Joe Gwinn <joegwinn@comcast.net> wrote:> On Thu, 17 Aug 2023 15:36:39 -0000 (UTC), Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>> On Thu, 17 Aug 2023 06:18:11 -0700 (PDT), Fred Bloggs >>> <bloggs.fredbloggs.fred@gmail.com> wrote: >>> >>>> On Thursday, August 17, 2023 at 6:47:11?AM UTC-4, John Larkin wrote: >>>>> On Thu, 17 Aug 2023 00:11:11 -0000 (UTC), Phil Hobbs >>>>> <pcdhSpamM...@electrooptical.net> wrote: >>>>> >>>>>> John Larkin <jlarkin@highland_atwork_technology.com> wrote: >>>>>>> >>>>>>> >>>>>>> While my sim is running, I can do all sorts of things. Grocery shop, >>>>>>> prowl the web, take a nap. >>>>>>> >>>>>>> https://xkcd.com/303/ >>>>>>> >>>>>>> Same idea. My alternator simulator simulation (!) takes about 25 >>>>>>> minutes to rev up, running 10 or so PPM of real time. It's nicely >>>>>>> settled in about an hour. >>>>>>> >>>>>>> >>>>>> >>>>>> It?s probably pretty linear, so you could solve the DE by hand. Then you?d >>>>>> have more info than a stack of sims. >>>>> It's a mess of PWM modulators, mosfet half-bridges, cycle-by-cycle >>>>> current limiters, 3-phase common-mode chokes, ferrite beads, about 50 >>>>> bypass caps. I'm not smart enough to do that analytically. >>>> >>>> Unless all those subelements interact, it's insane to simulate the >>>> whole shebang at once. >>> >>> Of course they interact! >>> >>> The 200 watt floating dc/dc conveter is reasonably independent so >>> that's a separate sim. Ditto my soft-start circuit that ramps up the >>> raw 48v bus in to the dc/dc. >>> >>> High school trig was some time ago, so I have a couple of sims to >>> verify the basic 3-phase math. Spice could eventually destroy all our >>> math skills; I use it for voltage dividers and RC timing circuits too. >>> >>> Is there an anlytical way to express delay lines? I think I saw the >>> delay case once, in a test for PE registration as a Controls Engineer. >>> >>> >> >> H(f) = exp(-j 2 pi f tau) > > Yes, but I think he means the Telegrapher's Equations: > > .<https://en.wikipedia.org/wiki/Telegrapher%27s_equations>Maybe. I use the one I gave much more often. It’s dead useful for modeling temperature controllers—you model the plant as a delay followed by an integrator. You then do a bump test, i.e. dump a half-scale current step into the TE cooler and measure the temperature response. You can read the model parameters right off the scope trace, or use a micro and auto tune. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
Spice is great!
Started by ●August 16, 2023
Reply by ●August 17, 20232023-08-17
Reply by ●August 17, 20232023-08-17
On 2023-08-17 17:36, Phil Hobbs wrote:> John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >> On Thu, 17 Aug 2023 06:18:11 -0700 (PDT), Fred Bloggs >> <bloggs.fredbloggs.fred@gmail.com> wrote: >> >>> On Thursday, August 17, 2023 at 6:47:11?AM UTC-4, John Larkin wrote: >>>> On Thu, 17 Aug 2023 00:11:11 -0000 (UTC), Phil Hobbs >>>> <pcdhSpamM...@electrooptical.net> wrote: >>>> >>>>> John Larkin <jlarkin@highland_atwork_technology.com> wrote: >>>>>> >>>>>> >>>>>> While my sim is running, I can do all sorts of things. Grocery shop, >>>>>> prowl the web, take a nap. >>>>>> >>>>>> https://xkcd.com/303/ >>>>>> >>>>>> Same idea. My alternator simulator simulation (!) takes about 25 >>>>>> minutes to rev up, running 10 or so PPM of real time. It's nicely >>>>>> settled in about an hour. >>>>>> >>>>>> >>>>> >>>>> It’s probably pretty linear, so you could solve the DE by hand. Then you’d >>>>> have more info than a stack of sims. >>>> It's a mess of PWM modulators, mosfet half-bridges, cycle-by-cycle >>>> current limiters, 3-phase common-mode chokes, ferrite beads, about 50 >>>> bypass caps. I'm not smart enough to do that analytically. >>> >>> Unless all those subelements interact, it's insane to simulate the whole shebang at once. >> >> Of course they interact! >> >> The 