Electronic – arduino – Amplifying and Reading a 0-1 V signal into Arduino

arduinomicrocontrolleroperational-amplifiersensorvoltage

I'm trying to read the (0~1V) output of a current transformer (CT) into the 10-bit ADC input of an Arduino Nano. The CT is sensing the L wire carrying 120V at 60Hz.

Current Transformer Specs:

  • Input Current: 0~30A AC
  • Output Mode: 0~1V
  • Non-linearity: ±1%
  • Build-in sampling resistance（RL): 62Ω
  • Turn Ratio: 1800:1

Since the Arduno accepts analog input of 0-5V, the CT's output have to be scaled to make full use of the 10 bits.

Additionally, I think the CT's output is a AC waveform, so it would vary between -1V and +1V. If this is correct, I would need to bias the output by AREF/2 (5V/2 = 2.5V) by diving the 5V and GND rails equally using a potential divider made out of 2 resistors.

How should I scale the 0-1V to 2.5V, assuming the output vary between -1V and 1V? Is there a solution that will both amplify the CT's output signal and bias it as well?

The circuit I'm using currently looks like

enter image description here

and a plot of the analogRead() values is shown below, where the x-axis represents the index number of the ADC sample, while the y-axis represent the ADC value (0-1024). Sampling rate is about 9 kHz (110us per sample). Peak-to-peak difference is about 55 samples, giving us a frequency of 165 Hz.

enter image description here

Best Answer

Just to move things forward I'm posting an idea (not an answer): -

enter image description here

I believe that the waveform shown above is current into a device containing a bridge rectifier, charging capacitor and load. It's too similar to the stereotype to be anything else (within reason) and the only conclusion of this is that the OP is incorrect about the sampling rate because between AC current peaks there are pretty much 56 samples, and, at 60Hz this must mean the sampling time is approximately 300 microseconds or the sampling rate is about 3.3kHz.

The OP is invited to state what the load is and, if it is a device that rectifies the AC supply then, he should recalculate the sampling frequency based on the diagram he has provided and if necessary amend his figure or amend the x axis of the graph.

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