10 | Keysight N1911A/N1912A P-Series Power Meters and N1921A/N1922A Wideband Power Sensors - Data Sheet
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: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1mW
2. Frequency: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1GHz
3. Calculate meter uncertainty:
Calculate noise contribution
– If in Free Run mode, Noise = Measurement noise x free run multiplier
– If in Trigger mode, Noise = Noise-per-sample x noise per sample multiplier
Convert noise contribution to a relative term 1 = Noise/Power. . . . . . . . . . . . . . . . . . . . . . . .
Instrumentation linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RSS of above three terms => Meter uncertainty = . . . . . . . . . . . . . . . . . . . . . . . . . .
0.03%
0.8%
–
0.8%
4. Zero Uncertainty
(Mode and frequency dependent) = Zero set/Power = . . . . . . . . . . . . . . . . . . . . . . . .
0.03%
5. Sensor calibration uncertainty
(Sensor, frequency, power and temperature dependent) = . . . . . . . . . . . . . . . . . . . .
4.0%
6. System contribution, coverage factor of 2 => sysrss =. . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.08%
(RSS three terms from steps 3, 4 and 5)
7. Standard uncertainty of mismatch
Max SWR (Frequency dependent) = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
convert to reflection coefficient, | ρSensor | = (SWR–1)/(SWR+1) = . . . . . . . . . . . . . . . . . . . .
Max DUT SWR (Frequency dependent) = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
convert to reflection coefficient, | ρDUT | = (SWR–1)/(SWR+1) = . . . . . . . . . . . . . . . . . . . . .
1.25
0.111
1.26
2.23
8. Combined measurement uncertainty @ k=1
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
2
0.115
Max(
r
DUT) • Max(rSensor
)
sysrss
UC
=
+
2
2
Expanded uncertainty, k = 2, = UC • 2 = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
±4.46%
1. The noise to power ratio is capped for powers > 100 uW, in these cases use: Noise/100 µW.
KEYSIGHT [ Keysight Technologies ]
