Geokon 4450 User manual

Instruction Manual
Model 4450
VW Displacement Transducer
No part of this instruction manual may be reproduced, by any means, without the written 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 © 1994-2017 by Geokon, Inc.
(Doc Rev P 11/27/2017)

Warranty Statement
Geokon, Inc. 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 specification, misapplication, misuse or other operating conditions outside
of Geokon's control. Components which wear or which 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 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 the installation or use of the product. The buyer's sole remedy for any breach of this
agreement by Geokon, Inc. or any breach of any warranty by Geokon, Inc. shall not exceed the
purchase price paid by the purchaser to Geokon, Inc. 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, Inc. 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.

TABLE of CONTENTS
1. INTRODUCTION...................................................................................................................................................7
1.1 THEORY OF OPERATION.......................................................................................................................................7
2. INSTALLATION ....................................................................................................................................................7
2.1 PRELIMINARY TESTS............................................................................................................................................7
2.2 DISPLACEMENT TRANSDUCER INSTALLATION.....................................................................................................8
2.3 SWAGELOK TUBE FITTING INSTRUCTIONS...........................................................................................................9
2.3.1 Installation..................................................................................................................................................9
2.3.2 Reassembly Instructions............................................................................................................................10
2.4 CABLE INSTALLATION AND SPLICING ................................................................................................................11
2.5 ELECTRICAL NOISE............................................................................................................................................11
2.6 LIGHTNING PROTECTION ...................................................................................................................................11
3. TAKING READINGS...........................................................................................................................................13
3.1 GK-404 READOUT BOX.....................................................................................................................................13
3.2 GK-405 READOUT BOX.....................................................................................................................................14
3.2.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached.............................................................14
3.2.2 Sensors with Bare Leads...........................................................................................................................14
3.2.3 Operating the GK-405 ..............................................................................................................................14
3.3 GK-403 READOUT BOX (OBSOLETE MODEL)....................................................................................................15
3.3.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached.............................................................15
3.3.2 Connecting Sensors with Bare Leads........................................................................................................15
3.3.3 Operating the GK-403 ..............................................................................................................................15
3.4 MEASURING TEMPERATURES.............................................................................................................................15
4. DATA REDUCTION ............................................................................................................................................16
4.1 DEFORMATION CALCULATION...........................................................................................................................16
4.2 TEMPERATURE CORRECTION.............................................................................................................................17
4.3 ENVIRONMENTAL FACTORS...............................................................................................................................18
5. TROUBLESHOOTING........................................................................................................................................20
APPENDIX A. THERMISTOR TEMPERATURE DERIVATION.....................................................................22
APPENDIX B. SPECIFICATIONS.........................................................................................................................23
B.1 MODEL 4450 DISPLACEMENT TRANSDUCER.....................................................................................................23
B.2 THERMISTOR (SEE APPENDIX AALSO)..............................................................................................................23
B.3 DIMENSIONS DRAWING FOR RANGES OF 50 MM (2”) AND BELOW ....................................................................24
B.4 DIMENSIONS DRAWING FOR RANGES OF 100 MM (4”) AND ABOVE...................................................................25

