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 ground loops.
2. Keep the wire length short to reduce the potential for interference.
3. Ensure that a main cut-off switch is fitted to disconnect power quickly in case of an emergency.

Software refers to the machine language that is installed on a computer or written into a PLC's control program. This software instructs the PLC to interact with its input and output hardware, managing the control processes and logic that drive the automation.

Installing anti-surge protection is crucial when working with PLCs because power surges, such as those caused by lightning strikes, can damage the PLC unit. This protection ensures the reliability and longevity of the PLC system by stabilizing the power supply and safeguarding its components.

A sensor is a device that detects an environmental condition and converts its characteristics into a form that can be used to influence other devices or processes.

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

A level sensor can be applied in monitoring the level of liquid in rivers and dams, providing alerts when levels rise or fall below preset thresholds.

An analogue device continuously changes states, providing a representative signal that can indicate varying levels of physical properties such as temperature or pressure.

The logic gate represented by the truth table is an OR gate.

This truth table represents a simple ladder logic diagram featuring the inputs A and B leading to an output F, where F is high if either A or B is high.

The logic function of FIGURE 6.5 can be expressed as: $F = A + B$

The logic program uses an ON-delay timer contact.

When the push button (I1) is pressed, the timer will be energized, leading the normally open contact of the timer to close. Consequently, the output Q will be high for a duration of 10 seconds, after which it will revert to low until the push button is pressed again.

The ladder logic diagram will show the start button and stop button controlling motors MC1 and MC2, making sure to include the necessary interlocks and wiring as depicted in FIGURE 6.7.

The purpose of the first stage is to convert the AC voltage supply into DC voltage using rectification, which is essential for the subsequent stages of the VFD operation.

In the third stage, speed control is achieved by utilizing pairs of switches that control the positive and negative half cycles of the output voltage, enabling variable voltage and frequency output to the motor.

If the switches remain ‘ON’ for an extended duration, the output waveform will become smoother, and the frequency of the supply will decrease, which means the motor will turn slower due to the reduced supply frequency.

1. Improves energy usage by controlling the power fed into the motor.
2. Reduces motor wear by providing smoother operation.
3. Allows for better process control, which can increase the efficiency of production processes.

One application of a VFD is in HVAC systems to control the speed of fans and pumps.

1. Volts-per-Hertz drive 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 is achieved by converting the mechanical energy of the motor back into electrical energy during braking, which can be reused in the system or fed back into the electrical supply.

Region A is known as the breakdown speed region.

At startup, the torque is at 200%, enabling a strong initial movement. As the motor reaches operational speed, the torque will increase up until the breakdown speed is observed, where torque demand may exceed the motor's capacity.