Printed circuit capacitance electrodes

A magnetic flowmeter comprising:

• A a cylindrical spool of dielectric material functioning as a flow tube for the fluid to be metered coaxially supported within a cylindrical casing to define an inner chamber;
• B a pair of electromagnets mounted within the inner chamber at opposing positions therein on a magnet axis perpendicular to the longitudinal flow axis of the spool to establish an electromagnetic field therein whose lines of flux are intercepted by fluid flowing therethrough to induce a voltage in the fluid;
• and
• C a pair of flexible printed circuit boards conforming to and secured to the outer surface of the spool and symmetrically disposed on either side of said magnet axis, said boards being so printed as to define capacitance metering electrodes having enlarged surfaces which extend under the electromagnets at diametrically-opposed positions on the spool on an electrode axis at right angles to the magnet axis and at right angles to the longitudinal flow axis whereby the voltage induced in the fluid is picked up by the electrodes to produce a signal which depends on the flow rate of the fluid, each electrode forming one plate of a capacitor whose dielectric is the spool and whose other plate is the fluid.