Patent ID: 6037784
Filing Date: 2000-03-14
Classification: G01N

Abstract:
Material resistivity measuring apparatus comprisinga) a transmitter includingan AC voltage source producing a signal at a frequency at which a measurement is to be made,a modulator for modulating the signal from the AC voltage source,a power amplifier for amplifying the signal from the modulator and producing a signal with increased voltage,a first electrode apparatus connected to the output of the power amplifier and coupled to the material being measured,a sensing circuit for sensing AC current in the first electrode apparatus, anda variable phase AC voltage source for applying a first modulating signal, at a phase dependent on the AC current in the first electrode apparatus, to an input of the modulator,b) a receiver includinga second electrode apparatus coupled to the material being measured and spaced from the first electrode apparatus for receiving modulated AC voltage created by transmitter AC current flowing in the material,a detector for detecting the phase of the modulated AC voltage, andapparatus for adjusting the received signal according to current level of the transmitter as determined by the detector.