CENTUM CS Fieldbus Communication Functions

다운로드 (81 KB)

MORI Hiroshi1 MIZUSHIMA Fuyuki1 TOMITA Shoji1 HAYASHI Shunsuke1

We have developed fieldbus communication functions for our distributed control system CENTUM CS that comply with the specifications of the Fieldbus Foundation. These new functions enable cascade control of the CENTUM CS control function and the field device control function, and also support the operation and monitoring functions of the field device control function. The fieldbus communication module (ACF11) interfaces with the fieldbus. It can also be connected to a node on the remote IO bus (RIO bus), thereby making the system construction flexible. This paper introduces the characteristics of the CENTUM CS fieldbus system, with the main focus on its communication functions.

  1. Industrial Automation Systems Business Div.


A fieldbus is a bidirectional, multidrop, digital communication system developed to replace the conventional 4-20 mA communication lines that connect intelligent field devices with a control system. Fieldbus is continually reviewed in an effort to standardize the fieldbus specifications to comply with the specifications of the IEC and ISA.1

The features of the fieldbus include a reduction in the amount of cable required, field-distributed control functions, and bidirectional transfer of control data. Among these, the fielddistributed control functions are attracting particular attention as field devices become increasingly "digital" and more and more "advanced." This means that the control functions implemented in a distributed control system are being distributed throughout the field. Drastic innovations in control systems are not always favorable though, and we believe there needs to be a way of shifting gradually from the existing systems to more advanced systems.2

The CENTUM CS fieldbus communication functions were developed with the aim of reducing the burdens of plant operation. This was achieved by standardizing the operation and monitoring functions, including the functions for the control of field devices, in an environment where the fieldbus coexists with a conventional analog communication line. One major technical challenge in this achievement was communication between field devices and higher-order control equipment while prioritizing the characteristics of fieldbus communication functions among other things.

The CENTUM CS fieldbus communication functions are designed to comply with the fieldbus standards specified by the Fieldbus Foundation, while still upholding Yokogawa Electric's traditional ideas of instrumentation. Accordingly, these functions integrate fieldbus capabilities into the CENTUM CS control, operation and monitoring functions, to form one of the key technologies for the Enterprise Technology Solutions (ETS) offer.


The CENTUM CS fieldbus system features:

  1. System Expandability
    • The fieldbus system can be installed in combination with a conventional 4-20 mA analog communication line. In addition, the system is designed to be flexible and accept step-by-step expansions, that is, additions and expansions according to growing application needs.
  2. Combination of DCS Control Functions and Field Device Control Functions
    • In anticipation of the fieldbus age, the CENTUM CS system has used floating-point data in its data processing from the outset. The system can therefore continue to produce precision data for control computations.
    • Like conventional discrete input/output data, the I/O data of a field device can be handled as process I/O data. Consequently, there is no need for the system to be aware of the fieldbus.
    • Whatever fault may occur, the fieldbus system can detect failures in field devices or in the process in virtually no time at all. In addition, the FCS function blocks are designed to act correctly (bumpless output control, for example) depending on the operating condition of the fieldbus function blocks.
  3. Operation and Monitoring of Field Device Control Functions
    • The fieldbus system provides a human-machine interface function that is designed to operate the control functions of field devices (parameter tuning, for example) and continuously monitor their operating condition. The interface allows the control functions to be operated and monitored in virtually the same way as done for earlier CENTUM CS control functions.
  4. Failure Monitoring
    • The fieldbus system can constantly monitor alarms for faults, such as failures in field devices and device alarms (such as I/O failures) raised by the field devices voluntarily. This makes preventive maintenance easy.
    • The extensive diagnosis functions of the fieldbus communication modules minimize functional degradation in the system due to imperfections.
  5. Field Device Management
    Using a device management tool, users can monitor the device status and parameter data that is essential for field device maintenance, from an off-site location such as the instrument room. This makes system maintenance easy.


Figure 1 CENTUM CS System Configuration

1. System Configuration

Figure 1 shows the system configuration. As shown in the figure, the CENTUM CS fieldbus system consists of the following equipment.

  1. Information and Command Station (ICS)
    The ICS performs the operation and monitoring function of a distributed control system. In addition to the conventional functions, the ICS can operate and monitor fieldbus function blocks and receive alert messages (alarms and events).
  2. Engineering Workstation (EWS)
    The EWS performs the engineering function of a distributed control system. In addition to the conventional functions, the EWS can engineer the fieldbus communication module (ACF11).
  3. Field Control Station (FCS)
    The FCS performs the control function of a distributed control system. In addition to the conventional functions, the FCS can run a process for cascade connection to the fieldbus and interface field devices with the ICS.
  4. Fieldbus Communication Module (ACF11)
    The ACF11 module serves as a link master in the fieldbus system and can relay data between the FCS and field devices.
  5. Personal Computer (PC)
    The PC runs software tools for engineering and maintaining field devices.

