Patent ID: 6653839
Filing Date: 2003-11-25
Classification: G01V

Abstract:
An electrical measurement apparatus for measuring an electrical characteristic of earth formations comprising:a sensor element; a guard element; a generator for generating an alternating voltage; first connecting means for communicating the alternating voltage to the sensor element; second connecting means for communicating the alternating voltage to the guard element; an operational amplifier having: an inverting input, a non-inverting input and an output; a feedback loop between the output and the inverting input, the operational amplifier being configured as a voltage follower in which the voltage at the output matches the voltage at the non-inverting input; the output being connected to the sensor element, and the non-inverting input being connected to the generator, so that the operational amplifier forms part of the first connecting means; and a measurement resistor located within the feedback loop between the output and the sensor element.