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PICList Thread
'Power Measurement'
1998\03\31@111541 by Tom Handley

picon face
  There has been some discussion on measuring power recently. Analog
Devices has a specialized A/D converter that's designed for this
application. It includes two differential A/D channels that feed a
multiplier with an output converted to frequency. It also includes a
voltage reference, conditioning circuitry, and runs off a 5V supply.
The recent flyer quotes a price of $3.20 in 10K volume.

  You measure voltage on one channel and current on the other. The
output frequency is related to power. I have an application where I'll
be measuring AC voltage and AC current (using a current transformer) to
monitor various loads and make decisions on when to `shed' or duty-cycle
loads. I wish I had this technology back when I was designing energy-
managemnet systems... For more info:

     Analog Devices Solutions Bulletin, Converters, March 98
     P/N AD7750
     http://www.analog.com/solutions/converters
     800-262-5643

  - Tom

1998\03\31@235758 by tjaart

flavicon
face
Tom Handley wrote:

>    There has been some discussion on measuring power recently. Analog
> Devices has a specialized A/D converter that's designed for this
> application. It includes two differential A/D channels that feed a
> multiplier with an output converted to frequency. It also includes a
> voltage reference, conditioning circuitry, and runs off a 5V supply.
> The recent flyer quotes a price of $3.20 in 10K volume.
>
>    You measure voltage on one channel and current on the other. The
> output frequency is related to power. I have an application where I'll
> be measuring AC voltage and AC current (using a current transformer) to
> monitor various loads and make decisions on when to `shed' or duty-cycle
> loads. I wish I had this technology back when I was designing energy-
> managemnet systems... For more info:
>
>       Analog Devices Solutions Bulletin, Converters, March 98
>       P/N AD7750
>       http://www.analog.com/solutions/converters
>       800-262-5643

Time for a South African plug <waving a lighter in the air and listening to
'Nkosi>

SAMES in South Africa make a range of power measurement chips that
can be controller via a serial bus. They are rugged and cheap. The link
for sames is on my page at :

http://www.wasp.co.za/~tjaart/electroniclinks.html

--
Friendly Regards

Tjaart van der Walt
spam_OUTtjaartTakeThisOuTspamwasp.co.za
_____________________________________________________________
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|       R&D Engineer : GSM peripheral services development    |
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'Power Measurement'
1998\04\02@073652 by Tom Handley
picon face
  More on power measurement. The current issue of Electronics Now
(May 98), has a good article by Don Lancaster in his Tech Musings
column. He talks about digital techniques as well as special IC's
like the AD7750 meantioned earlier and the MAX125 which measures 4
channels simultaneously. This is necessary for accurate power
measurement as you want to measure the volatage and current at the
same time. For those of you who want to use a PIC and two A/D channels,
this is an important consideration to keep in mind.

  He also mentions an interesting gadget that contains an IR sensor that
sticks on the glass of a utility power meter and counts the times a black
mark on the disk comes around. It's called the Systems Power Sentry by
Remote Measurement and costs $79. This concept is just `begging' to be
`PICified' ;-)

     Don Lancaster's Guru's Lair web site
     File: MUSE112.PDF
     http://www.tinaja.com

     Maxim
     P/N: MAX125
     http://www.maxim-ic.com

     Analog Devices Solutions Bulletin, Converters, March 98
     P/N AD7750
     http://www.analog.com/solutions/converters

     Remote Measurement
     Systems Power Sentry
     http://www.measure.com

  - Tom

1998\04\02@213523 by Scott Dattalo

face
flavicon
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Tom Handley wrote:
>
>    More on power measurement. The current issue of Electronics Now
> (May 98), has a good article by Don Lancaster in his Tech Musings
> column. He talks about digital techniques as well as special IC's
> like the AD7750 meantioned earlier and the MAX125 which measures 4
> channels simultaneously. This is necessary for accurate power
> measurement as you want to measure the volatage and current at the
> same time. For those of you who want to use a PIC and two A/D channels,
> this is an important consideration to keep in mind.

Actually, it's sufficient but not necessary to accurately measure
power by simultaneously sampling the voltage and current waveforms.
As long as you're nice to nyquist, it's possible to phase shift data
samples with an interpolation filter. It's not easy, but it is
possible...

1998\04\04@122306 by Tom Handley

picon face
At 06:45 PM 4/2/98 -0800, Scott Dattalo wrote:
>Actually, it's sufficient but not necessary to accurately measure
>power by simultaneously sampling the voltage and current waveforms.
>As long as you're nice to nyquist, it's possible to phase shift data
>samples with an interpolation filter. It's not easy, but it is
>possible...

  Scott, that's a great idea! For AC power applications with 50/60Hz
single phase lines, it should'nt be too difficult to compensate for the
measurement delay between two PIC A/D channels.

  - Tom

>Tom Handley wrote:
>>
>>    More on power measurement. The current issue of Electronics Now
>> (May 98), has a good article by Don Lancaster in his Tech Musings
>> column. He talks about digital techniques as well as special IC's
>> like the AD7750 meantioned earlier and the MAX125 which measures 4
>> channels simultaneously. This is necessary for accurate power
>> measurement as you want to measure the volatage and current at the
>> same time. For those of you who want to use a PIC and two A/D channels,
>> this is an important consideration to keep in mind.

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