How to measure RMS voltage and Current coming from AC supply and calculate

[Lchal.1]

Hi, i need to measure rms voltage and current choosing ADC channels in stm32f103.

i selected two channnels in ADC1 to read adc values . By using these channels i need to calculate rms voltage and current . But i am confused how to do it . is it necessary to do calibration also. can anyone help me how to write a code or how to start it please.

Thank you

[Imen.D]

Hello @Lchal.1​ ,

The current can be measured through a resistor: by measuring the voltage across this resistor.

The RMS is an average, so it must average the values taken by the ADC by software.

Perhaps I did not understand your question.

So, I suggest adding more details and clarify your request to increase the chances of getting you an answer.

Imen

[Lchal.1]

Thank you

[Lchal.1]

 if(HAL _ADC _Start _DMA(&hadc1, (uint32_t*) adc Buffer, TOTAL_CHANNELS) != HAL_OK)

  return 0;

if(RMS _Sample_ Counter<RMS_TOTAL_SAMPLES) // it is given inside timer interrupt by setting 1kz

{

for(index1=0;index1<2;index1++)

{

temp_ ADC = adc Buffer[index1];

V1[index1] = V1[index1]+((float)temp _ADC*(float)temp _ADC);

V2[index1] = V2[index1]+(float)temp _ADC;

}

RMS _Sample _Counter++;

}

while(1)

{

 Delay_Count++;

 if(Delay_Count>=2500)

 {

  Delay_Count = 0;

  if(RMS_Sample_Counter>=RMS_TOTAL_SAMPLES) // i have set RMS_TOTAL_Samples as 1000

  {

  for(indx=0;indx<2;indx++)

  {

  //RMS_value[indx] = ((sqrtf((V1[indx]/100000.0)-((V2[indx]/100000.0)*(V2[indx]/100000.0))))/15.5);

  RMS_value[indx] = ((sqrtf((V1[indx]/1000.0)-((V2[indx]/1000.0)*(V2[indx]/1000.0))))/caliberate_factor);

  if(RMS_value[indx]>1.5)

  {

  Actual_Amps[indx] = RMS_value[indx];

  }

  else

  {

  Actual_Amps[indx] = 0.0;

  }

 /*

  for(indx=0;indx<3;indx++)

  {

  //Amps_Reading[indx] += 0.1;

  if(Amps_Reading[indx]>30)

  {

  Amps_Reading[indx] = 0;

  }

  Actual_Amps[indx] = Amps_Reading[indx];

  }

 */

  V1[indx] = 0;

  V2[indx] = 0;

  }

  RMS_Sample_Counter = 0;

  }

 }

}

this is the code i have done to calculate rms voltage and current can anyone help me if anything i need to add or is my code correct please

Thank you

[Javier1 · Accepted solution]

True RMS calculation:

1.Detect the 0 crossing (here is where the magic is)

2. offset your adc readings tothat 0

3. calculate the root square of every sample and average the results.

(the more samples you get the more precise your result is) 

Cheap-fix RMS calculation:

if your signal is going to have a very stable dc component (same average all the time) you can just make a peak detector and do Vrms=(1/sqrt2)*(Vmax-Vavg)