Blue laser vs red laser triangulation sensors: which is better?

Laser triangulation sensors are one of the most sought-after non-contact sensor technology for measuring position, distance, level, displacement, proximity and profiles of objects. They are widely used in industrial process automation and control, as well as for test and measurement in process monitoring and validation. Currently, two technologies are available: red and blue laser sensors. The conventional red laser sensors are suitable, and offer good measurement stability, for most applications. However in some applications, blue laser sensors provide better performance.

Blue laser triangulation sensors are suitable when accuracy cannot be compromised. The blue laser with a shorter wavelength does not penetrate or diffuse into the target surface — which can lead to a lack of focus that causes inaccuracy. Choosing which laser type to use may depend on the type of surfaces, target materials and required measurement speed.

Surface types

As red laser penetrates deeper onto the target surfaces as compared with blue laser, it substantially increases the area of blurry region that is reflected back to the detector. This can cause the detector to not be able to detect the exact distance to the surface. This effect is minimised when used for measuring objects with matte or low-reflective surfaces.

In the case of blue laser sensors, the light being reflected back to the detector is minimised due to the shorter wavelength. Blue laser sensors perform well when used for measuring objects with shiny, reflective or highly-polished surfaces. For shiny surfaces, the shorter wavelength of blue laser generates much less speckling and a lower noise level (by a factor of three) when compared to the red laser.

Types of target materials

Red laser sensors also have limited use in measuring hot and glowing objects. A hotter object generally emits a high radiation intensity at a wavelength similar to that of the red laser, resulting in undesirable noise. This effect does not apply for blue laser as it operates at the opposite end of the visible light spectrum. The sensor will generate stable and accurate signals, unaffected by the object temperature. Blue laser sensors also triumph over red lasers when used for measurement on organic, food, transparent and translucent materials.

Measurement speed

Red laser sensors outperform blue laser sensors for highly dynamic applications due to the stability of the high-intensity laser in high speed applications. For example, when measuring package dimensions on a conveyor belt, red laser sensors are typically a better choice as they are able to accurately measure with high speed. They are also better in terms of overall performance and availability of measuring ranges, and are also more cost-effective compared to the blue laser sensors.

In summary, both blue laser and red laser triangulation sensors offer similar capabilities with one sensor more suitable than the other under certain conditions. Both of them can also be used for measurement of 2D and 3D profiles of objects. To select an appropriate sensor technology, the questions to be asked should be:

• How hot will the surfaces be?
• What are the surface characteristics of the target object?
• How dynamic is the application (how fast will the surface change)?
• What level of accuracy is required?
   

In most test and measurement cases, red laser triangulation sensor will be able to perform just fine. Blue laser triangulation sensors are not always feasible as they are higher priced than red laser triangulation sensors. However, they may be the only viable solutions in some applications.

Contact Bestech Australia at 03 9540 5100 or enquiry@bestech.com.au for more information.