Re: Power monitoring; ws Re: one wire sensors

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Wed, 08 Aug 2007 15:35:18 -0400, Marc_F_Hult
<MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote in message
<1qtjb35snrkpnrp5seiif22bim5bfcbq04@xxxxxxx>:

>On Wed, 08 Aug 2007 09:39:34 -0700, RickH <passport@xxxxxxxxxxxxxxxxxxxxx>
>wrote in message  <1186591174.960534.177300@xxxxxxxxxxxxxxxxxxxxxxxxxxx>:
>
>>
>>Would your circuit/concept require the homeowner to physically connect
>>each branch circuit (breaker) sensor directly to the powerline?
>>
>>I was thinking more in terms of sensing coils classed by wire gauge
>>(10, 14, 12 etc) and type (solid stranded) and power range (rating of
>>breaker), that the user would simply "clamp" around each wire after
>>identifying the gauge, type of wire and breaker amps.  Sort of like a
>>little clamping ampmeters hooked to each branch circuit, each coil
>>would have either a hardwire or RF link back to the microcontroller
>>unit that times the samples and accumulates/sends a data package back
>>to the software.  I've seen the C/H panels installed here at work,
>>pretty impressive.  But I was thinking more in terms of a system that
>>a homeowner can install without violating electrical codes.  The
>>microcontroller would calculate out any irregularities in the induced
>>current curve of the sensing coil, and provide a linear measurement of
>>amperage for logging.
>
>Yes. That's what I'm working on but it will take a few words for me to begin
>to explain my trajectory and rationale. Bear with me ...
>
[snip]


>If the waveforms were pure sine waves, and the loads purely resistive so
>that current and voltage were in phase, we could multiply the
>Root-Mean-Squared (RMS) 'average current measured in this way by a measured
>average (RMS) voltage, and compute the RMS power in watts at each
>transformer. Alas, the waveform is not perfect and current and voltage are
>out of phase for inductive and(or) capacitive loads, so this calculation is
>but an approximation in many cases.
>
>But for some loads and uses, this approach is plenty good enough.
>
>Gotta go. More later as time permits ... Marc

This photo www.ECOntrol.org/ItoV.jpg  shows a conventional Fluke True RMS
clamp meter and various current-clamp heads other attachments obtained on
eBay. When equipment changes, these accessories tend to get stranded and
sometimes get dumped for pennies on the dollar.

www.ECOntrol.org/THDA1_w_AD768.jpg shows the pcb and close up of the Analog
Devices AD736 RMS-to_DC converter IC of one of a batch of new, unused LEM
instruments THDA-1 AC millivolt to True RMS converters for I purchased on
ebay for a few dollars each.

Combined with one of the current transformers I posted previously at
www.ECOntrol.org/CTs.jpg one can provide a DC signal suitable for
conventional data loggers and HA controllers. Typically a simple op amp
configured to adjust the gain to the span of the ADC on the measuring device
is also helpful/needed.

Of course one could build these devices from scratch, but the price of the
AD736 converter IC alone ($7.50 from www.Digikey.com) is more than what was
paid for the entire  device.

... Marc
Marc_F_Hult
www.ECOntrol.org/porch_sale.htm