Abstract: The fluid conductivity sensor disclosed herein is adapted for the non-contacting measurement of fluid conductivity and utilizes first and second insulating tubes, each of which is provided with both the driving transformer and the sensing transformer. The sensor is immersed in the fluid to be tested so that the tubes fill with the fluid. The driving transformer's are oppositely poled so that the current induced in one tube tends to return through the other tube. Shrouds are provided which link the corresponding ends of the tubes and operate to obstruct in-fluid current flow not linking both of the tubes. Accordingly the influence of objects nearby in the fluid is substantially eliminated.

Abstract: A system for determining a property, such as conductivity, of a material in which a sensor provides a square wave sensor output signal the value if which is selected to the proper in response to a square wave driver signal. The sensor output signal is compared with a feedback signal to produce an error signal. A forward circuit responds to the error signal and provides an in-phase component thereof which is integrated to provide an integrated DC output signal. A feedback signal provides an in-phase square wave feedback signal the peak-to-peak amplitude of which has a precisely selected relationship with the integrated DC output signal for comparison with the square wave sensor output signal to reduce the error signal to zero. The integrated DC output signal can be digitized and suitably processed to provide a signal which represents the property of the material to a high degree of accuracy.