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Geokon 4500AL Instruction Manual Download Page 39

33 

 

APPENDIX E. - MODEL 4500AR PIEZOMETER

 

 

 

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                Ther 
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. 

Summary of Contents for 4500AL

Page 1: ... 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 ...

Page 2: ......

Page 3: ...re 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 t...

Page 4: ... 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 G...

Page 5: ...ONS 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 ...

Page 6: ...ORT 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...

Page 7: ...equest 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 read...

Page 8: ...th 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 e...

Page 9: ...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 b...

Page 10: ... 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...

Page 11: ...ction 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 ab...

Page 12: ...re 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 Alternat...

Page 13: ...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 thing...

Page 14: ...able 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 t...

Page 15: ... 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...

Page 16: ...sults 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...

Page 17: ... 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 correspon...

Page 18: ... 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 small...

Page 19: ... 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 sta...

Page 20: ...oils 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 t...

Page 21: ...er 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 16 20 60 degree female medium pressure fitting The maximum pressure for ...

Page 22: ...e 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 an...

Page 23: ...ended 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 protectio...

Page 24: ...ll 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 meas...

Page 25: ... 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 blin...

Page 26: ...il 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 v...

Page 27: ...e 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 1...

Page 28: ... 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 fro...

Page 29: ... 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...

Page 30: ...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 ...

Page 31: ... 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...

Page 32: ...ed 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 condition...

Page 33: ...ance 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 Gr...

Page 34: ...lding 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 c...

Page 35: ...S C 0 025 FS C 0 025 FS C Temperature Range 20 C to 80 C 20 C to 80 C 20 C to 80 C 20 C to 80 C 20 C to 80 C 20 C to 80 C 20 C to 80 C OD 75 19 05 mm 1 25 40 mm 75 19 05 mm 687 17 45 mm 437 11 10 mm 1 3 33 3mm 1 5 38 10 mm Length 5 25 133 mm 5 25 133 mm 10 254 mm 5 25 133 mm 6 5 165 mm 7 36 187 mm 6 5 165 mm Table 5 Vibrating Wire Piezometer Specifications Accuracy of Geokon test apparatus 0 1 Con...

Page 36: ...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...

Page 37: ... 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 0...

Page 38: ...re 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 No...

Page 39: ...alled 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 immediate...

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