Question

Which one of the following will be used for surface temperature measurement?

• A. Strain gauge
• B. Diaphragm
• C. RTD
• D. Thermocouple

Hint:

For the most accurate surface measurement, ensure the thermocouple leads are also in contact with the surface for a short distance to prevent "stem conduction" errors.

Answer 1

The Correct Option is D

Measuring the temperature of a solid surface requires a sensor that can maintain excellent thermal contact with the surface without acting as a "heat sink" that changes the temperature it is trying to measure. 1. Advantages of Thermocouples for Surfaces: Thermocouples are ideal for surface measurements because:

• Size: They can be made extremely small (fine wire junctions), allowing them to be taped or cemented directly to a surface.

• Thermal Mass: Their very low thermal mass means they respond rapidly to temperature changes and don't pull significant heat away from the spot being measured.

• Durability: They are rugged and can withstand being pressed against hot metal or machinery.

2. Why not the others?

• Strain gauges and Diaphragms: These are used to measure mechanical stress and pressure, respectively, not temperature.

• RTD: While RTDs are very accurate, they are usually bulky (enclosed in a metal probe) and have a higher thermal mass, making them better for measuring air or liquid temperatures rather than point-surface temperatures.