Re: [time-nuts] D term (was no subject)
Many thanks for the link, Attila. One of the authors of Volume 25 was Nichols of Ziegler-Nichols tuning fame (q.v.) Bill Hawkins -Original Message- From: Attila Kinali Sent: Monday, February 09, 2015 4:14 AM And here the link to the pdf's in case anyone is looking: https://www.jlab.org/ir/MITSeries.html ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] D term (was no subject)
On Fri, 06 Feb 2015 21:20:39 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: If anyone wants to dive into control theory I recommend reading the book Feedback control of dynamic systems by Franklin, Powell and Emami-Naeini. And if you are more of a historical bent, the MIT Radiation Lab series is the motherlode. And here the link to the pdf's in case anyone is looking: https://www.jlab.org/ir/MITSeries.html Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] D term (was no subject)
In message 20150206153214.4d5f42edbdda4639fee1a...@kinali.ch, Attila Kinali w rites: On Mon, 26 Jan 2015 20:15:12 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: The basic math of PID has been around for about 100 years. The invention of the servo (and synchro/resolver) is what makes its day... If anyone wants to dive into control theory I recommend reading the book Feedback control of dynamic systems by Franklin, Powell and Emami-Naeini. And if you are more of a historical bent, the MIT Radiation Lab series is the motherlode. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] D term (was no subject)
On Mon, 26 Jan 2015 20:15:12 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: The basic math of PID has been around for about 100 years. The invention of the servo (and synchro/resolver) is what makes its day... If anyone wants to dive into control theory I recommend reading the book Feedback control of dynamic systems by Franklin, Powell and Emami-Naeini. It's very accessible, requires only little more than high school math and is geared to an engineering approach (ie lots of real world examples and how to solve them) Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] D term (was no subject)
On 1/25/15 1:30 PM, WarrenS via time-nuts wrote: I second Poul-Henning Kamp's comments concerning D-terms, (mostly) as done in the TBolt and likely other GPSDOs. Bear in mind that a PID loop is basically a fairly simple control loop that is easily susceptible to linear analysis. They're simple to implement with analog controls, they're simple to analyze, and for a whole lot of applications, they'll work just fine. And there's decades, if not centuries, of experience with P, PI and PID controllers in a practical sense. A lot of people know how to *tune* the parameters based on observed system dynamics. But for a lot of systems:ones where there are significant nonlinearities and/or time delays and/or saturation/limiting effects a PID loop might not be a good choice. (for instance, if you're doing a closed loop position control with a stepper motor as the actuator, with a small motor and a big heavy load, with low friction...) For myself, I am seduced by the idea of a control system that builds and adjusts a model of the system being controlled, and then derives the needed control inputs from inverting that model (whether arithmetically, or by some clever algorithmic means). For instance, a PID controller doing temperature control doesn't have a *good* way of incorporating side information like the outside temperature. There's all kinds of schemes for doing this (double loops, extra terms, etc.) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] D term (was no subject)
Maybe we are getting a little off-topic here, but a very long time ago I was dealing with industrial ovens used to braze ceramics used to make microwave tubes. It was very difficult to maintain the precise temperature ramp up and down, particularly as the oven was not always loaded the same way. In order to automatically compensate for different oven loading (and ambient conditions), the controller injected a very low level random noise over the temperature setting and by analyzing how that noise was filtered by going through the oven, was able to determine the response of the oven itself and from that optimize the PID terms in real time as a function of the load. This was in the early 80's. It was pretty hot stuff then, even for an oven :) Didier KO4BB On Sun, Jan 25, 2015 at 8:12 PM, Jim Lux jim...@earthlink.net wrote: On 1/25/15 1:30 PM, WarrenS via time-nuts wrote: I second Poul-Henning Kamp's comments concerning D-terms, (mostly) as done in the TBolt and likely other GPSDOs. Bear in mind that a PID loop is basically a fairly simple control loop that is easily susceptible to linear analysis. They're simple to implement with analog controls, they're simple to analyze, and for a whole lot of applications, they'll work just fine. And there's decades, if not centuries, of experience with P, PI and PID controllers in a practical sense. A lot of people know how to *tune* the parameters based on observed system dynamics. But for a lot of systems:ones where there are significant nonlinearities and/or time delays and/or saturation/limiting effects a PID loop might not be a good choice. (for instance, if you're doing a closed loop position control with a stepper motor as the actuator, with a small motor and a big heavy load, with low friction...) For myself, I am seduced by the idea of a control system that builds and adjusts a model of the system being controlled, and then derives the needed control inputs from inverting that model (whether arithmetically, or by some clever algorithmic means). For instance, a PID controller doing temperature control doesn't have a *good* way of incorporating side information like the outside temperature. There's all kinds of schemes for doing this (double loops, extra terms, etc.) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] D term (was no subject)
On 1/26/15 5:55 AM, Poul-Henning Kamp wrote: In message 54c5a270.7090...@earthlink.net, Jim Lux writes: And there's decades, if not centuries, of experience with P, PI and PID controllers in a practical sense. Not quite a century I belive: Only the advent of electronics formalized the theory and developed the practice. Almost all mechanical governors er pure P. Maxwell strikes again http://upload.wikimedia.org/wikipedia/commons/b/b1/On_Governors.pdf definitely more than P controllers.. cups with liquid (Siemens governor), nonlinear mechanisms, etc. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] D term (was no subject)
