From: "Ali " <>
Newsgroups: comp.soft-sys.matlab
Subject: Re: How to create this non-linear equation
Date: Thu, 18 Mar 2010 08:47:08 +0000 (UTC)
Organization: The MathWorks, Inc.
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First of all, I have to thank you so much for your great reply & time consumed for me .. & I believe strongly you can help me with the following missed details:

Also, I don't forget TideMan's favour .. Thanks :)

This is not a homework; this is a course on-site project...

The objective of this modeling is to develop a PID controller for controlling the level of our process. We have CRT "Condensate Recovery Tank" which is used in the boiler in series between Gas and Steam Turbines (I mean Compained Cycle Power Plant). The temperature of the DEMIN Water will not effect on the level inside that tank; i.e, there is no apparent level comes from the generated bubbles, because there is no bubbles "it is just a warm water - around 62deg with normal pressure".

The inlet flow to the CRT Tank comes from the ACC Fans which means that the qi is not constant.

The level inside the CRT Tank should be controlled by measuring the level and adjusting the opening of the discharge control valve which is in series with constant speed pump on the exit stream.

Please see the following picture, I have drew it by paint program:

Off course, there is an override controller to bypass the inlet flow to the CRT Tank in case the outlet flow from the CRT Tank is more than enough for the Deaerator Unit; but this is not in our object .. Our object is just about how to maintain the level inside the CRT at the set value, and because there is no apparent level caused by bubbles inside the CRT so PI-Controller will achieve our object.

Mr. Roger,

I'm not an expert in the MATLAB .. & I think to find the Transfer Function of the above non-linear equation (to use it in our Feed-Back Control Loop) we need to plot the non-linear graph and then linearizing it by using some functions in the MATLAB.

Then, I don't know if the program has the facilities to find the PI Parameters; otherwise I should use DS or IMC for finding the PI Parameters.