# Question 1 - Step-by-Step Solution --- ## a) Three Differences Between Open and Closed Loop Systems ### **1. Feedback Mechanism** - **Open Loop:** No feedback from output to input. System acts on input only. - **Closed Loop:** Feedback exists; system adjusts based on output. **Diagrams:** - **Open Loop:** ``` [Input] → [Process] → [Output] ``` - **Closed Loop:** ``` [Input] → [Process] → [Output] ↑ | |_____________| Feedback ``` ### **2. Accuracy** - **Open Loop:** Less accurate, as errors aren't corrected automatically. - **Closed Loop:** More accurate, as feedback allows error correction. ### **3. Complexity and Cost** - **Open Loop:** Simple design, cheaper to build and maintain. - **Closed Loop:** More complex and expensive due to additional components for feedback. --- ## b) Block Diagram & Elements in a Typical Process Control System Loop ### **Block Diagram:** ``` [Set Point] → [Controller] → [Actuator/Final Control Element] → [Process] → [Sensor/Transducer] → [Feedback] → [Controller] ``` ### **Explanation of Elements:** - **Set Point:** Desired value of the process variable. - **Controller:** Compares set point with feedback and generates control signal. - **Actuator/Final Control Element:** Converts control signal into physical action. - **Process:** The plant or system being controlled (e.g., temperature, pressure). - **Sensor/Transducer:** Measures process variable and sends signal back. - **Feedback:** Path for returning measured value to controller. --- ## c) Explanation of Terms in Process Control ### i. **Transducer** - A device that converts one form of energy into another (e.g., temperature sensor converts heat to electrical signal). - **Diagram Example:** ``` [Physical Quantity] → [Transducer] → [Electrical Signal] ``` ### ii. **Noise** - Unwanted disturbances superimposed on a useful signal, causing errors in process control. - **Example:** Electrical interference affecting sensor readings. ### iii. **Self-Regulation Process** - A process that naturally settles at a stable value after a disturbance, without external intervention. - **Example:** Water tank level stabilizing due to overflow outlet. ### iv. **Hysteresis** - Difference in output when input is increasing versus decreasing, even if input values are the same. - **Example:** Thermostat turns heater on at 18°C and off at 22°C; doesn’t switch instantly. ### v. **Mounting Position** - The location and orientation of a sensor or device, affecting its performance and accuracy. - **Example:** Pressure sensor must be mounted vertically for correct readings. --- ## **Final Structured Answers** **a) Differences:** 1. Feedback (open: none, closed: present) 2. Accuracy (open: less, closed: more) 3. Complexity/cost (open: simple/cheap, closed: complex/expensive) **b) Block diagram elements:** - Set Point - Controller - Actuator/Final Control Element - Process - Sensor/Transducer - Feedback **c) Terms:** - **Transducer:** Converts physical signal to electrical. - **Noise:** Unwanted signal disturbance. - **Self-regulation:** Process naturally stabilizes. - **Hysteresis:** Output difference for same input depending on direction. - **Mounting Position:** Sensor/device placement affecting accuracy.