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Geokon 4000 Series, Instruction Manual

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Geokon 4000 Series Instruction Manual Download Page 12

6 

      3.5. Lightning Protection 

 
The Model 4000 Vibrating Wire Strain Gage, unlike numerous other types of instrumentation 
available from Geokon, does not have any integral lightning protection components, i.e. 
transorbs or plasma surge arrestors. 
 
Here are a few suggestions; 
 

  If the gage is connected to a terminal box or multiplexer components such as plasma 

surge arrestors (spark gaps) may be installed in the terminal box/multiplexer to provide a 
measure of transient protection.  Terminal boxes and multiplexers available from 
Geokon provide locations for installation of these components. 

  Lighting arrestor boards and enclosures are available from Geokon that install at the exit 

point of the instrument cable from the structure being monitored.  The enclosure has a 
removable top so, in the event the protection board (LAB-3) is damaged, the user may 
service the components (or replace the board).  A connection is made between this 
enclosure and earth ground to facilitate the passing of transients away from the gage.   
See Figure 5.  Consult the factory for additional information on these or alternate 
lightning protection schemes. 

  Plasma surge arrestors can be epoxy potted into the gage cable close to the sensor.  A 

ground strap would connect the surge arrestor to earth ground, either a grounding stake 
or the steel structure itself.  

 
 

Terminal Box/Multiplexer

Instrument Cable

LAB-3 Enclosure

LAB-3 Board

VSM-4000

Steel Beam

Ground Connections

Surface

(usually buried)

 

 

Figure 5 - Lightning Protection Scheme 

 
 
 
 
 
 

 

 

Summary of Contents for 4000 Series

Page 1: ...ritten consent of Geokon Inc The information contained herein is believed to be accurate and reliable However Geokon Inc assumes no responsibility for errors omissions or misinterpretation The information herein is subject to change without notification Copyright 1981 1996 2004 2005 2008 2009 2010 2012 2013 2014 2016 by Geokon Inc Doc Rev Z 8 16 ...

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Page 3: ...re are no warranties except as stated herein There are no other warranties expressed or implied including but not limited to the implied warranties of merchantability and of fitness for a particular purpose Geokon Inc is not responsible for any damages or losses caused to other equipment whether direct indirect incidental special or consequential which the purchaser may experience as a result of t...

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Page 5: ...ces 12 5 2 2 Steel Surfaces 12 5 3 INSTALLATION ON CONCRETE SURFACES USING ANCHOR STUDS 13 6 TAKING READINGS 13 6 1 OPERATION OF THE GK 403 READOUT BOX 14 6 2 OPERATION OF THE GK 404 READOUT BOX 14 6 3 OPERATION OF THE GK 405 READOUT BOX 15 6 4 MEASURING TEMPERATURES 15 7 DATA INTERPRETATION 16 7 1 CONVERSION OF THE READINGS TO STRAIN CHANGES 16 7 2 CONVERTING STRAINS TO STRESSES 16 8 TROUBLESHOOT...

Page 6: ...NDING ON AXIS XX 8 EQUATION 4 MAXIMUM STRESS 8 FIGURE 6B STRAIN GAGES MOUNTED ON FLANGES NOT RECOMMENDED ON TUNNEL ARCHES 9 FIGURE 6C AXIAL STRAIN MEASUREMENT AND BENDING MOMENT ABOUT YY AXIS ONLY 9 FIGURE 6D AXIAL STRAIN AND BENDING MOMENTS ABOUT XX AXIS 10 FIGURE 6E AXIAL STRAIN AND BENDING MOMENT AROUND AXIS XX NOT RECOMMENDED 10 FIGURE 7 PROTECTION ON DRIVEN PILES 11 FIGURE 8 INSTALLATION USIN...

Page 7: ... by plucking the wire and measuring its resonant frequency of vibration The wire is plucked and its resonant frequency measured by means of an electromagnetic coil positioned next to the wire See Figure 1 Figure 1 Model 4000 Vibrating Wire Strain Gage Portable readouts available from Geokon used in conjunction with the Vibrating Wire Strain Gage will provide the necessary excitation to pluck the w...

Page 8: ...should be obtained at the existing ambient temperature See Appendix C for the resistance versus temperature correlation Return any faulty gages to the factory Gages should not be opened in the field 2 2 Arc Welding the Mounting Blocks to Steel Surfaces Using the Spacer Bar The Model 4000 Vibrating Wire Strain Gage is attached to mounting blocks that must first be arc welded to the steel surface to...

