Improving Low-Frequency Performance of Measurement Device for Frequency-Dependent Soil Properties

It has been shown previously that low-frequency resistivity should be measured at very low frequencies if accurate measurement of the imaginary part of the permittivity is necessary. In some cases, frequencies of 1 Hz or lower may be required. In accordance with these findings, a previously developed measuring device has been substantially modified to perform resistivity measurements at frequencies below 1 Hz and to improve the accuracy of low-frequency measurements in general. For this purpose, the clock generation frequency range for the analog-to-digital converter was increased. In addition, all coupling capacitors were removed and a bias voltage was used instead. To improve measurement accuracy (especially for the real part of the permittivity at low frequencies), the “first-in, first-out” memory size was increased. Some other improvements have also been made: the power supply and sine generator circuitry have been modified. A different analog-to-digital converter was used. The voltage measuring probe was also improved. Finally, the measuring device has been released as open source hardware. The circuit diagram, printed circuit board and source code are available at gitlab.com/dmika/epsilon.