3.3.6 Data acquisition systems

An overview of data-acquisition system is shown in Photo 7. In general, both data acquisition system and the centrifuge machine are controlled in the operation room. The system need to be designed flexibly to accommodate the data acquisition for many types of centrifuge tests.

The positions of the slip-rings for data-acquisition system have changed dramatically over the last two decades. With the progress of micro-electronics and digital technology, it has become possible to have complete data-acquisition system on the model package with remote digital communication system to a centrifuge operator. The slip-rings may provide a bottleneck on the system, due to the number, bandwidth and capacity of the slip-rings available. Some of these constraints are being bypassed with the use of optical slip-rings and radio-LAN communication, or by multiplexing.

Fig.1 shows a typical data acquisition system with fiber-optic rotary joints. Various types of transducers are located on the model to measure displacements, pore fluid pressures, accelerations, loads and so on. These analog signals obtained from the transducers are amplified and filtered in the signal conditioning unit and converted to digital signals through A/D converter mounted near the axis of rotation. Digital signals are sent to the optic converting unit located in a data logger to convert to optical signals. After converting to electrical signals through the optic- electrical unit, the signals are sent to the computer for data acquisition. In terms of supplying the noise-free precise signals in the transmission system from transducers to the data acquisition, this digital communication on the fiber-optic rotary joints is probably better than that on sliprings.

Phillips, R. (1995) : Centrifuges in modelling: practical consideration, In Geotechnical Centrifuge Technology (ed Taylor, R.N.), Blackie Academic and Professional, Glasgow, pp. 34-60.