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Industrial ElectronicsProblems with solutions
ABBOTTABAD Lab Assignment#09
Subject: Industrial Electronics
Submitted By:
Naveed Mazhar FA09-BEE-143
Submitted To:
Sir Muhammad Sajjad Durani
Date: 8th
November, 2012
Question 1: Predict how the operation of this relay logic circuit will be affected as a result
of the following faults. Consider each fault independently (i.e. one at a time, no multiple
faults):
• Pushbutton switch A fails open:
• Relay coil CR2 fails open:
• Relay contact CR1-1 fails open:
• Relay contact CR2-1 fails shorted:
• Relay contact CR2-2 fails shorted:
For each of these conditions, explain why the resulting effects will occur.
Solution:
When no relay is defected
A B Lamp 1 Lamp 2
0 0 1 1
0 1 1 0
1 0 0 0
1 1 1 0
Results: Lamp 1= A’ + B ; Lamp 2 = (A+B)’
Case 1- Pushbutton switch A fails open
A B Lamp 1 Lamp 2
0 0 1 1
0 1 1 0
1 0 1 1
1 1 1 0
Results: Lamp 1= 1 (Always ON) ; Lamp 2 = B’
Case 2- Relay coil CR2 fails open
A B Lamp 1 Lamp 2
0 0 1 1
0 1 1 1
1 0 0 0
1 1 0 0
Results: Lamp 1= Lamp 2 = A’
Case 3- Relay contact CR1-1 fails open
A B Lamp 1 Lamp 2
0 0 0 1
0 1 1 0
1 0 0 0
1 1 1 0
Results: Lamp 1=B ; Lamp 2 = (A+B)’
Case 4- Relay contact CR2-1 fails shorted
A B Lamp 1 Lamp 2
0 0 1 1
0 1 1 0
1 0 1 0
1 1 1 0
Results: Lamp 1=1(Always ON) ; Lamp 2 = (A+B)’
Case 5- Relay contact CR2-2 fails shorted
A B Lamp 1 Lamp 2
0 0 1 1
0 1 1 1
1 0 0 0
1 1 1 0
Results: Lamp 1=A’ + B ; Lamp 2 = A’
Question 2: Predict how the operation of this motor control circuit will be affected as
a result of the following faults. Consider each fault independently (i.e. one at a time, no
multiple faults):
• "Stop" pushbutton switch fails open:
• Relay contact CR1-1 fails open:
• Relay contact CR1-2 fails open:
• Relay coil CR1 fails open:
For each of these conditions, explain why the resulting effects will occur.
Solution: When there is no fault, the above circuit is known as holding or latching circuit. Once the
pushbutton “Start” is pressed, it will excite relay coil CR1 and consequently the relay
contact CR1-1 will provide path for current, even after releasing the pushbutton. Relay
contact CR1-2 will be ON to make the motor ON. To stop the motor, “Stop” pushbutton
(normally closed) will be pressed.
Case 1- "Stop" pushbutton switch fails open In this condition, the relay coil CR1 will never get excited. So both contacts will not be ON.
Consequently, “Motor run” lamp and Motor will not be ON.
Case 2- Relay contact CR1-1 fails open In this condition, the relay coil CR1 will get excited up till “Start” pushbutton is pressed. As
CR1-1 will never be ON, so coil will de-excite after releasing the “start” pushbutton.
Consequently, “Motor run” lamp and Motor will be ON only when “Start” pushbutton is
pressed.
Case 3- Relay contact CR1-2 fails open In this condition, “Motor run” lamp will work as it should, but the motor will never ON
because of open condition of CR1-2.
Case 4- Relay coil CR1 fails open When CR1 coil fails open, neither relay contact CR1-1 nor CR1-2 will be ON. Hence, motor
will never be ON. The “Motor run” lamp will glow as the “start” pushbutton is pressed, but
it will also turn OFF after releasing “Start” pushbutton.
