Installation Manual
Model 6350
Vibrating Wire Tiltmeter
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 © 1995-2018 by Geokon, Inc.
(Doc Rev P, 06/28/18)
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
1.1 THEORY OF OPERATION ....................................................................................................................................... 1
1.2 TILT SENSOR CONSTRUCTION .............................................................................................................................. 2
2. INSTALLATIO N .................................................................................................................................................... 3
2.1 PRELIMINARY TESTS............................................................................................................................................ 3
2.2 INSTALLING THE MOUNTING BRACKETS.............................................................................................................. 4
2.2.1 Mounting with a Drop-in Anchor ................................................................................................................ 4
2.2.2 Mounting with an Anchor Rod .................................................................................................................... 5
2.3 SENSOR INSTALLATION........................................................................................................................................ 7
2.3.1 Installing Uniaxial Tiltmeters ..................................................................................................................... 7
2.2.2 Installing Biaxial Tiltmeters ........................................................................................................................ 8
2.4 FLUID DAMPING .................................................................................................................................................. 9
2.5 SPLICING AND JUNCTION BOXES.......................................................................................................................... 9
2.6 LIGHTNING PROTECTION ................................................................................................................................... 10
3. TAKING READ INGS ........................................................................................................................................... 11
3.1 GK-404 READOUT BOX ..................................................................................................................................... 11
3.1.1 Operating the GK-404 .............................................................................................................................. 11
3.2 GK-405 READOUT BOX ..................................................................................................................................... 12
3.2.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached ............................................................. 12
3.2.2 Connecting Sensors with Bare Leads ........................................................................................................ 12
3.2.3 Operating the GK-405 .............................................................................................................................. 12
3.3 GK-403 READOUT BOX (OBSOLETE MODEL) .................................................................................................... 13
3.3.1 Connecting Sensors with 10-pin Bulkhead Connectors Attached ............................................................. 13
3.3.2 Connecting Sensors with Bare Leads ........................................................................................................ 13
3.3.3 Operating the GK-403 .............................................................................................................................. 13
3.4 MICRO-10 DATALOGGER ................................................................................................................................. 14
3.4.1 Excitation .................................................................................................................................................. 14
3.4.2 Excitation Frequenc y ................................................................................................................................ 14
3.5 MEASURING TEMPERATURES ............................................................................................................................. 14
4. DATA REDUCTION ............................................................................................................................................ 15
4.1 TILT CALCULATION ........................................................................................................................................... 15
4.2 TEMPERATURE CORRECTION ............................................................................................................................. 15
5. TROUBLESHO OTING ........................................................................................................................................ 16
APPENDIX A. SAMPLE CALIBRA TION REPORT ........................................................................................... 18
APPENDIX B. SPECIFICATIONS ......................................................................................................................... 19
B.1 VIBRATING WIRE TILT SENSOR ........................................................................................................................ 19
B.2 THERMISTOR ..................................................................................................................................................... 19
APPENDIX C. THERMISTOR TEMPERATURE DERIVATION..................................................................... 20
FIGURES
IGURE 1 - MODEL 6350 UNIAXIAL TILTMETER INSTALLATION .................................................................................... 1
F
FIGURE 2 - MODEL 6350 TILT SENSOR .......................................................................................................................... 2
FIGURE 3 - TILTMETER MOUNTING BRACKETS .............................................................................................................. 4
FIGURE 4 - DROP-IN ANCHOR INSTALLATION (BIAXIAL MOUNTING BRACKET SHOWN) ............................................... 5
FIGURE 5 - ANCHOR ROD (UNIAXIAL MOUNTING BRACKET SHOWN) ........................................................................... 6
FIGURE 6 - UNIAXIAL INSTALLATION ............................................................................................................................ 7
FIGURE 7 - BIAXIAL INSTALLATION ............................................................................................................................... 8
FIGURE 8 - LIGHTNING PROTECTION SCHEME ..............................................................................................................10
FIGURE 9 - LEMO CONNECTOR TO GK-404 ..................................................................................................................11
FIGURE 10 - LIVE READINGS – RAW READINGS............................................................................................................12
FIGURE 11 - SAMPLE MODEL 6350 CALIBRATION REPORT ...........................................................................................18
TABLES
ABLE 1 - SAMPLE RESISTANCE ...................................................................................................................................17
T
TABLE 2 - RESISTANCE WORKSHEET ............................................................................................................................17
TABLE 3 - MODEL 6350 TILT SENSOR SPECIFICATIONS ................................................................................................19
TABLE 4 - THERMISTOR RESISTANCE VERSUS TEMPERATURE .....................................................................................20
EQUATIONS
QUATION 1 - DIGITS CALCULATION ............................................................................................................................15
E
EQUATION 2 - POLYNOMIAL EQUATION .......................................................................................................................15
EQUATION 3 - TEMPERATURE CORRECTION .................................................................................................................15
EQUATION 4 - RESISTANCE TO TEMPERATURE .............................................................................................................20
1. INTRODUCTION
1.1 Theory of Operation
The Geokon Model 6350 Vibrating Wire Tiltmeter is designed for permanent long-term
monitoring of changes in tilt of structures such as dams, embankments, foundation walls and the
like. The basic principle is the utilization of tilt sensors attached to the structure being studied to
make accurate measurement of inclination. See Figure 1.
