Mitsubishi Electric WS0-CPU0 Operating Manual page 202

Chapter 9
Figure 186:
State diagram for the
tolerant dual channel
monitor function block
Note
Figure 187:
Sequence/timing diagram
for the tolerant dual channel
monitor function block —
change to active
199
Logic programming – Function blocks
Discrepancy time
An optional discrepancy time can be defined. The discrepancy time defines how
long the two inputs are allowed to have discrepant values after a change in one of
the two inputs without this situation resulting in an error. The Discrepancy error
input A and Discrepancy error input B outputs indicate which input has not
followed in the expected time.
A discrepancy error (time-out) is reset once the active state has been achieved, i.e.
a correct sequence has been followed and as a result the Release output changes
to high.
Sequence/timing diagrams
For the change between the individual states of the tolerant dual channel monitor
the following rules apply:
The tolerant dual channel monitor can only transfer to active (Release output
changes from low to high) if the following criteria are met:
 both inputs have each switched off once since the last active state
and
 the discrepancy time has not elapsed or the discrepancy time monitoring for
switching on is deactivated.
This means that it is not possible to change from active to discrepant and back again
if only one input has switched off.
The sequence/timing diagrams shown in this section relate to the equivalent input
mode. For the complementary input mode, input B is to be considered inverted.
Status
Enable output
Inactive Discrepant Active Discrepant Active