Development of a high channel count distributed data acquisition system for shaking table testing

Collecting data during shaking table tests is often challenging because the presence of the instrumentation and the associated cabling has the potential to affect the dynamic behaviour of the model. This is particularly true if the specimen being tested exhibits any form of rocking behaviour as any instrumentation cabling running between the rocking components has the potential to add significant undesirable stiffness across the joints. This issue has been encountered in some ongoing research at the University of Bristol investigating the seismic performance of Advanced Gas Cooled Nuclear Reactor Cores. To overcome the limitations associated with conventional systems, a distributed acquisition system has been developed. The new system is comprised of high sample rate, 32 channel simultaneous-sample-and-hold acquisition units (µDAQs) that are small enough to be embedded inside the model components. These µDAQs are then daisy-chained together with miniature flexible ribbon cable that provides power, synchronisation and network communication signals. Data are collected on the micro SD cards integral to each µDAQ and from which they can be uploaded once a test is complete. This paper gives an overview of the design of the µDAQ system followed by a demonstration of its capability. Theoretically, the maximum channel count of the µDAQ system is circa 14,000 (i.e. 63 strings each of 7 µDAQs each acquiring 32 channels of data) with a rate of 5,000 samples per second. It has the potential for use in other experimental programmes where high channel count, high speed, simultaneous-sample-and-hold, and minimal-wiring data acquisition is required.