Temperature measurement – Non-contact methods: Which instrument measures temperature without touching the object?

Introduction / Context:
Non-contact temperature measurement is vital for moving targets, high temperatures, or sanitary constraints. Understanding which instruments are non-contact improves selection for process safety and accuracy.

Given Data / Assumptions:

• Non-contact relies on thermal radiation detection.
• Contact devices must physically touch or be inserted into the medium.

Concept / Approach:
Radiation or infrared pyrometers measure emitted thermal radiation proportional to surface temperature (with emissivity considerations), requiring no physical contact. Other listed devices sense temperature via conduction through a bulb, junction, or bimetal element.

Step-by-Step Solution:
Identify radiation-based method → infrared pyrometer.Contrast with contact methods → filled-system, mercury-in-glass, thermocouples, and bimetallic devices all touch the process.

Verification / Alternative check:
Pyrometer datasheets emphasize line-of-sight measurement and response to spectral bands without immersion.

Why Other Options Are Wrong:

• Filled-system/mercury/bimetal: require contact to equilibrate temperature.
• Thermoelectric pyrometer: thermocouple junction must be in contact with the object or medium.

Common Pitfalls:
Confusing the term “pyrometer” with “thermocouple”; only radiation pyrometers are non-contact.

Final Answer:
Radiation (infrared) pyrometer