5/18/2011 7:38 AM | |
Posts: 53 Rating: (0) |
Hi, Attachmentpid.pdf (1399 Downloads) |
5/19/2011 12:26 AM | |
Posts: 53 Rating: (0) |
Hi Aret, Thanks for your reply. Find attached the pdf of my code for the particular FC. We are controlling a steamcontrol valve to achieve the desired cooktemperature. The temperature setpoint for the is set from the HMI (db95.dbd74). network no 5 is to ensure the transition from Auto to manual is bumpless but not sure why it's not bumpless from manual to auto. please advise. Thanks, MS AttachmentFC52.pdf (1234 Downloads) |
5/19/2011 12:55 PM | |
Joined: 1/28/2009 Last visit: 9/10/2024 Posts: 6849 Rating: (1365) |
Hi You have option of using Modular PID Control as a software package from SIEMENS.I think 3 function of this package would be helpful: 2.1.20 PID: PID Algorithm parameter SMOO_CHG ,smooth change over from the manual mode to the automatic mode. 2.1.23 ROC_LIM: Rate of Change Limiter Ramp functions are used when the process must not be subjected to a step change at the input. For example when the set point or gain of PID algorithm change suddenly(Jump in these crucial parameters). 2.1.13 LMNGEN_C: Output Continuous PID Controlle parameter LMNRC_ON ,manipulated value rate of change on,ensures bumpless switchover in manipulated variable. regards |
Last edited by: hdhosseini at: 6/1/2012 2:51 PM |
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5/20/2011 5:02 AM | |
Joined: 7/2/2008 Last visit: 8/26/2024 Posts: 928 Rating: (308) |
Hello MS10, 1st make sure that auto mode resets manual bit and manual mode resets automatic bit. 2nd make sure that db102.dbw4 is the right word for valve position. If I may suggest, Try making it easy for yourself and use only one bit for automatic and manual and also use the output parameter LMN IF "DB_PID".COOK_TEMP_PID.Manual_Mode = 0 Movethe output parameter LMN to "DB_PID".COOK_TEMP_PID.Manual_CV Also as explained earlier by ARET, in manual mode it's better to transfer the process value to the setpoint So, IF "DB_PID".COOK_TEMP_PID.Manual_Mode = 1 Move the the output parameterPV to "DB_PID".COOK_TEMP_PID.Setpoint If you still face problems then It will be better if you upload your programhere somembers can check it for you. Best regards. H-H AttachmentFC52 with comments.pdf (891 Downloads) |
5/20/2011 10:26 PM | |
Joined: 1/28/2009 Last visit: 9/10/2024 Posts: 6849 Rating: (1365) |
Hi See the attachment Attachmentrate_limiter.zip (2001 Downloads) |
Last edited by: hdhosseini at: 10/29/2011 4:23 PM |
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5/21/2011 4:21 PM | |
Joined: 7/2/2008 Last visit: 8/26/2024 Posts: 928 Rating: (308) |
Hello MS10, I've simulated your software and it worked for me. In automatic mode your manipulated value from PID is returned back to manual value. Nothing is wrong. Please tell me how you test it and why you think it's not working. Best regards. H-H |
5/23/2011 5:47 AM | |
Joined: 1/28/2009 Last visit: 9/10/2024 Posts: 6849 Rating: (1365) |
Dear member
Using the function posted before may help you by changing steps to Ramps in CV.If you have such a jump, I think you may have high Proportional part in PID algorithm. To check the value of each section you can check LMNP, LMNI and LMND in FB41.If you have momentary high LMNP , so reduce gain to have lower LMNP. To obtain optimum P,I and D parameters for the algorithm, you can use PID SELF TUNER of SIEMENS.
If you scale your PV before applying to the PID controller and PVPER_ON reset to false ,you should have no problem.To be sure of result,you can check ER parameter to be near zero for steady state. regards |
This contribution was helpful to1 thankful Users |
5/23/2011 8:45 PM | |
Joined: 1/28/2009 Last visit: 9/10/2024 Posts: 6849 Rating: (1365) |
The function FB67 needs an input which likely to experience an STEP, for example in case of mode transition sudden jump in LMN may happen. So, LMN output of PID controller should be fed into the input parameter of FB67.I have checked your codes,so some modification can make the function applicable for your requirement. Also check this link for an similar example of working with peripheral inputs/outputs. On the FB58 itself in OB35 can we assign just a part of inputs and outputs (for example PV_PER and LMN_PER) and leave the others without any assignment?regards |
5/24/2011 11:25 AM | |
Joined: 1/28/2009 Last visit: 9/10/2024 Posts: 6849 Rating: (1365) |
Dear member Please check the attachment, this is the modified version of your PID controller.I insert the FB67, rate limiter function in the codes to avoid experincing sudden jumps in the process , this for sure make any transition in your controller bumpless.About the analog output ,the problem solved. For analog input,it is working fine for process variable in range of 0 to 100 (see the equation mentioned in the on line help of FB41).So, if the range of PV differes you should assign a value instead of default value 1 for PV_FAC. OUT_CPR_IN= PV_PER * (100 / 27648) OUT_PV_NORM=(OUT_CPR_IN*PV_FAC)+PV_OFF I think the equations are clear.But , if your PV is from 0 to 320 centrigrade, you should select PV_FAC=3.2 Hope to be helpful hdhosseini AttachmentPID_TEST.zip (531 Downloads) |
5/24/2011 12:45 PM | |
Joined: 1/28/2009 Last visit: 9/10/2024 Posts: 6849 Rating: (1365) |
Hi again Please check the attachment for a file which illustrates the functionality of rate limiter.In this test ,LMN of FB41 is manually changed and STEP with different values fed to FB67.You can see the ramp in analog output. regards Attachmentzip.zip (428 Downloads) |
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