Abstract: A sensor for measuring the dielectric constant of a fluid uses time of flight measurements. The sensor has a conduit for the fluid, preferably a transmission line. The dielectric constant of the fluid affects tranmission of electrical energy along the transmission line. An electrical generator, having as output an electrical transient, is operably connected to one end of the transmission line for transmitting the electrical transient along the conduit, where propagation of the electrical conduit is affected by the fluid. A receiver is connected to the other end of the conduit for detecting electrical transients that have passed along the conduit from the electrical generator.