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1. Important If a portable data logger is giving faulty readings or audio signals from all transducers a faulty readout unit must be suspected Another readout unit should be used to check the readings from the transducers and Soil Instruments Ltd should be consulted about the faulty readout unit Before proceeding to Steps 2 and 3 if possible the continuity should be checked between conductors and earthing screen of the electrical cable If a continuity exists a damaged cable is confirmed Step 2 The resistance across the two conductors of the electrical cable should be checked This can be done using a multimeter device across the two exposed conductors if the cable has not been connected to a terminal cabinet or can be done just as easily across the two conductors if the instrument has been connected to such a terminal or Dataloggers The resistance across the two conductors should be approximately of the order of 800 to 1809 The majority of these resistances arises from the transducer and the remainder from the electrical cable connected to the transducer Step 3 If the resistance across the two conductors is much higher than the values quoted in Step 2 or is infinite a damaged cable must be suspected Step 4 If the resistance across the two conductors is much lower than the values quoted in Step 1 say 800 or less it is likely that cable damage has occurred causing a short in the circuit Step 5 If the resistance is2. East SUSSEX THe TOL Standards Referenced Annex of l a 1 0 1d 2 3 2 60 2 0 20 5 4 50b amp 4 c Directive Technical Fire all Instruments Ltd ELI Low Voltage Directive 37 3 EEC as amended darss EEc Technical Documentation Issue 1 Cictober 2006 Vibrating Wire Instruments Ve hereby certify that the apparatus described above conforms with the protection requirements of F2 23 EEC Low Voltage Directive as amended by B3 BS EEC on the approximation of the laws of the Member States relating to Low voltage Equipment Signed M y E EU E Signatory Chris Rasmussen Technical Diirectar User Manual 17
3. from a concrete structural element they should be protected by a short length of plastic duct This will reduce the risk of the cable shearing off where it emerges from the concrete Once the cables have been fixed a full set of readings should be recorded for each instrument User Manual 9 Section 6 Monitoring Since the gauges are used to record changes in data and not absolute data the stage when the Base or Zero reading is recorded is flexible The reading recorded after the gauge has been fixed and prior to concreting is useful for record purposes only Where the effects of concrete curing are to be observed the Base reading should be recorded soon after the concrete has been placed and where necessary compacted All other operations such as removal of steel pile casing should have been completed before the Base reading is recorded Where loading tests are to be performed the Base reading for the test data should be recorded just prior to the beginning of the test Data from Vibrating Wire instruments can be recorded in 3 formats Period Linear or Engineering Units The required format should be established prior to any test beginning and remain consistent for the duration of the monitoring program The Soil Instruments Model 1030 amp 1050 Readout Loggers requires the Base reading to be recorded in Period units for automatic calculation of the applicable Engineering units See the Readout Logger Operation Manual for
4. situ materials Once a Young Modulus is calculated the following equations can be used to calculate the loading on the structural member at the location of the Strain Gauge User Manual 11 Force F 2 Stress S x Area A Where A Cross sectional area in m Where F units Newton s Where S units N m Stress S Young Modulus of Elasticity E x Strain Where E units N m Example calculation Steel pipe outside diameter 1 016m Steel pipe inside diameter 0 984m Calculated change from the strain gauges 54 688 Li Young Modulus of Elasticity of the steel pipe 200 000 000 000 N m Stress Ex 200 000 000 000 x 0 000054688 10937600 N m2 Area Ttr TE x outside diameter 2 2 TE x inside diameter 2 2 TE x 1 016 2 TE x 0 984 2 TE x 0 508 TE x 0 492 TE x 0 258064 TE x 0 242064 0 810732 m 0 760466 m 0 050266 m Force SxA 10937600 x 0 050266 549789 4N User Manual 12 Section 8 Temperature Effects The curing of concrete can generate large temperature changes It is therefore best practice to record temperature when you record strain readings You can then use the temperature data as well as strain data to analyse the behaviour of the structure Temperature induced expansions and contractions can cause real changes in stress in the concrete if the concrete is restrained these are superimposed on other load related stresses Differences between the coe
