videoXtens Extensometer

videoXtens is used for optical measurement of extension on contact-sensitive and highly elastic materials.

This extensometer provides non-contact measurement of tensile, compressive and flexural deformations of all types of plastics, metals, rubber, composites and films/foils and of two-dimensional point displacements within a matrix, e.g. on components.

It is also suitable for determining change in width, r-values as per ISO 10113 and ISO 10275 and offset yields in tensile tests to ISO 6892-1.

Hydraulic grips videoXtens

Key Advantages and Features

What versions is the videoXtens extensometer available in? How does this measuring system actually work? What is the correct way to prepare the specimen for accurate, reproducible measurement? How does the test work under extreme temperatures? All these answers and much more can be found here.

videoXtens versions

videoXtens

The basic version of videoXtens consists of a housing with a camera. It can be expanded with an additional camera in the housing or alternatively with a complete measuring head including a camera.

videoXtens with Second Camera

With this version measurements can be made in the coarse and fine ranges with seamless switching. A camera focuses on the initial range, achieving high resolution here. This is particularly advantageous with short initial gage-lengths. The second camera covers the entire range, enabling high measurement travel.

Alternatively the two cameras can be arranged in an array, with overlapping fields of view. This results in an enlarged FOV with the same high resolution.

A further alternative is to use a camera for change in width.

videoXtens with second camera in separate housing

The separate housings allow the cameras to be adjusted completely independently of each other. This means for example that the upper and lower gage marks can be viewed separately in the case of long gage lengths; high local resolution is achieved in each case. The minimum distance between the cameras is 180 mm.

videoXtens Array: multi-camera measuring system (3 cameras)

The resolution of videoxtens depends on the field of view of the camera. A smaller image means better resolution – but also a smaller measuring range. If an application requires large measurement travel combined with very high resolution, the Array version of videoXtens provides a flexible solution.

The overlapping fields of view of three cameras are combined into one large field of view. Markings exiting the field of view of one camera are automatically transferred to that of the next camera. videoXtens Array tracks at half crosshead speed; this keeps the testing operation in focus and makes optimum use of the measuring range.

videoXtens Array is ideal for testing heavy plate, constructional steels and wire, together with many plastics.

videoXtens Array: multi-camera measuring system (3 + 1 cameras)

The system can be equipped with an additional camera. This possesses a small field of view and can be used for measuring change in width.

Other versions of Array, for example in multiple videoXtens housings, are available on application.

ProLine videoXtens

ProLine videoXtens is specifically matched to ProLine machines and can only be used with them. This extensometer is a cost-effective variant for determining extension using two gage marks. It conforms to the ProLine concept and is pared down to the most essential functions. No options or additional cameras are therefore available and there is no hardware synchronization to the machine electronics (only software synchronization).

Advantages and features

  • Advantages of videoXtens
  • videoXtens has no effect on material characteristic values as it features non-contact operation.
  • It is the ideal system for strain measurement on whipping materials (safety belts, steel ropes, rubber ropes etc.).
  • Biaxial measurement: elongation measurement and optional change-in-width measurement can be performed simultaneously. No separate marking is required to measure change in width and width can be determined at one or more locations. This allows measurement of offset yields in tensile tests to ISO 6892-1, together with r and n-values as per ISO 10113 and ISO 10275.
  • Flexible illumination system (incident light/backlight) can be ideally adjusted to suit the testing situation.
  • Easy adjustment and alignment to the test axis.
  • Suitable for use with temperature chamber with plane-parallel glass insert with heated pane.
  • Mounting on the testing system is extremely flexible; in the upper or lower test area, depending on use; with or without temperature chamber.
  • High accuracy and resolution
  • Accuracy Class 1 to EN ISO 9513.
  • Resolution and measurement accuracy are high over the entire image.
  • Measurement travel can be varied and, depending on the image size or lens selected, can be very large.
  • Unique functions
  • Automatic gage-mark recognition and acquisition of initial gage-length L0.
  • Strain-rate-controlled tests can be performed if videoXtens is connected to testXpert II and testControl / testControl II.
  • Pattern recognition enables preparation-free testing of specimens with structured surfaces. Alternative preparation of specimens with homogeneous, non-structured surfaces using pattern spray.
  • Differing distances from specimen surfaces to camera (e.g. with tensile tests or components) can be compensated for.
  • Entire test sequence can be followed on-screen. Video sequence can be stored for subsequent evaluation.
  • Outstanding options
  • Optional Test Re-Run module enables retrospective recalculation of strain values on the basis of recorded image sequences, using different initial gage-lengths.
  • If the specimen is provided with additional marks, strain distribution and strain at break as per Annex H of ISO 6892-1 can optionally be determined.
  • Measurement of change in width plus deflection in 3 and 4-point flexure tests requires no additional hardware.
  • 2D dot matrix measurement allows determination of local strain and inhomogeneities on a planar specimen surface in two directions (2D).
  • Connection to testXpert II enables use of videoXtens' Video Capturing Plus function with no need for additional hardware. Associated with this is integration of the image sequence in testXpert II and synchronization with the test data for later evaluation of the test.

