ETS-Lindgren 6404 Helmholtz Coil - Manual (Page 5)

Introduction | 5
1.0 Introduction
ETS-Lindgren Model 6400 Helmholtz Coils create an extremely uniform low
frequency magnetic field between and in the center of the coils. The generated
field can be applied as a magnetic field immunity test system or a low frequency
calibrator. The strength of the magnetic field generated is directly proportional to
the number of turns in the coils and the current applied to them. The coils are
wound in series so that the magnetic field produced by current flowing in one coil
aids the field in the other coil. The windings on all standard Helmholtz coils are
wound of insulated magnet wires. The wire gauge varies depending upon the
model of the coil system and details are found in the Specification section of this
manual. The maximum current of a custom Helmholtz coil is determined by the
wire gauge.
Several of the Helmholtz coils are equipped with a rotatable, adjustable-height
pedestal capable of supporting equipment under test (EUT) in the center of the
assembly base. Equipment which is exposed to the homogenous magnetic field
should be placed on the equipment test table with the height adjusted so that the
center of the equipment is closely aligned with the axis of the coils.
Ferromagnetic objects within the cylindrical volume of the coil tend to distort the
magnetic fields in areas near the object. The coil system has been constructed
with minimal metallic components limited to the copper conductors, the electrical
connectors and the caster frames. The casters, however, are outside of the coil
cylinder and cause practically no field disturbance.
Precision in the manufacture of the coils and their support assembly are well
within a design tolerance of 0.5 cm (0.2 in) in both radius and axial separation.
The limit of this tolerance would produce a maximum error of 0.55% in the
accuracy of the magnetic field constant under the worst conditions. For this
reason the Helmholtz coil is considered a standard and produces a magnetic
field whose accuracy is governed by the accuracy of the current monitoring
equipment.