Geokon 4500 Series User manual

Instruction Manual
Model 4500
series
Vibrating Wire Piezometers
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 © 1983, 1996, 2002, 2004, 2005, 2007, 2008, 2009,2011, 2013 by Geokon, Inc.
(Doc Rev X 6/13)

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. THEORY OF OPERATION...................................................................................................................1
2. INSTALLATION......................................................................................................................................2
2.1 PRELIMINARY TESTS............................................................................................................................2
2.1.1 Establishing an Initial Zero Reading ........................................................................................2
2.1.2 Checking the Calibration............................................................................................................3
2.2 INSTALLATION IN STANDPIPES OR WELLS...........................................................................................4
2.3 INSTALLATION IN BOREHOLES .............................................................................................................4
2.4 INSTALLATION IN FILLS AND EMBANKMENTS.......................................................................................6
2.5 INSTALLATION BY PUSHING OR DRIVING INTO SOFT SOILS ................................................................7
2.6 DE-AIRING FILTER TIPS .......................................................................................................................8
2.6.1 Low Air Entry Filter, Model 4500S and 4500PN ...................................................................8
2.6.2 Removable Ceramic Filter, Model 4500S..............................................................................9
2.6.3 Model 4500DP .........................................................................................................................10
2.7 MODEL 4500H TRANSDUCER ...........................................................................................................10
2.8 SPLICING AND JUNCTION BOXES.......................................................................................................10
2.9 LIGHTNING PROTECTION ...................................................................................................................11
3. TAKING READINGS............................................................................................................................12
3.1 OPERATION OF THE GK-403 READOUT BOX....................................................................................12
3.2 OPERATION OF THE GK-404 READOUT BOX....................................................................................13
3.3 OPERATION OF THE GK-405 READOUT BOX....................................................................................13
3.4 MEASURING TEMPERATURES............................................................................................................14
4. DATA REDUCTION .............................................................................................................................14
4.1 PRESSURE CALCULATION..................................................................................................................14
4.2 TEMPERATURE CORRECTION ............................................................................................................16
4.3 BAROMETRIC CORRECTION (REQUIRED ONLY ON UN-VENTED TRANSDUCERS)...............................17
4.3.1 Vented Piezometers................................................................................................................18
4.4 ENVIRONMENTAL FACTORS...............................................................................................................18
5. TROUBLESHOOTING.........................................................................................................................19
APPENDIX A - SPECIFICATIONS..........................................................................................................20
APPENDIX B – STANDARD TEMPERATURE THERMISTOR TEMPERATURE DERIVATION
.......................................................................................................................................................................21
APPENDIX D - NOTES REGARDING THE MODEL 4500C...............................................................23
APPENDIX E - NON LINEARITY AND THE USE OF A SECOND ORDER POLYNOMIAL TO
IMPROVE THE ACCURACY OF THE CALCULATED PRESSURE.................................................24
APPENDIX F - QUICK INSTRUCTIONS FOR INSTALLING A VIBRATING WIRE
PIEZOMETER.............................................................................................................................................25
APPENDIX G -MODEL 4500AR PIEZOMETER...........................................................................26

