if you really wanted isolation, wouldn't it be best to put a lightbulb of
suitable voltage/wattage inside a plastic box (to keep out light) and run a
fiber optic cable from the bulb to some suitable remote location - then use
light intensity and a nomograph on your computer to calculate wattage.
>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