Geokon 4000 Series User manual

©2018, GEOKON. All rights reserved.
Document Revision: DD | Release date: 12/6/18
Model 4000 Series
(4050 included)
Vibrating Wire Strain Gauges
Instruction Manual

WARRANTY STATEMENT
GEOKON warrants its products to be free of defects in materials and workmanship,
under normal use and service for a period of 13 months from date of purchase. If the
unit should malfunction, it must be returned to the factory for evaluation, freight
prepaid. Upon examination by GEOKON, if the unit is found to be defective, it will be
repaired or replaced at no charge. However, the WARRANTY IS VOID if the unit shows
evidence of having been tampered with or shows evidence of being damaged as a
result of excessive corrosion or current, heat, moisture or vibration, improper specifi-
cation, misapplication, misuse or other operating conditions outside of GEOKON’s
control. Components that wear or are damaged by misuse are not warranted. This
includes fuses and batteries.
GEOKON manufactures scientific instruments whose misuse is potentially dangerous.
The instruments are intended to be installed and used only by qualified personnel.
There are no warranties except as stated herein. There are no other warranties,
expressed or implied, including but not limited to the implied warranties of merchant-
ability and of fitness for a particular purpose. GEOKON 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 the instal-
lation or use of the product. The buyer’s sole remedy for any breach of this agreement
by GEOKON or any breach of any warranty by GEOKON shall not exceed the purchase
price paid by the purchaser to GEOKON for the unit or units, or equipment directly
affected by such breach. Under no circumstances will GEOKON reimburse the
claimant for loss incurred in removing and/or reinstalling equipment.
Every precaution for accuracy has been taken in the preparation of manuals and/or
software, however, GEOKON neither assumes responsibility for any omissions or
errors that may appear nor assumes liability for any damages or losses that result
from the use of the products in accordance with the information contained in the
manual or software.
No part of this instruction manual may be reproduced, by any means, without the written consent of GEOKON. The
information contained herein is believed to be accurate and reliable. However, GEOKON assumes no responsibility
for errors, omissions or misinterpretation. The information herein is subject to change without notification.
The GEOKON® wordmark and logo are registered trademarks with the United States Patent and Trademark Office.

I
TABLE OF CONTENTS
1. INTRODUCTION............................................................................................................................................1
2. PRELIMINARY CHECKS......................................................................................................................2
3. GAUGE INSTALLATION.......................................................................................................................3
3.1 CONNECTING THE MOUNTING BLOCKS.......................................................................3
3.2 INSTALLATION ON STEEL SURFACES ............................................................................3
3.2.1 WELDING..............................................................................................................................................3
3.2.2 INSTALLATION ON DRIVEN STEEL PILES ..............................................................................4
3.3 INSTALLATION USING EPOXY CEMENTS....................................................................5
3.3.1 CONCRETE SURFACES ...................................................................................................................5
3.3.2 STEEL SURFACES .............................................................................................................................6
3.4 INSTALLING ON CONCRETE SURFACES USING ANCHOR STUDS.......6
3.5 SETTING THE STRAIN GAUGE ................................................................................................7
4. GAUGE PROTECTION.............................................................................................................................8
4.1 PROTECTION FROM MECHANICAL DAMAGE USING GEOKON
MODEL 4000-6.......................................................................................................................................8
4.2 PROTECTION FROM DIRECT SUNLIGHT AND RAPID CHANGES IN
AMBIENT TEMPERATURE ...........................................................................................................9
4.3 CABLE AND CONNECTOR PROTECTION........................................................................9
4.4 CABLE SPLICING AND TERMINATION............................................................................9
4.5 PROTECTION FROM CORROSION........................................................................................9
4.6 LIGHTNING PROTECTION............................................................................................................9
5. GAUGE LOCATION ................................................................................................................................11
5.1 END EFFECTS...................................................................................................................................... 11
5.2 WELDING EFFECTS........................................................................................................................ 11
5.3 BENDING MOMENTS................................................................................................................... 11
6. TAKING READINGS ............................................................................................................................. 15
6.1 STRAIN GAUGE READOUT POSITIONS ...................................................................... 15
6.2 GK-404 READOUT BOX.............................................................................................................. 15
6.2.1 OPERATING THE GK-404 ........................................................................................................... 15
6.3 GK-405 READOUT BOX.............................................................................................................. 16
6.3.1 CONNECTING SENSORS WITH 10-PIN BULKHEAD CONNECTORS
ATTACHED ....................................................................................................................................... 16
6.3.2 CONNECTING SENSORS WITH BARE LEADS................................................................... 17
6.3.3 OPERATING THE GK-405 ........................................................................................................... 17
6.4 GK-403 READOUT BOX (OBSOLETE MODEL) ........................................................ 17