5. within the values quoted in Step 1 i e 800 to 1800 AND no continuity exists between conductor and earth screen and on checking the reading from the transducer it proves to be still unstable or wildly fluctuating it must be assumed that the integrity of the circuit is good A faulty transducer must be suspected and Soil Instruments Ltd should be consulted TIP If the location on site of cable damage is found the cable can be spliced in accordance with recommended procedure with suitably qualified personnel User Manual 14 reading from portable Yes There is no reason to logger stable sensible and audio signal steady Does a continuity exist between earthing screen and conductor NO l Check magnitude of resistance R between conductors Yes gt suspect a faulty instrument A damaged cable or H is very high v A severed cable is suspected causing very high or infinite resistance It must be suspected that the portable H is between 80 amp 180 Ohm A faulty readout is suspected Check reading of instrument with another unit Is reading OK with logger used firstis 4 Yes faulty Contact Soil Instruments Ltd User Manual R 80 Ohm gt damaged cable joint are suspected y A damaged cable is suspected causing a short See step 4 A faulty instrument i
6. VasEFECFUSTEWERKEFWECEFREFRECVERERFVRREFEE ECC EWEREFRCKFREFREVERERFRRVEFP ERR RL UE 16 Section 1 Introduction Embedment Strain Gauges were developed by the British Transport amp Road Research Laboratory to measure the internal strain in concrete structures These waterproof gauges were developed in conjunction with Imperial College London and incorporate the latest materials and techniques to make these gauges suitable for use in hostile conditions The nature of the instrument dictates that it is used to measure changes in strain i e change in length per unit length The gauges are designed for use in installations where they are cast directly into the mass of the concrete structure The pre casting of the gauges into briquettes is recommended only where it can t be avoided User Manual 3 Section 2 Equipment Supplied Strain Gauges come supplied at pre set readings dependent on the expected magnitude and direction of strains to be recorded Each gauge is supplied with a user specified length of cable moulded to the gauge sensing coil and a securing clamp The cable can be spliced to other cables for routing to a terminal location Cables can be routed over distances in excess of 1000 metres without degradation of signal Each gauge is supplied with a thick walled silicon rubber sleeve over each barrel see Figurel to protect the gauge barrel when it is tied to support bars during mounting Although gauges are checked prior t
7. fficient of expansions of the concrete and that of the steel in the strain gauge itself give rise to an apparent change in strain in the concrete This apparent change can be corrected for using the equation below Aue corrected Aue TC TC x Temp Temp Where Aue is the change in strain TC is the thermal coefficient of concrete in 4E C TC is the thermal coefficient of the gauge 12 2 ue C Temp is the current temperature Temp is the initial temperature User Manual 13 Section 9 Troubleshooting Guide If a failure of any vibrating wire transducer or its electrical cable is suspected the following steps can be followed The transducers themselves are sealed and cannot be opened for inspection The Troubleshooting Flowchart should also be followed if any instrument failures are suspected The steps below and the Troubleshooting Flowchart are applicable generally to any vibrating wire instrument Step 1 Before any of the following steps are followed the readout unit should be used to verify the stability of the reading and the audio signal from the portable logger should be heard The period reading from the transducer should not vary by more than 3 units and the audio signal should be crisp and of a consistent tone and duration An unstable wildly fluctuating reading from a transducer or an unsteady audio signal are both indications of possible problems with instruments or their related electrical cables
8. full details A monitoring schedule should be established by the engineers responsible for the structure so that the monitoring personnel are aware of the data gathering requirements User Manual 10 Section 7 Data Interpretation Data from strain gauges is generally presented in micro strain ue where strain is the ratio of the change in length per unit length AL Practical K factor 34080 Gauge calibration constant Conversion of Period and Linear Units to micro strain is carried out using either of the formulae detailed below Period Units HE K l T o Where HE Change in strain in micro strain K Gauge Calibration Constant Ty Base reading in Period units x 10 T4 Current reading in Period units x 10 B Batch Factor supplied with each gauge 10 107 is positive the resultant strain is tensile m Please note when Linear Units ue K F Fo x10 5 x B Where HE Change in micro strain K Gauge Calibration Constant F Base reading in f 1000 units F Current reading in f 7 1000 units B Batch Factor supplied with each gauge Please note when F Fy is positive the resultant strain is tensile The calculation of Load in a member using data from strain gauges is often complex The fundamental problem is determining the composite Young Modulus E of the member since it is often difficult to accurately determine the properties of the in
