# Getting Incorrect Value of Current while Sensing Current Transfromer

I am working on AC Ammeter. To sense the current a current transformer is used which has 2500 Turns and sensing range up to 50A.

200 ohm Burden Resistor is used between the Ground and the Output Pin of Current Transformer.

I have previously worked on AC voltmeter and it worked fine and I used the same way to sense the current. As OUTPUT of current transformer is Sine wave, so I used RMS method to take out the value.

Here is what I have done :

#define ADC_BUFFER_LENGTH 40

{

// Time to Process and Display Data
{
}
// 625*625 = 390625
// 128*128 = 16384
// 625^2 / 128^2 = 23.8414
adc_filter_val_current *= 2; //To even Negative Pulse
ac_value_current = (float)sqrt(adc_filter_val_current);// root mean square
ac_value_current /= 1000;
}


What am I missing?

• Unless the current transformer manufacturer really REALLY specifies it can be that high, 200 Ohms is a very high burden resistor value. And, the resistor should be directly across the CT terminals. I'd probably start with 2 ohms and see how that works. Dec 5 '17 at 10:29
• The circuit is already made and working fine with another microcontroller and I am just replacing the controller with Low-cost one and writing code from scratch. Dec 5 '17 at 10:35
• What are you missing? Test inputs, predicted output and actual test output for a start. Dec 5 '17 at 11:47