Classification and Working Principle of Photoelectric Switch

Photoelectric switch is classified according to the detection method
The following is an example to introduce the classification method of photoelectric switches:
According to the detection method, it can be divided into three types: reflection type, through-beam type and mirror reflection type. The through-beam detection has a long distance and can detect the density (transparency) of translucent objects. The reflective working distance is limited to near the intersection of the beams to avoid background effects. The mirror reflection type has a long reflection distance, which is suitable for long-distance detection, and can also detect transparent or translucent objects.
Photoelectric switch is classified by structure
According to the structure, the photoelectric switch can be divided into three types: amplifier separation type, amplifier built-in type and power supply built-in type.

Omron Transmissive Photoelectric Sensor EE-SX3070

1) The amplifier separation type is to separate the amplifier from the sensor, and it is made by application-specific integrated circuit and hybrid installation process. Since the sensor has the characteristics of ultra-small size and variety, the function of the amplifier is more. Therefore, this type adopts the terminal block connection method, and can be used for both AC and DC power supplies. It has on-off and off-delay functions, can be set to switch between light and sound, can control 6 output states, and has two output modes of contact and level.
2) The amplifier built-in type integrates the amplifier and the sensor, is made of an application-specific integrated circuit and surface mount technology, and works with a DC power supply. Its response speed range (0.1ms and 1ms) can detect narrow and high-speed moving objects. Changing the polarity of the power supply can switch between bright and dark, and can set the self-diagnosis stable working area indicator light. It has two output modes of voltage and current, which can prevent mutual interference and is very convenient in system installation.
3) The type with built-in power supply integrates the amplifier, sensor and power supply device, and is made by application-specific integrated circuit and surface mount technology. It generally uses AC power, suitable for replacing contact travel switches at the production site, and can be directly used in strong current control circuits. You can also set the self-diagnosis stable work area indicator light by yourself. The output is equipped with SSR solid state relay or relay normally open and normally closed contacts to prevent mutual interference and can be tightly installed in the system.

Diffuse reflection photoelectric switch PNP, NPN normally open

Photoelectric switch working principle
After the modulated pulse generated by the oscillating circuit passes through the reflection circuit, the light pulse is radiated by the light emitting tube GL. When the measured object enters the range of the light receiver, the reflected light pulse enters the phototransistor DU. In the receiving circuit, the optical pulse is demodulated into an electrical pulse signal, and then amplified by an amplifier and shaped synchronously by gating, and then digital integration or RC integration is used to eliminate interference. Finally, after a delay (or no delay), the driver is triggered to output a photoelectric switch control signal.
Photoelectric switches generally have good hysteresis characteristics, so even if the detected object shakes in a small range, it will not affect the output state of the driver, so that it can be kept in a stable working area. At the same time, the self-diagnosis system can also display the light-receiving state and stable working area to monitor the work of the photoelectric switch at any time.

Omron photoelectric switch EE-SX3157-P1

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