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Writing FB to simulate discrete time system in SCL

Created by: Pandiani at: 1/10/2007 2:35 PM (13 Replies)

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1/12/2007 11:34 AM	Rate (0)
komatic Posts: 16 Rating: (0)	use this variables as static - it is right!!! because in future you can avoid many strange problem [:D]
komatic Posts: 16 Rating: (0)
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1/12/2007 12:01 PM	Rate (0)
Pandiani Silver Member Joined: 10/31/2005 Last visit: 4/22/2025 Posts: 366 Rating: (31)	Ok guys, thaks for help. Please can you comment "first_scan"? Is there more legenat way to do it. How would you solve problem first time (scan)initialization?

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1/13/2007 4:14 PM	Rate (0)
Pandiani Silver Member Joined: 10/31/2005 Last visit: 4/22/2025 Posts: 366 Rating: (31)	I also have one more dillema. What if my system has dead time, for example input delay? That means that input is delayed for some amount of time. For example in C, C++ or Scilab this can be easily simulated using loops. Something like this: for i=2:length(t) if i <=nDT xin(i)=x(1); else xin(i)=x(i-nDT); end y(i)=A1y(i-1)+Bxin(i-1)+C*xin(i-2); end How this can be simulated in S7 PLC, since it's real system? I was thinking to place timer and move instruction to input, so every time when timer counts appropriate amount of time, move instruction move value to FB's input? I'm not sure if this is the right way. Can you give any advice? Thanks
	Last edited by: Pandiani at: 1/13/2007 4:15 PM
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1/15/2007 7:23 AM	Rate (0)
Aret Posts: 2348 Rating: (265)	Timers are ok, but their amount may be not big enough. You can use some alternative methods: 1) Create delay conuter variable (type INT or LONG) in your FB. Create OB35 with small calling time 10 ms for example. In this OB write code to decrement this counter. If it has value=0 then delay ended. This method requeres good PLC, but don't use timers. 2) Similar thing can be done, but without OB35. For that purpose you can use CPU Clock Memory (you configure this in HWConfig->CPU properties). You can use SET command to get RLO=1 instead of these O XXX ON XXX.
Aret Posts: 2348 Rating: (265)
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