Optical extensometers are superior to contact-type extensometers in many respects. Since no physical contact is made with the specimen, its behavior is not influenced by test knife edges and drag forces. This eliminates the possibility of the test results being distorted by the testing instrument itself. As a result of decoupling, optical extensometers are well-protected from damage that could be caused by the specimens and are not negatively affected by brittle-fracturing specimens or specimens prone to whipping with high energy at break, such as elastomers, wires, and ropes. In addition, small or short specimens are available for optical systems if the contact-type systems do not have any more room between the fixtures. Measurements in temperature chambers are performed using a special glass pane and deliver better results than sensor arm extensometers since they can be taken in a closed system. videoXtens–The Versatile Extension Measurement Solution There are three different technologies within the optical, non-conact extensometer solutions from ZwickRoell. The most well-known technology is the camera-based videoXtens, which covers the widest range of applications. A camera with a lens is hidden in the extensometer. Depending on the height of rise of the lens, there is a small or large field of view which represents the area of the specimen from which the camera records. Gauge marks are applied to the specimen that mark the gauge length. The testXpert III software recognizes the gauge marks automatically and transfers the initial gauge length into the system. During the test, the marks are tracked in that they are displayed frame by frame. A special marking method and intelligent algorithms in the software produce excellent measurement accuracy. All measurement channels are synchronized exactly. The software for the optical extensometers is integrated into testXpert III, which allows all of the test data to be saved and evaluated together in a single software. A closer look with array technology Due to its modular design, the videoXtens system can be configured according to the application. The required measurement range for the test and the desired measurement values determine the specifications for the necessary field of view and the resolution of the lens. There is one correlation that applies here: A lens with a large field of view provides low resolution and a lens with a small field of view provides high resolution. In order to provide high resolution over a large measurement range, ZwickRoell developed its array technology, in which multiple cameras with high resolution lenses are connected in series. The overlapping fields of view are combined into a single large image via software, allowing the videoXtens to deliver very high resolution and have a large measurement range. For example, there is the videoXtens 2-120 HP, which provides a resolution of 0.15 µm in a measurement range of up to 140 mm. It also fulfills the strict calibration requirements of ISO 527-1 Annex C for determination of the tensile modulus, even for tests at elevated or lowered temperatures in ZwickRoell temperature chambers. A Closer Look, A Better View Since optical extensometers keep the entire specimen or a large portion of the specimen in view, there are various options for obtaining more information through a pure software option upgrade–no complex hardware upgrade necessary. For example, you can achieve simultaneous determination of transverse strain and biaxial measurement. Or multiple measuring points–up to 100–can be set on the specimen surface.