How to choose 485 communication cable, what kind of line is 485 line

The impedance of RVVP and RVSP is mismatched, and the attenuation is large, which is not suitable for RS485 high-speed and long-term transmission.

Use a dedicated 485 communication cable.

RS-485 is a physical interface, which is simply the hardware. RS-485 belongs to wired transmission, so it needs a hardware transmission medium, in fact, it is two wires, these two wires transmit the same signal, but the transmitter divides this signal into two, but the receiver will restore it to the original signal.

The electrical characteristics of RS-485 are as follows: Differential signal negative logic, logic "1" is represented by the voltage difference between the two wires as (2 6)V; The logic "0" is expressed as the voltage difference between the two wires as (2 6)v. The interface signal level is lower than that of RS-232-C, so it is not easy to damage the chip of the interface circuit, and this level is compatible with the TTL level, which can be easily connected to the TTL circuit.

The maximum communication distance of RS-485 is about 1219m, the maximum transmission rate is 10Mbps, the transmission rate is inversely proportional to the transmission distance, and the maximum communication distance can be reached at the transmission rate of 100kbps, if you need to transmit a longer distance, you need to add 485 repeaters. The RS-485 bus generally supports a maximum of 32 nodes, and if a special 485 chip is used, it can reach 128 or 256 nodes, and the maximum can support up to 400 nodes.

The above content refers to Encyclopedia-RS485 bus.

RS485 is a standard that defines the electrical characteristics of drivers and receivers in balanced digital multipoint systems, as defined by the Telecommunications Industry Association and the Electronics Industry Alliance.

Widely used in industrial and mining, transportation and other enterprises as weighing and measuring equipment of electronic truck scale in the data processing and other functions of the backward status quo, the SCS series of electronic truck scale display instrument data communication interface test and analysis research, proposed a weighing data acquisition method based on microcomputer RS232 serial communication interface, further combined with RS422 RS485 serial data communication interface standards and characteristics to achieve remote data acquisition and in practical application has been verified, has a certain promotion value.

RS422-RS232 communication interface conversion device.

RS422-RS232 communication interface conversion device, related to communication technology. The technical problem to be solved by the utility model is that an RS422-RS232 communication interface conversion device is provided, which has good anti-interference characteristics. The technical scheme adopted is that the RS422-RS232 communication interface conversion device is characterized in that, it is made up of RS232 interface, relay unit and RS422 interface in series.

Serial port is an interface standard, which stipulates the electrical standard of the interface, simply put, it is only a standard at the physical layer. There is no specification for the interface plug-in cable and the protocol used, so as long as the interface plug-in cable we use meets the serial port standard, it can be used flexibly in practice, and various protocols are used for communication and device control on the serial port interface standard. Therefore, 485 has a wide range of use and strong versatility.

Typical serial communication standards are RS232 and RS485.

Typical serial pass standards are RS232 and RS485, which define voltage, impedance, etc., but do not define software protocols, and the characteristics of RS485 include:1Electrical characteristics of RS-485:

The logic "1" is represented by the voltage difference between the two wires as +(2-6)v; The logic "0" is expressed as the voltage difference between the two wires as (2 6)v. The interface signal level is lower than that of RS-232-C, so it is not easy to damage the chip of the interface circuit, and this level is compatible with the TTL level, which can be easily connected to the TTL circuit. 2.

The RS-485 has a maximum data transfer rate of 10Mbps. 3.The RS-485 interface is a combination of balanced driver and differential receiver, and the anti-common-mode interference ability is enhanced, that is, the anti-noise interference is good.

4.The RS-485 interface has a maximum transmission distance of 4000 feet (about 1219 meters) as standard, but it can actually reach 3000 meters, and the RS-232-C interface only allows one transceiver to be connected on the bus, i.e. single-station capability. The RS-485 interface on the bus allows up to 128 transceivers to be connected.

This means that it has multi-station capability, so that users can easily set up a network of devices with a single RS-485 interface. The RS-485 interface is the preferred serial interface due to its good noise immunity, long transmission distance and multi-station capability. Because the half-duplex network composed of RS485 interfaces generally only needs two wires, the RS485 interfaces are transmitted using shielded twisted pair cables.

The RS485 interface connector uses the 9-pin plug socket of DB-9, the RS485 interface with the smart terminal uses DB-9 (hole), and the keyboard interface RS485 connected to the keyboard uses DB-9 (pin). The serial port protocol only defines the transmission voltage, impedance, etc., and the programming method is the same as that of ordinary serial port programming.

Hope it helps, give it a thumbs up! Thank you!

Characteristic impedance of 120 Twisted-pair shielded cables (including armoured types) are able to meet the EIA's RS485 standard, which is the RS485 cable! In layman's terms, it is also called the 485 line.

Of course, wireless is a very expensive cable, and there are specifications, you can buy one.

It is possible to use the shielded twisted pair cable that is commonly used in the world. It is recommended to use the model of shielded twisted pair for RVSP2 * two-core shielded twisted pair, each core is composed of 16 strands of wire). The use of shielded twisted pair cables helps to reduce and eliminate the distributed capacitance between the two 485 communication lines and the common-mode interference that comes from around the communication lines.

It is possible to use the shielded twisted pair cable that is commonly used in the world. It is recommended to use the model of shielded twisted pair for RVSP2 * two-core shielded twisted pair, each core is composed of 16 strands of wire). The use of shielded twisted pair cables helps to reduce and eliminate the distributed capacitance between the two 485 communication lines and the common-mode interference that comes from around the communication lines.