FIGURES
FIGURE 1-MODEL 4450 DISPLACEMENT TRANSDUCER................................................................................................ 7
FIGURE 2-TUBE INSERTION.......................................................................................................................................... 9
FIGURE 3-MAKE A MARK AT SIX O’CLOCK ................................................................................................................. 9
FIGURE 4-TIGHTEN ONE AND ONE-QUARTER TURNS .................................................................................................. 9
FIGURE 5-MARKS FOR REASSEMBLY ..........................................................................................................................10
FIGURE 6-FERRULES SEATED AGAINST FITTING BODY...............................................................................................10
FIGURE 7-TIGHTEN NUT SLIGHTLY.............................................................................................................................10
FIGURE 8-LIGHTNING PROTECTION SCHEME ..............................................................................................................12
FIGURE 9-LEMO CONNECTOR TO GK-404 ..................................................................................................................13
FIGURE 10 -LIVE READINGS –RAW READINGS............................................................................................................14
FIGURE 11 -ATYPICAL CALIBRATION SHEET..............................................................................................................19
FIGURE 12 -DIMENSIONS:RANGES OF 50 MM (2”) AND BELOW...................................................................................24
FIGURE 13 -DIMENSIONS:RANGES OF 100 MM (4”) AND ABOVE .................................................................................25
TABLES
TABLE 1-MODEL 4450 READING VERSUS POSITION IN THE RANGE ............................................................................. 8
TABLE 2-ENGINEERING UNITS CONVERSION MULTIPLIERS........................................................................................16
TABLE 3-THERMAL COEFFICIENT CALCULATION CONSTANTS ...................................................................................17
TABLE 4-SAMPLE RESISTANCE ...................................................................................................................................21
TABLE 5-RESISTANCE WORK SHEET...........................................................................................................................21
TABLE 6-THERMISTOR RESISTANCE VERSUS TEMPERATURE......................................................................................22
TABLE 7-MODEL 4450 DISPLACEMENT TRANSDUCER SPECIFICATIONS......................................................................23
EQUATIONS
EQUATION 1-DIGITS CALCULATION............................................................................................................................16
EQUATION 2-DISPLACEMENT CALCULATION..............................................................................................................16
EQUATION 3-THERMALLY CORRECTED DISPLACEMENT CALCULATION.....................................................................17
EQUATION 4-THERMAL COEFFICIENT CALCULATION .................................................................................................17
EQUATION 5-RESISTANCE TO TEMPERATURE .............................................................................................................22

7
1. INTRODUCTION
1.1 Theory of Operation
Geokon Model 4450 Vibrating Wire Displacement Transducers consist of a vibrating wire
sensing element, in series with a heat treated, stress relieved spring. One end of the spring is
connected to a vibrating wire, the other end to the transducer shaft. As the transducer shaft is
pulled out from the gage body, the spring is elongated, causing an increase in tension in the
vibrating wire. The increase in tension (strain) of the wire is directly proportional to the
extension of the shaft. This change in strain allows the Model 4450 to measure displacement
very accurately.
Model 4450 Displacement Transducers are fully sealed and can operate at pressures of up to 250
psi. They are designed to be read by one of the various readout boxes available from Geokon.
Figure 1 - Model 4450 Displacement Transducer
2. INSTALLATION
2.1 Preliminary Tests
CAUTION! Do not rotate the transducer shaft of the crackmeter more than 180 degrees.
This may cause irreparable damage to the instrument. The alignment pin on the
transducer shaft and slot on the body serve as a guide for alignment. Never extend the
crackmeter beyond its working range.
Before installing the gages in the field, perform a preliminary check by completing the following
1) Connect the gage to a readout box. (See Section 3 for information on using readout boxes.)
2) Take a reading. The reading should be stable and in the range of 4000 to 5000 digits.
3) To prevent damage during shipping, the transducer arrives with either a split PVC sleeve
taped to the body, or a metal dowel pin inserted into the shaft. Remove the PVC split sleeve
or dowel pin. When the shipping spacer is removed and the alignment pin is resting in the
alignment slot the reading should be in the range of 2000 to 3000.

8
4) A check of electrical continuity can be made using an ohmmeter. The resistance between the
two lead wires (usually red and black) should be around 180 ohms. Remember to add the
cable resistance at approximately 14.7Ω/1000' or 48.5Ω/km at 20 °C. Multiply this factor by
two to account for both directions.
5) Using an ohmmeter check the resistance between the two thermistor wires (usually white and
green). Using Table 6 in Appendix A, convert the resistance to temperature. Compare the
result to the current ambient temperature.
6) Resistance between any conductor and the shield should exceed two megohms.
2.2 Displacement Transducer Installation
1) Be sure to place the alignment pin of the transducer shaft into the alignment slot during
installation. This will prevent the internal wire from twisting.
2) With the #10-32 thread of the transducer shaft pressed against the shaft-mounting device,
rotate the transducer approximately 16 turns to tighten the transducer shaft onto the mounting
device.
3) Attach the red and black gage leads to the readout box. Select position B. (See Section 3 for
readout instructions.)
4) Gently pull on the transducer housing until the desired reading is obtained, see Table 1. Do
not extend the shaft further than the range of the gage! The transducer also may be
damaged if it is allowed to free fall through its stroke.
5) Hold the desired reading and secure the cable side of the gage against or inside the mounting
device. The transducer can be secured by using a Swagelok male connector with nylon front
and back ferrules. Tighten the Swagelok connector per the instructions in Section 2.3. Do not
rotate the gage tube relative to the shaft while securing!
6) Initial readings must be taken and carefully recorded along with the temperature at the time
of installation. These readings serve as a reference for subsequent deformation calculations.
Transducer Digit
Change
Minimum
Reading Maximum Reading Midrange
1/3
Compression
1/3 Extension
1/3 Extension
1/3 Compression
Standard 12,
25, and 50 mm
5,000 2000 7000 5000 6500 4000
Standard 100
and 150 mm
5,000 2000 7000 5000 6500 4000
Slim 12,
25, and 50 mm
10,000 3000 13000 8000 6000 9000
Table 1 - Model 4450 Reading versus Position in the Range

