Accurate measurement of d.c. and a.c. by transformer

The magnetic integrator, which uses an amplifier, the output of which is led back through a transformer, can be used as an ideal current transformer for measuring a.c. and bipolar d.c. with a large bandwidth. To eliminate drift of the working point (zero flux), a 2nd-harmonic modulator detects any deviation of the mean value of the flux from zero and controls the integrator, so that the balance is maintained. With this assembly, an accuarcy of the order of 10¿5 magnetomotive-force is obtained, and it is not influenced by distortion of the magnetic field around the primary current-carry conductor