LIST of FIGURES, TABLES and EQUATIONS
FIGURE 1-1 VIBRATING WIRE PIEZOMETER ................................................................................................. 1
FIGURE 2-1 TYPICAL LEVEL MONITORING INSTALLATIONS .......................................................................... 4
FIGURE 2-2 TYPICAL BOREHOLE INSTALLATIONS......................................................................................... 5
TABLE 1SHOWING CEMENT/BENTONITE/WATER RATIOS FOR TWO GROUT MIXES...................................... 6
FIGURE 2-3 TYPICAL DAM INSTALLATIONS................................................................................................... 7
FIGURE 2-4 TYPICAL SOFT SOILS INSTALLATION......................................................................................... 8
FIGURE 2-5 TYPICAL MULTI-PIEZOMETER INSTALLATION.......................................................................... 11
FIGURE 2-6 RECOMMENDED LIGHTNING PROTECTION SCHEME ............................................................... 12
FIGURE 3.1 GK405 READOUT UNIT ............................................................................................................ 14
EQUATION 4-1 DIGITS CALCULATION.......................................................................................................... 14
EQUATION 4-2 CONVERT DIGITS TO PRESSURE ........................................................................................ 15
TABLE 4-1 ENGINEERING UNITS MULTIPLICATION FACTORS..................................................................... 15
EQUATION 4-3 TEMPERATURE CORRECTION............................................................................................. 17
EQUATION 4-4 BAROMETRIC CORRECTION................................................................................................. 17
EQUATION 4-5 CORRECTED PRESSURE CALCULATION.............................................................................. 18
TABLE A-1 VIBRATING WIRE PIEZOMETER SPECIFICATIONS..................................................................... 20
TABLE B-1 STANDARD TEMPERATURE THERMISTOR RESISTANCE VERSUS TEMPERATURE......... 21
TABLE C1 HIGH TEMPERATURE.TEMPERATURE V THERMISTOR RESISTANCE......................................... 22

1. THEORY OF OPERATION
Geokon Model 4500 Vibrating Wire Piezometers are intended primarily for long-term
measurements of fluid and/or pore pressures in standpipes, boreholes, embankments,
pipelines and pressure vessels. Several models of the 4500 series are available (see
Appendix A). Contact Geokon sales engineers for specific application information.
The instrument utilizes a sensitive stainless steel diaphragm to which a vibrating wire
element is connected. See Figure 1-1. In use, changing pressures on the diaphragm
cause it to deflect, and this deflection is measured as a change in tension and frequency
of vibration of the vibrating wire element. The square of the vibration frequency is
directly proportional to the pressure applied to the diaphragm. Two coils, one with a
magnet, another with a pole piece, are located close to the wire. In use, a pulse of
varying frequency (swept frequency) is applied to the coils and this causes the wire to
vibrate primarily at its resonant frequency. When excitation ends the wire continues to
vibrate and a sinusoidal AC electrical signal, at the resonant frequency, is induced in the
coils and transmitted to the readout box where it is conditioned and displayed.
Filter
Filter Housing
O-rings
O-rings
Pressure Sensitive Diaphragm Pluck and Read Coils
Magnet
Pole Piece
Hermeticallysealed and evacuated space (unvented)
Piezometer Body
Wire Grip
Wire Grip Thermistor
Coil Wire
Coil Wire
Thermistor Wires
Internal Bulkhead Seal
Vibrating Wire
Cable
Plasma Surge Arrestor
Ground Connection
Piezometer Housing
O-ring
O-ring
Figure 1-1 Vibrating Wire Piezometer
To prevent damage to the sensitive diaphragm a filter is used to keep out solid particles.
Figure 1-1 illustrates. Standard filters are 50 micron stainless steel; high air entry value
tips are available on request.
All exposed components are made of corrosion resistant stainless steel and, if proper
installation techniques are used, the device should have an unlimited life. In salt water it
may be necessary to use special materials for the diaphragm and housing.
Portable readout units are available to provide the excitation, signal conditioning and
readout of the instrument. Datalogging systems are also available for remote
unattended data collection of multiple sensors. Contact Geokon for additional
information.
Calibration data are supplied with each piezometer for conversion of gage readings to
engineering units such as pressure or level. See Section 4.

