d-GMM (Spectre) Geotechnical Ground Movement Monitor

The SPECTRE d-GMM (Ground Movement Monitor) integrates a rugged magneto-strictive displacement sensor for geotechnical monitoring of rock deformation. It has an on-board microcontroller running YieldPoint’s proprietary d-Tech signal processing and transmission technology to provide a high precision single point displacement sensor.

The microcontroller provides linearization, temperature compensation and outputs an ASCII encoded RS485 signal digital signal. Output signals can be transmitted over 250m/900ft without distortion. Each instrument is individually calibrated to ensure that the resolution (<0.01mm) and accuracy (0.25% typical) are an order of magnitude better than for similarly priced technology.

The digital form of the signals eliminates the necessity for expensive analog-to-digital conversion and results in low cost monitoring peripherals that output data in real world units (mm and degC). The instrumental is fully compatible with d-Logger, d-Mesh and d-Reader and can be networked using the IoT gateway.


  • Borehole size: 30mm+
  • Core Technology: magnetostrictive displacement sensor
  • Output Signal: RS485 serial (9600,8,N,1) ASCII-encoded digital signal.
  • Stroke (F.S.): 145mm, 250mm. Temp: -40 to 125oC
  • Displacement Resolution: 0.01mm with hand held readout
  • Displacement Linearity: typically 0.25% F.S
  • Displacement Accuracy: better than +/- 0.5mm.
  • Temperature Range: –40 – 125oC
  • Temperature Accuracy: +/- 2oC –Digitally trimmed at 0oC and 25oC
  • Temperature Resolution: 0.1oC
  • Temp coeff for eddy current sensor : <0.01%FS/oC (0-50oC)

To order please specify:

  • Lead wire length
  • Lead wire polyethylene cover length


  • Individually calibrated for highest accuracy
  • High accuracy (0.5% FS) and resolution (0.01% FS)
  • Digital (d-Tech) 145mm stroke length
  • Individual calibration with coefficients stored in memory
  • RS485 Output signal (9600, 8, N, 1) ASCII encoded
  • Microcontroller provides output in real world units (mm and oC)
  • Unique ID facilitates plug-and-play networking
  • Digital temperature sensor for accurate compensation
  • Magnetostrictive, non-contact technology for immunity to hostile environments
  • Easy to interface with data loggers (d-LOGGER), Ethernet and radio telemetry
  • Competitively priced

Manual readout:

YieldPoint’s low cost d-READER readout unit or the new d-TAB. 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-TAB.

Automated data retrieval:
Clusters of instruments (4 per Logger) that are monitored using YieldPoint’s d4LOGGER 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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