Geokon 4425 User manual

Instruction Manual
Model 4425
VW Convergence Meter
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 © 1985-2016 by Geokon, Inc.
(Doc Rev L, 11/10/16)

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
Page
1. INTRODUCTION...........................................................................................................................................1
2. INSTALLATION.............................................................................................................................................2
2.1. PRELIMINARY TESTS ...................................................................................................................................2
2.2. CONVERGENCE METER INSTALLATION........................................................................................................2
2.3. CABLE INSTALLATION ................................................................................................................................4
2.4. ELECTRICAL NOISE.....................................................................................................................................4
2.5. INITIAL READINGS.......................................................................................................................................4
3. TAKING READINGS.....................................................................................................................................5
3.1. OPERATION OF THE GK-403 READOUT BOX...............................................................................................5
3.2 OPERATION OF THE GK404 READOUT BOX.................................................................................................5
3.3 OPERATION OF THE GK405 READOUT BOX.................................................................................................6
3.4. MEASURING TEMPERATURES......................................................................................................................6
4. DATA REDUCTION......................................................................................................................................7
4.1. DEFORMATION CALCULATION....................................................................................................................7
4.2. TEMPERATURE CORRECTION ......................................................................................................................9
4.3. ROD STRETCH CORRECTION......................................................................................................................10
4.4 CORRECTION FOR SAG...............................................................................................................................11
4.5 ENVIRONMENTAL FACTORS.......................................................................................................................13
5. TROUBLESHOOTING................................................................................................................................14
APPENDIX A - SPECIFICATIONS...............................................................................................................15
A.1. MODEL 4425 CONVERGENCE METER.......................................................................................................15
A.2. THERMISTOR (SEE APPENDIX BALSO)......................................................................................................15
APPENDIX B - THERMISTOR TEMPERATURE DERIVATION............................................................16
APPENDIX C - SWAGELOK FITTING ASSEMBLY INSTRUCTIONS...................................................17

LIST of FIGURES, TABLES and EQUATIONS
Page
FIGURE 1-MODEL 4425 CONVERGENCE METER................................................................................................ 1
FIGURE 2-MODEL 4425 CONVERGENCE METER INSTALLATION ........................................................................ 2
FIGURE 3-CONVERGENCE METER INSTALLATION DETAIL -TURNBUCKLE END ................................................. 4
FIGURE 4GK405 READOUT UNIT.......................................................................................................................... 6
EQUATION 1-DIGITS CALCULATION ..................................................................................................................... 7
EQUATION 2-DEFORMATION CALCULATION ........................................................................................................ 7
TABLE 1-ENGINEERING UNITS CONVERSION MULTIPLIERS ............................................................................... 7
FIGURE 5ATYPICAL CALIBRATION SHEET............................................................................................................. 8
EQUATION 3-TEMPERATURE CORRECTION......................................................................................................... 9
EQUATION 4-TRANSDUCER THERMAL COEFFICIENT CALCULATION .................................................................. 9
TABLE 2-TRANSDUCER THERMAL COEFFICIENT CALCULATION CONSTANTS .................................................... 9
EQUATION 5-THERMALLY CORRECTED DEFORMATION CALCULATION ............................................................ 10
EQUATION 6–ROD STRETCH CORRECTION....................................................................................................... 10
TABLE 3–YOUNGS MODULUS AND THERMAL COEFFICIENTS ........................................................................... 10
TABLE 4–SPRING RATES................................................................................................................................... 11
TABLE 5-DENSITIES ........................................................................................................................................... 12
EQUATION 8-CORRECTED DEFORMATION ........................................................................................................ 12
TABLE A-1 MODEL 4425 SPECIFICATIONS ......................................................................................................... 15
EQUATION B-1 CONVERT THERMISTOR RESISTANCE TO TEMPERATURE ........................................................ 16
TABLE B-1 THERMISTOR RESISTANCE VERSUS TEMPERATURE ........................................................................... 16

