Typical Dual-Wavelength Application

One of the greatest advantages of a dual-wavelength infrared thermometer is that the target can be smaller than the optical resolution of the sensor. This feature is particularly appropriate when viewing past an optical obstruction or when viewing a small or wandering target such as a thin wire (see Figure below). A wire may be heated for a number of reasons, including wire preheat for plastic coating of electrical wire, metallic diffusion coating used for steel belted tires, or wire drawing for light bulbs. For each process, accurate temperature measurement and control are critical for efficient production and consistent quality. At a well-known light bulb filament plant, for example, it had been impossible to measure wires in diameters of less than about 0.1 inch using traditional infrared thermometers because the small diameter combined with physical movement of the wire created impossible optical alignment challenges. For this application, the dual wavelength sensors are able to provide a relatively large target area of 0.5in diameter while measuring the significantly smaller wire. Using a dual-wavelength sensor it is possible to measure a wire that is less than 0.001in diameter and with a wander from side to side of as much as 0.2in. The dual wavelength design also automatically corrects for emissivity variations in the wire.