1. Potentiometer and pulley arrangement: We have to measure the water level, for this purpose we are going to use a pulley-float/potentiometer arrangement. Pulley will be hanged above the water and a float will be resting on the water surface using a rope. And potentiometer will be fixed at the center of the pulley. So as the water level goes up and down, respectively pulley and potentiometer will rotate. So eventually water level is converted into resistance of potentiometer. A constant current source is used to pass current through this potentiometer, so as to get a voltage drop. This voltage is given to amplifier.