Chapter 10
271
I/O modules
10 I/O modules
10.1 Dual channel evaluation and discrepancy time
monitoring
Dual channel evaluation
The safety I/O modules, e.g. WS0-XTIO or WS0-XTDI, can carry out a dual-channel
evaluation when predefined input elements from the Elements window (e.g. RE27,
C4000, …) are connected to them. If such an input element is selected, you do not
need a separate function block for dual-channel evaluation (e.g. light curtain
monitoring, safety gate monitoring or magnetic switch).
The dual-channel evaluation evaluates the correct sequence of the two input signals.
It is expected that if one of the two signals has caused a switching off, the other signal
will follow accordingly. Which values the two signals must have depends on the type
of the dual-channel evaluation. There are two possibilities:
Equivalent evaluation
Complementary evaluation
Discrepancy time
Dual channel elements can be evaluated with or without a Discrepancy time. The
discrepancy time defines for how long the two inputs may have discrepant values after
one of the both input signals has changed without this being considered as an error.
To activate or to deactivate the Discrepancy time either click on the checkbox or
on the 3D buttons on the right side of the element settings dialog.
For elements connected to WS0-XTDI and WS0-XTIO modules the following
restrictions apply:
The Value for the discrepancy time can be set to 0 = inactive or to a value from 4 ms
to 30 s. It will be rounded automatically to the next greater multiple of 4 ms due to the
internal sampling frequency of the modules.
If signals of tested sensors are connected to WS0-XTDI and WS0-XTIO modules,
the discrepancy time has to be greater than the test gap + the max. Off-on delay of
the used test output. You can find these values in the project report under
Configuration, I/O module, Test pulse parameter.
If you try to set a lower discrepancy time than allowed, the minimum value will be
shown in the dialog window.
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