200 watt floating dc/dc conveter is reasonably independent so >> that's a separate sim. Ditto my soft-start circuit that ramps up the >> raw 48v bus in to the dc/dc. >> >> High school trig was some time ago, so I have a couple of sims to >> verify the basic 3-phase math. Spice could eventually destroy all our >> math skills; I use it for voltage dividers and RC timing circuits too. >> >> Is there an anlytical way to express delay lines? I think I saw the >> delay case once, in a test for PE registration as a Controls Engineer. >> >> > > H(f) = exp(-j 2 pi f tau) > > Cheers > > Phil Hobbs >Which says, in the frequency domain, that the phase of the output is turned backwards in proportion to the delay and to the frequency. Delays are a nuisance in closed-loop feedback systems. Jeroen Belleman
Reply by ●August 17, 20232023-08-17
On Thu, 17 Aug 2023 16:29:53 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Joe Gwinn <joegwinn@comcast.net> wrote: >> On Thu, 17 Aug 2023 15:36:39 -0000 (UTC), Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>>> On Thu, 17 Aug 2023 06:18:11 -0700 (PDT), Fred Bloggs >>>> <bloggs.fredbloggs.fred@gmail.com> wrote: >>>> >>>>> On Thursday, August 17, 2023 at 6:47:11?AM UTC-4, John Larkin wrote: >>>>>> On Thu, 17 Aug 2023 00:11:11 -0000 (UTC), Phil Hobbs >>>>>> <pcdhSpamM...@electrooptical.net> wrote: >>>>>> >>>>>>> John Larkin <jlarkin@highland_atwork_technology.com> wrote: >>>>>>>> >>>>>>>> >>>>>>>> While my sim is running, I can do all sorts of things. Grocery shop, >>>>>>>> prowl the web, take a nap. >>>>>>>> >>>>>>>> https://xkcd.com/303/ >>>>>>>> >>>>>>>> Same idea. My alternator simulator simulation (!) takes about 25 >>>>>>>> minutes to rev up, running 10 or so PPM of real time. It's nicely >>>>>>>> settled in about an hour. >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> It?s probably pretty linear, so you could solve the DE by hand. Then you?d >>>>>>> have more info than a stack of sims. >>>>>> It's a mess of PWM modulators, mosfet half-bridges, cycle-by-cycle >>>>>> current limiters, 3-phase common-mode chokes, ferrite beads, about 50 >>>>>> bypass caps. I'm not smart enough to do that analytically. >>>>> >>>>> Unless all those subelements interact, it's insane to simulate the >>>>> whole shebang at once. >>>> >>>> Of course they interact! >>>> >>>> The 200 watt floating dc/dc conveter is reasonably independent so >>>> that's a separate sim. Ditto my soft-start circuit that ramps up the >>>> raw 48v bus in to the dc/dc. >>>> >>>> High school trig was some time ago, so I have a couple of sims to >>>> verify the basic 3-phase math. Spice could eventually destroy all our >>>> math skills; I use it for voltage dividers and RC timing circuits too. >>>> >>>> Is there an anlytical way to express delay lines? I think I saw the >>>> delay case once, in a test for PE registration as a Controls Engineer. >>>> >>>> >>> >>> H(f) = exp(-j 2 pi f tau) >> >> Yes, but I think he means the Telegrapher's Equations: >> >> .<https://en.wikipedia.org/wiki/Telegrapher%27s_equations> > >Maybe. I use the one I gave much more often. It�s dead useful for modeling >temperature controllers�you model the plant as a delay followed by an >integrator. > >You then do a bump test, i.e. dump a half-scale current step into the TE >cooler and measure the temperature response. > >You can read the model parameters right off the scope trace, or use a micro >and auto tune. > >Cheers > >Phil HobbsWhat about startup slewing? We use Spice to model fairly high-order tremperature controllers and the small-signal loop response is only part of the concern. A recent customer wanted an optical modulator to get stable to 0.05c in one hour from cold start, and that's substantially nonlinear. The hard part of simming that is modeling diffusion and estimating heat losses to ambient from various surfaces of the oven box.
