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IM 151-8 CPU

Created by: Eastern at: 11/25/2009 4:46 AM (6 Replies)

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11/25/2009 4:46 AM	Rate (0)
Eastern Posts: 557 Rating: (64)	Hi Can i developed the logic for 32 PID in IM 151-8 CPU.Is there any limintation in this CPU. regards
Eastern Posts: 557 Rating: (64)
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11/26/2009 6:21 PM	Rate (1)
J_Bell Posts: 5822 Rating: (412)	Hello, well, I admit I am not the greatest CPU specialist but as far as I know require the FBs and FCs... and DBs for sure, memory... but this is usually it. So if you have enough memory for your program ant the PID functions it should run... I see no problem in here. If someone has another idea I would appreciate every input. To make everything clear I would recommend to you to contact the international Customer Support to clarify this point. Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)
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This contribution was helpful to 1 thankful Users Eastern

12/1/2009 6:45 AM	Rate (0)
Eastern Posts: 557 Rating: (64)	Hi i have heared that this CPU will not support the instruction, which are use in PID block, So does not allow to download. How can i contact to international Customer Support. regards
Eastern Posts: 557 Rating: (64)
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12/1/2009 7:21 AM	Rate (0)
UMENCHO Diamond Member Joined: 3/21/2006 Last visit: 11/1/2024 Posts: 10229 Rating: (1181)	Hello, Support Request Best regards, Hristo Mihalev
	Last edited by: UMENCHO at: 12/1/2009 7:22 AM
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12/1/2009 8:34 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/18/2024 Posts: 3027 Rating: (1057)	Eastern .. i have heared that this CPU will not support the instruction, which are use in PID block, So does not allow to download. Hello Eastern I find that hard to believe, the IM 151-8 CPU is based on the 314 and has the same instruction set andexecution times as it (you'll find the instruction list download HERE). As suchFB41 (CONT_C PID block) will have to work in it a far as I'm concerned (there is nothing too "fancy" happening inside FB41 apart from some Floating point mathematicsand it does not contain any callsto SFC's or SFB's). As for being able to have 32 PID loops in it, I'd be tempted to say you should be fine, it does however depend on how "fast" you need them to be (i.e if you for whatever reason need to call all 32 PID loops every 10ms you may end up in strive with the execution time of your interrupt OB). The prove of the pudding is in the eating as they say and there is of course always the good old "staggered call" trick available which works as followed: Assumption: You needa PID call rate of 500msand need to call 50 PID loops Setup OB35 with a call rate of 100ms Have a simple counter at the start of OB35 whichcounts from 1 to 5 (e.g. icrement an INT every time OB35 is called and start again with 1 if value of >=5 is reached). Use a count value of"1"to enable the call of PID loops1-10 Use a count value of"2"to enable the call of PID loops11-20 Use a count value of"3"to enable the call of PID loops 21-30 Use a count value of"4"to enable the call of PID loops 31-40 Use a count value of"5"to enable the call of PID loops 41-50 Result: Every one of the 50 PID loop is called with a 500ms call rate, but only 10 are active per OB35 call (i.e. you keepthe OB35 execution times lower and minimse its impact on overall cycle time when its called). I hope this helps and please let us know what Siemens support answered you.
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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4/6/2010 7:29 AM	Rate (0)
Berg Silver Member Joined: 1/17/2006 Last visit: 11/18/2024 Posts: 554 Rating: (29)	Eastern Hi i have heared that this CPU will not support the instruction, which are use in PID block, So does not allow to download. How can i contact to international Customer Support. regards Hello Eastern ! Did you have any answer from Siemens' Support about this thread to tellus ? Best regards.
	"Educate the children and it won't be necessary to punish the men." Pythagoras
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4/6/2010 8:24 PM	Rate (1)
tomearp Posts: 51 Rating: (3)	in my experience the IM151-8 can run any of the PID blocks in the standard library having reasonably unrestricted access to an IM151-8 (it's sat doing hvac and security in my parents' house), i decided to experiment a little bit with adding PID loops to OB35 to see what difference it would make to scan cycle times. in short, not a lot. i guess if the CPU was already carrying out lots of computationally expensive routines then there might be more of an impact on scan cycle times. the CPU is 6ES7 151-8AB00-0AB0 running firmware 2.7 the cycle time of OB35 is set to 2.5 seconds. it's already got 8 PID routines for looking after various bits of the hvac in the property, there are also some PWM routines for some control valves in OB35 that are called every 25 seconds (i.e every 10 OB35 calls). the normal running scan cycle times are 25ms - 35ms (shortest/longest). i added 2 networks with 10x FB41 calls each and 1 network with 12x FB41 calls to OB35. this resulted in an increase in the size of OB35 by 9536 bytes. each of the 32 instance data blocks were 162 bytes (5184 bytes in total). i also created a shared data block in which to store the manipulated values from the 32 PID loops (36 bytes). so the total memory requirement for it was an additional14756 bytes. i added the PID loops in stages (+10, +20, +32). with an extra 10 or an extra 20 loops there was no increase in the longest scan cycle time. with 32 extra loops the longest scan cycle time increased to 38ms.
tomearp Posts: 51 Rating: (3)
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