Geokon 4500MLP Instruction Manual

Instruction Manual

Model 4500MLP

Multilevel 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.

(REV I, 10/23/17)

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. PRIOR TO INSTALLATION ................................................................................................................................ 3

SATURATING THE FILTER STONE .......................................................................................................................... 3

2.1

SWAGELOK TUBE FITTING INSTRUCTIONS ............................................................................................................ 3

2.2

2.2.1 Installation .................................................................................................................................................... 3

2.2.2 Reassembly Instr uct i ons ............................................................................................................................... 4

ESTABLIS HING AN INITIAL ZERO READING ........................................................................................................... 5

2.3

3. INSTALLATIO N .................................................................................................................................................... 7

3.1

GROUTING REQUIREMENTS ................................................................................................................................... 7

BOREHOLE INSTALLATION ................................................................................................................................... 8

3.2

3.2.1 The Drop Weight Method ............................................................................................................................. 8

3.2.2 Pneumatic Cutter Method ............................................................................................................................. 9

3.2.3 Pull-Pin Method ......................................................................................................................................... 12

SPLICIN G AN D JUNCTION BOXES ........................................................................................................................ 12

3.3

LIGHTNING PROTECTION .................................................................................................................................... 14

3.4

4. TAKING READINGS ........................................................................................................................................... 15

4.1

GK-404 READOUT BOX ...................................................................................................................................... 15

4.1.1 Operating the GK-404 ................................................................................................................................ 15

GK-405 READOUT BOX ...................................................................................................................................... 16

4.2

4.2.1 Connecting Sensors .................................................................................................................................... 16

4.2.2 Operating the GK-405 ................................................................................................................................ 16

GK-403 READOUT BOX (OBSOLETE MODEL) ..................................................................................................... 17

4.3

4.3.1 Connecting Sensors .................................................................................................................................... 17

4.3.2 Operating the GK-403 ................................................................................................................................ 17

MEASURING TEMPERATURES ............................................................................................................................. 18

4.4

CHECKING THE CALIBRATION ............................................................................................................................ 18

4.5

5. DATA REDUCTION ............................................................................................................................................ 20

5.1

PRESSURE CALCULATION ................................................................................................................................... 20

TEMPERATURE CORRECTION .............................................................................................................................. 21

5.2

BAROMETRIC CORRECTION (REQUIRED ONLY ON UNVENTED TRANSDUCERS) .................................................... 22

5.3

VENTED PIEZOMETERS ....................................................................................................................................... 23

5.4

ENVIRONMENTAL FACTORS ................................................................................................................................ 23

5.5

6. TROUBLESHO OTING ........................................................................................................................................ 24

APPENDIX A. SPECIFICATIONS ......................................................................................................................... 26

A.1

STANDARD PIEZOMETER WIRING ...................................................................................................................... 26

APPENDIX B. THERMISTOR TEMPERATURE DERIVATION ..................................................................... 27

APPENDIX C. HIGH TEMPERATURE TH ERMISTOR LINEARIZATION .................................................. 28

APPENDIX D. IMPROVING THE ACCURACY OF THE CALCULATED PRE SSURE ............................... 29

FIGURES

FIGURE 1 - MODEL 4500S VIBRATING WIRE PIEZOMETER ............................................................................................ 1

FIGURE 2 - CLOSE UP OF 4500MLP ............................................................................................................................... 2

FIGURE 3 - 4500MLP SYSTEM ....................................................................................................................................... 2

FIGURE 4 - TUBE INSERTION .......................................................................................................................................... 3

FIGURE 5 - MAKE A MARK AT SIX O’CLOCK ................................................................................................................. 4

FIGURE 6 - TIGHTEN ONE AND ONE-QUARTER TURNS .................................................................................................. 4

FIGURE 7 - MARKS FO R REASSEMBLY ........................................................................................................................... 4

FIGURE 8 - FERRULES SEATED AGAINST FITTING BODY ................................................................................................ 5

FIGURE 9 - TIGHTEN NUT SLIGHTLY .............................................................................................................................. 5

FIGURE 10 - 4500MLP ZIP TIED FOR DROP WEIGHT METHOD ...................................................................................... 8

FIGURE 11 - 4500MLP PRE-RELEASE ............................................................................................................................ 9

FIGURE 12 - PNEUMATIC CUTTER EQUIPMENT .............................................................................................................10

FIGURE 13 - 4500MLP POST-RELEASE .........................................................................................................................11

FIGURE 14 - TYPICAL MULTI-PIEZOMETER INSTALLATION ..........................................................................................13

FIGURE 15 - RECOMMENDED LAB-3 LIGHTNING PROTECTION SCHEME .......................................................................14

FIGURE 16 - LEMO CONNECTOR TO GK-404 ................................................................................................................15

