Geokon 4420 User manual

Instruction Manual
Model 4420
VW Crackmeter
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
b
e accurate and reliable. However, Geokon, Inc. assumes no responsibility
for errors, omissions or misinterpretation. The information herein is subject to change without notification.
Copyright © 1986, 1996, 2004, 2006, 2007, 2008 by Geokon, Inc.
(Doc Rev N, 9/08)

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. CRACKMETER INSTALLATION..................................................................................................................... 2
2.2.1. Installation using Weldable Fixtures ................................................................................................ 4
2.2.2. Installation using Groutable Anchors............................................................................................... 4
2.2.3. Installation using Expansion Anchors .............................................................................................. 5
2.3. CABLE INSTALLATION................................................................................................................................6
2.4. ELECTRICAL NOISE .................................................................................................................................... 6
2.5. LIGHTNING PROTECTION............................................................................................................................ 6
3. TAKING READINGS.................................................................................................................................... 7
3.1. OPERATION OF THE GK-401 READOUT BOX .............................................................................................. 7
3.2. OPERATION OF THE GK-403 READOUT BOX .............................................................................................. 7
3.3 OPERATION OF THE GK404 READOUT BOX ................................................................................................ 8
3.4. MEASURING TEMPERATURES ..................................................................................................................... 9
4. DATA REDUCTION ..................................................................................................................................... 9
4.1. DEFORMATION CALCULATION ................................................................................................................... 9
4.2. TEMPERATURE CORRECTION.................................................................................................................... 12
4.3. ENVIRONMENTAL FACTORS ..................................................................................................................... 13
5. TROUBLESHOOTING............................................................................................................................... 13
APPENDIX A - SPECIFICATIONS ............................................................................................................... 14
A.1 MODEL 4420 CRACKMETER ..................................................................................................................... 15
A.2 THERMISTOR............................................................................................................................................. 15
APPENDIX B - THERMISTOR TEMPERATURE DERIVATION ........................................................... 15

LIST of FIGURES, TABLES and EQUATIONS
Page
FIGURE 1: MODEL 4420-1-50/100/150/200/300 VIBRATING WIRE CRACKMETER..................................................1
FIGURE 2-MODEL 4420-1-12/25 DETAIL...............................................................................................................1
FIGURE 3-ANCHOR TYPES WITH DIMENSIONS .......................................................................................................2
TABLE 1-CRACKMETER ANCHOR SPACING DISTANCES.........................................................................................3
TABLE 2-CRACKMETER READING RANGES............................................................................................................3
FIGURE 4-INSTALLATION USING WELDABLE FIXTURES.........................................................................................4
FIGURE 5-INSTALLATION USING GROUTABLE ANCHORS .......................................................................................4
FIGURE 6-INSTALLATION USING EXPANSION ANCHORS.........................................................................................5
FIGURE 7-LIGHTNING PROTECTION SCHEME .........................................................................................................7
EQUATION 1-DIGITS CALCULATION ......................................................................................................................9
EQUATION 2-DEFORMATION CALCULATION..........................................................................................................9
TABLE 3-ENGINEERING UNITS CONVERSION MULTIPLIERS...................................................................................9
FIGURE 8-TYPICAL CRACKMETER CALIBRATION SHEET .....................................................................................11
EQUATION 3-THERMALLY CORRECTED DEFORMATION CALCULATION...............................................................12
EQUATION 4-THERMAL COEFFICIENT CALCULATION..........................................................................................12
TABLE 4-THERMAL COEFFICIENT CALCULATION CONSTANTS ............................................................................12
TABLE A-1 CRACKMETER SPECIFICATIONS..........................................................................................................15
EQUATION B-1 CONVERT THERMISTOR RESISTANCE TO TEMPERATURE..............................................................16
TABLE B-1 THERMISTOR RESISTANCE VERSUS TEMPERATURE ............................................................................16

1
1. INTRODUCTION
Geokon Model 4420 Vibrating Wire Crackmeters are designed to measure movement across
joints such as the construction joints in buildings, bridges, pipelines, dams, etc.; tension
cracks in soils and joints in rock and concrete.
The instrument 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 opening of the joint can be determined very
accurately by measuring the strain change with the vibrating wire readout box.
Figure 1: Model 4420-1-50/100/150/200/300 Vibrating Wire Crackmeter
The Model's 4420-12 and 4420-25 differ slightly from the standard Crackmeter in that they
provide for adjustment of the setting distance with a threaded extension rod and locking nut.
Figure 2 - Model 4420-1-12/25 Detail
CAUTION: Do not rotate the shaft of the Crackmeter. 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.

