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

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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.

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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

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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.

5
3.3 Preliminary check
A preliminary check should be performed before installing the gage in the field.
To perform the preliminary check, complete the following steps:
1) Using an ohmmeter, check the resistance between the two lead wires (usually red and black).
For Models 4200, 4200L, and 4210 it should be around 180 ohms. For Model 4202, it should
be around 50 ohms. Remember to add the cable resistance at approximately 14.7Ω/1000' or
48.5Ω/km at 20 °C. Multiply these factors by two to account for both directions.
2) Using an ohmmeter, check the resistance between the two thermistor wires (usually white
and green). Using Table 9 in Appendix C, convert the resistance to temperature. Compare the
result to the current ambient temperature. (For Model 4200HT see Table 10 in Appendix D.)
3) Connect the gage to a readout box. (See readout instructions, Section 5). Observe the
displayed readout. The reading should be around the midrange position as defined in Table 2.
4) Press on the gage ends and confirm that it makes the reading decrease.
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).
When casting the gage directly into the structure, care must be taken to avoid applying any large
forces to the end blocks during installation. This is most imperative when installing Model 4202
gages. Do not wrap an iron tie wire around the body of a 4202 gage; the gage could be damaged
due to its delicate construction. Instead, use the holes in the end blocks to affix the gage to the
rebar, being sure that the gage is not tensioned or compressed in the longitudinal direction.
Model 4200L strain gages are specifically designed to allow strains to be measured in curing
concrete. The 4200L is easily compressed and cannot be buried more than one meter deep
inside the wet concrete.

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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. Run the wire around the body of the strain gage and around the rebar. Then
twist the wire around itself to hold the gage in place.
3) Tie the instrument cable off to the rebar using nylon cable ties.
The wires should not be tied too tightly since rebar and tension cables tend to move during
concrete placement and vibration. Care should be taken not to damage the cable with the
vibrator. The gage can also be placed directly into the mix if it can be assured that the orientation
will be correct after the gage placement.
Figure 7 - Attaching Model 4200/4200L/4200HT Strain Gages to Rebar

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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. This can result in unstable readings or no readings at all! This effect disappears
once the concrete has been placed. For an alternative method, which avoids this potential
problem, see Section 4.3.
2) Select a length of soft iron tie wire, similar to the kind that is normally used for tying rebar
cages together. Wrap the wire around the rubber strips two times.
3) Twist two loops in the wire, one on either side of the gage, at a distance of about three cm
from the gage body. Repeat this process at the other end of the gage.
4) Position the gage between the rebar and twist the wire ends twice around the rebar, then
around itself.
5) Tighten the wire and orient the gage by twisting on the loops between the gage and the rebar.
6) Tie the instrument cable off to one of the rebar using nylon cable ties.
Figure 8 - Suspending Model 4200/4200L/4 200HT Strain Gages Between Rebar

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4.3 Alternative Suspension Method
Geokon strain gages may also be suspended by attaching two short pieces of steel rebar to the
existing rebar using nylon cable ties, and then securing the strain gage to the shorter pieces of
rebar with more cable ties, as shown in Figure 9. This method avoids the resonance problems
associated with using soft iron tire wires to suspend the gage as described in Section 4.2.
Figure 9 - Alternative Method for Attaching Model 4200/4200HT Strain Gages to Rebar
4.4 Using Precast Briquettes, Shotcrete, or Grouting
An alternate method to casting the units into the concrete mix directly is to precast the gages into
briquettes of the same mix as the mass concrete and then place the briquettes in the structure
prior to concrete placement. The briquettes should be constructed no more than three days prior
to installation, but no less than one day prior, and should be continuously cured with water while
awaiting placement in the mass concrete.
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. The gages may be placed by
packing the immediate area around the gage by hand and then proceeding with the shotcrete
operation.

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4.5 Cable Splicing and Termination
Terminal boxes with sealed cable entries are available from Geokon for all types of applications.
These allow many gages to be terminated at one location with complete protection of the lead
wires. The interior panel of the terminal box can have built-in jacks or a single connection with a
rotary position selector switch. Contact Geokon for specific application information.
Because the vibrating wire output signal is a frequency rather than a current or voltage,
variations in cable resistance have little effect on gage 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 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.
Cables may be terminated by stripping and tinning the individual conductors and then connecting
them to the patch cord of a readout box. Alternatively, a connector may be used which will plug
directly into the readout box or to a receptacle on a special patch cord.
The cable from the strain gages can also be protected by the use of flexible conduit, which can be
supplied by Geokon.
4.6 Lightning Protection
Unlike numerous other types of instrumentation available from Geokon, embedment strain gages
do not have any integral lightning protection components, such as transorbs or plasma surge
arrestors. Usually this is not a problem, as these types of gages are installed within concrete or
grout and somewhat isolated from potentially damaging electrical transients. However, there
may be occasions where some sort of lightning protection is desirable, for example, where the
gage is in contact with rebar that may be exposed to direct or indirect lightning strikes. In
addition, 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.

