Infrared Thermometers

How does an IR thermometer work?

Traceable Infrared Thermometers

An infrared thermometer measures temperature without contact through a point-and-click activity, which then measures temperature from black-body radiation or infrared energy produced by the material being targeted for temperature measurement.

All objects emit infrared energy. The hotter an object is, the more active its molecules are, and the more infrared energy it emits. An infrared thermometer houses optics that collect the radiant infrared energy from the object and focus it onto a Emissivity of Common Materials detector. The detector converts the energy into an electrical signal, which is amplified and displayed.


Emissivity Chart

HAn object’s ability to emit or absorb energy. Perfect emitters have an emissivity of 1. An object with an emissivity of 0.8 will absorb 80% and reflect 20% of the incident energy. Emissivity may vary with temperature and spectral response (wavelength).

Distance-to-Target-Size Ratio

The infrared thermometer focuses infrared energy from an object onto its detector at this ratio. For example, a 4:1 distance-to-target-size ratio means that the infrared thermometer will read a 1 inch diameter area 4 inches away. The object must fill the entire area for accurate readings.

  • Infrared thermometers have difficulty taking accurate temperature measurements of reflective metal surfaces unless compensation is made for the very low emissivity.
  • Measuring an object through glass generally gives the surface temperature of the glass, unless the glass is made of a special infrared transmitting material such as germanium.
  • Most IR thermometers are limited to a measuring distance of approximately 100 ft due to atmospheric considerations.
  • Plastic films under 15-mm thick are difficult to measure using standard infrared thermometers, depending on the plastic’s thickness, chemical composition, and other physical characteristics. Choose an IR thermometer specifically designed for measuring thin-film plastics.

How to choose an IR thermometer

When choosing an infrared thermometer, consider the temperature range required; size, material, environment, and distance of the measured object; and its spectral response. Portable infrared thermometers are most often used for preventative maintenance, troubleshooting, and quality control. Choose an online sensor to continuously monitor or control your process.

Related Articles