1. INTRODUCTION
The Model 4425 Vibrating Wire Convergence
Meter is designed to detect the deformation of
rock or soil masses by measuring the contraction
(or elongation) between 2 fixed anchor points.
Anchor points are established in the mass, and
connecting rods from one anchor lead back to
transducer assembly located at the second
anchor point. Changes in distance between the 2
anchors are conveyed by the connecting rods and
measured by the transducer.
The Model 4425 Convergence Meter consists of 3
basic components. They are 1) the 2 anchor
points, 2) 6 mm (¼") diameter connecting rods,
and 3) the spring-tensioned vibrating wire
transducer assembly. See Figure 1. Essential
accessories include a vibrating wire readout and
an installation tool kit (supplied).
The transducer consists of a vibrating wire
sensing element in series with a heat treated,
stress relieved spring which is connected to the
wire at one end and a connecting rod at the other.
The unit is fully sealed and operates at pressures
of up to 250 psi. As the connecting rod is pulled
out from the gage body, the spring is elongated
causing an increase in tension which is sensed by
the vibrating wire element. The tension in the
wire is directly proportional to the extension,
hence, the convergence can be determined very
accurately by measuring the strain change with
the vibrating wire readout box.
The convergence meter can operate in horizontal,
inclined or vertical orientations. In areas where
construction traffic is expected or where the
instrument may be left in an exposed location,
some form of protective housing should be
considered.
Figure 1 - Model 4425 Convergence Meter
Turnbuckle
Eye Hook
Swagelok Fitting
Thermistor
Spring
Transducer Shaft
Connecting Rod
Electromagnetic Coil
Instrument Cable
Swagelok Fitting
Eye Hook
Alignment Slot & Pin
Transducer Housing
Swagelok Fitting
Left-Hand Thread
Right-Hand Thread

2
2. INSTALLATION
2.1. Preliminary Tests
Upon receipt of the instrument, the gage should be checked for proper operation (including the
thermistor). See Section 3 for readout instructions. In position "B" the gage will read around
2000 when the threaded connector is pulled out approximately 3 mm (0.125"). Do not extend
the connector more than the range of the gage. The threaded connector on the end of the
gage should not be turned independently of the gage body.
Checks of electrical continuity can also be made using an ohmmeter. Resistance between the
gage leads should be approximately 180 , ±10 . Remember to add cable resistance when
checking (22 AWG stranded copper leads are approximately 14.7/1000' or 48.5/km, multiply
by 2 for both directions). Between the green and white should be approximately 3000 ohms at
25° (see Table B-1), and between any conductor and the shield should exceed 2 megohms.
2.2. Convergence Meter Installation
The first step is to unpack all the various components and lay them on a flat surface in their
relative positions (see Figure 1).
Next, the two anchor points must be installed. When the locations have been decided, drill
holes to accomodate the anchors. Cement the eyebolt anchors in place using quick-set
(hydraulic) cement or epoxy. Allow the cement or epoxy to set completely before attempting the
installation of the convergence meter.
Tunnel Cross Section
Convergence Meter Connecting Rod
Eyebolt Anchor Eyebolt Anchor
Figure 2 - Model 4425 Convergence Meter Installation

