For industrial enterprises, the systems delivering the most direct and obvious application benefits are industrial control systems, especially DCS (Distributed Control System).
Although some people predicted years ago that DCS would soon be replaced by FCS (Fieldbus Control System), DCS remains quite viable to this day.
In 2003, ARC Advisory Group published a global DCS market forecast report. It predicted that the global DCS market would maintain a 2.5% growth rate from 2002 to 2007, rising from $9.1 billion in 2003 to $10.3 billion. The modest growth of DCS was mainly due to slower economic growth in developed countries such as the United States. In contrast, China’s DCS market has grown at a rate of over 10% in recent years. Compared with DCS from a decade ago, today’s DCS has undergone fundamental changes.
DCS Has Entered the Fourth Generation
Driven by advances in information technologies — including network communication, computer hardware, embedded systems, fieldbus, configuration software, and databases — as well as growing user demand for advanced control and management functions, major DCS vendors (represented by Honeywell, Emerson, Foxboro, Yokogawa, and ABB) have continuously upgraded and expanded their DCS offerings.
A new generation of DCS has emerged, marked by:
Honeywell’s Experion PKS (Process Knowledge System)
Emerson’s PlantWeb
Foxboro’s A2
Yokogawa’s R3 (PRM – Plant Resource Management)
ABB’s Industrial IT
If Foxboro’s I/A Series is regarded as a milestone for the third-generation DCS, the latest systems mentioned above can be classified as fourth-generation DCS. The two key characteristics defining the fourth-generation DCS are Information and Integration, both starting with the letter “I”.
Technical Features of the Fourth-Generation DCS
The architecture of fourth-generation DCS mainly consists of four layers:
Field Instrumentation Layer
Control Unit Layer
Plant/Workshop Layer
Enterprise Management Layer
Most DCS vendors provide the first three layers, while the enterprise management layer connects to third-party management software platforms (ERP, CRM, SCM, etc.) through open database interfaces. Today’s DCS provides complete control and management functions at the plant/workshop level and integrates enterprise-wide information management.
DCS Fully Reflects Informatization and Integration
Informatization and integration define the evolution of modern DCS. Users can now collect data across the entire plant and process, and expect this data to be presented appropriately to support decision-making.
Informatization means DCS is no longer just a control-oriented system, but a comprehensive platform for information management. It provides a complete information channel from field devices to the workshop, plant, and enterprise group, with characteristics of comprehensiveness, accuracy, real-time performance, and systematicity.
Most DCS now integrate traditional DCS functions, SCADA (Supervisory Control and Data Acquisition), and major MES (Manufacturing Execution System) functions. Unlike ERP, MES integrates hardware and software components to manage and optimize the entire production process from order to finished product. It uses accurate real-time manufacturing information to guide, respond to, and report shop-floor activities, and supports enterprise decision-making with performance evaluation data.
MES functions include:
Resource allocation and status
Production unit dispatching
Document control
Data collection/acquisition
Labor management
Quality management
Maintenance management
Product tracking
Performance analysis
Integration in DCS appears in two forms: function integration and product integration.Modern DCS vendors focus on system integration and solution capabilities. In addition to traditional process control, DCS now integrates PLC (Programmable Logic Controller), RTU (Remote Terminal Unit), FCS, multi-loop controllers, and intelligent acquisition/control units.
Many DCS vendors no longer develop configuration software or hardware in-house, but adopt third-party integration or OEM solutions:
Foxboro uses Wonderware software
Emerson uses Intellution software
Foxboro uses Eurotherm I/O modules
Yokogawa R3 uses Fuji Processio I/O
Honeywell PKS uses Rockwell PLCs as field control stations
DCS Becomes a True Hybrid Control System
In the past, DCS and PLC were divided by application: process control vs. logic control. Fourth-generation DCS has blurred this distinction. Nearly all fourth-generation DCS support process control, logic control, and batch control in a single hybrid control system, matching real industrial requirements.
Most industrial processes — such as metallurgy, papermaking, cement, pharmaceuticals, food processing, power generation, and chemicals — combine continuous regulation and logic interlock control. Optimizing overall production requires a unified distributed integrated information system.
Nearly all fourth-generation DCS use the IEC 61131-3 standard for configuration software, originally designed for PLC programming. Some DCS (e.g., Honeywell PKS) directly use mature PLCs as control stations. Most can integrate small-to-medium PLCs as bottom-level control units. Today’s small and micro PLCs support basic logic, advanced computation, communication, and motion control.
DCS Incorporates FCS Functions and Further Decentralization
Some scholars and vendors once positioned DCS and FCS as competitors. In reality, major DCS manufacturers have been the main drivers of fieldbus development. DCS will not be replaced by FCS; instead, DCS will incorporate FCS to become a more complete system.
All fourth-generation DCS include various fieldbus interfaces and support standard fieldbus instruments and actuators.They have also abandoned the traditional centralized control station structure with rack-mounted I/O modules in cabinets, replacing them with:
Decentralized I/O modules (rail-mounted)
Compact field-mountable I/O units
Small-to-medium PLCs
Key advantages of distributed control:
Logical partitioning: control functions can be distributed to appropriate units for modular modification, download, and commissioning.
