Electromagnetic Water Current Meter

Theory is presented describing deviations from linearity and cosine response for cylindrical and spherical sensors. It shows sensor sensitivity varies with boundary layer thickness for sensors with flush electrodes as well as with electrodes protruding beyond the boundary layer. We calculate values of the boundary layer coefficientC_{B}. Deviations from linearity and cosine response are proportional toC_{B}R^{-1/2}whereRis Reynolds number. We show experimental data for sensors having negative, zero, and positiveC_{B}. A nearby flow boundary degenerates sensor sensitivity. Degeneration is neutralized by a conductive boundary; it is doubled by an insulating boundary; it is nominal with water-like boundary conductivity (as in a submerged jet). A sensor appended to a subsurface housing has tilt errors owing to circulation about the housing.