NORSTAT Safety Relays - Handbuch (Seite 38)

application guide safety relays from riese electronic page 36
7 Safety with contactor
Before safety relays where produced all electronic safety circuits where made with contactors. This
technology would be replaced by the safety relays.
(part of the siemens application book)
Function
After pressing the start bottom the contacts of the conductor K1 switches. All normally opened contacts
close and all normally closed contacts open. Then conductor K2 and K3 switches. After K2 and K3 had
switched K1 falls back in his basic position. Only after pressing the emergency stop bottom K2 and K3 will
fall back in there basic position.
If a failure at K2 or K3 happens for example the normally opened contact will not open then the normally
closed contact does not close.
When this happens the circuit could not be restarted.
Formally this safety circuit were realized with two conductors not with three. Because of safety reasons
this kind of safety circuit will not longer be used.
Emergency stop
Start
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