Atec Agilent-N1921A - Manual (Page 10)

10
Worked Example
Uncertainty calculations for a power measurement (settled, average power)
[Specification values from this document are in bold italic, values calculated on this page are underlined.]
Process:
1. Power level: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 mW
2. Frequency: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 GHz
3. Calculate meter uncertainty: In free run, auto zero mode average = 16
Calculate noise contribution
• If in Free Run mode, Noise = Measurement noise x free run multiplier = 50 nW x 0.6 = 30 nW
• If in Trigger mode, Noise = Noise-per-sample x noise per sample multiplier
Convert noise contribution to a relative term 1 = Noise/Power = 30 nW/100 μW . . . . . . . . . . . . . . . . . . . . . . . . 0.03 %
Instrumentation linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.8 %
Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –
RSS of above three terms ≥ Meter uncertainty = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.8 %
4. Zero uncertainty
(Mode and frequency-dependent) = Zero set/Power = 300 nW/1 mW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.03 %
5. Sensor calibration uncertainty
(Sensor, frequency, power and temperature-dependent) = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 %
6. System contribution, coverage factor of 2 ≥ sys
rss
= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.08 %
(RSS three terms from steps 3, 4 and 5)
7. Standard uncertainty of mismatch
Max SWR (frequency-dependent) = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25
convert to reflection coefficient, | ρ
Sensor
| = (SWR–1)/(SWR+1) = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.111
Max DUT SWR (frequency-dependent) = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.26
convert to reflection coefficient, | ρ
DUT
| = (SWR–1)/(SWR+1) = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.115
8. Combined measurement uncertainty @ k=1
U
C
=
( Max(ρ
DUT
) • Max(ρ
Sensor
) ) 2
+
( sys
rss
) 2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
√2 2
2.23 %
Expanded uncertainty, k = 2, = U
C
• 2 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±4.46 %
1. The noise-to-power ratio is capped for powers > 100 μW, in these cases use: Noise/100 μW.