Building on firm foundations. If the engineers responsible for the construction of the tower in Pisa had access to the specialist soil testing equipment designed and produced by GDS Instruments Ltd, then it may never have gained such fame as the 'leaning' tower. Based in Hook, Hampshire, GDS has more than a quarter of a century's experience of developing top quality soil testing equipment that today enjoys a well-earned reputation with research and testing laboratories around the world. Playing a key role at the heart of this equipment are LVDTs supplied by RDP Electronics Ltd. Screen display from the test setup Determining how soil samples perform under load provides critical data for engineers concerned with calculating building loads for foundations of structures such as dams, bridges, railways and buildings. GDS has developed a triaxial testing system where cylindrical soil samples are subjected to a confining pressure, an internal pressure and then use LVDTs to measure axial and radial strain in order for engineers to understand how the ground itself will deform. Test sample showing radial and axially mounted LVDT sensors
For test purposes the soil sample is encased in a rubber membrane and sealed with a top cap. Low pressure (up to 3500kPa) versions of the system use water as the confining medium and high pressure (up to 200 MPa) use oil. A confining pressure is applied to simulate the surrounding soil and an internal pressure is applied within the sample itself. A pair of RDP's D5/200H LVDTs are mounted in radial callipers to create a local strain measurement device while a further LVDT measures axial strain. According to Associate Director Clayton Dodd, RDP's D5 LVDT5 are selected because, 'they are small and light and so minimise disturbance to the sample'. As the sample 'barrels' under axial load, the LVDTs pick up these very small movements, accurately outputting data to a GDS signal conditioning and data acquisition unit. Within the Data Acquisition unit are three RDP S7AC in-line signal conditioning amplifiers that convert and amplify the output from the LVDTs in the test set-up. This output is utlised by GDS's specially developed software to produce graphical and numeric data that is presented on a PC screen. _________________________________________________________ For sales and technical information contact:- RDP Electronics Limited Grove Street, Heath Town, Wolverhampton WV10 0PY. UK. Tel: +44(0) 1902 457512. Fax: +44(0) 1902 452000 E-mail: Website: August 2005

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