d-Exto MPBX Geotechnical Extensometer

YieldPoint’s d-Exto is a 1 to 6 Point Multi-Point Borehole eXtensometer (MPBX). It combines a traditional multi-rod design with a small section form factor, modern materials and digital signal processing to result in dramatically improved accuracy and reliability compared to less well priced alternatives. This high precision digital extensometer comprises up to six variable induction displacement sensors. The hermetically sealed electronics operate indefinitely when submerged in water.

The instruments is delivered coiled on a 120cm/4ft diameter and is ready to use: already fully assembled, tested and calibrated. Simply drop it into the borehole,  grout, and the first readings can be recorded immediately. An
 on-board micro-processer performs digital signal processing and transmits readings  directly in real world units (mm and oC). The instrument  can be read using a low cost readout unit (d-Reader), a tablet (d-Tablet), dataloggers (d-Logger), and wirelessly networked (d-Mesh) for transmission to Cloud based servers. Output  signals are robust and can be transmitted over 800m of lead wire without loss of performance. If broken the lead wire can be twisted and taped together: no need for soldering. With only 4 conductors, repairs are fast and reliable.

d-Exto Features

  • Very durable design with high strength LexanTM outer sheath
  • Multiple Stainless Steel rods maintained straight and tight in multi-lumen extruded tube for maximum accuracy
  • Up to 6 anchor points
  • 125mm, 150, 200mm or 250mm stroke length
  • High individual sensor accuracy (0.5%FS) and resolution (0.01mm FS)
  • Output in real world units: millimeters
  • Unique instrument ID for easy and safe tracking
  • Calibration Coefficients stored in Flash memory
  • Small electronics head: 25mm diameter 150-300mm long
  • On-board digital temperature sensor for accurate compensation
  • High survivability following blasts and vibration even if toe is damaged
  • Easy to install and maintain—Arrives on site fully assembled

d-Exto Technology

The d-Exto design is based on a traditional multi-rod design using 1 to 6 Variable Inductive Displacement Sensors. The 6 stainless steel rods are housed individually in a central multi-lumen tube to maintain them perfectly straight and eliminate friction between rods. The individual rods are completely independent of one another and therefore if damaged by blasting the proximal sensors will continue to operate.

Each displacement sensor is individually calibrated and the coefficients are written to microcontroller memory. The d-Exto can easily detect and resolve sub-millimetric displacements with 0.01mm resolution. That is a 10 microns resolution!

Accuracy is enhanced by an on-board temperature sensor to provide compensation with the help of 2 extra and static rods. The d-Exto is virtually immune to changes in temperature.

d-Exto uses inductive, non-contact sensing: the design is inherently waterproof. Ask to see a live view of a d-Exto in our front lobby, that is underwater and completely flooded since late August 2014: it continues to operate with unaffected performance!

d-Exto readout

YieldPoint’s low cost d-Reader readout unit or the new d-Tablet. Both provide the temperature and displacement data directly in oC and mm.


Data from the d-Exto can be collected using YieldPoint’s d-Logger dataloggers: d1Logger and d4Logger. Data can be download by any computer device running Windows including the convenient d-Tablet.

Automated data retrieval:

Using our geotechnical d4Logger, clusters of up to 4 instruments can be wireless networked using:

  • dMesh: a 900MHz wireless mesh solution.
  • IoT GateWay if Ethernet is available

YieldPoint Inc. provides mine operators worldwide with tools, technology and service. YieldPoint's Digital (direct-to-digital) sensors combine accuracy and durability while keeping costs low.

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