The single rod extensometer employs a rod, anchored at one end of a drillhole, passing into a reference tube fixed in the drillhole collar. Relative movement between the end anchor and the reference tube is measured with either a dial depth gauge or a vibrating wire displacement transducer inserted through the reference tube and registering on to the free end of the rod. A range adjustment screw fitted to the end of the rod extends the reading range beyond that of the depth gauge. Multiple rod installations monitor displacements at various depths using rods of varying length. Several single rod units may be installed in close proximity in boreholes of small diameter; alternatively several rods may be installed radially in a single large hole.

Each rod individually isolated by a plastic sleeve. The complete assembly is grouted in place, fixing the anchors to the rock or soil but allowing free movement A multipoint reference housing receives all rods from the one drillhole installation. Facilities are available for manual or remote read- out and data logging. Rod extensometer units can, when required, be surface mounted, for example to measure displacements across tension cracks or joints, and can be buried in fill or cast in concrete.

Reliable, accurate, simple to Install and read.
Free from creep, kinking and other inaccuracies associated with tensioned wire systems.
The simple single rod instrument is ideal for safety monitoring during construction activities.
Monitoring and control of construction by the New Austrian Tunnelling Method (NATM).
Can be connected to Vibrating Wire displacement transducers for remote reading and data logging.
Installation in boreholes at any orientation or can be cast in concrete, surface mounted or buried in fill.
Up to 8 rods per drillhole with manual readout or 6 with vibrating wire displacement transducers.
Operating lengths in excess 1OOm possible.

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