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
GK-405 READOUT BOX ........................................................................................................ 19
5.2
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
TEMPERATURE CORRECTION ................................................................................................ 24
6.2
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 PRESSURE 32
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. 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.
1
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.
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.
3
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
5
3.2 Establishing an Initial Zero Reading
Vibrating Wire Piezometers differ from other types of pressure sensors in that they indicate a
reading when no pressure is exerted on the sensor. It is imperative that an accurate initial zero
reading be obtained for each piezometer, as this reading will be used for all subsequent
data reduction.
Generally, the initial zero reading is obtained by reading the instrument prior to installation.
There are several different ways of taking an initial zero reading. The essential element in all
methods is that the piezometer needs 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 usually takes 15 to 20 minutes for the temperature of all the
different elements to equalize.
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.
However, if the piezometer is equipped with a ceramic high air entry filter stone, then it must be
saturated while taking the zero readings.
It will be necessary to measure the barometric pressure only if the piezometer is unvented, and it
will be installed in a location that is subject to barometric pressure changes which 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, for which
barometric pressure compensation would be inappropriate. See Section 6.3 for more information
on Barometric corrections.
Calibration data is supplied with each gage, a factory zero reading taken at a specific temperature
and absolute barometric pressure is included. (See Figure 12 in Section 6 for a sample calibration
sheet.) Zero readings at the site should coincide with the factory readings within 50 digits, after
barometric and temperature corrections are made. Barometric pressures change with elevation at
a rate of approximately 3.45kPa (½ psi) per 300meters (1,000 ft.) The factory elevation is +580
feet. All stated barometric readings represent absolute pressure uncorrected for height above sea
level. A thermistor is included inside the body of the piezometer for the measurement of
temperature.
NOTE REGARDING THE 4500C: The construction of this very slender vibrating wire
transducer requires a miniaturization of the internal parts, which consequently are somewhat
delicate. Handle the transducer with care during the installation procedure. Despite taking
every precaution to ensure that the transducer arrives unharmed, it is possible for the zero to shift
during shipment due to rough handling. However, tests have shown that though the zero may
shift, the calibration factors do not change. Therefore it is doubly important that an initial no load
zero reading be taken prior to installation.
6
3.2.1 Recommended method:
1) Saturate the filter stone per Section 3.1
Caution: Do not allow the piezometer to freeze once it has been filled with water.
2) Replace the filter stone.
3) Hang the piezometer in the borehole at a point just above the water.
4) Wait until the piezometer reading has stopped changing.
5) Take the zero and temperature readings.
3.2.2 Alternative method 1:
1) Place the piezometer under water in a bucket.
2) Allow 15 to 20 minutes for the temperature of the unit to stabilize.
3) Lift the piezometer out of the water by the cable only; do not handle the piezometer
housing as body heat from the hand could cause temperature transients.
4) Immediately take a zero and temperature reading.
3.2.3 Alternative method 2:
1) Allow 15 to 20 minutes for the temperature of the unit to stabilize.
2) Lift the piezometer into the air by the cable only; do not handle the piezometer
housing as body heat from the hand could cause temperature transients.
3) Take a zero and temperature reading.
(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.)
3.2.4 Alternative method 3:
1) Lower the piezometer to a known depth marked on the piezometer cable. (The
diaphragm inside the piezometer is located approximately 3/4” (15mm), from the tip.)
2) Use a dip meter to accurately measure the depth to the water surface.
3) After temperature stabilization, read the piezometer pressure.
4) Using the factory calibration constants and a knowledge of the pressure of the water
column above the piezometer (height times density), calculate the equivalent zero
pressure reading if linear regression is used, or the factor C if the second order
polynomial is used.
3.3 Checking the Piezometer Performance
If a rough check of the piezometer performance is needed, the following procedure is
recommended:
1) Lower the piezometer to a point near the bottom of a water filled borehole, or below the
surface of a body of water.
2) Allow 15-20 minutes for the piezometer to come to thermal equilibrium.
3) Using a readout box, record the reading at the current depth.
4) Raise the piezometer by a measured increment.
5) Record the reading on the readout box at the new depth.
6) Using the factory calibration factor, calculate the change in water depth.
7) Compare the calculated change in depth with the measured depth increment. The two values
should be roughly the same.
Alternative Method using a dip meter:
1) Lower the piezometer tip to a measured depth below the water surface.
2) Allow 15-20 minutes for the piezometer to come to thermal equilibrium.
3) Using a readout box, record the reading at that level.
4) Calculate the elevation of the water surface using the given calibration factor.
5) Compare the calculated elevation to the elevation measured using the dip meter.
There are a couple of things that can affect this checking procedure:
If the density of the water is not 1gm/cc.
If the water is saline or turbid.