9
2.3 Swagelok Tube Fitting Instructions
These instructions apply to one inch (25 mm) and smaller fittings.
2.3.1 Installation
1) Fully insert the tube into the fitting until it bumps against the shoulder.
Figure 2 - Tube Insertion
2) Rotate the nut until it is finger-tight. (For high-pressure applications as well as high-
safety-factor systems, further tighten the nut until the tube will not turn by hand or
move axially in the fitting.)
3) Mark the nut at the six o’clock position.
Figure 3 - Make a Mark at Six O’clock
4) While holding the fitting body steady, tighten the nut one and one-quarter turns until
the mark is at the 9 o’clock position. (Note: For 1/16”, 1/8”, 3/16”, and 2, 3, and 4
mm fittings, tighten the nut three-quarters of a turn until the mark is at the 3 o’clock
position.)
Figure 4 - Tighten One and One-Quarter Turns

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2.3.2 Reassembly Instructions
Swagelok tube fittings may be disassembled and reassembled many times.
Warning: Always depressurize the system before disassembling a Swagelok tube
fitting.
1) Prior to disassembly, mark the tube at the back of the nut, then make a line along the
nut and fitting body flats. These marks will be used during reassembly to ensure the
nut is returned to its current position.
Figure 5 - Marks for Reassembly
2) Disassemble the fitting.
3) Inspect the ferrules for damage and replace if necessary. If the ferrules are replaced
the connector should be treated as a new assembly. Refer to the section above for
installation instructions.
4) Reassemble the fitting by inserting the tube with preswaged ferrules into the fitting
until the front ferrule seats against the fitting body.
Figure 6 - Ferrules Seated Against Fitting Body
5) While holding the fitting body steady, rotate the nut with a wrench to the previous
position as indicated by the marks on the tube and the connector. At this point, there
will be a significant increase in resistance.
6) Tighten the nut slightly.
Figure 7 - Tighten Nut Slightly

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2.4 Cable Installation and Splicing
The cable should be routed to minimize the possibility of damage due to moving equipment,
debris or other causes. The cable can be protected by the use of flexible conduit, which can be
supplied by Geokon.
Terminal boxes with sealed cable entries are available from Geokon for all types of applications.
These allow many gages 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 gage 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, which 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 itself in strength and electrical properties. Contact Geokon for
splicing materials and additional cable splicing instructions.
Cables may be terminated by stripping and tinning the individual conductors and then connecting
them to the patch cord of a readout box. Alternatively, a connector may be used which will plug
directly into the readout box or to a receptacle on a special patch cord.
2.5 Electrical Noise
Care should be exercised when installing instrument cables to keep them as far away as possible
from sources of electrical interference such as power lines, generators, motors, transformers, arc
welders, etc. Cables should never be buried or run alongside AC power lines; they will pick up
the noise from the power cable, which will likely cause unstable readings. Contact the factory
concerning filtering options available for use with the Geokon dataloggers and readouts.
2.6 Lightning Protection
Unlike numerous other types of instrumentation available from Geokon, displacement
transducers do not have any integral lightning protection components, such as transorbs or
plasma surge arrestors. Usually this is not a problem, however, if the instrument cable is
exposed, it may be appropriate to install lightning protection components, as the transient could
travel down the cable to the gage and possibly destroy it.

