Standards for communication networks installation in industrial sites
By Francesco Russo, Convenor of SC 65C/JWG 10: Industrial-process measurement, control and automation – Industrial networks cabling
The text of this white paper is the result of a consensus. JWG 10 would like to publish it as it stands. JWG 10 experts are invited to translate the white paper into their own language for appropriate local publication. It is the responsibility of each expert to ensure that the translation is consistent with the original text. For additional information or assistance, email: Francesco Russo, Convenor IEC SC 65C/JWG 10.
If communication networks in critical industrial sites are to work efficiently it is essential for them to be installed correctly. Proper installation can help mitigate problems caused by harsh environmental conditions, electromagnetic interference and security attacks, thus reducing the incidence of network malfunctions and resulting loss of production. IEC 61918 Ed.1 was published by the IEC in December 2007 as a guide for correct and complete installation of communication networks in industrial premises. This standard was developed by IEC SC 65C/JWG 10 with the following objectives in mind:
- specify a consistent set of installation rules covering industrial premises for both fieldbuses and generic cabling (of telecommunication infrastructures)
- harmonize approaches of major user groups and industrial consortia
- harmonize installation-related terminology and definitions
- cover responsibilities and requirements for each phase of the installation life cycle
- allow for additional technology-specific requirements to be described in a companion standard that extends or modifies the basic standard
- provide guidance for a wide range of technician skills
IEC SC 65C/JWG 10 work was coordinated with that of ISO/IEC JTC 1/SC 25: Interconnection of information technology equipment, responsible for the specification of generic telecommunications-related cabling for industrial premises. The paper is intended to outline the advantages of using IEC 61918 and its companion standards.
Process and factory automation rely more and more on communication networks and fieldbuses designed to cope with the specific environmental conditions of industrial premises. These networks and fieldbuses are designed to integrate the applications running on the various functional units of a plant/factory.
One of the benefits of integrating field-generated data with higher-level management systems is to reduce production costs. At the same time integrated data helps maintain or even increase the quantity and quality of production.
Communications availability and performance depend largely on correct network and fieldbus installation. In turn, this prerequisite implies that proper attention must be paid to the important aspects of industrial automation sites such as safety and security, environmental conditions and EMC conditions.
Communication cabling in industrial premises
This type of cabling may comprise:
- specific communication cabling within or between automation islands as specified in IEC 61158 fieldbus standard and its companion standard IEC 61784 parts 1, 2, 3, 4;
- generic telecommunications cabling for industrial premises as specified in ISO/IEC 24702;
- elements of generic cabling modified to meet the needs of specific communication cabling within an automation island in accordance with the installation profiles of the IEC 61784-5 series.
The design of generic cabling for industrial premises, specified in ISO/IEC 24702, provides a flexible cabling structure comprising a series of cabling sub-systems of specified transmission performance that are connected together either passively, using cords, or actively, using transmission equipment. Figure 1 shows the structure of generic cabling connected to specific communication cabling within an automation island. This figure is a variation of a figure from ISO/IEC 24702, where the TO (telecommunication outlet) interface has been replaced with an AO (automation outlet) interface.
ISO/IEC 24702 specifies design of generic telecommunications infrastructures within industrial premises and provides the foundations for some of the transmission performance specifications of IEC 61918. ISO/IEC 24702 specifies only the raw bandwidth capability of a communications channel; it does not specify a useful data transfer rate for a specific network using that channel or expected errors after taking into account interference during the communication process.
The IEC 61158 fieldbus standard and its companion standard IEC 61784 (including parts 1, 2, 3, 4 and relevant subparts) jointly specify a number of communication networks suitable for industrial automation islands that make up the automation site of an industrial enterprise. These networks specify a raw bandwidth capability and, in addition, they specify bit modulation and encoding rules for their fieldbus. Some networks also specify target levels for a useful data transfer rate, and maximum values for errors caused by interference during the communication process.
The Installation Standards
IEC 61918 provides a consistent set of installation rules for industrial premises as regards both generic cabling (of the telecommunication infrastructures) and fieldbuses used in the automation islands. In addition, it offers support for the definition and installation of the interfaces between automation island networks and generic cabling.
