The scenario
This circuit ensures that only one door can be unlocked at a time in a secure area, using relay logic. When a door is open, its door switch de-energizes the corresponding relay, opening the interlock contact for the other door's unlock circuit.
What is in this drawing
Read the decisions behind it.
01
Using normally-closed door switches for fail-safe operation
02
Employing NO relay contacts for interlocking rather than direct series wiring
03
Using separate pushbuttons to request access to each door
Suitable for mantrap configurations, cleanroom airlocks, or any two-door security system where simultaneous opening must be prevented.
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