12
Suggested Lightning Protection Options:
•If the instrument 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 the installation of these components.
•Lighting arrestor boards and enclosures are also 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 displacement transducer. See Figure 8.
•Plasma surge arrestors can be epoxied into the instrument cable, close to the transducer. A
ground strap then connects the surge arrestor to an earth ground, such as a grounding stake or the
rebar itself.
Consult the factory for additional information on available lightning protection.
Figure 8 - Lightning Protection Scheme

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3. TAKING READINGS
3.1 GK-404 Readout Box
The Model GK-404 Vibrating Wire Readout is a portable, low-power, handheld unit that is
capable of running for more than 20 hours continuously on two AA batteries. It is designed for
the readout of all Geokon vibrating wire gages and transducers, and is capable of displaying the
reading in either digits, frequency (Hz), period (µs), or microstrain (µε). The GK-404 also
displays the temperature of the transducer (embedded thermistor) with a resolution of 0.1 °C.
Before use, attach the flying leads to the GK-404 by aligning the red circle on the silver “Lemo”
connector of the flying leads with the red line on the top of the GK-404 (Figure 9). Insert the
Lemo connector into the GK-404 until it locks into place.
Figure 9 - Lemo Connector to GK-404
Connect each of the clips on the leads to the matching colors of the sensor conductors, with blue
representing the shield (bare).
To turn the GK-404 on, press the “ON/OFF” button on the front panel of the unit. The initial
startup screen will display:
Geokon Inc.
GK-404 verX.XX
After approximately one second, the GK-404 will start taking readings and display them based
on the settings of the POS and MODE buttons.
The unit display (from left to right) is as follows:
•The current Position: Set by the POS button, displayed as a letter A through F.
•The current Reading: Set by the MODE button, displayed as a numeric value followed
by the unit of measure.
•Temperature reading of the attached gage in degrees Celsius.
Use the POS button to select position Band the MODE button to select Dg (digits). (Other
functions can be selected as described in the GK-404 Manual.)
The GK-404 will continue to take measurements and display readings until the unit is turned off,
either manually, or if enabled, by the Auto-Off timer. If no reading displays or the reading is
unstable, consult Section 5 for troubleshooting suggestions.
For further information, consult the GK-404 manual.

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3.2 GK-405 Readout Box
The GK-405 Vibrating Wire Readout is made up of two components: The Readout Unit,
consisting of a Windows Mobile handheld PC running the GK-405 Vibrating Wire Readout
Application; and the GK-405 Remote Module, which is housed in a weatherproof enclosure and
connects via a cable to the vibrating wire gage to be measured. The two components
communicate wirelessly using Bluetooth®, a reliable digital communications protocol. The
Readout Unit can operate from the cradle of the Remote Module, or, if more convenient, can be
removed and operated up to 20 meters from the Remote Module.
3.2.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached
Align the grooves on the sensor connector (male), with the appropriate connector on the
readout (female connector labeled senor or load cell). Push the connector into place, and
then twist the outer ring of the male connector until it locks into place.
3.2.2 Sensors with Bare Leads
Attach the GK-403-2 flying leads to the bare leads of a Geokon vibrating wire sensor by
connecting each of the clips on the leads to the matching colors of the sensor conductors,
with blue representing the shield (bare).
3.2.3 Operating the GK-405
Press the button labeled “POWER ON (BLUETOOTH)”. A blue light will begin
blinking, signifying that the Remote Module is waiting to connect to the handheld unit.
Launch the GK-405 VWRA program by tapping on “Start” from the handheld PC’s main
window, then “Programs” then the GK-405 VWRA icon. After a few seconds, the blue
light on the Remote Module should stop flashing and remain lit. The Live Readings
Window will be displayed on the handheld PC. Choose display mode “B”. Figure 10
shows a typical vibrating wire output in digits and thermistor output in degrees Celsius. If
no reading displays or the reading is unstable, see Section 5 for troubleshooting
suggestions. For further information, consult the GK-405 Instruction Manual.
Figure 10 - Live Readings – Raw Readings

