Sigra manufactures and uses its own extensometers. These are multi-point devices that are cement grouted into boreholes. They consist of a central grout pipe for cementing and multiple rigid wires that are sheathed in plastic tubing. At the end of each of the wires is an anchor which is bonded into the cement grout. The movement of the anchored wires with respect to the top of the borehole may be measured manually using a dial gauge. The movement may also be monitored electronically and either be recorded on site or transmitted by a Sigra Field Data Logger.
A typical installation would be through an HQ drill string could involve 16 monitoring points. Typical installations would be to 50 m but may be much longer. The system may be used in vertical downwards, inclined or up holes.
The construction of the system means that the hole does not become a conduit for fluids. It is fully sealed on installation.
While the extensometers are generally used to measure extension they are able to be used to monitor moderate length shortening or compaction. There are some differences in construction if this use is envisaged.