Page 9: ...into the holes in the mounting blocks One end of the strain gage has a V groove in it make sure that this end goes inside the mounting block that has the single cone point set screw Tighten hard the cone point set screw into the V groove Now clip the coil housing around the gage and connect to the readout box Channel C Set the initial reading on the gage to the correct level depending on whether c...

Page 10: ...excessive handling of the gage prior to taking zero readings Always allow sufficient time for the gage temperature to stabilize before reading In any case it is always a good idea to record the temperature every time the strain reading is made so that any loads and strains caused purely by temperature changes can be assessed See also Appendix E and G In order to facilitate the measurement of tempe...

Page 11: ...sure A typical readout enclosure has a hinged and gasketed cover that keeps the ends of the lead wires and or plugs clean and dry Alternatively if many strain gages are to be read out at the same location a terminal box may be installed The front panel inside the terminal box can have a rotary switch or jacks or plug ins which facilitate the connection of the numerous gages to the patch cord from ...

Page 12: ...okon that install at the exit point of the instrument cable from the structure being monitored The enclosure has a removable top so in the event the protection board LAB 3 is damaged the user may service the components or replace the board A connection is made between this enclosure and earth ground to facilitate the passing of transients away from the gage See Figure 5 Consult the factory for add...

Page 13: ...structure a strain gage measures the strain at one point on the surface and this would be sufficient if it could be guaranteed that no bending was occurring in the member In practice this will only occur near the center of long thin members subjected to tensile loads Elsewhere bending moments are the rule rather than the exception and there will be a neutral axis around which bending takes place S...

Page 14: ...g from all four strain gages and multiplying by the modulus Equation 1 Axial Stress Calculation The stress due to bending is calculated by looking at the difference between pairs of gages mounted on opposite sides of the neutral axis Thus the maximum stress due to bending about axis yy is given by Equation 2 Stress due to bending on Axis yy The maximum stress due to bending about axis xx is given ...

Page 15: ... forces which affect only one gage but not the others It is not uncommon for welding to take place at points close to a strain gage and often this produces large strain changes in any strain gage close by Also it is not uncommon for local blocking e g tunnel arch supports and the addition of struts to cause strain changes on only a single gage close by It is always best to locate gages in pairs on...

Page 16: ...ges and cables It suffers from the greater disadvantage that local bending at one gage may not be felt by the other gage For example in one instance welding on the exposed flange of a soldier pile close to one gage produced large strain changes not felt by the other gage on the back side of the pile Figure 6E Axial Strain and Bending Moment around axis XX Not recommended The configuration shown in...

Page 17: ...ot necessary to use continuous welds Tack welding will do so long as it holds the angles or channels firmly in place Cables must be restrained by welding studs at 3 meter intervals to which the cables can be tied In order to prevent shock damage during driving special care must be taken The mounting blocks must be installed so that the upper mounting block is the one with the single set screw The ...

Page 18: ...nting blocks to the spacer jig as per section 2 2 above 4 Apply a thin layer of the premixed underwater epoxy to the center 2 3 rds of the mounting block see sketch below 5 Apply a thin layer of 410 Instant adhesive to the outside edges of the mounting blocks 6 Press the assembly firmly against the surface and hold in place for 2 minutes 7 Carefully remove the spacer bar from the mounting blocks 8...

Page 19: ...ection 2 2 to position them properly The studs are then grouted into the pre drilled holes using either fast setting hydraulic cement or a high strength epoxy Redhead epoxy type Epcon Ceramic 6 works well Groutable Anchor Groutable Anchor Grout or Epoxy Grout or Epoxy Setting Distance 5 875 149 mm Figure 9 Installation on Concrete using Groutable Anchors 6 TAKING READINGS The following three secti...

Page 20: ... Box The GK404 is a palm sized readout box which displays the Vibrating wire value and the temperature in degrees centigrade The GK 404 Vibrating Wire Readout arrives with a patch cord for connecting to the vibrating wire gages One end will consist of a 5 pin plug for connecting to the respective socket on the bottom of the GK 404 enclosure The other end will consist of 5 leads terminated with all...

Page 21: ...relessly using Bluetooth a reliable digital communications protocol The Readout Unit can operate from the cradle of the Remote Module see Figure 10 or if more convenient can be removed and operated up to 20 meters from the Remote Module Figure 10 GK405 Readout Unit For further details consult the GK405 Instruction Manual 6 4 Measuring Temperatures All Vibrating Wire Strain Gages are equipped with ...

Page 22: ...strains to computed stresses Strain changes with time are computed from strain gage readings taken at various times and by comparison with some initial readings taken at time zero This initial reading is best taken when the structural member is under no load i e the gages should be mounted while the member is still in the steel yard or warehouse This is not always possible and often strain gages a...

