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GDS LVDT Local Strain Transducers

Product Code : LVDT

The GDS LVDT Local Strain Transducers provide on-sample small strain measurements of axial and radial strain. Accurate determination of soil stiffness is difficult to achieve in routine laboratory testing. Conventionally, stiffness of a triaxial test specimen is based on external measurements of displacement which include a number of extraneous movements.

True soil strains can be masked by deflections which originate in the compliances of the loading system and load measuring system. Such equipment compliance errors add to a variety of sample bedding effects to give a poor definition of the stress-strain behaviour of the material under test, particularly over the small strain range. Most triaxial tests therefore tend to give apparent soil stiffnesses far lower than those inferred from field behaviour (Jardine, Symes & Burland, 1984). Need advice choosing the right transducer, view our options table here.

Further Information:

Discover more transducers and load cells equipment for soil testing.

GDS LVDT Local Strain Transducers
specification datasheet (PDF)
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Key features Benefits to the user
Axial and radial deformation measured directly on the triaxial test specimen: Removes bedding errors or “end effects”.
Inherently robust LVDT’s as they have no physical contact across the sensing element: Zero wear ensuring longer life and lower friction effects.
Submersible low pressure version (pictured above): Water version can be used up to 3500kPa.
Vented high pressure version: High pressure version for use in non-conducting oil up to 200MPa (Pressure relieved).
Temperature limits -20°C to 60°C &
-20°C to 110°C
 Suitable to use with GDS Environmental Triaxial Testing equipment, see page 8 for more information). Higher temperature versions available.
Measurement is taken in the middle third of the sample which is less restrained than the end zones: Therefore, it is highly desirable that radial and axial deformations are measured locally in this region if realistic deformation moduli are to be found.
Through bore configurations: Allows test to continue after the LVDT has passed its measurement range.
Radial sprung aluminium-bronze hinge for no backlash and low friction: The transducers measure sample effects not those of the measuring calipers.
Displacement Accuracy

0.1% FRO
Displacement Range

+/- 2.5mm or +/-5.0mm
Displacement Resolution

+/- 2.5mm = <0.1μm, +/- 5.0mm = <0.2μm typical values but dependant on data acquisition used
Sample Sizes

50mm, 70mm, 76mm, 100mm, 150mm, custom
Weight Approx (kg)

: Radial Caliper Weight, (based on a nominal 70mm caliper) = 74g : Axial Apparatus Weight (1 off) = 26g : Transducer Weight (1 off LVDT) = 20g


 

Tests supported by the GDS LVDT Local Strain Transducers, transducers and load cells equipment for soil testing :-

Axial or Radial Deformation

Axial deformation is measured by a displacement transducer in all GDS systems (LVDT, LDT or digital gauge).  Radial deformation is calculated as standard by measuring the volume change to 1mm3 directly on the back pressure controller.  For direct measurements of radial strain (i.e. transducers mounted upon the sample, and direct measurements of axial strain in the same way, GDS can supply a Hall Effect local strain set or an LVDT local strain set. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Axial or Radial Deformation soil test equipment
Local Strain Measurement

Accurate determination of soil stiffness is difficult to achieve in routine laboratory testing. Conventionally, stiffness of a triaxial test specimen is based on external measurements of displacement which include a number of extraneous movements.  By placing transducers directly on the sample, accurate measurements of strain may be obtained, particularly in the small strain area of the sample loading cycle where strain dependancy of soil stiffness (stiffer at low strains) can be otherwise be masked when using external transducers.

Local Strain Measurement soil test equipment
Maximum Shear modulus

Determination of the maximum (i.e., very small strain) shear modulus of a specimen. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Maximum Shear modulus soil test equipment

Standards for the GDS LVDT Local Strain Transducers, transducers and load cells equipment for soil testing :-