Video Extensometers VS. Clip-On Extensometers

Video Extensometers from Universal Grip

Video Extensometers vs. Clip-On Extensometers (Comprehensive Guide)If you’re trying to choose between a video (non-contact) extensometer and a clip-on (contact) extensometer, the best answer depends on what you test, how often you change specimen types, your accuracy needs, your risk tolerance for damaging samples, and—very often—budget. Below is a deep, practical breakdown, including use cases, cost drivers, similarities, and real-world decision logic.

What they are (in one sentence each)

• Video extensometer (non-contact): Uses one or more cameras and image tracking (targets/speckles/edges) to measure strain or displacement without touching the specimen.

• Clip-on extensometer (contact): A mechanical/sensor device that physically attaches to the specimen and measures elongation between two points (gauge length).

Biggest differences (the “why people buy it” version)

1) Flexibility & specimen range

Video extensometers are typically the most flexible because you can:

• Change gauge length in software

• Track many specimen sizes and shapes

• Measure on delicate, soft, thin, hot/cold, or brittle materials without introducing handling damage.

• Often measure strain over multiple regions (depending on system/features)

Clip-on extensometers are excellent but are usually more “fixed”:

• Designed around certain gauge lengths (or limited range)

• May have specimen thickness/width constraints

• Can be awkward or impossible on very small, thin, fragile, or highly flexible specimens

Rule of thumb:

• If your lab constantly changes specimen geometry/material types → video starts to win fast.

• If you run the same specimen all day, every day → clip-on can be the most efficient and economical.

2) Setup time & throughput

Video

• Fast once configured: adjust camera position, lighting, targets, and test method—then run

• Easy to switch between standards/specimens (software gauge length changes are a big deal)

• High throughput environments benefit when there are frequent changeovers

Clip-on

• Requires physical installation/removal every test (or at least frequent)

• Must be handled carefully to avoid damage to the extensometer or specimen

• Can slow down the test cycle in R&D/multi-test labs, but can be quick in steady QC workflows once procedures are dialed in

3) Risk to specimen & risk to equipment

Video

• No contact → reduces risk of nicking, crushing, or bending delicate specimens

• No inertia mass hanging on the specimen, so less chance of influencing results (especially on thin films, fibers, foams, elastomers)

Clip-on

• Physical contact can:

  • Damage sensitive surfaces (coatings, thin films)

  • Slip or “bite” into soft materials if not properly configured

  • Add mass/constraint to very compliant specimens

• Also a higher chance of operator-caused breakage (dropping the device, overextending it, mis-clipping)

Clip-On Extensometer for Universal Testing Machine

4) Budget (what you pay for and why)

Budget ranges vary widely by brand, accuracy class, features, and integration, but the general pattern is consistent:

Clip-on extensometer: typically lower initial cost

• Lower entry price for a single test method

• Strong ROI if your application is stable (same gauge length, same material, repeated test method)

• Replacement/repair costs can occur if operators regularly damage them

Video extensometer: higher initial cost, often lower “changeover cost” You pay for:

• Cameras + optics

• Mounting hardware / stand / arm

• Lighting

• Calibration routines

• Software features (tracking modes, strain mapping, multi-point, reporting)

• Integration with the UTM software (data streaming, synchronization, closed-loop strain control)

But the ROI can be excellent if:

• You run many specimen types

• You want fewer damaged specimens

• You want faster method changes

• You want non-contact on sensitive/expensive samples

• You need advanced measurement capabilities (multi-region, r-value/width strain, etc.)

Real-world budget guidance:

• Lean QC lab / single ASTM method: clip-on often wins on cost.

• Multi-user R&D lab / frequent test changes: video often wins on productivity and reduced headaches.

• High-cost specimens (composites, aerospace coupons, medical materials): video can pay for itself by preventing scrap and rework.

Use cases where video extensometers shine

A) Delicate, thin, soft, or easily damaged specimens

• Thin films, foils, papers, nonwovens

• Elastomers, foams (where clip-on mass/attachment can distort results)

• Coated materials where surface damage matters

• Small specimens where clipping is difficult

B) High temperature, cold temperature, or environmental chamber testing

• Non-contact is a major benefit when:

  • Access is limited through chamber windows

  • Operator handling is difficult in PPE / cold environments

  • You don’t want sensors physically exposed to extreme temperature gradients(Depending on the system, video can measure through chamber windows if optics/visibility are properly addressed.)