Reply by ●August 17, 20232023-08-17
On 2023-08-17 13:07, John Larkin wrote:> On Thu, 17 Aug 2023 16:29:53 -0000 (UTC), Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> Joe Gwinn <joegwinn@comcast.net> wrote: >>> On Thu, 17 Aug 2023 15:36:39 -0000 (UTC), Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>>>> On Thu, 17 Aug 2023 06:18:11 -0700 (PDT), Fred Bloggs >>>>> <bloggs.fredbloggs.fred@gmail.com> wrote: >>>>> >>>>>> On Thursday, August 17, 2023 at 6:47:11?AM UTC-4, John >>>>>> Larkin wrote: >>>>>>> On Thu, 17 Aug 2023 00:11:11 -0000 (UTC), Phil Hobbs >>>>>>> <pcdhSpamM...@electrooptical.net> wrote: >>>>>>> >>>>>>>> John Larkin <jlarkin@highland_atwork_technology.com> >>>>>>>> wrote: >>>>>>>>> >>>>>>>>> >>>>>>>>> While my sim is running, I can do all sorts of >>>>>>>>> things. Grocery shop, prowl the web, take a nap. >>>>>>>>> >>>>>>>>> https://xkcd.com/303/ >>>>>>>>> >>>>>>>>> Same idea. My alternator simulator simulation (!) >>>>>>>>> takes about 25 minutes to rev up, running 10 or so >>>>>>>>> PPM of real time. It's nicely settled in about an >>>>>>>>> hour. >>>>>>>>> >>>>>>>>> >>>>>>>> >>>>>>>> It?s probably pretty linear, so you could solve the DE >>>>>>>> by hand. Then you?d have more info than a stack of >>>>>>>> sims. >>>>>>> It's a mess of PWM modulators, mosfet half-bridges, >>>>>>> cycle-by-cycle current limiters, 3-phase common-mode >>>>>>> chokes, ferrite beads, about 50 bypass caps. I'm not >>>>>>> smart enough to do that analytically. >>>>>> >>>>>> Unless all those subelements interact, it's insane to >>>>>> simulate the whole shebang at once. >>>>> >>>>> Of course they interact! >>>>> >>>>> The 200 watt floating dc/dc conveter is reasonably >>>>> independent so that's a separate sim. Ditto my soft-start >>>>> circuit that ramps up the raw 48v bus in to the dc/dc. >>>>> >>>>> High school trig was some time ago, so I have a couple of >>>>> sims to verify the basic 3-phase math. Spice could eventually >>>>> destroy all our math skills; I use it for voltage dividers >>>>> and RC timing circuits too. >>>>> >>>>> Is there an anlytical way to express delay lines? I think I >>>>> saw the delay case once, in a test for PE registration as a >>>>> Controls Engineer. >>>>> >>>>> >>>> >>>> H(f) = exp(-j 2 pi f tau) >>> >>> Yes, but I think he means the Telegrapher's Equations: >>> >>> .<https://en.wikipedia.org/wiki/Telegrapher%27s_equations> >> >> Maybe. I use the one I gave much more often. It’s dead useful for >> modeling temperature controllers—you model the plant as a delay >> followed by an integrator. >> >> You then do a bump test, i.e. dump a half-scale current step into >> the TE cooler and measure the temperature response. >> >> You can read the model parameters right off the scope trace, or use >> a micro and auto tune.> > What about startup slewing?That's actually the beauty of the bump test autotune approach. Any time you've got a slow plant that you want to speed up by adding gain, you have to worry about windup. That's not too hard though--you just stop updating the integrator during slew. With TE coolers, the main issue is actually plain ol' linear overshoot. For a given cooler and heat sink, there's a drive current value where d(Tcold)/ dI crosses zero. At that point, the sign of the loop gain inverts, which leads to Bad Things. If your controller is underdamped, it's easy for the overshoot to put you in that territory, so you design the autotuning to give you 70 degrees or so of phase margin, which will prevent that from happening. (Obviously you put in some belt'n'braces safeguards as well.) To get good bandwidth with a TEC loop, I usually make the cold plate out of FR4 with lots of via stitching, with a bare ENIG pour up against the TEC. One or two 0603 thermistors solder to the pour, right beside the edge of the TEC. That's good for control bandwidths up to a couple of hertz with small coolers. (TECs are quicker than you might think--the cooling happens right where the PbTe bars solder to the alumina, whereas the I2R heating is distributed fairly uniformly along their length.)