RTO — Retentive Timer On
RTO
Timer
timer
(EN)
Preset
?
(DN)
Accum
?
Retentive on-delay timer. Like TON, but the accumulator survives rung transitions. Must be cleared explicitly with RES.
Operands
| Name | Type |
|---|---|
timer | TIMER |
How It Works
| Rung state | .EN | .TT | .ACC | .DN |
|---|---|---|---|---|
True, .ACC < .PRE | 1 | 1 | counting up | 0 |
True, .ACC ≥ .PRE | 1 | 0 | holds at .PRE | 1 |
| False | 0 | 0 | retained | retained |
A RES on the timer tag clears .ACC and .DN back to 0.
Example — Maintenance Hour Counter
Accumulate run-time across many start/stop cycles. Alert the operator once the machine has run for eight hours total.
Tag setup: RunHours is a TIMER with .PRE = 28800000 (8 hours in ms).
XIC(MachineRunning)RTO(RunHours);XIC(RunHours.DN)OTE(MaintAlert);XIC(ResetMaint)RES(RunHours)
The timer keeps counting only while MachineRunning is true, but never resets on its own. Pressing ResetMaint clears it back to zero.
When to Use
- Run-time accumulators, maintenance counters, total elapsed fault time.
- Any situation where timing must survive power cycles or intermittent triggers.
Common Mistakes
- Forgetting the
RES— the timer will stay.DN = 1forever after it finishes. - Confusing
RTOwithTON—TONresets automatically;RTOdoes not.
Related
- Timers overview — members, units, shared behaviour
- TON — non-retentive counterpart
- RES — clears the accumulator
- Counters overview — retentive accumulators for counts instead of time