scope:

General

This Standard presents a working outline detailing and illustrating the techniques for estimating measurement uncertainty for fluid flow in closed conduits. The statistical techniques and analytical concepts applied herein are applicable in most measurement processes. Section 2 provides examples of the mathematical model applied to the measurement of fluid flow. Each example includes a discussion of the elemental errors and examples of the statistical techniques.

An effort has been made to use simple prose with a minimum of jargon. The notation and definitions are given in Appendix A and are consistent with ISO 3534, Statistics - Vocabulary and Symbols (1977).

The Problem

All measurements have errors. The errors may be positive or negative and may be of a variable magnitude. Many errors vary with time. Some have very short periods and some vary daily, weekly, seasonally, or yearly. Those which can be observed to vary during the test are called random errors. Those which remain constant or apparently constant during the test are called biases, or systematic errors. The actual errors are rarely known; however, uncertainty intervals can be estimated or inferred as upper bounds on the errors. The problem is to construct an uncertainty interval which models these errors.