
Back to Fracture Mechanics Overview
- 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

MODEL 7641 High Temperature Clip-On Gages (600 °C)
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 600 °C (1100 °F) without any cooling.
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 E1820, E399, E647, etc. All units can be displaced slightly in compression for ease of installation.
The COD gage is supplied with the revolutionary 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.

Features
- 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
- All standard units meet existing, ASTM E399, ASTM E1820 and ISO 12135 requirements for accuracy
- 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.
Model 7641 Available Versions: ANY combination of gauge length and measuring listed below is available, except as noted. Other configurations may be available with special order; please contact Epsilon to discuss your requirements.
Specifications
Input: Includes power supply for your country (specify)
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
Linearity: 11 point linearization, ≤0.1% 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 2Hz-3 kHz digital filters
Temperature Range: Ambient to 600°C (1100°F) typical1
Temperature Sensitivity (Gain): <100 PPM / °C (0.01%FS/°C) typical
Temperature Sensitivity (Offset): 20 PPM / °C (0.002%FS/°C) typical
Sensor Cable: 2.5 ft (.7 m) tri-axial high temperature cable, plus 5 ft (1.5 m) room temperature extension cable
Operating Force: 1-5 k g typical, depending on model
Environment: Recommended for elevated temperature testing in dry air or some other gases
Options
- Connectors to interface to nearly any brand 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
> Specialty Knife Edges