---

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


***************************************************************
        TODAY'S HOME BREW DIGEST BROUGHT TO YOU BY: 

        Logic, Inc. - Makers of Straight A Cleanser
		   www.ecologiccleansers.com

    Support those who support you! Visit our sponsor's site!
********** Also visit http://hbd.org/hbdsponsors.html *********

DONATE to the Home Brew Digest. Home Brew Digest, Inc. is a 
501(c)3 not-for-profit organization under IRS rules (see the
FAQ at http://hbd.org for details of this status). Donations
can be made by check to Home Brew Digest mailed to:

HBD Server Fund
PO Box 871309
Canton Township, MI 48187-6309

or by paypal to address serverfund@hbd.org. DONATIONS of $250 
or more will be provided with receipts. SPONSORSHIPS of any 
amount are considered paid advertisement, and may be deductible
under IRS rules as a business expense. Please consult with your 
tax professional, then see http://hbd.org for available 
sponsorship opportunities.
***************************************************************


Contents:
  PID ("A. J. deLange")


* * * * * * * * * * * * * * * * * * * * * * * * * * * * *
*   Beer is our obsession and we're late for therapy!   *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * *

NOTE: With the economy as it is, the HBD is struggling to 
meet its meager operating expenses of approximately $3500
per year. If less than half of those currently directly
subscribed to the HBD sent in a mere $5.00, the HBD would
be able to easily meet its annual expenses, with room to 
spare for next year. Please consider it.

Financial Projection As of 03 March 2012
***      Condition:  Guarded      ***
501(c)3 revoked in process of retroactive reinstatement.
See Site News on http://hbd.org for details and progress. 
       Projected 2012 Budget  $3191.79
 Expended against projection  $ 721.78
      Unplanned expenditures  $  79.98
Projected Excess/(Shortfall) ($ 725.01)

As always, donors and donations are publicly acknowledged
and accounted for on the HBD web page. Thank you


Send articles for __publication_only__ to post@hbd.org

If your e-mail account is being deleted, please unsubscribe first!!

To SUBSCRIBE or UNSUBSCRIBE send an e-mail message with the word
  "subscribe" or "unsubscribe" to request@hbd.org FROM THE E-MAIL
  ACCOUNT YOU WISH TO HAVE SUBSCRIBED OR UNSUBSCRIBED!!!**
IF YOU HAVE SPAM-PROOFED your e-mail address, you cannot subscribe to
  the digest as we cannot reach you. We will not correct your address
  for the automation - that's your job.

HAVING TROUBLE posting, subscribing or unsusubscribing? See the HBD FAQ at
http://hbd.org.

LOOKING TO BUY OR SELL USED EQUIPMENT? Please do not post about it here. Go
instead to http://homebrewfleamarket.com and post a free ad there.

The HBD is a copyrighted document. The compilation is copyright 
  HBD.ORG. Individual postings are copyright by their authors. ASK 
  before reproducing and you'll rarely have trouble. Digest content 
  cannot be reproduced by any means for sale or profit.

More information is available by sending the word "info" to 
req@hbd.org or read the HBD FAQ at http://hbd.org.

JANITORs on duty: Pat Babcock (pbabcock at hbd dot org), Jason Henning,
                  Spencer Thomas, and Bill Pierce



----------------------------------------------------------------------


Date: Fri, 09 Mar 2012 01:23:25 -0500
From: "A. J. deLange" <ajdel at cox.net>
Subject: PID

Devonna is confusing the 'proportional band' of PID with proportional 
output. These are separate things. The PID algorithm determines how much 
output is required based on where the PV is in the proportional band 
(P)  i.e. the error, the integral of the error (I) and its differential 
(D). The 'tuneset' consists of the three gains applied to each of these 
before they are summed to form the output. How the output is controlled 
is a separate matter. In a 4-20 ma loop full output is requested by a 
current of 20 ma, 0 output by a current of 4. In a 0 - 5V output, 0 
volts corresponds to a demand for 0 output and 5 volts to a demand for 
full output. In an on/off output half power is signaled by logic 1 for 
half the output cycle time, 70% by logic one for 70% of the cycle time 
and so on. This gives infinite control just as the 4-20 loop and 0-5 
volt outputs do and it can, thus, do it for the full PID algorithm. I 
use full PID with on/off output (to open and close a steam valve on a 30 
second cycle) and recordings of temperature vs time show the PV 
eventually settling out right on the set point value (0 error) which 
would not happen if I were not active. What I am doing is, of course, 
PWM. It's just that the PRI is 1/30 Hz. As the bandwidth of the loop 
(determined by the thermal mass of the HLT and its rate of heat loss) is 
less than 1/30 Hz the recordings are smooth.

A.J.

Return to table of contents

---