JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year INTRODUCTION TO MECHATRONICS Previous Question Paper (August - 2022 - R16)

In a washing machine, sensors and actuators are critical components that facilitate automated control cycles. Sensors act as the input devices that monitor the state of the system, while actuators act as the output devices that perform physical actions based on control signals.

Sensors:

• Water Level Sensor (Pressure Switch): Detects the height of water in the drum by measuring air pressure in a tube, ensuring the machine does not overfill.
• Temperature Sensor (Thermistor): Monitors the water temperature to ensure it reaches the set level for specific wash cycles.
• Tachometer/Hall Effect Sensor: Mounted on the motor shaft to measure the rotational speed, providing feedback to the controller to maintain precise RPM during wash and spin cycles.
• Door Lock Sensor: A safety switch that confirms the door is securely closed before the cycle initiates.
• Vibration/Imbalance Sensor: Detects excessive movement or uneven load distribution during the spin cycle to prevent mechanical damage.

Actuators:

• Inlet Solenoid Valve: An electromechanical valve that opens or closes to control the flow of water into the drum.
• Drain Pump: An electric motor-driven pump that removes water from the drum at the end of wash or rinse cycles.
• Drive Motor: The primary actuator that rotates the drum. It can be a universal motor or a BLDC motor, controlled to provide different speeds and directions.
• Door Lock Solenoid: A mechanism that engages to lock the door during operation for user safety.
• Dispenser Actuator: A motor or solenoid that directs water flow into specific compartments to release detergent or fabric softener at the correct time.

Operational Amplifiers (Op-Amps) are versatile integrated circuits used to amplify low-level signals from sensors to a level suitable for processing by microcontrollers. The amplification is achieved through negative feedback configurations.

1. Inverting Amplifier: The input signal is applied to the inverting terminal (-) through a resistor R1, while the non-inverting terminal (+) is grounded. The gain is determined by the ratio of the feedback resistor Rf to R1.

2. Non-Inverting Amplifier: The input signal is applied directly to the non-inverting terminal. This configuration provides high input impedance, which is ideal for interfacing with sensors that have high output impedance.

3. Instrumentation Amplifier: This is a specialized circuit using three op-amps to provide high common-mode rejection ratio (CMRR) and high input impedance. It is essential for amplifying weak differential signals from sensors like strain gauges or thermocouples in noisy industrial environments.

By selecting appropriate resistor values, the op-amp scales the small voltage fluctuations from sensors (e.g., millivolts) into a usable range (e.g., 0-5V) for Analog-to-Digital Converters (ADC), ensuring high signal integrity and noise immunity.