Notes On Wiring - Pilz PSS Series Installation Manual

Notes on wiring

Where safety-relevant applications are concerned, it is essential that
short circuits and line breaks are unable to cause a hazardous condition
within a plant.
The way in which this is done will depend on the degree of hazard within
the plant itself, the switching frequency of the input devices and the level
of safety of the input devices and actuators. These points must be
assessed in conjunction with the relevant standards or approvals body
(e.g. BG or TÜV).
The following terms are important:
• Test pulses
These are signals which change status on several occasions within a
period of time.
• Single-channel safe input devices
These are positively-driven normally-closed contacts which open on
actuation (failsafe principle).
• Elimination of short circuits between signals
This is possible within electrically-enclosed areas and also outside
electrically-enclosed areas for signals conducted in different multicore
cables. However, all components must meet the relevant regulations in
accordance with EN, DIN and VDE.
• In principle, the possibility of earth faults and line breaks occurring
cannot be eliminated.
If a dual-pole switching output on the PSS is used to drive the actuators, a
test for short circuits and line breaks will automatically be carried out
during each cycle. For this purpose the actuator will be switched off for
approximately 100 µs. When using single-pole outputs or test pulses, a
switch-off test will only be carried out if designed into the self-check.
With multi-channel pulsed input devices, short circuits and line breaks can
be detected via feasibility checks in the control program.
The input test on the programmable safety system uses test pulses to
enable the system's operating program to carry out a test to detect short
circuits and line breaks. The following pages contain details of connection
examples which may be of use when wiring the unit.
Installation Manual: PSS 3056 Series
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