6.1 State THREE advantages of a PLC system over a hardwired relay system - NSC Electrical Technology Power Systems - Question 6 - 2017 - Paper 1
Question 6
6.1 State THREE advantages of a PLC system over a hardwired relay system.
6.2 Name TWO languages used to program PLCs.
6.3 Write the simplified Boolean equation fo... show full transcript
Worked Solution & Example Answer:6.1 State THREE advantages of a PLC system over a hardwired relay system - NSC Electrical Technology Power Systems - Question 6 - 2017 - Paper 1
Step 1
State THREE advantages of a PLC system over a hardwired relay system.
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Answer
Reduced Space: PLC systems can be more compact than traditional relay systems, which saves space in control panels.
Use Less Energy: PLCs are generally more energy-efficient compared to the multiple relay coils that would need to be energized in a hardwired system.
More Reliable: PLC systems are less prone to failure since they have fewer mechanical parts that can wear out compared to relays, leading to better overall reliability.
Step 2
Name TWO languages used to program PLCs.
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Answer
Ladder Diagram: A graphical programming language that resembles electrical relay logic.
Structured Text: A high-level textual programming language used in PLC programming.
Step 3
Write the simplified Boolean equation for the expression below. Use a three-variable Karnaugh map.
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Answer
To simplify the expression X=A′B′C+AB′C+A′BC+ABC, we will use a Karnaugh map.
Karnaugh Map Setup:
Group the terms in the K-map:
Place ‘1’ in the locations for respective combinations of A, B, and C.
Simplified Equation:
From the K-map, we find that:
X=A′C+AC+AB′
which can be further simplified to:
X=A′C+A(B′+C).
Step 4
Refer to FIGURE 6.4 below and determine output F.
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Answer
Using the given gate network:
The output F can be calculated as follows:
F=(A+B)(AB+C)
This results from combining the AND and OR operations of the logic gates in the figure.
Step 5
Simplify the following Boolean equation by using Boolean algebra.
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Answer
We start with the equation:
Q=A′B′C+AB′C+A′BC+ABC
Group Equal Terms:
Factor common terms:
=A′C(B+1)+AB′C
Since B+1=1, we simplify further to:
=A′C+AB′C
Final Simplified Form:
Q=A′C+AC.
Step 6
Draw the ladder logic diagram that will execute the same function in a PLC system. Use the same labelling given in FIGURE 6.6.
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Answer
The ladder diagram should consist of the following components:
Inputs: O/L, Stop, Start FWD, Start REV.
Outputs: MC FWD, MC REV.
Ensure a flow through the logical states which corresponds to the operation of the motor as specified in the figure.
Step 7
Give ONE example where the circuit in 6.6 may be used in an electrical application.
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One example of where the circuit could be used is in conveyor belt systems, where directional control is required to switch between forward and reverse operations depending on the process requirements.
