Home ยป Operating principles for photoelectric sensors
Operating principles for photoelectric sensors
These sensors use light sensitive elements to detect objects and are made up of an emitter (light source) and a receiver. Four types of photoelectric sensors are available.

Photoelectric sensor

Direct Reflection (Diffused) - emitter and receiver are housed together and use the light reflected directly off the object for detection. In the use of these photocells, it is important to bear in mind the color and the type of surface of the object. With opaque surfaces, the sensing distance is affected by the color of the object. Light colors correspond to the maximum distances and vice versa. In the case of shiny objects, the effect of the surface is more important than the color. The sensing distance in the technical data is related to matte white paper.

Reflection with Reflector (Retroreflective) - emitter and receiver are housed together and requires a reflector. An object is detected when it interrupts the light beam between the sensor and reflector. These photocells allow longer sensing distances, as the rays emitted are almost totally reflected towards the receiver.

Polarized Reflection with Reflector - similar to Reflection with Reflector, these photocells use an anti-reflex device. The use of such a device, which bases its functioning on a polarized band of light, offers considerable advantages and secure readings even when the object to be sensed has a very shiny surface. They are not in the technical data affected by random reflections.

Thru Beam - emitter and receiver are housed separately and detect an object when it interrupts the light beam between the emitter and receiver. These photocells allow for the longest distances.


Light On / Dark On Types Of Output: For the photocell, the same terminology as inductive and capacitive sensors is used: NO = normally open, NC = normally closed. This refers to the state of the unit in the absence of the product to be sensed. In the case of photocells, light on / dark on is used. In the case of the direct reflection types, NO is light on and NC is dark on. For the other types, NO is dark on and NC is light on.

Sensing Distance (Sn): The space in which it is possible to sense an object. In the case of direct reflection types, it is the maxi-mum distance between the photocell and the object. In the case of reflector or barrier types, it is the distance between the unit and the reflector or between units.

Power Supply: The supply voltage range that sensor will operate at.

Power On Delay: This is the time lapse between providing power and the operation of the output. This is to avoid unwanted switching when the unit is powered.

Power Drain: The amount of current required to operate a sensor.

Voltage Drop: The voltage drop across a sensor when driving the maximum load.

Switching Current (Max): The amount of continuous current allowed to flow through the sensor without causing damage to the sensor. It is given as a maximum value.

Short Circuit Protection: Protection against damage to a sensor if the load becomes shorted.

Operating Frequency: The maximum number of on/off cycles that the device is capable of in one second. According to EN 50010.

Light Immunity: The maximum limit of an incandescent light or sunlight. Beyond this limit, the photocell may not work correctly due to interference on the receiver.

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