Some Questions Regarding the Use of RS485 Communication in Electronic Belt Scale Instruments

Industrial instruments are technological tools and control devices for industrial automation. They have entered an era of digitization, intelligence, and networking with technological advancements.

The electronic belt scale instrument serves as the data processing and communication core for automated metering devices of industrial bulk materials. The communication capabilities of modern belt scale instruments are continuously strengthening, enabling multi-device networking, centralized monitoring and management, or communication with upper-level computers through various methods.

Among these, RS485 is a common and crucial communication method for electronic belt scale instruments. This article provides a brief introduction to the RS485 communication method and some common issues associated with it.

What is RS485 Communication?

RS485 is a serial communication standard, also known as TIA485/EIA-485-A. It defines the electrical characteristics of drivers and receivers in a balanced digital multipoint system, as specified by the Electronic Industries Alliance and the Telecommunications Industry Association. RS485 is commonly used in industries such as industrial automation, automotive, and building management.

Advantages and Characteristics of RS485 Communication

1. Long Transmission Distance and High Speed: RS485 can achieve speeds up to 10 Mbit/s and has a theoretical communication distance of up to 1200 meters (at 9600 baud), compensating for the short communication distance and low speed of RS-232.

2. Differential Transmission: RS485 employs differential transmission using a pair of twisted-pair wires, with one wire defined as A and the other as B. This differs from the single-ended transmission of RS-232 and offers stronger anti-interference capabilities and reliability, enhancing signal integrity during transmission.

3. Strong Anti-interference Capability: The RS485 interface transmits signals using a differential method, eliminating the need to detect signals relative to a reference point and enabling resistance to interference in environments with high electronic noise.

4. Flexible Connection: RS485 supports the connection of multiple devices, allowing multiple nodes to be connected on the same bus and enabling the configuration of multi-branch communication links.

Issues to Consider When Connecting RS485 Communication Links

When connecting RS485 communication links, the connection of the signal ground is crucial. Without a proper signal ground connection, common-mode interference and electromagnetic interference (EMI) issues may arise, affecting the stability and reliability of communication and potentially damaging the interface. Therefore, in high-speed, long-distance transmission, or environments with severe interference, impedance-matched RS485 dedicated cables or armored twisted-pair shielded cables should be used.

How to Eliminate Interference on RS485 Communication Lines

The RS485 communication line consists of two twisted wires that transmit signals through the voltage difference between them, known as differential voltage transmission. Differential-mode interference is transmitted between the two signal wires and is symmetrical. Methods to eliminate differential-mode interference include adding a bias resistor to the circuit and using twisted-pair wires.

Common-mode interference is transmitted between the signal wire and ground and is asymmetrical. Methods to eliminate common-mode interference include:

(1) Using shielded twisted-pair wires and ensuring proper grounding.

(2) Considering the use of galvanized pipe shielding in areas with strong electric fields.

(3) Keeping wiring away from high-voltage lines and avoiding bundling high-voltage power lines with signal lines.

(4) Not sharing the same power supply with electric control locks.

(5) Using linear regulated power supplies or high-quality switching power supplies (with ripple interference less than 50 mV).

The above introduction to RS485 communication knowledge for electronic belt scale instruments was provided by technicians from Guonuo Technology and compiled based on various sources. If you have any product-related questions, please feel free to contact us.