Fluke 8050A Instruction Manual page 29

OPERATION
RELATIVE MEASUREMENT
2. A shorted transistor will produce an overrange
indication on the display.
2-76. Transistor Leakage Test
2-77. Use the following procedure to test transistors for
leakage (Ices):
L Install the transistor, and connect the test
fixture to the 8050A (see preceding
paragraphs).
2. Set the switch on the test fixture to ICES.
3. Select the conductance function, 2 mS range on
the 8050A.
4. A reading of more than 0.0020 (6 }.'A) indicates
a faulty transistor (silicon).
2-78. Transistor Beta Test
2-79. Use the following procedure to test the beta of a
transistor:
1. Install the transistor and connect the test
fixture to the 8050A (see preceding
paragraphs).
2. Set the switch in the test fixture to BETA.
3. Select the conductance function, 2 mS range on
the 8050A.
4. Note the display reading on the 8050A, then
shift the decimal point three places to the right.
This will be the beta of the transistor.
NOTE
Beta is a temperature-sensitive measurement.
Allow sufficient timeforeach tested transistor
to stabilize. A void touching the transistor case
with your fingers while making beta
measurements.
2-80. Relative Measurement
2-81. The following paragraphs contain additional
information on and measurement techniques for relative
measurements.
2-82.
DECIBEL (dB) CIRCUIT GAIN OR LOSS
2-83. The relative function ofthe 8050A makes it easy to
determine the gain or loss (in decibels) of a circuit. By
using the relative function, any voltage level can be used
as the 0 dB reference point for dB measurements. Figure
2-13 describes how to use the relative function to measure
circuit gain or loss in dBs.
2-16
2-84. AC Voltage and Current Measurement
2-85. The following paragraphs contain additional
information on and measurement techniques for ac
voltage and current measurements.
2-86. TRUE-RMS MEASUREMENTS
2-87. One of the most useful features ofthe 8050A is the
direct measurement of true-rms ac voltages and ac
current. Mathematically, rms is defined as the square root
of the mean of the squares of the instantaneous voltages.
In physical terms, rms is equivalent to the dc value that
dissipates the same amount of heat in a resistor as the
original waveform. True-rms is the effective value of any
waveform and represents the energy level of the signal. It
is used directly in the relationships of Ohm's Law and
provides a reliable basis for comparisons of dissimilar
waveforms.
2-88. Most multimeters in use today have average-
responding ac converters rather than true-rms converters
like the 8050A. Usually the gain in average-responding
meters is adjusted so that the reading gives the rms value,
provided the input signal is a harmonic-free sinusoid.
However, if the signal is not sinusoidal, the average-
responding meter does not give a correct rrns reading.
2-89. The 8050A ac converter calculates the rms value
through analog computation. This means that 8050A
readings are accurate rms values for mixed frequencies,
modulated signals, square waves, sawtooths, lO%-duty-
cycle pulses, etc.
2-90. WAVEFORM COMPARISON (RMS VS
AVERAGING METERS)
2-91. Figure 2-14 shows the relationship between
common waveforms and the display readings of the
8050A compared to average-responding meters. Figure 2-
14 also illustrates the relationship between ac and dc
measurements for ac-coupled meters. For example, the
first waveform (in Figure 2-14) is a sine wave with a peak
voltage of 1.414V. Both the 8050A and the average
responding meters display the correct rms reading of
l.OOOV (the de component equals 0). However, the 1.414V
(peak) rectified square wave produces a correct dc reading
(O.707V) on both meters but only the 8050A correctly
measures the ac component (O.707V). The average
responding meter measures the ac component of the
rectified square as 0.785V, which is an error of 5.6%,
2-92. CREST FACTOR
2--93. The crest factor of a waveform is the ratio of the
peak to rms voltage. In waveforms where the positive and
negative half-cycles have different peak voltages, the
higher voltage is used in computing the crest factor. Crest
factors start at 1.0 for a square wave (peak voltage equals
rms voltage).