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Digital F I/O Module
Input delay
Note
If there is a risk of overvoltage on the lines, to avoid a safety shutdown for the fail-
safe digital inputs and the sensor power supply, you must set an input delay of
15 ms.
Short-Circuit Test Parameter
The cyclic short-circuit test is activated or deactivated using the short-circuit test
parameter. The short-circuit test is only useful for simple switches that do not have
their own power supply. The internal sensor supplies must be used whenever the
short-circuit test has been activated (see also Section 8.2.1).
Response to Discrepancy Parameter
As the "response to discrepancy", you set the value that is made available to the
safety program in the F-CPU while there is a discrepancy between the two input
channels involved; in other words, during the discrepancy time. You set the
response to discrepancy as follows:
•
"provide last valid value" or
•
"provide 0 value"
Requirements
You have set the following:
•
Sensor evaluation: "1oo2 evaluation" und
•
Type of sensor: "2-channel equivalent" or "2-channel non-equivalent"
"Provide Last Valid Value "
The last valid value (old value) before discrepancy occurs is made available in the
safety program in F-CPU as soon as a discrepancy is determined between the
signals of the affected input channels. This value remains available until the
discrepancy disappears or until the discrepancy time expires and a discrepancy
error is detected. The sensor-actuator response time is extended according to the
this time.
As a result, the discrepancy time of sensors connected over two channels must be
set for fast responses to short response times. It makes no sense, for example, if
sensors connected over two channels with a discrepancy time of 500 ms trigger a
time-critical shutdown. In the worst case, the sensor-actuator response time is
extended by an amount approximately equal to the discrepancy time:
•
For this reason, position the sensor in the process in such a way to minimize
discrepancy.
•
You should then select the shortest possible discrepancy time, which, on the
other hand, also provides adequate reserves against the erroneous triggering
of discrepancy errors.
8-6
ET 200eco Distributed I/O Station Fail-Safe I/O Module
A5E00297494-02
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