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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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| 7/8/2012 1:47 PM | |
Joined: 10/7/2005 Last visit: 1/22/2026 Posts: 3054 Rating:
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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 |
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