PH bias

Hence, by applying a bias emf corresponding to 2.3026RT/F pH, or by offsetting the mechanical zero of the potentiometer by pH units, the zero shift is compensated for any temperature within the range (about 20° C) over which pH is fairly constant. Modern instruments often include the possibility of varying the pH, bias (to allow the use of different electrode systems) by incorporating the isopotential bias into the meter circuits. 

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