The Electrochemical Rain Sensor (ERS) is a mass-spring system with air damping. The sensor acts like a switch which when rain falls on the same and thereby produces a deflection which allows to make contact with the electrolytes thereby creating current and running the wiper system as seen in Figure below.

How can we convert this sensor into a linear response variable by which we can measure any parameter like displacement proportional to deflection of the salt bridge?

Have a look at the sensor diagram attached.