Wils L Cooley

US Patent:

42097410, Jun 24, 1980

Filed:

Mar 8, 1978

Appl. No.:

5/884450

Inventors:

August D. Coby - Ripley WV
Wils L. Cooley - Morgantown WV

Assignee:

The United States of America as represented by the Secretary of the
Interior - Washington DC

International Classification:

G01R 2702

US Classification:

324 62

Abstract:

A system for measuring the resistance of an earth electrode such as a coal mine safety ground bed. Current is circulated between the bed and an auxiliary current probe installed approximately ten times the maximum linear dimension of the ground bed under test. By measuring the voltage level between the ground bed and an auxiliary voltage probe placed about 62 percent of the distance from the ground bed to the auxiliary current electrode along the straight line between them, the true resistance of the ground bed can be determined. To sense the current value of the current flowing into the ground bed, a current transformer is placed around the lead to the ground bed. Voltage measurements are made with a high impedance voltage amplifier connected between the ground bed and the auxiliary voltage probe. Continuous monitoring of the measurements obtained without the presence of operator is achieved by using an analog divider and filter with their output terminal being connected to a recorder.