C) Fast changeovers, many specimen geometries

• Contract test labs

• University research labs

• R&D departments with varied programs

D) Applications needing more than “just axial strain”

Depending on the system, video can enable:

• Transverse strain (Poisson’s ratio)

• Width/diameter changes

• Multiple gauge lengths at once (software-defined regions)

• Strain at different locations (e.g., near a notch vs. center)

• Edge tracking or pattern tracking for challenging materials

Video Extensometer in combination with an Environmental Chamber for Tensile Testing

Use cases where clip-on extensometers shine

A) Highly repetitive manufacturing/QC workflows

• Same specimen geometry

• Same gauge length

• Same standard all day (or most days)

• Operators trained on one method

Clip-ons can be:

• Very stable

• Simple in day-to-day operation

• Cost-effective per test

B) When test standards or customer specs demand a specific contact extensometer class

Certain compliance environments prefer (or historically specify) specific contact devices or accuracy classes. Even when video is acceptable, some customers maintain internal requirements that effectively “standardize” on clip-ons.

C) When visibility is poor for optical tracking

• Transparent specimens without good contrast (unless you add targets)

• Highly reflective surfaces (unless you treat/paint targets)

• Poor lighting or restricted line-of-sight Clip-ons don’t care about lighting, contrast, or camera view.

Similarities (important—because results and workflow overlap)

Despite being different technologies, they share several key traits:

1) They both measure strain/displacement over a gauge length

Both aim to provide accurate elongation data between two points to:

• Calculate strain (engineering strain, true strain depending on software)

• Determine modulus, yield, tensile strength properties depending on the standard and calculation method

2) Both can integrate with a universal testing machine for synchronized data

In many systems, both can:

• Stream data to the UTM controller/software

• Appear as a strain channel

• Be used for reporting and calculations

• Be used for closed-loop control (when supported)

3) Both require calibration and verification

A good lab will:

• Calibrate/verify gauge length accuracy, linearity, and repeatability

• Document performance as required by ISO/ASTM/internal QA systemsVideo uses optical calibration methods; clip-ons often use physical calibration rigs or reference standards.

4) Both can be “great” or “bad” depending on setup

A top-tier video system with poor lighting/targets can perform poorly.A high-accuracy clip-on used outside its intended range or misapplied can give unreliable results.

Pattern Spackling for Video Extensometer Full Field Strain Mapping

Accuracy, resolution, and data quality (how to think about it)

Clip-on accuracy is often extremely strong for its intended range

• Very consistent measurement when properly aligned and attached

• Less sensitive to “visual noise” issues

Video accuracy can be outstanding—but depends on conditions

Video performance is influenced by:

• Camera resolution and field of view

• Calibration quality

• Lighting stability and glare

• Target method (paint dots, tape markers, speckle pattern, edge tracking)

• Out-of-plane motion (specimen moving toward/away from camera)

• Vibration and camera mounting stability

Practical takeaway:Video can be “phenomenal” in a controlled setup—and can also be frustrating if the lab environment is not optimized (lighting/focus/contrast/mount rigidity).

Workflow & operator considerations

Training & consistency

• Clip-on: training focuses on proper attachment, alignment, and avoiding overload/damage.

• Video: training focuses on optics, focus, lighting, target application, camera positioning, and software regions.

Maintenance

• Clip-on: mechanical wear, knife edge wear, spring fatigue, accidental overload/dropping.

• Video: lens cleanliness, camera alignment, lighting replacement, software updates, calibration checks.

Safety & ergonomics

• Clip-ons require hands close to specimen and grips—more opportunity for pinch points or damage during mounting.

• Video reduces hands-on interaction near the test space once set.

Integration levels (basic to advanced)

Both technologies can be deployed at different “integration” tiers:

1. Standalone measurement

2. Extensometer provides strain output recorded separately or via DAQ

3. Integrated data acquisition

4. Strain channel displayed and recorded in UTM software

5. Used in calculations and reports

6. Closed-loop strain control

7. UTM crosshead movement is controlled based on extensometer strain feedbackThis can be valuable for standards that specify strain rate control or for precise modulus/yield characterization.

Decision matrix (fast way to choose)

Choose video extensometer if most of these are true:

• Many specimen types/gauge lengths

• Delicate or expensive samples

• Need non-contact or chamber testing

• Want faster changeovers

• Want potential for multi-region or transverse strain measurements

• You can invest more upfront and want productivity ROI

Choose clip-on extensometer if most of these are true:

• Repetitive testing, stable specimen geometry

• Tight budget

• Operators prefer a simple “clip and go” method

• Poor optical conditions / difficult-to-track surfaces

• You only need one or a few gauge lengths and don’t want camera/software complexity

“Best of both worlds” strategy (common in real labs)

Many labs end up with both:

• Clip-on for high-volume QC tensile tests on standard coupons

• Video for R&D, odd geometries, delicate materials, chamber tests, and faster changeovers

This combination often delivers the best total cost of ownership because each tool is used where it excels.

Contact Universal Grip for a free quote or consultation on your extensometer application:

www.universalgripco.com/contact

978-882-1480