Discrepancy Behavior - Siemens Simatic S7-1500 Manual

Parameters/address space
4.2 Explanation of parameters
1oo2 evaluation, equivalent/non-equivalent
With a 1oo2 evaluation equivalent/non-equivalent, two input channels are occupied by:
● a two-channel equivalent/non-equivalent sensor
● Two single-channel sensors
The input signals are compared internally for equivalence or non equivalence.
Note that in 1oo2 evaluation, two channels are combined into a channel pair. The number of
available process signals of the F-module is reduced accordingly. The evaluation result is
provided in the bit of the lower-order channel of the channel pair (channel n).
Discrepancy analysis
When using a two-channel sensor or two single-channel sensors which measure the same
process variable, the sensors interact with a slight time delay due to the limited precision of
their arrangement.
Discrepancy analysis for equivalence or non-equivalence is used for fail-safe inputs to detect
errors caused by the time characteristic of two signals with the same functionality. The
discrepancy analysis is initiated when different levels are detected in two associated input
signals (when testing for non-equivalence: the same level). A check is made to determine
whether the difference in levels (when testing for non equivalence: the same level) has
disappeared after an assignable time period, the so-called discrepancy time. If not, there is a
discrepancy error.
4.2.3.2

Discrepancy behavior

Function
For the "Discrepancy behavior", you assign the value that is supplied to the safety program
in the F-CPU during a discrepancy between two relevant input channels, which means while
discrepancy time is running. You assign the discrepancy behavior as follows:
● Supply last valid value"
● "Supply value 0"
Requirements
You have assigned the following:
● "Sensor evaluation": "1oo2 evaluation, equivalent" or "1oo2 evaluation, non-equivalent"
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Digital input module F-DI 16x24VDC (6ES7526-1BH00-0AB0)
Manual, 01/2016, A5E03858068-AA