ABSTRACT
A number of commonly used definitions used within the field of flow measurement and how they can be misapplied to create a misleading specification are discussed in this chapter. One of the main issues discussed is why the terms accuracy, inaccuracy, and error should only be used as qualitative terms and that no numerical values should be attached to them. Rather, we should make use of the term uncertainty – the doubt that exists about the result of any measurement – and what level of confidence exists regarding the measurement.
Despite these problems associated with the term accuracy, it still continues to be used by the majority of manufacturers and, by a more or less common agreement, is generally used to express the maximum deviation between the meter's indication and the true value of the process being measured. A comparison is then made in the differences between expressing accuracy in terms of percentage of span, percentage of reading, and percentage of the upper range value.
Other issues addressed in this chapter are clear definitions of the terms volumetric and mass flow rate, totalisation, turn down ratio, span, repeatability, and linearity.
