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AC Current Measurement

Question asked by jnnewton on Jun 29, 2011
Latest reply on Jul 7, 2011 by clairec

I need to add current measurement to an existing product, as part of a re-design.   The Input signal limits are: 85-265V 47-63Hz of 0-20A (Line Power). 

 

For the conversion to voltage, I have narrowed it down to either a current transformer (1V on the secondary for 20A on the input, although from what I understand, this could be adjusted somewhat without cause too much change in the frequency response, although I don't know if that would even be an issue.)  The other option is a halls sensor from allegro micro, their ACS712 (output 0.-4.5V for -20-20A with a 2.5V center).  I would prefer the transformer due to simplicity, unless there is a reason to use the halls sensor. 

 

Assuming I use the Current transformer, and I want to be able to sense the difference between 0A and 100mA, taking into account that there is probably going to be noise on the power lines (estimated flat 0-30% of the signal (random), I have estimated that a bare minimum of 10bit ADC is needed, and that's right on the edge (5-25% error @ 100mA) is what i'm seeing, by my calcs), so I am looking for a 12bit (3-10% error @ 100mA)

 

I see that all the energy measurment ic's use delta-sigma converters, so I would guess that is what is most suited, and after reading a bit, they seem to have quite a bit of advantage for faster sampling and noise issues. 

 

Now having said all that, I cannot seem to settle on a specific adc, and would like suggestions or comments on the matter.   Thanks for any help you can provide.

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