I have had som troble with my PH sensor. My ref. is 7 and it is equal to 2,5V.
When my PH selotion is at 5 its writing 9 and the voltage is increased to 3V
The voltage is fine put I need the PH value to fall to 5
is it possible to invert the outcom from the sensor?
Sorry for my english 
Here is my code:
//PH:
unsigned long int PH_avgValue; //Gem den gennemsnitlige værdi fra sensor feedback
int buffer_array[10], temp;
void setup()
{
Serial.begin(9600);
}
void loop()
{
//PH:
for (int i = 0; i < 10; i++) //PH: 10 prøver for at få en mere præcis værdi
{
buffer_array[i] = analogRead(A0);
delay(10);
}
for (int i = 0; i < 9; i++) //PH Sortere analog fra lille til stor
PH_avgValue = 0;
for (int i = 2; i < 8; i++) //Gennemsnitlig værdi fra 6 center prøver
PH_avgValue += buffer_array[i];
float phValue = (float)PH_avgValue * 4.15 / 1024 / 6; //Konventere analog til Volt og finde summen af de 6 center prøver
phValue = 3.5 * phValue; //Konventere Volt til PH værdi
if (phValue < 6)
{
Serial.print("PH for lav: ");
Serial.println(phValue);
delay(800);
}
else if (phValue > 8)
{
Serial.print("PH for høj: ");
Serial.println(phValue);
delay(800);
}
else
{
Serial.print("PH OK :");
Serial.println(phValue);
delay(800);
}
}
