SEN0169 very inaccurate on calibration
![userHead](https://dfimg.dfrobot.com/dfPortrait2.png)
Hi DFRobot,
I bought the following probe:
https://www.dfrobot.com/index.php?route ... ption=true
and have been attempting to calibrate it using the same code as listed here:
https://wiki.dfrobot.com/Analog_pH_Mete ... KU_SEN0169
Testing an input voltage across the probe of 4.96v, and water temperature ~24.0 degC, with buffer solutions @ 4.0 and 7.0:
pH 4.0 - 0.35v - calculated pH 1.22
pH 7.0 - 1.79v - calculated pH 6.27
So really inaccurate!
I can write a smoothing function to the code from your wiki (see below) but it concerns me that the readings are grossly inaccurate. I was lead to believe the probe would be +/- 0.2 out of the box. Am I missing something? Is the probe faulty?
kind regards,
Kenneth
I bought the following probe:
https://www.dfrobot.com/index.php?route ... ption=true
and have been attempting to calibrate it using the same code as listed here:
https://wiki.dfrobot.com/Analog_pH_Mete ... KU_SEN0169
Testing an input voltage across the probe of 4.96v, and water temperature ~24.0 degC, with buffer solutions @ 4.0 and 7.0:
pH 4.0 - 0.35v - calculated pH 1.22
pH 7.0 - 1.79v - calculated pH 6.27
So really inaccurate!
I can write a smoothing function to the code from your wiki (see below) but it concerns me that the readings are grossly inaccurate. I was lead to believe the probe would be +/- 0.2 out of the box. Am I missing something? Is the probe faulty?
kind regards,
Kenneth
Code: Select all
//input voltage tested at 4.96v, temp 23.9
//lowDrift = 2.78, highDrift = 0.73
static float low_pH_buffer = 4.0;
static float lowV = 0.35;
static float high_pH_buffer = 7.0;
static float highV = 1.79;
float m, c;
void setup(void)
{
...
//create a two point offset in the format y = mx + c
m = (low_pH_buffer - high_pH_buffer) / (lowV - highV);
c = low_pH_buffer - m * lowV;
}
void loop(void)
{
...
if(millis()-samplingTime > samplingInterval)
{
...
//pHValue = 3.5*voltage+Offset;
pHValue = m * voltage + c; //plot a line in the function y=mx+c using the two voltage/ buffer points
...
}
}
2020-03-24 19:28:37 Hello,
Please confirm whether the pH meter board can work fine. Please test it according to the following steps.
1. unplug the ph probe, then short circuit the input of the BNC connector
2. test the voltage output from the pH meter board. The voltage should be around 2.0V.
Youyou
Please confirm whether the pH meter board can work fine. Please test it according to the following steps.
1. unplug the ph probe, then short circuit the input of the BNC connector
2. test the voltage output from the pH meter board. The voltage should be around 2.0V.
![userHeadPic](https://dfimg.dfrobot.com/5cb460fd10d75c69f96135d2/makelog/38a94862f2cb86a63c9621be972f65cd_50x50.jpg)