Extensometers for materials testing

Deflection Gages (Deflectometers) – Model 3540

Widely used for measuring deformations in three and four point bend tests, compression tests and a variety of general purpose deformations. These strain gaged devices come with a magnetic base for easy mounting.

38 EXTENSOMETER MODELS are available in many thousands of variations. Our focus on helping customers has led to the development of models to cover nearly any test method.

Operation of these extensometers are


using in-house calibration systems that are calibrated with Epsilon’s laser interferometer system.


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

Deflection is measured with a single arm with an attached spherical contact tip, similar to those on a dial indicator. The full bridge strain gaged construction provides an electrical output compatible with any electronics designed for a strain gaged transducer.

The magnetic base furnished with the gage can be mounted to the desired reference surface, whether flat or round. The tip can then be positioned to measure the deformation encountered during the test. The magnetic base can only be used for low and standard temperature testing. Elevated temperature testing requires additional support considerations.

All models feature a spring loaded arm that can break free in the event of excessive displacement, protecting the deflection gauge from damage. The upper arm exerts a small spring force against the specimen, which is sufficient to allow dynamic cyclic testing if desired, yet light enough in force to avoid influence on the test. Because small variations in arm length can result in changes in the system calibration, the 3540 includes a mechanical stop for repeatable placement of the arm in situations where it becomes detached.

These units come standard with the arm set to measure downward deflections when oriented in the upright position. They can be used upside down or in any orientation. They may also be configured with the extensometer arm spring loaded downward. Specify this if desired. Note that the measuring ranges listed are total displacement.

The Model 3540 extensometers are strain gaged devices, making them compatible with any electronics designed for strain gaged transducers. Most often they are connected to a test machine controller. The signal conditioning electronics for the extensometer is typically included with the test machine controller or may often be added. In this case the extensometer is shipped with the proper connector and wiring to plug directly into the electronics. For systems lacking the required electronics, Epsilon can provide a variety of solutions, allowing the extensometer output to be connected to data acquisition boards, chart recorders or other equipment.

Download Data Sheet

  • Full bridge, 350 ohm strain gaged design for compatibility with nearly any test system.
  • Comes with an adjustable magnetic base for easy mounting.
  • Spring loaded arm detaches to prevent damage from overtravel.
  • Meets ASTM and ISO accuracy classes as follows.
    • -001M, -004M, -006M, -005T, -015T, -025T:
      ASTM E2309 Class A
      ISO 9513 Class 1
      ASTM E83 Class B-2 (assuming 50 mm gauge length per D790 and D6272)
    • -012M, -025M, -050M, -050T, -100T, -200T:
      ASTM E2309 Class B
      ISO 9513 Class 2
      ASTM E83 Class C (assuming 50 mm gauge length per D790 and D6272)
  • All standard units have linearity of 0.25% of FS or better.
  • Includes the Epsilon Shunt Calibration System for on-site electrical calibration.
  • Rugged, dual flexure design for improved performance.
  • Includes high quality foam lined case.

Download Data Sheet

Excitation: 5 to 10 VDC recommended, 12 VDC or VAC max.

Output: 2 to 4 mV/V, nominal, depending on model

Linearity: ≤0.25% of full scale measuring range

Temperature Range: Standard (-ST) is -40 °C to +100 °C (-40 °F to 210°F)

Cable: Integral, ultra-flexible cable, 2.5 m (8 ft) standard

Operating Force: 50 g typical



Download Data Sheet

  • Connectors to interface to nearly any brand of test equipment
  • Arm orientation

Download Data Sheet

Product Videos


Deflectometer example applications: four-point bending, three-point bending, and component deflection in various orientations


Ordering Information

Click table options to configure

Measuring Range i

mm or inches #
1.0 mm -001M 001M
4.0 mm -004M 004M
6.0 mm -006M 006M
12.0 mm -012M 012M
25.0 mm -025M 025M
50.0 mm -050M 050M
0.050 in -005T 005T
0.150 in -015T 015T
0.250 in -025T 025T
0.500 in -050T 050T
1.000 in -100T 100T
2.000 in -200T 200T

Temperature Range

degrees #
-270 ˚C to 100 ˚C (-454 ˚F to 210 ˚F) -LT LT
-40 ˚C to 100 ˚C (-40 ˚F to 210 ˚F) -ST ST
-40 ˚C to 150 ˚C (-40 ˚F to 300 ˚F)¹ -HT1 HT1
-40 ˚C to 200 ˚C (-40 ˚F to 400 ˚F)¹ -HT2 HT2
-270 ˚C to 200 ˚C (-454 ˚F to 400 ˚F)¹ -LHT LHT

Model Number:  3540_ _ _ __ _

Model Number:

3540_ _ _ __ _

Model 3540 Available Versions: ANY combination of measuring range and temperature range listed above is available. Other configurations may be available with special order; please contact Epsilon to discuss your requirements.

¹Magnetic base not suitable for high temperature use; 50 °C (125 °F) max.

Example: 3540-012M-ST: 12.0 mm measuring range, standard temperature option (-40 °C to 100 °C)


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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