How to use Eddy-currents in a sentence
For specimens of large sectional area it is necessary to apply corrections in respect of the energy dissipated by eddy currents and in heating the secondary circuit.
The current to be measured passes transversely across the disk and causes it to revolve in the magnetic field; at the same time the copper brake, geared on the same shaft, revolves in the field and has local or eddy currents produced in it which retard its action.
Induced or eddy currents are thus created in the copper disk, and the reaction of these against the magnetic field offers a resistance to the rotation of the disk.
Hence when a current is passed through the meter, the armature rotates and increases its speed until the driving force is balanced against the retarding force due to the eddy currents in the copper brake disk.
It consists of a disk of aluminium, the axis of which is geared to a counting mechanism and which runs between the poles of permanent magnets that create eddy currents in it and therefore exert a retarding force.Advertisement
Since the eddy currents induced in the disk are 90 degrees in phase behind the inducing field, the eddy currents produced by the main coil are in step with the magnetic field due to the shunt coil, and hence the disk is driven round by the revolution due to the action of the shunt coil upon the induced currents in the disk.
The framework and case of the instrument must be completely non-metallic, else eddy currents induced in the supports will cause disturbing forces to act upon the movable coil.
When these last coils are traversed by an alternating current they induce local or eddy currents in the disk.
Again the shunt circuit must have practically zero inductance and the series or current coil must be wound or constructed with stranded copper wire, each strand being silk Covered, to prevent the production of eddy currents in the mass of the conductor.