Helmholtz-Coils are especially designed to generate precisely defined magnetic fields from DC to the upper end of the audio frequency range and beyond. The generated fields are in a strongly linear relation to the coil current. The field strength can be calculated exactly by analytical (or numerical) methods, based on the coils' geometry, the number of turns and the coil current. Therefore the HHS 5218 is ideally suited for the calibration of magnetic field probes or sensors. Typical applications are magnetic immunity testing according to automotive standards or MIL-461F. When generating magnetic fields with Helmholtz coils coil current is directly proportional to the magnetic field strength. The calibration of the magnetic field is finally traceable to a current measurement(or to a voltage drop at a known resistor).

The Helmholtz Coil itself is usually considered as a primary standard due to the easily calculable relation between current and field strength. If this relation should be controlled, a loop sensor or monitoring loop can be used to determine the actual field strength.

The Helmholtz-Coils should be installed on a desk in a sufficiently large separation from sources of unintentional magnetic fields, e.g. transformers in power supplies, conductors carrying high currents, computer monitors, loudspeakers, cathode ray tubes (CRT), and more.... All kinds of magnetic material (e.g. steel, Nickel, Cobalt) should be removed from the near surrounding of the coil. The wires which are used to connect the current source with the Helmholtz- Coil should be twisted to avoid an unwanted injection of magnetic flux. The coil terminals are assigned with the characters A, B, C, and D. The generator (current source, audio-amplifier...) is connected to the terminals A and C, the terminals B and D are connected with the short cable supplied with the coil.

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