The water level inside the borehole may vary during the test. This is due to the
displacement of water caused by the cable as it is raised and lowered in the borehole. The
smaller the borehole is, the greater the displacement will be. For example, a 4500S-50kPa
piezometer lowered 50 feet below the water column in a one inch (.875 inch ID)
standpipe will displace the water level by more than four feet.
7
8
4. INSTALLATION
4.1 Installation in Standpipes or Wells
1) Saturate the filter stone and establish an initial zero reading by following the steps outlined in
Section 3.1 and Section 3.2
2) Mark the cable where the top of the well or standpipe will reside once the piezometer has
reached the desired depth. (The piezometer diaphragm lies 3/4 of an inch above the tip of the
piezometer.)
3) Lower the piezometer into the standpipe/well.
4) Be sure the cable is securely fastened to prevent the piezometer from sliding further into the
well and causing an error in the readings.
Figure 3 - Typical Level Monitoring Installation
It is not recommended that piezometers be installed in wells or standpipes where an electrical
pump or cable is 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, special care should be taken to avoid cutting
the cable jacket with the packer, as this could introduce a possible pressure leak in the cable.
4.2 Installation in Boreholes
Geokon piezometers can be installed in cased or uncased boreholes, in either single or multiple
piezometer configurations. If pore pressures in a particular zone are to be monitored, careful
attention must be paid to the borehole sealing technique. Two methods of isolating the zone to be
monitored are detailed below.
Boreholes should be drilled without using drilling mud, or with a material that degrades rapidly
with time, such as Revert. The hole should extend six to twelve inches below the proposed
piezometer location, and should be washed clean of drill cuttings. The bottom of the borehole is
then backfilled with clean fine sand up to a point six inches below the desired piezometer tip
location. The piezometer can then be lowered into position. (Preferably, the piezometer will be
encapsulated in a canvas bag containing clean, saturated sand.) While holding the instrument in
position, (a mark on the cable is helpful) fill the borehole with clean fine sand to a point six
inches above the piezometer. Continue by following the instructions for Installations A, B, or C
as detailed below.
Installation A:
Immediately above the area filled with clean fine sand, known as the "collection zone", the
borehole should be sealed by an impermeable bentonite-cement grout mix, or with alternating
layers of bentonite and sand backfill, tamped in place for approximately one foot, followed by
common backfill. (See Figure 4.)
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, as well as at interval between the
piezometer zones. When using tamping tools special care should be taken to ensure that the
piezometer cable jackets are not cut during installation, as this could introduce a possible
pressure leak in the cable.
Installation B:
The borehole is filled from the “collection zone” upwards with an impermeable bentonite grout.
(See Figure 4.)
9
10
Figure 4 - 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. The piezometer can be placed directly in
contact with most materials, provided that the fines are not able to migrate through the filter. The
latest thinking 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 placing the piezometer inside a canvas bag filled with sand before
grouting.
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 to cement
ratio. This is accomplished by mixing the cement with the water first. The most effective way of
mixing the two substances is to use a drill rig pump to circulate the mix in a 50 to 200 gallon
barrel or tub.
Any kind of bentonite powder, combined with Type 1 or Type 2 Portland cement can be used to
make drilling mud. The exact amount of bentonite needed will vary somewhat. Table 1 shows
two possible mixes for strengths of 50 psi and 4 psi.
11
Amount
Water
Portland
Cement
Bentonite
NOTES:
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 tremie piped, there is a danger that
the piezometer will be overranged and damaged. Pumping directly into the bottom of the
borehole should be avoided. It is good practice to read the piezometer while pumping.
For more details on grouting, refer to “Piezometers in Fully Grouted Boreholes” by Mikkelson
and Green, FMGM proceedings Oslo 2003. Copies are available from Geokon.
50 PSI Grout for Medium
4 PSI Grout for Soft Soils
to Hard Soils
30 gallons 2.5 75 gallons 6.6
94 lbs. (one sack) 1 94 lbs. (one sack) 1
25 lbs. (as required) 0.3 39 lbs. (as required) 0.4
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
Table 1 - Cement/Bentonite/Water ratios
Ratio by
Weight
Amount
The 28 day strength of this
mix is about 4psi,
similar to very soft clay.
Ratio by
Weight
12
4.3 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.
For 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.
In fills such as impervious dam cores, where subatmospheric 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. This type of filter should be carefully placed in direct contact with the compacted fill
material. (See Figure 5).
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. In high traffic areas and in
materials which exhibit pronounced "weaving", heavy-duty armored cable should be used.
Figure 5 - High Air Entry Filter
13
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 standard coarse tip (low air entry) measures the air
pressure when there is a difference between the pore air pressure and the pore water pressure.
The difference between these 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 tip filter is suitable for most routine measurements. Both the
installation shown in Figure 5 and the installation shown in Figure 6 may be used with the
standard piezometer filter.
