Ladder - Tank Fill on Level Switches
Seven rungs latch the fill valve on the low-level switch and leave the unlatch rung unpowered because the high-level switch has not made, run the 180 s overfill watchdog out to 96 s, and end on a deliberate interlock chain with no coil, so the engine reports both the never-energised overfill alarm and the rung whose logic is solved and thrown away.
Make it your own.
title "Process tank - fill on level switches with an overfill watchdog"
state: LSL_Low, Auto, Pump_Enable, LSH_High=0, Vent_Open=0
rung "Low level in auto latches the fill valve"
--] [--LSL_Low----] [--Auto----(S)--Fill_Valve
rung "High level is the only thing that unlatches it"
--] [--LSH_High----(R)--Fill_Valve
rung "Fill pump follows the valve while the pump is enabled"
xic Fill_Valve
xic Pump_Enable
ote Fill_Pump
rung "Watchdog - 180 s of filling with no high level"
xic Fill_Pump
xio LSH_High
ton T_Fill preset: 180 accum: 96 unit: s
rung "Overfill alarm on the watchdog done bit"
xic T_Fill.DN
ote Overfill_Alarm
rung "Vent fan runs while filling or while the vent is commanded"
branch
xic Fill_Pump
xic Vent_Open
ote Vent_Fan
rung "Interlock chain left without a coil - the destination was deleted"
xic Auto
xic Pump_Enable
xio Overfill_Alarm