Timers & CountersIntermediateIEC 61131-3

RTOR (Retentive Timer On with Reset)

Retentive on-delay timer with integrated reset input for accumulated time clearing.

The RTOR (Retentive Timer On with Reset) is a variant of the retentive on-delay timer that includes an explicit reset input as part of the function block interface. It accumulates time while enabled and retains the value when disabled. The built-in reset input provides a clean, self-contained way to clear accumulated time without requiring a separate reset instruction. RTOR is used in applications where run-time tracking with periodic reset is needed.

Parameters

Inputs

Name	Type	Description
IN	BOOL	Timer enable input
PT	TIME	Preset time value
R	BOOL	Reset input - clears ET and Q

Outputs

Name	Type	Description
Q	BOOL	Timer done output
ET	TIME	Accumulated elapsed time

Ladder Logic Example

// Ladder Logic - RTOR Timer
//
// |----[ Compressor_On ]----[RTOR Service_Timer]----|
// |                         IN: Compressor_On      |
// |                         PT: T#1000h            |
// |                         R:  Service_Complete   |
// |                         Q:  Service_Alarm      |

Structured Text Example

VAR
    Service_Timer : RTOR;
    Compressor_On : BOOL;
    Service_Alarm : BOOL;
    Service_Complete : BOOL;
END_VAR

Service_Timer(IN := Compressor_On, PT := T#1000h, R := Service_Complete);
Service_Alarm := Service_Timer.Q;

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Platform-Specific Implementation

Siemens (TIA Portal)

Use TONR with reset parameter in TIA Portal.

Allen-Bradley (Studio 5000)

Use RTO with RES instruction.

CODESYS

Custom implementation required using persistent variables.

Common Applications

Compressor service intervals
Belt replacement tracking
Bearing lubrication schedules
Total operating hour logs

Common Mistakes to Avoid

Confusing RTOR with standard TON behavior
Not persisting accumulated value across power cycles

Frequently Asked Questions

What is RTOR (Retentive Timer On with Reset) in PLC programming?

Retentive on-delay timer with integrated reset input for accumulated time clearing. The RTOR (Retentive Timer On with Reset) is a variant of the retentive on-delay timer that includes an explicit reset input as part of the function block interface. It accumulates time while enabled and retains the value when disabled.

What are common applications of RTOR (Retentive Timer On with Reset)?

RTOR (Retentive Timer On with Reset) is commonly used for: Compressor service intervals, Belt replacement tracking, Bearing lubrication schedules, Total operating hour logs.

How do I use RTOR (Retentive Timer On with Reset) in different PLC platforms?

Siemens: Use TONR with reset parameter in TIA Portal. Allen-Bradley: Use RTO with RES instruction. CODESYS: Custom implementation required using persistent variables.