Remarks on the “Guide to the Expression of Uncertainty in Measurement” (GUM) published by ISO and other international organisations – floating error analysis for an acoustic example

摘要

The 'Guide' establishes general rules for evaluating and expressing the uncertainty inmeasurement that are intended to be applicable to a broad spectrum of measurements. Theserequirements will be discussed by the example of an acoustic measurement procedure todetermine the sound power. The scope of the relevant ISO standards 3745, 3744 and 3746covers a very broad field of applications given by very different source properties (soundemission stability, directivity, spectral shape) and environmental conditions (roomreflections, back ground noises). The spread of these properties and conditions can bedescribed by a “situation matrix“ with columns for each of the influencing parametersshowing the magnitude of these parameters in each column in fine steps. Furthermore, forsound power determinations of technical sound sources, an error analysis is generally known.By this, the total error is splitted up into several partial errors such as impedance and angleerror (near field error), partial errors depending on the number of measurement positions anderrors due to background noise influences. While the relevant present standards giveinformation only for the total uncertainty of the procedures, the GUM rules requestinformation above the magnitude of the partial errors and their uncertainties, too.This extensive uncertainty information can be expressed as maximum values covering theentire field of standards application (“rigid system”) or individually rated on the parameters(“floating system”) relevant for the actual measurement situation. Only the floating partialerror descriptions, together with the accompanying uncertainty laws and practicalinstructions, allow both, the total uncertainty and the measurement effort which is at least ofinterest to be minimized.