Chapter 9
200
Logic programming – Function blocks
Fault present and resetting errors
The Fault present output is a combined error output and changes to high if one of
the following cases occurs:
The discrepancy time on switching on is activated and has elapsed or
The discrepancy time on switching off is activated and has elapsed.
All error states and error outputs (Discrepancy error input A, Discrepancy error
input B, Fault present) are reset on a successful change to the active state
(Release output changes from low to high). In addition, both inputs must have
previously switched off simultaneously.
Discrepancy error input A
Discrepancy error input B
Status
Enable output
Active ActiveDiscrepant
AND mode
If, for the Evaluation mode, the Dual channel/AND mode option has been
selected, then the two inputs are monitored based either on the tolerant dual
channel rules or only as a logic AND, depending on the Actuator released input.
If the AND mode is active, then it is possible to change back to the active state by
switching off and switching back on only one input, without the need for the other
input to switch as well. If one or both of the inputs switches off, in all cases the
Release output is also switched off. The value for switching off due to Input B is
also dependent on the input mode in the AND mode.
The AND mode is activated if a falling edge (transition from high to low) occurs on
the Actuator released input and the Release output is high. If the Release output is
high at this point in time, then this means that the switch off has been triggered by a
different signal path that is also acting on the actuator.
The AND mode is deactivated again if the Actuator released input is high or if the
Max. time for AND mode has elapsed. When the Max. time for AND mode
elapses it has no effect on the Fault present output.
In AND-mode the discrepancy time is not monitored.
Figure 188:
Sequence/timing diagram
for the tolerant dual channel
monitor function block —
resetting errors
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