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®.
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.
Copyright © 1985-2019 by Geokon®
(Doc Rev O, 2/21/2019)

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 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 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 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.

TABLE of CONTENTS
1. INTRODUCTION ...................................................................................................................................................1
2. INSTALLATION ....................................................................................................................................................2
2.1 PRELIMINARY TESTS............................................................................................................................................2
2.2 CONVERGENCE METER INSTALLATION................................................................................................................2
2.3 ELECTRICAL NOISE..............................................................................................................................................4
2.4 REMOVAL ............................................................................................................................................................4
2.5 CABLE INSTALLATION AND SPLICING ..................................................................................................................5
3. TAKING READINGS.............................................................................................................................................6
3.1 GK-404 READOUT BOX.......................................................................................................................................6
3.1.1 Operating the GK-404 ................................................................................................................................6
3.2 GK-405 READOUT BOX.......................................................................................................................................7
3.2.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached ...............................................................7
3.2.2 Connecting Sensors with Bare Leads..........................................................................................................7
3.2.3 Operating the GK-405 ................................................................................................................................7
3.3 GK-403 READOUT BOX (OBSOLETE MODEL)......................................................................................................8
3.3.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached ...............................................................8
3.3.2 Connecting Sensors with Bare Leads..........................................................................................................8
3.3.3 Operating the GK-403 ................................................................................................................................8
3.4 MEASURING TEMPERATURES...............................................................................................................................8
4. DATA REDUCTION ..............................................................................................................................................9
4.1 DIGITS .................................................................................................................................................................9
4.2 TEMPERATURE CORRECTION .............................................................................................................................10
4.3 ROD STRETCH CORRECTION ..............................................................................................................................11
4.4 CORRECTION FOR SAG .......................................................................................................................................12
4.5 ENVIRONMENTAL FACTORS...............................................................................................................................14
5. TROUBLESHOOTING........................................................................................................................................15
APPENDIX A. SPECIFICATIONS.........................................................................................................................17
A.1 MODEL 4425 CONVERGENCE METER ...............................................................................................................17
A.2 THERMISTOR (SEE APPENDIX BALSO) ..............................................................................................................17
APPENDIX B. THERMISTOR TEMPERATURE DERIVATION.....................................................................18
APPENDIX C. SWAGELOK TUBE FITTING INSTRUCTIONS ......................................................................19
C.1 INSTALLATION ..................................................................................................................................................19
C.2 REASSEMBLY INSTRUCTIONS ............................................................................................................................20
APPENDIX D. EXAMPLE CALIBRATION REPORT........................................................................................21

FIGURES
FIGURE 1-MODEL 4425 CONVERGENCE METER........................................................................................................... 1
FIGURE 2-OPERATION CHECK...................................................................................................................................... 2
FIGURE 3-MODEL 4425 CONVERGENCE METER INSTALLATION .................................................................................. 3
FIGURE 4-CONVERGENCE METER INSTALLATION DETAIL -TURNBUCKLE END........................................................... 4
FIGURE 5-LEMO CONNECTOR TO GK-404 ................................................................................................................... 6
FIGURE 6-LIVE READINGS –RAW READINGS............................................................................................................... 7
FIGURE 7-TUBE INSERTION .........................................................................................................................................19
FIGURE 8-MAKE A MARK AT SIX O’CLOCK ................................................................................................................19
FIGURE 9-TIGHTEN ONE AND ONE-QUARTER TURNS .................................................................................................19
FIGURE 10 -MARKS FOR REASSEMBLY ........................................................................................................................20
FIGURE 11 -FERRULES SEATED AGAINST FITTING BODY.............................................................................................20
FIGURE 12 -TIGHTEN NUT SLIGHTLY...........................................................................................................................20
FIGURE 13 -TYPICAL 4425 CALIBRATION REPORT.......................................................................................................21
TABLES
TABLE 1-CONVERGENCE METER LENGTH ................................................................................................................... 3
TABLE 2-ENGINEERING UNITS CONVERSION MULTIPLIERS ......................................................................................... 9
TABLE 3-TRANSDUCER THERMAL COEFFICIENT CALCULATION CONSTANTS .............................................................10
TABLE 4-YOUNG’S MODULUS AND THERMAL COEFFICIENTS.....................................................................................11
TABLE 5-SPRING RATES..............................................................................................................................................12
TABLE 6-DENSITIES ....................................................................................................................................................12
TABLE 7-SAMPLE RESISTANCE ...................................................................................................................................16
TABLE 8-RESISTANCE WORK SHEET...........................................................................................................................16
TABLE 9-THERMISTOR RESISTANCE VERSUS TEMPERATURE .....................................................................................18
EQUATIONS
EQUATION 1-DIGITS CALCULATION............................................................................................................................. 9
EQUATION 2-DEFORMATION CALCULATION ................................................................................................................ 9
EQUATION 3-TEMPERATURE CORRECTION .................................................................................................................10
EQUATION 4-TRANSDUCER THERMAL COEFFICIENT CALCULATION...........................................................................10
EQUATION 5-THERMALLY CORRECTED DEFORMATION CALCULATION ......................................................................11
EQUATION 6-ROD STRETCH ........................................................................................................................................11
EQUATION 7-ROD STRETCH CORRECTION...................................................................................................................11
EQUATION 8-SAG CORRECTION ..................................................................................................................................12
EQUATION 9-CORRECTED DEFORMATION...................................................................................................................13
EQUATION 10 -RESISTANCE TO TEMPERATURE ...........................................................................................................18