2
2. INSTALLATION
2.1. Preliminary Tests
Upon receipt of the instrument, the gage should be checked for proper operation (including
the thermistor). The Crackmeter normally arrives with it's shaft secured at
approximately 50% of it's range, by either a split PVC sleeve, (for crackmeters over
100mm (4 inch) range), or a nylon Tyrap, (see Figure 1). This holds the instrument in
tension thereby helping protect it during shipping. Remove this PVC split sleeve or Tyrap
before proceeding. Connect the gage to the Readout to take a reading (see section 3). The
reading should be stable and in the range of 4000 to 5000.
Checks of electrical continuity can also be made using an ohmmeter. Resistance between the
gage leads should be approximately 180 ohms, ±10 ohms. Remember to add cable resistance
when checking (22 AWG stranded copper leads are approximately 14.7Ω/1000' or 48.5Ω
/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. Crackmeter Installation
Three types of anchors are available from the factory for installing the Model 4420 Vibrating
Wire Crackmeter.
Figure 3 - Anchor Types with Dimensions
The weldable fixture is designed to install the Crackmeter on steel members. The machine
bolt expansion anchors and groutable anchors are used to install the Crackmeter on concrete
or rock. The anchors are installed at the appropriate spacing distance (see Table 1)
depending on the anticipated direction of movement, (extensions or compressions). The
following three sections detail instructions for each of the above three anchors.

3
Model & Range Mid-Range To Monitor Extensions To Monitor
Compressions
4420-12 mm
4420-.5" 325 mm 12.8" 319 mm 12.6" 331 mm 13.0"
4420-25 mm
4420-1" 333 mm 13.1" 321 mm 12.6" 345 mm 13.6"
4420-50 mm
4420-2" 379 mm 14.9" 354 mm 13.9" 404 mm 15.9"
4420-100 mm
4420-4" 543 mm 21.4" 493 mm 19.4" 593 mm 23.3"
4420-150 mm
4420-6" 686 mm 27.0" 611 mm 24.1" 761 mm 30.0"
4420-200 mm
4420-8” 740 mm 29.1” 640 mm 25.2” 840 mm 33.1”
4420-300 mm
4420-12 967 mm
38.1"817 mm
32.2"1117 mm 44"
Table 1 - Crackmeter Anchor Spacing Distances
When setting the gage position using a portable readout (see section 3) use the reading
ranges in Table 2 to determine the proper position.
Approx Mid-Range
Reading Approx Reading to Monitor Extensions Approx Reading to Monitor Compressions
4500-5000 2500-3000 6500-7000
Table 2 - Crackmeter Reading Ranges
Note also that the calibration sheet (Figure 8) supplied with the Crackmeter shows actual
readings at zero, 25%, 50%, 75% and 100% of the range of extension. These readings can be
used as a guide to set the Crackmeter in any part of it's range, either in anticipation of closure
or opening of the crack. The Crackmeter can be extended until the desired reading (see
Section 3 for readout instructions) is obtained and then held in this position while the
distance between the anchor points (threaded cap screws inside the swivel bearings), see
Figure 1) is measured. This measurement can then serve as a spacing guide for drilling or
welding the anchor points.
Caution: Do not rotate the shaft of the Crackmeter. 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.
Special note regarding installation of the Model's 4420-1-12 or 4420-1-25: If the reading
is not in the proper range after installation additional adjustment is provided for by the
inclusion of a threaded extension and locking nut as depicted in Figure 2. In order to use
this feature the transducer needs to be attached, at the coil assembly end, to the anchor.
Position (but do not attach) the opposite end of the Crackmeter over the threaded hole of
the anchor. If the reading is not in the proper range (see Table 2) loosen the locking nut
(Figure 2) and rotate the threaded rod which carries the rod end swivel bearing, in or out
of the end of the Transducer Shaft until the desired spacing and initial reading has been
achieved. The transducer shaft itself must not be rotated. It should be gripped while

