Fail-Safe Blocks
Fail-Safe Systems
8-98 A5E00085588-03
Error Information in Diagnostic Buffer
Error Code (W#16#...) Description
0x75D9
Invalid REAL number
0x75DA
Error in the safety data format (error due to online modification of the
Safety Program or internal CPU fault)
8.8.4 F_1oo2_R
Function
This block selects its output from one of two inputs based on the QBAD inputs.
IN1 will be output unless QBAD1 is set, which selects IN2 as the output. The
QBAD output will be set if both QBAD inputs are set.
Note
This function block is supplied as a block type. This adds one restriction to the
usage of this block: It may not be placed within another block type.
I/Os
Name Data Type Explanation Default
Inputs:
IN1 F_REAL Input variable 1 0.0
IN2 F_REAL Input variable 2 0.0
QBAD1 F_BOOL IN1 invalid 0
QBAD2 F_BOOL IN2 invalid 0
DELTA REAL Allowable difference 0.0
Outputs:
OUT F_REAL Selected value 0.0
QBAD BOOL Invalid selected value 0
DIS1 BOOL IN1 DELTA Discrepancy 0
DIS2 BOOL IN2 DELTA Discrepancy 0
The block employs a one-out-of-two selection scheme and is often used to detect
the failure of sensors and input processing subsystems. Typical use of this block
would have the V and QBAD outputs of two F_CH_AI blocks connected to the
F_1oo2_R’s respective IN and QBAD inputs.
At least one of the two inputs must have their QBAD input clear for QBAD output to
be clear.
The DIS outputs indicate a discrepancy between the respective input, the DELTA
input and the selected output (the difference between IN and OUT is greater than
DELTA).
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