Video & Laser Exensometers for
the Galdabini machine
Video and Laser Extensometers are used with a universal testing machine to measure sample strain when a contact extensometer is not practical. These types of situations arise for several reasons. The most common reason to use a video extensometer is because the sample is simply too small or delicate to support using a clip-on Extensometer. Other reasons for using a non-contact strain measurement device include the use of special grips or an enclosed environmental chamber.
In 2017, Galdabini released its re-designed Video Extensometer. The complete system including software was designed 100% in-house to allow for better support of the product as well as better pricing to the end-user. The price of a new Galdabini universal testing machine complete with a video extensometer is now virtually unbeatable.
5 Advantages of Galdabini's Video Extensometer:
- Adjustable Field of View allows the extensometer to test a wide range of samples. No need for 3-5 different clip-on extensometers, video extensometers can measure the strain of virtually any sample size. Ideal for 3rd party test labs.
- Easy to calibrate with the Calibration Plate. Just place the plate at the correct distance within the FoV and allow the software the automatically calibrate your pixel frame.
- Measures both elongation and striction. Measure strain in both the X and Y axis without the use of multiple strain gauges. A perfect solution for measuring Poisson's Ratio.
- Low Maintenance with no mechanical parts to service.
- Non-contact means no external inertia on the sample. The video extensometer also has no chance of slipping or breaking.
Video Extensometers look for a high contrast mark or sticker on the sample to use as a reference point. Markers and a calibration plate can be used for basic sample marking. To ensure accurate and repeatable sample marking, a small machine is usually used. The sample marking machine is a small punch tool which deposits a small bit of retro-reflective tape directly onto the sample. The tape sticks to the sample and provides a very high contrast target for the camera system to identify. Universal Grip offers both manual and automatic sample marking punch tools for video extensometers.
Video Extensometers use a CMOS based digital camera and frame grabber software algorithms in order to track pixel movement. The samples are usually marked using a high-contrast pen or sticker in order to establish a tracking point. These types of video strain measurement devices can be highly accurate, especially over a large testing range due to their large Field of View (FOV). The large FOV makes video extensometers ideal for situations where there is high elongation and measurements such as the Elongation Modulus and Max Elongation must be performed. Because the system uses optics, many types of polarizing filters and lighting techniques can be used in order to achieve the optimal high contrast image. Video Extensometers are also highly versatile and can be used in both tensile and compression testing, including shear procedures.
Laser Extensometers are highly accurate and use laser light to "speckle" an area on the sample. This speckled area is then tracked using a CMOS video camera, similar to how video extensometers operate. The laser light creates very small and bright point reflections which can be resolved and tracked easily by the camera. Resolutions of less than one micron can be achieved because of the highly focused laser light. These types of extensometers do not require that the sample be marked which speeds up sample preparation time in between tests. The laser light also works well on low contrast samples such a white plastics or dark carbon fiber composites. Lastly, laser extensometers are unaffected by changes in the surrounding ambient light which removes the need to setup elaborate lighting solutions. A video extensometer with lighting fixtures is still usually cheaper than a laser extensometer.