A photoelectric sensor, or photo eye, 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 different functional types: opposed,
retro-reflective, and proximity-sensing. Types
A self-contained photoelectric sensor contains the optics, along with the
electronics. It 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 remote sensing 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, itself, to be very small. Also, the controls for the sensor
are more 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. Sensing modes
A through beam arrangement consists of a receiver located within the
line-of-sight of the transmitter. In this mode, an object is detected when
the light beam is blocked from getting to the receiver from the transmitter.
A retroreflective arrangement places the transmitter and receiver at the same
location and uses a reflector to bounce the light beam back from the transmitter
to the receiver. An object is sensed when the beam is interrupted and fails
to reach the receiver. A proximity-sensing arrangement is one
in which the transmitted radiation must reflect off the object in order to reach
the receiver. In this mode, an object is detected when the receiver sees the
transmitted source rather than when it fails to see it. As in retro-reflective
sensors, diffuse sensor emitters and receivers are located in the same
housing. But the target acts as the reflector, so that detection of light is
reflected off the disturbance object. The emitter sends out a beam of light
that diffuses in all directions, filling a detection area. The target then enters
the area and deflects part of the beam back to the receiver. Detection occurs
and output is turned on or off when sufficient light falls on the receiver.
Some photo eyes have two different operational types, light operate and
dark operate. Light operate photo eyes become operational when the receiver
"receives" the transmitter signal. Dark operate photo eyes become operational
when the receiver "does not receive" the transmitter signal.
The detecting range of a photoelectric sensor is its "field of view", or the
maximum distance from which the sensor can retrieve information, minus the
minimum distance. A minimum detectable object is the smallest object the sensor
can detect. More accurate sensors can often have minimum detectable objects of
minuscule size. = Difference Between Modes=
See also List of sensors
Photodetector Sensor
References Mounting Brackets & Components for
Photoelectric/Automation Sensors, 2010, SoftNoze USA Inc, Frankfort, NY USA
Guide to Sensing, 2002, Banner Engineering Corporation, P/N 120236
ansducers_DetectorsPhotoelectric_Sensors