3
Follow these steps to install the convergence meter;
1. Attach the turnbuckle assembly to the convergence meter by screwing in the left-hand
threaded portion. Use thread locking cement and tighten the lock nut. Set the turnbuckle
such that about 10-12 mm (0.5") of thread is inside from each end.
2. Measure the total distance from anchor eyebolt to anchor eyebolt, inside to inside at the
points where they will touch the convergence meter eyehooks.
3. Check and confirm the convergence meter length against the length shown in the table
below. (The measurement is made from inside the eyehooks, at the point where they touch
the anchor eyebolts, to the end of the Swagelok fitting. To calculate the rod length that will
be needed, subtract the convergence meter length from the anchor eyebolt to anchor
eyebolt distance, now add 30mm (1.2”) to account for the distance the rod penetrates the
Swagelok fittings, This is the nominal rod length that will be required.
Range: 12 mm
0.50
inches
25 mm
1 inch 50 mm 2 inches 100 mm 4 inches 150 mm 6 inches
Convergence Meter
Length including
Swagelok eyehook
assembly:
710 mm
28"
710 mm
28"
865 mm
34"
1195 mm
47"
1615 mm
63.5"
4. Next, the connecting rods must be assembled. This is achieved using the Swagelok
fittings supplied with the instrument and the appropriate wrenches. Appendix C details
additional fitting assembly instructions.
Connect the first length of connecting rod to the sensor using the Swagelok fitting. Push
the rod into the fitting until it hits the stop. Tighten the nut 1½ turns, holding the body with
one wrench while tightening the nut with the other. Connect the second and successive
rods using the Swagelok fittings as described above.
5. Connect the Swagelok eyehook to one end of the rods and the convergence meter to the
other.
6. Hook the eyehook end into the installed eyebolt first.
7. Now, hook the convergence meter into the other eyebolt. It should go in without having to
extend the convergence meter spring. Remember that if the spring is extended beyond
the range of the transducer the transducer could be damaged.
8. Connect the readout box. To set the transducer to mid-range, rotate the turnbuckle until a
reading of approximately 5500 digits is obtained. To use the total range in convergence,
set the meter at 8000. To use the total range in extension, set the meter at 2500.
9. Tighten the locknuts on the turnbuckle. The installation is now complete.
10. To remove the system, loosen the turnbuckle all the way and then remove the
convergence meter. Disconnect the Swagelok fittings on the rods and disassemble the
rods to a manageable length. If the rod string needs to be lengthened (or shortened) for
the next installation, cut off the ferrules and reinstall new ferrules for the next installation.

4
Turnbuckle
Tunnel Wall
Anchor
Convergence Meter
Eyebolt
Figure 3 - Convergence Meter Installation Detail - Turnbuckle End
2.3. Cable Installation
The cable should be routed in such a way so as to minimize the possibility of damage due to
moving equipment, debris or other causes.
Cables may be spliced to lengthen them, without affecting gage readings. Always waterproof
the splice completely, preferably using an epoxy based splice kit such the 3M Scotchcast,
model 82-A1. These kits are available from the factory.
2.4. 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 with AC power lines!
The instrument cables will pick up the 50 or 60 Hz (or other frequency) noise from the power
cable and this will likely cause a problem obtaining a stable reading. Contact the factory
concerning filtering options available for use with the Geokon dataloggers and readouts should
difficulties arise.
2.5. Initial Readings
Initial readings must be taken and carefully recorded along with the temperature at the time of
installation.

5
3. TAKING READINGS
3.1. Operation of the GK-403 Readout Box
The GK-403 can store gage readings and also apply calibration factors to convert readings to
engineering units, ie. inches or millimeters. Consult the GK-403 Instruction Manual for
additional information on Mode "G" of the Readout. The following instructions will explain taking
gage measurements using Mode "B".
Connect the Readout using the flying leads or in the case of a terminal station, with a connector.
The red and black clips are for the vibrating wire transducer, the white and green clips are for
the thermistor and the blue for the shield drain wire.
1. Turn on the Readout. Turn the display selector to position "B". Readout is in digits (see
Equation 1).
2. Turn the unit on and a reading will appear in the front display window. The last digit may
change one or two digits while reading. 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 thermistor will be read and output directly in degrees
centigrade.
3. The unit will automatically turn itself off after approximately 2 minutes to conserve power.
3.2 Operation of the GK404 Readout 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 alligator
clips. Note the colors of the alligator clips are red, black, green, white and blue. The colors
represent the positive vibrating wire gage lead (red), negative vibrating wire gage lead (black),
positive thermistor lead (green), negative thermistor lead (white) and transducer cable drain wire
(blue). The clips should be connected to their respectively colored leads from the vibrating wire
gage cable.
Use the POS (Position) button to select position Band the MODE button to select Dg (digits).
Other functions can be selected as described in the GK404 Manual.
The GK-404 will continue to take measurements and display the readings until the OFF button
is pushed, or if enabled, when the automatic Power-Off timer shuts the GK-404 off.
The GK-404 continuously monitors the status of the (2) 1.5V AA cells, and when their combined
voltage drops to 2V, the message Batteries Low is displayed on the screen. A fresh set of 1.5V
AA batteries should be installed at this point

