On Thursday 05 January 2017 13:08:54 Jon Elson wrote: > On 01/04/2017 10:07 PM, Gene Heskett wrote: > > I can't think of a thing in that whole kit that would be > > switching at 335 KHz. Except the regulator in the pi's > > power input. > > Trust nothing. LCD monitors, especially with CCFL > backlight, are huge noise sources. > Take a small coil (solenoid type, not toroid) and hook it to > a scope probe. Then, wave it around the equipment looking > for the expected frequency. You should be able to quickly > locate the source of the noise. > > That doesn't solve it, of course, but at least once you know > which UNIT is producing it, you should be able to swap out > that unit for a different model. > Yeah, but I reconfigured all the common point grounding, which did helkp me isolate it. I found a ferrite choke, about 8 turns of 16 ga wound on a ferrite bobbin. None toroid IOW. Waving it around was largely inconclusive other that on top of a teeny little thing about 1/2" from the pi's dc input jack showed about a 38khz square wave, with some ringing on it of course.
Switching back to the bare hook tip on the probe, I found about a 15 volt square, with tons of ringing at about half the square parts amplitude, coming out of the cable up to the VFD, essentially identical, also in the mid 35KHz range, lots of FM, that crosses over quite a bit of stuff in getting to the SpinX1. This I assume is from the rectification of the 12 volts fed to the SpinX1 as a set of supply rails for the SpinX1's analog speed input. Ohmage to anything is infinite. But this phony VFD has no input terminal for a static ground. The only ground, that there is, carries the common earth ground symbol, is on the control terminal block, not the power block,so I am wondering if its kosher to ground it. But the biggest source of noise seems to be the output cables to the motors, shielded, 4 wire plus foil, with the shield itself being run back to the common bolt and only connected at that end. One is running at about 17 khz, the other, lower voltage at 22khz. Just the inductance of 4" of braid generates over 2 volts p-p on the scope. But it doesn't take much at 100+ megahertz to develop a good signal. I did put the 4a switcher back in and rearranged the bonding back to the common bolt to include the V- terminal. With just it running, noise at the output pins of the 7i90's center i/o sockets ground is about .550 v p-p. But from the reaction when I grasp the scopes ground lead and move it, that is the lead playing antenna. I moved the monitors power cord so its static was common to the lathes power cord. No diff. I haven't played with those noise filters yet, some doubts as to where they would do the most good. Suggestions? I'm tapped out, should go shove some snow off the decks but my enthusiasm for that got up and left without me. Only about 5" but it came down wet, and now the temps are forecast for close to zero the next 3 nights. If I was a bear, I'd go back to sleep till May... > Jon > > ---------------------------------------------------------------------- >-------- 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 > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
