Laser triangulation sensors are one of the most sought-after non-contact sensor technologies for measuring position, dimension and speed, and are widely used in industrial automation and robotic applications. Currently, two varieties are available: red and blue laser sensors. Choosing the most appropriate sensor type usually depends on several criteria: the target material, its surface type and temperature, and the required measurement speed.
Although conventional red laser technology generally performs well in most applications and provides good measurement stability on a wide range of surfaces, it performs worse than blue laser sensors in situations where accuracy cannot be compromised. Red lasers operate at a wavelength of 700nm, penetrate deeper into the target object and diffuse on the surface to create a blurry region of light that is reflected back to the detector, creating measurement errors due to the lack of focus. Blue lasers operate at a wavelength of 405nm, so they generate a much more focused point on the surface and penetrate less deeply into the object.
Red lasers are therefore better when used for measuring objects with a matte or low-reflective surface, while blue lasers are better with high-reflective surfaces, and when measuring food or organic, transparent and translucent materials. For shiny surfaces, the shorter wavelength of blue lasers generates much less speckling and a lower noise level, to maintain high measurement accuracy.
Red lasers also have limited use when measuring hot and glowing objects. For example, in the steel processing industry, hot glowing metal can reach temperatures as high as 1000ºC. A hot object generally emits a high intensity light at a wavelength similar to that of a red laser, which creates undesirable noise when the light is reflected back to the detector. Blue lasers operate at the opposite end of the visible light spectrum, so they will generate stable and accurate signals and be less affected by an object’s temperature, such as in automotive brake disc deformation testing or measurements on exhaust manifolds. They can also be an ideal way to measure the profile of objects in a processing line.
But red lasers outperform blue lasers in highly dynamic applications due to their high intensity. For example, when measuring package dimensions on a conveyor belt, red lasers are typically a better choice, as they are able to measure accurately at high speed. They are also better in terms of performance and measuring ranges, and are more cost-effective.
In short, in most test and measurement applications, red laser triangulation sensors will be able to perform to requirements. Blue laser triangulation sensors are not always feasible as they are higher priced than red laser triangulation sensors. However, in several niche applications, blue lasers may be the only solution.
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