Schwarzbeck FESP 5133-9 Circular Transmitting Loop Antenna

The Magnetic Handheld Coil FESP 5133-9 was designed to generate defined magnetic field strength in the frequency range up to 3 MHz. The main application is immunity testing against magnetic fields according to MIL VG 95377.

Depending on the current source characteristics magnetic fields up to 400 A/m can be generated for a short time. The generated magnetic field strength is proportional to the coil current. The 50 mm distance ring is supplied to ensure a well defined spacing between the coil plane and the equipment under test (EuT)-surface.

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 = 10 A/m field strength).

The main part of the generated magnetic field is perpendicular (orthogonal) to the surface of the equipment under test, 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 independent characteristics will be achieved (but the efficiency of field strength reduces).

Use as magnetic field probe

The FESP 5133-9 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 strongly recommended to use a highimpedance voltmeter when measuring magnetic fields. When using 50 Ω measurement devices the source impedance of the FESP 5133-9 has to be considered at higher frequencies (approx. 10 kHz) which is 124 Ω at 1 MHz and 1.24 Ω at 10 KHz. The diagram below shows the course of the open circuit voltage when measured with a highimpedance milli-voltmeter and in comparison to a 50 Ω measurement device.