Blocks for safe logic
Blocks for safe logic are used to develop safety-relevant applications.
For developing safety-related applications, you must use a Neuron Power Engineer version that has been qualified for this purpose. |
Base variant
The blocks for safe logic are particular system blocks that are highlighted as safe logic, if they are provided with a safe value as follows:
-
At least one block input (including the input
EN
) gets a safe value.
A safe value is the value of a →variable declared based on a safe data type. Expressions according to ST (including operands in ST and operators in ST) can be used to evaluate safe values – as long as no variable is used that provides a non-safe value.
Compare: A non-safe value is the value of a variable declared based on another →data type or an expression with such a variable. -
For all other block inputs, one of the following conditions applies:
-
The input is unconnected, i.e. not connected to any other FBD-element.
-
The input gets a safe value (see above).
-
The input gets a constant value from a value field containing a →literal. Expressions according to ST (incl. operands in ST and operators in ST) can be used to evaluate the constant value – as long as no variable is used that provides a non-safe value.
-
Example: The system block OR
is such a block for safe logic:
Explanation:
-
The left call is highlighted as safe logic because the 2nd function block input gets a safe value and all other inputs are not connected.
-
The right call is not highlighted as safe logic because the 1st function block input gets a non-safe value.
Special variant
The system block AND
is a block for safe logic that is highlighted as safe logic, if it is provided with a safe value as follows:
-
At least one block input (but excluding the input
EN
) gets a safe value (see above). -
For the input
EN
, one of the following conditions applies:-
The input
EN
is unconnected, i.e. not connected to any other FBD-element. -
The input
EN
gets a safe value (see above). -
The input
EN
gets a constant value from a value field containing a literal. Expressions according to ST (incl. operands in ST and operators in ST) can be used to evaluate the constant value – as long as no variable is used that provides a non-safe value.
-
-
The other block inputs are not relevant for the identification of the safe logic. This means that these inputs can also get a non-safe value.
Here the behavior of the system block AND
(based on the above example):
Explanation:
-
The left call is highlighted as safe logic because the 2nd function block input gets a safe value and the input
EN
is not connected. -
The right call is also highlighted as safe logic. The same conditions as for the left call apply. Here the 1st block input is supplied with a non-safe value but this is not relevant for highlighting the safe logic in the case of the
AND
block.
List of blocks (base variant)
Be sure to use the documentation "Safety instructions on working with the IDE" to determine whether there are conditions for using the following blocks when developing safety-related applications, e.g. whether actions are required from the system integrator for the block to actually be supported. |
The following blocks are provided as blocks for safe logic as of Neuron Power Engineer version 3.20.0:
Concept Information
List of blocks (special variant)
The following blocks are provided as blocks for safe logic (special variant) as of Neuron Power Engineer version 3.20.0: