Photoelectric sensors achieve control by converting changes in light intensity into changes in electrical signals. A typical photoelectric sensor consists of three parts: a transmitter, a receiver, and a detection circuit. The transmitter emits a light beam towards the target; the emitted beam typically originates from a semiconductor light source, such as a light-emitting diode (LED), laser diode, or infrared emitting diode. The beam is emitted continuously or with varying pulse widths. The receiver consists of a photodiode, phototransistor, or photovoltaic cell. Optical elements such as lenses and apertures are mounted in front of the receiver. Behind the receiver is the detection circuit, which filters out the valid signal and applies it.
In addition, the structural components of a photoelectric switch also include an emitting plate and optical fibers. The triangular reflector is a robust emitting device. It consists of very small triangular pyramidal reflective material, enabling the light beam to accurately return from the reflector, which is of practical significance. It can change the emission angle within a range of 0 to 25 degrees relative to the optical axis, ensuring that the light beam originates almost from a single emission line and returns along that same reflection line after reflection.
Photoelectric sensors are sensors that use photoelectric devices as conversion elements. They can be used to detect non-electrical quantities that directly cause changes in light intensity, such as light intensity, illuminance, radiation thermometry, and gas composition analysis; they can also be used to detect other non-electrical quantities that can be converted into changes in light intensity, such as part diameter, surface roughness, strain, displacement, vibration, velocity, acceleration, and the shape and working status of objects. Examples include automatic door sensors and color mark detection.
Due to the different principles by which luminous flux affects photoelectric elements, optical measurement and control systems are diverse. Based on the nature of the output of the photoelectric element (optical measurement and control system), they can be divided into two categories: analog photoelectric sensors and pulse (switching) photoelectric sensors. Analog photoelectric sensors convert the measured quantity into a continuously changing photocurrent, exhibiting a single-valued relationship with the measured quantity. Analog photoelectric sensors can be further classified into three main categories based on the method of measuring the target object: transmission (absorption), diffuse reflection, and light-blocking (beam obstruction). Transmission type refers to the object being measured being placed in the optical path; the light energy emitted by the constant light source passes through the object, is partially absorbed, and then the transmitted light is projected onto the photoelectric element. Diffuse reflection type refers to the light emitted by the constant light source being projected onto the object, then reflected from the object's surface before being projected onto the photoelectric element. Light-blocking type refers to the situation where a portion of the luminous flux emitted by the light source is blocked by the object, causing a change in the luminous flux projected onto the photoelectric element; the degree of change depends on the position of the object in the optical path.
Features of photoelectric sensors:
Long detection range. Maintaining a detection range of over 10 meters in through-beam systems enables the use of other detection methods.
It has fewer restrictions on the objects it can detect. Because it uses the light blocking and reflection caused by the object it detects as its detection principle, unlike proximity sensors which limit the detection of objects to metal, it can detect almost all objects such as glass, plastic, wood, and liquids.
Short response time. Light itself is high-speed, and the sensor's circuitry is entirely composed of electronic components, so there is no mechanical operating time. High resolution. High resolution can be achieved by focusing the projected light beam onto a small spot through advanced design techniques or by constructing a special light-receiving optical system. It can also detect tiny objects and perform high-precision position detection. Non-contact detection is possible. Detection can be performed without mechanical contact with the object being detected, thus preventing damage to the object and the sensor. Therefore, the sensor can be used for a long time.
It enables color discrimination. The reflectivity and absorptivity of light emitted by an object vary depending on the wavelength of the emitted light and the color of the object. This property allows for the detection of the object's color. It is also easy to adjust. In types that project visible light, the beam is visible to the eye, facilitating the adjustment of the object's position.
