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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)
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Table of Contents
Related Manuals for Geokon 4200 Series
Summary of Contents for Geokon 4200 Series
- Page 1 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.
- Page 3 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...
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Page 5: Table Of Contents
TABLE of CONTENTS 1. INTRODUCTION ................................1 2. MODELS ................................... 2 2.1 M 4200 4200L ............................2 ODELS 2.2 M 4202 ................................. 3 ODEL 2.3 M 4210 ................................. 3 ODEL 3. PRIOR TO INSTALLATION ............................4 3.1 A 4200 ......................4 DJUSTING ODEL TO THE... - Page 6 FIGURES 1 - O ........................1 IGURE NSTALLATION HOTO 2 - M 4200 4200L V ................2 IGURE ODEL IBRATING TRAIN 3 - M 4202 V .................... 3 IGURE ODEL IBRATING TRAIN 4 - M 4210 V .................... 3 IGURE ODEL IBRATING TRAIN...
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Page 7: Introduction
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. -
Page 8: Models
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. -
Page 9: Model 4202
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). -
Page 10: Prior To Installation
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). -
Page 11: Preliminary Check
Return any faulty gages to the factory. Gages should not be opened in the field. 4. INSTALLING THE GAGES IN CONCRETE Geokon strain gages are normally set into the concrete structure in one of two ways; casting the units directly into the concrete mix (see Sections 4.1 through 4.3) or casting them into briquettes that are subsequently cast into the structure (see Section 4.4). -
Page 12: Direct Attachment To Rebar
4.1 Direct Attachment to Rebar 1) Place two pieces of wood or Styrofoam between the gage and the rebar as shown in Figure 7. 2) Select a length of soft iron tie wire, similar to the kind that is normally used for tying rebar cages together. -
Page 13: Suspension Method
4.2 Suspension Method 1) Wrap a layer of self-vulcanizing rubber tape about three cm from each gage end, as shown in Figure 8. (This is not necessary for Model 4210 gages.) The layers of rubber serve as a shock absorber, dampening any vibration of the suspension system. Without the rubber layers the resonant frequency of the tie wires may interfere with the resonant frequency of the gage. -
Page 14: Alternative Suspension Method
Geokon strain gages may also be used in shotcrete, as well as in drilled holes in rock or concrete that are subsequently grouted. When used in shotcrete special care should be taken to protect the lead wires, such as encasing them in conduit or heavy tubing. -
Page 15: Cable Splicing And Termination
Splice kits recommended by Geokon incorporate casts, which are placed around the splice and are then filled with epoxy to waterproof the connections. When properly made, this type of splice is equal or superior to the cable itself in strength and electrical properties. Contact Geokon for splicing materials and additional cable splicing instructions. -
Page 16: Figure 10 - Lightning Protection Scheme
• Lighting arrestor boards and enclosures are also available from Geokon. These units install where the instrument cable exits the structure being monitored. The enclosure has a removable top to allow the customer to service the components or replace the board in the event that the unit is damaged by a lightning strike. -
Page 17: Taking Readings
20 hours continuously on two AA batteries. It is designed for the readout of all Geokon vibrating wire gages and transducers, and is capable of displaying the reading in either digits, frequency (Hz), period (µs), or microstrain (µε). The GK-404 also displays the temperature of the transducer (embedded thermistor) with a resolution of 0.1 °C. -
Page 18: Gk-405 Readout Box
5.2.2 Connecting Sensors with Bare Leads Attach the GK-403-2 flying leads to the bare leads of a Geokon vibrating wire sensor by connecting each of the clips on the leads to the matching colors of the sensor conductors, with blue representing the shield (bare). -
Page 19: Gk-403 Readout Box (Obsolete Model)
5.3.2 Connecting Sensors with Bare Leads Attach the GK-403-2 flying leads to the bare leads of a Geokon vibrating wire sensor by connecting each of the clips on the leads to the matching colors of the sensor conductors, with blue representing the shield (bare). -
Page 20: Measuring Temperatures
5.5 Measuring Temperatures All vibrating wire strain gages are equipped with a thermistor for reading temperature. The thermistor gives a varying resistance output as the temperature changes. The white and green leads of the instrument cable are normally connected to the internal thermistor. The GK-403, GK-404, and GK-405 readout boxes will read the thermistor and display the temperature in degrees C. -
Page 21: Data Reduction
6. DATA REDUCTION Table 3 shows the readout position, theoretical gage factors, and experimental data derived from batch calibrations for each model of strain gage. (Individual calibrations are available at an additional cost; contact Geokon for more information.) Model: 4200... -
Page 22: Readout Box Positionsd & E
