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	FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
		Digest Janitor: pbabcock at hbd.org


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Contents:
  PID Control Tuning ("Devonna Dieterle")


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Date: Thu, 8 Mar 2012 07:58:49 -0500
From: "Devonna Dieterle" <djdieterle at hughes.net>
Subject: PID Control Tuning

I have my controllers set to simple on/off control.  It's difficult to get
precise pid control without a way to vary the output. With gas, the burner
would have to be modulated in some way, either by infinite control of the
gas orifice flow or by controlling the air input and a zero governor
regulator that matches the gas flow to air. For electric, pwm control of the
element would be the simplest method.  Turning a heating element or a burner
on and off via a pid algorithm is not utilizing anything more than the
proportional element and that is  on/off control.  There is no way to get to
zero error without an infinitely variable output that can respond to the
integral and derivative tuning parameters.  So if you looking to build a
system, a controller capable of pid control would be overkill unless the
design incorporates a method of infinitely controlling the output. A on/off
controller with a narrow deadband would work fine. 


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