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3.3 GK-403 Readout Box (Obsolete Model)
The GK-403 can store gage readings and apply calibration factors to convert readings to
engineering units. The following instructions explain taking gage measurements using Mode
"B". Consult the GK-403 Instruction Manual for additional information.
3.3.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached
Align the grooves on the sensor connector (male), with the appropriate connector on the
readout (female connector labeled senor or load cell). Push the connector into place, and
then twist the outer ring of the male connector until it locks into place.
3.3.2 Connecting Sensors with Bare Leads
Attach the GK-403-2 flying leads to the bare leads of a Geokon vibrating wire sensor by
connecting each of the clips on the leads to the matching colors of the sensor conductors,
with blue representing the shield (bare).
3.3.3 Operating the GK-403
1) Turn the display selector to position "B".
2) Turn the unit on.
3) The readout will display the vibrating wire output in digits. The last digit may change
one or two digits while reading.
4) The thermistor reading will be displayed above the gage reading in degrees
centigrade.
5) Press the "Store" button to record the value displayed.
If the no reading displays or the reading is unstable, see Section 5 for troubleshooting
suggestions.
The unit will automatically turn off after approximately two minutes to conserve power.
3.4 Measuring Temperatures
All vibrating wire transducers are equipped with a thermistor, which gives a varying resistance
output as the temperature changes. The white and green leads of the instrument cable are
normally connected to the internal thermistor.
The GK-403, GK-404, and GK-405 readout boxes will read the thermistor and display the
temperature in degrees C.
To read temperatures using an ohmmeter: Connect an ohmmeter to the green and white
thermistor leads coming from the displacement transducer. (Since the resistance changes with
temperature are large, the effect of cable resistance is usually insignificant. For long cables a
correction can be applied, equal to approximately 14.7 Ωfor every 1000 ft., or 48.5Ωper km at
20 °C. Multiply these factors by two to account for both directions.) Look up the temperature for
the measured resistance in Appendix A, Table 6.

16
4. DATA REDUCTION
4.1 Deformation Calculation
The basic unit utilized by Geokon for measurement and reduction of data from Vibrating Wire
Displacement Transducers is "digits". Calculation of digits is based on the following equation:
Digits =󰇡1
Period󰇢2x 10-3 or Digits=Hz2
1000
Equation 1 - Digits Calculation
To convert digits to deformation use Equation 2.
Duncorrected = (R1- R0) ×G ×F
Equation 2 - Displacement Calculation
Where;
R1is the current reading.
R0is the initial reading, usually obtained during installation (see Section 2.2).
G is the calibration factor, usually millimeters or inches per digit.
F is an optional engineering units conversion factor, see Table 2.
From→
To↓
Inches Feet Millimeters Centimeters Meters
Inches
1
12
0.03937
0.3937
39.37
Feet
0.0833
1
0.003281
0.03281
3.281
Millimeters
25.4
304.8
1
10
1000
Centimeters
2.54
30.48
0.10
1
100
Meters
0.0254
0.3048
0.001
0.01
1
Table 2 - Engineering Units Conversion Multipliers
For example, if the initial reading (R0) is 6783 digits, the current reading (R1) is 7228, and the
calibration factor (G) is 0.011906 mm/digit, then the deformation change is calculated as
follows: D = (7228 −6783) ×0.011906 = +5.3 mm
(Note that increasing readings [digits] indicate increasing extension.)

17
4.2 Temperature Correction
Geokon’s Vibrating Wire Displacement Transducers have a small coefficient of thermal
expansion; therefore, in most cases correction may not be necessary. However, if maximum
accuracy is desired, or the temperature changes are extreme (>10° C), a correction may be
applied based on the following equation:
Dcorrected = ((R1- R0) ×G) + ((T1- T0) ×K)
Equation 3 - Thermally Corrected Displacement Calculation
Where;
R1is the current reading.
R0is the initial reading.
G is the calibration Factor.
T1is the current temperature.
T0is the initial temperature.
K is the thermal coefficient (see Equation 4).
Tests have determined that the thermal coefficient, K, changes with the position of the transducer
shaft. Hence, the first step in the temperature correction process is to determine the proper
thermal coefficient based on the following equation:
K = ((R1×TM) +TB) ×G
Equation 4 - Thermal Coefficient Calculation
Where;
R1is the current reading.
TM is the multiplier from Table 3.
TB is the constant from Table 3.
G is the calibration factor, usually millimeters or inches per digit.
Model
Multiplier
(TM)
Constant
(TB)
4450-3 mm / 4450-0.125”
0.000520
3.567
4450-12 mm / 4450-0.5”
0.000375
1.08
4450-25 mm / 4450-1”
0.000369
0.572
4450-50 mm / 4450-2”
0.000376
0.328
4450-100 mm / 4450-4”
0.000398
0.0864
4450-150 mm / 4450-6”
0.000384
-0.3482
4450-200 mm / 4450-8”
0.000396
-0.4428
4450-300 mm / 4450-12”
0.000424
-0.6778
Table 3 - Thermal Coefficient Calculation Constants

