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With a proper calibration value and good image processing Algorithm s, resolution of less than one Micrometer (1μm) can be achieved. Proper calibration value also depends on the calibration specimen. Which is usually a specially etched material with great precision. To calibrate, pictures are first captured with the calibration specimen under the same testing conditions to be used for the new specimen. Video Extensometer s are used primarily for materials which are complicated to test. Presently it is widely replacing Mechanical measurement units for some applications due to ease of use and convenience. Video extensometers are not the perfect solution for every test situation. When measuring the modulus of elasticity on 50 mm gauge length plastics to ISO 527 an accuracy of 1 µm is required. Most video extensometers cannot achieve this. For production testing it is better to use automated motorized digital extensometry rather than have operators manually attach marks to the specimen. Some low performance video extensometers have difficulty in achieving acceptable results when used to measure strain within temperature chambers. For applications demanding high accuracy non contact strain measurement laser speckle extensometers are emerging as a replacement of video extensometers In certain test applications they are superior due much higher resolution, and accuracy and are advantageous mainly because there is no need to manually attach marks to the specimen. In addition they are able to measure at high temperatures up to 1,600 oC (2,900 oC). Changing of ambient light conditions during test affects the test result to an extent. Therefore, most of the video extensometer suppliers, provide a bright background light and recommend shading windows / doors to prevent sudden change in brightness of the room. SEE ALSO |
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