> > We use Spice to model fairly high-order tremperature controllers and > the small-signal loop response is only part of the concern. A recent > customer wanted an optical modulator to get stable to 0.05c in one > hour from cold start, and that's substantially nonlinear.How hard that is depends almost entirely on its physical size. If it gets too big, you wind up having to use multiple zones, which gets complicated in a hurry.> The hard part of simming that is modeling diffusion and estimating > heat losses to ambient from various surfaces of the oven box.Diffusion isn't that difficult in homogeneous materials. If you have a squint at Section 20.3 in my thermal control chapter, <https://electrooptical.net/static/media/uploads/hobbsbeos3echapter20.pdf>, I go into a lot of that stuff in a semi-analytical way that has been super useful. Dunno about your particular case, of course, but most of mine have used a lot of chunks of homogeneous material. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●August 17, 20232023-08-17
On Thu, 17 Aug 2023 16:29:53 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Joe Gwinn <joegwinn@comcast.net> wrote: >> On Thu, 17 Aug 2023 15:36:39 -0000 (UTC), Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>>> On Thu, 17 Aug 2023 06:18:11 -0700 (PDT), Fred Bloggs >>>> <bloggs.fredbloggs.fred@gmail.com> wrote: >>>> >>>>> On Thursday, August 17, 2023 at 6:47:11?AM UTC-4, John Larkin wrote: >>>>>> On Thu, 17 Aug 2023 00:11:11 -0000 (UTC), Phil Hobbs >>>>>> <pcdhSpamM...@electrooptical.net> wrote: >>>>>> >>>>>>> John Larkin <jlarkin@highland_atwork_technology.com> wrote: >>>>>>>> >>>>>>>> >>>>>>>> While my sim is running, I can do all sorts of things. Grocery shop, >>>>>>>> prowl the web, take a nap. >>>>>>>> >>>>>>>> https://xkcd.com/303/ >>>>>>>> >>>>>>>> Same idea. My alternator simulator simulation (!) takes about 25 >>>>>>>> minutes to rev up, running 10 or so PPM of real time. It's nicely >>>>>>>> settled in about an hour. >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> It?s probably pretty linear, so you could solve the DE by hand. Then you?d >>>>>>> have more info than a stack of sims. >>>>>> It's a mess of PWM modulators, mosfet half-bridges, cycle-by-cycle >>>>>> current limiters, 3-phase common-mode chokes, ferrite beads, about 50 >>>>>> bypass caps. I'm not smart enough to do that analytically. >>>>> >>>>> Unless all those subelements interact, it's insane to simulate the >>>>> whole shebang at once. >>>> >>>> Of course they interact! >>>> >>>> The 200 watt floating dc/dc conveter is reasonably independent so >>>> that's a separate sim. Ditto my soft-start circuit that ramps up the >>>> raw 48v bus in to the dc/dc. >>>> >>>> High school trig was some time ago, so I have a couple of sims to >>>> verify the basic 3-phase math. Spice could eventually destroy all our >>>> math skills; I use it for voltage dividers and RC timing circuits too. >>>> >>>> Is there an anlytical way to express delay lines? I think I saw the >>>> delay case once, in a test for PE registration as a Controls Engineer. >>>> >>>> >>> >>> H(f) = exp(-j 2 pi f tau) >> >> Yes, but I think he means the Telegrapher's Equations: >> >> .