9. ion of the Installation All efforts must be taken to protect the gauge during concreting without significantly altering the reinforcement performance Where the gauge is installed in a vulnerable position good practice is to spray the area with marker paint as a warning and or cover the area with fine wire mesh It may be necessary to fix additional reinforcement steel around the gauge position to offer protection during concreting though this could affect subsequent gauge readings User Manual Section 5 Cable Routing and Protection Having established and marked the preferred route of the cables and decided upon the type of cabling arrangement to be adopted begin running the cables from the gauges furthest from the readout location Where cables are not to be ducted they should be strapped to the reinforcement in a position where they are least likely to be damaged using strong tape or cable ties Cable should be supported every 400 500mm and care should be taken to avoid over stretching the cables especially where movement loading could take place when placing the cage The reinforcement bars can be used to protect the cables for example by running the cables under the bars to reduce the risk of damage where vibrating pokers are to be used Where significant movement could take place the cable ties should be left a little slack and sufficient cable left free and positioned so that it cannot be damaged Where cables are to exit
10. no movement is allowed An indicative picture is below 4 4 ij Lid di d d di idi didi v 4 j A4 LG ij BN BZZASAESERAME od b did dididid didi Ad A dud didi didi d didi didi dididid d 3 02 Installation in Pre cast blocks An alternative to fixing to rebar is to pre cast the gauge into a block of concrete prior to this being cast into the main concrete pour This method takes more time but does protect the gauges better during the main pour To install in this way follow the steps below e Fabricate a mould for the desired size of block e Mix the concrete ensuring the mix is the same as that which will be used for the main pour Fill the mound and position the gauge in the middle of the fill User Manual 6 e Do not cure for more than 3 days or less than one day e Place blocks in position in main pour note comments on cable protection to follow in section 4 TABLE INDICATING SUGGESTED DIMENSIONS FOR SUPPORT BARS Refer to Figure 1 Gauge Length w mm INFORMATION If the reinforcement spacing exceeds 3 x A then bar size B should be increased The gauge positions should be marked if possible on the reinforcement cages and the cable route indicated IMPORTANT the final position of the gauge should be accurately recorded since this detail will be required for interpretation of its readings User Manual 7 Section 4 Protect
11. o leaving Soil Instruments damage can occur during transit It is suggested that the gauges are visually checked immediately upon receipt Additionally it is prudent to check the operation using a vibrating wire readout device to ensure steady readings if an audio signal is available on the readout device this can give a good indication of the quality of the signal Prior to installation secure the coil assembly to the gauge using the securing clamp as shown above Before installation a note should be made of the batch factors for the Strain Gauges for future data interpretation User Manual 4 Section 3 Installation The gauges are supplied sealed and pre tensioned no adjustment is necessary or possible It is good practice to connect a readout to the gauge and ensure that the reading in free air is stable and around the mid range position Gentle pressure applied to the gauge ends i e small compression should cause the F2 1000 reading to decrease The approximate mid position reading of the strain gauge is as follows 830 Hz 690 F2 1000 Linear 12038 Period units x 10 For sweep excitation readout units set the sweep range to 400 1200 Hz 3 01 Installation in Concrete The gauge can be installed in concrete in one of two ways either by direct casting following attaching the gauge to or between rebars or by pre casing into a concrete block which is then cast into the main concrete pour When affixing gauges to reba
