11/25/2009 4:46 AM | |
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 |
12/1/2009 7:21 AM | |
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 | |
Joined: 10/7/2005 Last visit: 11/7/2024 Posts: 3026 Rating: (1057)
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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 |
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