jdl

This isn't for homework, just for me to understand the mechanism behind a pH meter and other forms of ion-selective electrodes. So if the external reference electrode potential is constant, and if the internal reference electrode potential isn't affected by the potential difference that develops at the glass membrane (as a result of a difference in hydrogen ion concentration/activity outside the and inside the glass membrane) as ewmon says, then how is the membrane potential that inevitably develops at the glass membrane detected, and consequently alters the potential difference (voltage) between the two electrodes?

I understand that a potential difference is created between the inside and outside of the glass membrane, and that the potential difference is proportional to the hydrogen ion concentration. But how exactly does that potential difference affect the half cell reaction that occurs at the internal Ag/AgCl reference electrode? Thanks in advance.