→Feedback loop
also known as feedback path, according to →IEC-standard: A feedback path is said to exist in a →network when the output of a →function or →function block is used as the input to a function or function block which precedes it in the network; the associated →variable is called a feedback variable. ... A feedback variable can also be an output element of a function block data structure.
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Examples for feedback loops in the FBD-editor |
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This shows an explicit feedback loop. The variable run is the feedback variable. An explicit feedback loop is caused by a line connecting an output to a preceding input. Here the output of the →value field with the variable run has been connected to an input of OR. |
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This shows an implicit feedback loop. Here the variable run is the feedback variable, too. An implicit feedback loop is caused by using a variable receiving its value from an output and being the input value to a preceding input. Here the variable run receives its value from the output of ADD and it is used as input of OR. |
Feedback loops must be resolved for the →evaluation of networks.
Certain types of feedback loops are supported in logi.CAD 3 (
), others are not (
).
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By default, feedback loops for functions without a variable in between are highlighted as an error. Subsequently, it is not possible to build and load the application onto the PLC. |
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