Tesla List wrote:
> Original Poster: "Steve Young" <youngs-at-konnections-dot-com>
> I suspect he meant to say Electronic Design (ED), not EDN. The original
> article was in ED 14 Oct 1994, and an improved circuit is in ED 14 Apr
> > From: Tesla List <tesla-at-pupman-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: Wattmeter
> > Date: Monday, January 18, 1999 12:22 PM
> > Original Poster: fprice3 <fprice3-at-acnet-dot-net>
> > Tesla List wrote:
> > > Original Poster: David Sharpe <sccr4us-at-erols-dot-com>
> > >
> > > Terry, John, ALL
> > >
> > > The original wattmeter which I used was found in EDN magazine; October
> > > 14, 1994 edition, "Ideas for Design" segment titled Optical Isolator
> > > Computes Watts. I immeditely recognized that this circuit could help
> > > stop the banter about my KVA is bigger than your kVA BS and cut to the
> > > chase with a parameter which is a primary measurement standard; POWER.
> > >
> > I searched the EDN Mag database and got this answer:
> > " The following matches were found in the EDN Archives for the search
> > OPTICAL ISOLATOR
> > AND WATTS. The results are ordered with the closest match listed
> > Higher scores indicate better
> > matches.
> > The search engine found 0 item(s) matching the search criteria"
> > Their database only goes back to Jan 1994. Can you pls. give us more
> > .................................
> > > The circuits are in the public domain and are probably available by
> > > tool (the interthingy). All components are
> > > available at MCM or Digikey.
> > > Regards
> > > DAVE SHARPE, TCBOR
> > you are probably right, ave, but I would like a bit more info: do you
> have a
> > diagram you could post?
> > Thanks,
> > Federico Price
Terry, Steve, ALL
Sorry about the miscommunication.. :^C
Optoisolated wattmeter was in Electronic Design originally.
I've been spending time attacking this alligator for my high power
design and have come up with a possible solution:
1. Wind a 50:1 current transformer (CT) on ferrite core. Pass
main power path =insulated= conductor through opening with
additional polyethylene tubing insulation. This will feed
a shunt of approximately 12 milliohms.
2. Apply 0-240VAC in through a small ~50VA PCB mounted 120/240 to 12/24
step down transformer (mini-potential transformer [PT]). Excite
as is shown in drawing, except that no load is across the
PT; the PT feeds one end of the CT shunt and Vsense input, the
CT powers the shunt resistance. The rest of the circuit is
as shown with appropriate op-amp meter scaling. (0-10V = 0-10kW)
3. The op-amp output of 2 feeds a baragraph display consisting of
(5) LM3914 bargraph display driver IC's which feed 50 LEDs in a
semicircular configuration. Additional LEDS and switches are
placed in circuit to configure a WATTMETER CONTROLLER. If power
limit is achieved, a relay will drop main contactor (an independent
high speed overcurrent trip system in case of a component fault
or other high speed high power calamity :^C ).
4. Op amp in 2 also feeds a small DVM which read 0.0 to 10.0 which
corresponds to 0-10kW)
5. Entire smeter subsystem to be place in DOUBLE SHIELDED aluminum
mini-box, all field wiring to be one point shielded.
6. Estimated cost of entire system: <$150.
Will keep group appraised on progress (or lack thereof :^C )
DAVE SHARPE, TCBOR