Blackbody Sources Information
A blackbody is a physical material with zero reflectivity and perfect emission. This means that a blackbody at constant temperature absorbs all incident radiation at all angles and the spectrum of radiation it emits is based on solely temperature and no other physical property. Blackbody sources are uniform, temperature stable sources of infrared radiation that approximate the ideal blackbody. The primary function of a blackbody source is to provide certain sources for calibrating infrared sensors and systems.
Blackbody sources are comprised of two types, hot plate-types and cavity-types.
Hot plate-type blackbody sources are metal plates that are temperature controlled and are commonly painted a flat black to increase the plate's emissivity. The temperature of the plate is controlled by a simple thermostat or a more advanced temperature controller. Blackbody sources of this type can have emissivity up to 0.95.
The cavity-type blackbody is the most effective way at approximating an ideal black body. It is an opaque cavity with an opening or aperture. The cavity is kept at a stable temperature using a temperature controller. Any incident light on the opening will go into the cavity and will be thermalized to the same energy as the thermal radiation in the cavity. This means that the only radiation escaping will be thermal radiation based solely on the temperature of the cavity. This method can yield emissivity of 0.98 and greater.
There are several important specifications to consider when choosing a blackbody source.
Emissivity: Emissivity is a measure of how efficient a body or surface is emitting thermal radiation. A perfect blackbody will have an emissivity of 1.0 because the only radiation being emitted is thermal radiation from the body's temperature.
Temperature range: This is the temperature range in which the blackbody source is calibrated to operate.
Aperture size: This is the size of the blackbody source emitter. Aperture size can either be the size of the temperature-controlled area in a hot plate blackbody, or the size of the opening in a cavity-type black body source.
Handheld blackbody sources are excellent for field calibration of infrared sensors such as heat and flame detectors. Desktop-mounted blackbody sources work well for infrared thermometers.