GX Works2 Timer T0: Understanding K20, K30 and /T0

A timer is not just a “wait command.” It accumulates time while its condition remains true, then changes contact state so the sequence can move forward.

Confirm the timer base first

In an FX3U example where T0 uses a 100 ms time base, K20 means 2.0 seconds and K30 means 3.0 seconds. Timer bases can vary by PLC family and device range, so the useful habit is to verify the time base before treating the K value as seconds.

T0 and /T0 do opposite jobs

The T0 done contact is OFF before the preset expires and turns ON at completion. /T0 is true before completion and opens after the timer is done, which makes it useful for “allow only while timing” interlocks.

|----[ X0 ]----------------[ T0 K20 ]----|
|----[ T0 ]----------------( Y0 )--------|
|----[/T0 ]----------------( Y1 )--------|

Separate waiting from the next action

If a valve needs two seconds to stabilize before a motor starts, it is clearer to energize the valve first and let the T0 done contact release the motor later. A lamp or temporary warning that must stay active only during the wait can use /T0.

Common field mistakes

• Treating the K value as seconds without checking the timer base
• Forgetting that a non-retentive timer resets when its enabling condition drops
• Treating the done contact as a numeric value instead of a sequence state
• Letting timer logic delay a higher-priority stop or alarm condition