Correction characteristics for magnetic field probes
from the firm of Langer-EMV Technik GmbH
You can download the correction data for our special magnetic field probe types as xls-file.
- MFA type
- XF type
- RF type
- LF type
User of our software "ChipScan" please use the correction data in fdi-format.
"ChipScan" can handle these files.
Magnetic field strength and current determination
This paper explains how magnetic field strengths and the underlying currents are calculated from the results of near field measurements.
A magnetic field probe emits a voltage signal Uprobe which is dispersed into a spectrum by a spectrum analyzer. A correction factor KH is defined which describes the relationship between the voltage signal and the associated magnetic field HRF. The magnetic field HRF is linked with a current IRF. Another correction factor can thus be defined on the basis of the current IRF.
Magnetic field correction:
The magnetic field strength HRF in the magnetic field probe coil can be calculated from the voltage output signal of the Uprobe 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 (Fig. 2). The result is the average magnetic field that is enclosed by the probe coil (Fig. 1).
- Fig. 1: Field strength distribution in the probe coil
- Fig. 2: General application layout
Use of the correction factor KH 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 Uprobe and the mean magnetic field strength. The existing magnetic field strength is obtained if the correction factor is added to the measured voltage Uprobe (logarithmized quantity equation).
The mean magnetic field strength HRF can be determined from the measured curve Uprobe and the correction characteristic KH using the quantity equation. The result is shown in Figure 3.
- Fig. 3: Example of how the magnetic field correction characteristic is used
Current correction:
There is a consistent physical correlation between the magnetic field HRF and the current IRF which depends on the geometry of the current conductor layout. The given correction factor KI thus refers to a defined reference setup.
The determined current values Icorr are only correct if the geometric parameters coincide with the reference setup when the probes are used. If there are deviations from this setup, the current values Icorr will also deviate. The calculated current value Icorr can only be used as an orientation value.
The reference setup has the following geometric parameters (Fig. 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
- Fig. 4: Measurement setup for the R400-1, R50-1, R3-2, R0.3-3 field probes
- Fig. 5: Measurement setup for the B3-2, B0.3-3, K7-4, U2.5-2, U5-2 field probes
Use of the correction factor KI in the adapted quantity equation:
The example is based on a current that is constant over the frequency range (Fig. 6). This current induces a voltage in the magnetic field probe which is measured as Uprobe by the spectrum analyzer. The frequency-dependent correction factor is subtracted (logarithmically) from the voltage waveform to obtain the current in the conductor. Icorr is the current in dBµA which flows in the reference setup.
- Fig. 6: Current correction example (Current in dBµA [yellow])