Abstract: A fuel-gauging system has an ultrasonic probe mounted in a tank, the probe being connected to a processor unit via an electrical signal path comprising two lengths of electrical wires and a piezoelectric transformer connected in series between the two lengths of wires. The transformer has two piezoelectric elements mounted on opposite sides of the wall of the tank so there is no direct electrical passage into the tank. The piezoelectric elements are matched to the resonant frequency of the probe so that signals of different frequencies are heavily attentuated.