3909 Extensometers for Simple Performance Testing of Asphalt for Measuring Axial Displacements

The 3909 extensometers from Epsilon are engineered to measure axial displacements in the simple performance tests that are prescribed by NCHRP Report 465, and determine dynamic modulus of hot mix asphalt per AASHTO TP062.

These extensometers are usually mounted as two axial modules with independent outputs that are capable of measuring specimen deformations in two locations; however they can be mounted as a single unit or up to four on a sample. The extensometer can quickly clip onto gauge points mounted per the test requirements.

Magnets at each end of the extensometer snap instantly in place on the steel gage points glued to the test sample. The rapid attachment is most beneficial when testing preconditioned samples that are heated or cooled, as the extensometers can be mounted before the sample changing temperature considerably. Extensometers are available with modules rotated 90° for units that are intended to be used inside triaxial cells.

The standard Model 3909 features full scale measuring range of 0.5 mm (0.020”). Gage points are incorporated with the extensometers, and gluing fixtures are optionally available. Two standard 3909 units can be converted to the Model 3910 with the purchase of optional gauge length adapters.

As these extensometers are strain gaged devices, they are compatible with any electronics designed for strain gaged transducers. Often, the extensometers are connected to a test machine controller. The signal conditioning electronics for the extensometer is usually included with the test machine controller or may often be added.

In this case, the extensometer is delivered with the right connector and wiring so that it can be plugged directly into the electronics. Epsilon can provide a range of solutions for systems that do not have the required electronics. This enables the extensometer output to be connected to chart recorders, data acquisition boards, or other equipment.

Epsilon extensometers are compatible with almost every brand of test equipment and can come with the right connector to plug in directly, or can come with a separate conditioner and amplifier.

The company has over twenty 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.

The 36 Extensometer models are available in numerous variations and the company’s focus on helping customers has led to the development of models to cover virtually any test method.


The key features of the Model 3909 extensometers are as follows:

  • Easy mounting, attaches with magnets, which allows dynamic testing to 40 Hz
  • For simple performance testing per NCHRP Report 465, and for determining dynamic modulus of hot mix asphalt per AASHTO TP062
  • All standard units have linearity readings of 0.20% or better
  • Full bridge, 350 ohm strain gaged design for compatibility with nearly any test system
  • High quality foam lined case is provided
  • Rugged, dual flexure design for enhanced performance


The key specifications of the Model 3909 extensometers are as follows:

  • Excitation: 5 to 10 VDC recommended, 12 VDC or VAC maximum
  • Linearity: ≤0.20% of full scale measuring range, depending on model
  • Cable: Integral, ultra-flexible Teflon® cable, 2.5 m (8 ft) standard
  • Temperature range: Standard (-ST) is -40 °C to +100 °C (-40 °F to +210 °F)
  • Output: 2 to 4 mV/V, nominal, depending on model
  • Operating force: <30 g typical


The following options are available with the Model 3909 extensometers:

  • Gluing fixture for gage points
  • Gauge length adapters
  • Shunt calibration
  • Connectors to interface to nearly any brand test equipment

3909 Extensometers for Simple Performance Testing of Asphalt for Measuring Axial Displacements


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