2. Fieldbus Communication Module (ACF11)

Figure 2 is an external view of the ACF11 fieldbus communication module. The ACF11 module is installed in the node of an RIO bus and can be used in combination with conventional 4-20 mA analog modules. The functions provided by the ACF11 module include:

  1. Relaying data between a higher-order control function and field devices
  2. Link Active Scheduler (LAS) and Time Master functions based on FOUNDATION™ fieldbus specifications
  3. Monitoring failures in field devices
  4. Monitoring failures in FCS control functions and RIO bus
  5. Recovering equipment, including field devices, from momentary power failure

Table 1 Hardware Specifications of ACF11 Module

Specifications Item
Number of modules that can be installed 80 modules/FCS (i.e., [10 modules/RIO node] 5 8 nodes)
Number of fieldbuses 1 segment/ACF11 module
Communication speed 31.25 Kbps in the voltage wire mode
Connection By means of 4-mm screw terminals
Built-in bus power supply Output voltage: 18 to 20 V DC (fixed to 19 V DC)
Continuous output current: 80-mA maximum (with an overcurrent limiter)
Transient output current: 100-mA maximum (for a maximum duration of 2 ms)
External dimensions 188 (D) 5 215 (H) 5 43.6 (W) (mm)
LED indicator RDY, CTL, RCV and SND
Withstanding voltage 1500 V AC, tested between the fieldbus and the system
Maintenance Online maintenance is possible. (Equipment to be maintained: Module itself and cable connectors)
EMC standard Complies with CE marking (as part of a CENTUM CS system)



Figure 2 External View of
ACF11 Module

For momentary power failures that last less than the specified period of time, this function can prevent FCS function blocks from entering the MAN mode. Table 1 summarizes the hardware specifications of the ACF11 module. The module features:

  • Built-in bus power supply
    When there are only a small number of devices, no external power supply is required and engineering therefore extremely easy.
  • Error detection and correction (EDC) function
    Since the module's memory handles vast amounts of control I/O data, it is equipped with an EDC function in order to ensure reliability.
  • Maintenance support function
    The maintenance support function makes it easy to revise programs and provides a communication port for monitoring the internal operation.



1. Process I/Os

Figure 3 Block Connection

Figure 3 shows how FCS function blocks are connected to fieldbus function blocks. If viewed from the FCS function blocks in the figure, it is possible to handle the I/Os of the fieldbus function blocks in the same way as conventional process I/Os. In addition, these I/Os provide the following necessary functions for cascading between the FCS function blocks.

  1. Detection of Device Failures
    Since any device failure can be instantaneously determined from the data status of a fieldbus function block, it is possible for a control block in the primary loop to change to an appropriate mode.
  2. Detection of Clamped Output
    From the data status of a fieldbus function block, an FCS function block can detect any clamped output.
  3. Output Tracking
    Upon recovery from a failure in any field device or communication line, an FCS block can track the output of the field device in order to bumplessly continue the output action.

With these functions, the new fieldbus system enables flexible application design even in cases where control functions are distributed throughout the field. Though different from fieldbus function blocks, the FCS function blocks have the capability of initialization handshaking based on the data status. This allows the FCS function blocks to be connected to the fieldbus function blocks without problems.

2. Operation and Monitoring of Field Device Control Functions

Figure 4 Operation and Monitoring
Using a Faceplate Block

As a means of monitoring the operating condition of field device control functions (namely, the internal parameters of fieldbus function blocks), the CENTUM CS fieldbus system can display and set the parameters of fieldbus function blocks using on-demand communication functions.

Like the conventional process I/Os, each parameter of the fieldbus function blocks can be dealt with using a terminal number. By linking this terminal number with a faceplate block, the parameter can be viewed and set on a parameter tuning panel like those of FCS function blocks. This implements ICS-based operation and monitoring functions for fieldbus function blocks.

Figure 4 shows how each parameter of the PID control block relates to the process variable (PV), setpoint (SP), manipulated variable (MV) and mode of the faceplate block in a control loop consisting of an analog input (AI) block, PID control block and analog output (AO) block. Figure 5 shows a display of the faceplate block tuning panel.

3. Alarms and Events

Alert messages (alarms and events) issued by field devices are received by the ACF11 module and transferred through an FCS up to an ICS. These alerts are then stored in the ICS as historical messages. These messages can be referenced using the "historical report function" or viewed using the device management tool.


Figure 5 Faceplate Block Tuning Panel

The fieldbus engineering function is implemented by means of a tool that runs under Windows NT (fieldbus engineering tool) and coexists with other general-purpose tools. This tool enables the following:

  • Engineering even in cases when no field devices are connected (off-line condition)
  • Data exchange between tools using field device object files compliant to the Common File Format3
  • Automatic scheduling of fieldbus control and communication

Figure 6 shows an example of the various engineering tool builder screens.


