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RMT's ATEX Approved Remote Reading Extensometer and Telltale System


                    AND TELLTALE SYSTEM

Issue:              ISSUE 2

Date:               JULY 2009

Golder Associates (UK) Ltd, Bretby Business Park, Ashby Road, Stanhope Bretby, Burton on Trent, Staffordshire DE15 0QD –
Tel:+44 (0) 1283 522201 – Fax: +44 (0) 1283 522279 – E-mail– Registered Office: Golder Associates (UK)
          Limited trading as Golder RMT, Attenborough House, Browns Lane Business Park, Stanton-on-the-Wolds,
                                 Nottingham NG12 5BL, Registered in England No. 1125149
                                                              Golder Assocaites (UK) Ltd

                                                               Page No.

1.     INTRODUCTION                                                      1

2.     MEASUREMENT PRINCIPLE                                             1

3.     SYSTEM COMPONENTS                                                 1

4.     TRANSPONDER OPTIONS                                               1

5.     DATE CAPTURE                                                      2

6.     CHANNEL ALLOCATION AND REPLACEMENT OF                             3

7.     SYSTEM TOPOLOGY                                                   4

8.     DATA STORAGE AND ANALYSIS                                         5

9.     ATEX APPROVAL                                                     6

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                                                                  Golder Assocaites (UK) Ltd


       Golder Associates remote reading extensometer and telltale system offers a
       range of compatible transponders designed for measuring rock displacement
       in the roof and sides of mine roadways and other tunnels and which can be
       read in a variety of ways. The system has ATEX         ε  x  I M1 EEx ia I
       certification for use in explosive atmospheres in mines. The transponders
       have high resolution and repeatability to better than 0.5mm.

       The simplest configuration comprises individual transponders which are read
       by connecting each, in turn, to a portable readout unit. The data is noted in a
       book and analysed by subsequent input to a purpose written Excel
       spreadsheet. However the system has the advantage that up to 100 dual
       height or 50 four height transponders can be connected together using twin
       core cable and read from a single location. This reading can be accomplished
       locally with the portable readout unit or by a permanent installation which
       relays the data to a remote PC which can be located on the surface. There
       can be up to 2km of cable between the underground reading position and the
       most distant transponder. The remote PC can be up to 10km from the
       underground monitoring unit. One PC can monitor up to 4 sets of


       The highly accurate measurement system uses non contacting electrical
       components and works well in wet and dusty conditions. It has been designed
       and engineered for coal mining applications. The principle employed is that
       the inductance of a coil will vary depending on the position of a ferrite rod
       moving within it. The on-board electronics convert the inductance to a
       frequency which is transmitted down the line when the transponder is

       The variation in frequency with displacement is not perfectly linear and a
       linear conversion is carried out by the analysis software supplied.


       A system will comprise a mixture of measurement transponders temporarily
       connected to a portable readout or permanently connected to a data
       transmission system.


       A variety of displacement measuring transponders can be used with the
       system, ranging from a single channel closure transponder to a multiple
       anchor, fully grouted extensometer. The range of available transponders
       covers 4 main categories, telltales, wire extensometers, closure transponders
       and grouted extensometers.

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                                                                 Golder Assocaites (UK) Ltd

       The telltale transponders are available in single height, dual height or triple
       height versions. These are easy to install, wire extensometers designed to fit
       into 35-45mm diameter boreholes with a stainless steel wire attached to each
       borehole horizon using a simple spring anchor. These wires transfer the
       relative axial displacement of the rock to the measurement mechanisms
       located within the transponder body. They are distinguished from the wire
       extensometers by incorporating concentric visible indicators with 25mm
       coloured bands and millimetre scales to allow direct visual reading, as well as
       the electronic measurement system, and by utilising the weight of the visual
       indicators to tension the cables. They are very similar to Golder Associates
       (UK) Ltd’s well established range of visual telltales and are designed to be
       used in vertical holes only.

       The wire extensometers do not have the visual reading facility but have the
       advantage of a spring tensioning mechanism allowing them to be deployed in
       non-vertical boreholes. They are available in one, two, three and four height
       versions. The measurement mechanisms of both the remote reading telltales
       and wire extensometers are housed within a plastic tube located in the mouth
       of the borehole. The length of this tube depends upon the number of
       measurement “bays” or anchors (a) and can be calculated from equation 1

              Length = 0.325 x a (metres)          Equation 1.

       The length of the transponder tube will determine the minimum height of the
       bottom anchor in the hole.

       The closure transponder is a special single anchor version of the wire
       extensometer, designed to be mounted on the rock surface and used for
       general displacement measurement such as roof to floor or side to side
       closure in a tunnel.

       The groutable extensometer, deploys the measurement mechanisms within
       individual sealed plastic tubes grouted along the full length of the borehole.
       Measurements are made of the extension of each tube within the hole. There
       is therefore no limit on the number of bays which can be installed in a single
       hole, the only limitation being imposed by the minimum bay length of 325mm
       and the hole diameter.

