Phoenix Contact 2702924, User Manual

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Safety technology basics
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3 Safety technology basics
3.1 Cross-circuit detection
In both category 3 and category 4, a first fault must never lead to the loss of the safety func-
tion. This often makes it necessary to provide redundancy in the control structure.
Cross-circuit detection has the ability to detect short circuits, bridges or short circuits to
ground between two channels either immediately or within the framework of cyclic self-mon-
itoring.
A cross-circuit may be due to one of the following reasons:
– Squeezing
– High temperatures
– Chips
– Acids
– Etc.
Figure 3-1 Cross-circuit detection
L+
(L1)
A1 S11 S12 S21 S22
A2
(+)
( ) (GND) ( )
K1 K2
PTC
S33 S34
( )
( )
M
(N)
1.
2.
3.