•Four surface extensometers
were installed in 2004
to measure changes in distance
between fixed points spanning
major fissures on South Peak
•A fifth extensometer
was installed in summer 2006
These sensors were custom
designed and fabricated by Durham Geo Slope Indicator for the project.They consist of aircraft cable (very low
thermal expansion) that runs in a conduit and is anchored at one end and runs
over a pulley at the head (shown).At
the top of the pulley is a very sensitive rotary potentiometer that is
calibrated to provide deformation in fractions of a millimetre corresponding
to rotation of the potentiometer.The
anchoring of the cable limits the lower resolution, which is likely
millimetres rather than a fraction of.These installations have been very robust and dependable.