       The standard measurement range for all the transponders is 0 - 75mm per
       “bay”, a “bay” being the section of borehole between two adjacent anchors.
       This provides a measurement resolution of 0.04 mm. Transponders with a
       higher resolution and smaller range (0 - 40mm) can also be manufactured for
       specialist applications.


       Data from the transponders can be read using the battery powered RRT 1442
       PR portable readout unit or a permanently installed RRT 1342 IUA local
       interrogation unit which can also relay the data to a remote PC on the

O/NEWNET/INST/MAN /RRTT&EXTEN/ATEX…              July 2009                     Page 2 of 7
                                                                  Golder Assocaites (UK) Ltd

       Full instructions for using the RRT 1442 PR are given in a separate
       Operational Guidance Data Sheet. The unit contains a rechargeable battery
       and battery condition indicator and has two connectors (brown and blue) for
       attachment to the twin wires from a chain of transponders. The only controls
       are an On/Off switch and a Channel

       Select switch. Each transponder will have a number of unique channel
       identifiers allocated to it depending upon the number of anchors (see channel
       allocation section below) and the unit can be used to select a channel and
       then take the two readings (Low and High in Hertz) which are associated with
       that channel. The LCD display also shows the current consumption for each
       channel as it is selected and an indication of whether the Channel is “Locked”
       on. This information is important for confidence and fault diagnostics.

       Use of the portable readout requires the user manually to note the readings in
       a book and then transfer them to a surface computer spreadsheet for
       analysis. A similar approach can be used with the permanently installed RRT
       1342 IUA readout option in “Local” mode, but this unit also incorporates the
       option to transmit the data to a PC located on the surface.

       The RRT 1342 IUA has the same controls and display as the portable readout
       but, in addition, has a switch to change from “Local” to “Remote” mode. In
       “Remote” mode it is controlled by the “RRTelltales” and “Boltmon” software
       running on the surface PC which it is connected to via up to 10km of twisted
       pair cable, a RRT 1345 SC surface communication unit and a RRT 1345 SBU
       surface barrier unit. The RRT 1342 IUA must be permanently wired to an
       Intrinsically Safe 12v volt power supply, which can be supplied by Golder
       Associates (UK) Ltd if required. Further details of this option can be found in
       the Remote Reading Telltale System Brochure and User Manual and the
       RRTelltales Software Manual. The surface reading system can be used with 3
       and 4 height remote reading extensometers as well as the standard 2 and 3
       height telltales, though this aspect is not currently documented in the above
       mentioned manuals. Up to 4 RRT 1342 IUA units can be connected to a
       single surface PC, via a single RRT 1345 SC surface communications unit
       and RRT 1345 SBU surface barrier unit.


       A two height telltale or extensometer will be allocated a single Channel
       number at the time of manufacture and the data from this Channel, when
       selected, will comprise 2 frequencies (High and Low) measured in Hertz. The
       high frequency reading (e.g. 13550) will relate to the upper “bay” (B indicator)
       and the low frequency reading will relate to the lower “bay” (A indicator).

       A four height extensometer will be allocated two consecutive Channel
       numbers at the time of manufacture providing a total of four readings, one for
       each “bay”. The higher numbered Channel will provide the readings from the
       upper 2 bays and the lower numbered Channel will provide the readings from
       the lower 2 bays. This is explained in detail on the RRME04 extensometer
       instruction sheet.

       A single height telltale, extensometer or closure transponder will have one
       Channel number allocated to it and only one of the readings (Low frequency
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                                                                   Golder Assocaites (UK) Ltd

       band) will be used. A three height telltale or extensometer will have two
       Channels allocated to it. The highest Channel will just have one of the
       readings (Low frequency band) used, representing the upper bay (C
       indicator). The lower Channel number will utilise both frequency bands, as for
       the two height version (B and A).

       The maximum number of Channels that can be connected together in one
       chain of transponders is 100, giving readings from up to 200 bays. This could
       comprise 100 single or two height telltales, 50 three height or four height units
       or an appropriate combination of all these transponder types.

       It is not necessary to connect all transponders to a system at once. In a
       typical tunnel drivage situation additional transponders can be added as the
       tunnel progresses and the surface monitoring system, if used, will
       automatically detect their addition and allow reconfiguration.

       For the system to operate correctly it is essential that every Channel number
       in a connected chain or loop is unique. However there is no necessity for
       consecutive transponders to have consecutive Channel numbers; they can be
       in any order. Therefore, if a transponder needs to be replaced for any reason,
       it can be replaced with a transponder allocated either the same Channels as
       the original or any other Channel numbers which are not currently connected.
       It is therefore recommended that the mine carry a small stock of spare
       transponders with unused Channel numbers. If, for example, a transponder
       with Channels 49 and 50 failed, it could be replaced with a spare transponder
       with Channels 79 and 80, provided there is no transponder with these
       Channels currently connected. The mine could then order a replacement
       transponder with Channels 49 and 50 to replenish its stock of spares.


