Meaning of pyrometry in temperature measurement: In industrial metrology, “pyrometry” refers most correctly to the measurement of temperature that is primarily of which kind?

Introduction / Context:
Pyrometry is commonly used in furnaces, kilns, and metallurgical processes where temperatures exceed the safe or practical limits of liquid-in-glass thermometers and many contact sensors. Knowing what pyrometry implies helps in choosing between optical, radiation, or total radiation pyrometers and understanding their limitations.

Given Data / Assumptions:

• Industrial context: metals processing, refractory production, glassmaking.
• Temperatures often exceed several hundred degrees Celsius.
• Non-contact radiation techniques are typical but contact methods at high temperatures also exist.

Concept / Approach:
“Pyro” relates to heat/fire. Pyrometry broadly covers temperature measurement at high temperatures, frequently via radiant energy (optical or infrared) from a hot body. It does not specifically mean “mercurial” thermometry or “any direct contact method,” nor does it pertain to cryogenic regimes.

Step-by-Step Solution:

Verification / Alternative check:
Textbooks classify pyrometry under radiation thermometry, suitable where contact sensors are impractical or would be damaged.

Why Other Options Are Wrong:

• (a) Restricts to mercury-in-glass and low upper limit; not the definition.
• (b) Over-broad; pyrometry is not “any” direct contact method.
• (d) Includes incorrect statements; thus incorrect.
• (e) Pyrometry is not focused on cryogenics.

Common Pitfalls:
Assuming pyrometers always measure true temperature without emissivity correction; emissivity settings are crucial for accuracy.

Final Answer:
High temperatures (often non-contact radiation methods)