Microcones configured with full-bridge circuits

Abstract

Small-diameter microcones have been widely used for the characterisation of soil properties in the field and in the calibration chamber because the smaller probe may require a smaller penetrometer capacity and a smaller calibration chamber. As the cone size decreases, the area required for the installation of the strain gauges also decreases, and thus, the half-bridge circuit has been generally adopted. The objective of this study is the development and application of a microcone configured with a full-bridge circuit instead of the half-bridge circuit for the measurement of the cone tip resistance and sleeve friction. The diameter of the microcone is designed to be D = 15 mm, and thus, the projected area is 1.76 cm(2). The full-bridge circuit in the microcone is configured by extending the rod behind the connection part for the installation of four strain gauges. Two strain gauges are installed in the loading part, and two strain gauges are installed in the extended rod. In addition, the half-bridge circuit is also used for comparison of the cone tip resistance and sleeve friction in both circuits. The advantages of the microcone with the extended rod are verified through a theoretical background study and through experimental studies of various parameters, including temperature calibration, stress calibration, and densification monitoring. The test results show that the extended rod-type microcone with a full-bridge is less affected by environmental effects and produces better linearity between the output voltage and the stress. In addition, the full-bridge circuit yields more reasonable and reliable cone tip resistance and sleeve friction values than the half-bridge circuit. This study demonstrates that the extended rod-type microcone may be an alternative choice for the configuration of the full-bridge for better resistance measurements. (C) 2012 Elsevier Ltd. All rights reserved.