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 electrical issues.

2. Ensure that a main cut-off switch is fitted for safety during maintenance.

3. Use the correct size of wire, such as a minimum of 2 mm², to handle current safely.

Software in the context of a PLC refers to the machine language programming installed on a computer or device. This program instructs the PLC's hardware to interact with its input and output systems, controlling the operations of automated machinery.

Installing anti-surge protection is essential as it safeguards the PLC and its associated components from potential damage caused by voltage spikes, such as those from lightning strikes or electrical surges. This protection ensures the longevity and reliability of PLC systems.

A sensor is a device that detects environmental conditions and changes in its characteristics, allowing it to influence other devices or systems accordingly.

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

A level sensor can be used to monitor the level of liquid in tanks and reservoirs, triggering alerts or actions when the level falls below or rises above a specified point.

An analogue device is capable of continuously varying its output in response to changes in input, providing a representation of values in a range rather than discrete steps.

The logic function represented by the truth table is:

$F = A + B$

The logic program uses an ON-delay timer contact.

When the push button (I₁) is pressed, the timer is energized, closing the normal open contact of the timer. The output (Q) will go high immediately and remain high for 10 seconds. After 10 seconds, the output will drop back to low until the push button is pressed again.

The first stage of the VFD circuit is to convert AC voltage supply to DC voltage through rectification using diodes.

In the third stage, each pair of switches controls one half of the AC output cycle. One switch regulates the positive half, while the other controls the negative half, allowing for precise speed adjustments.

If the switches remain ‘ON’ for a longer duration, the output waveform will be smoother, and the frequency will decrease, causing the motor to run at a lower speed.

1. Improved energy usage by controlling the power fed into the motor.
2. Reduced wear on the motor, as speed adjustments can mitigate mechanical strain.
3. Enhanced process control and flexibility in production settings.

One application of a VFD is in HVAC systems for controlling fan speeds.

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

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

Regenerative braking transforms the kinetic energy of a moving vehicle into electrical energy, which can then be reused, leading to a reduction in energy waste.

Region A is known as the breakdown speed.

At start-up, the torque of the motor may peak at 200%. As the speed increases, the required torque will typically decrease, allowing the motor to accelerate smoothly until it reaches the desired operational speed.