Ideal Gas Thermometer and Temperature Measurement by Mechanical and Electrical Effects II — Lesson 2

This lesson covers the principles and techniques of temperature measurement using electrical effects, with a focus on Resistance Temperature Detectors (RTD). It explains how RTDs exploit the change in resistance of a material with temperature to detect temperature differences. The lesson also discusses the resistance of a conductor over a limited range of temperature and the role of the temperature coefficient. It further delves into the construction of RTDs, their calibration, and their placement in a Wheatstone bridge for temperature measurement. The lesson also highlights the potential errors in temperature measurement due to lead resistance and presents different wiring schemes to eliminate or reduce these errors.

Video Highlights

03:13 - Resistance of a conductor over a limited range of temperature
06:20 - Construction of resistance temperature detectors (RTD)
12:31 - Error in temperature measurement due to lead resistance
20:58 - Siemens three-wire scheme
26:44 - Calendar four-wire connection
33:33 - Floating point arrangement

Key Takeaways

- Resistance Temperature Detectors (RTDs) measure temperature by exploiting the change in resistance of a material with temperature.
- The resistance of a conductor over a limited range of temperature is given by a specific formula involving the temperature coefficient.
- RTDs are typically made of a filament of wire wound around an insulating spool and are often sealed in a ceramic or glass coating for electrical insulation and environmental protection.
- RTDs are placed in a Wheatstone bridge for temperature measurement, using null deflection for steady temperatures and deflection bridge for fluctuating temperatures.
- Errors in temperature measurement can occur due to the resistance of the leads connecting the RTD to the bridge.