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I want to measure grid voltage with AMC1200b. I used a resistor voltage divider and I lowered grid voltage from 110v(rms) to 110mv(rms). I fed the 110mv(rms) signal to AMC1200b (for the first side of AMC1200b I used a 5v power supply and for the second side I used an isolated 3.3v power supply). The problem is, based on the datasheet, the gain should be fixed and 8, but it is 4 and I am losing some resolution for sampling. I also used a filter for the shunt resistor like it was in the datasheet( 2*12ohm resistors + 330pF capacitor).

Could you please let me know what's wrong with the circuit?

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  • \$\begingroup\$ You do know the output is differential? If you take only one output it may seem as gain is 4. \$\endgroup\$
    – Jeroen3
    Commented Apr 30, 2021 at 18:41
  • \$\begingroup\$ 2Vpp/0.25Vpp =8 differential also the RC filter was for a much lower R shunt current resistor, not a voltage divider. What is your shunt R value? \$\endgroup\$
    – D.A.S.
    Commented Apr 30, 2021 at 18:52
  • \$\begingroup\$ Voltage divider = voltage measurement, Shunt = current measurement, Show your schematics and what are you measuring, \$\endgroup\$
    – Marko Buršič
    Commented May 1, 2021 at 7:44
  • \$\begingroup\$ Hi @Jeroen3, yes I do, and I connected the negative output to the ground directly \$\endgroup\$
    – ReZa Alavi
    Commented May 1, 2021 at 22:36
  • \$\begingroup\$ Hi @TonyStewartEE75, it is 12 ohm \$\endgroup\$
    – ReZa Alavi
    Commented May 1, 2021 at 22:37

1 Answer 1

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Hi @Jeroen3, yes I do, and I connected the negative output to the ground directly

The AMC1200 has a differential output. Gain 8 is achieved by using a differential input. Using only one output will seem to have half of total gain.
Shorting the output is not recommended.

If you only have a single ended ADC you need to convert it with a differential amplifier.
Or you can sample both signals with your single-ended ADC and subtract them in software.
You do get some error if you can't sample simultaneously.

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