Two brackets are available, one to measure tilt uniaxially, the other biaxially.
Wall
Mounting Bracket
Zero Adjust
1
-
Tilt
Side View
-
Tilt
+
Instrument Cable
(4 conductor, 22 AWG)
+
Tiltmeter
Anchor Rod
(epoxied in)
Top View
Figure 1 - Model 6350 Uniaxial Tiltmeter Installation
2
1.2 Tilt Sensor Construction
The sensor is comprised of a pendulous mass, which is supported by a vibrating wire strain gage
and an elastic hinge. See Figure 2. The strain gage senses the changes in force caused by rotation
of the center of gravity of the mass. The mass and sensor are enclosed in a waterproof housing,
which includes components for connecting the sensor to the mounting bracket. The housing is
constructed using stainless steel tubing to minimize the effects of corrosion. Biaxial systems use
a mounting bracket to mount two transducers at 90° to each other. In environments subject to
vibrations, a damping fluid can be used, as shown in the figure below.
Figure 2 - Model 6350 Tilt Sensor
To prevent damage during shipment the tilt sensors are locked in place by means of a
slotted head locking clamp screw. This slotted head locking clamp screw must be removed
and replaced by a Phillips head seal screw (provided), to render the tiltmeter operative.
2. INSTALLATION
2.1 Preliminary Tests
Prior to installation, the sensors need to be checked for proper operation. Each tilt sensor is
supplied with a calibration report, which shows the relationship between readout digits and
inclination. The tilt sensor electrical leads (usually the red and black leads) are connected to a
readout box (see Section 3 for readout instructions) and the current reading compared to the
calibration readings. After backing off the clamp screw three full turns, carefully hold the sensor
in a vertical position and observe the reading. It will take a few seconds to come to equilibrium
and the sensor must be held in a steady position. The readings should be in the range of the
factory reading, but will vary according to inclination. The indicated temperature should be close
to ambient.
Note: Vibrating wire tilt sensors are shock sensitive and severe shocks can cause a
permanent offset or even break the suspension. (The unit will not survive a two foot (.5 m)
drop onto a hard surface.) When transporting the tiltmeter tighten the locking clamp
screw.
3
Checks of electrical continuity can also be made using an ohmmeter. Resistance between the
gage leads should be approximately 180Ω, ±10 ohms. Remember to add cable resistance when
checking. Remember to add cable resistance when checking. The resistance of 22 AWG stranded
copper leads is approximately 14.7Ω per 1,000 feet (48.5Ω per km), multiply this factor by two
to account for both directions.
Resistance between the green and white leads varies by temperature. Using Table 4 in Appendix
C, convert the resistance to temperature and compare the result to the ambient temperature.
Resistance between any conductor and the shield should exceed two megohms.
4
2.2 Installing the Mounting Brackets
Two mounting brackets are available for the Model 6350. One is designed for uniaxial tilt
measurements the other for biaxial.
Figure 3 - Tiltmeter Mounting Brackets
Both bracket types may be mounted using a drop-in anchor or an anchor rod that is epoxied or
grouted in place. See Section 2.2.1 for instructions using a drop-in anchors, and Section 2.2.2 for
anchor rods.
2.2.1 Mounting with a Drop-in Anchor
1) Mark the location where the bracket will be installed.
2) Using a hammer drill, drill a half inch (12 mm) hole approximately 1.5" (37 mm)
deep. Clean the hole thoroughly, blowing out with compressed air if possible.
3) Insert the 3/8" drop-in anchor with setting pin into the hole. The threaded end should
be closest to the opening.
