Ladder - Conveyor Jam Watchdog

Six rungs where the photo-eye has been blocked for 8 s against a 6 s TON preset, so the jam latches on rung 4 after the belt coil was already solved true on rung 2 -- the one-scan lag that makes a real controller keep the belt running for one more pass -- with the beacon and horn coils drawn in series off the same latched fault.

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title "Belt conveyor - photo-eye jam detection"
state: Run_Cmd, E_Stop_OK, Guard_Closed, Eye_Blocked, Jam_Reset=0

rung "Safety chain must be healthy before anything runs"
  xic E_Stop_OK
  xic Guard_Closed
  ote Safe

rung "Belt runs on command while safe and not jammed"
  xic Run_Cmd
  xic Safe
  xio Jam_Fault
  ote Belt_Motor

rung "Photo-eye blocked longer than 6 s while running is a jam"
  xic Belt_Motor
  xic Eye_Blocked
  ton T_Jam preset: 6 accum: 8 unit: s

rung "Latch the jam fault - it must survive the belt stopping"
  xic T_Jam.DN
  otl Jam_Fault

rung "Panel reset is the only way out of the latch"
  xic Jam_Reset
  otu Jam_Fault

rung "Beacon and horn, two coils in series off one fault"
  xic Jam_Fault
  ote Beacon
  ote Horn