Geokon 4500S User manual

Instruction Manual
Model 4500 series
Vibrating Wire Piezometer
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 © 2003-2017 by Geokon, Inc.
(REV CC, 2/2/2017)

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. QUICK START INSTRUCTIONS......................................................................................... 2
3. PRIOR TO INSTALLATION................................................................................................. 2
3.1 SATURATING FILTER TIPS....................................................................................................... 2
3.1.1 Piezometers with low air entry (standard) filter housings.............................................. 2
3.1.2 Model 4500S equipped with option High Air Entry Ceramic Filter............................... 3
3.1.3 Model 4500C................................................................................................................... 4
3.2 ESTABLISHING AN INITIAL ZERO READING............................................................................. 5
3.2.1 Recommended method: ................................................................................................... 6
3.2.2 Alternative method 1:...................................................................................................... 6
3.2.3 Alternative method 2:...................................................................................................... 6
3.2.4 Alternative method 3:...................................................................................................... 6
3.3 CHECKING THE PIEZOMETER PERFORMANCE.......................................................................... 7
4. INSTALLATION...................................................................................................................... 8
4.1 INSTALLATION IN STANDPIPES OR WELLS............................................................................... 8
4.2 INSTALLATION IN BOREHOLES................................................................................................ 9
4.3 INSTALLATION IN FILLS AND EMBANKMENTS....................................................................... 12
4.4 INSTALLATION BY PUSHING OR DRIVING INTO SOFT SOILS................................................... 14
4.5 MODEL 4500H AND MODEL 4500HH TRANSDUCER ............................................................ 15
4.6 SPLICING AND JUNCTION BOXES........................................................................................... 16
4.7 LIGHTNING PROTECTION....................................................................................................... 17
5. TAKING READINGS............................................................................................................ 18
5.1 GK-404 READOUT BOX........................................................................................................ 18
5.1.1 Operating the GK-404................................................................................................... 18
5.2 GK-405 READOUT BOX........................................................................................................ 19
5.2.1 Connecting Sensors....................................................................................................... 19
5.2.2 Operating the GK-405................................................................................................... 19
5.3 GK-403 READOUT BOX (OBSOLETE MODEL)....................................................................... 20
5.3.1 Connecting Sensors....................................................................................................... 20
5.3.2 Operating the GK-403................................................................................................... 20
5.4 MEASURING TEMPERATURES................................................................................................ 21
6. DATA REDUCTION.............................................................................................................. 22
6.1 PRESSURE CALCULATION ..................................................................................................... 22
6.2 TEMPERATURE CORRECTION ................................................................................................ 24
6.3 BAROMETRIC CORRECTION (REQUIRED ONLY ON UNVENTED TRANSDUCERS) ...................... 25
6.4 VENTED PIEZOMETERS ......................................................................................................... 26
6.5 ENVIRONMENTAL FACTORS.................................................................................................. 26


7. TROUBLESHOOTING......................................................................................................... 27
APPENDIX A. - SPECIFICATIONS........................................................................................ 29
A.1 STANDARD PIEZOMETER WIRING ........................................................................................ 29
APPENDIX B. - THERMISTOR TEMPERATURE DERIVATION................................... 30
APPENDIX C. HIGH TEMPERATURE THERMISTOR LINEARIZATION................... 31
APPENDIX D. IMPROVING THE ACCURACY OF THE CALCULATED PRESSURE32
APPENDIX E. - MODEL 4500AR PIEZOMETER................................................................ 32

