A photoelectric sensor, or photoeye, is a device used to detect the distance, absence, or presence of
an object by using a light transmitter (often infrared) and a photoelectric receiver. They are used
extensively in industrial manufacturing. There are three functional types: opposed (a.k.a.
through-beam), retroreflective, and proximity-sensing.
A self-contained photoelectric sensor contains optics and electronics and requires only a power source.
The sensor performs its own modulation, demodulation, amplification, and output switching. Some
self-contained sensors provide such options as built-in control timers or counters. Because of
technological progress, self-contained photoelectric sensors have become increasingly smaller.
Remote photoelectric sensors, used for sensing over long distances or in hard-to-reach places, contain
only the optical components of a sensor. The circuitry for power input, amplification, and output
switching are located elsewhere, typically in a control panel. This allows the sensor to be very small
and the controls to be accessible, since they may be bigger.
When space is restricted or the environment too hostile even for remote sensors, fiber optics may be
used. Fiber optics are passive mechanical sensing components. They may be used with either remote or
self-contained sensors. They have no electrical circuitry and no moving parts and can safely pipe
light into and out of hostile environments.
