What is the purpose of a sense lead?

Positioning of the reference electrode is often not important, if you have a well-conducting solution. If you have a solution with low conductivity, you might experience Ohmic drop. The Ohmic drop is the amount of potential that is lost on the way from the reference electrode to the working electrodes.

The Ohmic drop is a result of the Ohmic resistance between the reference electrode and working electrode. The resistance depends on the distance between the electrodes, the conductivity of the solution and the frits used. The frits are fixed and can’t be influenced by the user.

The conductivity of the solution is often dictated by the experiments. In a solution of 100 mM KCl is the conductivity sufficiently high, that for most purposes the Ohmic drop is negligible. Corrosion studies sometimes require that the solution is chosen according to the real environment the sample will be exposed to, which could mean a low conducting solution. Here Ohmic Drop could be important.