II
6.4.1 CONNECTING SENSORS WITH 10-PIN BULKHEAD CONNECTORS
ATTACHED........................................................................................................................................ 17
6.4.2 CONNECTING SENSORS WITH BARE LEADS ................................................................... 17
6.4.3 OPERATING THE GK-403............................................................................................................ 17
6.5 MEASURING TEMPERATURES............................................................................................ 17
7. DATA REDUCTION................................................................................................................................. 19
7.1 CONVERSION OF THE READINGS TO STRAIN CHANGES ......................... 19
7.2 CONVERTING STRAINS TO STRESSES....................................................................... 19
8. TROUBLESHOOTING........................................................................................................................... 20
APPENDIX A. SPECIFICATIONS................................................................................................... 23
A.1 VIBRATING WIRE STRAIN GAUGE.................................................................................. 23
A.2 THERMISTOR ...................................................................................................................................... 23
A.3 4000-4 MOUNTING BLOCKS ................................................................................................ 23
APPENDIX B. THEORY OF OPERATION .............................................................................. 24
APPENDIX C. THERMISTOR TEMPERATURE DERIVATION ....................... 26
APPENDIX D. MODEL 4050 SPECIAL INSTRUCTIONS ................................... 27
APPENDIX E. TEMPERATURE EFFECTS ............................................................................. 28
APPENDIX F. TEMPERATURE CORRECTION WHEN USED ON
CONCRETE..................................................................................................................... 29
APPENDIX G. CALCULATIONS FROM THREE STRAIN GAUGES,
AT 60 DEGREES, ON A CIRCULAR PIPE ................................... 30
APPENDIX H. TWO STRAIN GAUGES MOUNTED ONE ABOVE
THE OTHER ................................................................................................................... 31

III
FIGURES
FIGURE 1: MODEL 4000 VIBRATING WIRE STRAIN GAUGE .........................................1
FIGURE 2: SPACING JIG ...................................................................................................3
FIGURE 3: WELDING SEQUENCE FOR THE MOUNTING BLOCKS ................................3
FIGURE 4: PROTECTION ON DRIVEN PILES ...................................................................4
FIGURE 5: INSTALLATION USING EPOXY .......................................................................5
FIGURE 6: INSTALLATION ON CONCRETE USING GROUTABLE ANCHORS ................6
FIGURE 7: COVER PLATE INSTALLATION, TOP VIEW ....................................................8
FIGURE 8: COVER PLATE INSTALLATION, SIDE VIEW ...................................................8
FIGURE 9: LIGHTNING PROTECTION SCHEME .............................................................10
FIGURE 10: STRAIN GAUGES MOUNTED ON CENTRAL WEB ....................................11
FIGURE 11: STRAIN GAUGES MOUNTED ON FLANGES .............................................13
FIGURE 12: AXIAL STRAIN MEASUREMENT/BENDING MOMENT ABOUT YY AXIS .13
FIGURE 13: AXIAL STRAIN AND BENDING MOMENTS ABOUT XX AXIS ..................14
FIGURE 14: AXIAL STRAIN AND BENDING MOMENT ABOUT AXIS XX (NOT
RECOMMENDED) .........................................................................................14
FIGURE 15: GK-404 READOUT .......................................................................................15
FIGURE 16: LEMO CONNECTOR TO GK-404 .................................................................15
FIGURE 17: GK-405 READOUT .......................................................................................16
FIGURE 18: MODEL 4050 VIBRATING WIRE STRAIN GAUGE .....................................27
FIGURE 19: THREE STRAIN GAUGES MOUNTED ON A CIRCULAR PIPE DIAGRAM .30
FIGURE 20: TWO STRAIN GAUGES MOUNTED ONE ABOVE THE OTHER .................31

