On Friday 02 October 2009, Steve Blackmore wrote: >On Thu, 01 Oct 2009 12:32:48 -0400, you wrote: >>And what I think I'm seeing is quantization noise in the time domain, the >>occasionally very narrow spike probably isn't there on your o-scope. But >> it (to me anyway) points to a problem in that the sampling is probably >> not being done in the base thread, but in the 1 millisecond thread. Can >> that not be moved to the base thread? >> >>>From that halscope shot, I think I'd slow the spindle revs to 100 just to >>reduce the noise effects of the sampling jitter. > >I've redone that at 100 rpm, and out of interest looked at the pulses >out for the Z axis, the position interpolation is linear, as shown in >halscope, the pulses out are anything but! Surely they should be linear >too? > >There are several screenshots so I bundled them into a pdf. > >On page 6 I changed the sampling rate to base thread. > >http://filebin.ca/wacbfm/screenshots.pdf > >Steve Blackmore >-- Page 5 and 6 show it but not at a good time scale, page 7 from the base thread sample shows it very clearly Steve. Noise. Until that is gone (and encoder A output could have a closer to 50% duty cycle too, I'd almost return that one in fact if its sealed and non adjustable), it isn't going to work, not even if we make sacrifices. :)
I have to assume the encoders cabling is shielded, and the shield ends at the encoder so there is no connection via the shield to the machine by way of how the encoder is mounted and driven. That would be what we call a ground loop, and that is usually a no-no. And that with everything unplugged from power, that there is good continuity from the encoder cable shielding all the way back to the computers case. I think what we need to see is both a good picture of the encoder, a good pix of where the encoder cable is connected into the system, and maybe some ohm- meter readings between the computer's ground and the machine's ground with all power cables connected to power. Something is letting noise into that circuit, or forcing it as the case may be. Basically, there should be a good connection from the machine frame to the round pin of the wall socket it is plugged into, and a good connection from the shielding of the encoder cable back to the round pin of the socket the computer is plugged into, and if the machine is unplugged, there should not be any continuity from the machine frame to the computer case. And there should be a very low, under 1 or 2 ohms, connection between the round holes of the duplex the computer is plugged into, and the round hole of the duplex the machine is plugged into. Preferably on the same circuit breaker. A different circuit means it would have to go all the way back to the service entrance box to hit the common 'static' ground. That is a lot of wire acting like an antenna, and it could get pretty noisy. This next test is sorta last ditch, but will detect poor work by past electricians who really should turn in their card, they didn't pass the test. Open the service box (it goes without saying, be careful) and trace the circuit the computer is running on, then turn off that breaker, lift the white wire of that cable away from the neutral buss and turn the breaker back on, now nothing on that circuit should have power, but that white wire will now have line voltage on it if anything on the circuit is turned on. It might read up to 50 volts with everything off just from capacitance on that circuit, so use a 4 to 15 watt lamp to detect that, if it lights, something is still turned on. If everything still works mostly normal, there is a non-code connection out there, so then put the white wire back on the neutral buss (turn the breaker off so you don't get zapped & put the service box back together, leaving that breaker off & follow that circuit through every junction box it hits until you find where it is connected, white (neutral wire) to the static (bare wire) ground, and disconnect it. Whites to whites ok, bares to bares ok, but not together. You may even have to replace some old, no static ground romex cable with modern cable that has the w/g in its type number. The static ground, and the neutral cannot be connected together _anyplace_ but at the neutral buss of the service entrance breaker box. And that point should have 2, 8 gauge ground wires to ground rods, going as close to straight down as possible bearing in mind the ground rods they have to connect to have to be a certain distance apart according to the NEC. Good luck. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> I am having FUN... I wonder if it's NET FUN or GROSS FUN? ------------------------------------------------------------------------------ Come build with us! The BlackBerry® Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9-12, 2009. Register now! http://p.sf.net/sfu/devconf _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
