AnsweredAssumed Answered

Wide Dynamic Range Current Sensing

Question asked by ChaitanyaB on Dec 28, 2011
Latest reply on Jan 6, 2012 by ChaitanyaB



I have a a requirement to measure current from 5mA to 15A commercial and industrial applications.

230V,50Hz, AC Current, Bidirectional.

CFL ,Mobile Charger,Motors, Pumps basically anything with fair accuracy and low power dissipation. I will have 6 such outlets to be measured and monitored.


I have few doubts

  1. Initially I was planning for 10 mOhm resistor. So that the Max dissipation will be 2.25 Watt. But the Min Voltage will be 50 uV. Can any PGA,INAMP,Diff Amp amplify this? I think offsets,Gain Errors and SNR might make a mess here.
  2. Can I connect this to an ADC?  Here I assume I will do the low side sensing? I think 69 dB Dynamic Range is possible with ADC say 16 bit Differential. But here I think I will not be able to do the High Side measurement. I think I will not be able to measure the Reactive discharge when the Switches are off.
  3. AD629 was the first thing in my mind. Can we do PGA with AD629?  I mean OPAMP after the AD629?
  4. Will this Diff Amp will be good for 50 uV?
  5. In-general why ADI has high voltage Diff Amps and Not INAMPs?
  6. What is the smallest voltage an INAMP/Diff Amp can Amplify practically? I have seen uV/mV from microphone reproduced very well? with Power Electronics will it work ??
  7. Is there any other solution from ADI, entirely different ? or Pls suggenst the ICs we can use in this application.



Please give your expert opinions.