FIGURE 17 - LIVE READINGS – RAW READINGS............................................................................................................16

FIGURE 18 - SAMPLE CALIBRATION SHEET ...................................................................................................................19

TABLES

TABLE 1 - CEMENT/BENTONITE/WATER RATIOS ........................................................................................................... 7

TABLE 2 - ENGINEERING UNITS MULTIPLICATION FACTORS ........................................................................................21

TABLE 3 - SAMPLE RESISTANCE ...................................................................................................................................25

TABLE 4 - RESISTANCE WORK SHEET ...........................................................................................................................25

TABLE 5 - VIBRATING WIRE PIEZOMETER SPECIFICATIONS ..........................................................................................26

TABLE 6 - STANDARD PIEZOMETER WIRING .................................................................................................................26

TABLE 7 - THERMISTOR RESISTANCE VERSUS TEMPERATURE ......................................................................................27

TABLE 8- THERMISTOR RESISTANCE VERSUS TEMPERATURE FOR HIGH TEMPERATURE MODELS ................................28

EQUATIONS

EQUATION 1 - DIGITS CALCULATION ............................................................................................................................20

EQUATION 2 - CONVERT DIGITS TO PRESSURE .............................................................................................................20

EQUATION 3 - TEMPERATURE CORRECTION .................................................................................................................21

EQUATION 4 - BAROMETRIC CORRECTION ....................................................................................................................22

EQUATION 5 - CORRECTED PRESSURE CALCULATION ..................................................................................................22

EQUATION 6 - RESISTANCE TO TEMPERATURE .............................................................................................................27

EQUATION 7 - HIGH TEMPERATURE RESISTANCE TO TEMPERATURE ............................................................................28

EQUATION 8 - SECOND ORDER POLYNOMIAL EXPRESSION...........................................................................................29

EQUATION 9 - LINEARITY CALCULATION .....................................................................................................................29

1. THEORY OF OPERATION

Geokon Model 4500 Vibrating Wire Piezometers are intended primarily for long-term measurements of fluid, and/or pore pressures in standpipes, boreholes, embankments, pipelines and pressure vessels. The Model 4500MLP is designed to permit the easy installation of several piezometers inside a single borehole. It eliminates the need for alternating sand and bentonite zones by allowing the entire hole to be backfilled with bentonite grout by tremie piping it in through a grout pipe.

The basic Model 4500S piezometer (Figure 1) utilizes a sensitive stainless steel diaphragm to which a vibrating wire element is connected. In use, changing pressures on the diaphragm cause it to deflect. This deflection is measured as a change in tension and frequency of vibration in the vibrating wire element. The square of the vibration frequency is directly proportional to the pressure applied to the diaphragm.

Two coils, one with a magnet insert, the other with a pole piece insert, are located close to the vibrating wire. In use, a pulse of varying frequency (swept frequency) is applied to the 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

Care needs to be exercised when choosing the pressure range of the piezometer. During installation, the full pressure of the wet bentonite grout will be felt by the piezometer. Geokon piezometers can withstand overranging up to 100 percent of the calibrated range without affecting the calibration, shifting the zero reading, or damaging the unit. At higher overrange pressures, the piezometer may temporarily cease reading until the grout sets up and the pressure returns to normal.

Figure 2 - Close up of 4500MLP

For the Model 4500MLP, the filter stone shown in Figure 1 is replaced by a tube leading to a much larger, curved, and porous filter stone, which is forced against the walls of the borehole by a spring mechanism. The spring mechanism can be actuated remotely after the piezometer has been lowered in its closed configuration to its desired location. This is shown schematically in Figure 2 and Figure 3.

With the filter stones pressed against the wall of the borehole in this manner, the borehole can be filled completely with bentonite cement grout without running the risk of getting the filter stone plugged with bentonite, or having substantial amounts of the impervious bentonite interposed between the piezometer diaphragm and the ground water in the surrounding soil.

Figure 3 - 4500MLP System

2. PRIOR TO INSTALLATION

2.1 Saturating the Filter Stone

1) Disconnect the Swagelok union at the transducer.

2) Immerse the whole assembly, upside down, in a bucket of water.

3) Apply a vacuum to the nylon filter tube using the large syringe supplied with the system.

This removes the entrapped air from the large filter stone.

4) Purge the transducer of air by injecting water into the Swagelok fitting as follows: a) Fill the syringe with water. b) Attach the small diameter tube supplied with the system to the syringe. c) Push the tube all the way down inside the Swagelok fitting and into the piezometer

cavity.

d) Inject water from the syringe into the piezometer cavity.

5) With the assembly still under water, reconnect the nylon tube from the filter stone to the

transducer. Tighten the Swagelok per the instructions in Section 2.2.

6) Keep the assembly under water until ready to lower into the borehole.

