Video optical transceivers, especially those used as front-end equipment, are usually installed in outdoor equipment boxes. The on-site environment is rather harsh and lightning protection is extremely important. The pros and cons of lightning protection measures directly determine the probability of faults in optical transceivers. The destruction modes of lightning are mainly divided into three forms: direct lightning, inductive lightning, and ground potential counter-attack. For video optical transceivers, the most important one is the ground potential counterattack.
The so-called ground potential counterattack is when lightning receptors and other lightning receptors will directly strike thunder and powerful lightning currents through the down conductor and the grounding body leaks into the earth. When the down conductor, the grounding body and the metal object connected to it will generate a very high moment Voltage, this high voltage will produce a huge potential difference between electronic objects such as metal objects and cables that are close to them but not in direct contact. The electric shock caused by this potential difference is the ground potential counterattack.
Ground potential counterattack is caused by the following forms of damage to the optical transceiver: When the lightning current leaks into the earth, the ground potential of the grounding network will be raised to tens or hundreds of thousands of volts within a few microseconds. Highly damaging lightning currents will flow from the grounded parts of various devices to these devices, or through the ground insulation to flow to other nearby equipment, eventually causing damage or damage to the equipment. The main damages are: PCB board of chassis power supply On the electronic components, video interface chip and its related electronic components, audio and data port chip.
Although the forms of destruction of lightning are various, it is still possible to reduce the chance of faults in optical transceivers by adopting scientific protective measures. First of all, ensuring that the grounding device works well is a prerequisite for lightning protection because all the induced currents are eventually discharged into the earth. In general, the smaller the grounding resistance is, the better the leakage effect is. Generally, it is better to control the grounding resistance within 4 ohms. You can use the grounding clamp to measure the grounding resistance.
For some areas where the soil resistivity is high, it may be considered to add a resistance-reducing agent to the soil to reduce the grounding resistance. Secondly, front-end equipment must be equipped with a surge protector. When the voltage is normal, the surge protector is in a high-impedance state, with only a small leakage current, and the power loss is very small. When overvoltage occurs in the line, the surge protector is In the low-resistance state, overvoltage flows through the surge protector into the ground in the form of a discharge current, and the overvoltage is suppressed. After the surge voltage is over, the surge protector is in a high-impedance insulation state when the line voltage returns to normal. The protector must have a good grounding device to match it.
The front camera's video signal output port and the transmitter's video input port are connected with a surge protector. If the transmitter is connected with some other data lines, it is necessary to install data lightning protection devices at the beginning and end of the control signal line. In addition, lightning protection devices such as power surge protectors are also applied to the power input terminals of cameras and optical transceivers. When installing the lightning protection device, make sure that the lightning protection device is close to the access port. If the lightning protection device is too far from the video port and the data port, the lightning protection effect cannot be achieved.
After adding lightning protection equipment, all that remains is the design of the grounding grid. Grounding piles must be put in place to ensure that the optical transceiver is well grounded. A good low impedance grounding network design can ensure the lightning protection equipment in the system to play a good effect and can effectively balance the voltage across the entire transmission system to prevent the ground potential difference in the line. Equipment interference, but also can effectively prevent the ground potential counterattack damage to the equipment.
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