Hi Hero,
A 'magflow' type flow device, is probably one of the simplest type of flowmeter
its possible to conceive, which can give a proportional electrical signal.
In a simple form, a magnetic field surrounds a plastic pipe, a connector on each
side of the pipe like a rivet makes a connection through the pipe onto the flow,
and forms the output terminals, the flow through the pipe bridges between the
connections, and the flow produces an emf across the two rivets.
Disadvantages:
The flow has to be of a conductive fluid.
Bubbles can upset the reading.
I think the output is very low and has to be amplified.
Ones i have seen have always had large coils to make the external magnetic field,
but these days of relatively strong permanent magnets, it may be possible to use
permanent magnets for the field.
Breifly, if the lines of magnetic force are vertical, above and below the pipe,
then the connectors would be placed either side, and the flow between the
connectors would essentially be the "conductor cutting magnetic lines" as 'aljamri'
has said.
I will try to draw a small diagram to illustrate.
Hope this is Ok, John