6.3 Readout Box Positions D & E Reading for Models 4200 (Channel D) and 4202 (Channel E) are displayed on the readout box directly in microstrain based on the theoretical equation: µε −3 = G (Δf × 10 theory Equation 2 - Theoretical Strain Where;... -
Page 23: Equation 4 - Correction For Temperature Effects On The Gage
Temperature can also affect the strain gage. Increasing temperatures will cause the vibrating wire to elongate and thus go slack, indicating what would appear to be a compressive strain in the concrete. This effect is balanced to some degree by a corresponding stretching of the wire, caused by expansion of the concrete. -
Page 24: Shrinkage Effects
Example: = 3000 on channel D = 2900 on channel D = 20°C = 30°C B = 0.975 (Batch calibration factor) Then; The apparent strain = (2900 – 3000) 0.975 = –97.5 µstrain (compression) The load related strain, corrected for temperature effects on the gage = (2900 –... -
Page 25: Creep Effects
6.7 Creep Effects It is also well known that concrete will creep under a sustained load. What may seem to be a gradually increasing load, as evidenced by a gradually increasing strain, may actually be strain due to the concrete creeping under a constant, sustained load. On some projects, gages have been cast into concrete blocks in the laboratory and kept loaded by means of springs inside a load frame. -
Page 26: Troubleshooting
Should difficulties arise, consult the following list of problems and possible solutions. Return any faulty gages to the factory. Gages should not be opened in the field. For additional troubleshooting and support, contact Geokon. Symptom: Thermistor resistance is too high: ... -
Page 27: Table 5 - Sample Resistance
Vibrating Wire Sensor Lead Grid - SAMPLE VALUES Black White Green Shield ≅180Ω (≅50Ω for Models infinite infinite infinite 4202 & 4200HT-T, ≅120Ω for Model 4200HT) ≅180Ω (≅50Ω for Models Black infinite infinite infinite 4202 & 4200HT-T, ≅120Ω for Model 4200HT) 3000Ω... -
Page 28: Appendix A. Specifications
APPENDIX A. SPECIFICATIONS A.1 Strain Gage Model 4200 4202 4204 4210 4212 4214 4200HT Range 3000 µε (Nominal) 1.0 µε¹ 0.4 µε¹ 1.0 µε¹ 0.4 µε¹ 0.4 µε¹ 0.4 µε¹ 1.0 µε¹ Resolution Calibration ±0.1% FSR Accuracy Typical 0.98 0.91 0.95 0.98 Batch Factor... -
Page 29: Appendix B. Theory Of Operation
APPENDIX B. THEORY OF OPERATION A vibrating wire attached to the surface of a deforming body will deform in a manner similar to that of the body to which it is attached. These deformations alter the tension of the wire, therefore altering its natural frequency of vibration (resonance). - Page 30 4) Combining the equations from steps one, two, and three gives: � ρa 5) Note that the tension (F) can be expressed in terms of strain, i.e.: ε Where; ε w is the wire strain (in./in.). Ε is the Young's Modulus of the wire (30 x 10 6 Psi). 6) Combining the equations from steps four and five gives: �...
- Page 31 11) Combining the equations from steps nine and ten gives: 97.75 ε ∙ Where; (for Model 4200) is 5.875 inches. is 6.000 inches. � � 12*) Therefore: ε = 3.304 x 10 � � 13*) The display on position "D" of the readout is based on the equation: ε...
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Page 32: Appendix C. Thermistor Temperature Derivation
APPENDIX C. THERMISTOR TEMPERATURE DERIVATION Thermistor Type: YSI 44005, Dale #1C3001-B3, Alpha #13A3001-B3 Resistance to Temperature Equation: A+B ( LnR ) +C(LnR) -273.2 Equation 8 - Resistance to Temperature Where; T = Temperature in °C. LnR = Natural Log of Thermistor Resistance. A = 1.4051 ×... -
Page 33: Appendix D. High Temperature Thermistor Linearization
APPENDIX D. HIGH TEMPERATURE THERMISTOR LINEARIZATION Resistance to Temperature Equation for US Sensor 103JL1A: A+B ( LnR ) +C(LnR) -273.2 +D(LnR) Equation 9 - High Temperature Resistance to Temperature Where; T = Temperature in °C. LnR = Natural Log of Thermistor Resistance. A = 1.127670 ×... -
Page 34: Appendix E. No Stress-Strain Enclosure
APPENDIX E. NO STRESS-STRAIN ENCLOSURE. Geokon’s Model 4200-4 No Stress-Strain Enclosure is a double walled enclosure. The walls are made of PVC and filled with Styrofoam. Figure 12 shows a typical 4200-4 installation. Figure 12 - No Stress Strain Enclosure... -
Page 35: Appendix F. Model 4200Ht-T High Temperature Strain Gage
APPENDIX F. MODEL 4200HT-T HIGH TEMPERATURE STRAIN GAGE Geokon Model 4200HT-T High Temperature Embedment Strain Gage is similar to the Model 4200, but is constructed using components that can withstand temperatures up to 220 °C. It is particularly useful for measurements in autoclaved spun concrete piles. -
Page 36: Appendix G. Measurement And Correction Of Temperature Effects
APPENDIX G. MEASUREMENT AND CORRECTION OF TEMPERATURE EFFECTS If the ends of the structural member are free to expand or contract without restraint, strain changes can take place without any change in stress. On the other hand, if the ends of the structural member are restrained by some semirigid medium, then any increase in temperature of the structural member will result in a buildup of compressive load related strain in the member, even though the actual strain would be tensile. -
Page 37: Equation 13 - Actual Strain
If, for whatever reason, the actual strain of the concrete member is required, (e.g., the change of unit length that would be measured by a dial gage attached to the surface,) this is given by the equation: με )B + (T actual Equation 13 - Actual Strain Where C...