lecture 17 Metallic-Resistance-Thermometers.pptx

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1. Metallic Resistance Thermometers Metallic Resistance Thermometers (RTDs) are temperature sensors that utilize the change in electrical resistance of a metal with temperature. They are known for their accuracy, stability, and wide temperature range. NS Presented by Nirma Kumari Sharma Assistant Professor Department of Electrical Engineering Faculty of Engineering & Technology

2. Working principle 1 Resistance Change The electrical resistance of a pure metal increases linearly with temperature. 2 Measurement The resistance change is measured using a Wheatstone bridge circuit. 3 Temperature Calculation The measured resistance is converted to temperature using a calibration curve.

3. Materials used Platinum Platinum is the most commonly used material due to its high purity, stability, and linear resistance-temperature relationship. Nickel Nickel is less expensive than platinum but has a lower resistance change and a narrower temperature range. Copper Copper is the least expensive material but has the lowest resistance change and the narrowest temperature range.

4. Applications 1 Process Control RTDs are widely used in industrial processes for monitoring and controlling temperature. 2 Scientific Research They are essential for accurate temperature measurements in scientific experiments and calibration. 3 Medical Devices RTDs are found in medical equipment for temperature monitoring and control, like incubators. 4 Aerospace They are used in aerospace applications due to their accuracy and stability in extreme environments.

5. Semiconductor Resistance Sensors (Thermistors) Thermistors are temperature sensors that utilize the change in electrical resistance of a semiconductor material with temperature. They are known for their high sensitivity, fast response time, and low cost.

6. Working principle Semiconductor Material The resistance of a semiconductor material decreases with increasing temperature due to increased electron mobility. Resistance Change The resistance change is significant, making thermistors highly sensitive to temperature variations. Measurement The resistance change is measured using a Wheatstone bridge circuit. Temperature Calculation The measured resistance is converted to temperature using a calibration curve.

7. Types Type Description NTC (Negative Temperature Coefficient) Resistance decreases with increasing temperature. PTC (Positive Temperature Coefficient) Resistance increases with increasing temperature.

8. Applications HVAC Systems Thermistors control the temperature in heating, ventilation, and air conditioning systems. Automotive They are used in engine management systems for temperature monitoring and control. Electronics Thermistors are used in smartphones and other electronic devices for temperature protection and management. Medical Devices They are used in medical thermometers for accurate temperature measurements.