Ansi c63. 19 -2a -2007 Revision of

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D.19True rms voltmeter
E.1WD near-field emissions measurement uncertainty
E.1.2Sample estimation

D.18TEM cell

Frequency range: 0.8 GHz to 3.0 GHz
VSWR over frequency range: < 1.50
Input impedance: 50 Ω
Septum height in test region: 2 times to 3 times maximum dimension of hearing aid
Field uniformity in test region: 0 dB to 6 dB

D.19True rms voltmeter

Input impedance: ≥ 100k Ω
Frequency range: 10 Hz to > 10 kHz
Averaging time: 0.1 sec and 3 sec
Input sensitivity: 0.7 mV or better
Accuracy: ± 3%

Annex E
(informative)
Sample measurement uncertainty estimates

Measurement uncertainty reflects the quality and accuracy of a measured result as compared to the true value. Such statements are generally required when stating results of measurements so that it is clear to the user of these measurement results that the results may differ when reproduced by different laboratories. Measurement results vary due to the measurement uncertainty of the instrumentation, and measurement technique, even when using this standard for test setups and compliance measurements.
Most uncertainties are calculated using the tolerances of the instrumentation used in the measurement, the measurement setup variability, and the technique used in performing the test. While not generally included, the variability of the equipment under test also figures into the overall measurement uncertainty.
Another component of the overall uncertainty is based on the variability of repeated measurements (so-called type A uncertainty). This may mean that the hearing aid immunity tests may have to be repeated by taking down the test setup and resetting it up so that there is a statistically significant number of repeat measurements to identify this very important aspect of measurement uncertainty. By combining the repeat measurement results with that of the instrumentation chain using the technique contained in NIS 81 and NIS 3003,^¹ the overall measurement uncertainty can be estimated.
This annex contains sample calculations and typical values for the tests contained in this standard.

E.1WD near-field emissions measurement uncertainty

This clause gives a sample uncertainty estimation for the WD near-field emission measurement.

E.1.1Primary uncertainty factors

The following are judged to be the primary contributors affecting measurement uncertainty for this test:
Contributor Influence quantity Type Source of information

RF reflections ± 0.8 dB Specification 4.2.1 (reflections < –20 dB)

Field probe conversion factor ± 1.76 dB Specification C.3

Field probe anisotropy ± 0.5 dB Specification Typical probe manufacturer data

Positioning accuracy ± 1.62 dB Specification E.2.3.1.3

Probe cable placement ± 1 dB Specification D.10 and D.11

System repeatability ± 2 dB Specification System repeatability is established by performing a series of measurements under equal conditions. For further guidance, consult UKAS M3003.

Repeatability of the WD ± 0.5 dB Std. Dev. Estimate informal

E.1.2Sample estimation

Table E.14—Near-field measurement uncertainty

WD near-field measurement uncertainty estimation
Contribution	Data dB	Data type	Prob. dist.	Weight	Uncertainty dB	Notes/comments
RF reflections	0.8	Spec	Rect	1/√3	0.46	Reflections < –20 dB
Field probe conv. factor	1.76	Spec	Rect	1/√3	1.02
Field probe anisotropy	0.5	Spec	Rect	1/√3	0.29
Positioning accuracy	1.62	Accy.	Rect	1/√3	0.94
Probe cable placement	1.0	Spec	Rect	1/√3	0.58
System repeatability	2.0	Spec	Rect	1/√3	1.15
EUT repeatability	0.5	Std. Dev.	Norm.	1	0.5
Combined standard uncertainty, u_c(y)			Norm.	1	2.03
Expanded uncertainty, U(y)			Norm.	k = 2	4.06

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