<https://en.wikipedia.org/wiki/Telegrapher%27s_equations> > >Maybe. I use the one I gave much more often. It�s dead useful for modeling >temperature controllers�you model the plant as a delay followed by an >integrator. > >You then do a bump test, i.e. dump a half-scale current step into the TE >cooler and measure the temperature response. > >You can read the model parameters right off the scope trace, or use a micro >and auto tune.Yes. Is the PE test for Control Engineers that advanced? Joe Gwinn
Reply by ●August 17, 20232023-08-17
On Thu, 17 Aug 2023 14:27:05 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> >On 2023-08-17 13:07, John Larkin wrote: >> On Thu, 17 Aug 2023 16:29:53 -0000 (UTC), Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> Joe Gwinn <joegwinn@comcast.net> wrote: >>>> On Thu, 17 Aug 2023 15:36:39 -0000 (UTC), Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>>>>> On Thu, 17 Aug 2023 06:18:11 -0700 (PDT), Fred Bloggs >>>>>> <bloggs.fredbloggs.fred@gmail.com> wrote: >>>>>> >>>>>>> On Thursday, August 17, 2023 at 6:47:11?AM UTC-4, John >>>>>>> Larkin wrote: >>>>>>>> On Thu, 17 Aug 2023 00:11:11 -0000 (UTC), Phil Hobbs >>>>>>>> <pcdhSpamM...@electrooptical.net> wrote: >>>>>>>> >>>>>>>>> John Larkin <jlarkin@highland_atwork_technology.com> >>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> While my sim is running, I can do all sorts of >>>>>>>>>> things. Grocery shop, prowl the web, take a nap. >>>>>>>>>> >>>>>>>>>> https://xkcd.com/303/ >>>>>>>>>> >>>>>>>>>> Same idea. My alternator simulator simulation (!) >>>>>>>>>> takes about 25 minutes to rev up, running 10 or so >>>>>>>>>> PPM of real time. It's nicely settled in about an >>>>>>>>>> hour. >>>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>> It?s probably pretty linear, so you could solve the DE >>>>>>>>> by hand. Then you?d have more info than a stack of >>>>>>>>> sims. >>>>>>>> It's a mess of PWM modulators, mosfet half-bridges, >>>>>>>> cycle-by-cycle current limiters, 3-phase common-mode >>>>>>>> chokes, ferrite beads, about 50 bypass caps. I'm not >>>>>>>> smart enough to do that analytically. >>>>>>> >>>>>>> Unless all those subelements interact, it's insane to >>>>>>> simulate the whole shebang at once. >>>>>> >>>>>> Of course they interact! >>>>>> >>>>>> The 200 watt floating dc/dc conveter is reasonably >>>>>> independent so that's a separate sim. Ditto my soft-start >>>>>> circuit that ramps up the raw 48v bus in to the dc/dc. >>>>>> >>>>>> High school trig was some time ago, so I have a couple of >>>>>> sims to verify the basic 3-phase math. Spice could eventually >>>>>> destroy all our math skills; I use it for voltage dividers >>>>>> and RC timing circuits too. >>>>>> >>>>>> Is there an anlytical way to express delay lines? I think I >>>>>> saw the delay case once, in a test for PE registration as a >>>>>> Controls Engineer. >>>>>> >>>>>> >>>>> >>>>> H(f) = exp(-j 2 pi f tau) >>>> >>>> Yes, but I think he means the Telegrapher's Equations: >>>> >>>> .