[stdacet]

I have tried a lot to understand the mechanism by which pH meter works. Still I have some confusion about the following points.

1. I cannot understand the function of salt bridge with reference electrode. Why its important for reference electrode to get connected with measuring solution.
2. The potential of the reference electrode remains constant due to constant concentration of chloride ions, but due to salt bridge, chloride ions  move out and sample solution ions diffuse, why does this movement not change the concentration of chloride ions in reference electrode and contaminate the inner solution.

I will really appreciate any guidance in this regard.