Materials Testing Furnaces with the 7651 High Temperature XY Planar Biaxial Extensometer (1200 °C or 1600 °C)

The 7651 High Temperature XY Planar Biaxial Extensometers from Epsilon simultaneously measures in-plane bi-axial strains at high temperatures on specimens that are tested in X-Y bi-axial machines. These extensometers are used with materials testing furnaces or induction heating up to 1600 °C (2900 °F). It can be used for bi-axial strain controlled fatigue. The extensometer comes with a slide mounting system, which enables mounting to hot specimens in seconds.

The 7651 extensometers measure combined in-plane strains in flat cruciform specimens tested in machines that are capable of simultaneous X and Y (perpendicular) axial loading and on standard flat samples tested in pure tension. All extensometer models are capable of bi-directional displacement in both axes and can be used for strain-controlled fatigue testing under fully reversed load and strain conditions at frequencies up to 10 Hz.

All 7651 extensometer models are capable of mounting rigidly on the load frame and incorporate slide mounting to move the extensometer into contact with the specimen. The gauge length of the extensometer is set automatically before mounting on the test specimen, which enables hot mounting after thermal equilibrium has been realized.

These units are specifically designed to eliminate crosstalk between axes and to provide high resolution, high accuracy measurements. They incorporate capacitive sensors for low operating force and include electronics with multi-point linearization and programmable filtering for enhanced performance and accuracy.

The overall design reduces, and in several cases almost eliminates, any influence from common lab environment vibrations.

These extensometers are water-cooled and are equipped with high purity alumina rods with conical rod tips for specimen when testing to 1200 °C (2200 °F). Silicon carbide rods are used for the 1600 °C (2900 °F) high temperature option.

The model 7651 extensometers are often tailored for specific test requirements. Epsilon can be contacted for a configuration that matches the user’s requirement.

Epsilon extensometers are compatible with almost every brand of test equipment and can be supplied with the correct connector so that it can be plugged it directly.

The company has 20+ years history of service for the materials testing community and will be there to stand behind their products when the user’s critical application requires it.

Operation of these, and all of Epsilon’s extensometers, are verified to applicable standards such as ISO 9513 or ASTM E83 using in-house calibration systems. The calibration systems are calibrated with Epsilon’s laser interferometer system.


The key features of the Model 7651 extensometers are as follows:

  • Self-setting gauge length with fine adjustment feature
  • Hot mountable and retractable
  • All models can measure in both tension and compression and can be used for cyclic testing at test frequencies up to 10 Hz
  • Delivered fully calibrated with calibration that is traceable to NPL; voltage output can be user-specified (typically 0-10 V)
  • Superior ambient vibration rejection; primary vibration mode >100 Hz typical
  • Power supply and digital controller are included. Provides high level DC voltage output with low noise. Easily interfaced to data acquisition boards, test controllers, and chart recorders.
  • Standard units meet ASTM class B-1 requirements for accuracy. Includes a test certificate. ISO 9513 class 0,5 test certificates are available upon request.
  • High speed analog and digital outputs are included
  • Web-based user interface for setup and data acquisition
  • Selectable analog and digital filter options from 2 Hz to 3 kHz
  • Integrated calibration reference and auto-zero features
  • Many extensometer calibration files can be loaded for use with one controller
  • Quick-disconnect water cooling fittings and signal cables
  • High quality foam lined case and a spare set of rods are provided
  • Can be used with specimens at elevated temperatures while only requiring room temperature calibration


The key specifications of the Model 7651 extensometers are as follows:

  • Analog output: User specified, ±10 VDC typical, ±10.8 VDC rail
  • Digital output: 24 bit high speed Ethernet output with built-in web interface
  • Cyclic testing: up to 10 Hz, based on test system and test amplitude
  • Linearity: 11 point digital linearization, ≤0.1% FS typical linearity
  • Hysteresis: ≤0.1% FS typical
  • Resolution: <75 PPM (0.0075%FS) RMS @ 4 kHz, <6 PPM (0.0006%FS) @ 100 Hz at gauge length
  • Crosstalk: none
  • Filter: Selectable 100 Hz analog and 2 Hz – 3 kHz digital filters
  • Specimen size range: Fits any flat cruciform or axial-only test specimen with a test area larger than the extensometer GL
  • Output cables: Flexible 2.4 m (8 ft) analog output cables
  • Operating force: <30 grams typical
  • Sensor cables: 2 m (6.5 ft) room temperature cables
  • Environment: Recommended for testing in vacuum, dry air, or inert / non-corrosive gases
  • Contact force: <560 grams typical
  • Power: Includes power supply for the user’s country


The following are the options available with the Model 7651 extensometers:

  • Bulkhead adapters for use in vacuum chambers
  • High temperature option (-HT suffix) for use to 1600 °C
  • Connectors to interface to virtually any brand test equipment
  • Load frame mounting brackets
  • Model 2050 constant temperature water re-circulating bath

Materials Testing Furnaces with the 7651 High Temperature XY Planar Biaxial Extensometer (1200 °C or 1600 °C)


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