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HELP ME FOR MORE THAN ONE PID CONTROL

Created by: erol at: 10/27/2008 9:55 AM (6 Replies)

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10/27/2008 9:55 AM	Rate (0)
erol Posts: 17 Rating: (0)	HELLO; i need your help about pid in s7 cpu 314 My projecthave 3 pid controlled equipments. At the first i used fb41(continuos control)for one of equipments in ob35, it is working correctly. After that i added second pid block (fb41, continuos control) in ob35 for second equipment and i renamedas fb141, fb41 and fb141 using different DBs. but i could not run correctly. i could not find the problem(s). plesae send me your comments. thanks EROL Attachment OB35.pdf (585 Downloads)
erol Posts: 17 Rating: (0)
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10/27/2008 10:17 AM	Rate (0)
dchartier Grandmaster Joined: 9/27/2006 Last visit: 9/13/2025 Posts: 12407 Rating: (2717)	Hello erol; What exactly do you mean when you say "it didn't work"? The process is not controlled properly, the CPU shows alarm LEDs, you can't download anymore... First there is no reason to rename FB41, when you call it with a different Instance DB (here DB67 and DB68) it is treated as a new call of the block. Second, the only limitation in the number of loops you can run in the PLC is the memory specs of thwis CPU. In one project we ran 25 loops in a CPU 313C-2DP, using multi-instance DBs to constrain memory usage. So your application should have no problem. Does one loop work, and not the other? Might be a tuning problem; you could start a new program where you only use one loop, the one that does not work, and see if you can set it up properly. I also noticed you did not include a signal for the Com_Rst input (it requires a rising edge,set a bit (say M10.0)in OB100, resetthe same bitin the last rung of OB1). COM_RST is part of the initialization routine of FB41; youneed tostart the loop controllers (FB41) when the CPU starts up. Also check that the CYCLE value is the same as the setting for your OB35; this is essential for proper calculations of the loop output by the FB41. Hope this helps, Daniel Chartier

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10/27/2008 12:30 PM	Rate (0)
erol Posts: 17 Rating: (0)	Thanks for your replyDaniel Chartier; I mean when i say "it didn't work'. PID out fixed maximum ouput value. No any CPU led alarm or dowload problem. iwas wrongabout rename FB41, i tried againwithout rename and i called different Instance DB (here DB67 and DB68) in a new project in Simatic Manager. I checked CYCLE value and i added setbitfor COM_RST in OB100 and reset inob35 afterpid network. When i run the CPU pid output valueinreasing from 0 to 27648. and fixed 27648. i am changing set valueor prosess value no any diffrence on output value. so i could not success aboutpid routine yet. Erol
erol Posts: 17 Rating: (0)
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10/27/2008 1:32 PM	Rate (0)
dchartier Grandmaster Joined: 9/27/2006 Last visit: 9/13/2025 Posts: 12407 Rating: (2717)	Hello erol; Did you parametrize the new set of FB41's same as the first loop controls were earlier? One quick check to start with: What is the present value of the parameters "FLOW_PID_PARA".MAN_ON and "H2SO4_PID_PARA".MAN_ON? Set them both to 0 if you want the loop to be processed in auto. It could be that your loop output, being in manual, simply ramps up to the maximum value allowed in manual mode (50% for the H2SO4 loop) and remains there. We will certainly have to talk about TI and TI parameters at a later time. Hope this heps, Daniel Chartier

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10/27/2008 1:45 PM	Rate (0)
erol Posts: 17 Rating: (0)	Hello Daniel Chartier; I tried again and again. At the end icreate a new project named PID_TEST andI am sendind my program in attachment. if you can please check my test program. Thanks Erol Attachment PID_TEST.zip (498 Downloads)
erol Posts: 17 Rating: (0)
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10/27/2008 3:51 PM	Rate (0)
H-H Platinum Member Joined: 7/2/2008 Last visit: 8/7/2025 Posts: 928 Rating: (309)	Dear Erol, I think you just forgot to enable Process variable periphery ON bit. I just set this bit and everything works fine. Please look at the picture. I also recommend to read DB41.DBD92 and DB42.DBD92 in your VAT. I find it hard to compare a Set point (Real) to a Periphery word (Word). Best regards. Attachment PID_PARA.JPG (561 Downloads)

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10/27/2008 4:26 PM	Rate (0)
erol Posts: 17 Rating: (0)	Dear H-H and Daniel Thank you vey much for your help. You solve my problem. Everything is ok. Best Regards. Erol
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