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.