A triangulation sensor is a device that typically uses optics to determine the position of an object. At least one light emitting diode (LED) and one photodiode are usually necessary for this type of system, though additional sensors can also be used. The location of an object can be triangulated based on the angles of the light from the LED and the light that returns to the photodiode. One common usage of this type of triangulation sensor is as a safety mechanism in automatic doors. These systems are able to determine when a person is near the door, since the person will tend to interfere with the path of the light from the triangulation sensor, and cause it to reflect at a different angle or not at all.
Triangulation is a process that can be used to find the location of an object by using two or more other known locations. In both cases, it uses certain known data and trigonomic identities to determine unknown information. One example of triangulation is the way that a cellphone signal can be located by its proximity to two or more cell towers. Another is how the position of an object can be determined based on a triangle drawn between that object and a known baseline, which results in two known angles and one known distance measurement. Trigonomic identities can then be used to determine the unknown distance.
Optical triangulation sensors can be useful in robotics and when measuring the location of objects that are fragile and could be easily damaged if physically touched with a probe. These sensors typically make use of an LED or another light source, and a one or more receptors such as photodiodes. The distance between the the receptors and the light source is known, so it is also possible to determine the angle at which the light left the LED and arrived at the photodiode. These three known figures can then be used to determine the distance of an object using trigonomic identities.
Another common use of a triangulation sensor is in the safety mechanisms of automatic doors. This type of triangulation sensor does not physically measure the location of the floor, but can sense when that position changes. When these devices are calibrated, the photodiode receptor is placed so that light from the LED will hit the floor, reflect, and then strike it. The system is able to sense when a person is near the door, since he will tend to obstruct the light and cause it to not strike the photodiode. This informs the system that a person or other object is present, which can help prevent a collision between an automatic door and a pedestrian.