485 communication line.

It is better to remove the branch line of the unconnected device from the bus, otherwise it is easy to form interference. If the unfinished end of the bus does not receive a good signal, you can add 120 ohms of unresisted wire to cross over at both ends of the signal line. Do not add intermediate equipment, otherwise it will increase the line loss and reduce the number and distance of equipment.

The 485 signal cable cannot be routed with the power cable. In the actual construction, because the wiring is through the pipeline, the construction party sometimes for the convenience of the figure, directly tie the 485 signal line and the power line together, because the strong current has a strong electromagnetic signal to interfere with the weak current, resulting in the instability of the 485 signal, resulting in the instability of communication.

The 485 signal cable can be routed using shielded wires or unshielded wires. Since the 485 signal is transmitted using differential mode, that is, the voltage difference between 485+ and 485- is used as the signal transmission.

1. Different uses.

Network cable: It is mainly used for data transmission in network communication such as computers, routers, switches, and landlines.

Line 485: A standard interface for industrial field device communication, which is used to transmit control signals.

2. The use of wires is different.

Network cable: 8 cores of shielded wire must be used, and at least 4 cores must be connected, and can not be connected incorrectly.

485 wire: 2 cores are required to transmit.

3. The functions are different.

Network cable: It is the network data that is obtained through the Internet.

Line 485: It is used to transmit control signals.

RS485 communicates with 485, wiring method:

The RS-485 operates in a half-duplex mode and supports multi-point data communication. The RS-485 bus network topology generally adopts a terminal-matched bus structure. That is, a bus is used to connect the nodes in series, and ring or star networks are not supported.

If you need to use a star structure, you must use a 485 repeater or a 485 hub. The RS-485 bus generally supports a maximum of 32 nodes, and if a special 485 chip is used, it can reach 128 or 256 nodes, and the maximum can support up to 400 nodes.

Common fieldbuses such as RS485 and CAN do not support hermaphroditic wiring. In particular, systems with a centralized power supply require two communication lines and two power lines. If the connection is wrong or reversed, the equipment on the bus will not be able to start, or even burn out.

In a large network with a few hundred slaves, the traditional bus has to connect thousands of lines. If one of them is reversed, the consequences are unimaginable.

On-site construction can only follow the hand-in-hand line topology, and bifurcation is not supported.

This is especially important for construction occasions such as buildings, which often need to be bifurcated to bring simplicity, and often due to the construction personnel.

The line is not in place and other reasons, resulting in equipment communication failure.

This is especially true for some applications where the power supply is centrally controlled. Power lines are required to traverse all network nodes. The wiring workload is large, the fault tolerance rate is low, and the loss is serious after any node is wrong.

Four wires are required for communication power supply.

Large amount of wiring. The wrong wire is damaged in a large area.

Arbitrary topologies are not supported.

Hermaphroditism is not supported.

Twisted pair must be used.

It must be threaded separately.

There is no short-circuit protection on the bus.

The maximum communication distance is 1000m

Termination resistors are required.

Slave communication needs to be isolated.

U Powerbus technology is a power supply bus technology that transmits both DC and signals on two lines.

u Two-wire communication + DC power supply.

u Support hermaphroditic wiring.

u There is no need to isolate communication and power supply.

u Automatic protection and recovery of short circuit, reporting.

u The communication distance can reach up to 3000m

Strong anti-interference ability, can be mixed with 220V mains.

u No need to thread separately.

u No termination resistor is required in any field.

u Transparent serial port, the original 485 program does not need to be changed.

u Support any cable: twisted pair, parallel cable.

Arbitrary topologies are supported: tree, star, and bus.

When wiring, A is connected to A and B is connected to B between master and slave

RS485 does have many problems during on-site construction wiring, which can be troubled from the following aspects.

1. Use non-standard cables. The IEEE standard requires the use of shielded twisted pairs. We apply it on the spot, twisted pair cable is also OK, but BV line and parallel wire BVVB definitely cannot.

2. Co-pipe threading. The AB line of 485 can only be threaded separately and cannot be mixed with 220V. However, during the actual construction, many on-site illegal construction, twisting or co-managing 220V and 485 lines.

3. There is a source of interference nearby. For example, frequency converters.

4. The cabling topology is not compliant. The 485 bus only accepts daisy-chain topology, also known as hand-in-hand. Star, tree, hybrid topologies are not accepted.

5. Communication problems due to the echo of the line. So to add a terminal resistor to absorb the echo. This is especially true when the communication distance is relatively long.

6. Because RS485 is a polar link, if one or more slaves AB on the bus are reversed, it is possible to affect the entire bus communication.

7. The 485 bus was connected to the power supply by mistake. Since many devices now use European-style sockets. Power and 485 are next to each other. So it's easy to make the wrong connection. Once the connection is wrong, the entire bus may be connected to high voltage, resulting in a large area of the slave station burning.

In short, the RS485 has a lot of problems when wiring. As a fieldbus, it is better to find a two-bus that supports non-polarity, arbitrary topology, and can be mixed with 220V to replace RS485, and there is no need to isolate the power supply B0505, and the cost is greatly reduced.

The diagram above illustrates that a pair of twisted pair has 2 cores terminated with RS485A+ B- at one end, 4:SG+ and 3:SG- at the other end of RJ11, and the cable shield terminates with 2:GND at one end and floats at the other end!

Gas waist wheel flowmeter 485 communication wiring method.