Siemens SIMATIC PCS 7 Operating Manual page 68

Configuring S7F/FH hardware
6.4 Setting system parameters for F-signal modules
Parallel interconnection
To improve performance you can connect two digital outputs of the module for an actuator in
parallel (channel coupling). This increase in performance is only permitted on the same
module and between the following channels:
● Channel 0 and channel 1: Connection between terminal 3 and 7
● Channel 2 and channel 3: Connection between terminal 11 and 15
Maximum dark test readback time
Dark periods arise during deactivation tests and the complete bit pattern test. In this process,
a test signal is connected to the output from the fail-safe output module while the output is
active ("1" output signal).
This deactivates the output briefly (= "dark period"). A sufficiently inactive actuator does not
respond to this and remains activated. Each output channel has its own configurable
maximum readback time for the dark test. Configure these parameters so that the module
reads back correctly and your actuator still does not react to the switch-off pulse.
Short-circuit level
The "short-circuit level" parameter determines the value of the load which, if undershot,
leads to the module diagnosing a short circuit and switching off the channel.
This means that in the range between employing the current limiting (the inflection point on
the output curve) and the reaching of the short-circuit level, no diagnostics are transmitted.
The channel remains switched on until the load undershoots the short-circuit level.
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Compendium Part B - Process Safety (V8.2)
Operating Manual, 07/2016, A5E35031794-AB