In message 5E5E892CF8A2440FBF18FFAD000B65FD@NewComputer, Lee Mushel writes: I'm fairly sure that Jim is right. I never had to worry about PID machine control before the late sixties and by the mid-seventies the concepts were firmly in place and in use. The basic math of PID has been around for about 100 years. The invention of the servo (and synchro/resolver) is what makes its day... Almost all mechanical governors er pure P. Maxwell strikes again http://upload.wikimedia.org/wikipedia/commons/b/b1/On_Governors.pdf definitely more than P controllers.. I said Almost all... :-) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] D term (was no subject)
In message CAMQqFumOdB4gcFfQjQ_nced0C_U=fbmyofwl7vuxm8wotqg...@mail.gmail.com , Didier Juges writes: In order to automatically compensate for different oven loading (and ambient conditions), the controller injected a very low level random noise over the temperature setting and by analyzing how that noise was filtered by going through the oven, was able to determine the response of the oven itself and from that optimize the PID terms in real time as a function of the load. This was in the early 80's. It was pretty hot stuff then, even for an oven :) Many off the shelf temperature controllers have an auto-tune button these days which does exactly that: Inject a heat-pulse, see what happens, do math... -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] D term (was no subject)
I'm fairly sure that Jim is right. I never had to worry about PID machine control before the late sixties and by the mid-seventies the concepts were firmly in place and in use. It certainly was the appearance of solid state industrial controls which made it all possible. And those ideas have made possible some system performance that I recall as being impossible only a few years earlier. Lee Mushel - Original Message - From: Jim Lux jim...@earthlink.net To: Poul-Henning Kamp p...@phk.freebsd.dk; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, January 26, 2015 8:21 AM Subject: Re: [time-nuts] D term (was no subject) On 1/26/15 5:55 AM, Poul-Henning Kamp wrote: In message 54c5a270.7090...@earthlink.net, Jim Lux writes: And there's decades, if not centuries, of experience with P, PI and PID controllers in a practical sense. Not quite a century I belive: Only the advent of electronics formalized the theory and developed the practice. Almost all mechanical governors er pure P. Maxwell strikes again http://upload.wikimedia.org/wikipedia/commons/b/b1/On_Governors.pdf definitely more than P controllers.. cups with liquid (Siemens governor), nonlinear mechanisms, etc. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] D term (was no subject)
I second Poul-Henning Kamp's comments concerning D-terms, (mostly) as done in the TBolt and likely other GPSDOs. A 'D-term' helps fast loops like a TPLL where you want a high bandwidth with the P gain as high as possible. For slow noisy loops like a cleanup osc or a GPSDO, what helps is a pre-filter. A D-term and a pre-filter do the opposite of each other and are therefore generally not used together because they tend to cancel each other. The Tbolt control loop has neither! What it does is: The P-gain in the Tbolt is set by the time-constant ( EFC-Gain) which sets the freq error recovery time constant. The Integrator gain is set with the Damping, which controls the Phase error recovery time-constant. If the damping is set high 10, the TBolt's loop becomes a P only controller, AKA a Freq-Lock-Loop (FLL) instead of a PLL. That is with a very high damping setting, The Tbolt then corrects for any freq error offsets but does not correct for any phase errors. The Tbolt is indeed very flexible, allowing usable time-constant settings from 1 sec to days in either a PLL or FLL mode. What it is missing is a pre-filter, and to get the best performance that must be added externally. ws * I have seen no evidence that the Thunderbolt, in particular, uses a D term. ... Charles Before anybody gets any ideas that causes them to waste a lot of time: D terms are themselves very temperamental because they, by definition, amplify measurement jitter noise. In the precision time/frequency domain, D-terms are almost never realistic. Poul-Henning Kamp * Without a D term, PI loops can be unstable when the gain (P) is increased. If you will, with a large error, the correction will itself be large and as the system corrects itself, it may overshoot the target value, going into a low (or high if you really blew it) level oscillation around the target value. The D term slows it down just enough and minimizes that overshoot while maintaining a high gain (low steady state error) and a fast response. Didier KO4BB On January 24, 2015 8:05:38 PM CST, Bob Camp kb8tq at n1k.org wrote: Hi A classic control loop in it's simplest form has only one term. That is often referred to as a proportional term. When the control signal (or error) changes by A the output changes by A times that term. Often in shorthand notation this term is refereed to as a P term. The next thing that some people add to a control loop is an integrator. It looks at the control signal (or error) has a constant offset of A, the integrator sums up the A's. The output of an integrator would eventually go to infinity with a constant control input (or error) into it. This term is often referred to as an I term. Lastly people add a term to the control loop that responds to the rate of change in the control signal (or error). The faster the change, the bigger this signal gets. This is commonly refereed to as a Derivative term. In shorthand it's talked about as the D term. The net result is a three element control loop running what's called a PID algorithm . The P and I can also be described by a time constant and a damping. That's what the Trimble software lets you do. The implication is that it's just a PI loop. In fact it appears to be a PID loop and you can't get at the D term. For a much more clearly worded explanation of all this, there's http://en.wikipedia.org/wiki/PID_controller ... There does appear to be a D in the TBolt loop. For what ever reason, that's not a changeable value. The D does scale with the time constant. . Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
