Is it worth learning the Planck’s law to use a blackbody?
- For any given wavelength, the Radiance level is an increasing function of the temperature,
- For any given temperature, the Spectral Radiance curve reaches a maximum which wavelength can be easily calculated from the easy-to-remember Wien’s law
Example: a blackbody at 800K (i.e. 527°C approx.) emits its maximum radiation at about 3.6 µm, i.e. in the MWIR spectral range.
What are the applications of a blackbody?
As the radiation level of a blackbody only depends on its temperature and is well-known through the Planck’s law, blackbodies are used as optical reference sources for optical sensors. Practically, as the temperatures values for blackbodies emitting over the visible range are very high and as, consequently, this leads to very expensive sources compared to classical lamps, the blackbodies are mainly used over the infrared spectral range starting from 1 µm. That’s why blackbodies are also known as Infrared Reference Sources.
The main applications are of course IR sensors calibration and their specifications measurement.
What types of blackbodies can I find on the market?
Depending on the applications and on the IR sensor range of sensitivity, the manufactured blackbodies are divided into 3 families usually defined by their temperature range:
- Low temperature extended area blackbodies, which temperature is set from approximately -40°C to more than 150°C
- High temperature extended area blackbodies, which temperature is set from above ambient temperature up to 600°C
- High temperature cavity blackbodies, which temperature is set from above ambient temperature up to more than 1200°C
How can I select the appropriate blackbody for my application?
Temperature range is the first parameter defining a blackbody: this can be obtained by considering the type of objects the IR sensor is supposed to look at. For example, if the sensor is looking at human bodies or vehicles or buildings, low temperature blackbodies should be considered.
The size of the emissive area is also an important parameter defining a blackbody.
Other parameters may be also critical depending on the application: regulation stability, emissivity, warm-up and cooling time, etc. Please contact EOI for any help.
What does a blackbody look like?
A blackbody is usually made up of two parts linked through a cable:
- emissive head: including an emissive surface coated with highly emissive coating or a cavity. An accurate temperature sensor is inserted into the emissive surface or cavity measuring the temperature of the source in real time. Depending on the temperature range the emissive head is also equipped with heating and/or cooling means.
- electronic controller: which brings power to the heating/cooling mean while acquiring and displaying the temperature of the emissive surface in real time. The electronic controller is equipped with accurate servo control loop for high-stability temperature regulation.