7.1 State TWO disadvantages of a relay control system in comparison with PLC control systems - NSC Electrical Technology Power Systems - Question 7 - 2023 - Paper 1
Question 7
7.1 State TWO disadvantages of a relay control system in comparison with PLC control systems.
7.2 Explain why a soft-wired system is cheaper to implement than a har... show full transcript
Worked Solution & Example Answer:7.1 State TWO disadvantages of a relay control system in comparison with PLC control systems - NSC Electrical Technology Power Systems - Question 7 - 2023 - Paper 1
Step 1
State TWO disadvantages of a relay control system in comparison with PLC control systems.
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Answer
Relays require regular maintenance and repairs, which can incur additional costs.
Relay systems consume more energy compared to PLC control systems.
Step 2
Explain why a soft-wired system is cheaper to implement than a hardwired system.
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Answer
A soft-wired system allows for modifications without the need for extensive rewiring. This reduces labor and material costs when changes are required.
Step 3
Explain the function of the timer in FIGURE 7.3.
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The timer in FIGURE 7.3 serves to delay the closing of the circuit to the lamp. This function prevents the lamp from being turned on immediately after the start button is pressed, allowing for a pre-set delay.
Step 4
Describe the operation of the program in FIGURE 7.3.
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Answer
When the ON button is pressed, the timer starts its countdown. If the timer reaches its set time, the circuit closes, energizing the lamp. The lamp will remain on until the OFF button is pressed, at which point the circuit stops.
Step 5
Differentiate between a relay and a contactor.
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A relay is a device that operates by opening or closing contacts in a circuit under specific conditions, primarily used in low-power circuits. In contrast, a contactor is designed to switch larger loads and is typically used in power circuits. It offers features such as overload protection.
Step 6
Explain how an OFF delay timer creates the time delay when de-energised.
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An OFF delay timer maintains its output after being de-energized until the pre-set time has elapsed, allowing controlled shutdowns in PLCS.
Step 7
State TWO applications of the proximity sensor.
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Measuring rotating speed in machinery.
Detecting the position of objects on a conveyor line.
Step 8
Name TWO types of proximity sensors.
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Inductive.
Capacitive.
Step 9
Redraw in the ANSWER BOOK and complete the ladder logic diagram for FIGURE 7.6 below that executes the same function as the one in FIGURE 7.6.
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Answer
Please refer to the provided diagram in the answer book for the complete ladder logic, ensuring it executes the same functions as in FIGURE 7.6.
Step 10
Explain why each overload is connected in series with the contactor coil.
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Each overload is connected in series to provide independent protection to each motor, ensuring that if one motor experiences an overload, it will deactivate without affecting the others.
Step 11
Describe the purpose of the MC1, N/O contact that is connected in series with Start motor 2.
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The MC1, N/O contact ensures that motor 1 must be engaged before motor 2 can start, providing a sequential activation to protect the motors.
Step 12
Explain voltage frequency control with reference to VSD.
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Voltage frequency control adjusts the input voltage's frequency to control motor speed and torque, providing efficient energy use in variable-speed applications.
Step 13
Name TWO examples where this braking method may be used.
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Lifts.
Electrical locomotives.
Step 14
Describe regenerative energy.
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Regenerative energy is the energy recovered from the motor when it slows down. This energy is converted to electrical energy, which can be reused or stored for future use.
