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 .
