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| 12/11/2009 9:23 PM | |
Joined: 12/5/2006 Last visit: 4/12/2023 Posts: 73 Rating:
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Hi All, I am in the process of converting an S5 application to an S7. Application does contain a PID loop usingOB251, typically using an FB41 would do the job. I followed FAQ http://support.automation.siemens.com/WW/view/en/17991108for the second time and concluded that this FAQ does not make sense: 0: KH = 0000; Reserved 1: KF = +00010; Parameter KP 2: KF = +00000; Reserved 3: KF = +00130; Parameter R 4: KF = +00000; Reserved 5: KF = +00100; Parameter TI 6: KF = +00000; Reserved 7: KF = +00000; Parameter TD 8: KF = +00000; Reserved 9: KF = +01050; Variable Setpoint W Following therules on this link would mean I would haveto put a Gain parameter in S7 of 0.000130 where we have Gain S7= KP X R which seems to me like an irrelevant gain value. Also for TI with a sampling rate of 250 ms I should have according to the FAQ TI s7=0.250/0.001 (factor 0.01) then I should have 250s which is a an exageratedS7TI. I am not sure if my calculations are accurate or something is wrong with those formulas. If someone has used those formulas before successfully I would appreciate any feedback.As I tried values for my PID loop around those ranges and I had no way to stabilize my loop with theS7 CPU. I have also used it in another project and thevalues put in the PI where far different from the ones calculated through those formulas. |
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