IV
TABLES
TABLE 1: STRAIN GAUGE READOUT POSITIONS...........................................................15
TABLE 2: SAMPLE RESISTANCE ......................................................................................21
TABLE 3: RESISTANCE WORK SHEET .............................................................................21
TABLE 4: SPECIFICATIONS ...............................................................................................23
TABLE 5: THERMISTOR RESISTANCE VERSUS TEMPERATURE ..................................26

V
EQUATIONS
EQUATION 1: AXIAL STRESS CALCULATION ................................................................. 12
EQUATION 2: STRESS DUE TO BENDING ON AXIS YY ................................................. 12
EQUATION 3: STRESS DUE TO BENDING ON AXIS XX................................................. 12
EQUATION 4: MAXIMUM STRESS .................................................................................. 12
EQUATION 5: THEORETICAL MICROSTRAIN ................................................................. 19
EQUATION 6: STRAIN CALCULATION............................................................................. 19
EQUATION 7: RESISTANCE TO TEMPERATURE ............................................................ 26
EQUATION 8: READING TO MICROSTRAIN ................................................................... 27
EQUATION 9: GAUGE-ONLY TEMPERATURE EFFECTS ................................................ 27
EQUATION 10: TEMPERATURE-INDUCED STRESS ...................................................... 28
EQUATION 11: APPARENT STRESS ................................................................................ 28
EQUATION 12: LOAD-RELATED STRESS........................................................................ 28
EQUATION 13: ACTUAL STRAIN ..................................................................................... 28
EQUATION 14: THERMAL CONCRETE STRAINS ........................................................... 29
EQUATION 15: ACTUAL STRAIN ..................................................................................... 29
EQUATION 16: STRAIN DUE TO LOAD CHANGES ONLY ............................................. 29
EQUATION 17: AVERAGE AXIAL STRAIN ....................................................................... 30
EQUATION 18: MAXIMUM BENDING STRAIN AROUND THE YY AXIS ...................... 30
EQUATION 19: MAXIMUM BENDING STRAIN AROUND THE XX AXIS ...................... 30
EQUATION 20: MAXIMUM STRAIN ................................................................................ 30

VI

MODEL 4000 SERIES (4050 INCLUDED) VIBRATING WIRE STRAIN GAUGES | INTRODUCTION | 1
1. INTRODUCTION
GEOKON Model 4000 Vibrating Wire Strain Gauges are intended primarily for
measuring strain on structural steel members such as tunnel linings, arches,
struts, piles, sheet piling, etc. They may also be used to monitor strain changes
on concrete or rock surfaces. Attachment to steel surfaces is accomplished by
arc welding the mounting blocks to the surface; other surfaces require special
mounting blocks with rebar anchors that are grouted into boreholes.
Strain is measured using the vibrating wire principle. A length of steel wire is
tensioned between two mounting blocks that are welded to the steel surface
being studied. Deformations of the surface will cause the two mounting blocks
to move in relation to each other, altering the tension in the steel wire. This
change in tension is measured as a change in the resonant frequency of
vibration of the wire.
FIGURE 1: Model 4000 Vibrating Wire Strain Gauge
Two coils, one with a magnet insert, the other with a pole piece insert, are
located close to the vibrating wire. In use, a pulse of varying frequency (swept
frequency) is applied to the coils causing the wire to vibrate primarily at its
resonant frequency.
Portable readouts and dataloggers are available from GEOKON. These models,
when used in conjunction with vibrating wire strain gauges, will provide the
necessary voltage pulses to pluck the wire. During vibration, a sinusoidal signal
is induced in the coils and transmitted to the readout box where it is conditioned
and displayed.
This manual contains installation instructions, readout instructions,
recommended maintenance, and troubleshooting procedures. The theory of the
gauge is also given, along with some suggestions for data interpretation.

