The bus system refers to a system mode in which a plurality of gas detectors and the like field devices share the same signal loop and a gas alarm controller, and generally adopts CANbus digital signal communication, and the following three methods are mainly used for the wiring method:
A) Tree type "T" distribution
The wiring method ensures the convenience of the installation of the bus device and facilitates the later maintenance, which is the recommended method of the bus system.
(1) Using a twisted pair cable as the bus, the nodes are connected in series, and the length of the lead line from the bus to each node should be as short as possible so that the reflected signal in the lead line has the least influence on the bus signal. Some network connections may work normally even at short distances and low speeds, but as the communication distance increases or the communication rate increases, the adverse effects will become more and more serious. The main reason is that the signals are reflected at the ends of each branch. After superimposing with the original signal, the signal quality will be degraded.
2) Attention should be paid to the continuity of the characteristic impedance of the bus, and the reflection of the signal occurs at the point where the impedance is discontinuous. This kind of discontinuity is easy to occur in the following cases: different sections of the bus use different cables, or too many transceivers on a certain bus are installed close together, and too long branch lines are led out to the bus. In summary, a single, continuous signal path should be provided as the bus.
B) "Hand in hand" wiring
This kind of wiring method perfectly guarantees the transmission of bus signals, but it is not suitable for most field installation situations from the convenience of bus equipment installation and post-maintenance. Therefore, this installation method should be determined according to the actual situation on site. C) "Star" wiring
This type of wiring is mainly for the case of installing bus devices on different floors or sub-areas. Since the star connection has an influence on the signal transmission of the bus system, the system may be unstable. Therefore, a relay isolator needs to be installed at the branch point. The isolator is used to isolate the bus devices on each branch circuit.
(1) 485 lines do not use twisted pair, or use low-end passive converter! 485 communication line can not go star-shaped connection, you must follow the standard hand-held bus mode.
(2) If the 485 trace is not standardized or exceeds the communication range, there will be a phenomenon that the communication is not on or sometimes the communication is not on the communication.
(3) 485 transmission is the differential mode transmission mode. Only 485+ and 485- are twisted pairs, which can make the 485 transmission mode suffer the least interference, the transmission is the farthest, and the transmission quality is the best. Some contractors do not use twisted pair cables, which makes the interference very large. Some engineers mistakenly think that the transmission quality of the line will be better, the twisted pair will be synthesized, and the other twisted pair will be combined. This is counterproductive. Greatly reduced communication quality.
USB Cable :1.Type A: almost every USB cable has a standard flat rectangular interface at one end. Most computers have a usb-a port to connect to only one USB port.
2.Type-B: almost square connector for printers and other active devices connected to computers. They are not common now because most devices have been moved to smaller connections.
3.Mini USB: a smaller connector type that was standard for mobile devices before micro USB. It's not common today, but you'll see it on some cameras, PlayStation 3 controllers, MP3 players, etc.
4.Micro USB: the current standard for mobile and portable devices, even smaller than Mini USB. Although you can still find micro USB on smartphones, tablets, USB battery packs and game controllers, some have turned to usb-c
5.Type-C: the latest USB standard, which is a reversible cable, promises higher transmission speed and higher power than previous USB types. It can also take into account a variety of functions.
USB Cable
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