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Dear all,
I've always wanted to create my own "home" monitoring system and just discovered Arduino and your community, which is really great !!
After I've successfully worked on temperature sensors, which is not very difficult... I'm working now on monitoring current energy consumption.

So my hardware consist in an Arduino Uno and a CT sensor YHDC SCT-013-030 (30 Amps).

According to what I understood, this CT sensor has a built in resistance and then delivers tension from 0 to 1V for 0 to 30A on AC side (primary). This is different from the 100A model which does not have this burden resistance.
Anyway I'm really fighting to get an accurate 0 to 1V tension reading on the ADC of the Arduino (I choosed A0) . Here is what I understood and what I've been through these last days :

• CT is providing an alternative (0...1V) current whereas Arduino Analog input is a 0 to 5V direct current.

• What you suggested on the following page is to use two 10kOhms resistance to set the "0V" level at half the maximum input of the Arduino, which then is 2.5V.

• Then my understanding is that the alternative 0..1V current will now move above and below the 2.5V input of the Arduino, from 1.5V to 3.5V at most.

• Now I've worked on different algorithms to "read" this alternative current and find the appropriate voltage of the CT and i've several problems / questions :

First I'm using a min/max and average method to calculate the "gap" between the highest and lowest value over a sufficient period of time. Does it sound good (code is below) ?

Second, I've put my Fluke multimeter at the output of the CT to get a clear voltage reading before it goes to the Arduino, and I also have an external fluke clamp to measure AC current of the AC cable directly. So I can compare :
- Current from my external AC clamp to to my Fluke multimeter voltage of the CT : this is really accurate (I just need to multiply the voltage of the CT by 30) as both are reading exactly the same number of Amps. One good news.
- Voltage from my fluke at the CT output and the voltage read from my algorithm using Serial.print by the Arduino. It is not so bad (meaning the difference is quite acceptable) if I've got only a few device plugged but as soon as Amps are going high the difference is way too high. What's wrong?
 

code :

const int sensorPin = A0;
const int number_of_samples = 50;

int vmin;
int vmax;
int sampleI;
int summax;
int summin;
int jmoy;
double moymax;
double moymin;
double Vrate;
double tension;
int topdepart;

void setup()
{
  Serial.begin(9600);
  Serial.println("temps;vmin;vmax;tension");
  summax = 0;
  summin = 0;
  jmoy= 0;

  topdepart = millis();
}

void loop(){

  vmin = analogRead(sensorPin);
  vmax = vmin;

  for(int i = 0; i <number_of_samples;i++){
    sampleI = analogRead(sensorPin);

    if (sampleI < vmin)
      vmin = sampleI ;

    if  (sampleI > vmax)
      vmax = sampleI ;

  }

  summax += vmax;
  summin += vmin;
  jmoy++;

  if(millis() >= (topdepart+1000)){

    moymax = summax / jmoy;
    moymin = summin / jmoy;

    Vrate = (moymax - moymin) / 2.0;
    tension = Vrate * 5000.0 / 1024.0;

    Serial.print(millis());
    Serial.print(";");
    Serial.print(moymax);
    Serial.print(";");
    Serial.print(moymin);
    Serial.print(";");
    Serial.println(tension);

    topdepart = millis();
    jmoy = 0;
    summax = 0;
    summin = 0;

  }

}