A new method of flow measurement for non conducting fluids

For the flow measurement of fluids with a minimum conductivity down to about 1 mu S/cm magnetic inductive flow sensors show many advantages among which the smooth inner tube walls, the absence of any obstacles or dead space and the independence of the flow profile are the most important ones. In the industrial flow measurement there is a need for a similarly elegant measurement principle which may be applied to non-conducting fluids as well. The paper presents a new idea which does not require a conductive flow medium but rather utilises its dielectric properties as given by the relative dielectric constant epsilon(r). Instead of the voltage induced in the medium the polarisation charge caused by a medium moving in a magnetic field will be evaluated. This charge can be picked up by electrodes inside the medium and then be measured by charge amplifiers. Charge measurement is a well established technique in the field of piezoelectric transducers applied to the measurement of force, torque, pressure, and acceleration. There too polarisation charges occur at the transducer electrodes. The measurement principle proposed may be used not only for fluid flow applications but for the flow of solids as well. While for solids the magnetic dipole field is the appropriate field configuration it turns out that the magnetic quadrupole field configuration is optimally adapted to the measurement of fluid flow since its results are independent of the flow profile.