Section 4 Engineering Interface Function Block Design
3BSE042835-600 51
Function Block Design
When programming using function block diagrams the layout of a function block is
important. The layout of a function block is determined by the order of the
parameters, the length of their name, and their direction.
The parameters of a function block type can be divided into groups reflecting their
usage, for example alarm handling, or group start handling. The parameters within a
group are order according to their direction as follows:
1. IN_OUT
2. IN
3. OUT
This order is also reflected in the layout of the function block since parameters with
In direction appears on the left side of the function block, and those with Out
direction on the right. Parameters with In_Out direction has a connection on both
sides of the function block, see Figure 7. This is relevant only to the FBD
programming language.
For all functions or function block types in the diagram editor it is recommended to
always connect 'true' to the EN port. For SIL1-2 and SIL 3 diagrams it is mandatory
to do so.
Parameter Names
The parameter names of the function blocks are visible in the function block
diagram and control diagram editors, and thus affect the element size. It is therefore
recommended that the names are as short as possible. The same applies to control
module parameters in the control diagram editor.
Short names of Function Block types and parameters are important with respect to
how many Function Block symbols that will fit on a screen or printed page in the
Function Block Diagram (FBD) language. In FBD, the possibility to simultaneously
see many symbols and their connections is essential for the easy reading of the
logic.
Unnecessary paging (both on screen and print-out) has a most awkward effect on
reading ease and requires more space for page references. Also note that using
upper and lower case letters improves the readability of names, for example
To Next Page
Loading...
Need help?
General