6
3.3 Operation of the GK405 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
The GK-405 Remote Module which is housed in a weather-proof enclosure and connects to
the vibrating wire sensor by means of:
1) Flying leads with alligator type clips when the sensor cable terminates in bare wires or,
2) By means of a 10 pin connector..
The two components communicate wirelessly using Bluetooth®, a reliable digital
communications protocol. The Readout Unit can operate from the cradle of the Remote Module
(see Figure 4) or, if more convenient, can be removed and operated up to 20 meters from the
Remote Module
Figure 4 GK405 Readout Unit
For further details consult the GK405 Instruction Manual.
3.4. Measuring Temperatures
Each Vibrating Wire Convergence Meter is equipped with a thermistor for reading temperature.
The thermistor gives a varying resistance output as the temperature changes. Usually the white
and green leads are connected to the internal thermistor. Note: The GK-403, gK-404 and GK-
405 readout boxes will read the thermistor and display temperature in C automatically
1. If an Ohmmeter is uded connect the ohmmeter to the two thermistor leads coming from the
convergence meter. (Since the resistance changes with temperature are so large, the effect
of cable resistance is usually insignificant.)
2. Look up the temperature for the measured resistance in Table B-1 (Appendix B). Alternately
the temperature could be calculated using Equation B-1 (Appendix B). For example, a
resistance of 3400 ohms equivalent to 22° C. When long cables are used the cable
resistance may need to be taken into account. Standard 22 AWG stranded copper lead
cable is approximately 14.7/1000' or 48.5/km, multiply by 2 for both directions.

7
4. DATA REDUCTION
4.1. Deformation Calculation
The basic units utilized by Geokon for measurement and reduction of data from Vibrating Wire
Convergence Meters are "digits". The units displayed by the all Readout Boxes in position "B"
are digits. Calculation of digits is based on the following equation;
Digits Period in onds 






23
110
(sec ) or Digits Hz
23
10
Equation 1 - Digits Calculation
To convert digits to deformation the following equation applies;
Duncorrected = (R1- R0) G F
Equation 2 - Deformation Calculation
Where: Duncorrected is the calculated deformation.
R
1is the current reading.
R
0is the initial reading usually obtained at installation (see section 2.4).
G is the calibration factor, usually in terms of millimeters or inches per digit.
F is an engineering units conversion factor (optional), see Table 1.
From
To
Inches Feet Millimeters Centimeter
s
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 1 - Engineering Units Conversion Multipliers
For example, the initial reading, R0, at installation of a convergence meter with a 12 mm
transducer range is 4919 digits. The current reading, R1, is 6820. The Calibration Factor is
0.00258 mm/digit. The deformation change is;
Duncorrected = (6820
 4919)  0.002402 = +4.566mm
Note that increasing readings (digits) indicate increasing extension.
A typical calibration sheet is shown in figure 5.

8
Figure 5 A typical Calibration Sheet

9
4.2. Temperature Correction
The Model 4425 Vibrating Wire Convergence Meter has a very small coefficient of thermal
expansion so in most cases correction is not necessary. However, if maximum accuracy is
desired or the temperature changes are extreme (>10° C) corrections may be applied. The
following equation applies;
Dtemperature = (T1- T0) (K + LKR+ KT)
Equation 3 - Temperature Correction
Where: Dtemperature is the deformation due to temperature change.
T
1is the current temperature in degrees C.
T
0is the initial temperature in degrees C.
K is the thermal coefficient of transducer, see Equation 4.
K
Ris the thermal coefficient of the connecting rod, see Table 3.
L is the length of the connecting rod, in millimeters or inches.
K
Tis the thermal coefficient of the turnbuckle/spring, 0.0007" or 0.0178 mm/°C.
Tests have determined that the transducer thermal coefficient, K, changes with the position of
the transducer shaft. Hence, the first step in the temperature correction process is
determination of the proper transducer thermal coefficient based on the following equation;
K = ((R1M) B) G
Equation 4 - Transducer Thermal Coefficient Calculation
Where: K is the transducer thermal coefficient.
R
1is the current reading in digits.
M is the multiplier from Table 2.
B is the constant from Table 2.
G is the calibration factor from the supplied Calibration Sheet.
Model: 4425-12
mm
4425-0.5"
4425-25
mm
4425-1"
4425-50
mm
4425-2"
4425-100
mm
4425-4"
4425-150
mm
4425-6"
Multiplier
(M): 0.000375 0.000369 0.000376 0.000398 0.000384
Constant
(B): 1.08 0.572 0.328 0.0864 -0.3482
Model: 4425-200
mm
4425-8.0"
4425-300
mm
4425-12"
Multiplier
(M): 0.000396 0.000424
Constant
(B): -0.4428 -0.6778
Table 2 - Transducer Thermal Coefficient Calculation Constants