2| PRELIMINARY CHECKS | GEOKON
2. PRELIMINARY CHECKS
Perform a preliminary check before installing the gauge in the field. To perform
the preliminary check, complete the following steps according to the instruction
in Section 6:
1. Connect the gauge to a readout box.
2. Observe the displayed readout. The reading should be around the midrange
position as defined in Table 1 on page 17. The temperature reading should
match the ambient temperature.
3. Gently pull on the gauge end blocks; confirm that numbers on the readout
rise as the tension increases. Do not apply excessive tension (greater
than 10 Kgm / 20 lb.), as this may break the vibrating wire!
Check electrical continuity using an ohmmeter. Resistance between the gauge
leads (usually red and black) should be approximately 180 ohms (50 ohms for
model 4050 gauges.) Remember to add cable resistance, which is
approximately 14.7per 1000 feet (48.5per km) of 22 AWG stranded copper
leads at 20 °C. Multiply this factor by two to account for both directions.
Resistance between thermistor leads (usually green and white) will vary based
on temperature; see Table 5 on page 26. Resistance between any conductor and
the shield should exceed two megohms.
Should any of these preliminary tests fail, see Section 8 for troubleshooting tips.

MODEL 4000 SERIES (4050 INCLUDED) VIBRATING WIRE STRAIN GAUGES | GAUGE INSTALLATION | 3
3. GAUGE INSTALLATION
3.1 CONNECTING THE MOUNTING BLOCKS
GEOKON vibrating wire strain gauges are held in place by two mounting blocks.
GEOKON can provide mounting blocks, spacer bars, and spacing jigs for different
gauge types and installations.
Assemble the mounting blocks onto the spacer bar as follows:
1. Fit the two mounting blocks over the ends of the spacer bar.
2. Position the mounting blocks and spacer bar onto the spacing jig.
FIGURE 2: Spacing Jig
3. Tighten the setscrews in the mounting blocks down onto the spacer bar so
that it will not slide. Avoid tightening excessively, since this could damage
the spacer bar.
4. Remove the completed mounting block and spacer bar assembly from the
spacing jig.
3.2 INSTALLATION ON STEEL SURFACES
3.2.1 WELDING
Once the correct spacing of the mounting blocks has been set using the spacing
jig, the mounting blocks may be welded to the steel surface as follows:
1. Clean the steel using a wire brush; remove all scale, rust, dirt, and oil.
2. Using the spacer bar as a handle, press the mounting blocks firmly against
the steel surface.
3. Weld the edges of the mounting blocks in the order shown in the following
figure.
FIGURE 3: Welding Sequence for the Mounting Blocks
Spacing Jig
NOTE: 4000-8 includes both spacer bar and spacing jig
4000-9 Spacer bar
Mounting block
Mounting block
#1
#3
#4
#2
Weld

4| GAUGE INSTALLATION | GEOKON
Avoid excessive heat while welding. Do not weld the end surfaces of the
mounting blocks; this would prevent removal of the spacer bar. Avoid welding
splatter, which could stick to the spacer bar. When many gauges are being
installed, it is advantageous to have more than one spacer bar available.
After welding, cool the mounting blocks with a water-soaked rag, then slacken
the setscrews and slide out the spacer bar. Clean away all welding slag using a
chipping hammer and wire brush.
Optional: Paint over the surface to provide some protection against corrosion.
Continue with the installation by proceeding to Section 3.5.
3.2.2 INSTALLATION ON DRIVEN STEEL PILES
Strain gauges mounted on steel piles need to be protected from being scraped
off as the pile is driven into the ground. This can be accomplished by welding
101 x 38 mm (4" x 1.5") channel iron or 64 mm (2.5") or larger angle iron over the
top of the gauges and cables. See the figure below.
To avoid burning the cables, the protection should be welded on before the
gauges and cables are installed. To accomplish this, leave windows in the steel
over the gauge locations. It is not necessary to use continuous welds; tack
welding is sufficient so long as it holds the angles or channels firmly in place.
Cables must be restrained by welding studs at three-meter intervals, to which
the cables can then be tied.
FIGURE 4: Protection on Driven Piles
Channel Iron Angle Iron
End View
Window for Gauge Install
Welded Stud
4000 Gauge
Mounting Block
Weld