18
Consider the following example, which uses the calibration factor from Figure 11, a sample
calibration sheet for Model 4450-25 mm. As can be seen from the obtained correction,
corrections for temperature change are small and can often be ignored.
R0= 4250 digits
R1= 5875 digits
T0= 10° C
T1= 20° C
G = 0.006152 mm/digit
K = ((5875 ×0.000369) + 0.572) ×0.006152 = 0.0168.
Dcorrected = ((R1- R0) ×G) + ((T1- T0) ×K)
Dcorrected = ((5875 - 4250) ×0.006152) + ((20 - 10) ×0.0168)
Dcorrected = 9.997 + .168
Dcorrected = +10.165 mm
4.3 Environmental Factors
Since the purpose of the displacement transducer installation is to monitor site conditions, factors
that may affect these conditions should always be observed and recorded. Seemingly minor
effects may have a real influence on the behavior of the structure being monitored, and may give
an early indication of potential problems. Some of these factors include, but are not limited to:
blasting, rainfall, tidal levels, traffic, temperature and barometric changes, weather conditions,
changes in personnel, nearby construction activities, excavation and fill level sequences, seasonal
changes, etc.

19
Figure 11 - A Typical Calibration Sheet.

20
5. TROUBLESHOOTING
Maintenance and troubleshooting of displacement transducers is confined to periodic checks of
cable connections and maintenance of terminals. Once installed, the gages are usually
inaccessible and remedial action is limited. Should difficulties arise, consult the following list of
problems and possible solutions. Return any faulty gages to the factory. Gages should not be
opened in the field. For additional troubleshooting and support, contact Geokon.
Symptom: Thermistor resistance is too high:
There may be an open circuit. Check all connections, terminals, and plugs. If a cut is located
in the cable, splice according to instructions in Section 2.4.
Symptom: Thermistor resistance is too low:
There may be a short. Check all connections, terminals, and plugs. If a short is located in the
cable, splice according to instructions in Section 2.4.
Water may have penetrated the interior of the transducer. There is no remedial action.
Symptom: Instrument Readings are Unstable:
Is the readout box position set correctly? If using a datalogger to record readings
automatically, are the swept frequency excitation settings correct?
Is the transducer shaft positioned outside the specified range (either extension or retraction)
of the instrument? Note that when the transducer shaft is fully retracted with the alignment
pin inside the alignment slot (as shown in Figure 1) the readings will likely be unstable
because the vibrating wire is out of its specified range.
Is there a source of electrical noise nearby? Likely candidates are generators, motors, arc
welding equipment, high voltage lines, etc. If possible, move the instrument cable away from
power lines and electrical equipment or install electronic filtering.
Make sure the shield drain wire is connected to ground. Connect the shield drain wire to the
readout using the blue clip. (Green for the GK-401.)
Does the readout work with another gage? If not, it may have a low battery or possibly be
malfunctioning.
Symptom: Instrument Fails to Read:
Is the cable cut or crushed? Check the resistance of the cable by connecting an ohmmeter to
the gage leads. Table 4 on the following page shows the expected resistance for the various
wire combinations; Table 5 is provided to fill in the actual resistance found. Cable resistance
is approximately 14.7 Ωper 1000' of 22 AWG wire. (Multiply this factor by two to account
for both directions.)
If the resistance is very high or infinite (megohms), the cable is probably broken or cut. If the
resistance is very low (<20Ω), the gage conductors may be shorted. If a cut or a short is
located in the cable, splice according to the instructions in Section 2.4.
Does the readout or datalogger work with another gage? If not, it may have a low battery or
possibly be malfunctioning.