RS-485 is a commonly used communication interface in industrial control, power communications, smart instruments and other fields. It uses a pair of twisted pairs for differential transmission. One line is defined as A and the other is defined as B. Its theoretical communication distance can reach 1200 rice.

However, the on-site communication environment is often the main factor leading to the large difference between the actual transmission distance and the theoretical transmission distance. The influencing factors of RS-485 communication distance are mainly related to driver chip, cable type, cable material, communication rate, wiring method, environmental interference, etc.

Although we can extend the communication distance of RS-485 as much as possible by selecting high-performance driver chips, shielded twisted pairs, increasing terminal resistance, reducing communication speed, etc., this distance is generally not higher than the theoretical value. How much. Then at this time, other methods need to be used to break through this distance limit.

To increase the RS-485 communication distance, you can add relays. Relays can be divided into two types: wired relays and wireless relays.

Wired relay

  1. The RS-485 wired repeater is a bridge device that can connect two RS-485 buses. The RS-485 repeater can automatically determine the bus status at both ends of the bridge and realize automatic switching of the sending and receiving status at both ends of the bridge. Reduce the transmission delay during sending and receiving.
  2. RS-485 repeater can effectively suppress lightning (LIGHTNING) and ESD, provide 600W lightning surge protection power per line, and minimize surge voltage and transient overvoltage generated on the line due to various reasons. The inter-electrode capacitance ensures the high-speed transmission of the RS-422/RS-485 interface, thereby protecting the stability of the 485 main channel.
  3. The isolation DC/DC module of the RS-485 repeater can completely isolate the power supply at both ends. It can effectively isolate the 485 buses from each other to prevent common ground interference.
  4. Using RS-485 repeaters can appropriately reduce the length of each level of transmission line, thereby increasing the transmission rate.

Wireless relay

Wireless relay means that the data exchange between two RS-485 devices no longer uses the RS-485 bus to connect directly, but uses a wireless device to connect the two.

Use wireless data transmission radio as RS-485 wireless relay device:

As a communication medium, wireless data transmission radio provides real-time and reliable data transmission of monitoring signals in private networks under certain special conditions. It has the characteristics of low cost, convenient installation and maintenance, strong diffraction ability, flexible network structure, and wide coverage. The long range is suitable for occasions with many scattered points and complex geographical environments. It can be connected to data terminals such as PLC, RTU, rain gauge, and liquid level gauge.

Advantages of wireless data transmission radio using LoRa solution:

(1) Long communication distance: The communication distance can be extended to 5Km under 100mW power. Only two transceiver devices can achieve the communication distance that can be achieved by 4 wired relays;

(2) Convenient device connection: Due to the omnidirectionality of electromagnetic waves, device connection can get rid of the traditional wired device connection method and does not have to follow the serial connection wiring method. One master device can connect to all devices within the communication range at the same time, realizing a star pattern. Internet connection. Ebyte E95M-DTU (400SL22-485) This wireless data transmission radio also supports wireless relay mode, which can realize multi-level relay networking, effectively extend the communication distance, and achieve ultra-long-distance communication.

Disadvantages of wireless data transmission radio using LoRa solution:

(1) Due to the LoRa modulated wireless communication method, data will be output to the 485 bus only after each packet of data is completely received. Due to the different lengths of the data packets, as well as the wireless communication distance and other factors, each packet of data has varying degrees of distortion delay.

Advantages of wireless data transmission radio using 4G solution:

(1) Wide communication range: Relying on the 4G network, it can be used immediately after connecting to the network. In cities and rural areas where the 4G network is widely covered, ultra-long-distance communication can be achieved;

(2) Device data can be monitored: 4G DTU needs to upload data to the server during the communication process, and then the server forwards it to the receiving device. The communication data can be recorded in the server to facilitate data analysis.

Disadvantages of wireless data transmission radio using 4G solution:

(1) The equipment needs to be connected to the Internet: Because it relies on the 4G network, the equipment needs to be installed in a location that can connect to the 4G network, and is not suitable for use in empty and uninhabited areas;

(2) Equipment needs to pay network access fees: existing 4G IOT providers will charge Internet of Things traffic fees, and customers who use them need to pay traffic fees to use the networking functions of the equipment.