| Direct extension and reduction-in-width measurement Some tests require measurement of the extension directly on the specimen in order to eliminate any measuring errors which could occur due to machine deformation, over-run of test tools or partial slippage of the specimen. There are various measurement systems for measuring extension: • Mechanical exensometers for contact measurement directly on the specimen, also for long-travel lengths. • Contact-free extensometers which do not affect the specimen and measure the extension with optical methods. • Clip-on extensometers which measure with high resolution and are clipped directly onto the specimen. |