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Suggested Lightning Protection Options:
•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 the installation of these components.
•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. A connection is made between the
enclosure and earth ground to facilitate the passing of transients away from the gage. See
Figure 10.
•Plasma surge arrestors can be epoxied into the instrument cable, close to the sensor. A
ground strap then connects the surge arrestor to an earth ground, such as a grounding stake or
the rebar itself.
Consult the factory for additional information on available lightning protection.
Figure 10 - Lightning Protection Scheme

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5. TAKING READINGS
5.1 GK-404 Readout Box
The Model GK-404 Vibrating Wire Readout is a portable, low-power, handheld unit that is
capable of running for more than 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.
5.1.1 Operating the GK-404
Before use, attach the flying leads to the GK-404 by aligning the red circle on the silver
“Lemo” connector of the flying leads with the red line on the top of the GK-404 (Figure
11). Insert the Lemo connector into the GK-404 until it locks into place.
Figure 11 - Lemo Connector to GK-404
Connect each of the clips on the leads to the matching colors of the sensor conductors,
with blue representing the shield (bare).
To turn the GK-404 on, press the “ON/OFF” button on the front panel of the unit. The
initial startup screen 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 reading of the attached gage in degrees Celsius.
Use the POS and MODE buttons to select the correct position and display units for the
model of strain gage purchased (see Section 5.4).
The GK-404 will continue to take measurements and display readings until the unit is
turned off, either manually, or if enabled, by the Auto-Off timer.
For more information, consult the GK-404 manual.

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5.2 GK-405 Readout Box
The GK-405 Vibrating Wire Readout is made up of two components: The Readout Unit,
consisting of a Windows Mobile handheld PC running the GK-405 Vibrating Wire Readout
Application; and the GK-405 Remote Module, which is housed in a weatherproof enclosure and
connects to the vibrating wire gage to be measured. The two components communicate
wirelessly using Bluetooth®, a reliable digital communications protocol. The Readout Unit can
operate from the cradle of the Remote Module, or, if more convenient, can be removed and
operated up to 20 meters away from the Remote Module.
5.2.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached
Align the grooves on the sensor connector (male), with the appropriate connector on the
readout (female connector labeled senor or load cell). Push the connector into place, and
then twist the outer ring of the male connector until it locks into place.
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).
5.2.3 Operating the GK-405
Press the button labeled “POWER ON (BLUETOOTH)”. A blue light will begin
flashing, signifying that the Remote Module is waiting to connect to the hand-held unit.
Launch the GK-405 VWRA program by tapping on “Start” from the hand-held PC’s
main window, then “Programs” then the GK-405 VWRA icon. After a few seconds, the
blue light on the Remote Module should stop flashing and remain lit. The Live Readings
Window will be displayed on the hand-held PC. Set the Display Mode to the correct letter
for the model of strain gage purchased (see Section 5.4). For more information, consult
the GK-405 Instruction Manual.

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5.3 GK-403 Readout Box (Obsolete Model)
The GK-403 can store gage readings, as well as apply calibration factors to convert readings to
engineering units. The GK-403 displays the thermistor temperature in degrees C.
5.3.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached
Align the grooves on the sensor connector (male), with the appropriate connector on the
readout (female connector labeled senor or load cell). Push the connector into place, and
then twist the outer ring of the male connector until it locks into place.
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).
5.3.3 Operating the GK-403
1) Turn the display selector to the correct position for the model of strain gage purchased
(see Section 5.4).
2) Turn the unit on.
3) A reading will appear in the front display window. (The last digit may change one or
two digits while reading.)
4) The thermistor will be read and displayed on the screen above the gage reading in
degrees centigrade.
5) Press the "Store" button to record the value displayed.
If the no reading displays or the reading is unstable, see Section 7 for troubleshooting
suggestions.
The unit will automatically turn itself off after approximately two minutes to conserve
power. For more information, consult the GK-403 manual.
5.4 Embedment Strain Gage Readout Positions
Model:
4200/4200HT
4202
4204
4210/4212/4214
Readout Position:
D
E
A (Mode: Digits)
B
Display Units:
microstrain (µε)
microstrain (µε)
digits (f2
×
10-3)
digits (f2
×
10-3)
Frequency Range:
450-1200 Hz
1400-3500 Hz
800-1600 Hz
1400-3500 Hz
Mid-Range Reading:
2500 µε
2500 µε
1700 Digits
6000 digits
Minimum Reading:
1000 µε
1000 µε
650 Digits
2000 digits
Maximum Reading:
4000 µε
4000 µε
2750 Digits
10000 digits
Table 2 - Readout Positions

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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. (Except when using the 4200HT strain gage, which must be read using
an ohmmeter.)
To read temperatures using an ohmmeter:
1) Connect an ohmmeter to the green and white thermistor leads coming from the strain gage.
(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 14.7 ohms per
one thousand feet. Multiply this factor by two to account for both directions.)
2) Look up the temperature for the measured resistance in Appendix C, Table 9. For the
4200HT use Appendix D, Table 10.