4) Insert the provided setting tool, small end first, into the anchor. Expand the anchor by
hitting the large end of the setting tool with several sharp hammer blows.
5) Thread the supplied 3/8-16 anchor rod into the anchor.
5
Top View
Flat Washer
2" 3/8-16 Anchor Rod
Flat Washers
Lock Washer
3/8-16 Nuts
Wall
3/8" Drop-In Anchor
Setting Pin
6) Attach the mounting bracket to the bolt using the supplied hardware, as illustrated in
Figure 4.
7) Use a leveling device to align the bracket vertically to the wall.
Figure 4 - Drop-in Anchor Installation (Biaxial Mounting Bracket Shown)
2.2.2 Mounting with an Anchor Rod
1) Mark the location where the bracket will be installed.
2) Using a hammer drill, drill a half inch (12 mm) hole approximately four inches (100
mm) deep.
3) Clean the hole thoroughly, blowing out with compressed air if possible.
4) Mix the grout or epoxy and fill the hole.
5) Push the 1/2-13 threaded anchor rod into the hole. (Use a hammer if necessary to get
the anchor to reach the bottom.)
6) Let the anchor rod set before continuing the installation.
6
7) After setting, attach the mounting bracket to the bolt using the supplied hardware as
illustrated in Figure 5.
8) Use a bubble level or other leveling device to align the bracket vertically to the wall.
Wall
Flat Washers
4" 1/2-13 Anchor Rod
Epoxy or Grout
Flats to Prevent Bolt Twisting
1/2-13 Nuts
Flat Washer
Lock Washer
Figure 5 - Anchor Rod (Unia xial Mounting Bracket Shown)
Top View
2.3 Sensor Installation
2.3.1 Installing Uniaxial Tiltmeters
Attach the tiltmeter to the mounting bracket using the supplied 10-32 cap screws,
washers, and nuts. Remove the slotted head locking clamp screw completely and
replace with the Phillips head seal screw (provided). This is very important if the
sensor is to remain waterproof. Do not tighten the cap screws yet. Attach a portable
readout such as the GK-404 or GK-405 (see Section 3 for readout instructions) and
observe the reading. Adjust the sensor in the slot of the mounting bracket while observing
the readout until the tiltmeter reads within ±50 digits of the zero reading as shown on the
calibration report supplied with the sensor. (See Appendix A for a sample calibration
report.) When the desired reading is reached, tighten the cap screws to secure the
tiltmeter in place. Check the reading again after tightening to make sure it still reads
within ±50 digits of the zero reading. Figure 6 shows the completed installation.
If the tiltmeter is installed in an exposed location in a construction area, and/or if the
installation is in direct sunlight, it should be covered with a protective enclosure and/or
insulation.
7
Wall
-
Top View
Figure 6 - Uniaxial Installation
Tilt
Instrument Cable
(Four conductor, 22 AWG)
10-32 Nuts
Tiltmeter Mounting Flange
Mounting Bracket
10-32 Cap Screws
+
8
Top View
Tilt
-
+
Wall
Tilt
-
+
10-32 Nuts
10-32 Cap Screws
Mounting Bracket
Tiltmeter Mounting Flange
2.2.2 Installing Biaxial Tiltmeters
The sensors may now be installed. Attach the tiltmeters to the mounting bracket using the
supplied 10-32 cap screws, washers, and nuts. Remove the slotted head locking clamp
screw completely and replace with the Phillips head seal screw provided. This is
very important if the sensor is to remain waterproof. Do not tighten the cap screws
yet. Attach a portable readout such as the GK-404 or GK-405 (see Section 3 for readout
instructions) and observe the reading. Adjust each sensor in their slots of the mounting
bracket while observing the readout until the tiltmeter reads within ±50 digits of the zero
reading as shown on the calibration report supplied with each sensor. (See Appendix A
for a sample calibration report.) When the desired reading is reached, tighten the cap
screws to secure the tiltmeter in place. Check the reading again after tightening to make
sure it still reads within ±50 digits of the zero reading. Figure 7 shows the completed
installation.
If the tiltmeters are installed in an exposed location in a construction area, and/or if the
installation is in direct sunlight, it should be covered with a protective enclosure and/or
insulation.
Figure 7 - Biaxial Installation
2.4 Fluid Damping
The vibrating wire tilt sensor acts as a self-damping system when used in vibration free
environments. When external ground or structural vibrations exceed a certain threshold, the
pendulous mass will continue to “swing” and stable readings may not be possible. In such cases,
additional damping can be achieved by adding a viscous damping fluid to a small reservoir
contained in the sensor. A thin, wide “paddle” is connected to the mass and when the fluid is
added the pendulum is damped by the action of the paddle in the damping fluid (see Figure 2).
