This clause gives sample uncertainty estimation for the WD ABM signal measurement.
E.3.1Primary uncertainty factors
Contributor Influence quantity Type Source of information
RF reflections ± 0.8 dB Specification 6.2.1
Acoustic noise ± 0.8 dB Specification 6.2.1
Probe coil sensitivity ± 0.5 dB Specification D.8
Reference signal level ± 0.5 dB Specification Calibration
Positioning accuracy ± 1.62 dB Specification E.2.3.1.3
Cable loss ± 1 dB Uncertainty Calibration
Frequency analyzer ± 0.5 dB Specification Calibration
System repeatability ± 0.5 dB Specification Estimate
Repeatability of the WD ± 0.5 dB Std. dev. Estimate
Table E.16—Sample WD uncertainty estimate
Contribution
|
Data (dB)
|
Data (%)
|
Data type
|
Probability distribution
|
Divisor
|
Std. uncertainty (%)
|
Std. uncertainty (dB)
|
RF reflections
|
0.80
|
20.2
|
Specification
|
Rectangular
|
√3
|
11.7
|
|
Acoustic noise
|
0.80
|
20.2
|
Specification
|
Rectangular
|
√3
|
11.7
|
|
Probe coil sensitivity
|
0.50
|
12.2
|
Specification
|
Rectangular
|
√3
|
7.0
|
|
Reference signal level
|
0.50
|
12.2
|
Specification
|
Rectangular
|
√3
|
7.0
|
|
Positioning accuracy
|
1.62
|
45.2
|
Specification
|
Rectangular
|
√3
|
26.1
|
|
Cable loss
|
1.00
|
25.9
|
Uncertainty
|
Normal
|
2
|
12.9
|
|
Frequency analyzer
|
0.50
|
12.2
|
Specification
|
Rectangular
|
√3
|
7.0
|
|
System repeatability
|
0.50
|
12.2
|
Standard deviation
|
Normal
|
1
|
12.2
|
|
Repeatability of the WD
|
0.50
|
12.2
|
Standard deviation
|
Normal
|
1
|
12.2
|
|
Combined standard uncertainty uc
|
|
|
|
Normal
|
|
39.6%
|
1.45 dB
|
Expanded uncertainty (coverage factor = 2) U
|
|
|
|
Normal
(K=2)
|
|
79.2%
|
2.53 dB
|
Annex F
(informative)
Use of Helmholtz coils for calibration
This paper was presented at the 1995 IEEE Symposium on Electromagnetic Compatibility in Atlanta, GA. Some typographical errors were discovered in the equations in the original published copy. It is therefore reproduced here, with typographical corrections, for the convenience of the reader.
Helmholtz Coils for Calibration of Probes and Sensors:
Limits of Magnetic Field Accuracy and Uniformity1
Abstract—Helmholtz coils have been around us for years, but few people now seem to understand their capabilities. The paper explains the accuracy and field uniformity limits of Helmholtz coils for use as a calibration standard for magnetic field probes and sensors. The magnetic field generation accuracy depends on the accuracy with which Helmholtz coils are constructed and the accuracy with which the current through them is maintained. The user is shown how to determine the accuracy of the generated magnetic field based on physical measurements of distance or spacing between the coils, their radii, the thicknesses of the windings on each coil and number of turns. Ways to estimate the maximum usable frequency and minimum space needed around them are given. Procedures are given so that the user may determine the field uniformity versus volume around the center point of the set of coils, and thus determine the coil characteristics needed to calibrate a particular probe or sensor. Or, if a given Helmholtz coil set can be used for calibration of a given sensor.
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