DCS communication network congestion and human-machine interface crash phenomenon - Database & Sql Blog Articles

There are multiple nodes connected to the DCS communication network, typically divided into two main categories. One category includes nodes directly interfacing with the production process through I/O boards, known as controllers. These controllers can be either data acquisition controllers or loop controllers, and sometimes they combine both functions in a single node. The second category consists of human-machine interface (HMI) nodes that communicate with operators. They collect data from the controller via the network and are further classified into operation stations, engineer workstations, historical trend stations, and dynamic data servers.

Operation stations are the primary tools used by factory operators. They need to read data from the controller and send user inputs back, making the communication bidirectional. Engineer workstations are responsible for configuring the system before it goes live. They load algorithms, set parameters, and ensure the system is ready for operation. This process, known as configuration, differs from traditional programming and is crucial for the system’s functionality.

The controller's memory contains various control algorithms, such as PID, mathematical operations, trigonometric functions, matrix operations, and even advanced techniques like the Smith predictor. If the monitoring software in the operation station cannot meet requirements, the engineering station can create custom dynamic flowcharts and upload them for use.

To upgrade the controller and operator stations, reverse engineering stations are used to read the current configuration without altering it, then download it to the upgraded hardware. These stations also help identify faults and analyze configurations for troubleshooting.

The dynamic data server is another key HMI component, acting as an interface between the DCS and MIS systems. It ensures secure data transfer and prevents downward data flow. It stores large volumes of data and often works alongside historical trend stations, which can function independently or merge with the server.

During initial system deployment, network congestion is common due to incomplete configurations. However, after some time, the system stabilizes. Recently, with the integration of the MIS system, frequent congestion has occurred, leading to crashes on various HMI nodes. Network congestion is influenced by multiple factors, including data volume and communication protocols.

When a node connects to the DCS network, it usually has a network interface where the controller sends data. The HMI reads this data using the network protocol. The physical network structure can be ring or bus-based, with bus networks often functioning as logical rings. Star topologies are used only in small systems with up to 100 I/O points. Common protocols include broadcast, where data is continuously sent to all nodes, and query-based methods, which may cause congestion if no data is found.

Operation station crashes have been a recurring issue since the 1970s. The main causes include software mismatches between the operating system, monitoring software, and controller drivers. In early systems, these were often developed in-house, leading to compatibility issues. Later systems used third-party software, which sometimes caused more frequent crashes due to limited testing.

Dynamic data servers were not initially part of many DCS setups but have become essential over time. As maintenance personnel change and configurations evolve, some settings become outdated or disconnected from actual I/O points. When the server connects, it reads all data points, including invalid ones, causing network overload and HMI crashes. A reverse engineering station can help identify and remove these invalid points, reducing congestion and improving stability.

Another critical consideration is ensuring all software versions are compatible when accessing the dynamic data server. Mismatched versions can disrupt data transmission. An effective solution to network congestion is the exception report method, which sends data only when changes occur. To prevent missed updates, reports are scheduled periodically. Adjusting the exception report parameters can reduce traffic and improve performance.

Modern operation stations often run on general-purpose OS like Windows NT, paired with widely used monitoring software such as FIX or Intouch. These systems benefit from broader adoption, resulting in fewer bugs and better stability. Open platforms allow easier maintenance and spare parts sourcing, reducing dependency on original manufacturers. This advancement marks a significant improvement in DCS technology.