Overview
The magnetic, handheld coil FESP 5133 was designed to generate defined magnetic field strength in the audio frequency range up to 100 kHz. The main application is immunity testing against magnetic fields according to e.g. (of professional studio equipment acc. to EN 55103), MIL-STD 461, VG 95377 part 13) and many others).
Depending on the current source characteristics magnetic fields up to 1000 A/m can be generated for a short time. The generated magnetic field strength is proportional to the coil current. Two different distance rings (50 mm and 100 mm separation) are supplied to ensure a well defined spacing between the coil plane and the EuT-surface. The highest field strength levels can be achieved using the shortest ring.
There are further rings available on request in order to provide a certain scaling between coil current and magnetic field strength (e.g. 1 Amp coil current = 100 Amp/m field strength). Economic current sources in the frequency range from 10 Hz up to 100 kHz are Audio amplifiers, which are available in nearly all power ratings. The main part of the generated magnetic field is perpendicular (orthogonal) to the EuT-surface, i.e. in the same direction as the 22 mm handle. The achievable accuracy for generating defined magnetic fields depends on the accuracy of current measurements.
In some cases (with moderate field strength requirements) it may be advisable to use a well known series resistor and measure the voltage across this resistor. The resistor can be scaled in a way to obtain a convenient voltage reading which corresponds to the generated magnetic field.
The larger the series resistor compared to the inductance, the more frequency independant characteristics will be achieved (but the efficiency of field strength generation reduces). FESP 5133 is usually delivered with 4 mm banana plugs. On request it can be manufactured with a BNC female connector. For higher currents the banana plugs are recommended.
Application as magnetic field probe
The FESP 5133 can also be used to measure existing magnetic fields. The open circuit output voltage is directly proportional to the magnetic field strength (at fixed frequency) or directly proportional to frequency (at constant magnetic field strength). The characteristic is shown in the graph below for some constant magnetic field strength values.
It is advisable to use high impedant measuring equipment for the output voltage of FESP 5133. If 50 Ω measuring equipment is used the source impedance of the FESP 5133 must be considered at frequencies above 10 kHz (207 Ω at 100 kHz, 21 Ω at 10 kHz). The following diagram shows the open circuit voltage measured with a high impedant voltmeter and the voltage across 50 Ω.
| Specifications | |
| Number of turns | 36 |
| Wire diameter | 1.25 mm Cu |
| Maximum coil current | 10 A, 5 min. |
| Nominal coil current | 5 A continuous |
| Maximum magnetic field strength | 1385 A/m, 5 min. |
| Nominal magnetic field strength | 700 A/m continuous |
| Magnetic field strength, 1 A coil current (with 50 mm distance ring) | 138.5 A/m |
| Current required for 1 A/m (with 50 mm distance ring) | 7.22 mA |
| Magnetic field strength, 1 A coil current (with 100 mm distance ring | 46.88 A/m |
| Current required for 1 A/m (with 100 mm distance ring) | 21.3 mA |
| Flux density with 50 mA at 50 mm distance | 138.8 dBpT 136.8 dBΩ/m |
| Inner coil diameter | 133 mm |
| Medium coil diameter | 135.5 mm |
| Spacing coil center to measurement plane | 50 mm / 100 mm |
| Mechanical dimensions | 0.16 m x 0.25 (0.3) m |
| Coil terminals | 4 mm banana plugs or BNC female |
| Shield | Electrostatic |
| Usable frequency range | 0 - 200 kHz |
| Inductance | ≈300 Ω |
| Resonance frequency | > 500 kHz |
| Resistance | 0.6 Ω |
| Weight | 1.1 kg |
