Boonton 4240 RF Power Meter Instrukcja Użytkownika Pobierz pdf (Strona 118)

Boonton 4240 Series RF Power Meter

Step 6: The Sensor Temperature Drift Error depends on how far the temperature has drifted from the sensor calibration

mperature, and the temperature coefficient of the sensor. In this example, an AutoCal has just been performed on the

nsor, and the temperature has not drifted at all, so we can assume a value of zero for sensor temperature drift uncertainty.

SnsrTempDrift

= ± 0.0 %

tep 7: This is a relatively low-level measurement, so the noise contribution of the sensor must be included in the uncertainty

alculations. We’ll assume default filtering. The signal level is -55dBm, or 3.16nW. The RMS noise specification for the

1075 sensor is 30pW, from the sensor’s datasheet. Noise uncertainty is the ratio of these two figures.

Noise Error

= ± (Sensor Noise (in watts) / Signal Power (in watts)) × 100%

= ± (30.0e-12 / 3.16e-9) × 100 %

= ± 0.95%

Step 8: The Sensor Zero Drift calculation is very similar to the noise calculation. For sensor zero drift, the datasheet

specification for the 51075 sensor is 100pW, so we’ll take the liberty of cutting this in half to 50pW, since we just performed

an AutoCal, and it’s likely that the sensor hasn’t drifted much.

Zero Drift

= ± (Sensor Zero Drift (in watts) / Signal Power (in watts)) × 100%

= ± (50.0e-12 / 3.16e-9) × 100 %

= ± 1.58%

9: The Sensor Calfactor Uncertainty is calculated from the uncertainty values in the Boonton Electronics Power Sensor

anual. There is no entry for 10.3GHz, so we’ll have to look at the two closest entries. At 10GHz, the calfactor uncertainty

4.0%, and at 11GHz it is 4.3%. These two values are fairly close, so we’ll perform a linear interpolation to estimate the

uncertainty at 10.3GHz:

CalFactor

= [ ( F - F1 ) * (( CF2 - CF1 ) / ( F2 - F1 )) ] + CF1

= [ ( 10.3 - 10.0 ) * (( 4.3 - 4.0 ) / ( 11.0 - 10.0 )) ] + 4.0

= 4.09%

Step

Application Notes

6-10

1 2 ... 113 114 115 116 117 118 119 120 121 122 123 ... 127 128

Brak uwag

Boonton 4240 RF Power Meter Instrukcja Użytkownika Strona 118