QUESTION 7: PROGRAMMABLE LOGIC CONTROLLERS (PLCs) 7.1 Explain the function of the central processing unit (CPU) with reference to the hardware of a PLC - NSC Electrical Technology Power Systems - Question 7 - 2022 - Paper 1

One advantage of soft-wired systems is flexibility. This means that changes can be easily made to the control logic without needing to physically rewire the system. Programmers can modify the logic through software, allowing for quicker adaptations to changes in processes.

The purpose of a timer function is to either activate or deactivate a device after a specified duration or pre-set interval. It can control processes by waiting a predetermined amount of time before executing a command, which is critical for processes that require precise timing.

An ON-delay timer will activate its output after a specified delay once the input condition becomes true. This means that the output remains off until the predetermined delay has passed. In contrast, an OFF-delay timer keeps its output active as long as the input condition is true and will turn off only after the delay period is completed once the input condition goes false.

1. Proximity sensor
2. Level sensor

1. Lighting systems controlled by a PLC to operate only during night time.
2. A sprinkler system programmed to activate only when there is insufficient natural light.

Begin with the following ladder logic programming for the control circuit:

|----[ START ]----+    |----( MC )-----
|                 |    |               |
|----[ STOP ]-----+    |               |
|                 |    |               |
|----[ O/L ]------|    |_______________|

Regenerative energy is energy that is recovered from a motor when it slows down. This energy conversion allows the system to either use this energy immediately or store it for later use, increasing overall efficiency and reducing energy consumption.

1. Lifts
2. Cranes
3. Electric trains

1. AC-to-DC converter (rectifier)
2. Filter

1. Limit start-up current, which reduces mechanical stress on equipment.
2. Improves energy efficiency by controlling the power fed into the motor.

Phase 1 - S1 and S4 Phase 2 - S3 and S6 Phase 3 - S2 and S5

The frequency to the motor is controlled by an AC controller that switches the IGBTs on and off at a certain frequency. This modulation allows the motor to operate at different speeds, adjusting the energy supplied effectively.

The DC is converted into AC by using a method where control switches (IGBTs) create a series of voltage pulses. These pulses mimic a sinusoidal waveform, effectively generating AC voltage at the required frequency for the motor's operation.