1.485 bus, what kind of communication should be used line? A number of bus devices can be attached?
RVSP shielded twisted pair must be used. Shielded twisted pair used for specification, communication lines with the 485 distance and the number of devices attached on the following table. Shielded twisted pair helps reduce and eliminate the two 485 lines and the distributed capacitance between the communication lines from around the resulting common-mode interference. The number of communication lines from the device communication standard 1-400m 1 - 32 units 0.5mm2 400-800m 1 - 16 units 0.5mm2 400-800m 17 - 32 units 0.75mm2 800-1200m 1 - 8 units 0.5mm2 800-1200m 9 - 21 units 0.75mm2 800-1200m 22 - 32 sets 1.0mm2 Contractors used by most cable or over Category 5 cable Category 5 as the 485 line, which is wrong. This is because: (1) does not shield ordinary network cable, can not prevent common mode interference. (2) cable is only 0.2mm square feet, the diameter is too small will result in reduced distance and reduced equipment can be attached. (3) network as the single strand of copper wire, compared to multi-core wire in terms of easy to break.
2. Why Ground
485 transceiver provides the common mode voltage between-7V to +12 V when to work properly. If you exceed this range will affect the communication, a serious damage to the communication interface. Common mode interference will increase the common mode voltage. Eliminate common mode interference is an effective means of communication line 485 as a ground shield, the equipment, computers and other network devices connected together, reliable access to the earth by one o'clock.
3. Electric Lock and controller / reader can use the same total power to the electricity?
Can not. Electric lock does not move in the case, SKPS ripple voltage is only 40-50mV; Once the action, that is, electronically controlled lock in opening and closing, the ripple voltage to rise to 100mV-300mV, the ripple will be passed to line into the controller and the reader, resulting in communications chips and CPU heat, resulting in communication instability, severe burn will chip. And electric power and power locks moment, electric control lock inside the coil, will produce a high charge and discharge pulse 850mA, if the electronic control both ends of the lock if there is no parallel diodes, the ripple signal will pass controller and card reader. A controller, and it recommended that all readers share the following mount a SKPS power; the controller electronically controlled lock each of the following each use a separate SKPS power.
4.485 lines of communication should be how to take the line?
Communication line as far as possible away from power lines, not parallel with the power cord, but not tied together.
5. Why are 485 structures to be used hand in hand, and not with star-shaped structure?
Star structure will produce the reflected signal, which affects 485. Bus to each terminal equipment branch line length should be short, usually not to exceed 5 meters. If you do not take the branch line of the terminal, there will be reflected signal, generated a strong interference on the communications, it should be removed. Access control system, there are two places applied to the 485 bus. First, mount the controller computer to the following, the second is mounted below the 485 controller to the reader.
6.485 device to device on the bus between the contacts can it?
In the same network, using the same cable, to minimize the contact lines. Contact Office to ensure a good weld, closely packed, to avoid loosening and oxidation. Ensure a single, continuous signal path as buses.
7. What is common mode and differential mode interference interference? How to eliminate the interference of the communication line?
485 line consists of two twisted-pair line formed by two lines of communication which is the voltage difference between the way to pass the signal, so called differential voltage transmission. Differential mode interference in transmission between two signal lines, belonging to the symmetry interference. Differential mode interference elimination method is to add a partial value of the circuit resistance, and a twisted pair; common mode interference is between the signal line and ground transport, a non-symmetric interference. Eliminate common mode interference include: (1) using shielded twisted pair and the effective ground (2) strong electric field of the areas we consider using galvanized pipe shield (3) away from the high voltage wiring, not to the high voltage power lines and alignment signal lines tied together (4) Do not share the same electric lock power supply (5), linear power supply or high-quality switching power supply (ripple disturbance is less than 50mV)
8. 485 under what circumstances to increase the termination resistors on the bus?
Under normal circumstances no additional termination resistors, only 485 more than 300 meters away from the case, to 485 the beginning of the end terminal resistance increases and the end client. In particular the 485 bus when there are fewer number of devices. When large number of devices (such as more than 22 units). Generally do not need to increase the terminal resistance, because the termination resistor will reduce the load capacity of 485. When the need to increase the termination resistors, as long as the controller above can set the terminal resistors jumper, if the other end is connected to the computer, then the converter 485 while the brown and white short-circuit.
9. How to extend the communication distance of 485
Specification is one of 485 network length of 1.2 km, 32 nodes. If you exceed this limit, then the hub must be used to expand the network of 485 distance or number of nodes. Using 485 hubs, 485 network can be divided into a large number of segments. Like the hub 485 between segments 485 "bridge." Of course, each segment 485, or follow the above specifications, the 1.2 km length and 32 nodes. Extend the network distance by 485 Hub Icon: the use of 485 485 fork hub to solve the problem, as shown: the use of the hub structure 485 Star 485 485 485 repeater hub is the Extension of the Concepts It not only solved the problem of multiple bifurcation, but also solve the problem of isolation between network segments, one segment that is a problem (such as short circuit, etc.), and will not affect other network segment, thereby greatly enhancing the large-scale network security and stability. We can see from the LAN to the star from the bus-based development process, to appreciate the star wiring network to our benefits. Likewise, the composition of the star hub 485 485 485 Network will also be a direction of network development.