Abstract: A method and apparatus for measuring the depth of fluid in a well and for controlling the speed of a pump which pumps fluid out of the well according to the measured depth is disclosed. The depth of fluid in a well is measured by sending an acoustic pulse into an annulus between the well casing and the production tubing and sensing reflections of the acoustic pulse from collars on the tubing and a reflection from the fluid surface. Since the collar spacing on the production tubing is known, the distance from the top of the well to the surface of the fluid can be obtained by accumulating the distance associated with the collars detected in the reflection signal. The collar reflections are sensed by converting the reflected acoustic wave into electrical signals and then amplitude demodulating the broadband electrical signals.