On Friday 15 June 2018 23:53:03 Chris Albertson wrote: > On Fri, Jun 15, 2018 at 7:58 PM Gene Heskett <ghesk...@shentel.net> wrote: > > On Friday 15 June 2018 20:20:20 jeremy youngs wrote: > > > > Aerotech mentions > > using 741's (op-amps) but the gain of a 741 above 10 hz falls like a > > rock, and that leaves the nyquist phase v stability angles in doubt. > > If the paper suggests using a 741, then the paper is very old.
That amazed me too, Chris. I was reading about 1960 technology. That pdf is from aerotech's own site, anybody can download it and read it. Were I to design a similar device today, I'd certainly use lf357's or better. Something with a speed approaching video usage. If I were to pick up some of them used, I'd certainly warm up the iron and change them. And check any electrolytic caps for old age, replacing as necessary. Offtopic sorta: I just went thru a $20 set of computer speakers using one of those $20 banggood parts testers, and replaced 6 of the 11 caps in it, sounds great again. The tester I used is similar to this device but only has one button: <https://www.banggood.com/Transistor-Tester-ESR-Capacitance-Meter-Resistance-Inductance-Measuring-p-1044840.html?rmmds=search> Biggest usage problem is the zif socket, not very sturdy. But it measures ESR, the most important characteristic of a cap after its capacity in u-f. Ontopic: If Jeremy got those used, they are probably takeouts from a 30 yo or older machine, And likely needing repairs as I am discussing to restore the original performance. Even NOS, sitting on the shelf gathering dust all this time, they would be suspect. > Today > you can of course buy better op amps. And of course today a micro > controller can precisely measure an qucoder at any speed from zero up > to some MHz. If you can, the simplest way is to connect the digital > encoder to the mesa card, let it keep the position count then use that > any way you wish, possible to create the analog output you want > By using pdm/pwm in the pwmgens. At 50 kilohertz, then integrating that to get your analog voltage. But no not pass the raw signal thru an opto-isolator, the control linearity will be destroyed. There are no such critters in the 7i90/7i42TA control, but there will be in common BoB's used with the 5i25's and such parport simulators. > I would not build an analog, op amp based digital rate the analog > output converter even with modern op amps. That is not the best > solution in 2018. A digital counter is the way to do. It is easy to > make and as exact as you want. But I think the existing FPGA based > hardware should be able to count and you'd not need to actually build > anything. Indeed. Its all in the .hal code today, no "parts" involved. I think what I would do is hook into the power supply's, disconnecting the old active stuff and use them to feed power to one of the pico systems pwm-servo's per axis controlled. The control bandwidth is fast enough that with a low resolution encoders quantization noise, it rattles the gear lash making you think you need to tear the head down and replace its vfx quality bearings, because it sounds like every ball in them is square. With a 1000 line encoder on the motor, my machine runs at least 30 db quieter. -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
