5

Design a ladder logic program for following process. A temperature control system consists of three thermostats. The system operates two heating units. The thermostats are set on 70°C, 75°C and 80°C. Below 70°C, two heaters are on. The temperature between 70°C and 75°C causes one heater to be on. Above 80°C, there is safety shutoff for two heaters in case one stays on by mistake. A master switch turns the system on and off.
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A mixing plant is to be controlled by PLC. There are two valves. A mixer is operated by a dc motor. A normally open START pushbutton is given to start the system and a normally closed STOP pushbutton is given to stop the system at any time. The system operates as per following sequences:
When START is pressed, valve-1 will open and 200 kg of first material will be added in the tank.
30 seconds later, valve-2 will open and 100 kg of second material will be added in the tank.
1 minute later, mixer will turn ON for 1 minute in one direction
5 seconds later mixer will run in another direction for 30 seconds and process will stop automatically.
Assume suitable inputs/outputs and draw a PLC ladder diagram to control the system
07
OR
Q.5

Explain various JUMP operations in PLC programming using suitable diagrams
07
3

Two potentiometers are connected to PLC inputs. The range of both the potentiometer output is 0 to 10 V DC. When both the potentiometer outputs are equal and more than a DC motor will be in ON condition; otherwise the motor will be in OFF condition. Furthermore if first potentiometer output is higher, a GREEN lamp will be in ON condition and if second potentiometer output is higher, a RED lamp will be in ON condition.
Assume suitable inputs/outputs and draw a PLC ladder diagram to control the system
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