RTO (Retentive Timer) Ladder Logic Instruction

Definition

The Retentive Timer instruction is a retentive timer that is enabled when the preceding logic is true. The timer is paused when the preceding logic is false. The RTO timer can be compared to a stop watch that can be paused. A value is entered into the preset and an accumulator keeps track of the time. When the accumulator reaches the preset, the timer-done bit is set. The timer-timing bit is set while the accumulator is active. The timer is reset with a separate Reset (RES) instruction referencing the timers tag. When reset the accumulator is set to 0 and the EN, TT, and DN bits are cleared.

List of arguments

TIMER STRUCTURE          PRE DEFINED STRUCTURE

Tag Structure

  • BOOL     Timer.EN             Enable Bit, set when instruction is enabled.
  • BOOL     Timer.TT              Timer Timing Bit, set when instruction is enabled and accumulating time.
  • BOOL     Timer.DN             Timer Done BIT, Set when the accumulator reaches the preset.
  • DINT      Timer.PRE           Timer Preset , target value in milliseconds.
  • DINT      Timer.ACC           Timer accumulator, running value of timer in milliseconds.

Note: Timer must be scanned at a minimum of once every 69 minutes. A major fault will occur if the preset or accumulator fall below 0 (are negative). The RTO instruction is reset in the ladder logic with the RESET instruction referencing the RTO tag.