MODEL 4000 SERIES (4050 INCLUDED) VIBRATING WIRE STRAIN GAUGES | GAUGE INSTALLATION | 5
To prevent shock damage during driving, please observe these additional
precautions:
Install the mounting block that possesses the single setscrew in the upper
position.
Tighten hard the setscrews that hold the gauge in the mounting blocks.
Use Loctite on the threads.
Glue the coil onto the flat area of the gauge tube. (Use any cyanoacrylate
product such as Eastman 910 or Crazy Glue.) Make sure that the cable side
of the coil points towards the top of the pile, i.e., towards the end of the
gauge with the V-groove.
As an added precaution, tighten hard when installing the hose clamp that
holds the coil on the gauge, and tighten using a nut driver.
When setting the gauges make sure they are reading around 3500 on
position C. This is very important.
Continue with the installation by proceeding to Section 3.5. After the gauges are
installed, seal the windows by welding a section of the appropriate material over
the window.
3.3 INSTALLATION USING EPOXY CEMENTS
GEOKON strain gauges can be epoxied to steel or concrete surfaces provided
these two factors are strictly observed:
1. Proper care must be taken to clean the surfaces to be bonded.
2. Sufficient time must be allowed for the epoxy to cure before the gauges are
attached to the mounting blocks.
Note: Due to the large number of variables associated with adhesive use
(thermal cycles, UV exposure, vibration, impact, moisture, corrosion of base
steel, etc.,) epoxy cement is recommended for short term monitoring only.
3.3.1 CONCRETE SURFACES
Materials needed:
Devcon Underwater Putty, Mfg. Part# 11800 — GEOKON Part# 6201-2
Loctite 410 Instant Adhesive, Mfg. Part# 41045 — GEOKON Part# 4000-15
1. Mix a quantity of the two-part underwater putty. The mix ratio is 1/1.
2. Grind and/or sand the surfaces to be bonded. (This includes both the
concrete and the end block surfaces.)
3. Clean surfaces with compressed air or aerosol cleaner.
4. Attach the mounting blocks to the spacer bar, per the instructions in Section
3.1.
5. Apply a thin layer of mixed underwater putty to the center two-thirds of the
mounting block, and a thin layer of 410 instant adhesive to the outside
edges of the mounting blocks (see the figure below).
FIGURE 5: Installation Using Epoxy
Bottom View Loctite 410 Instant Adhesive
Spacer bar
Devcon Underwater Putty
on two thirds

6| GAUGE INSTALLATION | GEOKON
6. Press the assembly firmly against the surface and hold in place for two
minutes.
7. Carefully remove the spacing bar from the mounting blocks.
8. Allow 24 hours curing time before the gauges are installed.
9. Continue with the installation by proceeding to Section 3.5.
3.3.2 STEEL SURFACES
Use Loctite Speedbonder H4500. This can be purchased in a cartridge which
automatically dispenses the two-part adhesive in its correct 10/1 mixture.
(Adhesive, dispenser, and nozzles are available from GEOKON.)
The adhesive reaches its maximum strength in 10 minutes, during which time
the mounting blocks should be held to the surface USING HAND pressure,
weights, or magnets.
Continue with the installation by proceeding to Section 3.5.
3.4 INSTALLING ON CONCRETE SURFACES USING ANCHOR
STUDS
Strains in the surface of concrete can be measured by utilizing special mounting
blocks that have reinforcing bar welded to them (GEOKON model 4000-5). Attach
the strain gauge to the concrete surface as follows:
1. Drill two 64 mm (2.5") deep holes in the concrete at the proper spacing,
using a minimum 13 mm (1/2”) drill bit. (A template is available, GEOKON
model 4000-11.)
2. Connect the mounting blocks to the spacer bar using the spacer block (see
Section 3.1).
3. Grout the rebar studs into the holes using fast-setting hydraulic cement or a
high strength epoxy. Redhead epoxy, type Epcon Ceramic 6 works well.
4. Once the grout has cured, continue with the installation by proceeding to
Section 3.5.
FIGURE 6: Installation on Concrete Using Groutable Anchors
Groutable Anchors
(Product 4000-5)
Grout or Epoxy
Setting Distance
5.875 inches / 149 mm