2
2. INSTALLATION
(For Quick Installation Instructions see AppendixE)
2.1 Preliminary Tests
Upon receipt of the piezometer the zero reading should be checked and noted (see
Sections 3.1 to 3.3 for readout instructions). A thermistor is included inside the body of
the piezometer (Figure 1-1) for the measurement of temperature (see Section 3.4 for
instructions).
Calibration data are supplied with each gage and a zero reading, at a specific
temperature and barometric pressure, is included. Zero readings at the site should
coincide with the calibration zero readings within +/- 50 digits after barometric and
temperature corrections are made. The factory elevation is +580 ft. all stated
barometric readings represent absolute pressure uncorrected for height above sea
level. (Barometric pressure changes with elevation at a rate of ≈½ psi per 1,000 ft.) See
Figure 4, for a sample calibration sheet.
2.1.1 Establishing an Initial Zero Reading
Vibrating Wire Piezometers differ from other types of pressure sensors in that they
indicate a reading at zero pressure. Therefore it is imperative that an accurate initial
zero pressure reading be obtained for each piezometer as this reading will be
used in all subsequent data reduction.
There are different ways of doing this but the essential element in all methods is that
the piezometer be allowed to thermally stabilize in a constant temperature environment
while the pressure on the piezometer is barometric only. Because of the way the
piezometer is constructed it takes about 5 to 15 minutes for the temperature of all the
different elements to equalize.
It will be necessary to measure the barometric pressure only if the piezometer is un-
vented and if it will be installed in a location that is subject to barometric pressure
changes that require correction, such as in an open well. A piezometer sealed in place at
depth could be recording pressures in groundwater that is not hydraulically connected to
the atmosphere, and, for which, barometric pressure compensation would be
inappropriate.
The recommended way to achieve temperature stability is to hang the piezometer in
the borehole at a point just above the water and wait until the piezometer reading has
stopped changing. Now take the zero reading and read the temperature, indicated by the
thermistor inside the piezometer.
Another way is to place the piezometer under water in a bucket and allow 5 to 15
minutes for the temperature to stabilize, then lift the piezometer out of the water and
immediately take a reading. When doing this, lift the piezometer by the cable only, do not
handle the piezometer housing as body heat from the hand could cause temperature
transients. Use the thermistor inside the piezometer to measure the water temperature.
Another way is to simply read the piezometer while in the air while making sure that
the temperature has had time to stabilized. If this method is chosen be sure that the
piezometer is protected from sunlight or sudden changes of temperature: Wrapping it in
some insulating material is recommended.
Yet another way is to lower the piezometer to a known depth as marked out on the
piezometer cable, (The diaphragm inside the piezometer is located approximately ¾ inch
(15mm), from the tip. Then use a dip meter to accurately measure the depth to the water
surface. Now, after temperature stabilization, read the piezometer pressure and, using
the factory calibration constants and a knowledge of the pressure (height x density) of

3
the water column above the piezometer, calculate either the equivalent zero pressure
reading, if the linear regression is used, or the factor, C, if the second order polynomial is
used.
A question may arise as to what to do with the filter stone while taking zero readings.
If a standard stainless steel filter is being used, it will not matter if the filter stone is
saturated or not. But if ceramic high air entry filter stone is in use then it must be
saturated while taking the zero readings and must not be allowed to dry out to the extent
that surface tension effects can affect the zero reading.
Caution. – do not allow the piezometer to freeze once it has been filled with water.
2.1.2 Checking the Calibration
The following procedure is recommended to verify the calibration factor as supplied on
the calibration sheet (Figure 4 shows a typical calibration sheet.). It should be borne in
mind that the piezometer measures water pressure and that the conversion to a water
level requires an accurate knowledge of the density of the water.
1. The best method is to remove the filter housing and filter stone from off the tip of
the piezometer: Pulling on the knurled ring will accomplish this. Alternatively,
saturate the filter stone and fill the space between it and the diaphragm with water
(Section 2.6).
2. Lower the piezometer to a point near the bottom of a water-filled borehole, or below
the surface of a body of water. The use of a dip meter to measure the actual depth
of the water in the borehole will be very desirable.
3. Allow 15-20 minutes for the piezometer to come to thermal equilibrium. Using a
readout box record the reading at that level.
4. Raise the piezometer by known depth increments. Record the pressure reading at
each depth increment. Calculate the in-situ calibration factor and compare to the
calibration factor on the calibration sheet. The two values should agree within ±
0.5%. Repeat test if necessary.
There are a couple of things that can affect the in-situ calibration:
•The density of the in-situ water may not be 1gm/cc if it is saline or turbid. If this is
the case then the factory calibration factor, should be adjusted to take into
account the actual water density.
•The water level inside the borehole may vary during the test due to the
displacement of the water level as the cable is raised and lowered in the
borehole. This effect will be greater where the borehole diameter is smaller. For
example, a Model 4500S-50 piezometer lowered 50 feet below the water column
in a 1 inch (.875 inch ID) standpipe will displace the water level by more than 4
feet! If a dip-meter is available it should be used to confirm the water levels at
each depth increment.

