High-temperature measurement choice: Which instrument is not generally suitable for measuring the temperature of a red-hot object in the range of 800–1600 °C under typical industrial, non-contact conditions?

Introduction / Context:
Red-hot objects in furnaces or moving product lines often require non-contact temperature measurement to avoid sensor damage and response delays. Pyrometers estimate temperature from emitted radiation and are widely used for this purpose in the 800–1600 °C range.

Given Data / Assumptions:

• Object temperature is between 800 and 1600 °C.
• Access is by line-of-sight; non-contact is preferred or required.
• Options include three types of pyrometers and a contact thermocouple.

Concept / Approach:
Optical, radiation, and photoelectric pyrometers are purpose-built for high-temperature, non-contact measurement. They thrive in the “red-heat” range because radiation intensity is sufficient for accurate detection. A thermocouple, while capable in principle (e.g., Pt/Pt-Rh), requires physical contact, protection sheaths, and often suffers from lag, drift, and survivability issues in moving or aggressive environments, making it generally less suitable in typical red-hot non-contact applications.

Step-by-Step Solution:

Verification / Alternative check:
Industrial best practice favors pyrometers for high-temperature rolling stock, kiln interiors, and melt surfaces due to durability and speed; thermocouples are used for probes, well-mounted sensors, or embedded measurement when contact is feasible.

Why Other Options Are Wrong:

Common Pitfalls:
Forgetting emissivity corrections with pyrometers; surface condition and window fouling can bias readings.

Final Answer:
Thermocouples