MODEL 4000 SERIES (4050 INCLUDED) VIBRATING WIRE STRAIN GAUGES | GAUGE INSTALLATION | 7
3.5 SETTING THE STRAIN GAUGE
Mount the strain gauge as follows:
1. Slide the strain gauge through the mounting blocks. The end of the gauge
that has the V-groove goes inside the mounting block that has only one
setscrew; the smooth end goes inside the mounting block with two
setscrews.
2. Tighten hard the setscrew in the mounting block with only one screw.
3. Slide the slot in the coil assembly (located at the end of the instrument
cable) over the narrow center of the gauge.
4. Connect the gauge to the readout box using the instructions in Section 6.
5. Adjust the reading by pulling or pushing on the free end of the strain gauge.
6. Set the initial reading on the gauge to the correct level depending on
whether compressive or tensile strains are anticipated. Strain gauges are
shipped with a reading of approximately 3000 to 3500 microstrain. This
level is okay for compressive strains. If tensile strains are to be measured,
set the initial reading to around 1500 microstrain. The useable range of the
strain gauge runs from around 1000 to 4000 microstrain. The midrange
reading is 2500 microstrain.
7. When the desired reading has been achieved, tighten hard the setscrews in
the mounting block with two setscrews.
8. Install the hose clamp over the assembly and tighten using a nut driver.
9. In order to remove any installation strains and stabilize the initial reading,
tap on the mounting blocks with a hard plastic tool, e.g., the handle of a
screwdriver. Continue tapping until the reading remains stable.
It is imperative that an accurate initial zero reading be obtained for each
strain gauge, as this reading will be used for all subsequent data
reduction.
It is preferable to install gauges on steel members while they are still in an
unloaded condition, i.e., prior to their assembly into the structure. When the
initial zero is established in this manner, the initial readings correspond to zero
load, otherwise, if the member is under load the initial readings will correspond
to some unknown load level.
Avoid excessive handling of the gauge prior to taking zero readings. Always
allow sufficient time for the gauge temperature to stabilize before taking a
reading. Be sure to record the temperature every time a reading is taken, along
with notes concerning the construction activity that is taking place. This data
might supply logical reasons for observed changes in the readings. (See also
Appendix E and F.)
Each strain gauge has a thermistor encapsulated along with the plucking coil.
GEOKON readout boxes display the temperature directly in degrees Celsius. An
ohmmeter can also be used. (The relationship between resistance and
temperature is shown in Appendix C.)

8| GAUGE PROTECTION | GEOKON
4. GAUGE PROTECTION
4.1 PROTECTION FROM MECHANICAL DAMAGE USING GEOKON
MODEL 4000-6
Special cover plates made from sheet steel formed into a channel shape are
available from GEOKON. Use the mounting hardware provided to install the cover
plates as follows:
1. Weld the two 9.5 x 51 mm (3/8 x 2") long hex bolts in place head down. The
bolts should be spaced at a nominal 530 mm (21") apart. A spacer jig is
available from GEOKON, or the cover plate can be flipped onto its back and
the holes in the cover plate can be used to mark the bolt locations. One hole
in the cover plate is slotted so that the spacing is not critical. Avoid welding
near the gauge as this will cause large local distortions of the metal. Use a
special stud welder or an arc welder to weld the head of the bolt to the
surface.
2. Place the cover plate over the welded bolts.
3. Install washers, then nuts. Avoid using excessive force while tightening the
cover retaining nuts as this will distort the underlying steel surface and can
give rise to spurious strain readings. The two figures below show the
completed installation.
FIGURE 7: Cover Plate Installation, Top View
FIGURE 8: Cover Plate Installation, Side View
21 inches
1.5 inches
3”

