Smart Pebble for Monitoring Riverbed Sediment Transport

The smart pebble (SP) has been developed to monitor sediment transport in riverbeds. The implementation employs small size and low-cost acceleration and angular motion sensors. In this paper, we focus on calibration and testing of the final version of the SP, as well as its packaging in a 4-cm diameter spherical package. Error analysis of the sensors as well as the whole system has been modeled to evaluate the performance of the final system´s outputs. The calibration was done in two separate stages: individual sensor calibration and overall system calibration. The complete SP unit was tested under linear motions generated by a shake table, and 2-D rotational motions using two manually controlled servomotors. Offline signal conditioning was done in MATLAB. Errors due to misalignment and gravity have been reduced. Experiments conducted by sampling a 1-Hz sinusoidal signal at different rates show that to keep the amplitude errors of the system under 5%, the sampling rate has to be at least ten times the maximum bandwidth of the signals acquired from the sensors. The SP has been tested in a real flume and the results show that the system provides enough accuracy in measuring its own accelerations as it moves inside the flume.