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Test analysis report :improving finger simulator & plethysmograph filtering for nano core

Kuipers, P. (2016) Test analysis report :improving finger simulator & plethysmograph filtering for nano core.

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Abstract:DEMCON has developed a blood pressure measurement system called the Nano Core. This independent module measures the blood pressure continuously using a finger cuff and can be attached to the Finapres NOVA, or other monitors, to read out this blood pressure. The work done during this internship covers two aspects: The main objective is to investigate possible improvements for the performance of the Nano Core. In order to do this the current closed loop controller was redesigned. In order to formulate possible improvements, a more accurate model of finger dynamics was obtained first. Previously it was assumed that the finger dynamics, mapping changes in pressure to the plethysmograph output signal, behaved as a second order model. To investigate if this is indeed correct, the frequency response behavior of fingers of a number volunteers has been identified. This has been done by applying a multi-sine signal around the mean blood pressure. Several transfer function models have been fitted to the frequency response information that was obtained by analyzing the frequency spectra of the in- and output. The assumption that the dynamics behaves roughly as a second order model is correct, however extensions were necessary to describe high frequent behavior of some fingers. After the dynamic finger models had been defined, a filter could be designed to try to improve the stability and performance of the closed loop blood pressure measurement of the Nano Core. A filter has been designed on the dynamic finger models that were identified, to maximize the phase margin (therefore minimizing overshoot) at a desired cross-over frequency, with sufficient gain margin to guarantee stability. This filter has been implemented on a Nano Core, next to the most often used settings of the current filter. Measurements on the finger simulator have shown that there is little difference between the performances of both filters: The current filters seem to be quite optimal for this application.
Item Type:Internship Report (Master)
DEMCON, the Netherlands
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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