luctuating ADC Reading for 4-20mA Pressure transducer input

[BHARGAVSHANKHALPARA]

Hello...

I am working on one project of water pressure measurement, in which i used pressure transducer which gives me output between 4-20mA Current form.

I am using one 250 ohm resistance to convert current into voltage, and than i give this voltage to ADC of arduino UNO channel 0 (A0).

ADC reading is continuously fluctuating up to 10 decimal numbers.

I have also check by connecting multi-meter and measure sensor current reading, for particular pressure. but current reading is stable (even not fluctuate 1 or 2 points.)

also i have checked voltage value after 250 Ohms +Ve and ground. converted voltage is also showing very stable.

but why ADC reading is fluctuating..?

i am using arduino uno, i doesn't have any changes in AREF, AVCC etc...

please suggest effective solution,

Thank in advance.

const int analogInPin = A0;  // Analog input pin that the potentiometer is attached to

int sensorValue = 0;        // value read from the pot

void setup() 
{
  // initialize serial communications at 9600 bps:
  Serial.begin(9600);
}



void loop() 
{
  
  // read the analog in value:
  sensorValue = analogRead(analogInPin);
 
 
  // print the results to the Serial Monitor:
  Serial.print("Reading: ");
  Serial.println(sensorValue);  
 
  delay(1000);
}

 

[barry]

Comparing the reading on your meter to the reading of the ADC is meaningless. Your DC meter is not going to detect high-frequency noise, spikes, etc. You should look at the signal with an oscilloscope.

 

[KlausST]

Hi,

What VRef do you use? Don't consider 5V as a stable reference voltage.
It will have high frequency noise, it will drift with time, temperature and load current.
Use proper decoupling capacitor.

What load is connected to the microcontroller? Especially cureent through the GND pins causes ground-bounce.

Is the signal to the ADC proper filtered? Even with low sampling rates I recommend to consider nyquist...

Klaus

 

[BHARGAVSHANKHALPARA]

Hello Barry...

I have tested my input using CRO, screenshot is attached, please see...and suggest solution

 

[barry]

Well, I think you've found your problem. It sure looks to me like 50Hz is getting into your signal. Is it on the power supply? Ground? Is it being picked up by a bad input cable?

First, try and find the source of the noise. Remove the input so that all you've got is that 250 ohm resistor; does the noise go away? If so, then the problem is your input connection(s).

You could try adding some filtering to the input. You could do some filtering (integration) in your software.