1
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 two 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 two
anchors are conveyed by the connecting rods and
measured by the transducer.
The Model 4425 Convergence Meter consists of
three basic components: the two anchor points, 6
mm (1/4") diameter connecting rods, and 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 gauge 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, so 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.
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
Figure 1 - Model 4425 Convergence Meter

2
2. INSTALLATION
2.1 Preliminary Tests
Upon receipt of the instrument, the gauge should be checked for proper operation (including the
thermistor). See Section 3 for readout instructions. In position “B” the gauge will read around
2000 when the threaded connector is pulled out approximately 3 mm (0.125").
Figure 2 - Operation Check
CAUTION! Do not extend the connector more than the range of the gauge. Do not turn the
threaded shaft at the end of the gauge more than 180 degrees or gauge failure may occur!
Checks of electrical continuity can also be made using an ohmmeter. Resistance between the
gauge leads (red and black) should be approximately 180 Ω, ±10 Ω. Resistance between the
thermistor leads (white and green) varies with temperature; see Appendix B. Resistance between
any conductor and the shield should exceed two megohms. (For long cables a correction can be
applied, equal to approximately 14.7 Ω per one thousand feet [48.5Ω per km] of 22 AWG
stranded copper leads. Multiply this factor by two to account for both directions.)
2.2 Convergence Meter Installation
1) The first step is to unpack all the various components and lay them on a flat surface in their
relative positions. (Refer to Figure 1 in Section 1.)
2) Next, the two anchor points must be installed. When the locations have been decided, drill
holes to accommodate 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.
3) 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
.
4) Measure the total distance from anchor eyebolt to anchor eyebolt, inside to inside at the
points where they will touch the convergence meter eyehooks.
5) Check and confirm the convergence meter length against the length shown in Table 1. 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,

3
add 30 mm (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"
Table 1 - Convergence Meter Length
6) Next, the connecting rods must be assembled. 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 Swagelok connector according to the instructions in Appendix C. Connect the
second and successive rods using the Swagelok fittings as described above.
7) Connect the Swagelok eyehook to one end of the rods and the convergence meter to the
other.
8) Hook the eyehook end into the installed eyebolt first.
9) 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.
Tunnel Cross Section
Convergence Meter Connecting Rod
Eyebolt Anchor Eyebolt Anchor
Figure 3 - Model 4425 Convergence Meter Installation

4
10) Connect the readout box. To set the transducer to midrange, 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.
11) Tighten the locknuts on the turnbuckle. (See Figure 4 below.)
12) Initial readings must be taken and carefully recorded along with the temperature at the time
of installation.
Figure 4 - Convergence Meter Installation Detail - Turnbuckle End
2.3 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.
2.4 Removal
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.