Photoelectric Sensors

Photoelectric presence sensors utilize photoelectric emitters and receivers to detect presence, absence, or distance of target objects. They can be categorized into three main categories, through beam, retroreflective, and proximity.  Through beam photoelectric sensors are configured with the emitter and detector opposite the path of the target and sense presence when the beam is broken.  Retroreflective photoelectric sensors are configured with the emitter and detector in the same housing and rely on a reflector to bounce the beam back across the path of the target. This type may be polarized to minimize false reflections.  Proximity photoelectric sensors have the emitter and detector in the same housing and rely upon reflection from the surface of the target. This mode can include presence sensing and distance measurement via analog output. The proximity category can be further broken down into five sub-modes: diffuse, divergent, convergent, fixed-field and adjustable field.  With a diffuse sensor presence is detected when any portion of the diffuse reflected signal bounces back from the detected object.  Divergent beam sensors are short-range diffuse-type sensors without any collimating lenses.   Convergent, fixed focus, or fixed distance optics (such as lenses) are used to focus the emitter beam at a fixed distance from the sensor.  Fixed-field sensors are designed to have a distance limit beyond which they will not detect objects, no matter how reflective.  Adjustable field sensors utilize a cutoff distance beyond which a target will not be detected, even if it is more reflective than the target.  Some photoelectric sensors can be set for multiple different optical sensing modes.  Reflective properties of the target and environment are important considerations in the choice and use of photoelectric sensors.

Important parameters to consider when looking for photoelectric sensors include sensing mode, detecting range, position measurement window, minimum detectable object, and response time.  Sensing modes can be presence or absence and position measurement.  With a presence or absence sensor, the sensor detects presence or absence in an on/off mode.  In a position measurement sensing mode the sensor can detect position in a linear region by the intensity of reflected light.  Analog output is linear with position in the measurement range.  The detecting range is the range of sensor detection.  For presence sensors, this goes up to the maximum distance for which the signal is stable.  For position measurement sensors, this is the distance range over which the position vs. output response is linear and stable.  The position measurement window is the width of linear region for the sensor.  For example, if the sensor could measure between 14 and 24 cm, this window would be 10 cm.  The minimum detectable object is the smallest sized object detectable by the sensor.  The response time is the time from target object entering detection zone to the production of the detection signal.

Common configuration features for photoelectric sensors include beam visibility, light-on or dark-on modes, light and dark programmability, adjustable sensitivity, self-teaching, laser source, fiber optic glass, and fiber optic plastic.  The body style of the sensor can be threaded barrel, cylindrical, limit switch, rectangular, slot, ring, and window or frame.  The sensor may be self-contained and may have a remote head.

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Part Numbers for Photoelectric Sensors