<https://en.wikipedia.org/wiki/Telegrapher%27s_equations> >>> >>> Maybe. I use the one I gave much more often. It�s dead useful for >>> modeling temperature controllers�you model the plant as a delay >>> followed by an integrator. >>> >>> You then do a bump test, i.e. dump a half-scale current step into >>> the TE cooler and measure the temperature response. >>> >>> You can read the model parameters right off the scope trace, or use >>> a micro and auto tune. > >> >> What about startup slewing? > >That's actually the beauty of the bump test autotune approach. > >Any time you've got a slow plant that you want to speed up by adding >gain, you have to worry about windup. That's not too hard though--you >just stop updating the integrator during slew. > >With TE coolers, the main issue is actually plain ol' linear overshoot. > For a given cooler and heat sink, there's a drive current value where >d(Tcold)/ dI crosses zero. At that point, the sign of the loop gain >inverts, which leads to Bad Things. > >If your controller is underdamped, it's easy for the overshoot to put >you in that territory, so you design the autotuning to give you 70 >degrees or so of phase margin, which will prevent that from happening. >(Obviously you put in some belt'n'braces safeguards as well.) > >To get good bandwidth with a TEC loop, I usually make the cold plate out >of FR4 with lots of via stitching, with a bare ENIG pour up against the >TEC. One or two 0603 thermistors solder to the pour, right beside the >edge of the TEC. That's good for control bandwidths up to a couple of >hertz with small coolers. > >(TECs are quicker than you might think--the cooling happens right where >the PbTe bars solder to the alumina, whereas the I2R heating is >distributed fairly uniformly along their length.) >> >> We use Spice to model fairly high-order tremperature controllers and >> the small-signal loop response is only part of the concern. A recent >> customer wanted an optical modulator to get stable to 0.05c in one >> hour from cold start, and that's substantially nonlinear. > >How hard that is depends almost entirely on its physical size. If it >gets too big, you wind up having to use multiple zones, which gets >complicated in a hurry. > >> The hard part of simming that is modeling diffusion and estimating >> heat losses to ambient from various surfaces of the oven box. > >Diffusion isn't that difficult in homogeneous materials. If you have a >squint at Section 20.3 in my thermal control chapter, > ><https://electrooptical.net/static/media/uploads/hobbsbeos3echapter20.pdf>, >I go into a lot of that stuff in a semi-analytical way that has been >super useful. Dunno about your particular case, of course, but most of >mine have used a lot of chunks of homogeneous material. ;) > >Cheers > >Phil HobbsHere's the eo gadget oven, with the big top off. https://www.dropbox.com/s/f6h8tfyq0xkqx1q/Oven_Cables_pub.jpg?dl=0 The eo modulator is inside the oven, on a secondary platform on some not super thermally conductive spacers. The temp sensor, a two-thermistor wheatstone bridge, is on the bottom of the platform with a flex cable going down to the controller. The heaters are a lot of mosfets on the bottom of the big box. The platform adds a second lag to the loop, which lowpass filters temp transients a bit but mostly prevents temp gradients from getting into the eo modulator. That's a dual-stage Mach-Zender modulator, which depends on cancellation of a zillion light wavelengths against a zillion and some plus 0.5 wavelengths, so it's pretty temperature sensitive and the customer wants extreme extinction. It was Spiced and came out about as expected. The coax cables conduct heat too, which was measured and included in the model.
Reply by ●August 18, 20232023-08-18
On a sunny day (Thu, 17 Aug 2023 11:55:31 -0400) it happened Joe Gwinn <joegwinn@comcast.net> wrote in <5igsdil470i700j5tmrei4fus3es26lurv@4ax.com>:>Yes, but I think he means the Telegrapher's Equations: > >.<https://en.wikipedia.org/wiki/Telegrapher%27s_equations>Thank you, nice link.
