Are you absolutely certain your lab is using the most cost-effective sensor for your specific materials?
As a global supplier of Universal Testing Machines at Qualitest, we see the constant debate surrounding the contact vs non contact extensometer setup. We’re going to call it: the best sensor is not always the one with the highest specifications on the datasheet. It is the one that survives the reality of your daily testing floor.
In this guide, we examine the differences to help you make a decision that makes financial sense for your facility.
Key Takeaways
- Contact extensometers are the most cost-effective choice for standard testing of rigid materials like metals and hard plastics.
- Non-contact systems provide a zero-influence solution that is essential for testing fragile films, biological tissues, and high-temperature samples.
- Video extensometers eliminate the risk of sensor damage during violent specimen fractures and save money on potential repairs.
- Both measurement technologies are fully capable of meeting strict ASTM E83 and ISO 9513 accuracy standards.
- Qualitest offers a complete range of both solution types to ensure your lab gets the right equipment for your specific budget and application.
The Basics: What Defines Each Type?
Before we offer our opinions, it is helpful to understand the mechanics of how these units operate.
Contact Extensometers
This is exactly what the name implies. Contact extensometers physically attach to a specimen in a universal testing machine to measure strain by tracking elongation directly. They are known for offering high accuracy and reliability for many materials and test conditions (Li, 2012; Zwick & Kennesaw, 2011; Mcenteggart, 1995; Kempny & Rozmus, 2021).
The most typical version is the clip-on extensometer (like our QM-S-Ext), which uses knife edges or small clamps to hold the sample. As the material begins to elongate, the device physically expands along with it, transmitting precise voltage changes to the controller. We still favor these for many applications because they are tactile, straightforward, and satisfyingly direct.
Non-Contact Extensometers
Non-contact extensometers, such as video or laser-based systems, measure strain without touching the specimen. This avoids any influence on the sample and enables full-field strain measurement (Li, 2012; Zwick & Kennesaw, 2011; Mcenteggart, 1995; Kempny & Rozmus, 2021).
Modern systems like our Quantum Series utilize Digital Image Correlation (DIC) software. These methods have advanced significantly, providing precise strain data comparable to contact devices while eliminating mechanical interference and setup complexity (Li, 2012; Wang et al., 2021; Kempny & Rozmus, 2021).
Contact vs Non-Contact Extensometer: The Comparison
When you are choosing between a non-contact vs contact extensometer, you are balancing three factors: how sensitive your material is, the temperature of your environment, and how much risk you can accept. Here is our unfiltered perspective.
1. Interaction with the Specimen
Contact
Because they clamp directly onto the sample, contact extensometers add mass. Contact extensometers may introduce slight mechanical loading or slip issues (Mcenteggart, 1995; Kempny & Rozmus, 2021).
Consider a heavy section of structural steel rebar or a rigid composite pipe; the weight of a sensor here is irrelevant. But for ultra-thin packaging foil or delicate textile fibers? That added drag is problematic. Experienced lab managers who have seen a sample sag under the weight of a clip know exactly what we are discussing.
Non-Contact
There is absolutely zero physical influence. We are convinced this is the only logical option for "non-clippable" materials. If you are questioning whether your sample is too fragile for a heavy clip—like bio-absorbable sutures or spider silk—it almost certainly is, and you should be considering optical options.
2. The Temperature Factor (Environmental Chambers)
This is where we have a strong preference based on operator feedback.
Contact
Attempting to place a clip-on sensor inside a heated chamber is difficult. You require expensive, specialized hardware with long ceramic arms just to reach inside. It is complex to set up, and you lose heat every time you open the door.
Non-Contact
We highly recommend video extensometers for this application. Non-contact systems excel in high-temperature or fragile specimen testing (Zwick & Kennesaw, 2011; Mcenteggart, 1995).
They observe the strain through the glass window, remaining cool and safe outside. It turns a complex setup into a simple operation, which is ideal for thermal testing of automotive engine components or aerospace paneling.
3. Equipment Risk
Contact
A significant limitation of traditional clip-on units is the risk of damage at the moment of fracture. We have seen many functional sensors destroyed because an operator forgot to remove them before the metal snapped. To save the device, you often must remove it early, meaning you lose that critical final section of data.
Non-Contact
A video extensometer can record a sample fracture repeatedly without sustaining a scratch. For us, the assurance that you can capture the entire event—including the violent break of a high-strength carbon fiber strand—without damaging your investment is incredibly valuable.
Common Industry Scenarios
To put this into perspective, here is how different sectors typically apply these technologies.
The Heavy Industry Sector
For a facility verifying thousands of steel reinforcement bars (rebar) or heavy fasteners, the environment is rough and the pace is relentless. A rugged clip-on extensometer is the standard choice here because it handles the grit, and the rigid specimens are completely unaffected by the clamp weight.
