Discrepancy Time - Siemens Simatic S7-1500 Manual

Supply last valid value"
The most recent valid value (old value) before the discrepancy occurred is 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. This value is supplied until the discrepancy disappears or
the discrepancy time expires and a discrepancy error is detected. The sensor-actuator
response time is correspondingly increased by this time.
This means the discrepancy time of connected sensors with 1oo2 evaluation must be
adjusted to fast response times. It makes no sense, for example, if connected sensors with a
discrepancy time of 500 ms trigger a time-critical shutdown. In the worst-case scenario, 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 which is also sufficient to compensate
for faulty triggering of discrepancy errors.
"Supply value 0"
As soon as a discrepancy between the signals of the two relevant input channels is detected,
the value "0" is made available to the safety program in the F-CPU.
If you have set "Supply value 0", the sensor-actuator response time is not affected by the
discrepancy time.
4.2.3.3 Discrepancy time
Function
You can set the discrepancy time for each channel pair.
Requirements
You have assigned the following:
● "Sensor evaluation": "1oo2 evaluation, equivalent" or "1oo2 evaluation, non-equivalent"
In most cases, a discrepancy time is started, but does not fully expire because the signal
differences are cleared within a short time.
● Set the discrepancy time high enough that in the error-free case the difference between
the two signals (when testing for non equivalence: the same levels) has always
disappeared before the discrepancy time has expired.
Behavior while discrepancy time is running
While the programmed discrepancy time is running internally on the module, either the last
valid value or "0" is returned to the safety program on the F-CPU by the input channels
involved, depending on the parameter settings for the behavior at discrepancy.
Digital input module F-DI 16x24VDC (6ES7526-1BH00-0AB0)
Manual, 01/2016, A5E03858068-AA
Parameters/address space
4.2 Explanation of parameters
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