MODEL 4000 SERIES (4050 INCLUDED) VIBRATING WIRE STRAIN GAUGES | GAUGE PROTECTION | 9
4.2 PROTECTION FROM DIRECT SUNLIGHT AND RAPID CHANGES
IN AMBIENT TEMPERATURE
The thermal coefficient of expansion of the steel vibrating wire inside the gauge
is the same as that for the steel of the structure to which the gauge is attached;
therefore, no temperature correction to the measured strain is required
when calculating load induced strains. However, this is only true if the wire
and the underlying steel structure are at the same temperature. If sunlight is
allowed to impinge directly onto the gauge, it could elevate the temperature of
the wire above the surrounding steel and cause large changes in apparent
strain. Therefore, always shield strain gauges from direct sunlight.
Protection from temperature changes is best provided by covering the gauges
with a layer of insulating material such as Polystyrene foam or fiberglass.
4.3 CABLE AND CONNECTOR PROTECTION
The cable should be protected from accidental damage caused by moving
equipment or fly rock. This is best accomplished by putting the cable inside
flexible conduit and positioning the conduit in as safe a place as possible.
(Flexible conduit is available from GEOKON.) The conduit can be connected via
conduit bulkhead connectors to the cover plates and then to a readout. (The
GEOKON cover plate has a stamped knockout which, when removed, provides a
hole for connecting the conduit connector.)
4.4 CABLE SPLICING AND TERMINATION
Terminal boxes with sealed cable entries are available from GEOKON for all types
of applications. These allow many gauges to be terminated at one location with
complete protection of the lead wires. The interior panel of the terminal box can
have built-in jacks or a single connection with a rotary position selector switch.
Contact GEOKON for specific application information.
Because the vibrating wire output signal is a frequency rather than a current or
voltage, variations in cable resistance have little effect on gauge readings;
therefore, splicing of cables has no ill effects, and in some cases may in fact be
beneficial. The cable used for making splices should be a high quality twisted
pair type, with 100% shielding and an integral shield drain wire. When splicing,
it is very important that the shield drain wires be spliced together.
Always maintain polarity by connecting color to color.
Splice kits recommended by GEOKON incorporate casts that are placed around
the splice and are then filled with epoxy to waterproof the connections. When
properly made, this type of splice is equal or superior to the cable in strength
and electrical properties. Contact GEOKON for splicing materials and additional
cable splicing instructions.
You can terminate a cable by stripping and tinning the individual conductors and
then connecting them to the patch cord of a readout box. Alternatively, you can
use a connector to plug directly into the readout box or to a receptacle on a
special patch cord.
4.5 PROTECTION FROM CORROSION
You can inhibit corrosion by applying a coat of rust preventative paint at the
weld points.
4.6 LIGHTNING PROTECTION
Unlike numerous other types of instrumentation available from GEOKON,
vibrating wire strain gauges do not have any integral lightning protection
components, such as transorbs or plasma surge arrestors.

10 | GAUGE PROTECTION | GEOKON
SUGGESTED LIGHTNING PROTECTION OPTIONS:
Lighting arrestor boards and enclosures are available from GEOKON. These
units install where the instrument cable exits the structure being monitored.
The enclosure has a removable top to allow the customer to service the
components or replace the board in the event that the unit is damaged by a
lightning strike. A connection is made between the enclosure and earth
ground to facilitate the passing of transients away from the gauge. See the
figure below.
Plasma surge arrestors can be epoxied into the instrument cable, close to
the sensor. A ground strap then connects the surge arrestor to an earth
ground, such as a grounding stake or the steel structure.
Consult the factory for additional information on available lightning protection.
FIGURE 9: Lightning Protection Scheme
Terminal Box
or Multiplexer
Ground Connections
Steel Beam
Copper Ground Wire
Instrument Cable
(usually buried)
Lab3
Enclosure
Gauge 4000