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Installation Manual 

Models 4911/4911A 

Vibrating Wire Rebar Strain Meters 

 

 

 

 

 

 

 

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 © 1989-2019 by Geokon

®

 

(Doc Rev R, 1/03/2019) 

Содержание 4911

Страница 1: ...ed 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 1989 2019 by Geokon Doc Rev R 1 03 2019 ...

Страница 2: ......

Страница 3: ...nnel 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 ...

Страница 4: ......

Страница 5: ...perating the GK 405 8 3 3 GK 403 READOUT BOX OBSOLETE MODEL 9 3 3 1 Connecting Sensors with 10 pin Bulkhead Connectors Attached 9 3 3 2 Connecting Sensors with Bare Leads 9 3 3 3 Operating the GK 403 9 3 4 MEASURING TEMPERATURES 10 4 DATA REDUCTION 11 4 1 STRAIN CALCULATION 11 4 2 TEMPERATURE CORRECTION 11 4 3 ENVIRONMENTAL FACTORS 13 4 4 SHRINKAGE EFFECTS 13 4 5 CONVERTING STRAINS TO LOADS 13 5 T...

Страница 6: ...ES TABLE 1 THERMAL COEFFICIENTS 11 TABLE 2 SAMPLE RESISTANCE 15 TABLE 3 RESISTANCE WORK SHEET 15 TABLE 4 MODEL 4911A 4911 STRAIN METER SPECIFICATIONS 16 TABLE 5 THERMISTOR RESISTANCE VERSUS TEMPERATURE 17 TABLE 6 UNBONDED SECTION DIMENSIONS 19 TABLE 7 MICROSTRAIN CONVERSION FACTORS 20 EQUATIONS EQUATION 1 DIGITS CALCULATION 11 EQUATION 2 APPARENT STRAIN 11 EQUATION 3 LOAD RELATED STRAIN 12 EQUATIO...

Страница 7: ...with a calibration report which shows the relationship between readout digits and microstrain The calibration report also shows the initial no load zero reading Model 4911 Vibrating Wire Rebar Strain Meter or Sister Bar Figure 1 comprises a short length of high strength steel welded between two sections of reinforcing bar It is designed to be wire tied in parallel with structural rebar The small d...

Страница 8: ...iply these factors by two to account for both directions Resistance between the two thermistor wires usually white and green varies with temperature Use Table 5 in Appendix B to convert the resistance to temperature and compare the result to the ambient temperature Resistance between any conductor and the shield should exceed two megohms If the strain meter fails any of the preliminary tests see S...

Страница 9: ...3 Figure 3 Model 4911 Sister Bar Installation Figure 4 Model 4911 Sister Bar Installation Detail ...

Страница 10: ...y be necessary to place wet rags between the weld area and the coil housing Take care not to damage or burn the instrument cable during welding After welding route the instrument cable along the rebar system and tie it off every three to four feet one meter using nylon cable ties Avoid using iron tie wire to secure the cable as the cable could be cut Figure 5 show a typical 4911 installation Be su...

Страница 11: ...gauge readings therefore splicing of cables has no ill effects and in some cases may in fact be beneficial The cable used for making splices should be a high quality twisted pair type with 100 shielding and an integral shield drain wire When splicing it is very important that the shield drain wires be spliced together Always maintain polarity by connecting color to color Splice kits recommended by...

Страница 12: ...able 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 A connection is made between the enclosure and earth ground to facilitate the passing of transients away from the strain meter See Figure 6 below Plasma surge arrestors can be epoxied into the ins...

Страница 13: ...een will be displayed After approximately one second the GK 404 will start taking readings and display them based on the settings of the POS and MODE buttons The unit display from left to right is as follows The current Position Set by the POS button Displayed as a letter A through F The current Reading Set by the MODE button Displayed as a numeric value followed by the unit of measure Temperature...

Страница 14: ...ale connector until it locks into place 3 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 3 2 3 Operating the GK 405 Press the button labeled POWER ON BLUETOOTH A blue light will begin blinkin...

Страница 15: ... 3 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 3 3 3 Operating the GK 403 1 Turn the display selector to position B 2 Turn the unit on 3 The readout will display the vibrating wire output ...

Страница 16: ...or and display the temperature in degrees C To read temperatures using an ohmmeter 1 Connect an ohmmeter to the green and white thermistor leads coming from the strain meter Since the resistance changes with temperature are large the effect of cable resistance is usually insignificant For long cables a correction can be applied equal to approximately 14 7Ω per 1000 ft 48 5Ω per km at 20 C Multiply...

Страница 17: ...ion report For an example of a typical strain meter calibration report see Figure 10 in Appendix D For example Assuming an initial reading R0 of 8000 digits a current reading R1 of 7700 and a calibration factor C of 0 343 microstrains per digit the strain calculation would be as follows εapparent 7700 8000 0 343 102 9 µε compression 4 2 Temperature Correction The assumption with strain meters embe...

