"This option is seldom used and probably not well documented,..." So, how many out there really make full use of the capabilities of the PIDA block, particularly with regard to self/adaptive tuning (FBTUNE/FFTUNE, etc.)? Documentation and training on how to do this is sorely lacking, and I haven't had/taken the time to experiment with it enough to teach myself. IMHO, this is a 1-day training class Foxboro ought to offer; The EXACT/PIxTAU/etc. capabilities are distinguishing features of the I/A system, and Foxboro out to play them up by helping their customers get the most out of them (especially now that competitors are adding interesting bits along these lines to their own DCS controllers). Corey Clingo BASF Corp. "Johnson, Alex P (IPS)" <alex.johnson@xxxxxxxxxxxxxxxx> Sent by: foxboro-bounce@xxxxxxxxxxxxx 03/22/2006 08:27 AM Please respond to foxboro@xxxxxxxxxxxxx To foxboro@xxxxxxxxxxxxx cc Subject Re: [foxboro] PH controller in Waste Water Treatment Robert, I'm not control expert but I've lived with, worked with, and sat next to lots of them. With that in mind, I'd like to make a couple of comments on the threads of response that you have received that I think deserve a comment: 1) There was a comment about the suitability of the PIDA algorithm and our control block set for various types of process control problems - large dead times, long lags, and combinations of both. The PIDA algorithm when used with the PIDTAU option is quite capable of dealing with long dead-times. This option is seldom used and probably not well documented, but if for some reason your process has a long dead time we do have a solution in our block. Long lag processes aren't too bad in general if the DT is short. [Yes, this is a general statement and there may be exceptions.] The real problem is long lags and large dead times. Those problems need extra help beyond our PID algorithm. 2) General comment on pH control Here's what I've learned from those who really do understand pH control: It is really, really easy to design a physical system for pH control that simply cannot control pH regardless of the algorithm used. The real issue with pH control is almost always related to the process equipment. At the end of the day, if the pH in the inflow can vary 2:1, you need a range of neutralizing flow that can support a 100:1 change in flow. That's a bit wide for most flow valves and generally requires separate tanks with separate neutralization flows and lots of mixers and so on. No control algorithm is going to control the pH if the physical equipment can't meet the process demands. Are you certain that your physical plant can meet the need? Regards, Alex Johnson Invensys Systems, Inc. 10900 Equity Drive Houston, TX 77041 713.329.8472 (voice) 713.329.1700 (fax) 713.329.1600 (switchboard) alex.johnson@xxxxxxxxxxxxxxxx _______________________________________________________________________ This mailing list is neither sponsored nor endorsed by Invensys Process Systems (formerly The Foxboro Company). Use the info you obtain here at your own risks. Read http://www.thecassandraproject.org/disclaimer.html foxboro mailing list: //www.freelists.org/list/foxboro to subscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=join to unsubscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=leave