Siemens SIMATIC, Руководство по эксплуатации

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Fail-Safe Electronic Modules
8.2 4 /8 F-DI/4 F-DO DC24V/2A PROFIsafe Digital Electronic Module
ET 200pro Distributed I/O System - Fail-Safe Modules
Operating Instructions, 05/2007, A5E00394073-02
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Short-Circuit Test Parameter
The cyclic short-circuit test is enabled and disabled using the short-circuit test parameter.
The short-circuit test is only useful for simple switches that do not have their own power
supply. If the short-circuit test has been enabled, the internal sensor supplies must be used
(see also
"Use Cases of the 8/16 F-DI DC24V PROFIsafe Electronic Module").
Behavior at Discrepancy Parameter
As the "behavior at discrepancy" you assign 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,
i.e., during the discrepancy time. You assign the behavior at discrepancy as follows:
●
"Provide last valid value", or
● "Provide value 0"
Requirements
You have assigned the following:
●
Evaluation of the sensors: "1oo2 evaluation"
"Provide last valid value"
The last valid value (old value) before discrepancy occurs is made available to the safety
program in the F-CPU as soon as a discrepancy is detected between the two relevant input
channel signals. This value is supplied until the discrepancy disappears or until the
discrepancy time expires and a discrepancy error is detected. The sensor-actuator response
time is extended by an amount equal to this time.
As a result, the discrepancy time of sensors connected via two channels must be set for fast
reactions to short response times. It makes no sense, for example, for a time-critical
shutdown to be triggered by sensors connected via two channels with a discrepancy time of
500 ms. 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 sensors in the process in such a way as to minimize
discrepancy.
● Then select the shortest possible discrepancy time that includes a sufficient cushion
against false tripping of discrepancy errors.
"Provide value 0"
The value "0" is made available to the safety program in the F-CPU as soon as a
discrepancy is detected between the signals of the two relevant input channels.
If you specified "Provide value 0", the sensor-actuator response time is not affected by the
discrepancy time.