The TON block delays output activation. While IN remains TRUE, the timer accumulates scans or time; after the configured delay is reached, Q becomes TRUE.
Typical FBD symbol
IN
TON
Q
Typical FBD symbol for TON
Inputs
Name
Type
Required
Description
IN
BOOL
Yes
Timer enable signal.
Outputs
Name
Type
Required
Description
Q
BOOL
Yes
TRUE after the configured delay has elapsed.
Parameters
Name
Type
Required
Default
Description
PT_SCANS
number
No
1
Delay threshold in scans.
PT
number
No
-
Delay in milliseconds when a time preset is used.
Stateful
Yes, the block keeps internal state between scans.
Behavior rule
When IN = TRUE, the timer accumulates scans; Q becomes TRUE when elapsed scans reach the threshold. When IN = FALSE, elapsed and Q reset.
Scan table
Example for PT_SCANS = 2.
Scan
IN
elapsed
Q
1
FALSE
0
FALSE
2
TRUE
1
FALSE
3
TRUE
2
TRUE
4
FALSE
0
FALSE
Practical use
turning on a fan after a delay;
filtering a short sensor pulse.
What to watch
Treating TON as a program pause. The PLC keeps scanning; the timer only produces a delayed logical output.
