Thermocouple applicability across temperature regimes: For which temperature regime(s) are thermocouples suitable in industrial measurement?

Introduction / Context:
Thermocouples are versatile due to their simple construction, self-powering nature, and broad temperature ranges. They are used from cryogenic applications to furnaces, provided the correct type and sheath are selected.

Given Data / Assumptions:

• Appropriate thermocouple types are chosen (e.g., Type T for sub-zero, Type K/N for general service, Type S/R/B for very high temperatures).
• Proper protective sheaths and atmospheres are considered.
• Calibration and cold-junction compensation are in place.

Concept / Approach:
Different alloy pairs tailor the sensitivity and stability across ranges. Copper–constantan excels at low temperatures; chromel–alumel handles broad ranges; noble-metal pairs measure extreme temperatures. Thus, thermocouples can be suitable across both high and low regimes when matched to the application.

Step-by-Step Solution:

Verification / Alternative check:
Standards and manufacturer charts show recommended ranges for each thermocouple type, from cryogenic (Type T/E) to high-temperature (S/R/B).

Why Other Options Are Wrong:

• Liquid only: Thermocouples measure gases, solids, and surfaces as well.
• Very high or very low only: Too restrictive; selection determines suitability.
• Under 300 °C only: Contradicts documented high-temperature applications.

Common Pitfalls:
Ignoring atmosphere compatibility; some alloys drift in reducing or sulfurous environments, requiring protective sheaths.

Final Answer:
Both high and low temperatures (wide usable range)