How does the ION 6200 calculate I4?

Issue

One is getting I4 readings without anything wired to it.  How is this calculated?

Product Line

ION6200

Resolution

I4 is calculated from the fundamental harmonic data.
Sequence for calculation:

• FFT on I1, I2, I3
• add up I1,I2,I3 real and imaginary fundamental values after calibrating to give complex sum
• get RMS from complex sum
• transfer into I4 register.

This means for high harmonic currents, 6200 I4 will only give the I4 fundamental current and will disagree with actual current that contains all harmonics. It used to be calculated on a sample by sample basis, but since calibration of samples is impossible, it used a "merged" calibration constant at the end of RMS sums. This only worked if the calibration constants were reasonably close and caused accuracy problems, hence it was switched to the FFT method.

NOTE: the 6200 only measures up to the 15th harmonic.