Cooled versus uncooled thermal imaging cameras

Jon Lawson

Today R&D specialists, researchers and scientists use thermal imaging cameras for a broad range of applications ranging from academics and research, industrial R&D, non-destructive testing and materials testing, and aerospace and defence.

When deciding which thermal imaging camera system to use for R&D applications, there is a lot of choice available. A frequently asked question is whether a cooled or uncooled thermal imaging system should be used and which one is the most cost effective. Actually there are two thermal imaging camera systems available at present, which are known as cooled and uncooled systems. 

Cooled thermal imaging cameras

A modern cooled thermal imaging camera includes an imaging sensor combined with a cryocooler. This device brings down the sensor temperature to cryogenic temperatures. This reduced sensor temperature is needed to minimise thermally induced noise to a level lower than that of the signal from the scene that is being imaged.

Cryocoolers have moving components designed to tight mechanical tolerances, which wear out over time, and also helium gas which steadily moves past gas seals. These are highly sensitive cameras, which can detect the slightest temperature difference between cameras. They can be designed to enable imaging in the mid-wave infrared (MWIR) band and the long-wave infrared (LWIR) band of the spectrum, where there is a high thermal contrast because of blackbody physics. Thermal contrast can be termed as a signal change for a target temperature change. The more thermal contrast there is, the easier it is to determine objects against a background not hotter or colder than the object.

Uncooled thermal imaging cameras

A camera wherein the imaging sensor does not need cryogenic cooling is known as an uncooled infrared camera. The design of the detector used in an uncooled camera is based on the microbolometer, which is a small vanadium oxide resistor which has a large temperature coefficient on a silicon element with good thermal insulation, low heat and excellent thermal isolation. Scene temperature changes cause bolometer temperature changes that are converted to electrical signals and processed into an image. Uncooled sensors function in the longwave infrared (LWIR) band, where most of their infrared energy is emitted by terrestrial temperature targets.

Uncooled cameras are generally cheaper than cooled cameras. These cameras have a lower number of moving components and have a longer service life when compared to cooled cameras under similar operating conditions. However cooled thermal imaging cameras offer an advantage when your application is a bit more demanding. For instance, in the event that very small temperature differences need to be seen, the best image quality is required or very fast or moving targets are involved, if the thermal imaging camera must be synchronised with other measuring devices, thermal objects need to be visualised in a very particular part of the electromagnetic spectrum, you’re your instrument of choice is a cooled thermal imaging camera.