4
2.2 Installation in Standpipes or Wells
•A zero reading is first established (follow the procedures outlined in Section
2.1.1). The filter stone is saturated (follow the procedures in Section 2.6). Make
a mark on the cable which will lie opposite the top of the standpipe, (well), when
the piezometer has reached the desired depth. (The piezo diaphragm lies ¾ inch
above the tip of the piezo).
Zero Reading
Well Cap Portable Readout
Piezometer
Water Level
Piezometer Cable
Ground Surface
Typical Installation
Well Cap Portable Readout
Piezometer
Water Level
Piezometer Cable
Ground Surface
Casing Bottom
Expected Change in Level
Casing Bottom
Figure 2-1 Typical Level Monitoring Installations
Be sure the cable is securely fastened at the top of the well or readings could be in error
due to slippage of the piezometer into the well.
It is not recommended that piezometers be installed in wells or standpipes where an
electrical pump and/or cable is present or nearby. Electrical interference from these
sources can cause unstable readings. If unavoidable, it is recommended that the
piezometer be placed inside a piece of steel pipe.
In situations where packers are used in standpipes the same sequence as above should
be noted and special care should be taken to avoid cutting the cable jacket with the
packer since this could introduce a possible pressure leakage path.
2.3 Installation in Boreholes
Geokon piezometers can be installed in boreholes in either single or multiple
installations per hole, in cased or uncased holes. See Figure 2-2. Careful attention
must be paid to borehole sealing techniques if pore pressures in a particular zone are to
be monitored.
Boreholes should be drilled either without drilling mud or with a material that degrades
rapidly with time, such as Revert. The hole should extend from 6 inches to 12 inches
below the proposed piezometer location and should be washed clean of drill cuttings.
The bottom of the borehole should then be backfilled with clean fine sand to a point 6
inches below the piezometer tip. The piezometer can then be lowered, as delivered,
into position. Preferably, the piezometer may be encapsulated in a canvas-cloth bag

5
containing clean, saturated sand and then lowered into position. While holding the
instrument in position (a mark on the cable is helpful) clean sand should be placed
around the piezometer and to a point 6 inches above it. Figure 2-2 details two methods
of isolating the zone to be monitored.
Installation A
Immediately above the "collection zone" the borehole should be sealed with either
alternating layers of bentonite and sand backfill tamped in place for approximately 1 foot
followed by common backfill or by an impermeable bentonite-cement grout mix. If
multiple piezometers are to be used in a single hole the bentonite-sand plugs should be
tamped in place below and above the upper piezometers and also at intervals between
the piezometer zones. When designing and using tamping tools special care should be
taken to ensure that the piezometer cable jackets are not cut during installation.
Installation B
Immediately above the "collection zone" the borehole should be filled with an
impermeable bentonite grout.
Installation A
Piezometer
Bentonite Cement Grout
Filter Sand
Piezometer Cable Portable Readout
Ground Surface
Installation B
Piezometer
Bentonite Grout
Filter Sand
Piezometer Cable Portable Readout
Ground Surface
Bentonite
Bentonite
Sand
Collection Zone Collection Zone
Figure 2-2 Typical Borehole Installations
Installation C
It should be noted that since the vibrating wire piezometer is basically a no-flow
instrument, collection zones of appreciable size are not required and the piezometer
can, in fact, be placed directly in contact with most materials provided that the fines are
not able to migrate through the filter. The latest thinking, (Mikkelson and Green,Piezometers in
Fully Grouted Boreholes.Proceedings of FMGM 2003, Field Measurements in Geomechanics, Oslo,
Norway, Sept. 2003. Contact Geokon for a copy o f this paper), is that it is not necessary to provide
sand zones and that the piezometer can be grouted directly into the borehole using a
bentonite cement grout only. However, good results have been obtained by first placing
the piezometer inside a canvas bag before grouting.

