Frank Georg Schulz | TERRATEST

Different Components of Light Weight Deflectometer

Feb 28th 2015 at 3:35 AM

The light falling weight deflectometer (otherwise referred to as dynamic plate load tester or light drop weight tester) is a portable device originally developed in Germany, used to measure soil compaction. It is used for compaction quality control of embankments, roads, and replacement fills, but its dynamic nature makes it suitable for use in coarse as well as mixed grained soils with maximum grain size up to 63 mm. A typical LWD device consists of basic components such as:

  • A top fix/release mechanism or system that holds the falling weight at and releases it from a constant height. When the mechanism releases the falling weight, it causes it to drop freely from the control height and transmit the resulting load pulse through the dynamic plate that securely rests on the material being tested.
  • A guide rod, allowing the free drop at a set distance (typically 720 mm).
  • A falling weight grip, which makes it easier for the operator to raise the falling weight up to the top fix, in preparation for release by the release mechanism.
  • A falling weight (typically 10 or 20 kg), which can be raised to a predetermined height just below the weight grip. The weight, as earlier mentioned, is guided by the low resistance rod so that the drop can impart a controlled force on the dynamic plate.
  • A lock pin that can be toggled between locked and unlocked positions for releasing and fixing the falling weight.
  • A damping system that supplies a controlled (transient) pulse length to the device's impact force in a typical range of 16 to 30 ms. The spring element can either be a series of cylindrical pads or rubber cones/buffers.
  • An anti-tipping fixture, preventing the guide rod and weight from toppling when parts are placed and the device is standing freely on the loading plate.
  • A sensor that connects to the electronic device in the center of the plate, recording plate movements while the test is carried out.
  • A loading plate that provides uniformly distributed impulse load on the tested surface.
  • A cable connecting the loading plate sensor to the data storage and processing systems. Measurements can automatically be allocated to the appropriate position via GPS and data can be printed out directly from the device through the in-built printer.
  • More advanced systems offer additional components and features like voice navigation, bluetooth/wireless connectivity, USB flash drive, internal memory, and software/app facilities for more advanced data analysis.

About The Author:

TERRATEST GmbH is world leader in development and manufacturing of Light Weight Deflectometers for dynamic load plate test. They offer the world’s first light weight deflectometerTERRATEST 5000 BLU” with Bluetooth and voice navigation. For more information about their products visit their website!

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