Sinusoidal output from Nitrate Ion selective electrode connected to Arduino Uno

Hi,

I got a Nitrate ISE from Alibaba :

https://www.alibaba.com/product-detail/972123-nitrate-ion-Selective-sensor_60668687813.html?spm=a2700.7724838.normalList.67.4d6272a1zpC9Qx

and I am trying to measure the concentration of Nitrate in water.

But ,all I am getting is a sinusoidal abrupt output ,even though I put the electrode in different solutions.
Also, the Voltage output at BNC connector is not stable ,it keeps on decreasing till zero when I measure it from Multimeter.

Code is simple:

const int analogInPin = A0;
int sensorValue ;

void setup()
{ Serial.begin(115200);

}

void loop() {

sensorValue=analogRead(analogInPin);
Serial.println(sensorValue);
delay(1000);
}

Please help me with this!!

It seems that the grounds aren't connected.

Most probes like that are not Arduino compatible, and require an amplifier.

Hi Jremington, thank you for responding. Do you have a workaround solution for this or if possible, can you please guide me on how should acquire data from the ISE.

What I would do is determine what amplifier is required for that probe, and either buy or build it. The seller or manufacturer can help with that.

Okay,thanks for the suggestion. I’ll work on that.

You might find this article informative: https://www.vernier.com/til/3635/

Some general information on a similar probe: http://www.nico2000.net/analytical/nitrate.htm

Most likely, the probe generates a voltage related to the nitrate ion concentration. Most such probes are high impedance, with several megohms internal resistance, and can output positive or negative voltages depending on the nature of the reference electrode. So in many cases, they cannot be directly read by the Arduino ADC.

I have read this document. But, the main problem with my ISE is ,it is giving a sinusoidal output ,whether it is dipped in solution or not. And ,once I convert it into voltage as per Nernst Equation,it only gives an enveloped sinusoidal signal. That's all.

Do you have any kind of amplifier board for your sensor? A generic pH probe amplifier probably works. Without such a board the readings you get are completely and utterly meaningless. The output of such a ion selective sensor is so high it is just about floating (you're in the tens or hundreds of MΩ easily, if not in the low GΩ), so without amplifier board you're looking at noise.

From the photos you posted it's impossible to tell what you have connected how. Do post a schematic.

it is giving a sinusoidal output

You have been told the reason for that. The probe is not properly grounded (picking up household AC power line interference), and is not connected to a suitable amplifier.

Please read the replies to your post.

Do you have any kind of amplifier board for your sensor? A generic pH probe amplifier probably works. Without such a board the readings you get are completely and utterly meaningless. The output of such a ion selective sensor is so high it is just about floating (you're in the tens or hundreds of MΩ easily, if not in the low GΩ), so without amplifier board you're looking at noise.

I have tried using a pH amplifier board. So, now I am getting a constant output i.e. ~ 880 mV and in Arduino,the analog output is between 175-182.

It is constant.

That sounds like a great improvement. Next step is calibration of the sensor.