Photo AI
6.1 State THREE advantages of a relay control system in comparison to PLC control systems - NSC Electrical Technology Power Systems - Question 6 - 2019 - Paper 1
Question 6
6.1 State THREE advantages of a relay control system in comparison to PLC control systems. 6.2 Explain the function of the following PLC hardware components: 6.2.1 ... show full transcript
Worked Solution & Example Answer:6.1 State THREE advantages of a relay control system in comparison to PLC control systems - NSC Electrical Technology Power Systems - Question 6 - 2019 - Paper 1
Step 1
State THREE advantages of a relay control system in comparison to PLC control systems.
Answer
-
Maintenance: Relay systems require regular maintenance and repair, whereas PLCs generally have lower maintenance needs due to their solid-state design.
-
Energy Efficiency: PLCs consume less energy compared to traditional relay systems.
-
Space Efficiency: PLCs require less physical space than relay systems, making them more suitable for compact installations.
Step 2
Explain the function of the following PLC hardware components:
Answer
6.2.1 Central Processing Unit (CPU): The CPU executes instructions provided as inputs and produces outputs. It is the brain of the PLC, facilitating data processing, and control logic execution.
6.2.2 Modulator-Demodulator (Modem): The modem is crucial for isolating the processor against any damage from random high voltage spikes and for facilitating communication between different PLCs.
Step 3
Refer to the safety of the PLC and explain why:
Answer
6.3.1 Supply Lines: Supply lines to the PLC should be installed with either a fuse or a circuit-breaker to prevent excessive over-current, ensuring the system’s integrity and safety.
6.3.2 Wiring Connections: Wiring connections must be checked before connecting the PLC supply to avoid any potential damage to the system.
Step 4
Differentiate between an ON-delay timer contact and an OFF-delay timer contact.
Answer
An ON-delay timer contact delays the activation of a control output until a specified time has elapsed after the input contact is activated. On the other hand, an OFF-delay timer contact deactivates the output after a specified time when the input contact is released.
Step 5
Step 6
Describe the operation in FIGURE 6.5.
Answer
In FIGURE 6.5, when the 'Start' button is pressed, it energizes the coil Y, activating the ON-delay timer (T). The lamp remains off until the timer completes its pre-set time. Once the timer elapses, the lamp turns on until the 'Stop' button is pressed.
Step 7
Refer to FIGURE 6.6A and FIGURE 6.6B below and state, with a reason, which figure represents:
Answer
6.6.1 An analogue input: FIGURE 6.6A represents an analogue input because it varies continuously over time.
6.6.2 A digital input: FIGURE 6.6B illustrates a digital input, as it consists of discrete levels or states.
Step 8
Refer to FIGURE 6.7.1 below and answer the questions that follow.
Answer
6.7.1 Logic Function: The logic function illustrated in FIGURE 6.7.1 is an Exclusive OR gate, which outputs true only when the inputs differ.
6.7.2 Truth Table: Below is the filled truth table:
| A | B | Lamp (output) |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Step 9
State ONE application of each of the following sensors:
Answer
6.8.1 Light Sensor: Used in automatic lighting systems that adjust brightness based on ambient light conditions.
6.8.2 Temperature Sensor: Often found in HVAC systems, it regulates temperature by monitoring the ambient environment.
Step 10
Refer to FIGURE 6.9 below and draw the PLC ladder logic diagram that would execute the same function.
Answer
The ladder logic diagram for the forward-reverse control circuit would have rungs that depict motor control signals based on the 'Forward' and 'Reverse' inputs, ensuring that only one motor can run at any given time.
Step 11
Refer to FIGURE 6.10 below and describe the function of each of the following:
Answer
6.10.1 Diode Bridge Rectifier: Converts alternating current (AC) supply voltage to direct current (DC) voltage.
6.10.2 Filtering Circuit: This circuit smooths out the AC ripple ensuring a stable DC voltage.
6.10.3 Inverter: Converts DC voltage back into AC voltage at a variable frequency, controlling motor speed based on the frequency supplied.
Step 12
Give THREE examples of where the variable speed drive may be used.
Answer
-
Water Pumping Systems: Equips pumps with the capability to adjust speed based on demand.
-
Heating Systems: Allows for better temperature control by varying fan speed.
-
Variable Air Volume Air Conditioning Systems: Increases efficiency by adjusting airflow according to occupancy.
Step 13
Refer to regenerative braking and answer the questions that follow.
Answer
6.12.1 Examples: This method is used in lifts to reduce energy consumption during descent and in electrical locomotives to recapture energy when braking.
6.12.2 Regenerative Energy: Refers to energy recovered from the motor during braking, which can either be used immediately or stored for later use.