Development of a novel electromagnetic groundwater flowmeter (2021)
Type of ContentTheses / Dissertations
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
The concept and implementation of an electromagnetic flowmeter has, until now, remained focused on industrial plant applications and oceanographic measurements. This thesis applies the existing body of electromagnetic flowmeter work to the problem of groundwater measurement. The theoretical framework provided by Shercliff and Bevir is applied to larger geometries through the construction of numerical simulations. The simulations provide the expected sensitivities for a given flowmeter and electrode geometry combination. A model of the measurable signals is constructed and applied through the use of linear least squares estimators. A pre-whitening filter is described to mitigate the low frequency 1/𝑓 noise as well as a gating algorithm to reduce the effects of the magnetic interference. The concept groundwater flowmeter is tested on two different geometries in the laboratory, at a range of excitation frequencies. The moving gantry laboratory experiments at 1 Hz yield a flow signal of 400 nV, compared to the simulation result of 600 nV. However, the results from a mini aquifer we less conclusive, presumed to be due to the magnetic interference changing with flow speed. An unexpected frequency dependence is present in the measured data preventing accurate results above 1 Hz. This is presumed to be a result of the coil power supply design. A likely source of zero offset drift is also identified as the magnetically coupled interference.
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