Types of Extensometers: Clip-On vs. Video vs. Long-Travel vs. 3D DIC (How to Choose)
Contact or non-contact? Every lab buying an extensometer ends up asking whether a traditional clip-on is enough or whether a video extensometer is worth the extra cost. The honest answer depends on your materials, your standards, how hard your specimens break and whether you test in a chamber. This guide compares all four extensometer types we supply, with the ISO 9513 and ASTM E83 accuracy classes behind them, which type each common standard calls for, and real setup videos from our lab. Browse the full range on our extensometers page.
Quick answer: which extensometer do you need?
Clip-on (contact) extensometer: best value for metals and rigid plastics with a fixed gauge length, high-volume QC and modulus or yield measurement to ASTM E8, E111 and D638.
Long-travel (automatic) extensometer: for rubber, elastomers, films and ductile plastics that stretch hundreds of percent.
2D video extensometer: for labs that test many materials, fragile or high-elongation specimens, violent breaks, small Type V specimens or tests inside a temperature chamber.
3D DIC (Vector series): for R&D, composites and sheet metal when you need full-field strain, transverse strain, Poisson's ratio or r-value.
The four types of extensometers compared
1. Clip-on (contact) extensometers
A clip-on extensometer attaches to the specimen with knife edges held by springs or clips. A strain-gauged flexure inside measures how far the two knife edges move apart. Because the knife edges sit right on the specimen, clip-ons are very accurate over small strains, which is exactly where modulus and yield are measured.
Pros: lowest cost, proven accuracy, simple to calibrate, works on reflective or transparent specimens that confuse cameras.
Cons: fixed gauge length per unit, limited travel, must usually be removed before break, knife edges can nick soft or brittle specimens and the added weight can bend thin samples.
Our model: the 3542 axial clip-on extensometer comes in gauge lengths from 10 mm to 80 mm (0.5 to 2 in), ranges from ±5 % to +100 % strain, and meets ASTM E83 Class B-1 (at gauge lengths of 20 mm and up) and ISO 9513 Class 0.5. See all clip-on extensometers.
2. Long-travel and automatic (balanced) extensometers
Long-travel extensometers mount on the testing machine column and ride on the specimen with light, counter-balanced arms. They follow the specimen all the way to break, so they are the standard contact solution for rubber and ductile plastics.
Micron XT: automatic long-travel extensometer, 25 mm up to 700 mm of elongation, for high-elongation metals such as aluminum and for plastics (data sheet).
Plast long-stroke: low-friction, counter-balanced, up to 700 mm travel, for elastomers, plastics and rubber (data sheet).
See both on our long-travel (XL) extensometers page.
3. 2D video (non-contact) extensometers
A video extensometer uses a camera and software to track gauge marks on the specimen. Nothing touches the sample, so it stays on from preload to final fracture, the gauge length is set in software, and one camera covers many specimen types.
Pros: no knife-edge damage or added mass, no risk of a broken extensometer at fracture, any gauge length within the field of view, measures to break on high-elongation materials, sees through a chamber window, and can record transverse strain.
Cons: higher upfront cost, needs gauge marks and steady lighting, and very shiny, transparent or tiny specimens need extra preparation.
Our range: the XSight ONE series from the compact M1 (80 mm, metals and wire) and the general-purpose M2 (110 mm, plastics and composites) up to the M9 (220 mm, rubber) and M16 (330 mm, long-gauge, highly deformable specimens). The M2 cut sheet lists ISO 9513 Class 0.5 over a 110 mm field of view. See all video extensometers.
4. 3D DIC extensometers (Vector series)
3D digital image correlation (DIC) uses two cameras to measure strain over the whole specimen surface, including out-of-plane movement that a single camera cannot see. Use it when you need more than a single strain number.
Vector U70: uniaxial 3D, 10 to 50 mm adjustable gauge length, specimens down to 2 mm wide.
Vector B80: biaxial, axial and transverse strain for Poisson's ratio and r-value.
Vector U200: large field of view with an onboard GPU for full-field strain maps.
Details and data sheets on the Vector 3D extensometer page.
What about laser extensometers? Laser extensometers are another non-contact option, but they share most of the pros and cons of video systems. We do not supply laser units; for most labs a video extensometer covers the same applications with more flexibility.
