YieldPoint’s unique 1 to 6-Point Multiple Rod Extensometer (d-EXTO) combines a traditional Multi-rod design and digital signal processing to result in dramatically improved accuracy reliability compared to similar priced existing technology. This high precision digital instrument comprises up to six (6) Variable Induction Displacement Sensors and an on-board digital temperature sensor.

Design features of the d-EXTO include a Lexan TM body sheath much stiffer, stronger and durable than polyethylene commonly used; a compact central core which will not be damaged by shear movements of up to 10mm; hermetically sealed electronics that operate indefinitely when submerged in water and robust torsionally straightened stainless steel rods.

The inherently digital nature of the signals eliminates the necessity for expensive analog-to-digital conversion and results in low cost readout unit that reads data directly in real world units (mm and oC). The sensor output is an ASCII (9600,8,N,1) digital signal which can be read by a low cost readout unit (d-READER), dataloggers (d-LOGGER), and wirelessly networked (dMESH) for transmission to cloud based servers. The signals themselves are robust and can be transmitted over 1000ft of lead-wire. If broken the lead-wire can be twisted and taped together.

  • `Super-Tough` design with high strength Lexan TM outer sheath
  • Multiple Stainless Steel rods maintained straight in multi-lumen extruded tube for maximum accuracy.
  • 1-6 anchor points
  • 150mm (6 inch) stroke length
  • High individual sensor accuracy (0.3%FS) and resolution (0.01mm FS)
  • Output in real world units
  • Unique instrument ID
  • Calibration Coeffs. in Flash memory
  • Smallest electronics head (25mm diameter 150mm 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
  • Key Feature: Fully integrated and preassembled borehole extensometer
  • Dimensions: 25mm diameter can be placed in 50mm hole.
  • Dimensions: Up to 6 Anchor points over lengths up to 30m
  • Disp. Range: 125, 150 (standard), 200 and 250mm.
  • Disp. Accuracy: typically 0.5% F.S(<10m) and 1% linearity (>10m). Depends on distance between anchor point and head.
  • Temp. range: -40 to 125 oC
  • Output Signal: RS485 with transmission up to 500m over 2 x tp.
  • Output Signal: Asynchronous serial signal - 9600,8,N,1. ASCII encoded. Values and units transmitted.
Datalogging and Telemetry:

Data from the d-EXTO can be collected using YieldPoint’s d-LOGGER dataloggers (d1LOGGER and d4LOGGER). The data-loggers require no configuration and are fully interchangeable with any other type of YieldPoint instrument (d-CABLE borehole extensometers, d-GMM, d-TILT, d-PLUCKER etc). Therefore arrays of instruments to monitor cable load and ground movement can easily be combined.

Clusters of instruments (4 per Logger) that are monitored using YieldPoint’s d4LOGGER can be wireless networked using dMESH – a 900MHz low cost Zigbee wireless mesh solution. Each low-cost wireless mesh (up to 20 modems) can be interfaced to a TCP/IP or WiFi network.

Case study: Pillar monitoring at 8000ft

As part of CEMI’s UDMN project YieldPoint has been working with Vale Canada’s to monitor a pillar in a hard-rock nickel mine located 8000ft underground in Sudbury, Ontario. A dense deployment of instruments was installed, including Borehole Pressure Cells and optical extensometers in addition to d-EXTO’s. By installing a dense deployment of borehole extensometers the deformation pattern in the pillar could be determined in considerable detail. By interpolating and contouring between instruments, Brad Forbes was able to provide the mine with a frame-by- frame playback of progressive deformation as the mining sequence evolved. A shear zone transecting the instrument array had a dramatic effect of the spatial distribution of deformation. The project team has recently submitted an abstract to the upcoming First International Conference on Underground Mining Technology to be held in Sudbury (Punkkinen et al, 2017). One conclusion is:

"Contouring between adjacent multi-point borehole extensometer measurements has provided an excellent depiction of the pillar behavior as development, using the current face destress procedure, approached a known shear zone."