Shape Accel Arrays (SAAs)
Shape Accel Arrays (SAAs) are manufactured in Canada by Measurand Inc. and distributed in the UK by Geotechnical Observations. An SAA is a rope-like array of sensors and microprocessors used to measure deformation. It is made up a number of rigid segments, 25mm in diameter, connected by flexible joints that can bend in any direction but cannot twist. Each segment has three temperature calibrated MEMS (Micro Electro Mechanical System) accelerometers, a temperature sensor and a microprocessor. The in-array microprocessors collect and send signal data through a single wire output.
The 3D shape of an SAA in near-vertical casing is determined from static accelerations of X and Y accelerometers. In near-horizontal mode, the Z accelerometers are used to determine 2D shape in a vertical plane.
SAAs are installed into 27mm diameter PVC casing and can be installed either vertically or horizontally. Any deformation that moves the casing is accurately measured as a change in shape of the SAA. SAAs are re-usable and are able to withstand huge deformations. Data can be collected from the SAAs either manually by use of a laptop or tablet computer and an SAA-PC Interface Box or in real-time remotely via a Datalogger.
During production, every sensor in every SAA is calibrated through a range of multiple temperatures and multiple orientations. Calibration constants are calculated and are programmed into the datalogger specific to the SAA. The only calibration procedure required after installation is to zero the SAAs when installed to produce a zero value for the SAA which will be used to compare all future readings to.