Fig.: Redundant two-channel outputs in different groups in connection with two-channel
switching-off circuit
Safety note:
• For a safety related assessment of the partial system output the data issued by the
respective manufacturer (MTTF
D
, FIT-numbers, B10d-value, etc.) must be used when
using external elements, e.g. for switching amplification, in the shut-down circuit.
• The DC-values listed in the table must be used conservatively and compliance with the
boundary conditions (see table under „Remarks“) must be ensured.
• According to the applicable standards, fault exclusions are permitted. The boundary
conditions mentioned in this context must permanently be met.
• When using elements for switching amplification in safety circuits, their function must be
monitored by means of suitable readback contacts, etc. (see circuitry examples). Suitable
readback contacts are contacts which are linked with the contacts in the shut-down circuit
in a positively switching way.
• The switching ability of the external switching amplifier must be cyclically tested. The time
between 2 tests must be determined in accordance with the requirements of the
application and ensured by suitable measures. Suitable measures may be of
organizational (On and Off switching at the beginning of a shift, etc.) or technical
(automatic, cyclic switching) nature.
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