Re: Process Control

Fri, 6 Jul 2001 16:19:39 -0500 

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<br><font size=2><tt>Lance,</tt></font>
<br><font size=2><tt>Here is a structure I've used multiple times on 
different</tt></font>
<br><font size=2><tt>systems. &nbsp;The two outputs compete through a low 
selector,</tt></font>
<br><font size=2><tt>and the final output is used as integral feedback 
(FBK)</tt></font>
<br><font size=2><tt>to the PID blocks.</tt></font>
<br>
<br><font size=2><tt>&nbsp; &nbsp; &nbsp; &nbsp; |--|<br>
 &nbsp; &nbsp; &nbsp; &nbsp;|PT|-- &nbsp; &nbsp; +---------------+<br>
 &nbsp; &nbsp; &nbsp; &nbsp;|--| &nbsp;| &nbsp;(FBK) &nbsp; &nbsp; &nbsp; &nbsp; 
&nbsp; &nbsp; |<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| &nbsp; &nbsp;V &nbsp; &nbsp; &nbsp; 
&nbsp; &nbsp; &nbsp; &nbsp; |<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; -&gt;|---| &nbsp; &nbsp; &nbsp; 
&nbsp; &nbsp; &nbsp; | <br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; |PIC|-- &nbsp; &nbsp; &nbsp; 
&nbsp; &nbsp; |<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; |---| &nbsp;| &nbsp; &nbsp; 
&nbsp; &nbsp; &nbsp;|</tt></font>
<br><font size=2><tt>&nbsp; &nbsp; &nbsp; &nbsp; |--| &nbsp; &nbsp; &nbsp; &nbsp; 
&nbsp; &nbsp;| &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;|<br>
 &nbsp; &nbsp; &nbsp; &nbsp;|FT|-- &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| &nbsp; &nbsp; 
&nbsp; &nbsp; &nbsp;|<br>
 &nbsp; &nbsp; &nbsp; &nbsp;|--| &nbsp;| &nbsp; &nbsp; &nbsp; &nbsp; | &nbsp; &nbsp; 
&nbsp; &nbsp; &nbsp;|<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;| &nbsp; &nbsp; &nbsp; &nbsp; | 
&nbsp; |---| &nbsp;|<br>
|--| &nbsp; &nbsp;|---| &nbsp;-&gt;|---| &nbsp; --&gt;|LOW| &nbsp;| &nbsp;|---|<br>
|LT|---&gt;|LIC|---&gt;|FIC|-----&gt;|SEL|--o-&gt;|VSD|<br>
|--| &nbsp; &nbsp;|---| &nbsp; &nbsp;|---| &nbsp; &nbsp; &nbsp;|---| &nbsp;| 
|&nbsp;|---|</tt></font>
<br><font size=2><tt>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
&nbsp;^ &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; |</tt></font>
<br><font size=2><tt>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
&nbsp;(FBK) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; |</tt></font>
<br><font size=2><tt>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
&nbsp;+---------------+</tt></font>
<br>
<br>
<br><font size=2><tt>Jim<br>
==========</tt></font>
<br><font size=2><tt>James D. Murphy<br>
Senior Process Control Engineer<br>
Eli Lilly and Company<br>
Phone: (317) 276-6859<br>
Email: [EMAIL PROTECTED]</tt></font>
<br>
<br>
<br>
<br>
<br>
<br>
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<td><font size=1 face="sans-serif"><b>Lance Dusing 
&lt;[EMAIL PROTECTED]&gt;</b></font>
<br><font size=1 face="sans-serif">Sent by: 
[EMAIL PROTECTED]</font>
<p><font size=1 face="sans-serif">07/06/01 09:11 AM</font>
<br><font size=1 face="sans-serif">Please respond to Foxboro DCS Mail List</font>
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<br><font size=1 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; Subject: &nbsp; &nbsp; 
&nbsp; &nbsp;Process Control</font></table>
<br>
<br><font size=2><tt>Hi everyone,<br>
<br>
Here is a process control question I have been pondering.<br>
<br>
Under normal process conditions, the control looks like this...<br>
<br>
 &nbsp; &nbsp; &nbsp; &nbsp;|--|<br>
 &nbsp; &nbsp; &nbsp; &nbsp;|FT|--<br>
 &nbsp; &nbsp; &nbsp; &nbsp;|--| &nbsp;|<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;|<br>
|--| &nbsp; &nbsp;|---| &nbsp;-&gt;|---| &nbsp; &nbsp;|---|<br>
|LT|---&gt;|LIC|---&gt;|FIC|---&gt;|VSD|<br>
|--| &nbsp; &nbsp;|---| &nbsp; &nbsp;|---| &nbsp; &nbsp;|---|<br>
<br>
However, if the pressure in the line with the VSD gets to large, corrective<br>
action needs be taken.<br>
How is the best way to control this?<br>
Limit the FIC hi output limit with logic? <br>
Switch to a PIC?<br>
Anything else?<br>
<br>
Lance<br>
<br>
<br>
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