Fail-Safe Blocks
Fail-Safe Systems
A5E00085588-03
8-93
I/Os
Name Data Type Explanation Default
Inputs:
U F_REAL Input variable 0.0
U_HL F_REAL Upper limit 100.0
HYS F_REAL Hysteresis 0.0
SUBS_IN F_BOOL Substitute Input 0
Outputs:
QH F_BOOL 1: Upper limit violation 0
QHN F_BOOL Negating output QH 1
U_HL_O REAL Upper limit 100.0
HYS_O REAL Hysteresis 0
Note
If, when you create the program, you preset the QH output in CFC the initial value
1, it will remain set after startup (cold restart or warm restart) if (U_HL - HYS)
<= U
< U_HL.
It is only reset if U < (U_HL - HYS).
Note that the initial values of the output parameters do not appear in the printout of
the CFC chart. They must be checked in the printout of the safety program.
Error Handling
In the event of an error that is critical to safety, the system function SFC F_CTRL
is called. This records the event in the Diagnostic Buffer and requests a switch to
the reserve CPU if the error occurred only on the master CPU. For non-redundant
systems or a common-cause error occurring in both CPUs, the shutdown logic can
be configured to either disable the erred F-run-time group or the entire Safety
Program.
Error Information in Diagnostic Buffer
Error Code (W#16#...) Description
75D9H
Invalid REAL number generated during the calculations involving U, U_HL,
HYS and SUBS_IN
75DAH
Error in the safety data format of the inputs U, U_HL, HYS
(Error due to online modification of the Safety Program or internal CPU
fault)
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