37 2TLC172001M0211_A
Output example 4: Polarized safety relays
InA TestInB
0V
Q2
A
B
Q3
B
A
Monitoring
I_/IQ_
+24
/IQ_
When using a safety relay for output expansion of output Q2 and Q3, the connection between
the Pluto output and the safety relay is failsafe against short circuit from foreign +24V. This
because it is operated by -24V and since the safety relay is polarized it cannot be switched on
by +24V. As long as a -24V potential does not exist in the cabinet (which is not normally the
case) the connection is failsafe.
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