YieldPoint’s recognizes that in many mining situation fast deployment of an ungrouted borehole extensometer is preferable. The d-MPBX is a unique 1 to 6-Point Multiple Point Borehole eXtensometer (MPBX) based on a single rod design. The anchors are fitted with stainless steel torsion springs that secure the instrument in a 38-54mm borehole. The d-MPBX incorporates digital signal processing to result in dramatically improved accuracy compared to similar priced existing technology.

Design features of the d-MPBX involves a stiff hermetically sealed and potted central core that includes all of the electronics. The anchors are a simple aluminum tube to which are attached torsion springs that secure the anchor against the borehole wall.

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 °C). 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 500m of lead-wire. If broken the lead-wire can be twisted and taped together.


  • ‘Robust’ design with high strength filament wound fiber glass core
  • Up to 6 spring loaded anchors
  • Does not require grouting
  • 150mm (6 inch) stroke length
  • High individual sensor accuracy (0.3%FS) and resolution (0.01mm)
  • 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 33-50mm 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 °C
  • 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-MPBX can be collected using YieldPoint’s d-LOGGER dataloggers (d1LOGGER, d4LOGGER and BluLogger). The data-loggers require no configuration and are fully interchangeable with any other type of YieldPoint instrument (d-CABLE, dEXTO 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 (up to 32 / logger) can be wirelessly monitored using YieldPoint’s Bluetooth 5 BluLogger or for longer range using 1for1 radios– a 900MHz low-cost Zigbee wireless mesh solution. Low cost battery powered wireless gateways can be interfaced to a TCP/IP or WiFi network. dMPBX can be configured with BluLink and read using the ViewPoint Android App.


Results and Data Analysis for a d-MPBX.

This presentation outlines the results from a d-MPBX installed in a salt mine. Annual variations in roof velocity are detected with higher rates of movement in the humid summer months. Analysis of the d-MPBX data revels that this is only a skin effect localized close to the excavation surface. The deeper movements indicate an almost constant , albeit stair-cased, long-term rate of movement versus time.