Choosing a Blackbody Calibration Source

Blackbody calibration sources from Calex allow the calibration of infrared temperature sensors with low uncertainty. This article explains what makes the best blackbody calibration source for a given application and what you should consider when choosing one. 

What is a Blackbody Calibration Source?

A blackbody calibration source is a tool for checking the calibration of an infrared temperature sensor. It consists of a heated (or cooled) target object whose temperature is precisely known, and is the basis for accurate calibration of infrared pyrometers.

A blackbody is an ideal radiator i.e. it emits thermal (visible and infrared) energy whose intensity at a given wavelength and temperature follows Planck’s Law of radiation. It completely absorbs and emits all radiation (it is extremely non-reflective) and has an emissivity value of 1.

Because there no material exists that could make a true perfect blackbody, in practice a blackbody calibration source always has a slightly lower emissivity than 1, however by careful design it is possible to get very close.

The emissivity setting of the sensor should be adjusted to match the emissivity of the blackbody, and the sensor should be mounted close enough that the measured spot diameter is no larger than half the aperture diameter.

Calex offers a range of blackbodies for different applications:

BB976 and BB982 Blackbody Calibration Sources

For very accurate calibration checks, the BB976 and BB982 blackbody sources provide the highest performance. These models are ideally situated in a calibration room or laboratory where a stable ambient temperature allows you to take full advantage of their performance, although the built-in carrying handle does allow them to be moved around the site if required.

The two models differ in their temperature range, being 30°C to 550°C (BB976) and -10°C to 80.0°C (BB982). Both have outstanding stability (±0.1°C) and a built-in temperature indicator with high resolution (0.01°C). They are supplied with a PC interface, software and a 3-point traceable calibration certificate.

These blackbodies consist of a temperature-controlled cylindrical thermal cavity which has a small aperture at one end. The cavity surfaces are covered with pigmented paint which gives a very high emissivity of 0.995 at the aperture. We can supply optional orifice plates which restrict the cavity aperture further. This can be helpful when calibrating thermal imagers.

A heating block heats the thermal cavity to the temperature selected on the built-in controller. Cooling elements in the BB982 allow the unit to reach temperatures below ambient. The infrared radiation emitted from the cavity can then be used to calibrate a non-contact temperature sensor whose field of view is aimed through the centre of the aperture. A separate built-in temperature indicator and platinum resistance contact thermometer (both included) provide an accurate reference measurement of the cavity temperature.

Radiometric calibration of these blackbodies is available, as is calibration of the platinum resistance thermometer.

An optional robust carrying case is also available.

Please contact Calex for details.

FTK Portable Blackbody Calibration Sources

The FTK is a simple, rugged and portable unit designed to provide calibration checks anywhere they are needed, from the factory to the workshop or laboratory. Eighteen models are available, each offering a fixed temperature from 35°C to 150°C. The FTK provides outstanding stability with less than ± 0.1°C deviation.

While the emissivity of the target surface (at 0.98) is not quite as close to 1 as the BB976 and BB982, it is more than adequate for quick, economical calibration checks.

We can supply an optional 1-point calibration certificate (FTKCALCERTA) for all new FTK models, and a re-calibration service with a 1-point certificate (FTKCALCERTB) for a returned unit.

An optional adjustable ball and socket mounting block (FTKMOUNT) is available:

Get in touch

If you have any further questions about our Blackbody Calibration Sources, please do not hesitate to contact Calex and we will do our best to help you.

By Barbara Miller