A system of detecting loading and unloading of mobile containers such as grain carts utilizes two low pass filters to determine whether the contents of the container are changing by subtracting one filter signal from the other, and using the sign of the difference. Weighing performance is improved by utilizing accelerometers to compensate for measurement dynamics and non-level orientation. Failure and degradation of weight sensors is detected by testing sensor half bridges. Loading and unloading weights can be tied to specific vehicles by utilizing RF beacons.