Re: Why don't we use ferrites??

--- 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.