6.1 Identify THREE programming methods used in programmable logic controllers (PLCs) - NSC Electrical Technology Power Systems - Question 6 - 2016 - Paper 1

1. Push Buttons
2. Limit Switches

1. Limited Flexibility: Hardwired systems are fixed and cannot easily be modified or expanded.
2. Increased Complexity: Rewiring can be complicated and might require extensive labor.
3. Higher Maintenance Costs: Troubleshooting and repairs can become more difficult and costly.

Low-current devices can be activated by connecting them to the output relay of a PLC, which provides a suitable voltage and current to trigger the device. For instance, a transistor can be switched on through the relay contacts, allowing it to control higher current loads.

By grouping the relevant terms in the Karnaugh map, we can derive the simplified equation:

$X = AB + \overline{C}D$

Starting with the equation:

$Q = \overline{A}BC + A\overline{B} + AB + A$

We can apply Boolean algebra rules for simplification:

1. Combine like terms: $Q = \overline{A}BC + A + AB$
2. Further simplify if necessary, but the equation is simplified to: $Q = A + \overline{A}BC$

W = A + B

X = A + C

Y = A . B

Z = (A + B)(A + C)(A . B)

6.8.1: Normally open contact / switch 6.8.2: Normally closed contact 6.8.3: Coil output

The diagram should represent the start and stop functionalities along with the holding circuit for the motor.

|----[ ]----[ ]----( )----|
|    START   STOP   MC_1   |

Where [ ] indicates contact points and ( ) indicates output coils.

A motor starter circuit might be used in industrial applications to control electric motors.