Overview: The document describes the Model 3909 extensometer, designed for measuring axial displacements in simple performance tests as per NCHRP Report 465. It is primarily used for testing asphalt specimens.

Specifications: The Model 3909 features a full bridge, 350-ohm strain-gaged design, compatible with most test systems. It meets ASTM class B-1 and ISO 9513, class 0.5 accuracy requirements. The extensometer has a full-scale travel of 0.020 inches (0.5 mm) and operates within a temperature range of -40 °C to +100 °C (-40 °F to +210 °F). It requires an excitation of 5 to 10 VDC, with a maximum of 12 VDC or VAC.

Design and Features: The extensometer consists of two axial modules with independent outputs, allowing measurements at two locations. It attaches quickly to gage points using magnets, which is beneficial for pre-conditioned samples. The standard model can be converted to Model 3910 with optional gage length adapters. It includes a high-quality foam-lined case and features a rugged, dual flexure design for improved performance.

Options and Accessories: The extensometer can be equipped with connectors for various equipment brands, shunt calibration modules, gage length adapters, and gluing fixtures for gage points. Custom gage lengths are available upon request.

Ordering Information: The Model 3909 is available in different gage lengths, such as 2.750 inches (70 mm), 3.000 inches (76 mm), and 4.000 inches (100 mm). Example: Model 3909-0300 has a 3.000-inch gage length with a full-scale measuring range of 0.020 inches (0.5 mm).

Applications: The extensometer is suitable for dynamic testing up to 40 Hz and can be used inside triaxial cells with rotated modules. It is compatible with electronics designed for strain-gaged transducers and can be connected to data acquisition systems, chart recorders, or other equipment.