Adapting a Hall Probe Controller for Current Control of an Air-Core Magnet

ABSTRACT: Air-core magnets are preferable to iron-core magnets for electron paramag-netic resonance (EPR) magnetic fields less than 150 G (15 mT). The preferred way to control the field of an air-core magnet is by direct control of the current. For imaging applications, magnetic fields produced by the gradient coils interfere with the use of the Hall sensor. Direct current control of the field avoids this problem. However, most suppliers of commercial EPR spectrometer systems provide only Hall effect control of the magnetic field. To provide direct current control of an air-coil magnet interfaced to a commercial console, an adapter was constructed that effectively converts the Hall effect probe into a current sensor by measuring the field produced in coils carrying the same current as the main magnet coils, but positioned away from and shielded from the main magnet. The effectiveness of this approach is demonstrated. © 2002 Wiley Periodicals, Inc