ON TOUR XTB (serv.man12) - JBL Audio EMC - CB Certificate (repair manual). Page 33

 

 

 

 

 

3.   Practical Explanation of the Meaning of Radiated Emissions Measurement Uncertainties 
 
In general, a “Statement of Measurement Uncertainty” means that with a certain (specified) confidence 
level, the “true” value of a measurand will be between a (stated) upper bound and a (stated) lower 
bound.   
 
In the specific case of EMC Measurements in this test report, the measurement uncertainties of the 
conducted emissions measurements and the radiated emissions measurements have been calculated 
in accordance with the method detailed in the following documents: 
 

o

  ANSI Z540.2 (2002) Guide to the Expression of Uncertainty in Measurement  

o

 NIS 

81:1994, 

The Treatment of Uncertainty in EMC Measurements (NAMAS, 1994) 

o

  NIST Technical Note 1297(1994), Guidelines for Evaluating and Expressing the Uncertainty of 

NIST Measurement Results (NIST, 1994) 

 

The calculation method used in these documents requires that the stated uncertainty of the 

measurements be expressed as an “expanded uncertainty”, U, with a k=2 coverage factor.  The 

practical interpretation of this method of expressing measurement uncertainty is shown in the following 

example: 

 

EXAMPLE:  Assume that at 39.51 MHz, the (measured) radiated emissions level was equal to 
+26.5 dBuV/m, and that the +/- 2 standard deviations (i.e. 95% confidence level) measurement 
uncertainty was +/- 3.4 dB.