Towards parallel, 192 channel, 40MS/s/ch data acquisition for optical tomography: A system for aero-engine exhaust emission diagnostics

To investigate novel engine and fuel designs for greener aviation, instrumentation is required that can spatially and temporally resolve gas concentrations within aero-engine exhausts. This paper presents work towards a parallel, high-speed, distributed data acquisition (DAQ) system that employs in-situ demodulation of tunable diode laser absorption spectroscopy (TDLAS) signals. We briefly describe how this sits within a wider tomographic instrument, the electrical system of this scalable design and preliminary characterization. Being remote from the end-user (approx. 60m) and deployed within an industrial environment, we have used a hierarchical, embedded strategy. This uses photodiode pre-amplification, filtering, digitization, signal demodulation, Ethernet packaging and microprocessor control implemented both on a multi-node, distributed basis and with the DAQ physically mounted on the same mechanical `ring' as the tomographic imaging array. Results show agreement with design but indicate that the first-generation interrupt-based direct-memory-access (DMA) between FPGA fabric memory and microprocessor memories is the predominant bottleneck.