7.1 Easy fault finding is one of the advantages of hard wiring - NSC Electrical Technology Power Systems - Question 7 - 2022 - Paper 1

A sensor is a device that detects and converts an environmental condition or change into an electrical signal. This signal can then be processed by a control system, such as a PLC, to perform specific functions or decision-making tasks. Sensors play a crucial role in automated systems by providing real-time data.

After receiving data from a temperature sensor, the PLC processes this information through its programmed logic. It evaluates the input against predefined thresholds to determine the necessary actions. For instance, if the temperature exceeds a certain limit, the PLC may trigger a cooling system or activate alarms. The PLC continuously monitors inputs, ensuring that any required actions are executed promptly.

1. Mining drills: Temperature sensors are used to monitor and control the temperature within drilling equipment to prevent overheating.
2. Battery chargers: They help manage the charging process by monitoring the temperature of battery cells, ensuring optimal performance and safety.

The control circuit identified in FIGURE 7.3 is the Forward Reverse starter circuit, which manages the operation of motors in both forward and reverse directions.

Latching in motor control circuits refers to the ability for a circuit to be triggered 'on' and to remain in that state even after the initial activating signal has been removed. This is accomplished by using additional contacts in the circuit that maintain the current flow once it has started. For example, pressing a start button momentarily closes a contact, allowing a relay to energize, which then latches itself until a stop signal is sent.

To execute the same function as in FIGURE 7.3, the completed ladder logic diagram should include rungs that reflect the logical flow for both the Forward and Reverse starting conditions with appropriate normally open and normally closed contacts, ensuring precise control of the motors.

The ladder logic diagram should consist of two output coils. Output 1 should be connected in parallel with two series normally open contacts corresponding to inputs 1 and 2, ensuring that either input is closed for output 1 to be high. Output 2 should be controlled by a series configuration of input 3, and input 4 must be closed, illustrated in parallel to allow flexibility.

A marker in PLCs refers to a storage memory that indicates whether certain processes have been completed. It enables different devices and program sections to be controlled more effectively by allowing specific flags to be set or reset, depending on the conditions met during operation.

The converter operates through the process of rectification, where it converts alternating current (AC) into direct current (DC). Each pair of diodes within the converter circuit rectifies one of the three AC phases, ensuring that the output is a steady DC voltage.

The filter's purpose is to smooth out any ripple voltages from the rectification process, ensuring a pure DC voltage on the DC bus. This is crucial for stable operation in subsequent stages of the variable speed drive system.

The inverter stage operates by modifying and controlling the pulsing of the DC voltage on the DC bus to create an AC output. It employs Insulated Gate Bipolar Transistors (IGBTs) which switch at varying durations and widths, producing a variable frequency and matching the motor's speed requirements.

1. Energy savings: VSDs can adjust motor speed to suit the load demands, thereby reducing energy consumption.
2. Better control of motors: VSDs provide precise speed control and smoother acceleration and deceleration profiles, which reduces mechanical stress on motor components.

1. Lifts: Regenerative drives in lifts can convert excess gravitational energy back into electrical energy for reuse in the system.
2. Cranes: When lowering a heavy load, cranes can harness regenerative energy, feeding it back into the power supply or using it to power other movements.