Accuracy classes: ISO 9513 and ASTM E83 explained
"Accurate" means nothing until you name the class. Both standards classify the whole extensometer system after calibration, and your test standard tells you which class you need.
ISO 9513 Class 0.5: relative error within ±0.5 % of reading (or ±1.5 µm at small displacements). The class most metals and plastics labs ask for.
ISO 9513 Class 1: within ±1 % (or ±3 µm). Accepted for proof strength and elongation in ISO 6892-1.
ASTM E83 Class B-1: error within 0.0001 strain or 0.5 % of reading, whichever is greater. Used for modulus on stiff materials.
ASTM E83 Class B-2: 0.0002 strain or 1 % of reading. Required for yield strength in ASTM E8 and for modulus in ASTM D638.
ASTM E83 Class C: 0.001 strain or 1 %. Fine for elongation at break and high-strain polymers and elastomers.
Both contact and non-contact extensometers can meet Class 0.5 / B-1. For a video extensometer the class depends on the field of view: a smaller field of view gives higher accuracy, which is why we size the camera to your specimen. Read more in Gauge length selection for video extensometers across ASTM standards.
Which extensometer for which standard?
ASTM E8 / ASTM A370 / ISO 6892-1 (metals): clip-on for yield and modulus; video or automatic if you want strain to break without removing the extensometer.
ASTM D638 / ISO 527 (rigid plastics): clip-on for Type I–III modulus; video for Type V specimens, soft plastics and chamber testing.
ASTM D412 (rubber and elastomers): long-travel or video (M9 / M16), since specimens stretch several hundred percent.
ASTM D882 (thin film): video, because knife edges tear thin film and add mass.
ASTM D3039 (composites): clip-on or video for modulus; 3D DIC (B80) when you also need Poisson's ratio.
ASTM D4595 (geotextiles): video, because wide specimens and large strains are hard to instrument with a contact unit.
Testing at high or low temperature
Clip-ons can go into a chamber, but you need a temperature-rated model and you cannot remove it mid-test without opening the door. The 3542 is available in versions rated from -270 °C up to 200 °C. Above that you need high-temperature extensometers with ceramic arms. A video extensometer stays outside the environmental chamber and looks through the window, so the same camera works at -70 °C and at +250 °C:
Cost and total cost of ownership
Upfront: a clip-on costs a fraction of a video system. Our video extensometers start at $14,999, with a 30-day try-and-buy program.
Hidden clip-on costs: one unit per gauge length, repairs after violent breaks, recalibration after damage, and operator time attaching and removing it every test.
Hidden video costs: gauge marking (fast with our marking tools), lighting and a short training curve.
Retrofit: both types fit the machine you already own. See Video extensometer retrofit for Instron, MTS and Shimadzu.
Common extensometer mistakes
Using crosshead displacement for modulus: it includes grip seating and frame compliance. See When should you use an extensometer?
Wrong class for the standard: check your test standard's E83 or ISO 9513 requirement before you buy.
Leaving a clip-on on through a violent break: remove it after yield, or switch to non-contact.
Poor gauge marks on a video system: marks that smear or fall off cause scatter. Follow The complete guide to sample marking for video extensometers.
Skipping calibration: verify to ASTM E83 or ISO 9513 at least once a year; we offer calibration services.
Extensometer FAQ
What is the difference between a contact and a non-contact extensometer? A contact extensometer touches the specimen with knife edges or arms; a non-contact (video, laser or DIC) extensometer measures strain optically with nothing touching the specimen.
Are video extensometers as accurate as clip-on extensometers? Yes, when sized correctly. Both can meet ISO 9513 Class 0.5; for video systems the class depends on the field of view.
Can one extensometer cover metals, plastics and rubber? A video extensometer comes closest, because the gauge length is set in software and it measures to break. Clip-ons usually need a different unit or travel range per material.
Do I need an extensometer for tensile testing? You need one to report modulus, yield strength or accurate low-strain elongation. Strength and break elongation can often be reported from crosshead travel.
Can I add an extensometer to my existing Instron, MTS or Zwick machine? Yes. Our clip-on, long-travel and video extensometers output a calibrated signal that connects to most testing machines.
Related reading
Get help choosing
Tell us your materials, standards, specimen sizes and testing machine and we will recommend the right clip-on, long-travel, video or 3D DIC extensometer. Fill in the video extensometer inquiry form or contact us for a quote.
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