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Setting New Standards In Electro-Optical Testing

An overview of IR calibration with blackbody radiation sources


6 July, 2016

The principle of radiation thermometry has been used in various industries for several decades. However, its recent application upsurge in factory maintenance, HVAC, energy, and aerospace industries has drawn unprecedented attention to the calibration equipment and infrared (IR) thermometers that support them. 

Types of IR temperature Calibrators
When scouting for a suitable infrared temperature calibrator, it is significant to understand that there are a plethora of target designs and form factors. Two of the most common IR temperature calibrators include:

1. The blackbody calibrators: a black body has the capability to absorb all the radiation it receives and to emit more thermal radiation for all wavelength ranges than other objects with the same area and temperature. Blackbody calibrators have empty cavities with small openings that often act as targets. They are usually conical or tube-shaped and are embedded in a bath, heat pipe or furnace. In radiation thermometry, they are used at the reference level due to their high sensitivity values. 

2. The flat-plate IR calibrators: these have painted targets surfaces that can be heated or cooled to the required calibration temperatures. The surfaces may have ridges/bumps or may be completely flat and smooth. The different types of surfaces are used by manufactures to manipulate their emissivity—though it also affects negatively their temperature uniformity. 

The type of IR calibrator that you need is primarily dictated by the type of IR thermometers you plan to calibrate. Some of the vital factors that you should consider include:

  • Emissivity of the thermometer
  • Distance to size of spot ratio (or the D:S ratio)
  • Temperature range
  • Your IR thermometer’s operational spectral band 
  • Calibration with a Blackbody Radiation Source 

When calibrating with a black body calibrator, you need to consider a few factors including: 

1. Blackbody type (cavity type or hot plate): This will dictate the construction and the overall performance of the unit.

2. Target emissivity: The higher the emissivity, the better the calibration. At lower emissivity, your IR thermometer’s wavelength bandwidth becomes an issue. Typically, at E=1.00, your Device Under Test’s wavelength bandwidth is not a factor. 

3. Target area (cavity opening or hot plate area): this indicates the area size that you can check with your IR thermometer. Generally, the target area should be bigger than the thermometer’s field of view otherwise your thermometer will be measuring the target area and the surrounding cooler areas. In most cases, IR thermometers are checked against blackbody sources at considerably closer distances—approximately 0.2 to 1 meters depending on your target area. 

Final Thoughts
For all your blackbody radiation sources, the experts to go to are the CI Systems. CI has been in the black body radiation sources business for over three decades. We have a solid and unmatched experience in developing high emissivity black body radiation sources with high surface uniformity and temperature accuracy. We boast of a wide range of blackbody aperture sizes with flexible temperature sensors that are tailored for shorter periodic calibrations. 

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