HP 436A - Page 56

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Model 436A
Operation
CALCULATING MEASUREMENT UNCERTAINTY
1.
For
this example
the
known values are: source SWR, 2.2
and
power sensor SWR, 1.16.
From
the
Mismatch Error Calculator
the
mismatch uncertainty is found
to
be
+0.24,
-0.25
dB.
2. Add
the
known uncertainties from paragraph 3-73,
(±
0.10 dB).
Our
total
measurement uncer-
tainty
is
+0.34, ---0.35 dB.
3. Calculate
the
relative measurement uncertainty from
the
following formula:
dB
=
10
log(:~)
dB
log
(:~)
=
10
1
=
log -
1
(
~~)
Po
If
dB is positive
then:
If
dB
is negative
then:
P
1
>
P
0
; let
Po
=
1
P1
<
Po;
let
P1
=
1
log -
1
(
~
J
MU
=
Po
=
1
=
=
-1
(0.34)
log
--
10
=
-l
(0.35)
log
--
10
=
1.081
1
=
-
1.082
=
0.923
4. Calculate
the
percentage Measurement
Uncertainty.
%MU
(P
1
-
Po)
100
%MU
-
(P
1
- Po)
100
=
(1.081-1)100
-
(1
-
0.923)
100
=
+8.1%
=
-7.7%
Figure
3-11.
Calculating
Measurement
Uncertainty
(Uncertainty
in
dB
Known)
3-35/3-36