HELP!!!! Using Shunt Resistor to measure Current

Other Hardware Sensors
1

Hello guys,

I need some help. I can't understand why it is not printing out any value beside 0. So I use a Shunt resistor that has the resolution of 50mV for 300A and an AD0623AN op-amps. The signal is amplified with the gain of 100. One wire connected to the load side of the Shunt resistor is hooked into pin 3 of the AD0623, the other end of the Shunt resistor goes to pin 2.

The pin 6 (output) on chip goes to A5 analog pin of the Mega 2560.

I run the regular command int sensor_value = analogRead(A5). This gives me the reading values varies from 12-60. So it is reading something...

But the real problem is, when I convert this number to Amps, I always get 0

amps = sensor_value *(5/1024) * (300/0.05) * (1/100)

by doing hand calculations, this formula gets me a value that make sense. Can somebody explain to me why I always get 0 at Serial.println(amps).

Thanks so much.

2

Is the opamp powered from Arduino's 5volt supply.

Are the shunt voltages within the common mode range of the opamp.

Is the ref input connected to ground or to mid-voltage.

What is the datatype of "amps".

Leo..

3

Hello Leo,

  1. Yes
  2. Yes
  3. Yes
  4. I declare it as long type

If the first three were not hooked up correctly, I would not be able to get any readings from analogRead(). Am I right?

Thanks,

4

Question three was to check if you use the sensor uni-directional or not.

Run this test sketch.

void setup() {
  Serial.begin(9600);

  long amps1 = 50 * (5 / 1024) * (1 / 100);
  float amps2 = 50 * (5.0 / 1024) * (1.0 / 100);

  Serial.print("long result is: ");
  Serial.println(amps1, 4);
  Serial.print("float result is: ");
  Serial.println(amps2, 4); // four decimal places
}

void loop() {
}

It seems the maths line can be changed to:

amps = analogRead(A5) * 300.0 / 1024; // 300A shunt

With amps declared as float.

Assuming opamp gain is 100x, and Vref (Arduino supply) is 5.0volt

No need to use the intermediate step "sensor_value", unless you want to use it elsewhere in your code.
Leo..