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4 Safety Function Blocks
4 - 2
NX-series Safety Control Unit Instructions Reference Manual (Z931)
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.”
The common input variables for safety FBs are listed in the following table.
Rules That Are Specific to Safety FBs
Item
Rule
Default signal
The default for all SAFEBOOL signals is FALSE (i.e., the safe state).
Signal levels
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.
Outputs
All outputs are refreshed each safety task period.
Omitting I/O parameters
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.
Start processing
Outputs are initially set to the default values.
Outputs are enabled after the first FB call.
Error handling and diagno-
sis
All safety FBs have two error-related outputs:
Error
and
DiagCode
.
Safety FB Common Input Variables
Input param-
eter name
Data type
Valid range
Default
Description
Activate
BOOL
TRUE or
FALSE
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.
Summary of Contents for NX-SL series
Page 8: ...CONTENTS 6 NX series Safety Control Unit Instructions Reference Manual Z931 ...
Page 28: ...Sections in this Manual 26 NX series Safety Control Unit Instructions Reference Manual Z931 ...
Page 98: ...2 Standard Functions 2 64 NX series Safety Control Unit Instructions Reference Manual Z931 ...
Page 104: ...2 Standard Functions 2 70 NX series Safety Control Unit Instructions Reference Manual Z931 ...
Page 110: ...2 Standard Functions 2 76 NX series Safety Control Unit Instructions Reference Manual Z931 ...
Page 265: ...I 1 I NX series Safety Control Unit Instructions Reference Manual Z931 Index ...
Page 268: ...I 4 NX series Safety Control Unit Instructions Reference Manual Z931 Index ...
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