FIGURES
FIGURE 1-MODEL 4500S VIBRATING WIRE PIEZOMETER .............................................................. 1
FIGURE 2-4500C SATURATION....................................................................................................... 4
FIGURE 3-TYPICAL LEVEL MONITORING INSTALLATION................................................................ 8
FIGURE 4-TYPICAL BOREHOLE INSTALLATIONS........................................................................... 10
FIGURE 5-HIGH AIR ENTRY FILTER.............................................................................................. 12
FIGURE 6-LOW AIR ENTRY FILTERS ONLY................................................................................. 13
FIGURE 7-TYPICAL SOFT SOILS INSTALLATION............................................................................ 14
FIGURE 8-TYPICAL MULTI-PIEZOMETER INSTALLATION.............................................................. 16
FIGURE 9-RECOMMENDED LIGHTNING PROTECTION SCHEME...................................................... 17
FIGURE 10 -LEMO CONNECTOR TO GK-404.................................................................................. 18
FIGURE 11 -LIVE READINGS –RAW READINGS............................................................................. 19
FIGURE 12 -TYPICAL CALIBRATION REPORT................................................................................. 23
FIGURE 13 -4500AR ..................................................................................................................... 33
TABLES
TABLE 1-CEMENT/BENTONITE/WATER RATIOS............................................................................ 11
TABLE 2-ENGINEERING UNITS MULTIPLICATION FACTORS.......................................................... 23
TABLE 3-SAMPLE RESISTANCE..................................................................................................... 27
TABLE 4-RESISTANCE WORK SHEET............................................................................................ 27
TABLE 5-VIBRATING WIRE PIEZOMETER SPECIFICATIONS........................................................... 29
TABLE 6-STANDARD PIEZOMETER WIRING.................................................................................. 29
TABLE 7-THERMISTOR RESISTANCE VERSUS TEMPERATURE........................................................ 30
TABLE 8- THERMISTOR RESISTANCE VERSUS TEMPERATURE FOR HIGH TEMPERATURE MODELS . 31
EQUATIONS
EQUATION 1-DIGITS CALCULATION ............................................................................................. 22
EQUATION 2-CONVERT DIGITS TO PRESSURE............................................................................... 22
EQUATION 3-TEMPERATURE CORRECTION................................................................................... 24
EQUATION 4-BAROMETRIC CORRECTION..................................................................................... 25
EQUATION 5-CORRECTED PRESSURE CALCULATION.................................................................... 25
EQUATION 6-RESISTANCE TO TEMPERATURE............................................................................... 30
EQUATION 7-HIGH TEMPERATURE RESISTANCE TO TEMPERATURE ............................................. 31

1
1. THEORY OF OPERATION
Geokon model 4500 Vibrating Wire Piezometers are intended primarily for long-term
measurements of fluid depths, and pore pressures in standpipes, boreholes, embankments,
pipelines, and pressure vessels. Several different models are available to suit a variety of
Geotechnical applications. Calibration data is supplied with each piezometer.
All Geokon vibrating wire piezometers utilize a sensitive stainless steel diaphragm (with the
exception of model 4500C, which employs bellows) to which a vibrating wire element is
connected. During use, changing pressures on the diaphragm cause it to deflect. 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. A filter is used to keep out solid particles and prevent damage to the sensitive
diaphragm. Standard filters are 50 micron stainless steel. High air entry value filters are available
upon request.
Two coils, one with a magnet insert, the other with a pole piece insert, are installed near the
vibrating wire. In use, a pulse of varying frequency (swept frequency) is applied to these coils,
causing the wire to vibrate primarily at its resonant frequency. When the excitation ends, the
wire continues to vibrate. During vibration a sinusoidal signal is induced in the coils and
transmitted to the readout box where it is conditioned and displayed.
Figure 1 - Model 4500S Vibrating Wire Piezometer
All exposed components are made of corrosion resistant stainless steel. 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. The
4500TI series piezometers are constructed from titanium and are specifically designed to be used
in this type of environment.
Portable readout units are available to provide the excitation, signal conditioning, and readout of
the instrument. See Section 5 for instructions on using Geokon readouts with vibrating wire
piezometers. Datalogger systems which allow remote, unattended data collection of multiple
sensors are also available. Contact Geokon for additional information.

