HELMHOLTZ COIL INSTALLATION AND CALIBRATION
Helmholtz Coil installation manual
The following manual provide information about the use of Bartington Helmholtz Coil system and
considerations on positioning and orientation of the coil in order to ensure optimum performances are
obtained from the system. The document refers to additional documents such as the operation manuals
for separate system elements.
1.
Positioning of the coil
The Bartington Helmholtz coil systems provide users with the ability to generate stable magnetic fields.
Due to the nature of the instrument however, the field generated are leaked out of the coil, and in reverse,
external fields have the ability to distort and affect the field inside the set of coils. Because these systems
are used to generate magnetic field of amplitude similar to or within about an order of magnitude of the
Earth’s magnetic field, they will be very sensitive to
external environmental factors.
The first consideration should therefore be about finding a suitable location for the Helmholtz coil.
Ideally the site should be:
•
A site where permanent field distortion or gradient within the coil are negligible
•
A site where transient field distortions are avoided.
Whilst each installation and each site will be unique, there are some general recommendations which
can be given here.
To prevent permanent gradients across the coils, the system should be installed in an area clear from
permanent/fixed ferromagnetic structures such as support beams, reinforced concrete, or steel shelving
as these will distort the local magnetic field. If a coil is located too close to these elements, they will cause
distortions of both the Earth’s field as well as any field generated by the coil, thus affecting the
homogeneous volume within the coil and creating gradients across the coil, reducing the performance of
the system. A non-exhaustive list of structures and elements to keep in mind is given here: metal beam
structures, metal partitions and wall covering, fences, reinforcement bars within concrete, DC current
carrying wires, metal shelving and furnitures, machinery, parked vehicles.
It is equally important to remove transient interferences caused, for example, by personnel moving
with equipment which can cause field distortions (this can range from tools with magnetic tips, to phone
or steel framed trolleys etc…), or objects having a consequential mass of ferromagnetic material moving
further away (vehicles, lifts etc…).
The movement of these objects will cause low frequency field
variations, but can also, if passing close to the coils, generate slowly varying gradients across the coils.
Another consideration especially if running the coil at AC is the effect eddy currents may have. The
presence of electrically conductive material in the vicinity of the coil can see itself affected by the field
generated by the coils. In turn, eddy-currents may circulate within the material and lead to the generation