4
rotating the rod end swivel bearing. After adjusting, align the hole in the rod end swivel
bearing over the anchor, place the cap screw through the hole and through the ½ inch
spacer and then tighten the cap screw into the anchor.
2.2.1. Installation using Weldable Fixtures
Figure 4 - Installation using Weldable Fixtures
Installation instructions;
(See section 2.2 for special instructions re Models 4420-1-12 and 4420-1-25)
1. Determine proper setting distance using figures in Table 1 or the readings on the
calibration sheet. Prepare the surface (grinding, sanding, etc.) of the steel around the
area of each weldable fixture.
2. Locate the welding fixtures on prepared surfaces, check spacing again and tack weld
to the member.
3. Remove the nylon tie securing the transducer shaft. Thread the cap screw through the
swivel bearing and through the ½ inch spacer on each end. Then tighten the cap
screws into the welding fixtures.
4. Check the reading with a portable readout. Use Table 2 or the readings on the
calibration sheet to check the position. The installation is now complete.
2.2.2. Installation using Groutable Anchors
Figure 5 - Installation using Groutable Anchors
Installation instructions;
(See section 2.2 for special instructions re Models 4420-1-12 and 4420-1-25)

5
1. Determine proper setting distance using figures from Table 1 or the readings on the
calibration sheet. Using a hammer drill or other suitable equipment, drill two ½"
holes approximately 3" deep at the proper locations. Shorter holes may be drilled if
the anchors are cut down accordingly.
2. Assemble the Crackmeter with cap screws threaded through the swivel bearings and
the spacers and threaded loosely into the groutable anchors. If installing the
instrument at the mid-range position, leave the nylon tie installed (see Figure 1) that
secures the transducer shaft. Fill the holes with grout or epoxy and push the anchors
in until the tops are flush with the surface. For holes drilled overhead use a quick
setting grout or epoxy.
3. Tighten the set screws after the grout or epoxy has set. Remove the nylon tie.
4. Check the reading with a portable readout. Use Table 2 or the readings on the
calibration sheet to check the position. Installation complete.
2.2.3. Installation using Expansion Anchors
Figure 6 - Installation using Expansion Anchors
Installation instructions;
(See section 2.2 for special instructions re Models 4420-1-12 and 4420-1-25)
1. Determine proper setting distance using figures from Table 1 or the readings on the
calibration sheet. Using a masonry drill or other suitable equipment, drill two 3/8
inch, (or 10mm), diameter holes 1¼", (32mm), deep at the proper locations.
2. Insert the expansion anchors into the holes, with the slotted end down and then, insert
the setting tool provided, small end first, into the anchor and expand the anchor by
hitting the large end of the setting tool with several sharp hammer blows.
3. Remove the nylon tie securing the transducer shaft. Push the cap screws through the
swivel bearings and spacers on each end of the crackmeter then tighten the cap
screws into the anchors.

6
4. Check the reading with a portable readout. Use Table 2 or the readings on the
calibration sheet to check the position. Installation complete.
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. Lightning Protection
The Model 4420 Vibrating Wire Crackmeter, unlike numerous other types of instrumentation
available from Geokon, do not have any integral lightning protection components, i.e.
transzorbs 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.
Note the following suggestions;
•If the gage is connected to a terminal box or multiplexer components such as plasma
surge arrestors (spark gaps) may be installed in the terminal box/multiplexer to provide a
measure of transient protection. Terminal boxes and multiplexers available from Geokon
provide locations for installation of these components.
•Lighting arrestor boards and enclosures are available from Geokon that install near the
instrument. The enclosure has a removable top so, in the event the protection board
(LAB-3) is damaged, the user may service the components (or replace the board). A
connection is made between this enclosure and earth ground to facilitate the passing of
transients away from the gage. See Figure 7. Consult the factory for additional
information on these or alternate lightning protection schemes.
•Plasma surge arrestors can be epoxy potted into the gage cable close to the sensor. A
ground strap would connect the surge arrestor to earth ground, either a grounding stake or
other suitable earth ground.

