Tape Extensometer

Geonor, Inc - Precision Instrumentation


The RST Tape Extensometer is a portable device, designed to measure the relative distance between reference anchors fixed to the excavation or structure.

The instrument consists of a precision punched steel tape incorporating a repeatable tensioning system and dial gauge readout. To obtain a reading, the swivel hook, on the fixed end of the extensometer, is connected to the stainless steel eye on the anchor. The tape is unwound, allowing the tape swivel hook to be attached to the opposing anchor eye. Coarse tension adjustment is accomplished by positioning the pin of the extensometer in one of the precision punched tape holes. Fine tension adjustment is by rotating a knurled sleeve until two index marks align. A precision dial gauge measures this fine adjustment, with the tape held under a consistent repeatable spring force. The instrument is then read by noting the tape position, and subtracting the dial gauge reading.

For maximum accuracy, we recommend that one instrument be dedicated to each project, a calibration frame be regularly used to check stability and determine a temperature correlation, new base readings are established if the tape is changed, and the instrument temperature be allowed to stabilize prior to use.


  • Rugged, simple design.
  • High accuracy and reliability.
  • Rapid one man operation.
  • Applicable in any orientation.
  • Supplied with robust, water/dust proof carrying case.


  • Mine roof sag.
  • Measurement of tunnel convergence.
  • Deformation of excavations.
  • Surface measurements for slope stability.
  • Monitoring and control of NATM (New Austrian Tunnelling Method) construction.


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