Siemens SIMATIC ET 200AL System Manual page 934

Parameters/address space
4.3 Explanation of parameters
During the execution time (duration of short-circuit test + startup time of sensor after the
short-circuit test) of the short-circuit test, the last valid value of the input before the start of
the short circuit test is passed to the F-CPU. The activation of the short-circuit test thus affects
the response time of the respective channel or channel pair.
Discrepancy time variation with short-circuit test
If your process input changes near when a short-circuit test is in progress, a discrepancy is
detected in less time than your configured discrepancy time.
Elements of discrepancy time variations are defined as follows:
• Tdisc = configured discrepancy time
• Tsct = configured short circuit test duration
• Tfilter = configured input filter time
• Tda = actual discrepancy time, time between process signal changes that can be detected
as a fault
The range of detected discrepancy time is as follows:
• If Tfilter < Tsct: {Tdisc - (Tfilter + Tsct)} <= Tda <= Tdisc
• If Tfilter >= Tsct: {Tdisc - (2 x Tsct)} <= Tda <= Tdisc
Your configured discrepancy time should account for this variation to avoid unexpected
passivations.
Interval for short-circuit test
You can specify how often the short-circuit test is executed (Interval) when the "Short-circuit
test" check box is selected. The interval defines the period of time between two consecutive
sensor supply OFF test pulses.
This value is the time between the OFF pulses of the sensor supply.
Note
The interval between pulses must be a minimum of eight times the duration of a pulse.
Short-circuit testing is performed on V
detect shorts between the two sensor supplies as follows:
28
and V independently, allowing module circuitry to
S1 S2
Digital I/O module F-DI 4+F-DQ 2x24VDC/2A, 4xM12 (6ES7146-5FF00-0BA0)
Equipment Manual, V1.0, 05/2021, A5E51082342-AA