(* Motor Starter: Seal-In, N.C. Stop and Warning Horn — Motor Starter scene
   X1 = Start (N.O.)   X2 = Stop (N.C., TRUE when not pressed)
   X3 = Motor overload aux contact (N.C., TRUE while healthy, maintained)
   Y1 = Motor contactor   Y2 = Green run light   Y3 = Warning horn
   Start sounds the horn for 2 s, then the contactor pulls in. Stop or an
   overload trip drops everything at once, and nothing restarts on its own. *)
VAR
  StartRequest : BOOL;   // sealed-in start request
  WarnTimer    : TON;    // 2 s warning before the contactor pulls in
END_VAR

(* Seal-in — Start latches the request; Stop or an overload trip breaks it.
   X2 and X3 are N.C., so they are TRUE when the machine is healthy. *)
StartRequest := (X1 OR StartRequest) AND X2 AND X3;

(* Warning timer — timed from the sealed-in request, not from X1.
   Losing the request resets it, so a stop during the warning aborts the start. *)
WarnTimer(IN := StartRequest, PT := T#2s);

(* Horn during the warning only, contactor after it, run light follows *)
Y3 := StartRequest AND NOT WarnTimer.Q;
Y1 := WarnTimer.Q;
Y2 := Y1;