Figure 6 - Low Air Entry Filters ONLY
14
4.4 Installation by Pushing or Driving into Soft Soils
The Model 4500DP piezometer is designed to be pushed into soft soils. In soft soils it can be
difficult to keep a borehole open. The 4500DP may eliminate the need for a borehole altogether.
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. See Figure 7. The units can also be
driven into the soil, but there is a possibility that the driving forces may shift the zero reading.
The ground conditions need to be relatively soft for the 4500DP to be effective. Soft soils (like
clays or silts) with SPT blow counts under 10 are ideal. In stiffer soils, it is possible to drill a
hole and then push the 4500DP only a few feet below the bottom of the hole, but if the soil is too
stiff the sensor may overrange or break.
Figure 7 - Typical Soft Soils Installation
The piezometer should be connected to a readout box and monitored during the installation
process. If pressures reach or exceed the calibrated range, the installation should be stopped.
Allow the pressure to dissipate before continuing.
The drill rod can be left in place or it can be removed. If it is to be removed, a special five foot
section of EW (or AW) rod with reaction 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 reaction wings prevent the EW rod from turning. A LH/RH adapter is available
from Geokon. This adapter is retrieved along with the drill string.
15
4.5 Model 4500H and Model 4500HH Transducer
Geokon Models 4500H and 4500HH are designed to be used in high temperature environments,
up to 250 degrees Celsius.
When connecting the Model 4500H transducer to external fittings, the fitting should be tightened
into the 1/4-18NPT female port by placing a wrench on the flats provided on the transducer
housing. Avoid tightening onto a closed system; the process of tightening the fittings could
overrange and permanently damage the transducer. If in doubt, attach the gage leads to a readout
box and take readings while tightening. For an easier and more positive connection to the
transducer, PTFE (plumber’s) tape on the threads is recommended. The maximum pressure for
the 4500H is 3MPa.
Geokon’s Model 4500HH is designed for high pressure environments. This model uses a 7/1620, 60 degree, female, medium pressure fitting. The maximum pressure for the 4500HH is
75MPa.
Both models employ a high temperature thermistor, see Appendix C.
CAUTION: All high pressure sensors are potentially dangerous. Care must be taken not to
overrange them beyond their calibrated range. Sensors are tested to 150% of their range to
provide a factor of safety.
16
4.6 Splicing and Junction Boxes
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 effect, and in some cases may in fact 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) could be made to connect the individual cables to a single mu lticonductor cable. (See Figure 8.) This multi-conductor cable would then be run to the readout
station. For these types of 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.).
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. Splice kits recommended by Geokon incorporate casts which are
placed around the splice and 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 readouts and dataloggers are also available. Contact Geokon for specific
application information.
Figure 8 - Typical Multi-Piezometer Installation
4.7 Lightning Protection
In exposed locations it is vital that the piezometer be protected against lightning strikes. A
tripolar plasma surge arrestor, which protects against voltage spikes across the input leads, is
built into the body of the piezometer. (See Figure 1.)
Additional lightning protection measures available include:
Placing a Lightning Arrestor Board (LAB-3) in line with the cable, as close as possible to
the installed piezometer. (See Figure 9.) These units utilize surge arrestors and transzorbs
to further protect the piezometer. This is the recommended method of lightning
protection.
Terminal boxes available from Geokon can be ordered with lightning protection built in.
The terminal board used to make the gage connections has provision for the installation
of plasma surge arrestors. Lightning Arrestor Boards (LAB-3) can also be incorporated
into the terminal box. The terminal box must be connected to an earth ground for these
levels of protection to be effective.
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, away from the instrument.
17
Figure 9 - Recommended Lightning Protection Scheme
18
5. TAKING READINGS
5.1 GK-404 Readout Box
The GK404 is a palm sized readout box which displays the vibrating wire value and the
temperature in degrees centigrade.
5.1.1 Operating the GK-404
Before use, attach the flying leads to the GK-404 by aligning the red circle on the silver
“Lemo” connector of the flying leads with the red line on the top of the GK-404 (Figure
10). Insert the Lemo connector into the GK-404 until it locks into place.
Figure 10 - 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:
Geokon Inc.
GK-404 verX.XX
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 GK404 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 the no reading
displays or the reading is unstable see Section 7 for troubleshooting suggestions.
For further details information the GK-404 manual.
19
5.2 GK-405 Readout Box
The GK-405 Vibrating Wire Readout is made up of two components: The Readout Unit,
consisting of a Windows Mobile handheld PC running the GK-405 Vibrating Wire Readout
Application; and the GK-405 Remote Module, which is housed in a weatherproof enclosure and
connects to the vibrating wire gage to be measured. The two components communicate
®
wirelessly using Bluetooth
, a reliable digital communications protocol. The Readout Unit can
operate from the cradle of the Remote Module, or, if more convenient, can be removed and
operated up to 20 meters from the Remote Module.