Reply by ●August 18, 20232023-08-18
On Thursday, August 17, 2023 at 11:04:11 AM UTC-4, John Larkin wrote:> On Thu, 17 Aug 2023 06:18:11 -0700 (PDT), Fred Bloggs > <bloggs.fred...@gmail.com> wrote: > >On Thursday, August 17, 2023 at 6:47:11?AM UTC-4, John Larkin wrote: > >> On Thu, 17 Aug 2023 00:11:11 -0000 (UTC), Phil Hobbs > >> <pcdhSpamM...@electrooptical.net> wrote: > >> > >> >John Larkin <jlarkin@highland_atwork_technology.com> wrote: > >> >> > >> >> > >> >> While my sim is running, I can do all sorts of things. Grocery shop, > >> >> prowl the web, take a nap. > >> >> > >> >> https://xkcd.com/303/ > >> >> > >> >> Same idea. My alternator simulator simulation (!) takes about 25 > >> >> minutes to rev up, running 10 or so PPM of real time. It's nicely > >> >> settled in about an hour. > >> >> > >> >> > >> > > >> >It’s probably pretty linear, so you could solve the DE by hand. Then you’d > >> >have more info than a stack of sims. > >> It's a mess of PWM modulators, mosfet half-bridges, cycle-by-cycle > >> current limiters, 3-phase common-mode chokes, ferrite beads, about 50 > >> bypass caps. I'm not smart enough to do that analytically. > > > >Unless all those subelements interact, it's insane to simulate the whole shebang at once. > Of course they interact! > > The 200 watt floating dc/dc conveter is reasonably independent so > that's a separate sim. Ditto my soft-start circuit that ramps up the > raw 48v bus in to the dc/dc. > > High school trig was some time ago, so I have a couple of sims to > verify the basic 3-phase math. Spice could eventually destroy all our > math skills; I use it for voltage dividers and RC timing circuits too. > > Is there an anlytical way to express delay lines? I think I saw the > delay case once, in a test for PE registration as a Controls Engineer.f(t) delayed by Td is f(t-Td). Now how that works in LTSpice is another question. They do have some kind of delay function for digital subcircuits. So maybe analog->digital-> delay-> analog is the way to squeeze that into a realistic simulation.
Reply by ●August 18, 20232023-08-18
On Fri, 18 Aug 2023 05:59:38 -0700 (PDT), Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:>On Thursday, August 17, 2023 at 11:04:11?AM UTC-4, John Larkin wrote: >> On Thu, 17 Aug 2023 06:18:11 -0700 (PDT), Fred Bloggs >> <bloggs.fred...@gmail.com> wrote: >> >On Thursday, August 17, 2023 at 6:47:11?AM UTC-4, John Larkin wrote: >> >> On Thu, 17 Aug 2023 00:11:11 -0000 (UTC), Phil Hobbs >> >> <pcdhSpamM...@electrooptical.net> wrote: >> >> >> >> >John Larkin <jlarkin@highland_atwork_technology.com> wrote: >> >> >> >> >> >> >> >> >> While my sim is running, I can do all sorts of things. Grocery shop, >> >> >> prowl the web, take a nap. >> >> >> >> >> >> https://xkcd.com/303/ >> >> >> >> >> >> Same idea. My alternator simulator simulation (!) takes about 25 >> >> >> minutes to rev up, running 10 or so PPM of real time. It's nicely >> >> >> settled in about an hour. >> >> >> >> >> >> >> >> > >> >> >It�s probably pretty linear, so you could solve the DE by hand. Then you�d >> >> >have more info than a stack of sims. >> >> It's a mess of PWM modulators, mosfet half-bridges, cycle-by-cycle >> >> current limiters, 3-phase common-mode chokes, ferrite beads, about 50 >> >> bypass caps. I'm not smart enough to do that analytically. >> > >> >Unless all those subelements interact, it's insane to simulate the whole shebang at once. >> Of course they interact! >> >> The 200 watt floating dc/dc conveter is reasonably independent so >> that's a separate sim. Ditto my soft-start circuit that ramps up the >> raw 48v bus in to the dc/dc. >> >> High school trig was some time ago, so I have a couple of sims to >> verify the basic 3-phase math. Spice could eventually destroy all our >> math skills; I use it for voltage dividers and RC timing circuits too. >> >> Is there an anlytical way to express delay lines? I think I saw the >> delay case once, in a test for PE registration as a Controls Engineer. > >f(t) delayed by Td is f(t-Td). Now how that works in LTSpice is another question. They do have some kind of delay function for digital subcircuits. So maybe analog->digital-> delay-> analog is the way to squeeze that into a realistic simulation.LT Spice has both ideal and lossy transmission lines. A lossy line is a decent model for a diffusive thing, like a thermal delay or a really terrible PCB trace. I think conductors inside digital ICs are essentially all diffusive, R and C and not much L. That's terrible for rise time.