Specimen marking

In the case of materials with smooth, monochrome surfaces the gage length is marked using a felt-tip pen or by means of self-adhesive gage-marks. Alternatively the specimen can be prepared by applying a pattern spray to the surface area. Extension is measured using the pattern created by the texture applied at points on the gage-length. Specimens with a structured surface can be tested even without additional marking; the surface texture serves as a natural pattern.

No extra marking is required for optional change-in-width measurement. Measurement is via a special edge-detection algorithm (Second Measurement Axis option).

The transverse-contraction gage-length can also be set by applying dots or by selecting areas of a natural or artificial pattern on the specimen surface.

Due to gage-length compensation the same degree of accuracy is not required when applying gage marks at distance L0 as with other fine-strain measurement methods. This eliminates error sources while speeding up test preparation.

Temperature chamber

When videoXtens is used in conjunction with temperature chambers, ensure that the panes in the observation port are made of anti-reflective glass; otherwise the signal quality may be significantly impaired by reflections and light loss.

The changed optical testing conditions will also have a negative impact on the measurement signal. In the temperature range from 0 to +250°C this basically refers to air currents which occur in the temperature chamber and cause an increase in signal noise of approximately 0.1 µm per 10 kelvin temperature increase.

In the minus temperature range down to -70°C, mist formation and icing of the specimen and fixture may occur; the effect on the measurement signal depends on the customer-specific configuration (coolant medium, specimen grips, illumination, specimen material etc.). In chambers employing CO2 and LN2 cooling there is a danger of mist formation, given suitable humidity levels and temperatures of approximately -20 to 0°C. It may then be necessary to wait several minutes before performing the test.

When standard self-adhesive marks are used the temperature range is limited to -40 to +120°C. Marker pens offer alternative options.

For applications requiring frontal illumination of the specimen the standard incident light lamps are available. These are mounted outside the chamber and light the specimen through the videoXtens observation port.

videoXtens with 2 cameras & videoXtens Array with 3 cameras

videoXtens Extensometer
videoXtens Array extensometer

videoXtens in Use

7:42

Ribbed steel test with 2-camera videoXtens extensometer

The test re-run software options and strain distribution facilitate measurement across the entire length of the specimen and a subsequent recalculation of the strain

Technical overview

videoXtens

videoXtens and additional cameras

Measuring head with digital camera, software for image acquisition and evaluation, plus accessory case for alignment and marking aids.

Item No.

1001282

Type

videoXtens

Initial gage length L0

5 to 1000[1]

mm

Resolution per field of view:

50 mm

0.25

µm

100 mm

0.5

µm

200 mm

1

µm

500 mm

2.5

µm

1000 mm

5

µm

Measuring frequency, max. (adjustable)

166

Hz

Max. test speed

1000

mm/min

Weight, approx.

7.5

kg

testXpert II minimum version

V 3.2

Accuracy

Accuracy class 1 to EN ISO 9513 for fields of view ≤ 200 mm

For fields of view > 200 mm, the following applies: the smallest measured value in Accuracy Class 1 is: FOV/1000.

Example: FOV=500⁢mm⇒500mm1000=0.5mm

Accuracy Class 1 is attained at a measured value of 0.5 mm or above.

