Cooled or uncooled camera

2019-10-12

There is plenty of choice when it comes to thermal imaging camera systems for R&D/science applications. An often-asked question is therefore: “Should I use a cooled or an uncooled thermal imaging system, and which one is the most cost effective?” In fact, there are two classes of thermal imaging camera systems available on the market today: cooled and uncooled systems. The component costs for these two classes of systems can be quite different, making it important to decide which way to go.

Cooled thermal imaging cameras

A modern cooled thermal imaging camera has an imaging sensor that is integrated with a cryocooler. This is a device that lowers the sensor temperature to cryogenic temperatures. This reduction in sensor temperature is necessary to reduce thermally induced noise to a level below that of the signal from the scene being imaged. Cryocoolers have moving parts made to extremely close mechanical tolerances that wear out over time, as well as helium gas that slowly works its way past gas seals.

Cooled thermal imaging cameras are the most sensitive type of cameras and can detect the smallest of temperature differences between objects. They can be produced to image in the mid-wave infrared (MWIR) band and the long-wave infrared (LWIR) band of the spectrum where the thermal contrast is high due to blackbody physics. Thermal contrast is the change in signal for a change in target temperature. The higher the thermal contrast, the easier it is to detect objects against a background that may not be much colder or hotter than the object.

Uncooled thermal imaging cameras

An uncooled infrared camera is one in which the imaging sensor does not require cryogenic cooling. A common detector design is based on the microbolometer, a tiny vanadium oxide resistor with a large temperature coefficient on a silicon element with large surface area, low heat capacity and good thermal isolation. Changes in scene temperature cause changes in the bolometer temperature, which are converted to electrical signals and processed into an image. Uncooled sensors are designed to work in the LWIR band, where terrestrial temperature targets emit most of their infrared energy.

Uncooled cameras are generally much less expensive than cooled infrared cameras. The sensors can be manufactured in fewer steps, with higher yields relative to cooled sensors and less expensive vacuum packaging. Uncooled cameras do not require cryocoolers, which are very costly devices. They also have fewer moving parts and tend to have much longer service lives than cooled cameras under similar operating conditions.

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