Application of Field Probe Correction Factors

To better achieve accurate field-level measurements, it is helpful to have an understanding of field probe calibrations, the factors generated, and what’s presented as data during testing. Previous application notes have dealt with field probe selection, proper use, and configuration. This application note shows the customer how to utilize the factors presented for inclusion into test data, how to generate composite measurements, and why calibrations are performed at selected frequencies.

Field Probe Measurements and Correction Factors

Upon purchase, Amplifier Research supplies correction factors with each of our field probes. As the manuals state, the field probe factors are given in both dB and linear multiplier values. For each probe, a 3-axis correction factor is given.

For many EMC test standards, only a composite value is required. To calculate the composite field value, a simple root-sum-of-squares calculation of the field values measured in each axis is performed.

MeasurementComposite=√(x²+y²+z²)

Where: x, y, and z are the individual axis measurements for the specific field probe

For each calibration frequency, the three (3) separate axis factors are given. It is up to the user to calculate the composite value using a script or spreadsheet.

Correction Factor Example

The given example shows the outcome of the composite measurement as derived from the three individual axis measurements and factors:

The equation, from above, would show the following (via a root-sum-of-squares calculation):

Measurement_Composite=√((0.99∗5.86)²+(0.98∗47.86)²+(0.99∗1.03)²)

Measurement_Composite=√(2234.56)V/m

Measurement_Composite=47.27V/m

When separable-axis field measurements cannot be used, and a composite factor must be used, a simple way to calculate the composite factor is to take an average of the 3-axis factors:

Factor_Composite=(x+y+z)/3

So, for the example above, the composite factor would be:

Factor_Composite=(0.99+0.98+0.99)/3=0.9867

If the uncorrected measurement above was 48.23 V/m, the corrected composite measurement is:

Measure_Composite=48.23∗0.9867=47.58V/m

from: https://arworld.us/application-of-field-probe-correction-factors/