GB645662A - Improvements in or relating to apparatus for measuring the electrical resistance of poor conductors - Google Patents

Abstract

645,662. Resistance measurements ; determining physical qualities of materials. GENERAL ELECTRIC CO., Ltd., HOULDIN, J. E., and THOMPSON, G. T. Oct. 12, 1948, No. 26573. [Class 37] For measuring the resistivity of a body of poorly conducting material such as earth, grain, electrolytic solutions, &c. four terminals T1, T2, T3, T4.are arranged to make contact with the body at four spaced points, the outer terminals T1, T4 being connected in series with the primary winding W1 of a transformer Z and the inner terminals T2, T3 being connected in series with the secondary winding W2 and a voltage indicator such as headphones D, a balancing resistance R being shunted across the secondary winding W2. An audio frequency supply is connected to input terminals 1, 2 and the balancing resistance R is adjusted until minimum response is obtained in the headphones D. The value of the resistance R then included between the inner points T2, T3 is a measure of the resistivity of the body and may be calibrated by the use of bodies of known resistivity. In a modification the headphones D are connected to a variable tapping on the resistance R. The contact terminals T1, T2, T3, T4 may be fixed as a unit in a spaced collinear relationship and may be equally spaced. The Specification states that the apparatus may be employed for measuring the moisture content of earth.