6
The general rule for installing piezometers in this way is to use a bentonite grout that
mimics the strength of the surrounding soil. The emphasis should be on controlling the
water-cement ratio. This is accomplished by mixing the cement with the water first.
The most effective way of mixing is in a 50 to 200 gallon barrel or tub using the drill-rig
pump to circulate the mix. Any kind of bentonite powder used to make drilling mud,
combined with Type 1 or 2 Portland cement can be used. The exact amount of bentonite
added will vary somewhat. The table below shows two possible mixes for strengths of 50
psi and 4 psi.
Add the measured amount of clean water to the barrel then gradually add the cement in
the correct weight ratio. Next add the bentonite powder, slowly, so clumps do not form.
Keep adding bentonite until the watery mix turns to an oily/slimy consistency. Let the
grout thicken for another five to ten minutes. Add more bentonite as required until it is a
smooth thick cream like pancake batter. It is now as heavy as it is feasible to pump.
When pumping grout, unless the tremie-pipe is to be left in place, withdraw the tremie-
pipe after each batch, by an amount corresponding to the grout level in the borehole.
Caution: if the grout is pumped into the hole, rather than tremied, there is a danger that
the piezometer will be over-ranged and damaged., So pumping direct into the bottom of
the borehole should be avoided. It is good practice to read the piezometer while
pumping.
Application Grout for Medium to Hard
Soils
Grout for Soft Soils
Materials
Weight
Ratio by
Weight
Weight
Ratio by Weight
Water
30 gallons
2.5
75 gallons
6.6
Portland
Cement
94 lbs
(1 sack)
1
94 lbs
(1 sack)
1
Bentonite
25 lbs
(as required)
0.3
39 lbs
(as required)
0.4
Notes
The 28 day compressive
strength of this mix is about 50
psi, similar to very stiff to hard
clay. The modulus is about
10,000 psi
The 28 day strength of this mix is
about 4psi, similar to very soft
clay.
Table 1 showing Cement/Bentonite/Water ratios for two grout mixes.
(For more details on this method of installation ask for a copy of the FMGM paper)
2.4 Installation in Fills and Embankments
Geokon piezometers are normally supplied with direct burial cable suitable for placement
in fills such as highway embankments and dams, both in the core and in the surrounding
materials.
In installations in non-cohesive fill materials the piezometer may be placed directly in the
fill or, if large aggregate sizes are present, in a saturated sand pocket in the fill. If
installed in large aggregate, additional measures may be necessary to protect the cable
from damage.

7
In fills such as impervious dam cores where sub-atmospheric pore water pressure may
need to be measured (as opposed to the pore air pressure) a ceramic tip with a high air
entry value is often used which should be carefully placed in direct contact with the
compacted fill material (see Installation A of Figure 2-3). In partially saturated fills if only
the pore air pressure is to be measured, the standard tip is satisfactory. It should be
noted that the coarse tip measures the air pressure when there is a difference between
the pore air pressure and the pore water pressure, and that the difference between the
two pressures is due to the capillary suction in the soil. The general consensus is that
the difference is normally of no consequence to embankment stability. As a general rule
the coarse (low air entry) tip is suitable for most routine measurements and, in fine
cohesive soils, sand pockets should not be used around the piezometer tip (see
Installation B of Figure 2-3). In high traffic areas and in material which exhibit
pronounced "weaving", a heavy-duty armored cable should be used.
Cables are normally installed inside shallow trenches with the fill material consisting of
smaller size aggregate. This fill is carefully hand compacted around the cable.
Bentonite plugs are placed at regular intervals to prevent migration of water along the
cable path.
Installation A
Fill Layer
Fill Layer
Fill Layer
Heavy Duty Piezometer
Filter in direct contact with fill
(high air entry)
Heavy Duty Cable
(in trench)
Pocket excavated in compacted fill
Fill material compacted by hand
Installation B
Fill Layer
Fill Layer
Fill Layer
Heavy Duty Piezometer
Filter in direct contact with sand
(low air entry)
Heavy Duty Cable
(in trench)
Pocket excavated in compacted fill
Sand compacted byhand
Figure 2-3 Typical Dam Installations
2.5 Installation by Pushing or Driving into Soft Soils
The Model 4500DP piezometer is designed for pushing into soft soils. See Figure 2-4.
The unit is connected directly to the drill rod (AW, EW or other) and pressed into the
ground either by hand or by means of the hydraulics on the rig. The units can also be
driven but the possibility of a zero shift due to the driving forces exists.
The piezometer should be connected to the readout box and monitored during the
driving process. If measurement pressures reach or exceed the calibrated range, the
driving should be stopped and the pressures allowed to dissipate before continuing.

