The present invention relates to fluid conductivity sensors, and more particularly to a non-contacting fluid conductivity sensor which generates essentially no external current field and thus is not influenced by nearby objects in the fluid in which the sensor is immersed.
Industrial process control systems often require the measurement of the electrical conductivity of a fluid e.g. seawater, used in the system. Sensors for fluid conductivity measurement usually fall into one of two categories, i.e, contacting sensors and non-contacting sensors. Contacting sensors rely on a direct electrical contact between the measurement electronics and the material to the fluid, while non-contacting sensors typically employ driving and sensing transformers which, respectively, induce and measure a flow of current in the conductive fluid, the measurement of the induced current being a function of the conductivity of fluid. One problem which has existed with existing non-contacting conductivity sensors is that they may be influenced by objects a considerable distance from the sensor in the body of fluid into which the sensor is immersed. This influence is caused by the fact that conventional, immersible sensors typically have an external current field which extends a substantial distance from the sensor in the fluid in which the sensor is immersed. This is a significant problem in that calibration performed initially in the calibration laboratory will not be the same as calibration in the field.