Figure 6 Engineering Tool Builder Screens

Fieldbus technology is expected to spread dramatically by the year 2000 as a replacement for 4-20 mA analog transfer technology. Yokogawa Electric strongly supports fieldbus standardization, participating in the Fieldbus Foundation's development of fieldbus specifications and demonstrating the usefulness of fieldbus technology in experiments and other activities.

The CENTUM CS fieldbus communication functions discussed in this paper have been developed as a forerunner of fieldbus technology on the basis of Yokogawa Electric's previous experience and expertise. We believe these new functions will contribute significantly to the spread and development of fieldbus technology.

We will continue to research further functional improvements and cost reductions in new fieldbus systems, taking into consideration a balance of fieldbus systems and distributed control systems, in order to offer users the full advantages of fieldbus technology.

  • CENTUM is a registered trademark of Yokogawa Electric Corporation.
  • Windows NT is a trademark of Microsoft Corporation, USA.
  • Ethernet is a registered trademark of XEROX Corporation.


  1. Kai Tadamichi, "The Fieldbus Fundamentals Handbook," Ohmsha, pp. 128 (1995).
  2. Mori Hiroshi, Kawano Takafumi and Shirai Toshiaki, "Fieldbus System Integrated into DCS," ISA/96 Advances in Instrumentation and Control, Volume 51 (1996).
  3. Tomia Shoji, et al., "Standardized File Exchange Eases Fieldbus Interoperability Design," Intech, Volume 44, No. 3, pp. 46-49 (1997).


  • 벌크화학

    석유 화학 제품, 무기물 또는 중간체를 생산하든 관계없이 화학 회사는 안전하고 호환되는 작업을 유지하면서 적시에 효율적인 방법으로 제품을 제공하는 비용과 마진 압박에 시달리고 있습니다. 또한 화학 회사들은 공급 원료 및 에너지 가격의 변동에 적응하고 가장 수익성 높은 제품 혼합을 시장에 제공해야 합니다.

    Yokogawa는 벌크 화학 시장의 자동화 요구 사항을 세계적으로 지원해 왔으며 이 시장에서 인정받는 선두 주자입니다. Yokogawa는 제품, 솔루션 및 업계 전문 기술을 통해 시장 및 생산 요구 사항을 이해하고 플랜트의 수명주기를 통해 안정적이고 비용 효율적인 솔루션을 제공하기 위해 협력합니다.

    See More
  • 전력

    1970년대 중반, Yokogawa는 EBS 전기 제어 시스템 (EBS Electric Control System)의 출시와 함께 전력 사업에 진출했습니다. 그 이후로 Yokogawa는 전 세계 고객에게 최상의 서비스와 솔루션을 제공하기 위한 기술과 역량의 개발을 꾸준히 지속해 왔습니다.

    Yokogawa는 역동적인 글로벌 전력 시장에서 더욱 적극적인 역할을 수행하기 위해 글로벌 전력 솔루션 네트워크를 운영했습니다. 이로 인해 Yokogawa 내에서 보다 긴밀한 팀워크가 가능해져서 글로벌 리소스와 업계 노하우를 하나로 모았습니다. Yokogawa의 전력 산업 전문가들은 각 고객에게 정교한 요구 사항에 가장 적합한 솔루션을 제공하기 위해 협력합니다.

    See More
  • 정수 및 하수 처리

    Yokogawa는 보다 효율적인 사회를 만들기 위하여 에너지 최적화 기술 개발, 온실가스 감축, 오염 물질로부터 환경을 보호하는 견고한 제품 제작 등을 통해 지속 가능한 수자원 생산을 위한 제어 솔루션을 제공하고 있습니다. Yokogawa의 첨단 기술과 폭넓은 애플리케이션 노하우를 통해 고객과 협력하여 사업을 활성화하고 플랜트 수명주기 전반에 걸쳐 높은 가치를 제공할 수 있는 지속 가능한 솔루션을 제공합니다. 당사의 기술과 제품은 플랜트의 성능을 향상시키고 오늘날의 수자원 시장에서 경쟁적으로 운영할 수 있도록 보장하며 운영비를 절감합니다. Yokogawa는 지자체 및 공업용수 처리 시장에서 광범위한 수처리 응용 분야를 지원합니다.

    See More

Related Products & Solutions


    CENTUM CS는 1993년에 출시된 이후 정유, 석유 화학, 화학, 철강, 비철금속, 금속, 시멘트, 종이 펄프, 식품 및 제약 산업, 전력, 가스 및 수도 설비 및 다른 공익 사업에 다양하게 응용되고 있습니다.

    See More
  • 분산 제어 시스템 (DCS)

    Yokogawa는 프로세스 자동화를 위해서 중요한 운영 인프라를 제공합니다. 분산제어시스템(DCS)은 플랜트 또는 산업 공정의 자동화 된 제어 및 운영을 위한 플랫폼입니다. 10,000개 이상의 플랜트에서 고객의 생산 목표 달성하기 위해서 Yokogawa DCS가 적용되었습니다.

    See More