Damping fluid kits are available from Geokon (part number 6350-4).
Most in-place tiltmeter installations will not require this fluid. However, if the instrument gives
unstable outputs, or it is known that the structure is constantly vibrating, the fluid can be added.
The fluid is a very high viscosity silicone oil which must be injected into the sensor with a
syringe.
The sensor must be held upright during the injection of the fluid and at all times following the
injection. This makes it necessary to perform this operation in the field. The following applies
for a typical in-place installation.
9
1) Remove the clamp screw on the bottom side of the sensor (see Figure 2).
2) Using the syringe applied, first pull the piston from the syringe and squeeze the silicone from
the tube into the syringe. Replace the piston and start the fluid out of the “needle” end.
3) Inject 2.00 cc of the damping fluid into the hole in the sensor. Immediately following this
operation, the seal screw should be replaced in the sensor.
4) The sensor may now be attached to the mounting bracket.
2.5 Splicing and Junction Boxes
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.
10
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 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.
2.6 Lightning Protection
The Model 6350 Tiltmeter, unlike numerous other types of instrumentation available from
Geokon, does 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 advisable 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 tiltmeter 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 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 this enclosure and earth ground to facilitate the passing of
transients away from the gage. See Figure 8. 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.
Terminal Box/Multiplexer
Wall
Instrument Cable
(usually buried)
LAB-3 Enclosure
Ground Connections
Figure 8 - Lightning Protection Scheme
Model 6350 Tiltmeter
Surface
LAB-3 Board
3. TAKING READINGS
3.1 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.
3.1.1 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 9).
Insert the Lemo connector into the GK-404 until it locks into place.
11
Figure 9 - 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 display. 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 button to select position B and the MODE button to select Dg (digits).
(Other functions can be selected as described in the GK-404 Manual.)
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.
If no reading displays or the reading is unstable, see Section 5 for troubleshooting
suggestions. For further information, consult the GK-404 manual.
12
3.2 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 from the Remote Module.
3.2.1 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.
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
blinking, signifying that the Remote Module is waiting to connect to the handheld unit.
Launch the GK-405 VWRA program on the handheld PC by tapping on “Start”, 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, indicating that the remote module
has successfully paired with the handheld PC. The Live Readings Window will be
displayed on the handheld PC. Figure 10 shows a typical vibrating wire piezometer
output in digits and thermistor output in degrees Celsius.
If the no reading displays or the reading is unstable, see Section 5 for troubleshooting
suggestions. For further information, consult the GK-405 Instruction Manual.
Figure 10 - Live Readings – Raw Readings
3.3 GK-403 Readout Box (Obsolete Model)
The GK-403 can store gage readings and apply calibration factors to convert readings to
engineering units. The following instructions explain taking gage measurements using Mode
“B”. Consult the GK-403 Instruction Manual for additional information.
3.3.1 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.
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 in digits (See Equation 1 in Section
4.1.) The last digit may change one or two digits while reading.
4) The thermistor reading will be displayed 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 5 for troubleshooting
suggestions.
The unit will automatically turn off after approximately two minutes to conserve power.
13
14
3.4 MICRO-10 Datalogger
The following parameters are recommended when using the Model 6350 with the MICRO-10
datalogger or any other CR10 based datalogger:
3.4.1 Excitation
The 2.5V excitation directly off the wiring panel is ideal for these sensors. The five volt
supply from the AVW-1 and AVW-4 modules is also usable, but the 12V excitation
should be avoided as it tends to overdrive the sensor. The default excitation voltage used
in MICRO-10 systems is 5V.
3.4.2 Excitation Frequency
The starting and ending frequencies of the excitation sweep should be kept in a relatively
narrow band for these sensors to maximize the stability and resolution of the output. The
exact values can be calculated for a given sensor from the supplied calibration report.
Ideally, the settings should be calculated by taking an initial reading and then setting the
starting frequency to 200 Hz below and the ending frequency 200 Hz above. Alternately,
the low-end frequency sweep setting should be set to 14 (1400 Hz), the high end, 35
(3500 Hz).
3.5 Measuring Temperatures
All vibrating wire piezometers are equipped with a thermistor, which 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.