5.2.1 Connecting Sensors
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.
Connecting Sensors with Bare Leads:
Attach the GK-403-2 flying leads to the bare leads of a Geokon vibrating wire sensor by
connecting each of the clips on the leads to the matching colors of the sensor conductors,
with blue representing the shield (bare).
5.2.2 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 by tapping on “Start” from the handheld PC’s main
window, then “Programs” then the GK-405 VWRA icon. After a few seconds, the blue
light on the Remote Module should stop flashing and remain lit. The Live Readings
Window will be displayed on the handheld PC. Figure 11 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 7 for troubleshooting suggestions.
For further information consult the GK405 Instruction Manual.
Figure 11 - Live Readings – Raw Readings
20
5.3 GK-403 Readout Box (Obsolete Model)
The GK-403 can store gage readings and also apply calibration factors to convert readings to
engineering units. The following instructions explain taking gage measurements using Modes
"B" and "F" (similar to the GK-401 switch positions "B" and "F"). Consult the GK-403
Instruction Manual for additional information.
5.3.1 Connecting Sensors
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.
Connecting Sensors with Bare Leads:
Attach the GK-403-2 flying leads to the bare leads of a Geokon vibrating wire sensor by
connecting each of the clips on the leads to the matching colors of the sensor conductors,
with blue representing the shield (bare).
5.3.2 Operating the GK-403
1) Turn the display selector to position "B" (or "F").
2) Turn the unit on.
3) The readout will display the vibrating wire output in digits ( See Equation 1 in
Section 6.) 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 7 for troubleshooting
suggestions.
The unit will automatically turn itself off after approximately two minutes to conserve
power.
5.4 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. (High temperature versions use a different thermistor which must be
read using an ohmmeter.)
To read temperatures using an ohmmeter:
1) Connect an ohmmeter to the green and white thermistor leads coming from the strain gage.
(Since the resistance changes with temperature are large, the effect of cable resistance is
usually insignificant. For long cables a correction can be applied, equal to 16 ohms per one
thousand feet.)
2) Look up the temperature for the measured resistance in Appendix B, Table 7. For high
temperature models use Appendix C, Table 8.
21
22
6. DATA REDUCTION
6.1 Pressure Calculation
The digits displayed by the Geokon Models GK-403, GK-404, and GK-405 Readout Boxes on
channel B are based on the equation:
Digits =
1
2x 10-3 or Digits
Period
Hz
1000
2
Equation 1 - Digits Calculation
For example, a piezometer reading 8000 digits corresponds to a period of 354s and a frequency
of 2828 Hz. Note that in the above equation, the period is in seconds. Geokon readout boxes
display microseconds.
Digits are directly proportional to the applied pressure.
Pressure (Current Reading - Initial Reading) Linear Calibration Factor
Or:
P = (R1 – R0)G
Equation 2 - Convert Digits to Pressure
Since the linearity of most sensors is within ±0.2% FS, the errors associated with nonlinearity are
of minor consequence. However, for those situations requiring the highest degree of accuracy, it
may be desirable to use a second order polynomial to get a better fit of the data points. The use
of a second order polynomial is explained in Appendix D.
The instrument’s calibration report, a typical example of which is shown in Figure 12, shows the
data from which the linear gage factor and the second order polynomial coefficients are derived.
Columns on the right show the size of the error incurred by assuming a linear coefficient and the
improvement which can be expected by going to a second order polynomial. In many cases the
difference is minor.
The calibration report gives the pressure in certain engineering units. These can be converted to
other engineering units using the multiplication factors shown in Table 2.
From
To
psi 1 .036127 .43275 .0014223 1.4223 .49116 .019337 14.696 .014503 14.5039 .14503 145.03
"H2O
'H2O
mm H20
m H20
"HG 2.036 .073552 .882624 .0028959 2.8959 1 .03937 29.920 .029529 29.529 .2953 295.3
mm HG 51.706 1.8683 22.4196 .073558 73.558 25.4 1 760 .75008 750.08 7.5008 7500.8
atm .06805 .002458 .029499 .0000968 .0968 .03342 .001315 1 .000986 .98692 .009869 9.869
mbar 68.947 2.4908 29.8896 .098068 98.068 33.863 1.3332 1013.2 1 1000 10 10000
bar .068947 .002490 .029889 .0000981 .098068 .033863 .001333 1.0132 .001 1 .01 10
kPa 6.8947 .24908 2.98896 .0098068 9.8068 3.3863 .13332 101.320 .1 100 1 1000
MPa .006895 .000249 .002988 .0000098 .009807 .003386 .000133 .101320 .0001 .1 .001 1
psi
27.730 1 12 .039372 39.372 13.596 .53525 406.78 .40147 401.47 4.0147 4016.1
2.3108 .08333 1 .003281 3.281 1.133 .044604 33.8983 .033456 33.4558 .3346 334.6
704.32 25.399 304.788 1 1000 345.32 13.595 10332 10.197 10197 101.97 101970
.70432 .025399 .304788 .001 1 .34532 .013595 10.332 .010197 10.197 .10197 101.97
"H2O
'H2O
mm H20
m H20
"HG
mm HG
atm
mbar
Table 2 - Engineering Units Multiplication Factors
bar
kPa
MPa
(Note: Due to changes in specific gravity with temperature, the factors for mercury and water in
the above table are approximate.)
