Function blocks (FB) for process control Part 1: Overview of system aspects
|Publication Date:||1 October 2003|
|ICS Code (IT applications in industry):||35.240.50|
|ICS Code (Interface and interconnection equipment):||35.200|
This part of IEC 61804 is a Technical Specification which
provides guidelines for suppliers to meet evolving requirements for
digital process control systems through which users can be assured
of the compatibility, the interworkability, the
This Technical Specification defines the requirements for FBs to provide control and to facilitate maintenance and technical management as applications which interact with actuators and measurement devices:
• control covers functions necessary to bring and hold the process at the desired behaviour;
• maintenance covers functions to acquire information about the state of the process equipment and the state of automation devices including their adjustments, for example, calibrate a sensor that has drifted;
• technical management deals with information for the optimization of the process.
It is concerned primarily with the economics of the process and plant equipment. This relates in particular to the evaluation of performance and reliability of specific items of plant or equipment for all the installed period and comparison of performance and reliability of items from different suppliers performing an identical function in the same operating environment. An example of performance is the number of cycles achieved before failure of two valves from different suppliers. This allows for the production of detailed and valid statistical analysis to support management decisions and plant equipment modifications.
A prerequisite for designing, implementing and operating a FB-based process control system is that the tools, the devices and other components follow the same architecture based on a common specification. The architecture is required to define the components of the systems, for example FB, device, data, data connections and more as well as relations between these components. The IEC 61499 series generic FB model on which this Technical Specification is related is able to provide these basic components for FBs for process control. One add-on to the IEC 61499 series is the specification of parameters and functions of FBs that are implementable in devices.
The architecture and the range of FBs that have to be specified are described in 7.4 contains a minimum set of FBs that will be required for the process industries. These are presented in TWO different clauses. One deals with "rich" FBs covering complex but common functions such as control loop (for example proportional, integral, differential - PID) required by the majority of the process industries. Another covers a set of elementary FBs (EFB) such as Boolean functions required to compose very specific and unique functionality.
FBs are used during the complete life cycle of process control systems but viewed from different aspects. This is covered in detail in Annex A. The process design starts with the Piping and Instrumentation Diagram (P&ID) which gives the requirements of the process and instrumentation from a purely functional point of view. From the P&ID, the desired behaviour of the process control system is extracted into a functional requirements diagram (FRD) without considering the detailed behaviour of the underlying devices. The bricks making up the FRD are application blocks (AB), the representation of the data and algorithms in the design phase. After discussion between the process and automation engineers (end-user and system integrator), the FRDs are turned into detailed designs for the application via several design using devices available on the market together with interconnections and configurations of these devices. In this way a PID loop shown in via bubbles on a P&ID will be transformed into implementable FBs in specific field and/or control-room devices. It should be noted that many parts of the process industries, in particular those with many similar and relatively simple processes (for example, the water industry), do not use the concept or term FRD. They go directly from P&IDs to the implementable FBs and will use a variety of names to describe the process and the resulting design documents. The FRD approach is used here since it represents the most formal view of the design cycle and illustrates the use of FBs at the earliest of phases in the life cycle. Clause 4 summarizes the requirements from this lifecycle point of view.
This Technical Specification specifies a system (an industrial-process measurement and control system based on distributed FB application). A system is described stepwise in terms of architecture, models and the life cycle. The architecture is the "road map" which names the components and presents the structure of the system. The models describe the details of the components, i.e. their functions in the system. The life cycle makes visible how the components work together during their use in different phases of the lifetime, i.e. it makes the operation visible.
Figure 2 shows the different influences, basic specifications and technology support on IEC 61804 from the top-down and bottom-up point of view.
The influences are international standards and projects
(PROFIBUS and Fieldbus Foundation1), which relate to the
same area as IEC 61804. These standards are either
The main purpose of this part is the harmonization of different views, models and starting points of end-users, system providers and device manufacturers. It will be the reference document leading the discussions during the specification and the guideline for the readers of IEC 61804-2.
1 PROFIBUS is the registered trade mark of PROFIBUS International (PI). PI is a non-profit trade organization to support the fieldbus PROFIBUS. This information is given for the convenience of users of this Technical Specification and does not constitute an endorsement by CENELEC of the trademark holder or of any of its products. Compliance to this profile does not require use of the trade name PROFIBUS. Use of the trade name PROFIBUS requires permission of the trade-name holder.
Foundation Fieldbus is the trade name of the consortium Fieldbus Foundation. This information is given for the convenience of users of this Technical Specification and does not constitute an endorsement by CENELEC of the product named. Equivalent products may be used if they can be shown to lead to the same results.