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 14.7Ω per 1,000
feet or 48.5Ω per km, multiply this factor by two to account for both directions.
2) Look up the temperature for the measured resistance in Appendix C, Table 4.
15
∆θ
θ
4. DATA REDUCTION
4.1 Tilt Calculation
Tilts are measured in digits on Position B of either the GK-404 or GK-405 Readout Box. The
relationship between these digits and the change of the angle of inclination (tilt) is given by the
equation:
= (R1 − R0) G degrees
Equation 1 - Digits Calculation
Where;
R1 is the current reading in digits.
R0 is the initial reading in digits.
G is the Calibration Factor in degrees/digit.
The linear equation works very well for tilt angles of less than two degrees. More than this and
the linearity errors increase. The error incurred by using the linear equation is shown on the
calibration chart.
For better accuracy at larger inclinations, use the polynomial equation:
= R2A + RB + C
Equation 2 - Polynomial Equation
Where;
A, B and C are the coefficients supplied on the calibration report. Calculate θ for R = R1 and R =
R0 then subtract to find the difference ∆θ for (R1 – R0).
4.2 Temperature Correction
The Model 6350 Tiltmeter has a very slight temperature sensitivity on the order of – 0.5 digit per
°C rise, i.e. the reading falls by 0.5 digits for every 1 °C rise of temperature. The temperature
correction is:
+K (T1-T0) degrees
Equation 3 - Temperature Correction
Where K = 0.5G.
Normally, corrections are not applied for this small effect because the structure being monitored
usually is affected to a much greater degree. An important point to note, also, is that sudden
changes in temperature will cause both the structure and the Tiltmeter to undergo transitory
physical changes, which will show up in the readings. The gage temperature should always be
recorded for comparison, and efforts should be made to obtain readings when the instrument and
structure are at thermal equilibrium. The best time for this tends to be in the late evening or early
morning hours.
16
5. TROUBLESHOOTING
Maintenance and troubleshooting of vibrating wire piezometers is confined to periodic checks of
cable connections and maintenance of terminals. The transducers themselves are sealed and are
not user serviceable. Gages should not be opened in the field.
Should difficulties arise, consult the following list of problems and possible solutions. For
additional troubleshooting and support, contact Geokon.
Symptom: Thermistor resistance is too high:
Is there an open circuit? Check all connections, terminals, and plugs. If a cut is located in the
cable, splice according to instructions in Section 2.4.
Symptom: Thermistor resistance is too low:
Is there a short? Check all connections, terminals, and plugs. If a short is located in the cable,
splice according to instructions in Section 2.4.
Water may have penetrated the interior of the tilt sensor. There is no remedial action.
Symptom: Tiltmeter Readings are Unstable:
Is the readout box position set correctly? If using a datalogger to record readings
automatically, are the swept frequency excitation settings correct?
Is there a source of electrical noise nearby? Most probable sources of electrical noise are
motors, generators, and antennas. Make sure the shield drain wire is connected to ground.
Does the readout work with another tilt sensor? If not, the readout may have a low battery or
be malfunctioning.
Symptom: Tiltmeter Fails to Read:
Is the cable cut or crushed? This can be checked with an ohmmeter. Table 1 shows the
expected resistance for the various wire combinations; Table 2 is provided for the customer
to fill in the actual resistance found. Cable resistance is approximately 14.7Ω per 1000 feet
(48.5Ω per km) of 22 AWG wire. Multiply this factor by two to account for both directions.
If the resistance reads very high or infinite (megohms), a cut wire must be suspected. If the
resistance reads very low (<100Ω), a short in the cable is likely.
Does the readout or datalogger work with another tilt sensor? If not, the readout or datalogger
may be malfunctioning.
