A photoelectric sensor is a sensor device that detects light signals and converts them into electrical signals. It can be used to detect non-electrical quantities that directly cause changes in light intensity, such as light strength, illuminance, radiation thermometry, and gas composition analysis; it can also be used to detect non-electrical quantities that can be indirectly converted into changes in light intensity, such as part diameter, surface roughness, strain, and displacement. Due to its high performance, fast response, and non-contact nature, photoelectric sensors have important applications in industrial automation devices and robotics. In particular, the emergence of image sensors in recent years has opened a new chapter for the further development of photoelectric sensors.
Working principle of photoelectric sensors
A photoelectric sensor mainly consists of three parts: a transmitter, a receiver, and a detection circuit. The transmitter is used to align the light beam emitted by a semiconductor light source, light-emitting diode, laser diode, infrared emitting diode, etc. The receiver can be a photodiode, phototransistor, or photovoltaic cell, etc. Optical elements such as lenses and apertures are mounted in front of the receiver, primarily used to receive the target light beam and convert the received optical signal into an electrical signal. The detection circuit detects the received electrical signal, filters out the valid signal, and transmits it to the next module for practical application.
Classification of photoelectric sensors
(1) Slot-type photoelectric sensor
A slotted photoelectric switch consists of a light emitter and a receiver mounted face-to-face on opposite sides of a slot. The emitter emits infrared or visible light, which the receiver can pick up when there is no obstruction. However, when an object passes through the slot, the light is blocked, triggering the photoelectric switch. It outputs a control signal to cut off or connect the load current, thus completing a control action. The detection distance of a slotted switch is typically only a few centimeters due to the limitations of its overall structure.
(2) Through-beam photoelectric sensor
Separating the emitter and receiver increases the detection distance. A photoelectric switch consisting of one emitter and one receiver is called a through-beam photoelectric switch, or simply a through-beam photoelectric switch. Its detection distance can reach several meters or even tens of meters. In use, the emitter and receiver are installed on opposite sides of the path of the object being detected. When the object passes by and blocks the light path, the receiver activates and outputs a switch control signal.
(3) Reflector type photoelectric switch
A photoelectric switch that integrates the emitter and receiver into a single device, with a reflector mounted in front of it, and utilizes the principle of reflection to achieve photoelectric control, is called a reflector-type (or mirror-type) photoelectric switch. Under normal circumstances, the light emitted by the emitter is reflected back by the reflector and received by the receiver; however, if the light path is blocked by an object being detected, and the receiver cannot receive light, the photoelectric switch activates, outputting a switch control signal.
(4) Diffuse-reflective photoelectric switch
Its detection head also contains a light emitter and a light receiver, but there is no reflector in front. Under normal circumstances, the light emitted by the light emitter cannot be detected by the light receiver. When the object being detected passes by, it blocks the light and reflects part of the light back, and the light receiver receives the light signal and outputs a switching signal.
For more information, please follow the Sensor Channel.