  1. Depending on field of view (FOV). FOV can be expanded via a second camera or Z-axis.

A free slot in testControl II is required for the INC module (included in delivery).

videoXtens Array

videoXtens Array and additional cameras

Expanded measuring head with three digital cameras, software for image acquisition and evaluation, plus accessory case for alignment and marking aids.

Item No.

1001392

Type

videoXtens Array (3 cameras)

Initial gage-length L0

5 to 300

mm

Resolution per field of view:

140 mm (f = 50 mm lens)

0.25

µm

230 mm (f = 55 mm lens)

0.4

µm

340 mm (f = 25 mm lens)

0.6

µm

Accuracy

Class 1

to EN ISO 9513

Measuring frequency, max. (adjustable)

166

Hz

Max. test speed

1000

mm/min

Weight, approx.

15

kg

testXpert II minimum version

V 3.4

A free slot in testControl II is required for the INC module (included in delivery).

videoXtens for ProLine

ProLine videoXtens

Measuring head with digital camera, software for image acquisition and evaluation, plus accessory case for alignment and marking aids.

Item No.

013561

Type

ProLine videoXtens

Initial gage length L0

5 to 1000

mm

Resolution per field of view:

50 mm

0.5

µm

100 mm

0.5

µm

200 mm

1

µm

500 mm

2.5

µm

1000 mm

5

µm

Accuracy (for fields of view ≤ 200 mm)

Class 1

to EN ISO 9513

Measuring frequency, max. (adjustable)

166

Hz

Max. test speed

1000

mm/min

Weight, approx.

7.5

kg

testXpert II minimum version

V 3.0

Connected directly to PC, no module required.

Software options 

testXpert II testing software offers various options for precise, traceable non-contact extension and strain distribution measurement. 

Test Re-Run and strain distribution

The optional Test ReRun module enables retrospective recalculation of strain on the basis of an image series recorded during a test, using a different initial gage-length (provided multiple markings are present). This can be particularly advantageous in component testing, for example, when it is necessary to evaluate local strain at different locations, or in standard tensile tests when specimen necking has occurred outside the original initial gage-length.

The recalculated strain can naturally be synchronized retrospectively with the other measured values via testXpert II.
This option is available with testXpert II Version 3.4 onwards.

The Strain Distribution option enables determination of local strains at multiple measuring locations along the specimen gage-length. These are available as channels in testXpert. Up to 16 measuring locations are automatically recognized and evaluated during the test. This option also allows automatic real-time symmetrical adjustment of the initial gage-length around the necking (as per ISO 6892-1, Annex H).

Video Capturing

The testXpert II Video Capturing software option is recommended if recording of the test is additionally required (without retrospective recalculation). The recording is synchronized with the measured curve, enabling the test to be viewed retrospectively. The option includes no hardware, as recording and synchronization take place entirely via the videoXtens system.
This option is free of charge.

2D dot matrix

This option allows two-dimensional measurement of dots applied to a planar specimen surface. This enables determination of local strains and specimen inhomogeneities under load. X and Y co-ordinates plus the distances between dots are available as measured values.

Up to 100 measurement dots can be measured in any desired arrangement or in matrix form. Display in testXpert II is limited to 15 channels.

This option uses only one camera for measurement; any other cameras present are switched off beforehand.

Optional second measurement axis 

This option allows biaxial measurement; transverse strain (e.g. change in width) can be recorded at the same time as longitudinal strain. Alternatively, change in width can naturally be measured alone.

  • Two versions are available for measurement of transverse strain:
  • measurement directly on the specimen edge with no additional markings (required for determination of r-value); a backlight is required for this version
  • measurement on the specimen surface using dot markings or sprayed-on pattern; with this version specimen illumination is via incident light.

Deflection measurement 

videoXtens can also be used for flexure tests. There are several options for measuring specimen deflection, depending on the type of test and the specimen condition and properties:

  • measurement using incident light via marks on the specimen
  • measurement using backlight on the specimen lower edge
  • measurement of deflection in the test axis or of the polynomial approximation of the curve.

Maximum deflection that can be measured: with videoXtens the maximum deflection corresponds to the FOV; with videoXtens Array to 1/3 of the total FOV (deflection is measured with one camera only in this case).

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