Re: Wattmeter

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 )