Siemens SIMATIC S7 System Manual page 381

100-millisecond resolution
The 100-ms timers count the number of 100-ms timer intervals that have elapsed since the
active 100-ms timer was last updated. These timers are updated by adding the accumulated
number of 100-ms intervals (since the previous scan cycle) to the timer's current value when
the timer instruction is executed.
The current value of a 100-ms timer is updated only if the timer instruction is executed.
Consequently, if a 100-ms timer is enabled but the timer instruction is not executed each
scan cycle, the current value for that timer is not updated and it loses time. Likewise, if the
same 100-ms timer instruction is executed multiple times in a single scan cycle, the number
of 100-ms intervals is added to the timer's current value multiple times, and it gains time.
100-ms timers should only be used where the timer instruction is executed exactly once per
scan cycle.
Since the timer can be started anywhere within a 100-ms interval, the preset must be set to
one time interval greater than the minimum desired timer interval. For example, to guarantee
a timed interval of at least 2100 ms using a 100-ms timer, the preset time value should be
set to 22.
TON On-delay timer example
LAD
Timing Diagram
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
100 ms timer T37 times out after 1 s
(10 x 100 ms)
I0.0 ON = T37 enabled,
•
I0.0 OFF = disable and reset T37
•
T37 bit is controlled by timer T37
Program instructions
STL
Network 1
LD I0.0
TON T37, +10
Network 2
LD T37
= Q0.0
7.17 Timer
381