Re: Power factor/ frequency / true rms measurement of a 230V AC 50hz signal


John Larkin wrote:
On 29 Oct 2006 21:53:37 -0800, mgkelson@xxxxxxxxx wrote:

chetanthegreat wrote:
hey People !
For my engg final year project i am in a dire
need of figuring out ways to measure power factor and the rest of these
paramaeters using a microcontroller ..the one i hav selected is
dsPIC30F6014 . Plz can somebdy direct me to the algorithms needed for
these?
For frequency i guess i can use the DFT
interpolation or zero crossing detection method and stuff ..but for the
power factor i hav absolutely no threads !!
I wud b really grateful if smbdy cud help me
out with this.

Since voltage and current are not always sinusoidal, this strikes me as
a difficult project. I would guess that you are also going to need some
sort of high-power, low-resistance, precision resister, like a short
steel bar or something. In addition, I suppose you would need an
expensive A/D converter and timer.

My advice would be to select an easier project.

I did a decent residential meter design using a manganin current
shunt, a couple of opamps, and a 90-cent MC68HC05 uP with onboard
mux'd 8-bit ADC. It passed the ANSI C12 electric meter accuracy specs.

This sounds like an excellent project to me. Mediocre
proof-of-principle results are easy to come by, and there's fertile
ground for insights and improvements.

Oh, steel makes a horrible current shunt.

Yah, I'm not surprised--that was just off the hip. With a 3-minute
search, I found an example shunt at: http://www.elexp.com/tst_50a.htm.
I wonder if you have to rectify the current first? Oh, never mind. I
think I'm getting to deep into this :> :>

How would one measure true power, though? Maybe they sometimes do it
based on heat. Here's something I found on the internet:

"A thermal converter consists of a resistive heater in close thermal
contact with one or more thermocouples. When current flows through the
heater, the temperature rises. Thermocouples give an output voltage
proportional to the temperature difference between their junctions, in
this case proportional to the square of the current, and so make
suitable transducers for the construction of thermal wattmeters."

In any case, I imagine you could get a lot of information by simply
putting "wattmeter" into Google.

You can buy a watt meter now days, by the way, for about $25.00.

http://www.pricegrabber.com/p__P3_International_Kill_A_Watt_Power_Meter,__8968629/search=kill+a+watt/skd=1
http://www.safehomeproducts.com/SHP2/data/manuals/Kill-A-Watt_Meter_Report.pdf


John

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