10
All of the above thermal corrections describe an expansion of components with an increase in
temperature. Hence, the calculated thermal corrections must be added to the deformation
calculated using Equation 2.
Dtcorrected = Duncorrected + Dtemperature
Equation 5 - Thermally Corrected Deformation Calculation
Experience has shown that the most stable readings are obtained when the system is at a
stable temperature. Taking readings late at night or early in the morning will eliminate the
transient effects of sunlight and rapid warming of sensor components. If a datalogger is used,
readings will show the trends associated with thermal effects during the day and through the
seasons, and allow corrections for these effects to be accurately made.
4.3. Rod Stretch Correction
Rod Stretch =
Where; P is the rod tension (lbs. or Newtons).
L is the rod length (inches or mm).
a is the rod area of cross section (sq inches or square mm).
E is the Youngs modulus (lbs/sq inch or MPa).
P depends on the spring rate, S, of the large exterior tension spring and the
amount of deformation (Dtcorrected),
i.e. P = S Dcorrected so that:
D
rodstretch =
Equation 6 – Rod Stretch correction
Values for KRand E are as follows:
Rod Material E, Youngs Modulus KRThermal Coefficient
Lbs/sq in. MPa Per º C
Stainless Steel 28.5 x 1060.196 x 10617.3 x 10-6
Graphite 17 x 1060.117 x 1060.2 x 10-6
Invar 21 x 1060.145 x 1061.1 x 10-6
Fiberglass 6 x 1060.041 x 1066.0 x 10-6
Table 3 – Youngs Modulus and Thermal Coefficients
Increasing tensions cause the rod to elongate so that the required correction would be positive,
when Dtcorrected is positive.
PL
aE
SDL
aE

11
Values for S are as follows:
Range Spring Rate
Model Number Inches mm lbs/in. Newtons/mm
4425-12 ½ 12 34 5.95
4425-25 1 25 34 5.95
4425-50 2 50 17 2.98
4425-100 4 100 17 2.98
4425-150 6 150 8.5 1.49
Table 4 – Spring Rates
4.4 Correction for Sag
Correction for sag = - LW2/24P2or -L3ω2/24P2…………… Equation 7 Sag Correction
Where L = length of rods (The distance over which the measurement is made).
W = weight of rods
P = tension. The springs used have an initial tension of 13lbs, (57.8N), and this must be added
to the force caused by the diplacement = SD
ω= weight of rods per unit length (See Table 5)
For convergence the correction is negative, for extensions the correction is positive.
For example: consider a horizontal convergence meter consisting of 60ft of graphite rods with
spring constant of 17 lbs per inch.
L = length of rods = 60ft (The distance over which the measurement is being made).
W = weight of 60ft of graphite rods = 2 lbs
P0= 47lbs and P1= 30 lbs (These values are obtained from a knowledge of the spring tension
at various extensions), and that an apparent measured convergence of 1.000 inch has taken
place.
The correction to L for sag initially is -60 x 4 / 24 x 47 x 47 = - 0.0045ft = - 0.054 inches
The correction for sag at T1is - 60 x 4 / 24 x 30 x 30 = - 0.0111ft = - 0.133 inches
So after correction for sag the true convergence is 1 – (0.133 – 0.054) = 0.921 inches