Vibrating Wire Sensor Lead Grid - SAMPLE VALUES
≅180Ω
≅180Ω
3000Ω
25°
3000Ω
25°
Red Black White Green Shield
17
Red N/A
Black
N/A infinite infinite infinite
White infinite infinite N/A
Green infinite infinite
infinite infinite infinite
at
C
at
N/A infinite
C
Shield infinite infinite infinite infinite N/A
Table 1 - Sample Resistance
Vibrating Wire Sensor Lead Grid - SENSOR NAME/## :
Red Black White Green Shield
Red
Black
White
infinite
Green
Shield
Table 2 - Resistance Worksheet
18
APPENDIX A. SAMPLE CALIBRATION RE P ORT
Figure 11 - Sample Model 6350 Calibration Report
APPENDIX B. SPECIFICATIONS
Model:
6350
Range:¹
±10°
Resolution:²
±0.5 mm/m (eight arc seconds)
Accuracy:³
± 0.1% FSR
Linearity:
± 0.3% FSR
Thermal Zero Shift:
± 4 arc seconds/°C
Operating Temperature:4
-20 to +80 °C
-4 to 176 °F
Operating Frequency:
1400-3500 Hz
Coil Resistance:
180 Ω
Diameter:
1.250" (32 mm)
Length:
7.375" (187 mm)
Weight:
1.5 lbs. (0.7 kg)
Materials:
304 Stainless Steel
Electrical Cable:
Two twisted pair (four conductor) 22 AWG
Foil shield, PVC jacket, nominal OD=6.3 mm (0.250")
B.1 Vibrating Wire Tilt Sensor
19
Table 3 - Model 6350 Tilt Sensor Specifications
Notes:
¹ Consult the factory for other ranges.
² Depends on readout equipment. With averaging techniques, it is possible to achieve one arc
second
³ Derived using second order polynomial.
4
Versions to -40 °C available on request.
B.2 Thermistor
(Also see Appendix C.)
Range: -80 to +150° C
Accuracy: ±0.5° C
20
Ohms
Temp
Ohms
Temp
Ohms
Temp
Ohms
Temp
Ohms
Temp
201.1K
-50
16.60K
-10
2417
+30
525.4
+70
153.2
+110
187.3K
-49
15.72K
-9
2317
31
507.8
71
149.0
111
174.5K
-48
14.90K
-8
2221
32
490.9
72
145.0
112
162.7K
-47
14.12K
-7
2130
33
474.7
73
141.1
113
151.7K
-46
13.39K
-6
2042
34
459.0
74
137.2
114
141.6K
-45
12.70K
-5
1959
35
444.0
75
133.6
115
132.2K
-44
12.05K
-4
1880
36
429.5
76
130.0
116
123.5K
-43
11.44K
-3
1805
37
415.6
77
126.5
117
115.4K
-42
10.86K
-2
1733
38
402.2
78
123.2
118
107.9K
-41
10.31K
-1
1664
39
389.3
79
119.9
119
101.0K
-40
9796 0 1598
40
376.9
80
116.8
120
94.48K
-39
9310
+1
1535
41
364.9
81
113.8
121
88.46K
-38
8851 2 1475
42
353.4
82
110.8
122
82.87K
-37
8417 3 1418
43
342.2
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
85.7
132
44.16K
-27
5177
13
965.0
53
250.9
93
83.6
133
41.56K
-26
4939
14
929.6
54
243.4
94
81.6
134
39.13K
-25
4714
15
895.8
55
236.2
95
79.6
135
36.86K
-24
4500
16
863.3
56
229.3
96
77.6
136
34.73K
-23
4297
17
832.2
57
222.6
97
75.8
137
32.74K
-22
4105
18
802.3
58
216.1
98
73.9
138
30.87K
-21
3922
19
773.7
59
209.8
99
72.2
139
29.13K
-20
3748
20
746.3
60
203.8
100
70.4
140
27.49K
-19
3583
21
719.9
61
197.9
101
68.8
141
25.95K
-18
3426
22
694.7
62
192.2
102
67.1
142
24.51K
-17
3277
23
670.4
63
186.8
103
65.5
143
23.16K
-16
3135
24
647.1
64
181.5
104
64.0
144
21.89K
-15
3000
25
624.7
65
176.4
105
62.5
145
20.70K
-14
2872
26
603.3
66
171.4
106
61.1
146
19.58K
-13
2750
27
582.6
67
166.7
107
59.6
147
18.52K
-12
2633
28
562.8
68
162.0
108
58.3
148
17.53K
-11
2523
29
543.7
69
157.6
109
56.8
149
Table 4 - Thermistor Resistance Versus Temperature
55.6
150
APPENDIX C. THERMISTOR TEMPERATURE DERIVATION
Thermistor Type: YSI 44005, Dale #1C3001-B3, Alpha #13A3001-B3
Resistance to Temperature Equation:
1
T=
A+B(LnR)+C(LnR)
Equation 4 - Resistance to Temperature
Where;
T = Temperature in °C.
LnR = Natural Log of Thermistor Resistance
A = 1.4051 × 10-3
B = 2.369 × 10-4
C = 1.019 × 10-7
Note: Coefficients calculated over the −50 to +150° C. span.
-273.2
3
Loading...