Abstract

Electromagnetic sensors are typically loaded with an external resistance value that provides an effective damping factor of 0.7. The velocity response of the sensor is given by a third-order equation but can be approximated by an equation of second order if the coil inductance is neglected. We propose to use a capacitor in series with the resistance (series RC load) instead of a resistance only. The transfer function is then given by a fourth-order equation that can be reduced to a third-order one, as a zeros-poles analysis shows. This is the simplest and cheapest way to extend the response of an electromagnetic sensor. If appropriated values of R and C are selected, then the flat band of the frequency response is increased by moving the corner frequency down by a factor of 1/4 without any effective gain reduction.

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