I. Characteristics of Photoelectric Switches
1. Common contact-type limit switches not only have poor operating speed and low accuracy, but also easily damage their internal structure when detecting objects, resulting in a shortened lifespan. While transistor proximity switches are not very stable and cannot directly detect non-metallic materials, photoelectric switches overcome all these shortcomings. Furthermore, photoelectric switches are small in size, convenient for transportation, and offer excellent object detection with a long service life.
2. Photoelectric switches detect objects by sensing the speed of light, and are considered a type of sensor. They convert changes in the intensity of light at the output and input terminals into varying current strengths, thereby detecting objects. However, the transmitting and receiving circuits of a photoelectric switch are electrically isolated, allowing it to be used in various applications.
3. The biggest feature of photoelectric switches is that they process changes in the speed of light and, through internal components and the action of a medium, reflect the light beam back to the object being detected.
4. New photoelectric components manufactured using modern circuit technology and SMT surface mount technology offer numerous intelligent features compared to traditional switches, such as extended response time, resistance to mutual interference, high security, and self-diagnosis. Furthermore, these photoelectric switches utilize pulse modulation technology, creating highly proactive photoelectric detection switches. By employing different cold light sources, they enable rapid identification of objects and control of objects in various states.
II. Application Methods of Photoelectric Switches
1: Fluctuations in input power supply voltage
For DC input, attention should also be paid to its fluctuation value, which is usually allowed to be ±10%.
2: Wiring
Proper wiring is essential, and cables should be used within specified lengths under certain conditions. While noise reduction is often a primary consideration in wiring, it is also important to ensure safety by isolating them from power lines. High-voltage lines, power lines, and photoelectric sensors should not be placed in the same conduit or cable tray, as this can cause (sometimes) malfunctions or damage to photoelectric switches due to induction. Therefore, they should be wired separately in principle.
3: Response time
Choose a photoelectric switch with sufficient response speed based on the size and speed of the object being measured. In addition, for through-beam switches, since the thickness of the beam affects the detection, the time for blocking the entire beam must be calculated in advance.
4: Sensitivity
Regarding the setting distance, in harsh environments, when using through-beams, a margin of at least 4 times must be left, and when using reflective beams, a margin of at least 1.5 to 2 times must be left.
5: Protective Measures
Typically, DC-powered photoelectric switches have reverse polarity protection, while AC switches do not require polarity protection.
DC-powered photoelectric switches with transistor outputs all have overcurrent and short-circuit protection. The protection methods include intermittent and self-locking types, each with its own characteristics. Intermittent protection activates at the critical point of maximum output current, and the load current must be controlled within the rated output current of the photoelectric switch during use. Self-locking protection, after overload or short-circuit events, will result in no output after the protection circuit is activated, requiring power interruption and re-energization to restore normal operation.
For contactless output protection, the collector of the freewheeling transistor is typically used. However, if there is a high-power inductive load, it is best to use an external surge protection circuit.
6: Vibration and Impact Resistance
If the vibration is 0-2000 times/minute and the re-vibration width is about 2mm, it has little impact on general photoelectric switches. However, for those using incandescent lamps as the light source, a vibration-resistant equipment structure is required.
7: Interference light
Due to variations in the light source and modulation of photoelectric switches, their resistance to interference light differs. Typically, infrared photoelectric switches resist 3,000 Lux of ambient light from incandescent bulbs and 10,000 Lux from sunlight. However, in direct sunlight, which contains infrared wavelengths, optical filters alone are insufficient to improve interference resistance. Teopto photoelectric products offer 100,000 Lux resistance specifically designed for strong ambient light. For direct current light types, direct exposure to ambient light should be avoided as much as possible. Due to ambient light interference, fine-tuning of the sensitivity is necessary to meet practical application requirements. When the angle between the photoelectric switch (receiver)'s optical axis and the strong light source cannot be changed, a light-shielding plate or a long light-shielding tube can be installed around the top of the photoelectric switch.
