ASTM D7235 Guide for Establishing a Linear Correlation Relationship
ASTM D7235 Standard Guide for Establishing a Linear Correlation Relationship Between Analyzer and Primary Test Method Results Using Relevant ASTM Standard Practices
4. Significance and Use
4.1 This guide is intended to be used in conjunction with Practice D3764 (Case 1) and Practice D6122 (Case 2). Methodology in this guide can be used to determine if a linear correlation can improve the performance of the total analyzer system in terms of its ability to predict the results that the PTM would have been if applied to the same material. This methodology, which is based on the same statistical data treatment as Practice D6708, is use to derive the parameters of the linear relationship and to assess the degree of improvement.
4.2 This guide provides developers or manufacturers of process stream analyzer systems with useful procedures for developing the capability of newly designed systems for industrial applications that require reliable prediction of measurements of a specific property by a primary test method of a flowing component or product.
4.3 This guide provides purchasers of process stream analyzer systems with some reliable options for specifying performance requirements for process stream analyzer systems that are used in applications requiring reliable prediction of measurements of a specific property by a primary test method of a flowing component or product.
4.4 This guide provides the user of a process stream analyzer system with useful information on the work process for establishing the PTM prediction relationship and prediction performance.
4.5 Prediction (correlation) relationship obtained in the application of this guide is applicable only to the material type and property range of the materials used to perform the study. Selection of the property levels and the compositional characteristics of the samples must be suitable for the application of the analyzer system. Users are cautioned against extrapolation of the prediction relationship beyond the material type and property range used to obtain the relationship.
4.6 The degree-of-agreement assessment promoted in this guide is based on the statistical principles articulated in Practice D6708, which is purely statistical in nature. No attempt is made in assessing the degree of similarity in the analytical technique between the process analyzer and the PTM; hence, results between the PTM and analyzer unit can be highly correlated, but their measurement principles may be completely different, and may not be the principal cause for correlation. Users are therefore cautioned that a high degree of correlation between results does not necessarily imply a high degree of similarity in the measurement principles; nor does it imply a similar degree of agreement can be expected in future measurements. In general, if sample-specific biases are detected, it suggests that the measurement principles may be different, and may affect the degree-of-agreement in future use of the scaling/bias-correction equation. Presence or absence of sample-specific effect can be used as a measure of the robustness of the correlation equation to sample composition or matrix differences.
4.7 Implementation of this guide requires that the process stream analyzer system complies with the following conditions:
4.7.1 Meets the principles set forth in PART II Process Stream Analyzers of API TP-550,
4.7.2 Meets the supplier's recommendation,
4.7.3 Complies with operating conditions specified by the manufacturer,
4.7.4 A predicted PTM algorithm has already been established if necessary, and
4.7.5 Meets applicable quality assurance, data collection and data telemetry protocols.
4.8 After installation or major maintenance, conduct such diagnostic tests as recommended by the manufacturer to demonstrate that the analyzer meets manufacturer's specifications, historical performance levels or both. If necessary, adjust the analyzer system components so as to obtain recommended analyzer output levels for specified reference materials.
4.9 Inspect the entire analyzer system to ensure it is installed properly, is in operating condition, and is properly adjusted after completion of the initial commissioning procedures.