23
Figure 12 - Typical Calibration Report
24
6.2 Temperature Correction
The materials used in the construction of Geokon’s vibrating wire piezometers have been
carefully selected to minimize thermal effects; however, most units still have a slight temperature
coefficient. Consult the calibration sheet supplied with the instrument to obtain the coefficient
for the individual piezometer.
Since piezometers are normally installed in a tranquil and constant temperature environment,
corrections are normally not required. If this is not the case for the selected installation,
corrections can be made using the internal thermistor for temperature measurement. See Section
5.4 for instructions regarding obtaining the piezometer temperature.
The temperature correction equation is as follows:
Temperature Correction (Current Temperature - Initial Temperature) Thermal Factor
Or:
PT = (T1-T0) x K
Equation 3 - Temperature Correction
The calculated correction would then be added to the pressure calculated using Equation 2. If the
engineering units were converted, remember to apply the same conversion to the calculated
temperature correction.
For example: If the initial temperature was 22 C, and the current temperature is 15 C, and the
thermal factor (K on the calibration report,) is +0.1319 kPa per C rise. The temperature
correction is +0.1319(15-22) = -0.92 kPa. Refer to the calibration report provided with the
instrument for the initial temperature and thermal factor.
25
6.3 Barometric Correction (required only on unvented transducers)
Since the standard piezometer is hermetically sealed, it responds to changes in atmospheric
pressure. Corrections may be necessary, particularly for the sensitive, low pressure models. For
example, a barometric pressure change from 29 to 31 inches of mercury would result in
approximately one PSI of error (or 2.3 feet if monitoring water level in a well). Thus it is
advisable to read and record the barometric pressure every time the piezometer is read. Having
an onsite barometer also allows the monitoring of barometric changes in order to judge what
extent they may be affecting the reading. A separate pressure transducer (piezometer), kept out
of the water, may also be used for this purpose.
The barometric correction equation is as follows:
Barometric Correction (Current Barometer - Initial Barometer) Conversion Factor
Or:
PB = (S1-S0) x F
Equation 4 - Barometric Correction
The calculated barometric correction is subtracted from the pressure calculated using Equation 2.
If the engineering units were converted remember to apply the same conversion to the
calculated barometric correction.
Barometric pressure is usually recorded in inches of mercury. The conversion factor for inches of
mercury to PSI is 0.491, and from inches of mercury to kPa is 3.386. Table 2 lists other common
conversion factors.
The user should be cautioned that this correction scheme assumes ideal conditions. In reality,
conditions are not always ideal. For example, if the well is sealed, barometric effects at the
piezometer level may be minimal or attenuated from the actual changes at the surface. Thus
errors may result from applying a correction which is not required. In these cases we recommend
independently recording the barometric pressure changes and correlating them with the observed
pressure changes in order to arrive at a correction factor.
An alternative to making barometric corrections is to use piezometers that are vented to the
atmosphere. (See Section 6.4.) However, vented piezometers only make sense if the piezo is in
an open well or standpipe and the user is only interested in the water level. If the piezo is buried
it is not certain that the full effect of the barometric change will be felt immediately at the
instrument and is more likely to be attenuated and delayed, in which case a vented piezo would
automatically apply a correction that is too large and too soon.
Equation 5 shows the pressure calculation with temperature and barometric correction applied.
P
corrected
= (R1 – R0)G + (T1-T0) K - (S1-S0) F
Equation 5 - Corrected Pressure Calculation
26
6.4 Vented Piezometers
Vented piezometers are designed to eliminate barometric effects. The space inside the transducer
is not hermetically sealed and evacuated; instead it is connected via a tube (integrated with the
cable) to the atmosphere. A chamber containing desiccant capsules is attached to the end of the
tube to prevent moisture from entering the transducer cavity. Vented piezometers require more
maintenance then unvented types, and there is always a danger that water may find its way inside
the transducer and ruin it.
In order to keep the desiccant fresh during storage and transportation, the end of the desiccant
chamber is closed off by means of a seal screw before being shipped from the factory. THIS
SEAL SCREW MUST BE REMOVED BEFORE THE PIEZOMETER IS PUT INTO
SERVICE!
