Boonton 4240 RF Power Meter Uživatelský manuál stáhnout pdf (Strana 117)

Boonton 4240 Series RF Power Meter

6.2.3 Sample Uncertainty Calculations.

The following example shows calculations for a CW power sensors. The figures used in these examples are meant to show

technique, and do not apply to ion se” assumptions have been made to

illus calculation exa e, a some understanding of your specific

mea

Typ Powe

424

dBm (3. )

ti fficient t 10.3

Cal Source: Internal 50M

re: 25C

In th performed on th iately before the measurement.This

will

CalLevel

= ± 2.45%

tep 3: The Calibrator Mismatch Uncertainty is calculated using the formula in the previous section, using the 50MHz

= (1.15 - 1) / (1.15 + 1) = 0.070 (calculate reflection coefficient of 51075, max SWR = 1.15 at 50MHz)

0.34%

Step 4: e he previous section, using the DUT’s

specifica on

on the 51075’s datasheet.

SRCE

cient at 10.3GHz)

SNSR

= (1.40 - 1) / (1.40 + 1) = 0.167 (calculate reflection coefficient of 51075, max SWR = 1.40 at 10.3GHz)

SourceMismatch

= ± 2 × ρ

SRCE

× ρ

SNSR

× 100 %

= ± 2 × 0.20 × 0.167 × 100 %

= ± 6.68%

tep 5: The uncertainty caused by Sensor Shaping Error for a 51075 CW sensor that has been calibrated using the AutoCal

method can be assumed to be 1.0%, as per the discussion in the previous section.

ShapingError

= ± 1.0 %

the general every applicat . Some “common sen

trate the fact that uncertainty is not an ct scienc nd requires

surement conditions.

ical Example #1: Model 51075 CW r Sensor

0 Series measurement conditions:

Source Frequency: 10.3 GHz

Source Power: -55 16 nW

Source SWR : .50 (reflec on coe = 0.2) a GHz

Auto Hz Calibrator

AutoCal Temperature: 25C

Current Temperatu

is example, we will assume that an A oCal has been e sensor immed

reduce certain uncertainty terms, as discussed below.

Step 1: The Instrument Uncertainty figure for the 4240 Series is ± 0.23%. Since a portion of this figure is meant to include

temperature drift of the instrument, and we know an AutoCal has just been performed, we’ll estimate (for lack of more

detailed, published information) that the instrument uncertainty is ± 0.115%, or half the published figure.

Instrument

= ± 0.115%

Step 2: The Calibrator Level Uncertainty for the power meter’s 50MHz calibrator may be read from the calibrator’s

specification. It is ± 0.105dB, or ± 2.45% at a level of -55dBm.

calibrator’s published figure for ρ

CAL

and calculating the value ρ

SNSR

from the SWR specification on the 51075’s datasheet.

CAL

= 0.024 (calibrator’s reflection coefficient at 50MHz)

SNSR

CalMismatch

= ± 2 × ρ

CAL

× ρ

SNSR

× 100 %

= ± 2 × 0.024 × 0.070 × 100 %

= ±

Th Source Mismatch Uncertainty is calculated using the formula in t

ti for ρ

and calculating the value ρ

SNSR

from the SWR specification

SRCE

= 0.20 (source reflection coeffi

Application Notes

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