Boonton 4500B Peak Power Meter Manual de usuario descargar pdf (Pagina 332)

Boonton 4500B RF Peak Power Analyzer

Application Notes

6-22

Step 9: The Sensor Calfactor Uncertainty needs to be interpolated from the uncertainty values in the Boonton Electronics

Power Sensor Manual

that we are performing our AutoCal at a frequency of 1GHz, which is very close to the measurement frequency. This means



between 0.5GHz and 1GHz to estimate a value. 900MHz is only 20% (one fifth) of the way from 1GHz down to 500MHz,

so the uncertainty figure at 0.5GHz can be scaled by one fifth.

CalFactor

= 1.99 × (900

- 1000) / (500 - 1000)

= 1.99 × 0.2

= ±0.40%

Step 10: Now that each of the individual uncertainty terms has been determined, we can combine them to calculate the

worst-case and RSS uncertainty values:

U (±%) K (U×K)

( %

)

1. instrument uncertainty 0.20 0.500 0.0025

2. calibrator level uncertainty 3.11 0.577 3.2201

3. calibrator mismatch uncertainty 1.27 0.707 0.8062

4. source mismatch uncertainty 0.80 0.707 0.3199

5. sensor shaping error uncertainty 2.00 0.577 1.3333

6. sensor temperature drift uncertainty 1.69 0.577 0.9509

7. sensor noise & drift uncertainty 0.00 0.500 0.0000

8. sensor calibration factor uncertainty 0.40 0.500 0.0400

___________________________

Total worst case uncertainty: ±18.43%

Total sum of squares: 6.6729 %

Combined Standard uncertainty U

(RSS) : ±2.58 %

Expanded Uncertainty U (coverage factor k = 2) : ±5.17 %

From this example, different error terms dominate. Since the measurement is close to the calibration frequency, and

matching is rather good, the shaping and level errors are the largest. Expanded uncertainty of 5.16% translates to an

uncertainty of about 0.22dB in the reading.

It should be noted that measurement uncertainty calculation is a very complex process, and the techniques shown here are

somewhat simplified to allow easier calculation. For a more complete information, the following publications may be

consulted:

1. 

International Organization for Standardization, Geneva, Switzerland

ISBN 92-67-10188-9

2. 

National Conference of Standards Laboratories, Boulder, CO 80301

ANSI/NCSL Z540-2-1996

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