The desiccant capsules are blue when fresh. They will gradually turn pink as they absorb
moisture. When they have turned light pink in color they should be replaced. Contact Geokon for
replacement capsules.
6.5 Environmental Factors
Since the purpose of the piezometer installation is to monitor site conditions, factors which may
affect these conditions should always be observed and recorded. Seemingly minor effects may
have a real influence on the behavior of the structure being monitored, and may give an early
indication of potential problems. Some of these factors include, but are not limited to: blasting,
rainfall, tidal levels, traffic, temperature and barometric changes, weather conditions, changes in
personnel, nearby construction activities, excavation and fill level sequences, seasonal changes,
etc.
27
7. 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 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: Piezometer fails to give a reading
Check the resistance of the cable by connecting an ohmmeter to the sensor leads. Table 3
shows the expected resistance for the various wire combinations. Cable resistance is
approximately 16 per 1000' of 22 AWG wire. If the resistance is very high or infinite the
cable is probably broken or cut. If the resistance is very low the gage conductors may be
shorted. If a cut or a short is located in the cable, splice according to instructions in Section
4.6.
Vibrating Wire Sensor Lead Grid - SAMPLE VALUES
Red Black White Green Shield
Red N/A
Black
N/A infinite infinite infinite
White infinite infinite N/A
Green infinite infinite
infinite infinite infinite
infinite
at C
at C
N/A infinite
Shield infinite infinite infinite infinite N/A
Table 3 - Sample Resistance
Vibrating Wire Sensor Lead Grid - SENSOR NAME/## :
Red Black White Green Shield
Red
Black
White
Green
Shield
Table 4 - Resistance Work Sheet
28
Check the readout with another gage.
The Piezometer may have been overranged or shocked. Inspect the diaphragm and housing
for damage.
Symptom: Piezometer reading unstable
Connect the shield drain wire to the readout using the blue clip. (Green for the GK-401.)
Isolate the readout from the ground by placing it on a piece of wood or other insulator.
Check for sources of nearby noise such as motors, generators, antennas or electrical cables.
Move the piezometer cable if possible. Contact the factory for available filtering and
shielding equipment.
The Piezometer may have been damaged by overranging or shock. Inspect the diaphragm and
housing for damage.
The body of the Piezometer may be shorted to the shield. Check the resistance between the
shield drain wire and the Piezometer housing.
Symptom: Thermistor resistance is too high
Likely there is an open circuit. Check all connections, terminals, and plugs. If a cut is located
in the cable, splice according to instructions in Section 4.6.
Symptom: Thermistor resistance is too low
Likely there is a short. Check all connections, terminals, and plugs. If a short is located in the
cable, splice according to instructions in Section 4.6.
Water may have penetrated the interior of the piezometer. There is no remedial action.
APPENDIX A. - SPECIFICATIONS
0-10
0-25
FS/°C
1"
5.25"
1
4500AR 4500B 4500C 4500DP
0-10
0-25
0-50
0-150
0-50
FS 2 FS 2 FS 2 FS 2 FS
<0.05%
FS/°C
-20°C to
+80°C
.75"
19.05 mm
10”
254 mm
0-100
0-250
<0.025%
FS/°C
-20°C to
+80°C
.687"
17.45 mm
5.25"
133 mm
0-50
0-100
0-250
<0.05%
FS/°C
-20°C to
+80°C
.437"
11.10 mm
6.5"
165 mm
0-250
0-500
0-750
0-1000
0-1500
0-3000
0-5000
0-10000
<0.025%
FS/°C
-20°C to
+80°C
1.3”
33.3mm
7.36”
187 mm
45802
0-1
0-5
0.1% FS
<0.025%
FS/°C
-20°C to
+80°C
1.5"
38.10 mm
6.5"
165 mm
Model 4500S
0-50
0-100
0-150
0-250
Available
Ranges
(psi)
Resolution 0.025% FS 0.025% FS 0.025% FS 0.025% FS 0.05% FS 0.025% FS 0.01% FS
Linearity
Accuracy
Overrange
Thermal
Coefficient
Temperature
Range
OD
Length
0-500
0-750
0-1000
0-1500
0-3000
0-5000
0-10000
0-15000
< 0.5% FS3 < 0.5% FS3 < 0.5% FS3 < 0.5% FS3 < 0.5% FS3 < 0.5% FS3 < 0.5% FS3
0.1% FS4 0.1% FS4 0.1% FS4 0.1% FS4 0.1% FS4 0.1% FS4
2 FS 2 FS 2
<0.025%
FS/°C
-20°C to
+80°C
.75"
19.05 mm
5.25"
133 mm
4500AL
<0.05%
-20°C to
+80°C
25.40 mm
133 mm
Table 5 - Vibrating Wire Piezometer Specifications
Accuracy of Geokon test apparatus: 0.1%
Contact Geokon for specific application information.
