A low-power AC differential ohm-meter

Abstract

A direct reading AC differential ohm-meter circuit for electron transport measurements in the standard four terminal configuration is described. This circuit can easily detect changes in resistance of 10^-5 Omega in a 1 Omega resistor. Power dissipation of a fraction of a microwatt in the sample makes the apparatus suitable for use in a dilution refrigerator. The value of the sample resistance can be read directly in ohms and small changes in this value are obtained as a voltage which is linearly related to the change in resistance. This voltage can be simply calibrated and used for recording directly on a plotter or as input for a control system or data acquisition system.