Overview
The Helmholtz-Coils are especially designed to generate precisely defined magnetic fields from DCup to approx. 5 MHz. The generated fields are in a strongly linear relation to the coil current. The fieldstrength 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 5201-6 is ideally suited for the calibration of magnetic field probes or sensors. Due to the high temperature proof copper wire packet it is possible to generate magnetic fields up to approx. 3 kA/m for short times. Typical applications are magnetic immunity testing according to automotive standards or MIL STD 461. When generating magnetic fields with Helmholtz coils the coil current is directly proportional to the magnetic fieldstrength.
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 does not require a calibration. Alternatively a small loop sensor can be used to determine the actual fieldstrength.
Installation
The Helmholtz-Coils should be installed on a desk in a sufficiently large seperation 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 kind of magnetic material (e.g. steel, Nickel, Cobalt) shold be removed from the near surrounding of the coil. The wires which are used to connect the current source with the HelmholtzCoil 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.
An additional verification can be done by measuring the magnetic fieldstrength between the coils. Assuming a wrong connection, the fieldstrength decays very sharply in the center between the coils, because the fields compensate each other.
The Helmholtz coils can be operated at three different coil separations. The recommended operation mode has a coil spacing of S=60 mm (measured between each center plane of the coils), which results in high fieldstrength levels and good field homogenity and medium EuTvolume. Higher fieldstrength levels can be achieved by decreasing the coil separation to less than 60 mm. The useable EuT-volume decreases, the maximum fieldstrength can be found in the center between the coils. Larger Separations than 60 mm result in an increase of EuT volume, but the fieldstrength and homogenity is reduced.
The following drawing shows the HHS 5201-6 with the medium coil spacing / separation S.
| Specifications | |
| Number of turns (per Coil) | 6 |
| Maximum Coil Current | 40 A / 1 min. 15 A / 15 min. |
| Nominal Coil Current | 12 A cont. |
| Coil Spacings | 50 ... 80 mm |
| Recommended Coil Spacing (The following data refers to a coil separation of 60 mm) | 60 mm |
| Maximum Magnetic Field Strength | 2860 A/m / 1 min |
| Nominal Magnetic Field Strength | 860 A/m |
| Magnetic Fieldstrength, 1 A Coil Current | 71.55 A/m |
| Current required for 1 A/m | 13.98 mA |
| Conversion Current-Fieldstrength | 37.1 dB |
| Coil diameter | 120 mm |
| Mechanical Dimensions | 290 x 220 x 130 mm |
| Terminals | 4 mm female with universal wire fixture : |
| Usable Frequency Range | DC ... 5 MHz |
| Inductance (per Coil) | 8 µH |
| Inductance (Pair of Coils) | 18.7 µH / 50 mm 18.2 µH / 60 mm 17.9 µH / 70 mm |
| ParallelCapacitance | 60 pF |
| Resistance | < 38 m? |
| Resonant Frequency (Pair of Coils) | > 8 MHz |
| Weight | 2.8 kg |
