Siemens SIMATIC ET 200SP Manual page 21

Setting readback time dark test
Because the fault reaction time is extended by the length of the readback time dark test, we
recommend that you set the readback time dark test as low as possible, but high enough
that the output channel is not passivated.
In case of the "Connecting a load per digital output" (Page 27) application, see the warnings
and notes in the section describing the application.
To determine the readback time required for your actuator, refer to the diagram in the section
Switching capacitive loads (Page 51).
Setting readback time dark test with unknown actuator capacity
If the capacity of the actuator is not known, it may be necessary for you to determine the
value for the readback time dark test by trial and error. This may also be necessary due to
the part variances in the actuator or external influences.
Proceed as follows:
● Set the readback time dark test so that the output channel can be read back correctly but
your actuator does not respond yet.
● For verification use a 1-signal with a minimum duration that corresponds to the "Maximum
test period".
● If the output channel is passivated sporadically, set a higher value for the maximum
readback time dark test.
● If the output channel is passivated, the readback time dark test is too small for a
connected capacitive load. The discharge cannot take place during the configured
readback time dark test. Increase the readback time dark test.
If you have set the readback time dark test to the maximum value of 5 ms and there is still a
passivation of the output channel, there is either an external fault or the connected capacity
is outside the permitted range.
To increase availability, we recommend that you maintain an interval to the determined limit
for the times.
Digital output module F-DQ 8x24VDC/0.5A PP HF (6ES7136-6DC00-0CA0)
Manual, 05/2017, A5E38578424-AA
Parameters/address space
4.2 Explanation of parameters
21