Reply by ●August 18, 20232023-08-18
On Friday, August 18, 2023 at 10:25:58 AM UTC-4, John Larkin wrote:> On Fri, 18 Aug 2023 05:59:38 -0700 (PDT), Fred Bloggs > <bloggs.fred...@gmail.com> wrote: > >On Thursday, August 17, 2023 at 11:04:11?AM UTC-4, John Larkin wrote: > >> On Thu, 17 Aug 2023 06:18:11 -0700 (PDT), Fred Bloggs > >> <bloggs.fred...@gmail.com> wrote: > >> >On Thursday, August 17, 2023 at 6:47:11?AM UTC-4, John Larkin wrote: > >> >> On Thu, 17 Aug 2023 00:11:11 -0000 (UTC), Phil Hobbs > >> >> <pcdhSpamM...@electrooptical.net> wrote: > >> >> > >> >> >John Larkin <jlarkin@highland_atwork_technology.com> wrote: > >> >> >> > >> >> >> > >> >> >> While my sim is running, I can do all sorts of things. Grocery shop, > >> >> >> prowl the web, take a nap. > >> >> >> > >> >> >> https://xkcd.com/303/ > >> >> >> > >> >> >> Same idea. My alternator simulator simulation (!) takes about 25 > >> >> >> minutes to rev up, running 10 or so PPM of real time. It's nicely > >> >> >> settled in about an hour. > >> >> >> > >> >> >> > >> >> > > >> >> >It’s probably pretty linear, so you could solve the DE by hand. Then you’d > >> >> >have more info than a stack of sims. > >> >> It's a mess of PWM modulators, mosfet half-bridges, cycle-by-cycle > >> >> current limiters, 3-phase common-mode chokes, ferrite beads, about 50 > >> >> bypass caps. I'm not smart enough to do that analytically. > >> > > >> >Unless all those subelements interact, it's insane to simulate the whole shebang at once. > >> Of course they interact! > >> > >> The 200 watt floating dc/dc conveter is reasonably independent so > >> that's a separate sim. Ditto my soft-start circuit that ramps up the > >> raw 48v bus in to the dc/dc. > >> > >> High school trig was some time ago, so I have a couple of sims to > >> verify the basic 3-phase math. Spice could eventually destroy all our > >> math skills; I use it for voltage dividers and RC timing circuits too. > >> > >> Is there an anlytical way to express delay lines? I think I saw the > >> delay case once, in a test for PE registration as a Controls Engineer. > > > >f(t) delayed by Td is f(t-Td). Now how that works in LTSpice is another question. They do have some kind of delay function for digital subcircuits. So maybe analog->digital-> delay-> analog is the way to squeeze that into a realistic simulation. > LT Spice has both ideal and lossy transmission lines. A lossy line is > a decent model for a diffusive thing, like a thermal delay or a really > terrible PCB trace. > > I think conductors inside digital ICs are essentially all diffusive, R > and C and not much L. That's terrible for rise time.By diffusive I take it to mean frequency dependent time delay. That's much more complicated than a simple time shift. No wonder your runtime is taking forever. Do you really need to model these diffusive delays for a relay driver board??? Seems overkill.
