Abstract: Apparatus is provided for estimating a flow rate of a fluent solid material in a generally horizontal pipe having a movable transportation element such as an auger in the pipe for transporting the material along the pipe including distance sensors mounted in the pipe in an upper part of the pipe and arranged to detect the distance of the material in a lower part of the pipe from the sensor. Another sensor is provided to detect the rate of movement of the transportation element for example by detecting the metal of the auger flight. The output from the sensors is fed to a control system for analyzing the output signals from the sensors over time to provide the estimate of flow rate. The sensors can be mounted in a pressurized enclosure to prevent escape of dust though openings for the sensors.