Geokon 4200 Series User manual

Instruction Manual
Model 4200 Series
Vibrating Wire Strain Gages
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 ©1986-2018 by Geokon, Inc.
(Doc Rev AA, 06/05/2018)

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 ............................................................................................................................................................1
2. MODELS...........................................................................................................................................................................2
2.1 MODELS 4200 AND 4200L ............................................................................................................................................2
2.2 MODEL 4202.................................................................................................................................................................3
2.3 MODEL 4210.................................................................................................................................................................3
3. PRIOR TO INSTALLATION.........................................................................................................................................4
3.1 ADJUSTING MODEL 4200 TO THE DESIRED RANGE........................................................................................................4
3.2 GAGE AND CABLE ASSEMBLY.......................................................................................................................................4
3.3PRELIMINARY CHECK ....................................................................................................................................................5
4. INSTALLING THE GAGES IN CONCRETE..............................................................................................................5
4.1 DIRECT ATTACHMENT TO REBAR..................................................................................................................................6
4.2 SUSPENSION METHOD...................................................................................................................................................7
4.3 ALTERNATIVE SUSPENSION METHOD............................................................................................................................8
4.4 USING PRECAST BRIQUETTES,SHOTCRETE,OR GROUTING............................................................................................8
4.5 CABLE SPLICING AND TERMINATION.............................................................................................................................9
4.6 LIGHTNING PROTECTION...............................................................................................................................................9
5. TAKING READINGS....................................................................................................................................................11
5.1 GK-404 READOUT BOX..............................................................................................................................................11
5.1.1 Operating the GK-404 .......................................................................................................................................11
5.2 GK-405 READOUT BOX..............................................................................................................................................12
5.2.1 Connecting Sensors............................................................................................................................................12
5.2.2 Operating the GK-405 .......................................................................................................................................12
5.3 GK-403 READOUT BOX (OBSOLETE MODEL) .............................................................................................................13
5.3.1 Connecting Sensors............................................................................................................................................13
5.3.2 Operating the GK-403 .......................................................................................................................................13
5.4 EMBEDMENT STRAIN GAGE READOUT POSITIONS.......................................................................................................13
5.5 MEASURING TEMPERATURES ......................................................................................................................................14
6. DATA REDUCTION......................................................................................................................................................15
6.1 READOUT BOX POSITION A.........................................................................................................................................15
6.2READOUT BOX POSITION B.........................................................................................................................................15
6.3 READOUT BOX POSITIONS D&E................................................................................................................................16
6.4 STRAIN RESOLUTION...................................................................................................................................................16
6.5 TEMPERATURE CORRECTIONS.....................................................................................................................................16
6.6 SHRINKAGE EFFECTS ..................................................................................................................................................18
6.7 CREEP EFFECTS...........................................................................................................................................................19
6.8 EFFECT OF AUTOGENOUS GROWTH.............................................................................................................................19
6.9 CONVERTING STRAIN TO LOAD...................................................................................................................................19
6.10 EFFECTIVE MODULUS ...............................................................................................................................................19
7. TROUBLESHOOTING.................................................................................................................................................20
APPENDIX A. SPECIFICATIONS..................................................................................................................................22
A.1 THERMISTOR..............................................................................................................................................................22
A.2 STRAIN GAGE.............................................................................................................................................................22
APPENDIX B. THEORY OF OPERATION ...................................................................................................................23
APPENDIX C. THERMISTOR TEMPERATURE DERIVATION..............................................................................26
APPENDIX D. HIGH TEMPERATURE THERMISTOR LINEARIZATION ...........................................................27
APPENDIX E. NO STRESS-STRAIN ENCLOSURE. ...................................................................................................28
APPENDIX F. MODEL 4200HT-T HIGH TEMPERATURE STRAIN GAGE ..........................................................29
APPENDIX G. MEASUREMENT AND CORRECTION OF TEMPERATURE EFFECTS.....................................30

FIGURES
FIGURE 1-ON SITE INSTALLATION PHOTO ................................................................................................................... 1
FIGURE 2-MODEL 4200 AND 4200L VIBRATING WIRE STRAIN GAGE.......................................................................... 2
FIGURE 3-MODEL 4202 VIBRATING WIRE STRAIN GAGE ............................................................................................ 3
FIGURE 4-MODEL 4210 VIBRATING WIRE STRAIN GAGE ............................................................................................ 3
FIGURE 5-ADJUSTING WIRE TENSION.......................................................................................................................... 4
FIGURE 6-ASSEMBLED GAGE AND COIL HOUSING....................................................................................................... 4
FIGURE 7-ATTACHING MODEL 4200/4200L/4200HT STRAIN GAGES TO REBAR......................................................... 6
FIGURE 8-SUSPENDING MODEL 4200/4200L/4 200HT STRAIN GAGES BETWEEN REBAR ........................................... 7
FIGURE 9-ALTERNATIVE METHOD FOR ATTACHING MODEL 4200/4200HT STRAIN GAGES TO REBAR ...................... 8
FIGURE 10 -LIGHTNING PROTECTION SCHEME ............................................................................................................10
FIGURE 11 -LEMO CONNECTOR TO GK-404 ................................................................................................................11
FIGURE 12 -NO STRESS STRAIN ENCLOSURE ...............................................................................................................28
FIGURE 13 -MODEL 4200HT-T....................................................................................................................................29
TABLES
TABLE 1-HEAT SHRINK COLOR DESIGNATIONS........................................................................................................... 2
TABLE 2-READOUT POSITIONS....................................................................................................................................13
TABLE 3-EMBEDMENT STRAIN GAGE FACTORS..........................................................................................................15
TABLE 4-EFFECTIVE MODULUS ..................................................................................................................................19
TABLE 5-SAMPLE RESISTANCE ...................................................................................................................................21
TABLE 6-RESISTANCE WORK SHEET...........................................................................................................................21
TABLE 7-STRAIN GAGE SPECIFICATIONS ....................................................................................................................22
TABLE 8-EMBEDMENT STRAIN GAGE THEORETICAL PARAMETERS............................................................................23
TABLE 9-THERMISTOR RESISTANCE VERSUS TEMPERATURE ......................................................................................26
TABLE 10-THERMISTOR RESISTANCE VERSUS TEMPERATURE FOR MODEL 4200HT...................................................27
EQUATIONS
EQUATION 1-PERIOD TO DIGITS CONVERSION............................................................................................................15
EQUATION 2-THEORETICAL STRAIN ...........................................................................................................................16
EQUATION 3–APPARENT STRAIN ................................................................................................................................16
EQUATION 4–CORRECTION FOR TEMPERATURE EFFECTS ON THE GAGE.....................................................................17
EQUATION 5–TRUE,LOAD RELATED STRAIN CORRECTED FOR TEMPERATURE ...........................................................17
EQUATION 6-ACTUAL STRAIN ....................................................................................................................................18
EQUATION 7-STRAIN TO LOAD FORMULA ...................................................................................................................19
EQUATION 8-RESISTANCE TO TEMPERATURE .............................................................................................................26
EQUATION 9-HIGH TEMPERATURE RESISTANCE TO TEMPERATURE............................................................................27
EQUATION 10 -TEMPERATURE INDUCED STRESS .........................................................................................................30
EQUATION 11 -COMBINED TEMPERATURE AND LOAD RELATED STRESS.....................................................................30
EQUATION 12 -EXTERNAL LOAD STRESS.....................................................................................................................30
EQUATION 13 -ACTUAL STRAIN ..................................................................................................................................31

