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2002 Mar 26 10:27

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Re: [vox] [OT] Smoothing out the powerline signal?
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Re: [vox] [OT] Smoothing out the powerline signal?

On Tue, 26 Mar 2002, Mark K. Kim wrote:

> On Tue, 26 Mar 2002, ME wrote:
> > How close is your fridge to your computer and other devices?
> Umm... it's a mini fridge... doubly serving as my printer stand :)
> I can't believe an EM from the fridge can disturb a huge device like an
> electron gun inside the CRT, especially when the monitor is shielded.
> Plus, the power line is fluctuating all the time (60Hz) but that's not
> very apparent at all; why would it become so apparent only when the fridge
> turns on/off?  Can you convince me it's at least plausible?

During startup, the motor in a refrigerator presents a very low impedance
at the connector.  If the connector feeds into a power strip, and some
connection between the power strip and the distribution panel (such as the
strip plug) has a relatively high resistance, then a voltage divider
effect will drag the strip voltage down.  Any devices sharing that power
strip may respond to this temporary (a few 16ms cycles long) dip in their
supplied RMS voltage.  One solution is to put the sensitive devices on a
UPS... another is to re-route the refrigerator to a different household
power circuit, or at least a different wall plug.

I think it is possible for the magnetic field around a motor to affect the
CRT, but it would have to be unusually close to the monitor.  Radio
frequency inteference could also bypass conducted paths, but it would be
more likely to come from brushes, and be unlikely to cause gross image
distortion... it would be more likely to affect fine-grained image
distortion and not be associated with startup.


    "Back EMF in electric motors"


Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil@dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
                                      Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...2k

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