Proper validation of new weathering instruments

 
Instruments for accelerated weathering can control the most relevant weathering stress factors. However, some factors are not controlled but can still be monitored. This can include phase dynamics, dry times and surface temperatures. Even if not controlled directly, these factors play an important role in material ageing and degradation. For reliable, repeatable and reproducible testing, it is crucial not only to control the parameters given in standards and test methods, but also to monitor how the test environment and the test specimen react to these parameters. Validation is expected from the instrument manufacturer during the development process of a new instrument. This often includes testing of known reference materials. Parameter control and reference material performance is typically performed to the most relevant test methods within the requirements of those test methods. Since performance-based standards allow a range of parameter performance, it is recommended also to the user of a laboratory instrument to implement their own validation process. This is especially important if the new instrument needs to be compared to existing instruments or is planned as a replacement. The focus should be the integration into existing internal company processes combined with the objective of the test methods, the investigated materials and relevant properties. It is demonstrated with recent instrument development how proper instrument validation should look like. It is also shown what the instrument user should do, to achieve reliable and comparable testing when using a new instrument. Tools for instrument validation include the use of additional, external and independent sensors and reference materials. Independent sensors can be a valuable tool to detect differences in instrument performance [1]. It is recommended to study multiple sensors or materials within the complete test field for statistics and uniformity statements. SAE J2413 [2] gives guidance on proper uniformity validation. Another source of information are the instrument log-files. Especially inconsistencies in the dynamic parameter performance can be detected here.