2
2. QUICK START INSTRUCTIONS
For those familiar with Geotechnical instrumentation and its installation, the following quick
start instructions may be used. For more detailed instructions see Sections 3 and 4.
1) Prior to installation, allow the piezometer to come to thermal equilibrium with the ambient
temperature for a minimum of 15 minutes. (Alternatively, if the instrument is attached to a
readout box, wait until the piezometer reading has stabilized.)
2) Take an initial zero reading at zero (atmospheric) pressure.
3) Verify that the initial zero reading is compatible with the factory supplied zero reading on the
calibration sheet.
4) Record the barometric pressure and the temperature.
5) Carefully measure and mark the cable where it will lie at the top of the borehole, well, or
standpipe, once the piezometer has reached the desired depth. (The piezo diaphragm lies 3/4
of an inch above the tip of the piezometer.)
6) Saturate the piezometer filter. (See Section 3.1)
7) For installation in standpipes or wells see Section 4.1, for boreholes Section 4.2, and for fills
and embankments Section 4.3.
3. PRIOR TO INSTALLATION
3.1 Saturating 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 saturation and then reassembled. To maintain
saturation, the unit should be kept underwater until installation. (IMPORTANT: The filter stone
and housing of model 4500C piezometers are not removable. Any attempt to remove the filter
stone or the housing will destroy the transducer!)
The saturation procedures are as follows:
3.1.1 Piezometers with low air entry (standard) filter housings
For accurate results, total saturation of the filter is necessary. For low air entry filters no
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, filling the filter
and the space above it entirely with water.
To speed up the saturation process, remove the filter from the piezometer by carefully
twisting and pulling on the filter housing assembly (or unscrewing the point of the
piezometer for model 4500DP). Holding the piezometer so the filter is facing up, fill the
space above the diaphragm with water. Next, slowly replace the filter housing, allowing
the water to squeeze through the filter stone as it is installed. For piezometers with a
range of less than 10 psi, take readings with a readout box while reinstalling the filter
housing to ensure the piezometer is not overranged.

3
If the piezometer is used in a standpipe where it is raised and lowered frequently, the
filter housing may loosen over time, and 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.
Filter stones may be replaced with screens for standpipe installations. Salts in the water
can be deposited into the filter causing it to become clogged if it is allowed to dry out
completely. Screens available from Geokon are less likely than standard filters to collect
salt and become clogged.
3.1.2 Model 4500S equipped with option High Air Entry Ceramic Filter
Because of the high air entry characteristics of the ceramic filter, de-airing is particularly
important. Different air entry values require different saturation procedures.
One 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) Reassemble the filter housing and piezometer under the surface of a container of de-
aired water. While installing the filter, use a readout box to monitor the diaphragm
pressure. If the piezometer begins to overrange, allow the pressure to dissipate before
pushing further. Be sure that no air is trapped in the transducer cavity.
Two Bar and Higher:
The proper procedure for de-airing and saturating these filters is somewhat complex, it is
recommended that saturation be done at the factory by Geokon. If saturation must be
done in the field, carefully follow the instructions below:
1) Place the assembled piezometer, filter down, in a vacuum chamber which has 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 maximum vacuum has been achieved, allow de-aired water to enter the
chamber until it reaches an elevation a few inches above the piezometer filter.
4) Close off the inlet port.
5) Release the vacuum.
6) Observe the transducer output. It may take up to 24 hours for the filter to completely
saturate and the pressure to rise to zero.
7) 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.

4
3.1.3 Model 4500C
The filter housing is not removable on the 4500C. Any attempt to remove the filter
stone or the housing will destroy the transducer!
If the pressure to be measured is less than 5 psi the filter stone must be saturated. A hand
operated vacuum pump and short length of 1/2" surgical tubing is required. Hand pumps
and tubing are available from the factory. (A hand pump that has been used successfully
is the MityvacII®by Lincoln Industries Corp. of St. Louis, MO.)
The saturation procedure is as follows:
1) Attach the tube to the transducer as shown in Figure 2.
2) Fill the tubing with approximately 2" (5 cm) of water.
3) Attach the other end of the tube to the hand vacuum pump.
4) While holding the transducer so that the water rests on the filter but does not enter the
pump, squeeze the hand pump to initiate a vacuum inside the tubing. This will draw
the air out of the filter and the area behind it, replacing it with water.
5) A vacuum of 20-25" Hg. (50-65 cm Hg.) is sufficient for proper air evacuation.
Figure 2 - 4500C Saturation