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Ladder logic (PLC) templates

Ladder - Motor Start/Stop Seal-In

Five rungs of a direct-on-line starter solved with the start button already released: the parallel Start_PB/Motor_Run branch seals the coil in through the healthy stop and overload contacts, the run-hours CTU sits at 412 of its 500-hour preset so the done bit stays low, and the engine reports the service lamp as the one output never energised in this state.

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Template previewLadder logic (PLC)
Motor starter - seal-in, overload and run-hours counterDECLARED INPUT STATEStart_PB = 0Stop_PB = 1Overload_OK = 1Motor_Run = 1Fan_Request = 0L1N1Seal-in: the start button latches through the motor's own contactTRUEStart_PB0Motor_Run1Stop_PB1Overload_OK1Motor_Run12Contactor follows the run bitTRUEMotor_Run1Contactor13Run-hours counter, service due at 500 hTRUEMotor_Run1CTURun_HoursPRE 500 hrsCV 412 hrsDN4Service lamp on the counter done bitFALSERun_Hours.DN0Service_Lamp05Cooling fan runs with the motor or on operator demandTRUEMotor_Run1Fan_Request0Fan15 rungs solved in one scan: 4 true, 1 false. 11 tags, 5 declared as inputs.1 output is never energised in this state: 'Service_Lamp'.

Make it your own.

title "Motor starter - seal-in, overload and run-hours counter"
state: Start_PB=0, Stop_PB, Overload_OK, Motor_Run, Fan_Request=0

rung "Seal-in: the start button latches through the motor's own contact"
  branch
    --| |--Start_PB
    --| |--Motor_Run
  --| |--Stop_PB
  --| |--Overload_OK
  --( )--Motor_Run

rung "Contactor follows the run bit"
  xic Motor_Run
  ote Contactor

rung "Run-hours counter, service due at 500 h"
  xic Motor_Run
  ctu Run_Hours preset: 500 accum: 412 unit: hrs

rung "Service lamp on the counter done bit"
  xic Run_Hours.DN
  ote Service_Lamp

rung "Cooling fan runs with the motor or on operator demand"
  branch
    xic Motor_Run
    xic Fan_Request
  ote Fan