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PID loop

Created by: Import-User-1 at: 8/31/2005 4:23 PM (1 Replies)

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8/31/2005 4:23 PM

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Import-User-1

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Dear Sirs,
I am using an S7-200 CPU224 and it's the first time that I am going to use a PID loop.I have read carefully the manual and I have some questions.
In page 150 of your documentation " S7-200 Programmable Controller System Manual" regarding the PID loop you give a formula for normalizing the loop inputs. RNorm=((Rraw/Span)+Offset) and you say that this would give a value between 0.0 and 1.0. If my AIW0 gets values from 6400 to 32000 then my span is 25600 and this would give a Rnorm grater than 1.0
Again if my offset is 0.5 and Rraw is 32000 RNorm will be grater than 1.0 .Can you please clarify this to me?
Again for normalizing the output you multiply the PID outcome by 32000. If the span of the input(4-20mA) is 25600 I have to multiply my output by 25600 or 32000?
In the PID example that you give you want the setpoint of the system to be 75% of the tank being full and you put 0,75 as the setpoint. My variable is flow and I want the flow to be 10cubic meters/hour.Will the setpoint be 10 or something else.
Regards
George Fragoudes

8/31/2005 4:24 PM	Rate (0)
Import-User-2 Silver Member Joined: 8/10/2005 Last visit: 4/9/2024 Posts: 1486 Rating: (32)	Dear customer, regarding your questions: The EM23x has only a 0..20mA mode. You should adjust the process variable and the span. RNorm=((Rraw/Span)+Offset) Example: (14080-6400) ------------------- + 0.0 = 0.3 (32000-6400) The offset 0.5 is only for bipolar values. You should use the PID assistant in Step7-Microwin. The assistants up to Microwin V.3+SP4 don't contain a normalisation for the setpoint. This must be done by the user. Form Microwin V3.2+SP4 (V3.2.4.27) the PID assistant contains the normalisation for setpoint too. Please place S7-200 related topics in the section "Simatic S7-200". Your Technical Support

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Created by: Import-User-1 at: 8/31/2005 4:23 PM (1 Replies)

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