ADS1115: Differential Mode, estrange readings when using the 4 channels simultaneously.

Joseph

Thank for you quick response, I will try to understand how to implement single-shot conversion mode through Adafruit library, this is the code that i´m using to read the the values from SCT-013 50A/1V:

#include <Adafruit_ADS1015.h>

#define ads_add_0 (0x48)

Adafruit_ADS1115 ads0(ads_add_0);

void setup() {

ads0.setGain(GAIN_TWO); // ±2.048V 1 bit = 0.0625mV
ads0.begin();

}

float getCorriente(byte bomba)
{
long tiempo = 0;
long rawAdc = 0;
long minRaw = 0;
long maxRaw = 0;
float voltagePeak = 0;
float voltageRMS = 0;
float currentRMS = 0;

switch (bomba) {
case 1:
if (BomEnc1 == 1) {
tiempo = millis();
rawAdc = ads0.readADC_Differential_0_1();
minRaw = rawAdc;
maxRaw = rawAdc;
while (millis() - tiempo < 2000)
{
rawAdc = ads0.readADC_Differential_0_1();
maxRaw = maxRaw > rawAdc ? maxRaw : rawAdc;
minRaw = minRaw < rawAdc ? minRaw : rawAdc;
}
maxRaw = maxRaw > -minRaw ? maxRaw : -minRaw;
voltagePeak = (maxRaw * (FampB1)) / 1000;
voltageRMS = voltagePeak * 0.70710678118;
currentRMS = voltageRMS * 50;
currentRMS = currentRMS / 10000;
Serial.print("medida currentRMS B1:");
Serial.println(currentRMS);
return (currentRMS);
}
else return (0.00);
break;

case 2:
if (BomEnc2 == 1) {
tiempo = millis();
rawAdc = ads0.readADC_Differential_2_3();
minRaw = rawAdc;
maxRaw = rawAdc;
while (millis() - tiempo < 2000)
{
rawAdc = ads0.readADC_Differential_2_3();
maxRaw = maxRaw > rawAdc ? maxRaw : rawAdc;
minRaw = minRaw < rawAdc ? minRaw : rawAdc;
}
maxRaw = maxRaw > -minRaw ? maxRaw : -minRaw;
voltagePeak = (maxRaw * (FampB2)) / 1000;
voltageRMS = voltagePeak * 0.70710678118;
currentRMS = voltageRMS * 50;
currentRMS = currentRMS / 10000;
Serial.print("medida currentRMS B2:");
Serial.println(currentRMS);
return (currentRMS);
}
else return (0.00);
break;

}
}

I will try to implement single-shot conversion mode, and see if this fix the problem, i will reach you when do it.

Thanks very much for your help¡

Manuel

Joseph

This is the schematic, the first SCT013 is connected to A0 - A1, the second one on A2 - A3 :

Manuel,

One of the images in your last post didn't make it through. In your next response, why don't you add it then. In the mean time, I think I have a basic understanding of your system measurement.

I think the problem is that the your measurement does not have a defined common-mode input. As I mentioned in my last post, the absolute value of the inputs (AINP and AINN) must be within the GND to VDD range to be accurately measured by the ADC. Howeveer, in your setup, the output of the transformer does not have a common voltage to ensure that the inputs are within this range. They could float outside GND to VDD and not be accurately measured.

To ensure that the inputs are within the range of the ADC you would need a setup similar to this:

Here, the midpoint of the transformer output would be tied to 2.5V, which is the midpoint of the ADC supply (and midpoint of the ADC input range). The GND connection would be the same as the ADC ground. This would ensure that the input is in the input range for measurement.

For your setup, it may not be easily done if your output doesn't have center tap for this kind of setup. If you can restrict your outputs to only positive outputs, then you can tie the negative input to ground. This would at least be a good test of the inputs.

If you can't restrict your inputs to only positive inputs, you may need some sort of FDA for ensuring the input range.

Joseph Wu

Joseph

here the images missed:

The device doesn't have center tap, how can I restrict the inputs to only positive ?

Thanks for you help¡

Greetings

Manuel

The last image

Sorry can't upload the last image, don´t know why.....

Manuel,

When you insert images into the post, you can't use copy/paste (ctrl-c/ctrl-v). You need to use the picture icon (that says Insert /Edit Media).

Joseph Wu