High Temperature Clip-On Gages (700 °C) – Model 7641

Designed for fracture mechanics testing in environmental chambers where the entire gage must be exposed to elevated temperatures. These capacitive sensors may be used up to 700 °C (1300 °F) without any cooling.

The Model 7641 INTRODUCES SEVERAL IMPROVEMENTS to Epsilon’s offerings for an uncooled, axial extensometer including:

  • A new body style to optimize mechanical performance and reduce weight and size
  • A new probe design that also provides many improvements including lower noise, better frequency response, improved flexibility and durability
  • Increased operational temperature
  • The ability to store calibrations of multiple extensometers with one signal conditioner

Epsilon extensometers are COMPATIBLE WITH VIRTUALLY EVERY BRAND OF TEST EQUIPMENT and can be supplied with the correct connector to plug in directly.


to the materials testing community, you know we will be there to stand behind our products when your critical application requires it.

These COD gages use a high-temperature capacitive sensor and do not require any cooling. They will operate up to the maximum temperature limit of most environmental chambers used in materials testing. The Model 7641 is ideal for determination of fracture mechanics parameters such as JIC, KIC, R-curve, fatigue crack growth rate (da/dN), and testing to standards such as ISO 12135, ASTM E1820, E399, E647, etc. All units can be displaced slightly in compression for ease of installation.

The COD gage is supplied with the advanced DT6229 controller. The standard output is 0-10VDC analog signal, factory calibrated with the COD gage. This system provides a number of functional enhancements including: high speed digital output, built in calibration and tare functions, analog and digital filters, and more.

The 7641 is readily interfaced with most existing test controllers and may be directly connected to a data acquisition system or chart recorder, or directly to a PC. The 7641 may be used for strain-controlled tests such as JIC.

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  • May be left on through specimen failure.
  • Improved performance at high temperature.
  • Improved noise rejection, resolution, and accuracy.
  • Improved clearance with most clevis designs.
  • Improved linearity and reduced stiffness.
  • Reduced size and weight, and improved high frequency performance.
  • All standard models are suitable for cyclic testing.
    • >25 Hz is typical for 10mm GL and larger, up to 100 Hz for some configurations
    • Typically limited by the user’s test apparatus, software settings, and filter selection
  • Digital controller and power supply included. Provides high level DC voltage output with low noise. Easily interfaced to test controllers, data acquisition boards and chart recorders.
    • Includes high speed analog and digital outputs
    • Intuitive web-based user interface for setup, calibration, and data acquisition
    • Built-in calibration reference and auto-zero features
    • Multiple extensometer calibration files may be loaded for use with one controller
    • Multiple temperature-specific calibrations may be stored
    • Selectable analog and digital filter options from 2 Hz to 3 kHz
  • Ships fully calibrated with electronics (traceable to NPL (UK)) with user specified voltage output.
  • Mechanical over-travel protection.
  • Durable stainless steel knife edges.
  • Includes high quality foam lined case.
  • Rugged, dual flexure design for strength and improved performance. The next-generation design enables cyclic testing at much higher frequencies.

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Analog Output: User specified, ±5 VDC or ±10VDC typical, ±10.8VDC rail

Digital Output: 24 bit high speed Ethernet output with built-in web interface

Accuracy: All standard configurations meet ASTM E1820, ISO 12135, and ISO 9513 Class 0.5 requirements for accuracy. A test certificate is included. Models that additionally meet ASTM E399 accuracy requirements are available. A test certificate for ASTM E399 is included with those models.

Linearity: 11 point linearization, ≤0.15% FS typical linearity

Resolution: <55 PPM (0.006%FS) RMS @ 4 kHz, <6 PPM (0.0006%FS) @ 100 Hz

Cyclic Testing: >25 Hz typical @ 10mm GL, >10 Hz @ 5mm GL

Analog Filter: Selectable 100 Hz analog and 2 Hz – 3 kHz digital filters

Temperature Range: Ambient to 700 °C (1300 °F). Use up to 800 °C is possible – contact Epsilon for details. Springs may require periodic adjustment or replacement after long-term testing above ~600 °C.

Temperature Sensitivity (Gain): <100 PPM / °C (0.01%FS/°C) typical (see Temperature Sensitivity Compensation)

Sensor Cable: 0.7 m (2.5 ft) tri-axial high temperature cable, plus 1.5 m (5 ft) room temperature extension cable

Operating Force: 1-5 kg typical, depending on model

Environment: Recommended for elevated temperature testing in dry air or inert / non-corrosive gases

Overall Dimensions: Contact Epsilon for overall dimensions

Power: Includes power supply for your country (specify)




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  • Connectors to interface to nearly any brand of test equipment
  • Bulkhead adapters for vacuum chambers
  • Dual-channel DT6229 controller available
  • Bolt on knife edges for attachment to test specimens without machined attachment points 

Download Data Sheet

Product Videos


COD gage for high-temperature fracture mechanics and fatigue crack growth testing up to 700 °C


Ordering Information

Click table options to configure

Gauge Length

mm or inches #
3.0 mm -003M¹ 003M
5.0 mm -005M² 005M
6.0 mm -006M 006M
10.0 mm -010M 010M
12.0 mm -012M 012M
0.20 in -0020² 0020
0.25 in -0025 0025
0.40 in -0040 0040
0.50 in -0050 0050

Measuring Range

extension #
+2.5 mm * -025M³ 025M
+4.0 mm * -040M 040M
+6.0 mm ** -060M 060M
+8.0 mm ** -080M 080M
+10.0 mm ** -100M 100M
+12.5 mm ** -125M 125M
+0.10in * -010T³ 010T
+0.25 in ** -025T 025T
+0.40 in ** -040T 040T
+0.50 in ** -050T 050T

Model Number:  7641_ _ _ __ _ _ _

Model Number:

7641_ _ _ __ _ _ _

Model 7641 Available Versions: ANY combination of gauge length and measuring listed above is available, except as noted. Other configurations may be available with special order; please contact Epsilon to discuss your requirements.

¹Special order, <5 Hz typical; not available in 8.0 mm, 10.0 mm or 12.5 mm measuring ranges
²Not available in 12.5 mm and 0.50 inch measuring ranges
³Suitable for front-face mounting only
* Tilted cable exit
** Vertical cable exit

Example: 7641-010M-060M: 10.0 mm gauge length, +6.0 mm measuring range


If your unit is in need of service, calibration or repair, initiate the RMA process with us and we will be happy to assist.

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