With reference to PLCs: 6.1.1 Name the system used for automated machine control for industrial production before PLCs were developed - NSC Electrical Technology Power Systems - Question 6 - 2019 - Paper 1

1. Maintain a single ground for the PLC to prevent potential differences that can cause interference.
2. Ensure that a main cut-off switch is fitted for emergency stops.
3. Use the correct size of wire, preferably at least 2 mm², to prevent overheating and ensure proper current flow.

Software refers to the machine language installed on a computer or written into a PLC’s control program. This language instructs the PLC to interact with its input and output hardware, allowing it to execute specific tasks and control industrial machinery effectively.

Installing anti-surge protection is crucial because power surges from events such as lightning strikes can damage PLC components. This protection helps to ensure longevity and reliability of the PLC system by safeguarding it against unexpected voltage spikes.

A sensor is a device that detects changes in the environment or specific physical characteristics, which can then influence other devices or systems.

1. Proximity sensor
2. Temperature sensor
3. Light sensor

An application of a level sensor is in water treatment facilities where it monitors water levels in tanks to ensure optimal operation.

An analogue device continuously monitors and provides varying outputs that correspond to the measurements of the physical quantity being observed, often resulting in a smooth range of values.

The truth table represents an OR gate, which outputs true (1) if at least one of the inputs A or B is true (1).

The ladder logic can be depicted as two parallel branches, where each branch corresponds to one input leading to an output that is activated when either input is high.

The logic function can be expressed as: $F = A + B$, where $F$ is the output and $A$ and $B$ are the inputs.

The logic program uses an ON-delay timer contact.

When the push button (I1) is pressed, the timer is energized. As a result, the normally open contact of the timer will close, leading the output (Q) to be high. This output will remain high for 10 seconds, after which it will return to a low state until the push button is pressed again.

The ladder logic diagram will depict the start and stop buttons as controlling the operation of motor contactors for the lamp, ensuring the lamp lights up when the start button is engaged and turns off when the stop button is pressed.

The purpose of the first stage is to convert AC voltage supply to DC voltage through rectification using each pair of diodes.

In the third stage, speed control is achieved by utilizing pairs of switches to control the positive and negative half cycles of the output voltage, effectively regulating the power supplied to the motor.

If the switches remain 'ON' for a longer period, the output waveform will become smoother, and the frequency will decrease, causing the motor to run at a slower speed.

1. Improves energy usage by controlling the power fed into the motor.
2. Reduces motor wear, resulting in lower maintenance costs.
3. Provides better process control, allowing for more precise speed adjustments based on the type of production.

One application of a VFD is in HVAC systems for fan and pump control.

1. Volts-per-Hertz (V/Hz) drive control
2. Direct torque control (DTC)
3. Pulse Width Modulation (PWM)

1. Cranes
2. Electrical locomotives or trains
3. Battery-powered electric vehicles

Regenerative braking is achieved by converting the kinetic energy of the moving vehicle back into electrical energy, which is then fed back into the power supply system.

Region A is known as the breakdown speed region.

At startup, the torque is at 200%, allowing for rapid acceleration. As the speed increases, the torque rises initially, but will eventually decrease as the motor reaches its rated speed, minimizing stress and wear on the motor.