On Tuesday 06 October 2009, Ian W. Wright wrote: >Thanks guys, > >That's that then, controllers in a cabinet again! > >Gene, >Having worked on installing mainframe computers for many >years I do normally use star earths for anything electronic >and my previous controller cabinet certainly has this - a >central bolt - for all the stepper control stuff and the >wiring for each stepper was done in shielded cable with the >shielding tied to the star point and the shielding extended >right up to, but not tied to the motors..
100% right so far. >The spindle - a >mains high speed brush motor, however was separately fed via >a thyristor speed control board from a relay in the control >cabinet. The motor has suppressors across the brushes Ouch! If the motor is being fed by an HF switching VSD, like mine is, that would put a heavier than normal stress on the HexFet such a speed controller uses to control the motor. The problem with the noise filters is that they contain capacitors used as bypasses to shunt the noise to ground, and the charge they absorb at the instant either the thyristor in your control, or the HexFet in mine, are turned on. Then those capacitance's need to be recharged to operating voltage and can absorb 10 of amps for a microsecond or so. That sure can telegraph back through the mains wiring for that drive. I had the top cap off of my spindle motor once because I was curious as to how much trouble it might be to renew the brushes in my PM field universal motor. I did not find any noise suppression in mine. So in my case, all I have is the relatively square wave at about 150 volts peak, at about 25 khz, which _should_ be at least as noisy as the brush arcing. However there is not another power load on the machine, so the green wire in the motors power cord, which now goes back to the VSD I took out of the gear head and put into the same box as the PMDX-106, that ground carries on to the PMDX-106, and on through the control signal cable running the PMDX-106, and hence eventually to my central 'star' point. The only theory I can come up with quickly is that while the machine itself may be grounded via whatever it might have for a power cord, lighting maybe, but that the Z might not be tied to the frame very well due to the lube on the ways. Any number of scenarios can be imagined depending on the machine configuration. In my case, the whole Z drive is bolted solidly to the top of the z post, so that is fairly well grounded. But the Z sled and gibs could lead to some isolation of the noise, again due to the lube on the ways. If you have a decent scope, float its power cord with a 3 to 2 adapter, and ground the probes to a heavier wire that is tied to the star point, and just go poking around to see where the noise is coming from. Bear in mind that long ground will be a good antenna, picking up quite a bit of noise all by itself, but after a while, you get the feel for what is different. Because we're looking for something that is pretty noisy, I'd turn up the gain and just go look for maximum noise that is not the chopper of the axis drives. Just for grins, I'm going to haul my scope out there and see what I find, and I'll report back. Curiosity bumps need rubbed and scratched you know. >and to >earth and all the earths on this side of things were tied to >an earthing point on the machine and so I suppose that there >is a vague possibility that interference could have tracked >back through the mains wiring although here again, the mains >to both parts was fed from the same wall socket. However, I >am skeptical of this as the only axis that was affected was >the Z-axis - the one nearest the spindle motor. And that, to me, is the puzzling part. There can be borderline situations where just one axis is sensitive enough to be effected, but the instances of it being the z are all out of proportion. >I tried >several spindle motors without curing the problem ( the axis >would very slowly feed down into the work ) and only solved >it when I changed to a synchronous-type of motor. Maybe >there was something amiss with the stepper which made it >susceptible to interference - I don't know. > >Ian >_______________ >Ian W. Wright >Sheffield UK > >--------------------------------------------------------------------------- >--- 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 > -- 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> Catsup and Mustard all over the place! It's the Human Hamburger! ------------------------------------------------------------------------------ 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
