Volume 29, Issue 6 (November 2001)
Laboratory and Field Evaluation of Piezoelectric Weigh-in-Motion Sensors
This paper presents the results of the laboratory and field evaluation of the piezoelectric weigh-in-motion (WIM) sensors of two manufacturers, namely Vibracoax (VC) and Measurements Specialties Incorporated (MSI). The laboratory evaluation involved fatigue testing of two sensor types for each manufacturer, one factory-encapsulated and the other bare. The fatigue testing involved three contact stresses as well as dry and wet conditions. Significant sensor fatigue was experienced only under wet conditions. The field evaluation of these sensors was carried in both asphalt concrete (AC) and Portland concrete (PC) installations. The facilities at Nevada's WesTrack and at a CalTrans Heavy Vehicle Simulator site were used, respectively. All sensors exhibited high raw signal precision at any given time. Raw signal amplitude seemed to depend on temperature for the sensors installed in the AC pavement. For increasing pavement temperature, the raw signal amplitude of the VC sensors decreased, while that of the MSI sensors increased. The signal-to-noise ratio of the raw signal increased with increasing temperature for the sensors installed in the AC pavement. WIM load measurement precision and sensitivity to temperature varied between sensors. The poor load precision of some of the sensors was attributed to the load calculation algorithm in the WIM data acquisition system, rather than to sensor malfunctioning. During the period of the field tests, no consistent changes in WIM axle load measurements were observed that could be attributed to piezoelectric sensor fatigue.