Fields of application

RF field measurement for E- and H-field with near-field probes and a spectrum analyzer or an oscilloscope.

Correcting Characteristic Curves of Magnetic Field Probes

RF-type probes from Langer EMV-Technik GmbH

Magnetic field strength and current determination

The following paragraph explains how magnetic field strength and underlying currents are calculated from the results of near-field measurements.

A magnetic field probe emits a U_probe voltage signal output which is dispersed into a spectrum by a spectrum analyzer. A correction factor K_H is defined which describes the relationship between the voltage signal and the associated magnetic field H_RF. The magnetic field H_RF is linked with a current I_RF. Another correction factor can, thus, be defined based on the current I_RF.

Magnetic field correction:

The magnetic field strength H_RF in the coil of the magnetic field probe can be calculated from the voltage output signal of the U_probe magnetic field probe by means of the correction characteristic. The correction factor of the magnetic field probe is independent of the measurement geometry in each individual application, i.e. the probe can be guided at an arbitrary distance and angle relative to the electric conductor without any correction error (Figure 2). The result is the average magnetic field that is enclosed by the probe coil (Figure 1).

Use of the correction factor K_H in the adapted quantity equation:

Example of how the quantity equation is used, Figure 3:

In Figure 3 the magnetic field probe was located in a magnetic field that is constant over the frequency range. Due to the coupling factor the voltage which is induced in the probe depends on the frequency. The coupling factor intermediates between the measured voltage U_probe and the mean magnetic field strength. The existing magnetic field strength is obtained if the correction factor is added to the measured voltage U_probe (logarithmized quantity equation).

The mean magnetic field strength H_RF can be determined from the measured curve U_probe and the correction characteristic K_H using the quantity equation. The result is shown in Figure 3.

Current correction:

There is a consistent physical correlation between the magnetic field H_RF and the current I_RF which depends on the geometry of the current conductor layout. The given correction factor K_I thus refers to a defined reference set-up.

The determined current values I_corr are only correct if the geometric parameters coincide with the reference set-up when the probes are used. If there are deviations from this set-up, the current values I_corr will also deviate. The calculated current value I_corr can only be used as an orientation value.

The reference set-up has the following geometric parameters (Figures 4 and 5):

• Width of the conductor run 2 mm
• Height of the conductor run above the ground system 1 mm
• Probe placed on the conductor run

Use of the correction factor K_I in the adapted quantity equation:

The example is based on a current that is constant over the frequency range (Figure 6). This current induces a voltage in the magnetic field probe which is measured as U_probe by the spectrum analyzer. The frequency-dependent correction factor is added (logarithmically) from the voltage waveform to obtain the current in the conductor. I_corr is the current in dBµA which flows in the reference set-up.

Download Correction Characteristics

You can download the correction data for our special magnetic field probe types as xlsx-file.

• LF probes
• RF probes
• RF E-field probes
• XF probes
• XF E-field probes
• SX probes
• SX-E 03 probe
• MFA probes

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