12
Rod Material Weight per unit length
Lbs/inches Kgm/mm
Stainless Steel 0.0139 248 x 10-6
Graphite 0.00275 49.1 x 10-6
Invar 0.0139 248 x 10-6
Fiberglass 0.0035 62.4 x 10-6
Table 5 - Densities
Summing all the various effects.
Dcorrected = Duncorrected + Dtemperature + Drodstretch + Dsag
Equation 8 - Corrected Deformation
Again, consider the following example from a Model 4425-12 Convergence Meter attached to 30
meters of ¼ inch diameter graphite rod.
R0= 4919 digits
R1= 6820 digits
T0= 15.3° C
T1= 32.8° C
(T1– T0) = + 17.5° C
G = 0.002402 mm/digit
L = 30 meters = 30,000mm
S = 5.95 N/mm
a = 31.67 sq mm
E = 0.117 × 106 MPa
ω= 0.049Kgm/m = 0.481N/m (0.033 lbs/ft)
P0= 133N
P1 = 163N

13
From Equation 4
K = ((6820
 0.000375) + 1.08)  0.002402 = 0.0087mm
From Equation 2
Duncorrected = (6820 - 4919)
 0.002402 = + 4.566 mm
The plus sign indicates an extension
From Equation 3
Dtemperature = + 17.5(0.0087 + 0.2
 10-6  30,000 + 0.0178)
= + 0.568 mm
From Equation 5
Dcorrected = + 4.566 + 0.568 = + 5.134 mm
From Equation 6
Drodstretch = 5.95
 5.045  30,000 / 31.67 × 0.117 × 106= +0.243mm
From Equation 7 ( Not required if the convergence meter is vertical)
Dsag =[303x 0.4812/24 x 133 x 133] -[303x 0,4812/24 x 163 x 163] = + 4.918 mm
From Equation 8
The true extension
Dcorrected = + 4.566 + 0.568 +0.243 + 4.918 = + 10.29 mm
4.5 Environmental Factors
Since the purpose of the convergence meter installation is to monitor site conditions, factors
which 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, excavation and fill levels and sequences, traffic, temperature and
barometric changes, changes in personnel, nearby construction activities, seasonal changes,
etc.

14
5. TROUBLESHOOTING
Maintenance and troubleshooting of Geokon Vibrating Wire Convergence Meters are confined
to periodic checks of cable connections and maintenance of terminals. The Convergence
Meters contain no user-servicable components. However, consult the following list of problems
and possible solutions should difficulties arise. Consult the factory for additional troubleshooting
help.
Symptom: Convergence Meter 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 of the Convergence Meter positioned outside the specified range of
the instrument? Note that when the transducer shaft is fully retracted with the alignment pin
inside the alignment slot (Figure 1) the readings will likely be unstable because the
transducer is now out of range.
Is there a source of electrical noise nearby? Most probable sources of electrical noise are
motors, generators, transformers, arc welders and antennas. Make sure the shield drain
wire is connected to ground whether using a portable readout or datalogger. If using the
GK-401 Readout connect the clip with the green boot to the bare shield drain wire of the
pressure cell cable. If using the GK-403 connect the clip with the blue boot to the shield
drain wire.
Symptom: Convergence Meter Fails to Read
Is the cable cut or crushed? This can be checked with an ohmmeter. Nominal resistance
between the two transducer leads (usually red and black leads) is 180, 10. Remember
to add cable resistance when checking (22 AWG stranded copper leads are approximately
14.7/1000' or 48.5/km). If the resistance reads infinite, or very high (>1 megohm), a cut
wire must be suspected. If the resistance reads very low (100) a short in the cable is
likely. Splicing kits and instructions are available from the factory to repair broken or shorted
cables. Consult the factory for additional information.
Does the readout or datalogger work with another Convergence Meter? If not the readout or
datalogger may be malfunctioning.
Symptom: Thermistor resistance is too high.
Is there an open circuit? Check all connections, terminals and plugs. If a cut is located in
the cable, splice according to instructions in Section 2.3.
Symptom: Thermistor resistance is too low.
Is there a short? Check all connections, terminals and plugs. If a short is located in the
cable, splice according to instructions in Section 2.3.
Water may have penetrated the interior of the Convergence Meter. There is no remedial
action.