1 - 36 HS70A Service Manual
▐Acoustic Measurement Precision and Uncertainty
The Acoustic Measurement Precision and Acoustic Measurement Uncertainty are described below.
Quantity Precision Total Uncertainty
PII.3 (derated pulse intensity integral) 3.2 % +21 % to - 24 %
Wo (acoustic power) 6.2 % +/- 19 %
Pr.3 (derated rarefaction pressure) 5.4 % +/- 15 %
Fc (center frequency) < 1 % +/- 4.5 %
Systematic Uncertainties
For the pulse intensity integral, derated rarefaction pressure, Pr.3, Center frequency and pulse
duration, the analysis includes considerations of the effects on accuracy of:
Hydrophone calibration drift or errors.
Hydrophone / Amp frequency response.
Spatial averaging.
Alignment errors.
Voltage measurement accuracy, including.
- Oscilloscope vertical accuracy.
- Oscilloscope offset accuracy.
- Oscilloscope clock accuracy.
- Oscilloscope Digitization rates.
- Noise.
The systematic uncertainties of acoustic power measurements using a radiation force are measured
through the use of calibrated NIST acoustic power sources.
We also refer to a September 1993 analysis done by a working group of the IEC technical committee 87
and prepared by K. Beissner, as a first supplement to IEC publication 1161.
The document includes analysis and discussion of the sources of error/measurement effects due to:
Balance system calibration.
Absorbing (or reflecting) target suspension mechanisms.
Linearity of the balance system.
Extrapolation to the moment of switching the ultrasonic transducer (compensation for ringing and
thermal drift).
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