Notes:
1
Accuracy of test apparatus: 0.05%
2
Other ranges available upon request.
3
0.1% FS linearity available upon request.
4
Derived using second order polynomial.
29
A.1 Standard Piezometer Wiring
Pin Function Wire Color
A Vibrating Wire Gage + Red
B Vibrating Wire Gage - Black
C Thermistor White
D Thermistor Green
E Cable Shield Shield
F-K Not Used
Table 6 - Standard Piezometer Wiring
30
APPENDIX B. - THERMISTOR TEMPERATURE DERIVATION
Thermistor Type: YSI 44005, Dale #1C3001-B3, Alpha #13A3001-B3
Resistance to Temperature Equation:
1
T=
A+BLnR+C(LnR)
Equation 6 - 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.
Ohms Temp Ohms Temp Ohms Temp Ohms Temp Ohms Temp
201.1K -50 16.60K -10 2417
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
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
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
3000 25
Table 7 - Thermistor Resistance versus Temperature
1
1535 41 364.9 81 113.8 121
624.7 65 176.4 105 62.5 145
30
-273.2
3
525.4
70
153.2
55.6 150
110
R
R
f
R
RLnR
f
APPENDIX C. HIGH TEMPERATURE THERMISTOR LINEARIZATION
High Temperature Thermistor Linearization using SteinHart-Hart Log Equation
Thermistor Type: Thermometrics BR55KA822J
Resistance to Temperature Equation:
1
T=
A+BLnR+C(LnR)
Equation 7 - High Temperature Resistance to Temperature
Where;
T Temperature in C.
LnR Natural Log of Thermistor Resistance
A 1.02569 10-3
B 2.478265 10-4
C 1.289498 10-7
Note: Coefficients calculated over the -30 to +260 C. span.
Temp
-30 113898 11.643 1578.342 -30.17 0.17 0.06 120 407.62 6.010 217.118 120.00 0.00 0.00
-25 86182 11.364 1467.637 -25.14 0.14 0.05 125 360.8 5.888 204.162 125.00 0.00 0.00
-20 65805 11.094 1365.581 -20.12 0.12 0.04 130 320.21 5.769 191.998 130.00 0.00 0.00
-15 50684.2 10.833 1271.425 -15.10 0.10 0.03 135 284.95 5.652 180.584 135.00 0.00 0.00
-10 39360 10.581 1184.457 -10.08 0.08 0.03 140 254.2 5.538 169.859 140.01 -0.01 0.00
-5 30807.4 10.336 1104.068 -5.07 0.07 0.02 145 227.3 5.426 159.773 145.02 -0.02 -0.01
0 24288.4 10.098 1029.614 -0.05 0.05 0.02 150 203.77 5.317 150.314 150.03 -0.03 -0.01
5 19294.6 9.868 960.798 4.96 0.04 0.01 155 183.11 5.210 141.428 155.04 -0.04 -0.01
10 15424.2 9.644 896.871 9.98 0.02 0.01 160 164.9 5.105 133.068 160.06 -0.06 -0.02
15 12423 9.427 837.843 14.98 0.02 0.01 165 148.83 5.003 125.210 165.08 -0.08 -0.03
20 10061.4 9.216 782.875 19.99 0.01 0.00 170 134.64 4.903 117.837 170.09 -0.09 -0.03
25 8200 9.012 731.893 25.00 0.00 0.00 175 122.1 4.805 110.927 175.08 -0.08 -0.03
30 6721.54 8.813 684.514 30.01 -0.01 0.00 180 110.95 4.709 104.426 180.07 -0.07 -0.02
35 5540.74 8.620 640.478 35.01 -0.01 0.00 185 100.94 4.615 98.261 185.10 -0.10 -0.04
40 4592 8.432 599.519 40.02 -0.02 -0.01 190 92.086 4.523 92.512 190.09 -0.09 -0.03
45 3825.3 8.249 561.392 45.02 -0.02 -0.01 195 84.214 4.433 87.136 195.05 -0.05 -0.02
50 3202.92 8.072 525.913 50.01 -0.01 -0.01 200 77.088 4.345 82.026 200.05 -0.05 -0.02
55 2693.7 7.899 492.790 55.02 -0.02 -0.01 205 70.717 4.259 77.237 205.02 -0.02 -0.01
60 2276.32 7.730 461.946 60.02 -0.02 -0.01 210 64.985 4.174 72.729 210.00 0.00 0.00
65 1931.92 7.566 433.157 65.02 -0.02 -0.01 215 59.819 4.091 68.484 214.97 0.03 0.01
70 1646.56 7.406 406.283 70.02 -0.02 -0.01 220 55.161 4.010 64.494 219.93 0.07 0.02
75 1409.58 7.251 381.243 75.01 -0.01 0.00 225 50.955 3.931 60.742 224.88 0.12 0.04
80 1211.14 7.099 357.808 80.00 0.00 0.00 230 47.142 3.853 57.207 229.82 0.18 0.06
85 1044.68 6.951 335.915 85.00 0.00 0.00 235 43.673 3.777 53.870 234.77 0.23 0.08
90 903.64 6.806 315.325 90.02 -0.02 -0.01 240 40.533 3.702 50.740 239.69 0.31 0.11
95 785.15 6.666 296.191 95.01 -0.01 0.00 245 37.671 3.629 47.788 244.62 0.38 0.13
100 684.37 6.528 278.253 100.00 0.00 0.00 250 35.055 3.557 45.001 249.54 0.46 0.16
105 598.44 6.394 261.447 105.00 0.00 0.00 255 32.677 3.487 42.387 254.44 0.56 0.19
110 524.96 6.263 245.705 110.00 0.00 0.00 260 30.496 3.418 39.917 259.34 0.66 0.23
115 461.91 6.135 230.952 115.00 0.00 0.00
(ohms)
LnR Ln
