Magnetic Potentiometer

a device for measuring the difference in magnetic potential between two points of a magnetic field or the magnetomotive force along a closed circuit that encircles conductors carrying a current that produces a magnetic field.

Magnetic potential is a hypothetical concept, since the closure of the lines of force of a magnetic field (the absence of magnetic charges in nature) means that the field is not a potential field. However, in engineering calculations and measurements, use is often made of the concept of a difference between magnetic potentials ΔU_mag at two points of a field, defining ΔU_mag as the work done per unit magnetic charge in taking the charge between the chosen points.

A magnetic potentiometer is an induction coil (field coil). It has a flexible or rigid frame (usually flat with a constant cross section) around which a fine wire is wound uniformly. The ends of the coil are connected to a meter, which is usually a ballistic galvanometer or microfluxmeter for measurements in constant magnetic fields or a voltmeter or oscillograph for alternating magnetic fields. When the magnetic potentiometer is situated in a constant magnetic field with its ends at the points of different magnetic potential, the magnetic flux running through the device (the magnetic linkage of the potentiometer) is proportional to the difference in magnetic potential between the ends (ΔU_mag). When the magnetic potentiometer is removed from the field, when its ends are connected, or when the field is turned off, there is a deflection of the needle on the ballistic galvanometer proportional to the change in the magnetic linkage AO. The measured magnetic potential difference ΔU_mag = Δπ/k, where k is the potentiometer constant. The average magnetic field intensity H_av between the ends of the potentiometer is computed from the value of ΔU_mag: H_av = ΔU _mag/l, where l is the distance between the fixed points of the field. If a magnetic potentiometer completely encircles the conductors carrying the current producing the magnetic field, then the measured ΔΦ is proportional to the magnetomotive force. A magnetic potentiometer can measure a magnetic potential difference (magnetomotive force) as low as 10^-3 -10_-2 amperes. (In the International System of Units, magnetomotive force is measured in ampere-turns or amperes.)