Fluke 8050A Instruction Manual page 30

OPERATION
AC VOLTAGE/CURRENT MEASUREMENT
1. Using the dB function on the 8050A measure the voltage at TP1 (or intended
reference).
2.
While measuring the intended reference, set the RELATIVE switch to
ON.
3. In this circuit, 1 mV becomes the 0 dB reference. All subsequent dB measurements
in the circuit are displayed as the loss or gain of the circuit m dB.
TP1 TP2 TP3 TP4
~
TP5
OdB
+60 dB +57.5 dB +74 dB +66 dB
(ref)
TP1
TP2
TP3 T 4 T 5
Figure 2-13.
dB
Circuit
Gain or Loss
Measurements
2-94. The 8050A can measure signals with a crest factor
of 3.0 or less, at full scale. Figure 2-15 illustrates some
typical signals and their crest factors. The waveforms in
Figure 2-15 show that a signal with a crest factor of
greater than 3.0 is not common.
2-95. To ensure that a signal measured with the 8050A
has a crest factor below 3.0, measure the peak value with
an ac coupled oscilloscope. If the peak value is not more
than three times the true-rms reading of the 8050A, then
the signals crest factor is 3.0 or less. Another method of
verifying the error caused by the crest factor of a signal is
to compare the reading of the 8050A with a reading on the
next higher range of the 8050A. The 8050A crest factor
capability increases from 3.0 for readings less than full-
scale. The crest factor capabilty of the 8050A is shown by
the following equation:
Crest Factor Capability = 3"'; Range
Input
The error caused by exceeding the crest factor of 3.0 at full
scale, will be reduced significantly on the next higher
measurement range of the 8050A . The crest factor
capability at 1/10 scale approaches 10.
2-96. COMBINED AC AND DC SIGNAL MEASURE-
MENTS
2-97. It is sometimes necessary to measure an ac signal
riding on a dc level. An example of this type of signal
is
shown in Figure 2-16. To obtain an accurate
measurement of the total rms value for these signals,
perform the following steps:
I. Measure the ac component of the signal using
the AC V function.
2. Measure the de component of the signal using
the DC V function.
3. Use the following formula with the values
obtained in steps I and 2 to determine the total
rms value of the signal:
Total RMS Value
=
v(ac component rms)2
+
(de component)2
2-17