8
Drill Rod
(AW, EW or other)
Soft Soils
Piezometer
Piezometer pushed through soft soils to final location
Reaction Wings
(if required)
Piezometer Cable
Casing Advanced Borehole
5' above final location
Left/Right Adaptor
EW Rod Adaptor
EW Rod
Augered or
Filter Housing
Figure 2-4 Typical Soft Soils Installation
The drill rod can be left in place or it can be removed. If it is to be removed then a
special 5 foot section of EW (or AW) rod with wings and a left hand thread are attached
directly to the piezometer tip. This section is detached from the rest of the drill string by
rotating the string clockwise. The left hand thread will then loosen. The wings prevent
the special EW rod from turning. A special LH/RH adapter is available from Geokon.
The adapter is retrieved along with the drill string.
2.6 De-airing Filter Tips
Caution. – do not allow the piezometer to freeze once it has been filled with water.
Most Geokon filter tips can be removed for saturating and re-assembly. The procedures
are as follows:
2.6.1 Low Air Entry Filter, Model 4500S and 4500PN
For accurate results, total saturation of the filter is necessary. For the low air entry filter
normally supplied, this saturation occurs as the tip is lowered into the water. Water is
forced into the filter, compressing the air in the space between the filter stone and the
pressure sensitive diaphragm. After a period of time, this air will dissolve into the water
until the space and the filter is entirely filled with water. To speed up the saturation
process, remove the filter assembly and fill the space above the diaphragm with water,
then slowly replace the filter housing allowing the water to squeeze through the filter
stone. With low pressure range piezometers (<10 psi) take readings with a readout box
while pushing the filter housing on so as not to over-range the sensor.

9
To maintain saturation, the unit should be kept under water until installation.
If the 4500S piezometer is to be used in standpipes and raised and lowered many times
the filter may loosen. A permanent filter assembly may be required. The removable
filter may be fixed permanently by prick punching the piezometer tube approximately
1/16" to 1/8" behind the filter assembly joint.
Screens are also available for standpipe installations. Screens are less likely than
standard filters to become clogged where salts in the water can be deposited if the filter
is allowed to dry out completely.
2.6.2 Removable Ceramic Filter, Model 4500S
The ceramic filter on the 4500S piezometer is also removable for de-airing. Because of
the high air entry characteristics, de-airing is particularly important for this filter
assembly. Filters with different air entry values require different procedures.
1 Bar Filters
1. Remove the filter from the piezometer by carefully twisting and pulling on the
filter housing assembly.
2. Boil the filter assembly in de-aired water.
3. Re-assemble the filter housing and piezometer under the surface of a container
of de-aired water. Be sure that no air is trapped in the transducer cavity. While
pushing the filter on use a readout box to monitor the diaphragm pressure. Allow
over-range pressure to dissipate before pushing further.
4. To maintain saturation, the unit should remain immersed until installation.
2 Bar and Higher
The proper procedure for de-airing and saturating these filters is somewhat complex and
should be done either at the factory by Geokon or by carefully following the instructions
below:
1. Place the assembled piezometer, filter down, in a vacuum chamber with an inlet
port at the bottom for de-aired water.
2. Close off the water inlet and evacuate the chamber. The transducer should be
monitored while the chamber is being evacuated.
3. When the maximum vacuum has been achieved, allow de-aired water to enter
the chamber and reach an elevation a few inches above the piezometer filter.
4. Close off the inlet port. Release the vacuum.
5. Observe the transducer output. It will take as long as 24 hours for the filter to
completely saturate (5 bar) and the pressure to rise to zero.
6. After saturation the transducer should be kept in a container of de-aired water
until installation. If de-aired at the factory a special cap is applied to the
piezometer to maintain saturation.

