Optocoupler (referred to as optocoupler) is a semiconductor optoelectronic device that encapsulates light-emitting elements and photosensitive elements in the same housing, and transmits electrical signals through the conversion of electricity → light → electricity. According to different requirements, optocouplers can be combined into many series of optocouplers by combining different types of light-emitting elements and photosensitive elements. At present, the most widely used photocoupler is a combination of light-emitting diodes and phototransistors.
Optocouplers use optical signals as the medium to realize the coupling and transmission of electrical signals. The input and output are completely isolated electrically, and have the characteristics of strong anti-interference performance. For the industrial application measurement and control system including both the weak current control part and the strong current control part, the use of optocoupler isolation can well realize the isolation of weak current and strong current and achieve the purpose of anti-interference. However, the use of optocoupler isolation needs to consider the following issues:
① When the optocoupler is directly used to isolate and transmit analog quantities, the nonlinear problem of the optocoupler should be considered;
② When the optocoupler isolates and transmits digital quantities, the response speed of the optocoupler should be considered;
③ If the output has power requirements, the power interface design of the optocoupler must also be considered.
According to shielding, twisted pair can be divided into unshielded twisted pair (UTP: Unshilded Twisted Pair) and shielded twisted pair (STP: Shielded Twisted Pair).
fiber optic coupler
Shielded twisted pair
According to different shielding methods, shielded twisted pair cables are divided into two types, namely STP (Shielded Twicted-Pair) and FTP (Foil Twisted-Pair). STP refers to a shielded twisted pair with each line having its own shielding layer, while FTP is a shielded twisted pair that uses overall shielding. It should be noted that the shielding is only provided on the entire cable with a shielding device, and both ends are properly grounded. case works. Therefore, the entire system is required to be shielded devices, including cables, sockets, crystal plugs and distribution frames, etc. At the same time, the building needs to have a good grounding system.
The outer layer of the shielded twisted-pair cable is wrapped with aluminum to reduce radiation, but it cannot completely eliminate radiation. Shielded twisted-pair cables are relatively expensive and more difficult to install than unshielded twisted-pair cables. Similar to coaxial cable, it must be equipped with special connectors and corresponding installation techniques that support the shielding function. But it has a higher transmission rate, which can reach 155Mbps within 100 meters.
Unshielded twisted pair
Unshielded twisted pair cables are made up of twisted pairs and a plastic sheath. The International Electrical Industries Association defines five different quality classes for twisted-pair cables.
Commonly used in computer networks are the third and fifth categories and super five and the current six types of unshielded twisted pair cables. The third type of twisted pair is suitable for most computer local area networks, while the fifth and sixth types of twisted pair use increased winding density and high-quality materials to greatly improve the properties of the transmission medium.
According to the electrical performance, the twisted pair can be divided into: Category 1, Category 2, Category 3, Category 4, Category 5, Category 5e, Category 6, Category 6, Category 7, a total of 9 twisted pair types. The larger the type number, the newer the version, the more advanced the technology, the wider the bandwidth, and of course the more expensive the price. These different types of twisted pair marking methods are stipulated in this way: if it is a standard type, it will be marked as "catx", such as the commonly used category 5 line, then it will be marked as "cat5" on the outer sheath of the line, and the letters are usually lowercase , rather than capitalized. And if it is an improved version, it will be marked as "xe", such as the super category 5 line, it will be marked as "5e", and the same letter is lowercase, not uppercase.
Twisted pair technical standards are formulated by the American Telecommunications Industry Association (TIA), and its standard is EIA/TIA-568B, as follows.
Category 1 (Category 1) line
It is the most original unshielded twisted pair copper cable in the ANSI/EIA/TIA-568A standard, but its original purpose of development was not for computer network data communication, but for telephone voice communication.
Category 2 (Category 2) line
It is the first unshielded twisted pair cable that can be used for computer network data transmission in ANSI/EIA/TIA-568A and ISO Class 2/Class A standards. The transmission frequency is 1MHz and the transmission rate is 4Mb/s. It is mainly used in old Token Web.
Category 3 (Category3) line
It is an unshielded twisted pair cable specially used for l0BASE-T Ethernet in ANSI/EIA/TIA-568A and ISO Class 3/B standards, with a transmission frequency of 16MHz and a transmission rate of up to 10Mb/s.
Category 4 (Category 4) line
It is an unshielded twisted pair cable used in Token Ring network in ANSI/EIA/TIA-568A and ISO Category 4/Class C standards, with a transmission frequency of 20MHz and a transmission rate of 16Mb/s. Mainly used for token-based LAN and 10BASE-T/100BASE-T.
Category 5 (Category 5) line
It is an unshielded twisted pair cable used to run CDDI (CDDI is an FDDI network based on twisted pair copper wire) and Fast Ethernet in ANSI/EIA/TIA-568A and ISO Category 5/Class D standards, with a transmission frequency of 100MHz, The transfer rate reaches l00Mb/s.
Category excess 5 (Category excess 5) line
It is an unshielded twisted pair cable used to run Fast Ethernet in ANSI/EIA/TIA-568B.1 and ISO Category 5/Class D standards. The transmission frequency is also 100MHz, and the transmission rate can also reach 100Mb/s. Compared with Category 5 cables, Category 5e has greatly improved the four main indicators of near-end crosstalk, crosstalk sum, attenuation and signal-to-noise ratio.
Category 6 (Category 6) line
It is an unshielded twisted pair cable specified in ANSI/EIA/TIA-568B.2 and ISO Category 6/Class E standards. It is mainly used in Fast Ethernet and Gigabit Ethernet. Because its transmission frequency can reach 200-250MHz, which is twice the bandwidth of Super Category 5, and the maximum rate can reach 1000Mb/s, which meets the needs of Gigabit Ethernet.
Category excess 6 (Category excess 6) line
It is an improved version of Category 6 cable, and it is also an unshielded twisted-pair cable specified in ANSI/EIA/TIA-568B.2 and ISO Category 6/Class E standards, and is mainly used in Gigabit networks. In terms of transmission frequency, it is the same as Category 6 line, which is also 200-250MHz, and the maximum transmission rate can reach 1 000Mb/s, but there is a great improvement in crosstalk, attenuation and signal-to-noise ratio.
Category 7 (Category 7) line
It is the latest twisted pair in the ISO Category 7/F class standard, mainly to adapt to the application and development of 10 Gigabit Ethernet technology. But it is no longer an unshielded twisted pair, but a shielded twisted pair, so its transmission frequency can reach at least 500MHz, which is more than twice that of Category 6 and Super Category 6 cables. Up to 10Gb/s.
