Abstract: A system for the measurement of the difference between two fluid flows in two separate ducts using one or more monitoring electrodes or the like arranged in respective ducts is disclosed. The fluid flow in one duct is adapted so that it is capable of being transferred to the other duct. This can be done, for example, using means for the alternate change-over of the fluid flows from their respective ducts to the opposite duct, so that ultimately all the electrodes and/or duct walls are acted upon to a substantially equal extent. Alternatively, this may be achieved using means for conducting one and the same fluid flow through both ducts where the fluid flow difference becomes zero and the measured value can be used as a new zero value for the continued measurement.

Abstract: A filtering device is disclosed which includes a pressure sensitive control valve to allow for overflow. The filtering device is particularly suitable for use in the medical treatment of blood, e.g., hemofiltration and plasmapheresis.