10
2.6.3 Model 4500DP
The 4500 Drive Point is de-aired in the same way as the above models by first
unscrewing the point of the piezometer assembly and then following the instruction for
the 4500S.
2.7 Model 4500H Transducer
When connecting the Model 4500H transducer to external fittings, the fitting should be
tightened into the ¼"-NPT thread with a wrench on the flats provided on the transducer
housing. Also, avoid tightening onto a closed system since the process of tightening the
fittings could over-range and permanently damage the transducer. If in doubt, attach the
gage leads to the readout box and take readings while tightening. Teflon tape on the
threads makes for easier and more positive connection to the transducer.
CAUTION: All high pressure sensors are potentially dangerous and care must be
taken not to over-range them beyond their calibrated range. Sensors are tested to
150% of the range to provide a factor of safety.
2.8 Splicing and Junction Boxes
Because the vibrating wire output signal is a frequency rather than current or voltage,
variations in cable resistance have little effect on gage readings and, therefore, splicing
of cables has no effect either and, in some cases, may be beneficial. For example, if
multiple piezometers are installed in a borehole, and the distance from the borehole to
the terminal box or datalogger is great, a splice (or junction box, see Figure 2-6) could
be made to connect the individual cables to a single multi-conductor cable. This multi-
conductor cable would then be run to the readout station. For such installations it is
recommended that the piezometer be supplied with enough cable to reach the
installation depth plus extra cable to pass through drilling equipment (rods, casing, etc.).
The cable used for making splices should be a high quality twisted pair type with 100%
shielding (with integral shield drain wire). When splicing, it is very important that the
shield drain wires be spliced together! Splice kits recommended by Geokon incorporate
casts placed around the splice 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.
Junction boxes and terminal boxes are available from Geokon for all types of
applications. In addition, portable readout equipment and datalogging hardware are
available. See Figure 2-5. Contact Geokon for specific application information.

11
AC Adaptor
RF Antenna
AC Power
Grounding Stakes
Ground Connections
Portable Readout
Portable Computer
Multiconductor Cable
Piezometer Cables
Datalogger (with internal battery)
Junction Box or Splice
RS-232 Connection
Terminal/Multiplexer BoxManual Switch
Datalogger/Multiplexer Interconnect Cable
Phone Line
Piezometers
Solar Panel
Equipment Shed
Ground
Connection
Figure 2-5 Typical Multi-Piezometer Installation
.
2.9 Lightning Protection
In exposed locations it is vital that the piezometer be protected against lightning strikes.
A tripolar plasma surge arrestor (Figure 1-1) is built into the body of the piezometer and
protects against voltage spikes across the input leads. Following are additional lightning
protection measures available;
1. If the instruments will be read manually with a portable readout (no terminal box) a
simple way to help protect against lightning damage is to connect the cable leads to
a good earth ground when not in use. This will help shunt transients induced in the
cable to ground thereby protecting the instrument.
2. Terminal boxes available from Geokon can be ordered with lightning protection built
in. There are two levels of protection;
•The terminal board used to make the gage connections has provision for
installation of plasma surge arrestors (similar to the device inside the
piezometer).
•Lightning Arrestor Boards (LAB-3) can be incorporated into the terminal box.
These units utilize surge arrestors and transzorbs to further protect the
piezometer.
In the above cases the terminal box would be connected to an earth ground.

