Zero offset in electromagnetic flowmeters.

In electromagnetic square-wave flowmeters, it should be theoretically possible to determine zero flow by turning off the magnet drive. In actuality, this is not possible. A major source of zero offset in many commercial flowmeters lies in the fact that the very large voltage transients, seen as the flowmeter drive switches polarity, are distorted by the input amplifiers. This can be corrected by improved amplifier design. A second source of zero offset when flow probes have been immersed in conducting fluids is resistive leakage between the drive voltage and the input electrodes. This can be minimized through the use of shielded coils, with shield grounded, and by the use of a magnet drive isolated from ground. If both of these sources of zero offset are corrected, offset is greatly reduced. Polarization of the flowmeter electrodes, which has previously been suggested as a cause of zero offset, was not detected.