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ph scaling to measure ph value

Hello,

I'm using labVIEW to measure the pH of a solution using an in-line pH probe and NI DAQ card. To get the pH directly in labVIEW, I need to do scaling. I measured the voltage for two different pH values and found the line equation for the two points. Then I used this equation as my scaling equation in labVIEW. This unfortunatly didn't give the accurate readings I need! Any ideas what should I do to get the exact pH measurements.

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Hi Zooz,
              
              Any pH electrode requires both a sensing electrode and a reference electrode. The sensing electrode consists of a thin hydrogen permeable membrane containing a solution and an electrode. The membrane of the sensing electrode allows hydrogen ions to slowly pass, creating a positive voltage across the membrane. The voltage created in this electrode is then compared to the voltage in the reference electrode. The voltage difference between the two electrodes is then used to determine the pH of the unknown solution using the Nernst equation
E(pH) = E(constant) + (2.3* RT/nF) * log [H+]

Where:
E(pH) = Voltage difference between sensing electrode and Reference electrode (V)
E(constant) = Voltage difference in a solution with pH = 7 (V)
R = Gas Constant (8.314 J/K*mole)
T = Temperature in Kelvin (K)
n = Number of Valence Electrons per Mole (1 for H+)
F = Faraday’s Constant (96500 J/V*mole e-)

E(pH) = E(constant) - 1.98158 x 10-4 Volts/Kelvin * T *pH (6)
 
Also See to the attachment for complete Ph measurement guide
 
Hope this solves your problem
 
Kudos are Welcome 😄

 


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Certified LabVIEW Developer
Best LabVIEW Programmer @NIDAYS 2015
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