FABRICATION AND EVALUATION OF AN ALTERNATING CURRENT SOURCE RESISTIVITY METER FOR GROUND WATER AND SOLID MINERALS EXPLORATIO

Abstract

A compact, low-cost alternating current source resistivity meter with a stable current output was designed and
fabricated for geo-electric sounding in an in – situ measurement to a depth of about 100 meters using locally
sourced electronics and electrical components. Four contact principle of Van der Pauw conduction geometry was
used for designing the circuit which consists of transmitter and receiver units. The transmitter unit consisted of a
voltage generator integrated circuit (SG3524) which feed two π radian out of phase pulse trains, at the frequency
of 225 Hz to a current generator unit, through two buffer transistors (BC558). A current limiter circuit was
designed and incorporated in the transmitter circuit for selectable Signal Currents (SI) to be passed in-situ through
the current electrodes. The receiver unit comprised a differential operational amplifier signal detector (AD8277A)
connected through a low pass filter circuit to a microcontroller (PIC16F877A) and liquid crystal display. A
microcontroller code was developed using a miKroBasic program which calculated the medium resistance using
signal averaging technique. Pre-fabrication Simulation (PfS) tests of the whole circuit were carried out using
proteus 7.2 professional. The fabricated meter and a Standard resistivity meter (Campus Omega) were used
simultaneously for field measurements at two purposively selected test sites using vertical electrical sounding,
while the degree of fitness (R2) between measurements of both equipment were analysed and compared using
inferential statistics. The statistical result shows that there was no significant difference between Standard
resistivity meter and fabricated resistivity meter.