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"Provide 0 value"
The value "0" is immediately made available to the safety program in the F-CPU as
soon as a discrepancy is detected between the signals of the two affected input
channels.
If you assigned the parameter "Provide 0 value", the sensor-actuator response time
will not be affected by the discrepancy time.
Discrepancy Time
Here, you can specify the discrepancy time for each pair of channels. The value
entered is rounded to multiples of 10 ms.
Requirements
You have set the following:
•
Sensor evaluation: "1oo2 evaluation" und
•
Type of sensor: "2-channel equivalent" or "2-channel non-equivalent"
Discrepancy Analysis and Discrepancy Time
If you use a 2-channel, one non-equivalent, or two 1-channel sensors, that
measure the same physical process variable, the sensors will respond with a slight
time delay among each other due to the limited accuracy of the arrangement.
Discrepancy analysis for equivalence or nonequivalence is used for fail-safe inputs
to determine faults based on the time characteristic of two signals with the same
functionality. Discrepancy analysis is initiated when different levels are detected for
two associated input signals (for nonequivalence testing, when the same levels are
detected). The signals are checked to establish whether the difference (when
checking for non-quality: the match) has disappeared following a selectable time
known as the discrepancy time. If not, this means that a discrepancy error exists.
The most cases, the discrepancy time is started but is not elapse fully since the
signal differences disappear after a short time.
Select a discrepancy time that is long enough so that when no error has occurred,
the difference between two signals (the match between two signals when checking
for non-equality) disappears before the discrepancy time elapses.
Response While the Discrepancy Time Is Running
While the discrepancy time is running internally on the module, either the last valid
value or "0" is provided for the safety program on the F-CPU by the input channels
involved depending on the parameter settings for the response to discrepancy.
Response after the Discrepancy Time Elapses
If the input signals do not match after the selected discrepancy time has elapsed
(when checking for non-equivalence) for example due to a break in the sensor
wire, a discrepancy error is detected and the "discrepancy error" diagnostic
message is generated in the diagnostic buffer of the F-I/O module indicating the
faulty channels.
ET 200eco Distributed I/O Station Fail-Safe I/O Module
A5E00297494-02
Digital F I/O Module
8-7
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