Q214 : Computing a voltage difference (as opposed to a GPR difference) with HIFREQ.

Question
How can I compute a voltage difference with HIFREQ?

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Answer
At low frequencies, the voltage difference between two points can often be approximated by the difference in scalar potential between those two points. Since we are usually interested in the voltage difference between two points located on conductors, this voltage difference can be computed by taking the difference in GPR at those two points. This information can be obtained from Configuration plots in Output Toolbox for HIFREQ or from the program's output file (*.f09). One important point to remember is to take proper care of the phase angle of the GPR at those two points.

This approximation is not always valid, however, even at low frequencies. The approximation fails if the two points are far apart and there are important sources of induction. It also fails regularly at high frequencies. In such cases, the voltage difference must be obtained by integration of the electric field between the two points (along a path following the conductors) and includes a vector potential term in addition to the scalar potential difference.

To account for the vector potential term, you should define computation profiles at the surface of the conductors along the path connecting the two points, then request the computation of the vector potential. There should be a few observation points (about 10) for each profile.

When this is done, the program will automatically compute the voltage difference between all points on the profiles and the origin of the profile. A new table showing these values will be written in the program's ouput file, right after the table listing the vector potential values in the F09 file.

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