Re: mystery signal

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Fri, 11 Nov 2005 21:26:30 -0500, "Robert Green"
<ROBERT_GREEN1963@xxxxxxxxx> wrote in message
<Uc-dnfeDu865zujenZ2dnUVZ_vmdnZ2d@xxxxxxx>:


>Been to Dave's hometown lately, Marc?  (-:

Several times last week ...

>IMHO, these car owners are in a lot worse shape than Dave, who could solve
>his problem with some $$$, an electrician and a couple of whole-house
>blockers.

Unless  one installs an appliance that uses high-frequency waveshaping and
is oneself unwittingly generating the noise ...


>Well, thanks for answering my question about why a triac-based problem
>would
>appear to be random.

Did I?  hmmm.. I wonder when ;-)

 >hat are the advantages of using IGBT's?  Are the
>cheaper?  More efficient?  And why wouldn't they sync with the zero
>crossing?  It still seems odd that a lamp dimmer of any kind would output
>such random interference.  I guess I'll have to Google IGBT's and learn
>more about how they work.

An IGBT used in a dimmer creates less noise than a random-phase TRIAC used
for dimming. That's because in this configuration, the IGBT is turned on at
the zero-crossing and off when enough power has flowed through the device at
which time it is biased off. A TRIAC cannot be turned off during the cycle
and so the dimming is accomplished by delaying conduction. IGBT's used as I
described are dubbed 'reverse phase' (I presume) because a graph of
voltage-time is the reverse of that for a TRIAC. Used in this mode, they are
much quieter than TRIACS and don't require massive inductors to filter
noise.

However the fact that IGBT's can be turned on and off during at any point of
the cycle means that they can be used in other circuit designs. Specifically
a modified sine-wave with lower amplitude can be created by switching the
IGBT rapidly on/off (eg at 120khz). This is the mode that would be the
problem wrt power line control devices.

>You're certainly right when you imply that X-10 users may have to face the
>fact that to keep things running smoothly, they'll have to fork out for a
>whole-house blocker.

And forego some sorts of devices which are becoming more prevalent.

>And you're certainly right when you say that the most
>reliable approach is hard-wiring.  ..... Hardwiring my house for hardwired
lighting control ex post facto
>would be incredibly hard.  X-10 isn't as good as hardwire, but by God it's
>a hell of lot easier to install and uninstall ...

... which is a good thing because one needs to do so very often ;-)

... Marc
Marc_F_Hult
www.ECOntrol.org