Field test on RT11 bridge
This is the first field test of WISAN. The tasks for this test included:
- Comparison of wired data transmission vs wireless transmission of WISAN
- Preliminary testing of different acceleration sensors
- Identification of natural frequencies, and range of accelerations and displacements from ambient excitation
Vibration data were acquired using a custom made sensor module that interfaced a MEMSIC MXR2999 and an Applied MEMS SF1500S acceleration sensors. The output of each sensor was buffered and connected to the 12-bit ADC of a WISAN node and to a 16-bit USB data acquisition system. Data acquisition software was written in Labview and supported simultaneous data acquisition from the wireless and wired interfaces at 100Hz sampling rate.
The following figures show the sensor module and Labview interface.
Two sensor modules were placed on the overpass bridge over Raquette river on RT11 in Potsdam, NY. The temperature during the test was about 32F or 0C. The bridge was excited by passing traffic.
Both sensors were attached on the girder number 4 under the deck. One of the sensor boxes was attached in the close proximity of the support column, while another sensor box was attached at various locations.
Sensor location close to a support column.
First sensor location. Midspan of the girder
First sensor location. Midspan of the girder.
Second sensor location: Moving closer to the support.
Third sensor location
Test has shown very good correlation between wired and wireless data. The slight difference in results is caused by sample-to-sample asyncronization on the order of 10ms.
Wired data from Applied MEMS sensor (normalized by average)
Wireless data from the same sensor
Overplot of wireless and wired data shows good visual match between time series
Cross-correlation function of the time domain wired and wireless series clearly indicates a single point of the best match between series.
Power spectral density of the wired time series
Power spectral density of the wireless time series
Overplot of the frequency data indicates very good match in in the 10Hz frequency band.
The cross-correlation function in the frequency domain is almost identical to the cross-correlation function in time domain and indicates a single point of best match between the wired and wireless data