It depens on the linearity of the transformer. Small transformers tend to have quite bad regulation and this can greatly affect the linearity. This is why the Elektor article had two in series so the 230v primaries were only run at 115v to move the transformers response into a more linear region.

Best suggestion I can make it to get a voltmeter of the appropriate type and measure the mains voltage at the same time you measure the output of the transformer to see if it is linear. If you can find a variac it makes it very easy as you just ramp up/down the voltage and plot the i/p to transformer o/p ratio.

I'll have a look for the CC info - I have found the folder with it in - Its ISSUE 164 - March 2004
FROM THE BENCH Intelligent Current Sensing: Harness the Power of the ACS750 Hall Effect Current Sensor, by Jeff Bachiochi, p.68

Code is at ftp://ftp.circuitcellar.com/pub/Circ...-Bachiochi.zip

Bill.