Finest 509 - Page 17

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As you can see from this
table, both THD-R (%)
and THD-F (%) va l ues
are essentially the same
when measuring line
voltage where THD
readings are often 5% or
less. The v alues differ
only when THD levels
exist above about 20%.
The maximum THD
levels on line voltage of
around 5% and the
maximum THD levels on
line current of around
20% are common for a
power line.
THD-R (%) versus THD-F (%)
THD-R (%) THD-F (%)
0.00 0.00
5.00 5.01
10.00 10.05
15.00 15.17
20.00 20.41
25.00 25.82
30.00 31.45
35.00 37.36
40.00 43.64
50.00 50.39
55.00 57.74
60.00 65.86
65.00 75.00
70.00 85.53
75.00 98.02
80.00 113.39
85.00 133.33
90.00 161.36
95.00 206.47
95.00 304.24
100.00 ∞
Follow these steps to measure THD-R (%) in the power line.
1. Set function and range switch to the AC Volts or Amps range.
2. When measuring voltage or amperes in the 50Hz (or 60H z )
power line, press and hold down the DC/AC button for 2
seconds to select the THD @ 50/60Hz mode.
3. When this Meter enters into the THD mode, the digital reading
(that is, the True-RMS value of voltage or amperes being
measured) disappears and the symbol, %, and decimal points
are displayed on the LCD.
4. After about 2 seconds from this moment, the THD-R (%) will be
displayed.
5. To exit this mode, press and hold down the DC/AC button for 2
seconds again. The symbol, %, disappears and the Meter will
return to the AC functions.
4.6 Measuring Capacitance
CAUTION!
D ISCHARGE ALL CAPACITORS BEFORE ATTEMPTING TO
MAKE MEASUREMENTS. FAILURE TO DO SO CAN RES U LT
IN DAMAGE TO THE METER.
CREST FACTOR versus THD-R (%) [or THD -F (%)]
A CREST FACTOR simp l y indicates whether harmonic contents
are included or not in the power line. However, THD-R (%) [or
THD-F (%)] at 50Hz (or 60Hz) indicates what percent of harmonic
contents is included in the power line. Both features are typically
found in much more expensive professional power ana l y zing
instruments.