Страница 18: ...ng the strain corrected for temperature i e due to load changes only can be calculated as follows εload related 7700 8000 0 343 60 20 12 2 10 14 9 µstrain compression Please note that the actual strain undergone by the concrete e g that which would be measured by a tape measure is given by the formula εactual R1 R0 C T1 T0 Ksteel Equation 4 Actual Strain Apparent strain 7700 8000 x 0 343 103 µstra...

Страница 19: ...de to keep the concrete under a constant condition of water content but this is frequently impossible on concrete structures exposed to varying weather conditions The shrinkage and or swelling effect may be measured by casting a strain gauge inside a concrete block that remains unloaded yet still exposed to the same moisture conditions as the active gauges Strains measured on this gauge may be use...

Страница 20: ...settings correct Is there a source of electrical noise nearby Likely candidates are generators motors arc welding equipment high voltage lines etc If possible move the instrument cable away from power lines and electrical equipment or install electronic filtering Make sure the shield drain wire is connected to ground whether using a portable readout or datalogger Connect the shield drain wire to t...

Страница 21: ...infinite infinite infinite White infinite infinite N A 3000Ω at 25 C infinite Green infinite infinite 3000Ω at 25 C N A infinite Shield infinite infinite infinite infinite N A Table 2 Sample Resistance Vibrating Wire Sensor Lead Grid SENSOR NAME Red Black White Green Shield Red Black White Green Shield Table 3 Resistance Work Sheet ...

Страница 22: ...914 mm 36 1105 mm 43 5 Materials Grade 60 Rebar 60 ksi yield and High Strength Steel Electrical Cable Two twisted pair Four conductor 22 AWG Foil shield PVC jacket nominal OD 6 3 mm 0 250 Table 4 Model 4911A 4911 Strain Meter Specifications Notes 1 The standard factory setting allows for 2000 µε in compression and 1000 µε in tension Other initial settings available upon request 2 Consult the facto...

Страница 23: ...2 83 107 9 123 77 66K 36 8006 4 1363 44 331 5 84 105 2 124 72 81K 35 7618 5 1310 45 321 2 85 102 5 125 68 30K 34 7252 6 1260 46 311 3 86 99 9 126 64 09K 33 6905 7 1212 47 301 7 87 97 3 127 60 17K 32 6576 8 1167 48 292 4 88 94 9 128 56 51K 31 6265 9 1123 49 283 5 89 92 5 129 53 10K 30 5971 10 1081 50 274 9 90 90 2 130 49 91K 29 5692 11 1040 51 266 6 91 87 9 131 46 94K 28 5427 12 1002 52 258 6 92 85...

Страница 24: ...ter Schematic To convert the observed change in readout digits R into a strain εt for the entire length of the unbonded section 7 5 in 19 05 cm requires the following equation εt ε1 L1 ε2 L2 ε3 L3 L1 L2 L3 Equation 7 Total Strain Calculation Where L1 is 2 000 5 08 cm L2 is 5 000 12 7 cm L3 is 0 500 1 27 cm εt is the total strain of the unbonded section ε1 is the strain in zone one determined empir...

Страница 25: ...calibration factor expressed as lbs or kg per readout digit Rebar Size Diameter a2 a3 4 0 500 in 1 27 cm 0 196 in2 1 264 cm2 0 248 in2 1 60 cm2 5 0 625 in 1 59 cm 0 3058 in2 1 973 cm2 0 357 in2 2 303 cm2 6 0 750 in 1 905 cm 0 390 in2 2 516 cm2 0 442 in2 2 852 cm2 7 0 875 in 2 222 cm 0 549 in2 3 542 cm2 0 601 in2 3 877 cm2 8 1 000 in 2 54 cm 0 733 in2 4 729 cm2 0 785 in2 5 065 cm2 9 1 125 in 2 858 ...

Страница 26: ... the microstrain digit gauge factor C from the lbs or kg per digit gauge factor F Rebar Size Conversion Formula English Conversion Formula Metric 4 C 0 0957 F x 0 12220 C 0 0957 F x 0 2707 5 C 0 0957 F x 0 07888 C 0 0957 F x 0 2091 6 C 0 0957 F x 0 06205 C 0 0957 F x 0 1373 7 C 0 0957 F x 0 04416 C 0 0957 F x 0 0977 8 C 0 0957 F x 0 03310 C 0 0957 F x 0 0733 9 C 0 0957 F x 0 02584 C 0 0957 F x 0 0...

Страница 27: ...21 APPENDIX D SAMPLE CALIBRATION REPORT Figure 10 Sample Model 4911 Calibration Report ...

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