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Title: What Does Accuracy Mean To You?
Author: Raymond Kalivoda Peter Sims
Source: 2009 South East Asia Flow Measurement Conference
Year Published: 2009
Abstract: Accuracy! Now, more than ever accuracy is critically important to the petroleum industry. Crude oils and refined petroleum products are bought and sold on the worldwide market. They may be transported over thousands of miles and change ownership many times on their journey from the well head to the end user. Each time the product changes ownership, a custody transfer is completed and both buyer and seller expect the product to be accurately measured. In all transactions it is increasingly important to reduce measurement errors. This is especially true for large volume custody transfers by pipeline or ship where validating the degree of accuracy can be most difficult and costly. Accuracy is a seemingly easy concept but determining the precise volume measured, even with a high quality custody transfer meter, is challenging. In fact, the accuracy of a dynamic measurement can only be expressed quantitatively as an inaccuracy or uncertainly. The problem is the true value is unknown so a mathematically exact value is not possible. The measurement can only be determined as a probability within a specific range. Accuracy can be defined as the closeness in the agreement between the result of a measurement and the true value of the measurement. The quantitative expression of accuracy is in terms of uncertainty which is defined in statistical terms. The Guide to the Expression of Uncertainty in Measurement (GUM) is an international standard published by ISO that defines the quantitative aspects of accurate measurement. It allows the user to determine the degree of accuracy of a given measurement and how much each of the input factors influences it. Used in this manner, uncertainty analysis is a cost-effective way to evaluate and optimize a measurement system.

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