HP 436A - Page 53

Operation
Model 436A
3-32
CALCULATING MEASUREMENT UNCERTAINTY
1. Calculate
the
reflection coefficient from
the
given SWR.
SWR-1
p
=
SWR
+
1
Power Sensor
#1
Power Sensor
#2
Power Source
p
1.5-1
p
1.25
-1
p
2.0-1
=
=
I
1.5
+
1
2
1.25
+
1
s
2.0
+
1
0.5
0.25
1.0
=
=
--
2.5
2.25
3.0
=
0.2
=
0.111
0.333
2.
Calculate
the
relative power
and
percentage power mismatch uncertainties from
the
reflection
coefficients. An initial reference level
of
1 is assumed.
PU,
=
{1
±
((0.2)(0.333)]}
2
{1
±
0.067}
2
=
{i.061}
2
and {o.933}
2
=
1.138
and
0.870
Relative
Power
Uncertainty
PU
=
[
1
±
(p
P ) ]
2
where P
n
=
SWR
of
Power Sensor
Ti=
n
n s
P
s
=
SWR
of
Power Source
PU
2
=
{1
± [(0.111)(0.333)] }
2
= {1
± 0.037}
2
=
{i.031}
2
and {o.963}
2
=
1.073
and
0.938
Percentage
Power
Uncertainty
%PU
=
(PU
- 1)
100%
for
PU>
1
and
-(1-
PU) 100%
for
PU<
1
%PU
1
=
(1.138 - 1)
100%
and
-(1
-
0.870) 100%
(0.138)
100%
and
-(0.130)
100%
13.8%
and
-13.0%
%PU
2
=
(1.073
- 1)
100%
and
-(1
-
0.928) 100%
=
(0.073) 100%
and
-(0.072)
100%
=
7.3% and
-7.2%
Figure
3-9.
Calculating
Measurement
Uncenainties
(1
of
2)
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