To measure accurately, an IR pyrometer must be aimed at the surface or part of the surface of interest. For very large areas such as steel slabs or web processes this does not present a problem, but for smaller surfaces such as wire, pc board components, weld bead etc., a more precise aiming method is required.
Process Sensor’s pyrometers can incorporate a variety of sighting methods such as throughlens, where an installer can aim through the same lens that focuses the IR energy on the detector; or laser aiming via a built-in laser beam that illuminates the center of the target area. The pyrometers can also incorporate a video output that presents a picture of the area being measured on the image. A reticle defines the exact spot size of temperature measurement.
Where there is no direct line-of-sight between the pyrometer and the target, a flexible fiber optic cable can be used to carry the IR energy around obstacles and corners. Specifically used in high-strength magnetic fields, high ambient temperature and vacuum environments, it allows the IR sensor’ electronics to be placed remotely, outside from these difficult conditions.
The infrared energy radiated by the target is transferred via focusable lenses either directly on the detector (standard version) or onto one end of a fiber optic cable. For applications where the lens must be refocused during operation, a remote focusable lens is available.
Some pyrometers are designed with adjustable focusing. This does not necessarily mean that the target must be a sharp, clear image in order to obtain an accurate measurement, as would be the case with a camera. Pyrometer focusing is simply intended to permit the pyrometer to “see” the smallest spot size at a given distance. This is helpful when measuring through small openings or for avoiding obstacles in the sight path.
The sight path is the space between the pyrometer lens and the object being measured. For accurate measurement the sight path must be clear and free of obstacles, steam and water droplets, and heavy concentrations of particles. Devices such as fans and air purges, or careful sighting can usually ensure that this condition is met, but sometimes the use of a Two Color or ratio pyrometer can be helpful.