DH-485 Network

DH-485 Network: A Detailed Description

1. Introduction

2. Network Architecture

• Topology: The DH-485 Network typically employs a multi-drop bus topology. In this configuration, multiple devices are connected to a single communication bus, which is usually a cable. This setup allows for straightforward installation and easy addition or removal of devices along the bus. The bus acts as a shared medium through which all the connected devices can communicate with each other, making it a cost-effective solution for interconnecting multiple components in an industrial system.
• Nodes and Devices: A diverse range of devices can function as nodes on the DH-485 Network. These include programmable logic controllers (PLCs), operator interfaces, remote I/O modules, sensors, and actuators. Each device is assigned a unique address within the network, which enables targeted communication between specific nodes. The network can support a certain number of nodes depending on its design and the capabilities of the associated hardware and software, typically accommodating several dozen devices to meet the requirements of different industrial applications.

3. Communication Characteristics

• Data Transfer Rate: The DH-485 Network offers a specific data transfer rate that is suitable for many industrial communication needs. It commonly operates at speeds such as 19.2 kbps or 38.4 kbps, which might seem relatively slow compared to modern high-speed networks but is well-suited for transmitting the types of data typically involved in industrial automation, like sensor readings, status updates, and simple control commands.
• Message Format: Data is transmitted in messages with a defined format. These messages typically consist of a header that includes details like the source address (identifying the sending device), the destination address (specifying the receiving device), and other control information. The payload section contains the actual data being sent, such as the value of a sensor measurement or a command for an actuator. Error-checking mechanisms, such as parity bits or checksums, are often incorporated into the message format to detect and correct any errors that might occur during transmission, ensuring the integrity of the communicated data.
• Communication Distance: The network can cover a reasonable distance within an industrial facility. The maximum cable length for a single segment depends on various factors, including the cable type, the data transfer rate, and the electrical characteristics of the environment. Generally, it can extend for several hundred meters, but in larger installations, repeaters or other extension devices can be used to increase the network's reach and connect different areas or groups of devices.