Siemens SIMATIC S7-1500 Manual page 27

PP operation
The M-switch is meaningless during the switch-on test in PP operation. The switch-on test
corresponds to the light test and current flows through the load. The light test is always
activated in PP operation.
①
Image 4-5
This parameter allows you to set the time for the readback.
If the signal was not read back correctly once the time has expired, the output channel is
passivated.
The switch on test detects the following faults:
● Short-circuit to L+ with output signal "0"
● Short-circuit to ground with output signal "0"
Through the configured readback time, short-circuits (cross-circuits) to an interfering signal
with a frequency > 1 / (2 x configured readback time) Hz can be suppressed (50:50
sampling ratio).
Short-circuits (cross-circuits) to an output of the same module are recognized.
Setting readback time switch on test
Because the fault reaction time is extended by the length of the set readback time, we
recommend that you set the readback time as low as possible, but high enough that the
output channel is not passivated.
To determine the readback time required for your actuator, refer to the diagram in the section
Switching capacitive loads (Page 55).
Digital output module F-DQ 8x24VDC/2A PPM (6ES7526-2BF00-0AB0)
Manual, 01/2016, A5E03858037-AA
Readback
Functional principle of the switch on test (PP switching)
WARNING
Parameters/address space
4.2 Explanation of parameters
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