More about Photoelectric Sensors

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Photoelectric sensors are devices that respond to changes in light and generate an output signal based on these responses. Typically, the incoming light is generated by an emitter, and the sensor is aligned so that any obstruction of the light will trigger a change in its output signal. Lasers and light-emitting diodes are frequently employed as the light source in a photoelectric sensor system. Sensors are also calibrated to the emitter in order to minimize interference or confusion caused by environmental conditions; modulation of the light source also reduces potential problems caused by ambient light.

Although there are a wide variety of sensors available, operationally they function based on one of two principles: beam interruption and beam reflection. Those responding to interruptions in a beam will trigger when an object blocks or partially blocks an incoming beam from hitting the sensor. Photoelectric devices that respond to beam reflection have an emitter positioned with the sensor; when the emitted light hits a nearby object, it is reflected back to the sensor, generating a signal. The degree of detected light can also be used to determine the position of the nearby object.

Sensor units in a photoelectric device are generally photoconductive cells, photovoltaic cells or phototransistors. Photoconductive cells are essentially resistors that become less effective as light increases, so that a bright light will allow more electricity to pass through it. Photovoltaic cells actually generate electricity when struck by light, and the intensity of their output varies based on the intensity of incoming light. In a phototransistor, the flow of electric current changes based on the level of light entering the device.

Photoelectric sensors find use in a wide range of automated manufacturing operations, as they signal system status to control units. They can be used to inspect the quality of products, to count and log items on a conveyor, to signal system problems, and for a variety of other automation operations.