Design and Fabrication of Micro-Controller based 120Hz Earth Tester

Abstract

The basic idea behind the operation of earth tester is to measure the voltages drop and leakage current through ground. Correspondingly the value of earth resistance is obtained using micro-controller based circuit. The aim of the work was to design & fabricate micro-controller based 120Hz Earth Tester. The micro-controller used in the fabrication of this earth tester is AT89S8252. The fabricated instrument is calibrated and then tested in the laboratory. The ground resistance values obtained using the fabricated instrument are compared with those obtained using current injection 3-point method. The various circuits sections that are used to fabricate 120Hz Earth tester are as follow:- 1. SMPS(Switched Mode Supply) is used to provide 100V by using Fly Back Topology with Boost up voltage from 12V Battery To 100Volts.This voltage is feeding to high voltage electrode where as the second electrode is connected directly with the reference ground and by changing the position of third electrode we are getting the no. of outputs. 2. Microcontroller section having 2 no’s of Analogous to Digital converter, one of them which is used to provide voltage reading and the other one is providing current readings. 3. Frequency generating section using 556 timer circuits is used to provide 120Hz frequency. 4. Operational Amplifier section is used to invert the signal. 5. Additional Power supply is used to run operational amplifier section. 6. Switching section-MOSFET (Metal oxide field effect transistor) is used as a switch.