Page 23: ...ge will read again Set the gage to some new datum and retighten the setscrews If the gage does not respond to re setting and if the old plucking coil will pluck a new gage then the gage should be replaced Is there a source of electrical noise nearby Most probable sources of electrical noise are motors generators and antennas Move the equipment away from the installation or install electronic filte...

Page 24: ... Calibration 0 1 FS Batch Calibration 0 5 FS Individual Calibration 0 1 FS Zero Stability 0 02 FS yr 0 02 FS yr Linearity 0 5 FS 0 5 FS Thermal Coefficient 12 2 C 12 2 C Dimensions gage Length Diameter 6 5 long 0 50 165 12 5 mm 12 625 x 0 50 321 12 5 mm Dimensions end blocks Width Height 1 x 7 8 25 x 22 mm 1 x 7 8 25 x 22 mm Dimensions coil 0 875 0 875 22 22 mm Internal Frequency Range 450 1250 Hz...

Page 25: ...n length and mass by the equation Where Lw is the length of the wire in inches F is the wire tension in pounds m is the mass of the wire per unit length pounds sec 2 in 2 2 Note that Where W is the weight of Lw inches of wire pounds g is the acceleration of gravity 386 in sec 2 3 and Where is the wire material density 0 283 lb in 3 a is the cross sectional area of the wire in 2 4 Combining equatio...

Page 26: ...es Where for the Model 4000 Strain Gage Lw is 6 250 inches Lg is 5 875 inches 12 Therefore Note that T is in seconds x 106 and ε is in inches per inch 13 The display on position C of the GK 401 403 Readout is based on the equation Note that in this formula ε is in micro inches per inch and T is in seconds x 106 Alternatively ε 4 062 x 10 3 f 2 microstrain Where f is the frequency in Hz The squarin...

Page 27: ...66K 36 8006 4 1363 44 331 5 84 105 2 124 72 81K 35 7618 5 1310 45 321 2 85 102 5 125 68 30K 34 7252 6 1260 46 311 3 86 99 9 126 64 09K 33 6905 7 1212 47 301 7 87 97 3 127 60 17K 32 6576 8 1167 48 292 4 88 94 9 128 56 51K 31 6265 9 1123 49 283 5 89 92 5 129 53 10K 30 5971 10 1081 50 274 9 90 90 2 130 49 91K 29 5692 11 1040 51 266 6 91 87 9 131 46 94K 28 5427 12 1002 52 258 6 92 85 7 132 44 16K 27 5...

Page 28: ...ssion 10000 for mid range set to 6000 Note if a CR10 is being used the excitation range 1400 3500 Hz should be selected To set the gage pull or push on the end of the gage tube where the cable exits not the cable itself Convert the position B reading to microstrain using the individual calibration factor expressed in terms of microstrain digit supplied with the instrument Microstrain R1 R0 GF To c...

Page 29: ...mber The temperature induced stresses can be separated from the load induced stresses by reading both the strain and temperature of the strain gages at frequent intervals over a period of time in which the external loading from construction activity can be assumed to be constant When these strain changes are plotted against the corresponding temperature changes the resulting graph shows a straight...

Page 30: ... the equation με actual R1 R0 B T1 T0 x CF1 G2 Where CF1 represents the coefficient of expansion of steel 12 2 microstrain C and R1 R0 B is the apparent strain recorded by the readout box To calculate the strain in the concrete due to load changes only load μεactual thermal 2 1 0 1 0 1 CF CF T T B R R G3 Note the following example where B 0 91 R0 3000 microstrain T0 20 C R1 2900 microstrain T1 30 ...

Page 31: ...1 732 Maximum Bending Strain around the XX Axis Y ε1 ε2 ε3 3 ε1 The maximum strain P Xcosθ Ysinθ A and tanθ Y X Example Let ε1 20 ε2 192 and ε3 88 all tensile strains Average Axial Strain A 20 192 88 3 100 microstrain tension X 104 1 732 60 Y 300 3 20 80 Tanθ 80 60 1 333 and θ 53 degrees from the X axis P 60 x 0 60 80 x 0 8 100 200 microstrain tensile and 0 microstrain minimum P Θ θ ε1 Y Y X X P ε...

Page 32: ... one mounted above the other to separate axial strains from strains due to bending E1 and E2 are two measured strains at distances d1 and d2 from the neutral axis of a steel member e g a sheet pile If R d2 d1 The Axial Strain along the neutral axis RE1 E2 R 1 The Bending Strain at a distance d1 from the neutral axis E2 E1 R 1 Neutral Axis Ε2 Ε1 d 1 d 2 ...

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