One of the problems IEC 61918 seeks to overcome is the situation that comes about when different parts of a large automation site are provided by suppliers using non-homogeneous installation guidelines with different structures and contents. This lack of consistency greatly increases the potential for errors and mismatch situations liable to compromise the communication system.
The installation of a communication system is supported by IEC 61918 and used in conjunction with the relevant installation profile. The installation profile establishes which requirements apply as they are in IEC 61918, or which have been extended, modified, or replaced.
For the installation of the fieldbus defined in the IEC 61784 series, installation profiles are available in the IEC 61784-5 series (see Figure 2). IEC/TR 61158-1 describes the relationship between the fieldbus and the relevant installation profiles.
For the installation of generic cabling, this standard is to be used in conjunction with ISO/IEC 14763-2 (see Figure 2).
One of the advantages of this structure is that the users of a network know which installation requirements are common to most networks and which are specific to a particular network.
Benefits of using IEC 61918 and its companion standards
There are both simple and complex distributed plant/factory automation systems. The strong trend is however for separate DCS (Distributed Control System) and PLC (Programmable Logic Controller) automation entities to be connected both to each other and to the plant/factory management systems. Every single plant/factory has its own installation needs in accordance with the specific critical conditions that apply to the specific application. IEC 61918 and the companion standards described above provide a set of mandatory installation requirements ("shalls") and a number of recommendations ("shoulds").
It is up to the owners of industrial enterprises to explicitly request that the cabling installation is implemented in accordance with these standards and up to the installation planners, installers, controllers, and so on to implement the cabling installation in accordance with these standards.
Benefits for owners of industrial enterprises
By requesting that installation of their networks is carried out in accordance with the installation requirements of these standards, owners of industrial enterprises can improve the quality of their investments and reduce the likelihood of future communication problems and unscheduled loss of production. Owners have the possibility to go one step further by making mandatory not only the "shalls" of the installation standards but also those "shoulds" that best suit their application. Various cases of cost/benefit trade-off actions are indicated in the standard. For example, during the acceptance test-phase, after taking into consideration the characteristics of the specific application, the requirement that all connections be fully tested could be judged to be an unnecessary expense. So in some cases, after discussing possible consequences with the owner, it may be decided to specify a reduced set of tests. Also, by reviewing the requirements for network maintenance and selecting the options suitable for their particular enterprise, owners will be better informed on how to apply their current system of organisation to their networks, thus optimizing maintenance and administration.
Benefits for installation designers/planners
Planners of cabling installation are responsible for producing detailed installation designing and planning documentation that is to be followed by the installers. IEC 61918 lists the documentation to be produced together with an exhaustive description of the requirements, several of which are approached in an innovative way in order to provide suitable solutions for installation problems. Use of some foundations of the design of generic cabling, earthing, safety, security, and MICE environmental description method are just some examples of these requirements.
Benefits for installers
Cabling installers "shall" implement detailed guidelines described in the installation designing & planning documentation. They are assisted in their work by precise instructions together with clear descriptions and figures that cover the key steps. Installers can also refer to descriptions of installation errors that may result in consequences not easily recognized at first, but later possibly resulting in major communication problems.
Benefits for verifiers
Verifiers of installed cabling "shall" verify that the installed components correspond to and are fitted in a way that fully complies with the detailed description provided by the detailed designing and planning documentation. A clear description of the key steps of their work is outlined in the standards.
Benefits for acceptance test personnel
Personnel carrying out installed cabling acceptance tests "shall" follow a defined list of measurements in order to document the actual connection performances and ensure that these comply with the application needs. Clear descriptions of the tests to be performed are provided in the standards.
Benefits for troubleshooting personnel
Their work is supported by two tables that list typical problems and clarify causes and recommended solutions.
Conclusions
IEC 61918 and its companion standards promote homogeneous working practices, whatever the network. They are intended to assist the work of all those involved in the installation of communication networks in industrial sites.
Each companion standard complements IEC 61918 common requirements with additions, modifications, and replacements applicable to specific networks. Thus, network users know which installation requirements are common to most networks and which ones are specific to a particular network.
IEC 61918 and its companion standards are accepted worldwide, with possible geographical modifications, as the basic standards for the network installation in industrial premises.
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