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Measurement Uncertainty Analysis – Power Reference Level Test
Measurement Introduction
Agilent E4416A/E4417A Service Guide B-5
A normal distribution is assumed, as the 3458A Manual has not specified the type of
distribution used on the measurement.
Both V
0
and V
1
values are calculated by subtracting V
ref
from V
comp
as measured at
the output of the 432A using a 3458A DMM. The approximate values of V
comp
and
V
ref
for no power (V
0
) and for 1mW power (V
1
) are 5V with the DMM on the 10V
scale.
For the 3458A DMM, the specified accuracy for the 10 volt scale is:
8ppm of Reading + 0.5ppm of Range
with;
0.15ppm of Reading + 0.01ppm of Range per °C (temp coefficient Tcal ±5 °C)
± 8.75 ppm of Reading + 0.55ppm of Range
Therefore,
For V0 and V1, two measurements are taken, so the uncertainty is equated to the RSS
of using two DMMs;
Mismatch
The Mismatch uncertainty was previously determined as being:
Note This is the worst-case uncertainty for mismatch and occurs when the
incident and reflected waves are 180 degrees out of phase.
Voltage measurement Uncertainty
U(Vcomp) 49.25 µV
U(V
0
) 69.65 µV
U(V
1
) 69.65 µV
UV
comp
()UV
ref
()
8.75 5
×
1000000
-----------------------
0.55 10
×
1000000
------------------------+± 49.25uV±== =
MsUncertainty magnitude()2P
s
P
d
=