I didn't follow the subject closely. However a current transformer
without a secondary closed circuit (I mean a circuit which may pass
the current, and a too high resistor load could be an open circuit)
works as a high voltage transformer. Ie 1Amps in the primary, an open
circuit secondary could means a few thousen of volt. I'm much more
familiar with 1600A/5A transformers where an open secondary circuit is
tragedy (up to 10 kilovolt at the nominal primarily current).
I don't know what sensing transformer you have, but a current to
voltage transformer as you suggest, with a linear output
caracteristic, I didn't saw.
Measure first the transformer characteristic using not a clamp meter
but a precision current transformer and an ammeter. If you don't close
the clamp corectly, every time you'll measure a different thing, check
this too.

best regards,
Vasile

On 4/27/05, Lou Tiberia <loutiberia@yahoo.com> wrote:
> Hello.
> Thanks to everybody for the help with this power meter.
> I've built up a system, using a diode bridge before the burden resistor, as
> suggested by Harold H.
> The output voltage goes to AN3 on a PIC18F242.
> The system is running, however the voltage read at AN3 is strange.
> The current sense transformer spec says that it will track current at 100 mV
> AC per 1 AMP AC.
> I do not see this occuring.
> For example, I have these measurements:
> (I used a handheld clamp meter to read these AMPs, the voltage is read using
> my system)
> 2.2 AMP = .13 V, 4.7 AMP = .26 V, 12 AMP = .57 V.
> So I measure anywhere from 100 mV AC per 1.69 AMP  to 100 mV per 2.1 AMP.
> This also does not seem to be a linear mapping.
>  I have double-checked my RMS firmware with some test data, and the
> algorithm implementation seems correct.
> Reading the output voltage with a volt meter produces different values,
> these values also do not correlate with 100 mV AC per 1 AMP AC.
> Does anyone have any ideas what I have done wrong?
> Thank you,
> Lou
> 
> 
> >Hello.
> >I'm building a power meter to measure how much AC current some electronic
> equipment is drawing (from 0 to 17 Amps).
> >I'm using a Triad Magnetics CSE187 current sense transformer.
> >This current sense transformer rates primary 0-240V 0-30 AMPs and secondary
> outputs 0-3.5V proportional to the current.
> >I have a 56 ohm resistor between the 2 transformer secondary pins, with one
> secondary pin (pin 5) to ground, and the other secondary pin (pin 8) routed
> to the analog input of a PIC18F242.
> >I'm using the PIC to perform the RMS current (IRMS) algorithm.
> >Here are my 3 questions: 
> >Is there any circuit needed between the output of the transformer and the
> PIC analog input?
> >It seems to me that nothing additional is needed because the transformer
> secondary is 0-3.5V and the PIC analog is 0-5V.
> >Is this method accurate? 
> >Is any calibration needed or possible?
> >Thank you,
> >Lou
> 
> 
> 
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