To understand how a pH amplifier works, we must learn a bit about what the pH electrode(Probe) does. In the most basic sense a pH probe is a very simple single cell battery, where the voltage produced is proportional to the hydrogen ion concentration around the probe and therefore proportional to the Log of the hydrogen ion concentration as expressed here pH = -log10(ah).
All this means is when the concentration is greater on the outside of the probe, the ion flow is inward causing a slight voltage(+) difference between the probes electrodes. This tells us whether we are measuring a base or an acid. The voltage can tell us the concentration of the test solution and which side of the probe the concentration is on. For each pH step we see a ten fold concentration change, for example a pH of 8 has 1/10th the ion activity as a pH of 7.