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 Diagram: A graphical programming language resembling electrical relay logic diagrams.

2. Structured Text: A high-level programming language that allows for complex algorithms.

Using a Karnaugh map, we can simplify the expression. The input terms are:

• A'B'C (Cell (0,0,0))
• AB'C (Cell (1,0,1))
• A'BC (Cell (0,1,0))
• ABC' (Cell (1,1,0))

Combining these in the Karnaugh map yields:

egin{array}{|c|c|c|c|} \hline ext{BC} & 00 & 01 & 11 & 10
\hline ext{A'} & 1 & 1 & 0 & 1
\hline ext{A} & 0 & 0 & 1 & 0
\hline \end{array}

This results in: $X = A'C + AC$ Final simplification yields: $X = C(A + A') = C$

To find the output F, we analyze the given logic circuit. We identify the inputs A, B, and C through the gates.

Using the provided logic gates:

• The output F can be expressed as: $F = (A + B)(AB' + C)$

This means F is the output from the AND and OR combinations based on inputs A, B, and C.

We can apply Boolean algebra to simplify the equation.

Starting with Q:

1. Combine terms: $Q = A'BC' + ABC + A'BC$
2. Rewrite Q:
   $Q = A'BC' + A'BC + ABC$
3. Factor out A': $Q = A'[BC' + BC] + ABC$
4. Apply Absorption Law: $Q = A'B + ABC$
5. Final step: $Q = C(A + A') = C$

A simple ladder logic diagram representing the functions in FIGURE 6.6 would be constructed as follows:

|----[ O/L ]-----+----( START_FWD )
|                |
|----[ STOP ]----+----( START_REV )
|                |
|----[ MC1 FWD ]---( MC2 FWD )
|                |
|----[ MC1 REV ]---( MC2 REV )

This ladder diagram shows the control flow for forwards and reverse operations.

An example of where the circuit in FIGURE 6.6 may be used is in controlling the movement of a conveyor belt system. The circuit allows for starting and reversing the direction of the belt, enabling the transport of materials in both directions.