12. r for direct encasing into concrete care must be taken to avoid over range forces being applied to the gauge end blocks by the speed and or weight of concrete being poured Do not tie the gauge too tightly to the rebar as this can move during pour and or curing and thus damage the gauge If placing the gauge between rebar please note the following e Wrap self amalgamating or a few turns of plastic insulating tape around the gauge where the soft wire ties will contact it to act as a shock absorber e Use only soft iron wire as used by rebar erectors and make at most 3 turns around the gauge each 3 4 cm from the end blocks either side of the coil e Loop the wire by twisting between the gauge and the rebar either side to allow for some expansion movement Above soft iron wire used to secure the gauge between reinforcing bars User Manual OA Rk A D D fe ee Le e eb ON i AR DO OD A As Med AB tet 08 A lt ew Ok et LL ee ee ee Hi E t t x t Li E E 1 B H Li H 2 E i 2 E H z BH amp ES f z E z H 2 E 2 t t H z i t Li Above soft iron wire used to secure the gauge between reinforcing bars Plan View As an alternative to the above small rebar sections cut to length can be used to replace the soft steel wire with cable ties attaching these short lengths to the gauge and the main rebar If this method is selected under no circumstances over tighten the cable ties so that
13. s alternative logger No v possible Contact Soil Instruments Ltd 15 Appendix A Vibrating Wire Data Frequency Units f The tension of a wire can be measured by registering the frequency note at which it naturally vibrates If the wire is plucked electronically the frequency at which it vibrates can be measured The most common units used to express frequency are Hertz Hz or Kilohertz KHz The disadvantage of these units is that there is no linear conversion from Hertz to change in wire tension Linear Units L In order to overcome the problem of a linear conversion described above the frequency value can be squared thereby rendering it linear but quite large To reduce its size it is often divided by 1000 or multiplied by 107 The expression f2 1000 or f2 x 10 is the most commonly adopted as a linear digital output Period Units P Electronic devices and digital technology often utilise the counter function available in some common circuits Period Units represent the time taken for the wire to vibrate over one full oscillation expressed in seconds Due to the very small size of the number generated most equipment manufacturers display the unit multiplied by 10000000 or 10 The relationship between Period Units and frequency units is expressedas Pu 1 frequency Period units are therefore convenient to measure but do not have a linear relationship to change in wire ten
14. scil INSTRUMENTS Vibrating Wire Embedment Strain Gauge User Manual Man142 6 0 3 06 08 14 P Day Andy Small Chris Rasmussen Manual No Revision Date Originator Checked Authorised for Issue User Manual Contents Section 1 Section 2 Section 3 3 01 3 02 Section 4 Section 5 Section 6 Section 7 Section 8 Section 9 Appendix A User Manual ETRE OCLUICENOND ee eT UR 3 EGUIDMENT SUPPE ais eres noa Tos eE Ec pa a IRE EIFE RACK EuEREI VEDI EU E MEVM MER ENA NA UR EAEM EMI IA EEEN MEET KNEE 4 Installations EC ORRARREIMEERPRRRFIRISRRKE MC PIRCDNRU RR KRRDRERX ERRARE KM MERC ZRU RR VERREM NM RR REN ER ESO DENS 5 Installatlon IirCOMChCUS sanchialeiin UE 5 Itistallatior dE PES Gast DIOCKS avrete ais daateatnadars We oat de baa o ics vi ied aU i a raid CE Lapi 6 Protection of the Installation s kunana aaa E RRERRE RA E REEERR RM SEEEENN NE ERE 8 Cable Routing and Protection 4sekas xkERRXRRAXERREERSREKEEE REQUE ci IEEE AXECR ERE AEKEEM I REDE EKEE VE KEEN RE E 9 MODBIEOFIHG eer a il OCC ROO GARDER RUGGED CORRER errr errr rrrtr rrr rer rrr rr rr rrr Tr 10 Data Interpretation sciswesssrsncseveccensevavencvessedessevsseusveversrsveusveusversedssvessseucseresesseswrescrenne 11 Temperature Effects vix vuve Vo Yu a FEEKRRERKU CREE FEK VERE 13 Troubleshooting Guld6 iissesunu a usssVudu CsVAMEnTELA MU M EE AA EK M EV QM MEM MM M REU M EUM MIA E MC RR UN M RR E 14 Vibrating Wire Data iissssexsw x ssxiuvRs
15. sion Calibration Constants Fach instrument is supplied with a Calibration Constant value to convert the raw data into engineering units The value of the calibration constant will vary depending upon the engineering units into which the data is to be converted and the readout units For example the data from piezometers may convert into Kg cm mH20 Bar Psi etc and therefore the Calibration Constant for each will be different Some instruments have Generic Calibration Constants and others are calibrated to generate the Constant The constant is generated by using the following calculation Constant K Range Reading Full Range Reading Range Zero x 10 Soll INSTRUMENTS Bell Lane Uckfield East Sussex t 44 0 1825 765044 e info itmsoil com TN22 1QL United Kingdom f 44 0 1825 744398 w www itmsoil com Soil Instruments Ltd Registered in England Number 07960087 Registered Office 5th Floor 24 Old Bond Street London W1S 4AW User Manual 16 DECLARATION OF CONFORMITY WITH COUNCIL DIRECTIVE 3 23 EEC as Amended by 93 68 EEC Date of Issue 12 October 2008 Dol Ref s ll CEA VvDANSVITB Directive FA 23 EEC Low Voltage Directive as amended by 93 6 o EEG Conforming Apparatus All Vibrating V ire Instruments Manufactured by Soll Instruments Ltd see pages 3 10 af Technical File Manufacturer Soil Instruments Ltd Responsible Person Chris Rasmussen sul Instruments Ltd Rell Lane Uckfield
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