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Need help understanding the following S5 STL please.

Created by: Sah1 at: 7/6/2012 8:32 PM (2 Replies)

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7/6/2012 8:32 PM	Rate (0)
Sah1 Posts: 4 Rating: (0)	Hello Guys, I am very new at Step5 programing. I am going thru these old programs to figure them out. Please help me understand what these mean: Cross Reference: PW 182 = FIZGSFLOW NATURAL GAS FLOW RATE PW 190 = FIZNFCANYL NITROGEN GAS FLOW RATE Program Block: Name :READPW AI : PW 182 AO : DW 26 : :JU FB 49 Name :READPW AI : PW 190 AO : DW 35 : :JU FB 49 Function Block 49: Name :READPW Decl :AI I/Q/D/B/T/C: I BI/BY/W/D: W Decl :AO I/Q/D/B/T/C: Q BI/BY/W/D: W :L =AI :SLW 1 :SRW 4 :L KF +512 :-F :T =AO : :L =AO :L KF -1 :<=F :JC =M001 : :L =AO :L KF +2048 :>F :JC =M002 :BEU : M001 :L KF +0 :T =AO :BEU : M002 :L KF +2048 :T =AO :BE I didn't find the DW 26 and the DW 35 in my files (in case you wonder). I would greatly appreciate if you can explain the lines of code. Thanks for your help. Thanks! Sah1
Sah1 Posts: 4 Rating: (0)	Last edited by: Sah1 at: 7/6/2012 9:53 PM
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7/8/2012 1:47 PM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 10/5/2024 Posts: 3024 Rating: (1054)	Hello Sah1 put simply, the FB does a range check and limiting of an Analogue Input value. Your S5 AI value is of type 4-20mA which means it has a healthy raw AI range of 512 to 2560. Your FB49 then does the following: Subtract 512 from the raw AI value (e.g. make it 0-2048). If the result is < 0 (=4 mA): LimitDW 26 to 0 If the result is> 2048 (=20 mA): Limit DW 26 to 2048 If the result is>= 0 and <= 2048: copy it to DW 26 The SLW 1followed by SRW 4 are done to get rid of the sign bit (i.e. make the value always positive) as well as bits 0-2 of the raw AI value (which contain status info like error andoverflow etc.). Have a look at the attached pic which is an example from a 95U manual but similarily applicable for other S5 AI's (do a search for your S5 model @ https://support.automation.siemens.comand you shouldfind it's manual). I hope this helps Attachment S5 AI value representation (95U manual).jpg (316 Downloads)
	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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7/10/2012 2:35 PM	Rate (0)
Sah1 Posts: 4 Rating: (0)	Hey Fritz! Thank you so much! I really appreciated your help! You're the MAN! Thanks for the picture, it is very valuable! Sah :-)
Sah1 Posts: 4 Rating: (0)
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