I. Photoelectric Switch
A photoelectric switch, short for photoelectric proximity switch, detects the presence or absence of an object by utilizing its ability to block or reflect light. A synchronous circuit activates the circuit, activating the switch. The object is not limited to metal; any object that reflects light (or blocks light) can be detected. The photoelectric switch converts the input current into a light signal at the transmitter, which is then emitted. The receiver detects the target object based on the intensity or presence of the received light. Common applications in security systems include photoelectric smoke detectors, and in industry, they are frequently used to count the number of movements of robotic arms.
Because the output and input circuits of a photoelectric switch are electrically isolated (i.e., electrically insulated), it can be used in many applications. A new generation of photoelectric switches, manufactured using integrated circuit technology and SMT surface mount technology, features intelligent functions such as delay, pulse width expansion, external synchronization, anti-interference, high reliability, stable operating range, and self-diagnosis. This novel photoelectric switch is an active photoelectric detection system electronic switch using pulse modulation. It utilizes cold light sources such as infrared, red, green, and blue light, enabling non-contact, non-destructive, rapid control of the state and actions of various substances, including solids, liquids, transparent bodies, black bodies, soft bodies, and smoke. It boasts advantages such as small size, multiple functions, long lifespan, high precision, fast response speed, long detection distance, and strong resistance to light, electrical, and magnetic interference.
II. Working Principle of Photoelectric Switch
The modulation pulse generated by the oscillation circuit is reflected by the reflection circuit, and then interference is eliminated by a digital integrating photoelectric switch or RC integration method. Finally, the photoelectric switch control signal is output by the driver after a delay (or no delay).
Using optical elements, a light beam is altered in the middle of a propagation medium; the beam is used to reflect objects; and the emitted beam returns instantaneously after traveling a long distance. A photoelectric switch consists of three parts: a transmitter, a receiver, and a detection circuit. The transmitter aims at the target and emits a light beam, typically from a light-emitting diode (LED) or laser diode. The beam is emitted continuously or with varying pulse widths. The intensity of the pulse-modulated beam is selected multiple times during emission, ensuring it travels continuously towards the target. The receiver consists of a photodiode or phototransistor. Optical elements such as lenses and apertures are mounted in front of the receiver. Behind it is the detection circuit, which filters out the valid signal and applies it.
An optocoupler is an electro-optical-electrical conversion device that uses light as a medium to transmit electrical signals. It consists of two parts: a light source and a light receiver. The light source and receiver are assembled in the same sealed housing, isolated from each other by a transparent insulator. The pins of the light source are the input terminals, and the pins of the light receiver are the output terminals. Common light sources are light-emitting diodes (LEDs), and common light receivers are photodiodes, phototransistors, etc. There are many types of optocouplers, including photodiode type, phototransistor type, photoresistor type, photothyristor type, photodarlington type, and integrated circuit type. The working principle is as follows: Applying an electrical signal to the input terminal of the optocoupler causes the light source to emit light. The intensity of the light depends on the magnitude of the excitation current. When this light shines on the packaged light receiver, a photocurrent is generated due to the photoelectric effect, which is led out from the output terminal of the light receiver, thus realizing the electro-optical-electrical conversion.
The modulated pulse generated by the oscillation circuit is reflected by the light-emitting diode GL and then emitted as a light pulse. When the object being measured enters the effective range of the photodetector, the reflected light pulse enters the phototransistor DU. The photoelectric switch demodulates the light pulse into an electrical pulse signal in the receiving circuit, which is then amplified and synchronously gated and shaped. Interference is then eliminated using digital integration or RC integration, and finally, the photoelectric switch control signal is output by the driver after a delay (or no delay). Photoelectric switches generally have good hysteresis characteristics, so even if the object being measured moves within a small range, it will not affect the output state of the driver, thus keeping it in a stable operating range. At the same time, the self-diagnostic system can also display the light receiving status and stable operating range to monitor the operation of the photoelectric switch at any time.
