Patent ID: 8860415

Claim:
A fluid resistivity measurement apparatus, comprising: a fluid column defining structure configured to allow a fluid, whose resistivity is to be measured, to fill a fluid column inside the fluid column defining structure; two current injecting electrodes disposed inside the fluid column defining structure, at different positions in a longitudinal direction, the two current injecting electrodes being configured to inject a known current into the fluid column; voltage measurement electrodes disposed inside the fluid column defining structure, at different measurement positions in the longitudinal direction, between the positions of the two current injecting electrodes, the voltage measurement electrodes being configured to measure a voltage across at least one measurement column, which is a portion of the fluid column; two additional electrodes disposed inside the fluid column defining structure, outside of the positions of the two current injecting electrodes in the longitudinal direction, the two additional electrodes being electrically connected to each other to have the same electrical potential; a fluid resistivity calculating unit configured to receive the measured voltage, and to calculate a resistivity of the fluid passing through the fluid column defining structure, using the known current and known geometrical characteristics; and wherein the fluid resistivity calculating unit is configured to estimate a portion of the known current flowing between the measurement electrodes based on a ratio between (i) a distance between the two current injecting electrodes, and (ii) a sum of distances between each one of the additional electrodes and a respective closer one of the two current injecting electrodes, and the fluid resistivity calculating unit is configured to iteratively obtain a corrected resistivity value, when the resistivity is lower than a predetermined resistivity value, in each iteration using a corrected value of the ratio based on a known dependence of the ratio of resistivity.