7
Terminal Box/Multiplexer
Instrument Cable LAB-3 Enclosure LAB-3 Board
Model 4420 Crackmeter
Structure
Ground Connections
Surface
(usually buried)
Crack
Figure 7 - Lightning Protection Scheme
3. TAKING READINGS
3.1. Operation of the GK-401 Readout Box
The GK-401 is a basic readout for all vibrating wire gages.
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 gage, the green or blue clip for
the shield drain wire. The GK-401 cannot read the thermistor (see Section 3.4).
1. Turn the display selector to position "B" (or "F"). Readout is in digits (Equation 4-1).
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. Record the value displayed. If zeros are
displayed or the reading is unstable see section 5 for troubleshooting suggestions.
3. The unit will automatically turn itself off after approximately 4 minutes to conserve
power.
3.2. 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. Consult the GK-403 Instruction Manual for additional information on

8
Mode "G" of the Readout. The following instructions will explain taking gage
measurements using Modes "B" and "F" (similar to the GK-401 switch positions "B" and
"F").
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 gage, the white and green clips
are for the thermistor and the blue for the shield drain wire.
1. Turn the display selector to position "B" (or "F"). Readout is in digits (Equation 4-1).
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.
3.3 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

9
3.4. Measuring Temperatures
Each Vibrating Wire Crackmeter 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.
The GK 401 readout box will not read temperatures – an ohmmeter is required
1. Connect the ohmmeter to the two thermistor leads coming from the Crackmeter.
(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. Alternately the
temperature could be calculated using Equation B-1.
Note: The GK-403 and GK-404 readout boxes will read the thermistor and display
temperature in °C automatically.
4. DATA REDUCTION
4.1. Deformation Calculation
The basic units utilized by Geokon for measurement and reduction of data from Vibrating
Wire Crackmeters are "digits". Calculation of digits is based on the following equation;
Digits Period =⎛
⎝
⎜⎞
⎠
⎟×−
23
110 or Digits Hz
=
2
1000
Equation 1 - Digits Calculation
To convert digits to deformation the following equation applies;
Duncorrected = (R1- R0) ×G ×F
Equation 2 - Deformation Calculation
Where; R1is the current reading.
R
0is the initial reading, usually obtained at installation (see section 2.4).
G is thegage factor, usually millimeters or inches per digit (see Figure 8).
F is an optional engineering units conversion factor, see Table 3.
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 3 - Engineering Units Conversion Multipliers

10
For example, the initial reading R0, at installation of a crackmeter is 2500 digits. The current
reading, R1, is 6000. The gage factor is 0.004457 mm/digit. The deformation change is;
Duncorrected = (6000
− 2500) × 0.004457 = +15.60 mm
Note that increasing readings (digits) indicate increasing extension.
To use the Polynomial Gage factors given on the Calibration Sheet, use the value of R0 and
Gage Factors A and B with D set to zero to calculate the new value of C. then substitute the
new value of R1and use A,B and the new value of C to calculate the displacement D

11
Figure 8 - Typical Crackmeter Calibration Sheet

12
4.2. Temperature Correction
The Model 4420 Vibrating Wire Crackmeters have a small coefficient of thermal expansion
so in many cases correction may not be necessary. However, if maximum accuracy is
desired or the temperature changes are extreme (>10° C) corrections may be applied. The
temperature coefficient of the mass or member to which the Crackmeter is attached should
also be taken into account. By correcting the transducer for temperature changes the
temperature coefficient of the mass or member may be distinguished. The following
equation applies;
Dcorrected = ((R1- R0) ×G) + ((T1- T0) ×K)
Equation 3 - Thermally Corrected Deformation Calculation
Where; R1is the current reading.
R
0is the initial reading.
G is the linear gage factor.
T
1is the current temperature.
T
0is 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 determination
of the proper thermal coefficient based on the following equation;
K = ((R1×M) +B) ×G
Equation 4 - Thermal Coefficient Calculation
Where; R1is the current reading.
M is the multiplier from Table 4.
B is the constant from Table 4.
G is the linear gage factor from the supplied calibration sheet.
Model: 4420-6 mm
4420-0.25’’ 4420-12 mm 4420-0.5" 4420-25 mm 4420-1" 4420-50 mm 4420-2" 4420-100 mm 4420-4" 4420-150 mm 4420-6"
Multiplier (M): 0.00073 0.000295 0.000301 0.000330 0.000192 0.000216
Constant (B): 0.583 1.724 0.911 0.415 0.669 0.491
Model: 4420-200 mm
4420-8” 4420-300 mm 4420-12”
Multiplier (M): 0.000305 0.000245
Constant (B): 0.240 0.564
Table 4 - Thermal Coefficient Calculation Constants
Consider the following example using a Model 4420-25 mm Crackmeter;