Automation and Drives - SCE
5.4 Exercise Example
To accommodate the system step response, a few modifications have to be made in OB 35 and DB41. The following steps have to be performed for this:
Save your old project under a new name, and change the wiring of (S)FB 41 as follows: 1. With STEP7, specify the manipulated value directly.
The manipulated value is to be specified in the network below in a way that with a switch S1 (I 124.0), a selection can be made between two manipulated values.
| L | 0.000000e+000 | //Manipulated value 0% as 32 bit floating point number |
| UN | I 124.0 | //Negation of S1 (I 124.0) |
| SPB | M001 | //Jump if RLO = 1 to label M001 |
| L | 1.000000e+002 | //Manip.value 100% as 32 bit floating pt. nbr. |
M001: | T | MD 20 | //Transfer the value to flag double word MD 20 |
Now, for the switch position S1(I 124.0) ON, the manipulated variable y = 100%, and for OFF, the manipulated variable y = 0%. Consequently, a step of the manipulated value from 0 to 100% can be brought about with Switch S1. (For systems that tend to overshoot, the high manipulated value should amount to 90% or less.).
The external analog values and the manipulated value are assigned in OB1 as follows:
MAN | := | MD 20 | //Specify the manipulated value as manual value |
PV_PER | := | PEW 130 | //Actual value x |
LMN_PER | := | PAW 128 | //Manipulated variable y |
Switch manipulated value to manual mode
| Preface Fundamentals | Discontinuous Action Controller Controller Block (S)FB41 | Setting the System Appendix |
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| T I A Training Document | Page 57 of 64 | Module | |
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| B3 | |
Issued: 02/2008 |
| Control Engineering with STEP 7 | ||