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3. Improved protection using the LAB-3 can be had by placing the board in line with the
cable as close as possible to the installed piezometer (see Figure 2-6). This is the
recommended method of lightning protection.
Piezometer
Piezometer Cable
To Terminal Box/Readout Equipment
Lightning Arrestor Board (LAB-3)
(in special enclosure
Ground Stake
Ground Connection
accessible from surface)
Figure 2-6 Recommended Lightning Protection Scheme
3. TAKING READINGS
3.1 Operation of the GK-403 Readout Box
The GK-403 can store gage readings and also apply calibration factors to convert
readings to engineering units. Consult the GK-403 Instruction Manual for additional
information on Mode "G" of the Readout. The following instructions will explain taking
gage measurements using Modes "B" and "F" (similar to the GK-401 switch positions "B"
and "F").
Connect the Readout using the flying leads or in the case of a terminal station, with a
connector. The red and black clips are for the vibrating wire gage, the white and green
leads are for the thermistor and the blue for the shield drain wire.
1. Turn the display selector to position "B" (or "F"). Readout is in digits (Equation 4-1).
2. Turn the unit on and a reading will appear in the front display window. The last digit
may change one or two digits while reading. 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 thermistor will be read and output directly in
degrees centigrade.
3. The unit will automatically turn itself off after approximately 2 minutes to conserve
power.

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3.2 Operation of the GK-404 Readout Box
The GK404 is a palm sized readout box which displays the Vibrating wire value and the
temperature in degrees centigrade.
The GK-404 Vibrating Wire Readout arrives with a patch cord for connecting to the
vibrating wire gages. One end will consist of a 5-pin plug for connecting to the
respective socket on the bottom of the GK-404 enclosure. The other end will consist of
5 leads terminated with alligator clips. Note the colors of the alligator clips are red,
black, green, white and blue. The colors represent the positive vibrating wire gage lead
(red), negative vibrating wire gage lead (black), positive thermistor lead (green), negative
thermistor lead (white) and transducer cable drain wire (blue). The clips should be
connected to their respectively colored leads from the vibrating wire gage cable.
Use the POS (Position) button to select position Band the MODE button to select Dg
(digits).
Other functions can be selected as described in the GK404 Manual.
The GK-404 will continue to take measurements and display the readings until the OFF
button is pushed, or if enabled, when the automatic Power-Off timer shuts the GK-404
off.
The GK-404 continuously monitors the status of the (2) 1.5V AA cells, and when their
combined voltage drops to 2V, the message Batteries Low is displayed on the screen.
A fresh set of 1.5V AA batteries should be installed at this point
3.3 Operation of the 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
•the GK-405 Remote Module which is housed in a weather-proof enclosure and
connects to the vibrating wire sensor by means of:
1) Flying leads with alligator type clips when the sensor cable terminates in bare wires
or,
2) by means of a 10 pin connector..
The two components communicate wirelessly using Bluetooth®, a reliable digital
communications protocol. The Readout Unit can operate from the cradle of the Remote
Module (see Figure 3.1) or, if more convenient, can be removed and operated up to 20
meters from the Remote Module

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Figure 3.1 GK405 Readout Unit
For further details consult the GK405 Instruction Manual.
3.4 Measuring Temperatures
Each vibrating wire piezometer is equipped with a thermistor for reading temperature.
The thermistor gives a varying resistance output as the temperature changes. Usually
the white and green leads are connected to the internal thermistor. High temperature
versions use a different thermistor than the standard versions.
The GK-403, GK404 and GK 405 readout boxes when used with the standard
temperature thermistor will display the temperature in °C automatically. They will not do
this with high temperature thermistors. The GK 401 readout box will not read
temperatures directly, instead an ohmmeter must be used.
1. Connect the ohmmeter to the two thermistor leads coming from the piezometer.
(Since the resistance changes with temperature are so large, the effect of cable
resistance is usually insignificant. For long cables a correction can be applied –
equal to 16 ohms per thousand feet.)
2. For standard temperature models, look up the temperature for the measured
resistance in Table B-1.Page 21Alternately the temperature could be calculated
using Equation B-1. For high temperature models use Table C1 or the equation C1
given on page 22.
4. DATA REDUCTION
4.1 Pressure Calculation
The digits displayed by the Geokon Models GK-403, GK-404 or GK-405 Readout Boxes
on channel B are based on the equation
Digits Period =



×
−
23
110
or
Digits Hz =
2
1000
Equation 4-1 Digits Calculation