Boonton 4540 Peak Power Meter User Manual Instrukcja Użytkownika Pobierz pdf (Strona 244)

Boonton 4540 Series RF Power Meter

Application Notes

6-16

6.5 Measurement Accuracy

The 4540 Series includes a precision, internal, 50 MHz RF reference calibrator that is traceable to the National Institute for

Standards and Technology (NIST). When the instrument is maintained according to the factory recommended one year

calibration cycle, the calibrator enables you to make highly precise measurements of CW and modulated signals. The error

analyses in this chapter assumes that the power analyzer is being maintained correctly and is within its valid calibration

period.

An external 1 GHz calibrator is also available - see Appendix. The Model 2530 1 GHz Calibrator is fully controlled by the

manual and remote interfaces of the 4540 Series. The operation of the internal 50 MHz calibrator is not affected.

Measurement uncertainties are attributable to the instrument, calibrator, sensor, and impedance mismatch between the sensor

and the device under test (DUT). Individual independent contributions from each of these sources are combined

mathematically to quantify the upper error bound and probable error. The probable error is obtained by combining the linear

(percent) sources on a root-sum-of-squares (RSS) basis. RSS uncertainty calculations also take into account the statistical

shape of the expected error distribution.

Note that uncertainty figures for individual components may be provided given in either percent or dB. The following

formulas may be used to convert between the two units:

= (10

(UdB/10)

- 1) × 100 and U

= 10 × Log

(1 + (U

/ 100))

Section 6.5.1 outlines all the parameters that contribute to the power measurement uncertainty followed by a discussion on

the method and calculations used to express the uncertainty.

Section 6.5.2 continues discussing each of the uncertainty terms in more detail while presenting some of their values.

Section 6.5.3 provides Power Measurement Uncertainty calculation examples for Peak Power sensors with complete

Uncertainty Budgets.

6.5.1 Uncertainty Contributions.

The total measurement uncertainty is calculated by combining the following terms:

Uncertainty Source Distribution Shape K

1. Instrument Uncertainty Normal 0.500

2. Calibrator Level Uncertainty Rectangular 0.577

3. Calibrator Mismatch Uncertainty U-shaped 0.707

4. Source Mismatch Uncertainty U-shaped 0.707

5. Sensor Shaping Error Rectangular 0.577

6. Sensor Temperature Coefficient Rectangular 0.577

7. Sensor Noise Normal 0.500

8. Sensor Zero Drift Rectangular 0.577

9. Sensor Calibration Factor Uncertainty Normal 0.500

The formula for worst-case measurement uncertainty is:

WorstCase

= U

+ U

+ ... U

where U

through U

represent each of the worst-case uncertainty terms.

1 2 ... 239 240 241 242 243 244 245 246 247 248 249 ... 269 270

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