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CPU312 & PID Loops?

Created by: Tomy Master at: 4/26/2011 11:52 PM (10 Replies)

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4/26/2011 11:52 PM	Rate (0)
Tomy Master Gold Member Joined: 5/4/2009 Last visit: 5/28/2024 Posts: 914 Rating: (40)	Dear friends, Currently, I am in the final steps before ordering some CPUs and signal modules, but I am facing a little problem about PID loops. I am wondering how many PID loops can the CPU312 with 64KB memory card? Regards. Tomy.
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4/27/2011 4:03 AM	Rate (2)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 11/18/2024 Posts: 12296 Rating: (2691)	Hello Tomy; Do you mean a CPU 6ES7 312-1AD10-0AB0, with 16 kB of RAM memory integrated and a 64 kB MMC inserted as load memory? Calculations for the number of loops depends on the available work memory (16 kB) and the available ressources of the cPU, which with the cPU 312 are rather limited. Since you will call all your loops from OB35, they will all be present in work memory at the same time.Expect SFB 41 to load at a bit more than 1,5 kB per call, plus the IDB itrequires, you approach 2kB per loop. With analog conversion and other logic requirements, you could expect to run maybe 4 or 5loops in parallel. What kind of controls are you trying to setup here? Actually it should be easy to test this, by creating a dummy program with an increasing number of call of SFB 41 in your cyclic OB, and check howthe online memory parameters increase with every new download. Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 4/27/2011 4:05 AM
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4/27/2011 11:10 AM	Rate (0)
Tomy Master Gold Member Joined: 5/4/2009 Last visit: 5/28/2024 Posts: 914 Rating: (40)	Dear friend, I am using FB58 as PID temperature controller. Regards. Tomy.
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4/27/2011 2:36 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 11/18/2024 Posts: 12296 Rating: (2691)	Hello Tomy; The same logic applies,you can test the number of loops you can write using FB 58 in the way describe earlier. But you can also start by looking at the appendix of the PID temoperature control manua, which describes the FB 58 functionnalities; the attachment shows requirements for FB 58 in work and load memory. How many heating zones are you planning to control? Hope this helps, Daniel Chartier Attachment FB58 size.JPG (294 Downloads)
	Last edited by: dchartier at: 4/27/2011 2:47 PM Added attachment Last edited by: dchartier at: 4/27/2011 2:37 PM
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4/29/2011 6:32 PM	Rate (0)
Tomy Master Gold Member Joined: 5/4/2009 Last visit: 5/28/2024 Posts: 914 Rating: (40)	Dear friend, I have 5 air conditioning zones, but I have refered to the technical specification of CPU312 and I did not see any indication that CPU312 has the capability to deal with PID loops! Is that right? Regards. Tomy.
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4/29/2011 7:24 PM	Rate (1)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 11/18/2024 Posts: 12296 Rating: (2691)	Hello Tomy; Your cPU is not enabled to use SFB41/42/43, which are the Standard Function Blocks for PID loop control. However, in the Standard Library, PID control, you should find FB 41/42/43, which are PID instructions you can load directly from the library to the CPU program. Depending on various factors, you might even find FB58 in the same library. Look in the program instructions you have in Step 7 and tell us if you locate theese FBs. Also, have a look at the following thread, which discusses issues of FB41 that could help out with other PID loop instructions; /tf/WW/en/Posts/33184 Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 4/29/2011 7:52 PM Added link to FB41 thread
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5/9/2011 9:31 AM	Rate (0)
Tomy Master Gold Member Joined: 5/4/2009 Last visit: 5/28/2024 Posts: 914 Rating: (40)	Dear friend, Yes I have found FB58, but I need a clear confirmation that CPU312 has the ability to deal with FB58. Regards. Tomy.
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5/9/2011 10:51 AM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 10/26/2024 Posts: 6852 Rating: (1365)	Tomy Master Yes I have found FB58, but I need a clear confirmation that CPU312 has the ability to deal with FB58. Dear tomy Master Please note that FB58 is set of arithmatic and mathematic instructions and by using them the algorithm is implemented.So ,I think the CPU you mention can handle the algorithm (In some cases in communication functions, some SFBs are not included in the firmware of old CPU,so they are capble of processing them.you need to upgrade the firmware).So, now you check, does this function fit the work memory available? As I calculated you need ~13k out of 16kbyte work memory for processing 5 loops.If you have extensive logic beside them, it is not a good solution. Try to find a CPU with better resources. regards
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5/9/2011 12:27 PM	Rate (0)
Tomy Master Gold Member Joined: 5/4/2009 Last visit: 5/28/2024 Posts: 914 Rating: (40)	Dear friend, I have tried to work with VAT, and I tried to start the "auto-tune" process by setting "TUN_ON" as true and then by setting the "TUN_ST" as true, but I have noticed that there no response from the FB58. By the the way I have copied FB58 and DB58 from a sample program provided by Step7 software !!!! You can refer to the attached pic you can see that the "PHASE" and "STATUS" variables still "0". Please I need some help. Thank you in advance. Tomy. Attachment VAT.gif (232 Downloads)
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5/10/2011 9:17 AM	Rate (2)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 10/26/2024 Posts: 6852 Rating: (1365)	Tomy Master I have tried to work with VAT, and I tried to start the "auto-tune" process by setting "TUN_ON" as true and then by setting the "TUN_ST" as true, but I have noticed that there no response from the FB58. By the the way I have copied FB58 and DB58 from a sample program provided by Step7 software !!!! You can refer to the attached pic you can see that the "PHASE" and "STATUS" variables still "0". In order to initiate the tuning algorithm, you need to put a enough jump in "DB_TCONT_CP".SP_NT parameter of FB58.It means,you should change this value 10 to 15 degree centigrade more than the ambient temperature to provide process data for optimization algorithm.The procedure reminds me of STEP response in control courses. regards Attachment tuner_parameter.zip (267 Downloads)
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