Contact extensometers remain valuable for their simplicity and robustness in many universal testing machine applications (Li, 2012; Zwick & Kennesaw, 2011; Mcenteggart, 1995). Additionally, automotive labs testing sheet metal for body panels heavily favor video extensometers to capture the full flow curve without interruption.
Precision & Delicate Applications
Conversely, a lab analyzing soft biological tissues, latex gloves, or arterial stents cannot risk physical contact. Even the slightest pinch from a clip creates a stress concentration that ruins the results.
In these scenarios, optical systems are the dominant solution. Similarly, testing advanced carbon-fiber composites or micro-wires often requires the precision of non-contact systems to avoid "noise" caused by slipping clips or physical impossibility.
At a Glance: Feature Summary
To help you decide, here is the reality regarding the features:
| Feature | Contact Extensometer (Clip-On) | Non-Contact Extensometer (Video/Laser) |
|---|
| Initial Capital | Low to Medium (Budget-friendly) | Medium to High (Larger investment) |
| Preparation | Fast (Clamp and test) | Moderate (Requires lighting/marking) |
| Specimen Influence | Physical contact (added drag) | None (Zero influence) |
| Equipment Risk | High risk of sensor damage | 100% safe during fracture |
| Thermal Testing | Requires specialized hardware | Simple (View through glass) |
| Maintenance | Mechanical parts wear out | No moving parts (Low maintenance) |
Which One Is More Cost-Effective?
This is where the discussion often settles. Our view on "cost" extends beyond the purchase price.
Clip-on extensometers possess a lower initial price tag. For labs testing standard metals or hard plastics where high volume is the goal, a clip-on model is a remarkably reliable workhorse. If your routine is standard, we suggest you stick with contact.
On the other hand, non-contact systems require a larger upfront payment. However, we genuinely believe they pay for themselves in flexibility. One video camera can replace multiple clip-on units of different sizes. Furthermore, you eliminate the recurring expense of repairing sensors damaged by violent specimen breaks.
Accuracy and Standards (Compliance)
We frequently hear the misconception that camera-based solutions are less precise than physical ones.
We want to address that immediately. Compliance is mandatory for us. Regardless of the technology you select, both our contact and non-contact extensometers are constructed to satisfy strict international standards like ASTM E83 and ISO 9513.
Clip-on units easily achieve Class 0.5 or Class B-1 accuracy without issue. Video extensometers, thanks to high-resolution lenses, now match these accuracy classes perfectly. We stand by the data from our optical systems just as firmly as our physical ones.
However, it is worth noting that non-contact extensometers can be more sensitive to environmental factors like lighting and surface conditions, potentially causing measurement inaccuracies if not set up correctly (Mcenteggart, 1995; Kempny & Rozmus, 2021).
Our Perspective: Making the Decision
At Qualitest, our priority is supplying the tool that fits your specific needs, not just the most expensive option. The choice between contact and non-contact extensometers depends on the material, test environment, required accuracy, and ease of use (Zwick & Kennesaw, 2011; Mcenteggart, 1995).
- Select a Contact Extensometer (like the QM-S-Ext) if: You are testing standard metal coupons at room temperature; you have a standard routine (e.g., ISO 6892); and you require a durable, budget-conscious solution.
- Select a Non-Contact Extensometer (like the Quantum Series) if: You are testing elastomers, thin films, or performing thermal testing in a chamber; you need to record strain until failure without risk; or you want a lab that is prepared for varied specimen sizes ranging from tiny wires to large composites.
Upgrade Your Capabilities with Qualitest
Whether you decide that a rugged clip-on or an advanced video system is the correct choice, we have the solution. We pride ourselves on offering cost-effective products that do not compromise on quality.
From our reasonably priced QM-Series Universal Testing Machines to our modern Quantum Series Video Extensometers, our equipment is built to deliver precise, repeatable data for years.
Review our full range of extensometers and UTMs today!
References
- Li, Y. (2012). Application of Non-contact Video Extensometer in Mechanical Properties Test.
- Zwick, Z., & Kennesaw, K. (2011). Choosing the Right Extensometer for Every Materials Testing Application.
- Mcenteggart, I. (1995). Contacting and non-contacting extensometry for ultra high temperature testing. 157-169.
- Kempny, M., & Rozmus, R. (2021). An evaluation of the mechanical properties of 13MnSiCr7 steel by digital image correlation. Computer Methods in Material Science.
- Wang, F., Krause, S., Hug, J., & Rembe, C. (2021). A Contactless Laser Doppler Strain Sensor for Fatigue Testing with Resonance-Testing Machine. Sensors (Basel, Switzerland), 21.