Table 8- Thermistor Resistance versus Temperature for High Temperature Models
3
Calculated
Temp
Dif
FS
Error
Temp
-273.2
3
(ohms)
Ln
3
Calculated
Temp
Dif
Error
31
FS
32
APPENDIX D. IMPROVING THE ACCURACY OF THE CALCULATED
PRESSURE
Most vibrating wire pressure transducers are sufficiently linear ( 0.2 % FS) so that the use of
the linear calibration factor satisfies normal requirements. However, it should be noted that the
accuracy of the calibration data, which is dictated by the accuracy of the calibration apparatus, is
always 0.1 % FS.
This level of accuracy can be recaptured, even where the transducer is nonlinear, by the use of a
second order polynomial expression, which gives a better fit to the data then does a straight line.
The polynomial expression has the form:
2
BR C
= G(R1 –R0 ) -P
x 100%
2
+ B(9074) from which C = 1595.7
x 100%
Pressure = AR
Where R is the reading (digits channel B) and A, B, C are coefficients. Figure 12 shows a typical
calibration sheet of a transducer which has fairly normal nonlinearity. The figure under the
“Linearity (%FS)” column is:
Calculated pressure- True pressure
Full-scale Pressure F.S
Note: The linearity is calculated using the regression zero for R0 shown on the calibration report.
For example when P= 420 kPa, G (R1 – R0 ) = - 0.1795( 6749-9082), the calculated pressure is
418.8 kPa. The error is 1.2 kPa equal to 122mm of water.
Whereas the polynomial expression gives a calculated pressure of A (6749) 2 B (6749)
1595.7 = 420.02 kPa. Therefore the actual error is only 0.02 kPa or 2mm of water.
Note: If the polynomial equation is used it is important that the value of C be taken in the field,
following the procedures described in Section 3.2. The field value of C is calculated by inserting
the initial field zero reading into the polynomial equation with the pressure, P, set to zero.
If the field zero reading is not available, the value of C can be calculated by using the zero
pressure reading on the calibration sheet. In the above example the value of C would be derived
from the equation 0 = A(9074)
It should be noted that where changes of water levels are being monitored it makes little
difference whether the linear coefficient or the polynomial expression is used.
APPENDIX E. - MODEL 4500AR PIEZOMETER
33
Figure 13 - 4500AR
The Model 4500 AR piezometer is designed to be used with readout systems that can read
frequency but do not have the capability to “pluck” the VW gage. The sensor has built-in
electronics that cause the gage wire to vibrate continuously at its resonant frequency. The output
from the sensor is a five volt DC square wave at this frequency.
A DC input voltage in the range of 6 to 24 volts is required to operate the gage. The current
consumption is approximately 21 mA at 12VDC. The gage output is independent of the input
voltage.
Multiple sensors powered simultaneously can be read at quite fast rates, (up to five sensors per
second,) and dynamic measurements on a single sensor can be made up to approximately 20Hz.
The gage is installed in the field in the same way that the Model 4500 standard piezometer is
installed. (See Section 3 and Section 4.)
Piezometer Wiring: The three pair cable is wired in pairs, with each pair comprising one
colored and one black lead.
Red +6-24 VDC Power
Red’s black Ground
White Output
White’s black Output Ground
Green Thermistor +
Green’s black Thermistor –
Bare Shield
Upon power up the gage will immediately start to “ring” at the resonant frequency and will
continue to do so until the power is removed. Continuous operation will have no effect on the
gage life.
Note: The sensor is comprised of two transducers: the VW pressure sensor, and a thermistor for
measuring temperature. The signal from the VW transducer is a high level frequency and it will
interfere with the thermistor output if left powered during the period that the thermistor is being
read. If the temperature reading is important the power to the pressure sensor should be switched
off while the thermistor reading is taken.
Loading...