Infrared (IR) is the band just below red visible light on the electromagnetic spectrum. An IR tester is any of a wide range of products that interact with and get information from or about this spectrum. These devices can be part of motion detectors, remote control systems, wireless communication devices, or environmental testing equipment. The heavy usage of this band is common in many parts of modern technology.
In general terms, an IR tester is any device that will check the status of an IR-using device or one that uses IR as a way of gaining information. This means that an infrared thermometer and an automatic door calibration machine are both a form of IR tester. Since the definition is so wide, the easiest method to use for understanding and recognizing an IR tester is simply an understanding of the underlying technology.
One of the most likely common factors is the use of optics. This is usually a lens or reflector that sends and/or receives infrared signals. Since these signals are invisible to human eyes, these lenses don’t always look like ones common to things like cameras or telescopes. These can have dark, nearly opaque, coverings or pinhole-sized openings. When a sending system emits an IR signal, it blankets the whole area with invisible light. Since the light is so bright to an IR receiver, the opening and lenses don’t need to be as large.
This difference in lens assumes that the device is not something that a human uses to see. Some of these devices are made to allow a human to actually look at the IR in-use. The portable types of these devices often look like scopes or binoculars. When these devices are in use, they shift the light coming through the lenses to the visible spectrum. The IR will appear similar to how an IR receiver would see it.
The primary uses for such technology are checking up on other IR sources. These systems will point out a person using an IR gun scope on the battlefield or allow a worker to properly position a motion-sensitive light near a doorway. They are rarely used for other tasks, as the spectrum shift heavily distorts visible light.
When a system isn’t using a standard optic, it is often using other forms of receivers to transform infrared radiation into a digital image. This type of IR tester is commonly seen in movies and on television as the device that makes a thermal representation of something, often at a distance or through solid objects. These are reading thermal radiation, basically heat, within the IR spectrum. These readouts are digitally modified into an image viewable by humans.