Siemens SIMATIC Manual page 78

Examples for the Temperature Controllers
Putting the Sample into Operation
To put the sample into operation, follow the steps outlined below:
1. Copy the sample to a CPU.
2. In HW Config, set the cycle time of OB35 to 20 ms. If a time error occurs in the
cyclic interrupt level, you must extend the cycle time. In this case, the
simulation will run more slowly. When you control the real process, the cycle
time of OB35 and the sampling time of FB 59 "TCONT_S" must match.
The screenshot below illustrates controller tuning with TCONT_S:
zEn 13
Process value
The schematic above first shows a setpoint step change from 20°C to 36°C. The
manipulated variable limit is not reached, the temperature overshoots by
approximately 5°C (30%). With the subsequent setpoint step change from 36°C to
70°C, the upper limit of the manipulated variable is reached. This avoids overshoot
of the process variable.
If you want to avoid overshoot with small setpoint changes as well, you must
reduce PFAC_SP (for example, from 1.0 to 0.8).
6-14
Setpoint
Prosess value
Manip. variable
Zoom
PID Temperature Control
A5E00125039-02