Dynamic characterization of a high speed gamma-ray tomograph

Abstract

A HSGT (High Speed Gamma-ray Tomograph) has been designed and built at the University of Bergen with the objective to monitor rapid changes in multiphase hydrocarbon flow regimes. In order to perform real-time image reconstruction with photon integration times as low as 10 ms, a novel DACS (Data Acquisition and Control System) has been developed. The DACS is based on FPGA (Field-Programmable Gate Array) programming of the CompactRIO module from National Instruments to minimize its data acquisition and control time. The CompactRIO module includes a reconfigurable FPGA, which provides hardware-level data acquisition and control determinism with a time resolution of 25 ns. The data acquisition and control time for the HSGT obtained with the novel DACS interface design is 0.18 ms, which corresponds to a data transmission bandwidth of 1.35 Mbytes/s given that the HSGT data frame consists of 85 channels each comprising a 24 bit resolution. The DACS also facilitates FPGA sensor data pre-processing, i.e. normalization, of the acquired tomograph data to speed up the image reconstruction. Dynamic characterization of the HSGT for rotational and translational movements is presented in this paper, which is based on calculation of the RMSE (Root Mean Square Error) of the acquired tomogram compared to that of the test phantom. The test phantom consists of two spherical holes with different radius in a polypropylene sample. The results of the dynamic characterization show that the HSGT can sustain imaging of a rotational object with angular velocities ∼30 rad/s. For translational movement (free fall) the HSGT is able to detect internal cross-sectional structures with velocities up to ∼4 m s −1.