1
1. INTRODUCTION
Geokon Vibrating Wire Embedment Strain Gages are designed for direct embedment in
concrete. This can be accomplished by attaching the gage to rebar or tensioning cables and then
casting the gage into a concrete briquette, which is subsequently cast into the structure, or
grouting the gage into boreholes in the concrete.
Strains are measured using the vibrating wire principle. A length of steel wire is tensioned
between two end blocks that are firmly in contact with the mass concrete. Deformations in the
concrete will cause the two end blocks to move in relation to each other, altering the tension in
the steel wire. This change in tension is measured as a change in the resonant frequency of
vibration of the wire.
Two coils, one with a magnet insert, the other with a pole piece insert, are located close to the
vibrating wire. In use, a pulse of varying frequency (swept frequency) is applied to the coils
causing the wire to vibrate primarily at its resonant frequency.
Portable readouts and dataloggers are available from Geokon. These models, when used in
conjunction with vibrating wire strain gages, will provide the necessary voltage pulses to pluck
the wire. During vibration, a sinusoidal signal is induced in the coils and transmitted to the
readout box where it is conditioned and displayed.
Figure 1 - On Site Installation Photo

2
2. MODELS
Geokon vibrating wire strain gages come in a variety of models. The following sections describe
in brief the various embedment strain gages available from Geokon.
2.1 Models 4200 and 4200L
Geokon Models 4200 and 4200L are designed primarily for long-term strain measurements
inside mass concrete, in structures such as foundations, piles, bridges, dams, containment
vessels, tunnel liners, etc. The 4200L is a low modulus version designed to enable early curing
strains to be measured. The length of the 4200 gage is six inches (152 mm).
Figure 2 - Model 4200 and 4200L Vibrating Wire Strain Gage
The various 4200 strain gage models are easily identifiable by the color of heat shrink which
covers the protective tubes, as show in Table 1.*
Model
Heat Shrink Color
4200
Blue
4200L
Black
4200-5,000µε
Red
4200-10,000µε
Green
4200X
Yellow (Dependent on the
reason for the X designation.)
Table 1 - Heat Shrink Color Designations
*Applicable only to products manufactured after September 2016.

3
2.2 Model 4202
Model 4202 is designed for direct embedment in grout, mortar, and small aggregate concrete. It
is also useful for model studies. The length of the 4202 gage is two inches (50 mm).
Figure 3 - Model 4202 Vibrating Wire Strain Gage
2.3 Model 4210
Model 4210 is designed for embedment in large aggregate concrete (greater than 3/4 of an inch).
The standard gage length is 10 inches (254 mm), other gage lengths available include: Model
4212: 12 inches (305 mm), and Model 4214: 14 inches (356 mm).
Figure 4 - Model 4210 Vibrating Wire Strain Gage

4
3. PRIOR TO INSTALLATION
3.1 Adjusting Model 4200 to the Desired Range
Geokon embedment strain gages are supplied fully sealed and pretensioned. Model 4200 gages
are normally supplied with the wire tension set near the middle (about 2500 microstrain) of their
range (from 1000 to 4000 microstrain). If the range needs to be adjusted for some reason, the
wire tension may be changed by the following procedure:
Attach the red and black leads to a readout box that has been set to position D, reading in
microstrain. Grip the small collar under the shrink tube and rotate the end flange as shown in
Figure 5. Rotate clockwise to decrease the initial reading and counterclockwise to increase the
reading. For example, if the gage will see all compression it should be set to around 4000
microstrain.
Figure 5 - Adjusting Wire Tension
3.2 Gage and Cable Assembly
Insert the flat part of the gage into the slot in the coil assembly located at the end of the cable.
Slide the hose clamp over the assembly and tighten.
Figure 6 - Assembled Gage and Coil Housing
Alternatively, the coil housing can be glued in place using cyanoacrylate glue. If this method is
chosen, it will no longer be possible to remove the gage from the coil housing.