Measuring ~2000°C on incandescent mantles:\nWhich instrument is most appropriate to measure the very high temperature (around 2000°C) of an incandescent gas mantle or filament?

Introduction / Context:
At temperatures approaching 2000°C, contact sensors face survivability and measurement-error challenges. Non-contact optical methods that rely on visible incandescence are preferred for filaments and mantles. This question distinguishes between optical, radiation, and contact approaches at extreme temperatures.

Given Data / Assumptions:

• Target is a bright, incandescent surface with high radiance.
• Line-of-sight measurement is available.
• Emissivity is reasonably stable or can be accounted for by the technique.

Concept / Approach:
An optical pyrometer (disappearing-filament type) compares the brightness of a calibrated filament to the target’s brightness at a specific wavelength. When the filament “disappears” against the target, their brightness temperatures match. This technique works well from roughly 700°C up to 3000°C and is ideal for incandescent mantles. Total-radiation pyrometers are also high-temperature capable but are generally used for larger, opaque targets; classic exam convention associates filaments/mantles with optical pyrometers.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer datasheets for optical pyrometers list upper ranges near or above 2500°C, confirming suitability for incandescent sources.

Why Other Options Are Wrong:

• Special thermocouples: Possible with protection, but intrusive and less accurate for tiny bright sources.
• Total-radiation pyrometer: Valid for very hot bodies, but the standard pairing for filaments is optical (brightness) pyrometry.
• Mercury thermometer: Impossible at such temperatures.

Common Pitfalls:
Assuming any radiation pyrometer is equivalent; brightness (optical) pyrometers are textbook choices for incandescent mantles.

Final Answer:
Optical pyrometer