Electrical resistance measurement strategies and their implementation in OhmPi

Various strategies can be envisaged to optimise the performance of an automatic resistivity meter when measuring electric resistances on a quadrupole. The objectives may be, for example, to maximise the signal-to-noise ratio of each measurement, to minimise the power delivered while ensuring that the voltage measured at the receiver reaches a fixed threshold, or to try to inject a given current independently of variations in the contact resistances. We describe how the variables controlled at the transmitter affect the signals received at the receiver as a function of the uncontrolled quantities during a soil resistivity measurement. We then propose some strategies for acquiring soil resistivity measurements based on these relationships, taking into account the physical characteristics and limitations of the transmitter and receiver. These strategies have been implemented in the software redesign included in version 2024 of OhmPi, an open-source resistivity meter.