6.1 State THREE advantages of a PLC system over a hardwired relay system - NSC Electrical Technology Power Systems - Question 6 - 2017 - Paper 1

1. Ladder Diagrams: A graphical programming language that represents relay logic.

2. Function Block Diagrams: Another graphical representation used for designing complex processes.

To simplify the expression $X = A'B'C + AB'C + A'BC + ABC + AB'C$, we first construct a Karnaugh map for three variables: A, B, and C. The map shows overlapping positions which help in grouping the 1s.

After grouping, the simplified expression is:

$X = A'C + AB'$

From the figure and applying Boolean algebra, we can express the output F as:

$F = (A + B)(AB' + C)$

This equation captures the logic depicted in the given gate network.

Starting with the equation $Q = A'BC + AB'C + A'B + ABC$, we simplify it as follows:

1. Combine terms: $Q = A'C(B + 1) + AB'C + A'B = A'C + AB'C + A'B$
2. Factor where possible: $= A'B + A'C + AB'C$
3. The final simplified form is:

$Q = A'B + A'C + B'C$

The ladder logic diagram consists of the following elements:

• Inputs: O/L, Stop, and Forward/Reverse Start buttons.
• Outputs: Control operations for motors MC1 and MC2.

The configuration includes contacts in series and parallel branches that represent the conditions for each motor's operation according to the status of the input devices.

One example of an application for this circuit is in conveyor belt systems, where the PLC controls the direction of motorized belts, allowing for forward and reverse operation based on sensor inputs.