Re: mystery signal

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Fri, 11 Nov 2005 16:02:54 GMT, nobody@xxxxxxxxxxxx (Dave Houston) wrote
in message  <4374b9f2.38688863@xxxxxxxxxxxxx>:

>I'm seeing a nearly continuous 2Vpp 120kHz signal on one 'phase'. The other
>'phase' is clear. There are what resemble triac noise bursts approximately
>1.6ms after each zero crossing and the 120kHz seems to be in sync with
them.
>
>I say nearly continuous because the signal is absent on what appear to be
>random half cycles (again in sync with the triac-like bursts, 1.6ms past
>ZC).
>
>I say 'phase' because while the two circuits seem to have no communication,
>they are in phase when observed on a scope. My apartment was originally two
>apartments and there are two meters which might be a factor.
>
>The signal is not coming from anything in my place but there are 4
>apartments in the building and 4 more in another building across the street
>which shares the transformer.
>
>A random snapshot of 24 half cycles is 101101101110111110110110 with 1
>indicating 120kHz presence and 0 its absence. I've been unable to discern
>any clear pattern other than the OFFs never last beyond a single half
cycle.
>
>The triac noise pulses have been here for a few years but yesterday was the
>first time I saw the nearly continuous signal. It blocks X-10. It shows up
>as noise on my ESM1.
>
>Any ideas?

Dave writes " It blocks X-10 ".

Did you recently download or install X-blocker? Could be one that is
malfunctioning and working on only one phase. You may not know that it may
have been reported elsewhere that these are being distributing to neighbors
of folks that have claimed that "X10 can be highly
reliable if you understand the various gotchas."  </joke>

Dave understands the various gotchas (and has an oscilloscope with a
specialized interface connected for monitoring the AC line.  So in his case,
does "reliable" encompass being "reliably blocked" ?

There are not applicable enforced standards for powerline quality in the US,
so the AC powerline is becoming a free-fire war zone with increasing random
fatalities.  This is a problem faced by all powerline carrier (PLC)
technologies including X-10, INSTEON and CEbus.

INSTEON reliability is increased by signal repetition) with increasing
number of INSTEON devices which simultaneously _decreasing_  X-10
reliability by lowering the impedance of the AC line at 120khz ("signal
sucking'). This may not be a "friendly-fire" fatality ...

But back to the question:

Unlike the ubiquitous TRIAC-based lighting dimmers that turn the AC off
during the AC cycle and are turned back on again only at the zero-crossing,
dimmers based on IGBT (Insulated Gate Bipolar Transistors)  devices can turn
the AC on *and* off during the cycle, not just at zero crossing. IGBT
dimmers are becoming more prevalent.

As best I know, there is no reason why a manufacturer of a dimmer has to
avoid 120khz (X-10) or 130khz (INSTEON) when choosing a frequency to control
("dim") an IGBT. And 120khz _is_ the maximum frequency reported for some
popular IGBT devices.

So Dave's new-found dependability may be from a newer, IGBT-based dimmer
running at about 120khz for light dimming or motor control. Doesn't bode
well for PLC in general.

...Marc
Marc_F_Hult
www.ECOntrol.org