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Integrating the Yieldpoint d-Exto MPBX
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Integrating the Yieldpoint d-Exto MPBX
Sensor Application Note #27
Revision 06/08/2017
Overview
The Yieldpoint d-Exto is a multi-position (1-6) borehole extensometer or MPBX. It differs from traditional
MPBX’s in that it arrives fully assembled and ready for installation. Typically, it is installed by grouting into a drill
hole. The assembly consists of a series of groutable anchors attached to fiberglass rods. These rods are
protected in Lexan tubing and terminate in a head assembly which integrates displacement transducers.
Transducers are available in several ranges including 125mm, 150mm and 250mm. The transducers measure
the relative movement between each anchor and the head assembly. These measurements provide for
understanding deformation of the rock being monitored.
The head assembly is usually installed at the collar of the drill, but can also be installed at the bottom of the drill
hole. Measurements are then relative to the collar or the bottom, respectively, as illustrated below in Figure 1.
(Figure 1)
Integrated to the head assembly are electronics to read each displacement transducer and convert it to a digital
format. A typical measurement response is shown below.
:YP,160341050,d3EXTO,41,+ 19.9,C, 16.12,mm, 16.96,mm, 16.78,mm, <CR><LF>
The head assembly also includes a RS-485 half-duplex (2-wire) interface for transmitting the digital string over
long distances. A two-wire RS-485 interface is utilized.
System wiring is detailed in the following section.
