GB1111981A - Improvements in flow meters - Google Patents

Abstract

1,111,981. Fluid-flow meters, electrical. SOC D'INSTRUMENTATION SCHLUMBERGER. March 6, 1965, No. 19213/65. Heading G1N. Relates to the elimination of short circuiting of potentials induced in a flowing liquid in the region of the pick-up electrodes of an induction type fluid-flow meter having a flow channel lined with non-magnetic metal. The meter comprises a non-magnetic pipe 10 (Fig. 2) with a stainless steel lining 16 separated therefrom by plastics insulating material 22 except where it is fixed to the pipe flanges 12, 14. Diametrically opposed pick-up electrodes 52, 56, insulated from the lining 16 by surrounds 54, 58 are disposed on a diameter perpendicular to the direction of a magnetic field produced by a permanent or electromagnetic (preferably A. C., not shown). Surrounding each electrode is a pair of concentric copper guard rings 60, 64 and 62, 66, which are brazed to the lining 16. A third electrode 68 is electrically connected to the lining to act as a reference potential point. The electrodes are connected to the inputs of differential amplifiers 70, 72 (Fig. 3) the outputs of which are connected to the guard rings. If for instance the gain of amplifier 70 is zero then the metal lining 16 constitutes an electrical connection between points in the liquid where different potentials exist. This alters the potentials particularly where the electrical conductivity of the liquid is low. If the gain is increased progressively from zero to unity currents are induced in the lining which produce potentials, in the region of the rings, identical to those which would be found if the lining was insulating. The potential of the rings will become equal to the potential of the associated electrode when the amplifier gain is unity. The outputs of the amplifiers are also connected to a mV meter to indicate the flow rate.