Read harmonic results.
Sets harmonic analyser mode if not
already set.
Waits for next unread data if necessary.
Clears new data available bit read by
DAV?
11 data values separated by commas:
freq,mag1,mag2,hmag1,hmag2,h%1,
h%2,thd%1,thd%2,hphase1,hphase2
magnitude and percentage for each
harmonic, one channel per line
magnitude and phase for each harmonic,
one channel per line