Chapter 3
Front Panel Operation
3.1
Measurement Setup
Central to setting the proper range of the instrument is the Crest Factor. Crest factor is the ratio of the peak value
of a waveform to the RMS value of the waveform. For example, a perfect sine wave crest factor RMS value is
0.707*Peak. The crest factor is the inverse of the normalized RMS value,
0
.
707
−
1
= 1
.
414
. In many cases, like the
current waveform of a AC-DC power supply, the crest factor is a larger value. For accurate measurement, the signal
measured should stay within the measurement range of the instrument. For example, a 100V RMS signal with a
crest factor of 5 has peaks of 500V. If the range selected is smaller than 500V than innacuracy will occur as the
signal will be clipped.
3.1.1
Crest factor
The Crest Factor, the ratio of the peak to the RMS value, has two settings, 6 or 3. This setting applies to both current
and voltage simultaneously, and modifies the available ranges listed in Section
3.1.2
. Essencially, by knowing the
RMS signal level and the peak value, the setting of this parameter is determined. For an 117V RMS AC line signal with
little distortion and a purely real load (power factor = 1), the peak value is
1
.
414∗117
V
= 165
V
.
1.414 is the approximate Crest Factor of a Sine wave. So, the appropriate setting will be 3 (CF3).
As this meter also measures the DC level of the signal, this must also be accounted for when choosing the Crest
Factor. If the the signal will exceed the range of the unit (crest factor * range) then the measurement value will be
clipped and the value innaccurate. Conversely, by choosing a Crest Factor and Range combination that
accomodates the peak value of the signal, a larger crest factor than set may be measured. The tradeoff is then the
accuracy, and is listed in the specifications, Chapter
9
.
Example (Range=150 V, CF = 6):
The maximum input signal and crest factor are as follows:
V
rms
= 100
Range
= 150
V
V
maxrange
= 900
V
So, a signal with a peak that is 9 times that of the RMS value (Crest Factor 9) is measureable using these settings.
3.1.2
Set Measurement Range
The appropriate measurement range (voltage and current range) must be set for accurate measurement.
12
1.
In the “Meter” interface Press the soft key corresponding to either “U
-
RANGE” or “A
-RANG
E”, and use the
knob or the arrow keys to select the voltage or current range desired. See Table
3.1