Pyrometry classification: which instrument is a contact-type pyrometer used by touching or inserting a sensing element into the hot medium?

Introduction / Context:
Pyrometers are broadly divided into contact and non-contact types. Contact pyrometers sense temperature through physical contact (electrical resistance or thermoelectric effect), while non-contact pyrometers infer temperature from thermal radiation in the visible/infrared spectrum.

Given Data / Assumptions:

• Choices include resistance, optical, radiation, and infrared instruments.
• “Contact” implies the sensor is inserted or touches the hot body.

Concept / Approach:
A resistance pyrometer (e.g., platinum resistance thermometer or high-temperature resistance element) measures temperature via change in electrical resistance upon contact. Optical/radiation/infrared pyrometers are line-of-sight devices that require no contact; they measure emitted radiation and apply emissivity corrections.

Step-by-Step Solution:
Identify which options require physical contact with the medium.Resistance pyrometer → contact; all others → non-contact radiation methods.Select “Resistance pyrometer.”

Verification / Alternative check:
Instrumentation manuals list resistance/thermocouple probes under contact methods and optical/radiative devices under non-contact pyrometry.

Why Other Options Are Wrong:
Optical/radiation/infrared/two-color pyrometers determine temperature from radiant energy without physical contact.

Common Pitfalls:
Assuming “optical” implies contact through a sighting tube; it still measures radiation remotely.

Final Answer:
Resistance pyrometer