May the below description, part of my PIDA manual could bring some light in the darkness: Unfortunately the drawings do no copy into the email, see therefore the attachment Regards, Hub Stapper (Invensys Operations management, The Netherlands. 8- Old and New structures for PI(D) controllers Figure 8- 1 shows the evolution that has taken place in the algorithms used for PI(D) controllers. Figure 8- 1: Old and new PID controller structures In the Old PID structure the error (SP-M) was calculated and the controller proportional, integral and derivative actions were calculated without interaction: P action was = (SP-M)*k, where k = controller GAIN I action was = (SP-M)*(1/Tr*s) where Tr = the reset (or integral) time D action was = (SP-M)*Td*s where Td = the derivative time In these controllers the proportional, integral and derivative actions were non-interactive; this means that when changing the controller gain, only the proportional action was influenced. So when controller gain k is increased with a factor 2, the proportional action would increase with factor 2, while the slope of the integral action would stay as it was before. Therefore, the term repeat time for integral action, can not be used for these non-interacting controllers. Under new PID structures there are two new schemes: The first scheme (a) shows that the proportional tuning parameter (PB) will have an effect on all three actions, the proportional, the integral and the derivative, as the error (SP_M) is multiplied by 100/PB; this result is being used to calculate the proportional, integral and derivative actions P action was = (SP-M)*(100/PB), where PB = controller Prop. Band I action was = (SP-M)*(100/PB)*(1/Tr*s) where Tr = the reset (or integral) time D action was = (SP-M)*(100/PB)*Td*s where Td = the derivative time This structure can be found in old Foxboro controller, like SPEC 200 For these controllers the proportional, integral and derivative actions do interact. When PB is decreased with factor two, the integral action will be increased with factor 2 (slope will be twice as steep) and the differential action will also be twice as big. For the integral action it means that the repeat time (this is the time it takes for the integral action to become as big as the proportional action is constant = Tr. The structure under new PID structure b shows yet another difference: here the derivative action (Td*s) is only active in the term with the Measurement (M). The Setpoint (SP) only has proportional and integral action. This means that there will be no derivative action when the setpoint of the controller is changed. Derivative action will only be seen on changes in the measurement. This has great advantages, as setpoint changes usually are step changes, giving a big "bump" to the derivative component of the output of the controller. This structure can be found in Foxboro Spectrum and I/A controllers. -----Original Message----- From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On Behalf Of Gregory A Hurwitt Sent: Thursday, March 17, 2011 2:26 PM To: foxboro@xxxxxxxxxxxxx Subject: Re: [foxboro] PID Equations [Sorry about the previous attempt. Let's try one more time.] You should have a look at "Integrated Control Block Descriptions", document number B0193AX. Per the documentation, the available modes on the PIDA block are: Proportional (P) Integral (I) Proportional-plus-Derivative (PD) Proportional-plus-Integral (PI) Proportional-plus-Integral-plus-Derivative (PID) Non-Interactive PID (NIPID) Proportional, integral, deadtime (interacting if derivative not 0) (PITAU) Non-interacting proportional, integral, derivative, deadtime (PIDTAU) The documentation also has a (very limited) writeup of when you might want to use some of these. See the section headed "PIDA is Recommended Over Other PID Algorithms" under the writeup for the PIDA block. (Section 94.1.1, at least in Rev. S of the document.) Perhaps some of the list members with more experience on the topic can expand on typical uses for some of the different modes. Greg Hurwitt BASF - Freeport, TX foxboro-bounce@xxxxxxxxxxxxx wrote on 03/17/2011 03:09:13 AM: > From: > > "Ravindrakumar Ratnakumara \(PLM/MLNG\)" <ravindrakumar@xxxxxxxxxxxxxxx> > > Hey List, > > Noob here. What are the available PID equations on Foxboro? I've heard > of P > on Error and P on PV, does this refer to these equations? Why do we > need each of these different equations and on what circumstances do we > > choose to use them? > > Thank you and best regards. J > > TES/5 - Making Automation Work! > > RAVINDRAKUMAR RATNAKUMARA > _______________________________________________________________________ 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 *** Confidentiality Notice: This e-mail, including any associated or attached files, is intended solely for the individual or entity to which it is addressed. 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