Velocity measurements in slow flow by the conductance-tracer method

The conductance tracer velocity measurement method, which is usually employed for determination of mean velocity, is extended to point velocity measurement of the order of a few millimeters per second with accuracies of the order of 10%. Velocity is determined by the time required for a conducting solution to travel between two measuring stations. At each station the conductance between two electrodes is sampled and the resulting conductance time trace is analysed numerically. Cross talk and electrolysis problems are overcome by AC current, alternate switching conductance measurements. The leading edge criteria, suggested in this work, seem to be best suited for travel time determination in such flows. The existence of shear does not seem to have an influence on the validity or the accuracy of the measurement.