Siemens SIMATIC ET 200AL, System Manual

Page: 940 / 2255

Parameters/address space
4.3 Explanation of parameters
Digital I/O module F-DI 4+F-DQ 2x24VDC/2A, 4xM12 (6ES7146-5FF00-0BA0)
34
Equipment Manual, V1.0, 05/2021, A5E51082342-AA
Proceed as follows:
•
Set the "Maximum readback time" so that the output channel can be read back correctly
but your actuator does not respond yet.
• For verification, use the process value "0" with a minimum duration that corresponds to
the "maximum test period" parameter. Execute a process value change from "1" to "0".
• If the output channel is passivated, the "Maximum readback time" is too small for the
connected capacitive load. The discharge cannot take place within the configured
"Maximum readback time". Increase the "Maximum readback time".
If you have set the "Maximum readback time" to the maximum value of 400 ms and there is
still a passivation of the output channel, there is either an external fault or the connected
capacitance is outside the permitted range.
Dark test
Dark tests are switch-off tests which occur during an output bit-pattern test sequence.
When dark test is disabled on an output channel, the parameter "Maximum readback time" is
only relevant for the process value change.
For a dark test, one of the output channel's switches is briefly turned OFF while the output
channel is active (output signal "1"). As a result, current flow through the output is
interrupted for a short time. A sufficiently slow actuator does not respond to this and remains
switched on.
① Readback
Figure 4-1 Functional principle of the dark test (PM switching)