PROVA 21 - Total Harmonic Distortion (% THD-F) of AC Current

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measured.
c. Press the FUNC button twice. The symbols of “Harmonic” and “NO” will
be shown in LCD. The n-th order (1 to 99) will be shown in front of the
reading of the percentage (%) of the current.
d. Press the
▲
or
▼
button to increment or decrement the order of
harmonics in front of the reading. The number will roll over when the
maximum (99) or minimum (1) is reached.
III.1.5. Total Harmonic Distortion (% THD-F)
a. Set the rotary switch at the position of “mA” or “A” depending on the range
of AC current. Then select the correct fundamental frequency by moving
the sliding switch at the side of the tester.
b. Press the trigger to open the jaw and fully enclose the conductor to be
measured.
c. Press the FUNC button three times. The symbols of “THD” and “%” will be
shown in LCD. The total harmonic distortion in percentage with respect to
the fundamental frequency (50 or 60 Hz) will be measured and displayed.
%THD-F = (
√
(V2
2
+ V3
2
+ … V49
2
+ V50
2
) / V1) * 100
Where,
V1: magnitude at the fundamental frequency
V2: magnitude at the second harmonics
…
V50: magnitude at the 50-th harmonics.
NOTE: In the measurement of THD, the response to the button or switch
operation becomes slow due to heavy math calculation.