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OPERATION
If AC coupling
is in effect, however,
the instrument
response rolls off at low frequencies.
Thus AC coupling
should not be used in cases where this attenuation
factor
might lead to significant
errors in the measurement of low
frequency
signals, unless AC coupling
is necessary to
remove the DC component
of a" applied signal.
Volt-Hertz
Considerations
With almost any measuring instrument,
there exists a limit
as to the maximum
volt-hertz
product
that can be
measured. Simply stated, the volt-hertz
product defines
the maximum peak voltage that can be measured at a give"
frequency.
For example, the maximum
normal-mode
input that can
be safely applied to the Model 194 is 2 x 10' V*Hz. From
this value, you can easily determine
the maximum
fre-
quency at a given peak voltage by dividing
the volt-hertz
product by that voltage. For example, the maximum
fre-
quency at 20V peak would be:
2 x 107V'Hz
fMAX =
20
fMAX = lMHz
3.22 TYPICAL
APPLICATIONS
Applications
for the Model 194 are many and varied and
will depend largely on your particular needs. Basically, the
Model 194 operates much like an ordinary
DMM in that
it measures DC voltages. However, special characteristics
such as high sampling rates, a large measurement
buffer,
and built in math functions allow application
of the instru-
ment to measurements
not possible with more ordinary
units.
In the following
paragraphs, we will discuss Some typical
applications for the Model 194 High Speed Voltmeter. Keep
in mind that these examples are only representative
of
Model 194 capabilities,
and by no means even begin to ex-
haust the possible uses for the unit.
3.22.1 Periodic
Waveform
Analysis
Probably one of the more obvious situations for the Model
194 is in cases calling for rapid sampling of the input signal,
as is the case when analyzing
periodic waveforms. The
type of analysis, of course, will depend on the waveform
as well as your particular
requirements.
For example, assume that a 50kHz sine wave like the one
shown in Figure 3-25 is to be analyzed. Our fit
task would
be to set up the instrument
to properly
sample the
waveform at hand. Operating
modes such as range, sam-
pling rate and interval, and trigger mode would be set up
in accordance with our knowledge
of the waveform being
sampled.
Since the nominal
peak-to-peak value of the waveform is
+lOV, we could place the instrument
on the 32V range.
With a frequency of 50kHz, the waveform has a period of
li50kHr
= 20psec. Thus, to capture at least one complete
cycle
of the waveform,
we would have to choose a sam-
pling interval of 20ksec. The maximum number of samples
per cycle would then be 20 since the minimum
sampling
interval is l@ec.
If the instrument
is left in the continuous
trigger mode,
the measurement
sequence will be repeated on a con-
tinuous basis. The various mathematical
functions
could
then be used to provide important information
such as the
peak-to-peak,
RMS, and average values.
r
10"
-
tn
vpp-20"
I
VAVG=OV
VRMS-7.07"
"PEAK 4~ = +lO"
VPEAK-
_
~10"
v
t
Figure 3-25. Periodic Waveform Analysis
3-46
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