Pilz PSS SB HYD, Basic license - Manual (Page 30)

3-6
Safety
Modular Block System: Hydraulic Presses
Pulsed input signals
Input devices for inputs with infrequent operation (e.g. E-STOP, off
buttons, etc.) must be pulsed using test signals. The connection of test
pulses to input devices is described in the “Installation Manual”.
Test pulses should also be used for input devices which have an important
safety function and frequent operation (e.g. two-hand, camshaft etc.).
Self test on the outputs
PSS output modules regularly carry out function tests. Using these tests,
dual-pole switching output modules on the PSS are automatically able to
detect and deal with open circuits, short circuits and external power
sources in the periphery wiring.
Single-pole switching output modules can detect short circuits but not
open circuits.
Fault prevention
Not all potential faults can be detected and managed. Such faults must be
excluded by suitable wiring.
Example: If the feed to the input device and the feedback from the input
device to the input use the same multicore cable, a short circuit between
the two wires could short out the input device. Such a fault would go
undetected.