Lasers

Lasers are a subset of photoelectric sensing, with the distinction of having a well collimated light beam, compared to non-laser photoelectric sensors which have the beam spreading outward with increasing distance from the source.  Most laser based photoelectric sensors are visible red LED light sources, and since the light is collimated in a single point, it is typically easy to see the where the projected beam strikes the target.

Lasers are available for all three modes of sensing, as covered in the Photoelectric Sensing segment, above.  For clarification, this includes proximity mode, through-beam mode, and retro-reflective mode.

The advantages of laser-based photoelectric sensors include the ability to only see a small segment or spot on the target material, and thus ignore the rest of the surrounding product area.  This is extremely helpful in many inspection tasks, where the inspection is confined to a given spot or location on the product.  Another advantage of laser-based photo-electrics, is the long sensing range, and the ability to ignore other nearby, unintended targets.

Disadvantages of the laser is that it is typically a visible red wavelength, which is significantly absorbed by black or darker target materials, when used in the proximity mode, effectively reducing the sensing range.  Another significant disadvantage of a laser is the precision alignment necessary for a highly collimated light beam to strike a small target.  The longer the sensing distance, the more critical is alignment.  Bracketry for mounting should be rigid, include some fine adjustment, and be able to lock in position to maintain that alignment.  This is even more critical in the through-beam mode, where the receiver is physically just a small as the sender, and alignment between the two is challenging.

Incident angle with respect to the target, especially in the proximity mode, is critical, as the collimated beam may be easily reflected to some other location than the sensor.

Lasers come in different classifications, for human safety.  Because the beam is collimated and represents a significant amount of energy in a relatively small area, users should always avoid looking directly into the source of the laser beam, to prevent possible damage to their eyes.

Traditionally, the laser may be a slightly higher price than its non-laser equivalent.  The author’s opinion is that lasers have their place, but should not be considered as one-product for all applications, just because they sound high-tech.