Measurement of Deformations by MEMS Arrays, Verified at Sub-millimetre Level Using Robotic Total Stations

Abstract

Measurement of sub-millimetre-level deformations of structures in the presence of ambient temperature changes can be challenging. This paper describes the measurement of a structure moving due to temperature changes, using two ShapeAccelArray (SAA) instruments, and verified by a geodetic monitoring system. SAA is a geotechnical instrument often used for monitoring of displacements in soil. SAA uses micro-electromechanical system (MEMS) sensors to measure tilt in the gravity field. The geodetic monitoring system, which uses ALERT software, senses the displacements of targets relative to control points, using a robotic total station (RTS). The test setup consists of a central four-metre free-standing steel tube with other steel tubes welded to most of its length. The central tube is anchored in a concrete foundation. This composite “pole” is equipped with two SAAs as well as three geodetic prisms mounted on the top, in the middle, and in the foundation. The geodetic system uses multiple control targets mounted in concrete foundations of nearby buildings, and at the base of the pole. Long-term observations using two SAAs indicate that the pole is subject to deformations due to cyclical ambient temperature variations causing the pole to move by a few millimetres each day. In a multiple-day experiment, it was possible to track this movement using SAA as well as the RTS system. This paper presents data comparing the measurements of the two instruments and provides a good example of the detection of two-dimensional movements of seemingly rigid objects due to temperature changes.

Test of the Precision and Accuracy of the ShapeAccelArray Sensor

“…Therefore, comparison of the results of these two articles is inappropriate. However, Beran [4] presents standard deviation of the position about 0.5 mm for 4 m long part of the sensor, this value precisely corresponds to the value presented by Measurand (precisely calculated it could be up to 0,54 mm).…”

“…The real accuracy of the sensor itself was not already solved in available publications with only one exception, but the comparative method used by Beran [4] was not significantly more accurate than the accuracy of the tested device as it should be. Moreover, the testing was carried out with the device installed in plastic pipe, which have unknown influence on the determined displacements.…”

“…An interesting comparison of geotechnical and geodetic relative displacements measuring methods is published by Beran et al [4]. A comparison between the SAA in the near vertical installation with a geodetic measuring system formed by the robotic total station with automated data collection and processing is presented there.…”

Shallow movements in clay rich rocks detected during subnormal percipitation period

“…With regard to the published results of former testing, we assume that this effect had significantly minor importance in this case. Beran et al (2014) presented result of the experiment when temperature fluctuations in range of 25°C caused submilimeter errors in the position at the end of 4 m long SAA sensor, which were characterized by standard deviation of 0.6 mm. In our case SAA sensor is 15 m long, but temperature changes affect significantly no more than top 4 meters of the sensor.…”

Analysis of the variations of measured values in continuous long-term geodetic monitoring

“…[1]) or even sub-millimetre level measuring of structures (e.g. [2]). The measurements are usually realized by the terrestrial methods (e.g.…”