BS EN 61158-6-21:2012 PDF

What is BS EN 61158-6-21 - Type 21 application layer about? The Fieldbus Application Layer (FAL) provides user programs with a means to access the Fieldbus communication environment. In this respect, the FAL can be considered a window between corresponding application programs. BS EN 61158-6-21 part of IEC 61158 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 61158-6-21 defines the externally visible service provided by the FAL in terms of: