The Sketch in the Arduino IDE (Examples/Analog/AnalogInOutSerial.ino) should show some values on the serial monitor. You might test the pH of some known reference liquid, and see if it needs the correction factor mentioned in your post (adjusted value = read value * 1.024).
And of course the arduino 5v ref may not be exactly 5v - measure it and scale appropriately.regardsAllan
I believe that you should use fresh buffers to calibrate and you need to measure also fluid temperature.Remember that float and double have equal dimension on Arduino: 4 bytes.
So to conclude we are only concerned above 25C.
And below 25C the pH of neutral water is higher than 7 because autoionization is less as temperature drops so there's less H+ and the pH is higher. So you should also be concerned with temp below 25C if you want to be really accurate. And beyond the actual pH changes with temperature, temperature also affects the electrochemistry in your probe. Your response slope will change with temperature, as will the membrane permeability, and the equilibrium in your reference cell.
Since the pH varies with temperature, 25C was chosen to be the reference temperature. It is usually the reference temperature for other measurement.Buffers change slowly with time but they change and usually there is an expiry date printed somewhat like food.You will find temperature correction in Phidgets web site, in the same page where there are the other information about your board.
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