Analog modules
9.3 SM 336; F-AI 6 x 0/4 ... 20 mA HART
Fail-safe signal modules
272
Installation and Operating Manual, 01/2010, A5E00085586-10
If the process value does not represent the standard value at an instant but is outside the
tolerance window, a discrepancy exists.
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Figure 9-40 Example of a relative tolerance window
with
discrepancy (parameter assignment:
standard value = MAX)
The assigned discrepancy time starts as soon as a discrepancy is detected. The discrepancy
time runs as long as the discrepancy exists.
Depending on the configuration of the standard value (MAX or MIN), the next higher or lower
"old" value is forwarded as the process value.
If the input channels fall below the specified tolerance prior to expiration of the discrepancy
time (input channels are no longer discrepant), the discrepancy time is cleared and is
restarted only when a new discrepancy is detected.
If the input channels are discrepant after startup or after a channel fault, 7FFF
H
is output and
the discrepancy time is started.
If the input channels are no longer discrepant when the discrepancy time expires, the
standard value is output and the channel fault must be acknowledged. In this case, a
channel-specific diagnosis is not signaled.
If the discrepancy time expires, an error is signaled and the process value is set to 7FFF
H
. In
S7 Distributed Safety, the fail-safe value 0 is provided in the PII for the safety program in
place of 7FFF
H
. In
S7 F/FH Systems the fail-safe value assigned at the input SUBS_V of the
channel driver will be provided in the PII.
A discrepancy error is handled by the safety program in the same way as a channel fault.
For more information, refer to the
S7 Distributed Safety Configuring and Programming or S7
F/FH Systems Configuring and Programming Programming and Configuring Manual.
