Abstract: A source vessel weight monitoring assembly for use in reactor systems to provide real-time and direct measurements of the availability of source or process materials from a source vessel. The assembly includes one or more force or load sensors, such as load cells, positioned between a bottom wall of the source vessel and a support element for the vessel (e.g., a base of a source vessel enclosure). The sensors are positioned to at least partially support the vessel, and a signal conditioning element processes the output electrical signals from the sensors, then a controller processes the output signals from the signal conditioning components with a conversion factor, for example, to determine a current weight of the source vessel and process material (e.g., solid, liquid, or gaseous precursor) stored therein. The controller uses this weight to calculate the amount of available process material or chemistry in the source vessel.