The sensor is photo-electric

Photo-electric sensors are used in many industries for ensuring exact detection of objects without physical contact.

In the majority of the main forms the photo-electric sensor can be considered as the device like the trailer switch in which function of the mechanical drive or a shoulder of the lever is carried out by a beam or light. Photo-electric sensors work, finding changes in intensity of light which either is reflected, or is late the found object (target). Changes in intensity of light can be result of presence or lack of a target or result of change of the size, a form, coefficient of reflection or color of a target.