Re: Why don't we use ferrites??

Hi Caudlet,

Thanks for the comments. Although I think the subject was more in
reference to filtering INSIDE the driver/PS boxes. As I just wrote Bill
(off list),

> It's funny, but I put a VARIAC speed controller back on my old Sherline
> mill, and also set up the monitor ON TOP OF my newly completed driver/PS
> box, and THAT's when I started to see a lot of JUMPING in the screen
> with the spindle motor running. Initially I routed the spindle motor
> power through the driver/PS box, as I put in a solid state switch (SSS)
> to control it with my controller program, and first saw it. I've since
> routed spindle power around the box, but it didn't help. So maybe it IS
> just electrical noise. I don't remember getting that much jumping
> before. I don't know. I'll try the caps and ferrite beads, I've got
> that stuff laying around, or maybe the new mill I have coming will be
> QUIET?

I had changed several things at once (UPGRADE time!), and was surprised
to see all the hash (the wavy lines you describe)! I was wishing I had
some Mu-metal for a shield, but I can string some monitor cables
together to get some DX (distance) between the monitor and the motor for
a test.

I'm once again using Sherline's old motor controller (AC/DC), with a
TRIAC (correction to Bill's email, I HAD been using a VARIAC to control
speed), so this could account for the additional hash.

I'm hoping the new Sherline will be better and fix about 4 problems for
me! (wishful thinking?)

Alan KM6VV


caudlet wrote:

>
> --- In CAD_CAM_EDM_DRO@y..., wanliker@a... wrote:
> > In a message dated 8/5/2002 12:08:48 PM Mountain Daylight Time,
> > KM6VV@a... writes:
> >
> >
> > > But my biggest complaint nowadays is the motor of the Sherline
> mill
> > > messing up my monitor's display!
> Monitors are especially sensitive to electromagnetic noise because
> the electron beam can be easily deflected by good old low frequency
> stuff. Monitors have shielding around their picture tubes to help
> but some are sheilded better than others.
>
> EMI in a monitor shows up as wavey lines or stripes (ususally
> horizontally across the screen) or as bending/distortion in the
> image. If you can move the monitor a foot or two further away from
> the source and the distortion pattern changes it's probably EMI. If
> your picture has lots of random noise glitches it's probably higher
> frequency that can be solved with caps and ferrites.
>
> The computer can also be a possible suspect since the signals come
> from the video card. A lot of new monitor cables have Ferrite traps
> built in the DB15 cable.(more for emissions than external
> interference).
>
> EMF is best solved by either a reposition of the equipment or the
> introduction of a metal sheild between the source and the monitor. A
> grounded piece of sheet steel slightly wider than the monitor can
> tell you if it can be blocked. The thicker the sheet the better the
> shielding.
>
> BTW try www.bgmicro.com for a source for low cost ferrite cores.
>
> Handling noise in any place that switches large amounts of current in
> a short amount of time (DV/DT) is always a challenge.
>