Users’ Manual
EDS-71V/P Single point borehole extensometer
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9
3 INSTALLATION OF SINGLE POINT BOREHOLE EXTENSOMETER
NOTE:
Procedure described below is for installing single point borehole extensometer with fibreglass
connecting rods for in a downward sloping hole using groutable anchors. For installation in
an upward to horizontally sloping borehole, or for using packer anchors, modify procedure
suitably.
Due to many permutations and combinations in type of BHE required by users and widely
varying conditions encountered from site to site, the procedure described is suggestive and
may be used as a guide only. The installation personnel will have to use experience in
devising the best method of installation.
3.1 Site preparation before installation
3.1.1 Drill hole of 50 mm diameter to a depth of 0.8 m more than specified length.
NOTE:
In case borehole extensometer is to be mounted horizontally and design permits, it is
desirable to provide a downward slope of 5
o
or more to borehole. This facilitates grouting of
anchors as grout can easily flow in.
3.1.2 At mouth of borehole, increase diameter of drilled hole to 63 mm up to a depth of 300 mm for 50
mm displacement sensor or 425 mm for 100 mm and 560 mm for 150 mm displacement sensor.
This is for wrapping outside of housing with rags or jute cloth strips soaked in cement during
installation.
3.1.3 Insert reference head assembly centralised in the 63 mm borehole. Taking holes on flange as
reference, drill four holes 12 mm diameter x 125 mm deep for fastening flange to borehole. Remove
reference head assembly from borehole.
3.1.4 Wash hole clean up to bottom by pumping in fresh water.
3.2 Check sensor before installation
The cable from Vibrating wire sensor is four wired. Red and black cores are for frequency signal while
green and white are for temperature monitoring through a thermistor. The cable from Potentiometric sensor
is also four wired. Red and black cores are for (+) and (-) excitation while green and white are for (+) and
(-) output. Check working of sensor as follows:
3.2.1 Connect sensor to portable indicator model EDI-51V (for vibrating wire sensor) and EDI 53P (for
Potentiometric sensor. With displacement shaft in retracted position enter sensor constants from
Test Certificate and set reading in engineering units at zero mm.
NOTE:
Data entry of sensor constants
in the EDI-51V/ EDI 53P will later on be used to set sensor in
flanged housing during installation process.
3.2.2 Using a scale, move the shaft by about 25 mm. The indicator should read around 25 mm. This
change in reading ensures proper functioning of displacement sensing system. The sensor can
now be installed in the housing assembly (5) when required.
Figure 3.1 – Displacement sensor
Displacement (mm)
V W sensor – L in mm.
Potentiometeric. sensor – L in mm.
50
290
325
100
420
425
150
550
525
L
