Interfels Digital Tape Extensometer is specially designed for displacement measurement in tunnels, excavations, retaining walls and other structures.

The instrument measures displacement between pairs of reference studs or eyebolts permanently grouted into holes on the surface of a structure or excavation. Demountable extension studs are available for fixing in locations where, for instance, additional shotcrete is applied to the surface to be monitored.

The tape extensometer unit comprises a stainless steel measuring tape (in a tape reel) with equally spaced precision punched holes and a "hook" connector. The other end of the tape is also fitted with another hook connector. It also incorporates a tape tensioning device and a digital LCD readout.

The instrument is engaged between two reference studs by the hooks at either ends and utlising the knurled collar, the tape is tensioned and the distance is given as summation of the readings from the tape and the digital LCD. Repeatability of 0.1mm is achievable with an experienced operator.

An initial base reading is taken and by comparing it with subsequent readings change is distance between any pairs of reference points can be determined.