Principle of Infrared Thermometry

Definition

Infrared thermometry is a non-contact method for measuring surface temperature based on Planck's blackbody radiation law. It calculates temperature by detecting the infrared energy emitted from an object's surface, requiring no physical contact with the target.

Infrared temperature measurement is a non-contact method that calculates surface temperature by detecting infrared energy emitted from an object, based on Planck's blackbody radiation law. No physical contact with the measured object is required.

Alias

Detailed explanation

All objects with a temperature above absolute zero (273.15°C) emit infrared energy. The intensity of this radiation is proportional to the fourth power of the object's absolute temperature, according to the Stefan-Boltzmann law (E = ε·σ·T⁴). Infrared thermometers operate based on this principle. The complete infrared measurement process involves 5 steps: 1. Radiation Collection: An optical system (lens or mirror) focuses the object's infrared radiation onto the detector. 2. Band Selection: A filter selects a specific wavelength band (commonly 8–14μm long-wave or 3–5μm mid-wave). 3. Photoelectric Conversion: An infrared detector (thermopile, pyroelectric, InGaAs, HgCdTe, etc.) converts the radiation into an electrical signal. 4. Signal Processing: Amplification, A/D conversion, and temperature calculation algorithms are applied. 5. Emissivity Correction: The emissivity ε (0.01–1.00) is set based on the material to eliminate errors caused by material differences. Key advantages of infrared thermometry include non-contact measurement, fast response (< 1s), and the ability to measure moving or high-temperature objects. Key limitations are that it measures only surface temperature and is susceptible to variations in emissivity, ambient radiation, and atmospheric conditions (water vapor, CO₂).

Calculation Formula

Typical Value

{"Low-temperature measurement": "-50~500°C, select long-wave 8–14μm", "High-temperature measurement": "500~3000°C, select short-wave 0.7–1.6μm", "Metal emissivity": "0.05–0.4", "Plastic/ceramic emissivity": "0.85–0.95", "Human skin emissivity": "0.98"}

Unit

°C (temperature) / μm (wavelength)