Infrared camera (IR camera)

An infrared camera is a focal-plane array of detectors, each converting the infrared radiation falling on it into an electrical signal, assembled into an image the way a visible-light camera assembles a picture from visible photons. The result is a thermal image: every pixel carries an apparent-temperature value derived from measured radiance, not a directly sensed temperature — the method behind that conversion is thermography.

The infrared band a camera works in decides what it can see. A long-wave infrared sensor is built for objects near ambient to moderately elevated temperature, and is the band most industrial and welding thermal cameras use. A short-wave infrared sensor instead covers very hot or self-luminous sources — an open arc, a molten weld pool, a furnace — when filtered to a narrow band, without saturating, which is why the two bands serve different jobs on the same welding cell rather than competing for the same one. A camera built for one band cannot substitute for the other by changing a setting; the detector material itself differs.

An infrared camera differs from a pyrometer in exactly the dimension that matters for weld monitoring: a pyrometer reports one number for one point, while a camera reports a field of values, which is what lets a monitoring system see the shape of the heat-affected zone, the symmetry of the weld pool, or the location of a cold spot rather than only its presence. That spatial information is why camera-based systems, not single-point sensors, are the basis of real-time monitoring on the welding monitoring system side of thermal inspection.

Every apparent-temperature reading a camera outputs still depends on the emissivity assumed for the surface being viewed, so an absolute-temperature claim from a camera is only as good as the emissivity behind it — the same limitation a pyrometer carries, inherited by every pixel rather than by one point.