Axial Current Electro-Magnetic Flowmeters

Electro-magnetic flowmeters, in which measurable potential differences are induced in liquids flowing in pipes under transverse magnetic fields, are in wide use in nuclear reactors and elsewhere. Kolin has proposed another type of meter, in which a circular magnetic field is produced by an axial current flowing through liquid metal in the direction of flow. An e.m.f., proportional to flow rate, is induced between the centre of the pipe and the walls. In this paper, the characteristics of this, the current bearing liquid meter, are discussed. An alternative design, which may be termed the central conductor meter and which avoids some of the difficulties of the other axial current meter, is then discussed. Initial tests with mercury on a stainless steel central conductor meter are described and are fairly promising. The main advantages claimed for these meters are insensitivity to upstream flow disturbances and to variation in liquid/solid contact resistance, and the feasibility of using the meters even when the pipe walls have to be ferro-magnetic.