BS EN 61158-5-21:2012 PDF

What is BS EN 61158-5-21 - Type 21 application layer service definition about?

BS EN 61158-5-21 is part of a series produced to facilitate the interconnection of automation system components. BS EN 61158-5-21 is related to other standards in the set as defined by the “three-layer” fieldbus reference model described in IEC/TR 61158-1 . BS EN 61158-5-21 provides the common elements for basic time-critical and non-time-critical messaging communications between application programs in an automation environment as well as material specific to the Type 21 protocol. The term “time-critical” is used to represent the presence of a time window within which one or more specified actions are required to be completed with some defined level of certainty. Failure to complete specified actions within the time window risks failure of the applications requesting the actions, with attendant risk to equipment, plant, and possibly human life. BS EN 61158-5-21 defines, in an abstract way, the externally visible service provided by the FAL in terms of:

An abstract model for defining application resources (objects) capable of being manipulated by users via the FAL service The primitive actions and events of the service The parameters associated with each primitive action and event, and the form that they ta...