One might argue that a magnetostrictive instrument is not an “echo” technology in the strictest
sense of the word. Unlike ultrasonic, radar, and laser instruments, we are not reflecting a wave off
a discontinuous interface between materials. Instead, a mechanical wave (pulse) is generated at the
location of a magnetic float in response to an electrical pulse. However, the principle of measuring
distance by the wave’s travel time is the same. At the top end of the rod (above the process liquid
level) is a sensor and electronics package designed to detect the arrival of the mechanical wave.
A precision electronic timing circuit measures the time elapsed between the electric current pulse
(called the interrogation pulse) and the received mechanical pulse. So long as the speed of sound
through the metal waveguide rod remains fixed, the time delay is strictly a function of distance
between the float and the sensor, which we already know is called ullage