Given the simplified current transformer setup and a transformer with 100 A : 50 mA ratio, how would I calculate back the actual current given a voltage reading on the ADC?


simulate this circuit – Schematic created using CircuitLab

Is there a formula that accepts voltage reading as seen on the ADC and will be able to output the actual current being measured by the current transformer?


1 Answer 1


The CT will output 50mA for 100A in the primary, so with 20R total burden resistor you can easily work out the RMS voltage. The ADC readings you’ll get depend on the full-scale range of the ADC and the number of bits you’re reading from it. Since you’ve got no filtering I’d guess you’re sampling at significantly higher than the AC line frequency and then doing your own RMS calculations. Is that any help or do you need advice on anything more specific?

  • \$\begingroup\$ please ignore the actual performance of the adc for now. Lets say i get a reading of 1v at the moment of reading, how do i convert it back to current? Heres my attemp though, assuming i read +1v on my adc I = 1/20 , x = I*100A/ 0.05. would that be correct? SO answer is 100A ... weird , am i correct>? \$\endgroup\$
    – DrakeJest
    Commented Feb 21, 2022 at 5:53
  • \$\begingroup\$ Yes that’s right. \$\endgroup\$
    – Frog
    Commented Feb 21, 2022 at 19:07

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