       The system is extremely flexible in the ways that individual transponders can
       be connected together in a chain or ring. Each transponder is supplied with
       two 3m twin core cables attached (or one 6m cable according to customer
       preference) and the simplest form of connection involves running one cable
       back towards the previous transponder in the chain and one forward towards
       the next one. The gaps between these cables can be filled with standard
       cable of the appropriate specification supplied in bulk. Connections between
       cables can be made using simple grease filled crimps, as supplied with each
       transponder. Alternatively the colliery’s own preferred electrical junction boxes
       can be used. In this configuration the transponders are connected in series.

       The transponders can also be connected in parallel. This is particularly useful
       when a transponder needs to be run into a crosscut or if it is desirable to run
       a cable along the side of a roadway and run a single connecting cable to each
       transponder mounted in the centre of the roadway. In this configuration, with
       the transponders connected as “spurs”, only one of the cables supplied
       connected to the transponder is used and the other can be cut off and/or
       terminated, provided the two conductors are not short circuited. Alternatively,
       if requested, the transponders can be supplied with only one cable attached.
       This configuration also has the advantage that, if the spur is broken for any
       reason, the rest of the system will continue to operate provided, again, that
       there is no short circuit.

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                                                                   Golder Assocaites (UK) Ltd

       Combinations of these two configurations are also possible as illustrated in
       figure 1. In all cases it is important that the blue leads are always connected
       to each other and similarly the brown leads are connected to each other. Blue
       leads should never be connected to brown leads.

              Figure 1. Example of complex transponder topology.

       It is also possible to run a cable back from the furthest extreme of the chain to
       the reading point, forming a ring. This will ensure the ability to continue to
       obtain readings for all transponders, even if the ring is broken in one place.

       The main limitation to connecting transponders is that any one chain is limited
       to a maximum included cable length of 2km, although a ring could be
       somewhat longer. Each chain or ring can be permanently connected to an
       RRT 1342 IUA local interrogation unit for local reading and data transmission
       to the surface or temporarily connected to a battery powered RRT 1442 PR
       portable readout unit for local reading only.


       If data is obtained locally in a notebook, then this can be analysed using a
       series of purpose written Excel spreadsheets, supplied by Golder Associates
       (UK) Ltd, which can store and present the data graphically. The data from
       each transponder will be stored in a separate spreadsheet, the type of
       spreadsheet used depending upon the type of transponder. The
       spreadsheets can produce graphs as either relative anchor displacement
       against time (with the mouth of the hole used as the reference point for each
       anchor) or as cumulative bay strain against time which provides a more
       intuitive representation of the distribution of displacements within the hole.

       If the data is transmitted to, and stored on, a surface PC then there are more
       ways of dealing with it. The user interface program, RRTelltales, which runs
       permanently on the surface PC, displays the data for immediate information
       and also handles data storage. A typical RRTelltales screen display is shown
       in Figure 2.

O/NEWNET/INST/MAN /RRTT&EXTEN/ATEX…               July 2009                      Page 5 of 7
                                                                    Golder Assocaites (UK) Ltd

                    Figure 2. RRTelltales user interface screen

       The right hand side of the screen displays the latest reading for each
       transponder. For one or two height transponders, a single line is used for
       each, and for three or four height transponders two lines on the display are
       used. This part of the screen also shows rate of movement in mm/hour for
       each bay and whether any bay or the total movement has exceeded a preset
       warning level. The left hand side of the screen allows the user to scroll
       backwards for up to one week and view a single reading for each bay for
       each day. This provides a fast, real time impression of how movement has
       been developing.

       This RRTelltales program stores the received data such that it can accessed
       and analysed in more detail offline. A separate “PRC” file is created to store
       all the data from a system for each day. Another program, “PRC Analysis”
       can be used to read these files into an ACCESS database and to select data
       from this database for plotting in Excel. This provides the user with full control
       of the amount of data plotted and how it is presented.


       The system is approved under the EU ATEX Directive 94/9/EC by three
       certificates as follows:

       MECS 02ATEX 7013, covers the Surface Communications System,
       comprising the RRT 1345 SC and SBU units.

       SIRA 05ATEX 2248X, covers the RRT-1442-PR RRTT/EXTO Portable

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                                                                  Golder Assocaites (UK) Ltd

       MECS 02ATEX 4014, covers the Remote Reading Telltale System,
       comprising a Local Interrogation Unit connected to a number of transponders
       via a single two-core cable arranged as a “daisy chain”. It also includes
       connection to the Surface Communications System. This certification
       specifies that the power supply must be separately certified intrinsically safe,
       nominally 12v.

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