The need to increase the sensing range, reduce cost, and expand capabilities led to the development of ultrasonic and photoelectric sensors optimized for detecting clear objects. As cost continues to decrease and capabilities continue to increase, photoelectric technology is expected to increase its dominance in installations for detecting clear objects. These marketing strategies have generated the newest translucent and clear soaps, moisturizing gels, soft drinks, and a continually increasing use of clear plastic packaging for a wide range of consumer products. Commonly used clear packaging consists of glass or plastic containers and bottles. Plastic shrink-wrap is widely used for packaging and palletizing products and materials for shipment.
Clear objects pose a challenge for all photoelectric sensors.
The sensor is typically set for maximum sensitivity and operates with high margin, or excess gain, which means the unblocked light beam is many times stronger than that required to energize the sensor's output. The result is a very small change in signal. If the light beam is polarized, the direction and extent of polarization will be altered to a greater or lesser degree depending on the optical properties of the material. This alteration could depolarize the light beam and reflect a strong detectable signal. Most plastics used for containers and packaging are optically active.