IEC 61158-1:2014 pdf free download – Industrial communication networks – Fieldbus specifications
5 Concept of the IEC 61158 series
Conceptually，a fieldbus is an industrial digital communication network for integration ofindustrial control and instrumentation devices into a system. Examples of such devices aretransducers, sensors，actuators and controllers.
The IEC 61158 series specifies a number of fieldbus protocol types.Each protocol type isdesigned to permit multiple measurement and control devices to communicate. Devicescommunicate directly only with other devices of the same protocol type. The basicrequirements of industrial communication networks for measurement and control are given inClause 11.
Devices which use the same lower-layer protocols in a compatible fashion but differ in theirhigher-layer protocols may be able to share a lower-layer medium.
In all cases, a particular data-link layer protocol type may be used without restriction whencoupled with physical layer and application layer protocols of the same type or with othercombinations as specified in lEC 61784-1 and lEc 61784-2.Use of the various protocol typesin other combinations may require permission from their respective copyright holders.
The protocol types in IEC 61158 have been engineered to support information processing,monitoring and control systems for any industrial sector and related domains.An exampleapplication for high-integrity low-level communication between sensors，actuators and localcontrollers in a process plant, together with the interconnection of programmable controllers,is shown in Figure 1.
6.1overview
IEC 61158 protocol types are described using the principles,methodology and model of ISO/IEC 7498-1.The OSl model provides a layered approach to communications standards,whereby the layers can be developed and modified independently. IEC 61158 specifiesfunctionality from top to bottom of a full OSl stack and,potentially,some functions for theusers of the stack. Functions of the intermediate OSl layers,layers 3 through 6, may beconsolidated into either the lEC 61158 data-link layer or the lEc 61158 application layer,ormay be realized by a separate layer. Likewise, some features common to users of the fieldbusapplication layer may be provided by the IEC 61158 application layer to simplify useroperation.
Table 1 shows the OSl layers，their functions，and the equivalent layers in the lEC 61158basic fieldbus reference model (see Figure 3).
7.2The lEC 61158 data-link layer
In the absence of persistent errors,the lEC 61158 data-link layers (see lEC 61158-3-tt andIEC 61158-4-tt) provide basic time-critical support for data communications among devices inan automation environment.The term “time-critical” is used to describe applications having atime-window，within which one or more specified actions are required to be completed withsome defined level of certainty.Failure to complete specified actions within the time windowrisks failure of the applications requesting the actions，with attendant risk to equipment,plantand possibly human life.
Although these services specify，from the perspective of applications，how request andresponses are issued and delivered, they do not include a specification of what the requestingand responding applications are to do with them. That is，the behavioral aspects of theapplications are not specified; only a definition of what requests and responses they cansend/receive is specified. This permits greater flexibility to the FAL users in standardizingsuch object behavior. ln addition to these services, some supporting services are also definedto provide access to the FAL to control certain aspects of its operation.