General Rules For Safety Function Blocks - Omron NX-SL series Instruction & Reference Manual

4 Safety Function Blocks
General Rules for Safety Func-
tion Blocks
This section gives the general rules for safety function blocks. Safety function block is abbreviated as
"safety FB" and "function block" is abbreviated as "FB."
Rules That Are Specific to Safety FBs
Item
Default signal
Signal levels
Outputs
Omitting I/O parameters
Start processing
Error handling and diagno-
sis
Safety FB Common Input Variables
The common input variables for safety FBs are listed in the following table.
Input param-
eter name
Activate BOOL
4 - 2
The default for all SAFEBOOL signals is FALSE (i.e., the safe state).
The values of SAFEBOOL variables have the following meanings.
• FALSE: Indicates the safe state for a system output.
• TRUE: Indicates that operation is correct in terms of system safety (e.g., that correct opera-
tion is possible).
These definitions reflect the functionality in an IEC 61131 standard. For example, if an error
occurs, all outputs change to FALSE as defined in the default signal rule.
All outputs are refreshed each safety task period.
You can omit parameters. Defaults are applied for any omitted parameters.
However, these defaults will not lead to a non-safe state for the system under any circum-
stances.
Defaults are defined for attributes (i.e., for variables or constants) and for FBs.
Outputs are initially set to the default values.
Outputs are enabled after the first FB call.
All safety FBs have two error-related outputs: Error and DiagCode.
Data type Valid range
TRUE or
FALSE
Rule
Default
FALSE Enables and disables the FB.
You can input a variable or a constant.
The default is FALSE.
You can input a variable that gives the status of the
input device to evaluate for this parameter in order to
disable the FB and to prevent unrelated diagnostic
data from being output. If this parameter is FALSE, all
output variables take their default values.
Normally, input a TRUE constant to enable the FB.
NX-series Safety Control Unit Instructions Reference Manual (Z931)
Description