Thermal imagers detect heat patterns in the infrared wavelength spectrum.  Thermal imagers rely on the emission of thermal or infrared energy by all objects above 0 Kelvin. They detect energy emissions (heat) in the infrared wavelength spectrum of 1 micron to 100 microns.  Thermography, thermology, thermal wave imaging, thermovision and thermal infrared night vision use thermal imagers, some of the actual devices appear like slightly oversized video cameras, while others appear a bit bulkier. They have been getting smaller since the introduction of Focal Plane Array (FPA) detectors.  The specific uses of the imagers are widespread. Several major cost saving uses depend upon the temperature measurement capability of the specific imaging equipment and a great many commercial and industrial uses produce significant cost savings or cost avoidance.  Thermal imaging devices provide the observer with instruments that can collect ( just like a video or still camera) and convert the thermal infrared radiation emitted (and also reflected) by objects into images that can be seen on a view screen or computer display.

Specifying Thermal Imagers

There are several parameters important in specifying thermal imagers, measurement temperature range, spectral range, accuracy, resolution and maximum frame rate.  The measurement temperature range is the temperature range of object to be measured.  Spectral range can be broken into one of four ranges, near IR:  0.75-3 microns, middle IR: 3-6 microns, far IR: 6-15 microns  and extreme IR: 15-30 microns.  The accuracy value represents the accuracy or measurement uncertainty expressed as a percent of the reading value.  The temperature resolution represents the smallest unit of temperature uncertainty.  Maximum frame rate is the speed or image update rate.

Detector Types

Thermal imagers may have one of three common detector types, flying spot, scanning and line array.  A flying spot detector is a single point detector scanned to build image.  A scanning detector is a line detector that scans to produce an image.  An array detector is a two-dimensional array of sensors or detectors.

Most IR detectors must be kept at a constant temperature ranging from -100C to -196C, therefore they have cooling mechanisms in their design.  These may be thermoelectric, liquid nitrogen, active built-in cryogenic cooling or the detector may not be cooled at all.  Thermoelectric designs cool via Peltier cooling.  Liquid nitrogen cooling may be used to absorb any unwanted heat and associated noise.  With built-in cooling the infrared imager is supplied with on-board cooling to cryogenic temperatures.

Thermal imagers have both a horizontal and vertical spatial resolution that represents the number of pixels in either direction.  The greater the resolution, the smaller the unit of temperature that can be measured.

Common Features

Features common to thermal imagers include batteries, built-in cameras, built-in microphones, frame grabbers, portability, protective cooling jacket, remote heads, removable data storage, and infrared or spectral filters.