Sampling Time; Initialization - Siemens SIMATIC Manual

4.3.2

Sampling Time

You specify the sampling time at the CYCLE parameter. You can also enter the
sampling time using the parameter assignment tool. The sampling time CYCLE
must match the time difference between two calls (cycle time of the cyclic OB
including scan rates).
Rule of Thumb for the Controller Sampling Time CYCLE
The controller sampling time should not exceed 10 % of the calculated integral time
of the controller (TI). Generally, you must set the sampling time to a much lower
value to achieve the required accuracy of the step controller (see numeric example
below).
Numeric Example
Required
Accuracy G
0.5 %
4.3.3

Initialization

FB "TCONT_S" has an initialization routine that is processed when the input
parameter COM_RST = TRUE is set. After processing the initialization routine, the
block sets COM_RST back to FALSE.
All outputs are set to their initial values.
If you require initialization when the CPU restarts, call the block in OB100 with
COM_RST = TRUE.
PID Temperature Control
A5E00125039-02
Temperature Step Controller FB59 "TCONT_S"
MTR_TM CYCLE = MTR_TM*G
10 s 0.05 s
Comment
The sampling time is
determined by the required
accuracy of the step controller.
4-7