TON Timer in Sysmac Studio: Complete On-Delay Programming Guide

The TON (On-Delay Timer) instruction in Sysmac Studio delays energizing an output (Q = TRUE) for a specified preset duration (PT) after its input condition (In) turns TRUE. Standardized under IEC 61131-3 across the Omron NJ/NX machine controller family, TON is the primary timing block used in machine automation for sensor debouncing, motor star-delta starter transitions, pneumatic travel verification, and sequential interlocks.

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Technical Specifications and Timer Matrix

Parameter / Feature	Value / Specification	Notes
Controller Families	Omron NJ101, NJ301, NJ501, NX102, NX1P2	All Sysmac MAC platforms
Instruction Standard	IEC 61131-3 Standard Timer	On-Delay Function Block
Languages Supported	Ladder Diagram (LD), Structured Text (ST)	Deterministic cycle evaluation
Input Variable (In)	BOOL	Starts timing on rising edge (FALSE → TRUE)
Preset Time (PT)	TIME (T#0ms to T#106751d_23h_47m_16s_854.775807ms)	Resolution: 1 ns (evaluated per task period)
Output Variable (Q)	BOOL	Stays FALSE until ET = PT, then switches to TRUE
Elapsed Time (ET)	TIME	Accumulator tracking elapsed time from T#0s to PT

Sysmac Studio Timer Comparison Matrix

Timer Type	Output Turn-ON Condition	Output Turn-OFF Condition	Primary Industrial Application
TON (On-Delay)	Delays ON by PT after In goes TRUE	Immediately when In goes FALSE	Sensor debouncing, cylinder travel verification
TOF (Off-Delay)	Immediately when In goes TRUE	Delays OFF by PT after In goes FALSE	Cooling fan overrun, conveyor clearing
TP (Pulse Timer)	Immediately on rising edge of In	Fixed duration PT, independent of In	Pneumatic blow-off, camera strobe pulses
AccumulationTimer	Accumulates time whenever In is TRUE	Resets via dedicated Reset input	Operating hours monitoring, tool life tracking

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Programming TON: Ladder Diagram vs. Structured Text

Sysmac Studio allows creating TON timer instances in either graphical Ladder rungs or Structured Text routines:

Ladder Diagram Implementation

In Ladder Diagram, assign a dedicated tag of data type TON (e.g., TON_Instance):

Structured Text (ST) Syntax

In Structured Text routines, call the instance and map its inputs and outputs:

// TON Timer Invocation in Structured Text
TON_Instance(
    In := Sensor_Detect,    // BOOL: Execution condition
    PT := T#2s,             // TIME: 2-second delay preset
    Q  => Actuator_Enable,  // BOOL: Output delayed flag
    ET => Current_ET        // TIME: Elapsed time monitor
);

Parameter Reference Table

Variable	Direction	Data Type	Meaning	Operational Rule
In	Input	BOOL	Timer Input	TRUE starts timing. FALSE resets ET to 0 and turns Q to FALSE.
PT	Input	TIME	Preset Time	Delay duration. Uses the T# format: T#500ms, T#2s, T#1h.
Q	Output	BOOL	Timer Output	Switches to TRUE when ET >= PT. Stays TRUE until In drops.
ET	Output	TIME	Elapsed Time	Current elapsed duration since In became TRUE.

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Operational Mechanics: Normal vs. Interrupted Execution

Understanding the difference between full timing completion and interrupted input signals is fundamental to machine reliability:

Scenario 1: Normal Full-Cycle Timing

In the example below, a 5-second TON timer is monitored. When input contact A turns TRUE, elapsed time accumulator def starts counting. When def reaches 5 seconds, output abc energizes. When contact A drops to FALSE, output abc de-energizes immediately and def resets to zero.

Scenario 2: Interrupted Cycle (Early Drop of Input)

What happens if contact A drops to FALSE before the 5-second preset time expires? In the GIF below, contact A goes FALSE at approximately 4 seconds. The timer immediately aborts, elapsed time def is cleared to zero, and output abc never energizes.

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Detailed Timing Diagram

The timing chart below illustrates the exact behavior of In, Q, and ET in Sysmac Studio:

Key timing principles:

1. When In transitions to TRUE, ET begins incrementing each task period.
2. When ET reaches set time PT, Q transitions to TRUE and ET stops incrementing.
3. When In transitions to FALSE, ET resets to 0 and Q transitions to FALSE.
4. If In transitions to FALSE before ET reaches PT, the timer resets immediately.

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Dynamic Runtime Preset Time (PT) Modification

If PT is dynamically altered (e.g., from an HMI recipe or formula) while In is already TRUE:

Current Timer State	Output Q State	New PT Value	Controller Action
Timing Complete (ET = PT)	TRUE	Any value	Q remains TRUE. ET remains unchanged at the previous value.
Timing in Progress (ET < PT)	FALSE	PT_new >= ET	Timing continues until reaching PT_new.
Timing in Progress (ET < PT)	FALSE	PT_new < ET	Output Q transitions to TRUE immediately.

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Field Notes & Practical Engineering Tips (“Saha Notu”)

Practical engineering tips learned from machine commissioning on factory floors:

• Optical & Proximity Sensor Debouncing: In high-speed packaging applications, vibrations and mechanical bounce can create false triggers. A TON timer with PT := T#10ms or T#20ms placed immediately after the physical input effectively filters noise spikes.
• Motor Star-Delta Transition Delay: When transitioning between star and delta contactors in large conveyor drives, always interlock the delta contactor through a TON delay (T#80ms to T#120ms) to guarantee the star contactor’s physical arc has fully extinguished before delta energization.
• Do Not Enclose TON in Conditional Blocks: Never place a TON instance inside a conditionally executed IF statement, CASE branch, or action block. When the conditional block is bypassed, Sysmac Studio will not scan the timer, causing the internal accumulator to freeze or exhibit erratic behavior when re-entered. Always run the timer unconditionally in the main task and conditionally evaluate its Q output instead.
• Sysmac Jitter & Task Cycles: Sysmac Studio evaluates timer instances during each primary task execution. While the internal timer counter has 1 ns resolution, jitter between task periods is typically bounded between -100 ns and +(100 ns + 1 task period). For sub-millisecond precision, use high-speed interrupt tasks or EtherCAT Distributed Clock (DC) timestamping.
• Fault Diagnostic: If an unexpected timer condition causes a cycle time fault or task overrun, look up the hexadecimal controller code with the Omron Sysmac Error Code Lookup tool.

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Related Guides

• Sysmac Studio TOF Timer (Off-Delay) Complete Guide
• Installing EtherCAT ESI XML Device Profiles in Sysmac Studio
• Omron PLC and Sysmac Studio Error Code Search Engine