Field installation: reduces cabling and improves control response.
Some DCS include distributed local HMI stations, enabling a smart factory with seamless human-machine integration (e.g., Emerson DeltaV, Foxboro A2, Ovation).
Modern DCS vendors focus on practicality rather than concept hype. A single DCS can support multiple field architectures:
Fieldbus intelligent instruments
Field-mounted intelligent I/O modules (saving cables without expensive smart instruments)
Cabinet-mounted centralized installation (ideal for retrofits)
Solutions are tailored to on-site conditions.
DCS Enters a Low-Cost Era
In the 1980s and even 1990s, DCS was high-tech, complex, and expensive. With wider adoption and better understanding of information technology, DCS has become affordable and commonplace.
Another hallmark of fourth-generation DCS is the use of off-the-shelf software and hardware (I/O) and flexible scaling, significantly lowering costs.Automation using modern DCS now costs little more than traditional instrumentation, but delivers far stronger functions.
The cost per physical signal has dropped from about 1,500 RMB to around 800 RMB.Foreign DCS were once only economical for large systems. Fourth-generation DCS, with flexible configurations, are now cost-effective for both large and small systems.
Open DCS Platforms and Specialized Services
Openness has been a major industry topic for 20 years. In the past, limited communication technology made openness difficult. Concepts such as the MAP 7-layer network protocol under CIMS were proposed but not widely adopted.
Today, advances in networking, databases, software, and fieldbus enable true openness. Intensified competition has encouraged DCS vendors to shift from independent development to integration and collaboration.
Openness of Fourth-Generation DCS
Openness allows third-party connectivity at three levels:
Enterprise management layer: supports ERP, CRM, SCM, etc.
Plant/workshop layer: supports advanced control, SCADA, MES, BATCH software, and multiple network protocols (mainly Ethernet).
Unit control layer: supports DCS, PLC, RTU, intelligent control units, and standard fieldbus instruments/actuators.
While openness offers benefits, safety and reliability must come first. Unscheduled shutdowns can cost far more than savings from open-component selection. Unnecessary functions — especially network and peripheral options — increase risks of viruses, hacking, or unauthorized software (e.g., games), which can cause system failure.
As open systems mature, hardware and software become more flexible. However, each application requires a unique solution, making specialized knowledge and experience critical for automation vendors and integrators.Vendors now compete based on industry-specific solutions and professional services, which are also their main profit sources.
Overview of Domestic DCS Technology and Application
After 10 years of development, three major Chinese DCS vendors have launched their own systems:
Hollysys: MACS‑Smartpro fourth-generation DCS
SUPCON: Webfield (ECS) system
Shanghai Xinhua: XDPF‑400 system
These systems have been successfully applied across industries and gained user recognition:
Xinhua: strong in thermal power generation
SUPCON: leading in chemical process control
Hollysys: successful in nuclear power, cogeneration, chemicals, cement, pharmaceuticals, and papermaking
These three domestic suppliers have become strong competitors. Their competition has forced foreign DCS prices to drop to below 40% of original levels, greatly promoting DCS adoption in Chinese industrial enterprises, especially small and medium-sized ones.
Evolution of Process Control Systems
Fifty years ago, process control relied on pneumatic instruments with 3–15 psi signals — the first-generation Pneumatic Control System (PCS).Systems using analog current signals (0–10 mA / 4–20 mA) formed the second-generation Analog Control System (ACS).
In the 1970s, digital computers enabled centralized digital control — the third-generation Computer Control System (CCS).In the 1980s, microprocessors gave rise to Distributed Control Systems (DCS) — the fourth generation.In the 1990s, fieldbus technology created the Fieldbus Control System (FCS).
Advantages of Fieldbus Control System (FCS)
Fieldbus is regarded as the 21st-century standard for industrial process measurement and control networks. It provides intelligent, simplified, standardized field-device interfaces, enabling system design, installation, and operation in a low-cost, portable, and expandable environment. It represents a new revolution in automation with broad application and market potential.
Fieldbus products form a communication network that interconnects bottom-layer field devices and instruments for process and manufacturing automation, integrating field communication and control systems. The key shift is replacing DCS with FCS.
Compared with DCS, FCS offers multiple advantages:
Saves about 60% of cables and cable trays
Reduces cabling, installation, and commissioning costs by over 50%
Cuts secondary development costs and shortens cycles; initial investment reduced by 30%
Reduces spare parts and simplifies maintenance
Supports comprehensive automation strategies, helping enterprises move from extensive to intensive operations
Since the late 1980s, several fieldbus technologies have matured:
HART (Highway Addressable Remote Transducer)
CAN (Controller Area Network)
LON (Local Operating Network)
PROFIBUS (Process Fieldbus)
FF (Foundation Fieldbus)
Each has unique features and has significantly advanced fieldbus technology.
