Beam currents in particle accelerators are commonly measured by passing them through the center hole of a toroidal transformer. By definition, the response is limited to a.c. components of the signal. The paper describes a combination of magnetic modulator and active L/R integrator in a common feedback loop whereby a current transformer with flat frequency response down to zero frequency is obtained. The scheme is analogous to the well known chopper stabilized d.c. amplifier and offers high accuracy and sensitivity, together with a large dynamic range and good zero stability. The full frequency range from d.c. to more than 200 MHz is achieved by adding to this arrangement a fast passive current transformer with composite core and active back-up loop. Copyright © 1969 by The Institute of Electrical and Electronics Engineers, Inc.