Caution! Do not allow the piezometer to freeze once it has been filled with water.

2.2 Swagelok Tube Fitting Instructions

These instructions apply to one inch (25 mm) and smaller fittings.

2.2.1 Installation

1) Fully insert the tube into the fitting until it bumps against the shoulder.

Figure 4 - Tube Insertion

2) Rotate the nut until it is finger-tight. (For high-pressure applications as well as high-

safety-factor systems, further tighten the nut until the tube will not turn by hand or move axially in the fitting.)

3) Mark the nut at the six o’clock position.

Figure 5 - Make a Mark at Six O’clock

4) While holding the fitting body steady, tighten the nut one and one-quarter turns until

the mark is at the nine o’clock position. (Note: For 1/16”, 1/8”, 3/16”, and 2, 3, and 4 mm fittings, tighten the nut three-quarters of a turn until the mark is at the three o’clock position.)

Figure 6 - Tighten One and One-Quarter Turns

2.2.2 Reassembly Instructions

Swagelok tube fittings may be disassembled and reassembled many times.

Warning: Always depressurize the system before disassembling a Swagelok tube fitting.

1) Prior to disassembly, mark the tube at the back of the nut, then make a line along the

nut and fitting body flats. These marks will be used during reassembly to ensure the nut is returned to its current position.

2) Disassemble the fitting.

3) Inspect the ferrules for damage and replace if necessary. If the ferrules are replaced

the connector should be treated as a new assembly. Refer to the section above for installation instructions.

Figure 7 - Marks for Rea ssembly

4) Reassemble the fitting by inserting the tube with preswaged ferrules into the fitting

until the front ferrule seats against the fitting body.

Figure 8 - Ferrules Seated Against Fitting Body

5) While holding the fitting body steady, rotate the nut with a wrench to the previous

position as indicated by the marks on the tube and the connector. At this point, there will be a significant increase in resistance.

6) Tighten the nut slightly.

Figure 9 - Tighten Nut Slightly

2.3 Establishing an Initial Zero Reading

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. Vibrating Wire Piezometers differ from other types of pressure sensors in that they indicate a reading when no pressure is exerted on the sensor.

Calibration data is supplied with each gage, a factory zero reading taken at a specific temperature and absolute barometric pressure is included. (See Figure 18 for a sample calibration sheet.) Zero readings at the site should coincide with the factory readings within 20 digits after barometric and temperature corrections are made. (Barometric pressures change with elevation at a rate of about 3.45 kPa (1/2 psi) per 300 meters (1,000 ft.) A thermistor is included inside the body of the piezometer for the measurement of temperature.

To take an initial zero reading, complete the following:

1) Saturate the filter stone per the instructions in Section 2.1.

2) Allow the assembly to sit under water in a bucket for 5 to 15 minutes while the temperature

stabilizes. (If possible, the temperature of the water in the bucket should be the same as the temperature of the water in the borehole. Use the thermistor inside the piezometer to measure the water temperature.)

3) Once the temperature has stabilized, take a zero reading. (See Section 4 for readout

instructions.)

4) Note the barometric pressure if possible, or record the time for later referral to local weather

station data.

5) For maximum accuracy, record the depth of the piezometer below the water surface at the

time of the reading. (The piezometer diaphragm is at the same level as the lowest leaf spring.)

50 PSI Grout for Medium

to Hard Soils

Ratio by

Weight

Ratio by

Weight

Water

30 gallons

2.5

75 gallons

6.6

Portland

Cement

The 28 day compressive strength of this mix

clay. The modulus is about 10,000 psi

The 28-day strength of this

similar to very soft clay.

3. INSTALLATION

Borehole sizes are not critical but they should be at least 100 mm (four inch) in diameter and not more than 30 mm larger than the nominal size for which the spring-loaded mechanism was

designed.

3.1 Grouting requirements

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.

The general rule for grouting multilevel piezometers is to mimic 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 is in a 50 to 200 gallon barrel or tub, using the drill rig pump to circulate the mix.

Any kind of bentonite powder used to make drilling mud, combined with a Type 1 or Type 2 Portland cement can be used. The exact amount of bentonite added will vary somewhat. Table 1 shows two possible mixes for strengths of 50 psi and 4 psi.

Amount

94 lb. (one sack) 1 94 lb. (one sack) 1

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, similar to 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.

25 lb. (as required) 0.3 39 lb. (as required) 0.4

is about 50 psi, similar to very stiff to hard

Table 1 - Cement/Bentonite/Water ratios

4 PSI Grout for Soft Soils

Amount

mix is about four psi,

3.2 Borehole Installation

In steeply inclined boreholes directed downwards, the drop weight method of installation is recommended. See Section 3.2.1.

(Note that the drop weight method cannot be used in holes that will not stay open, and in holes which require the casing to be removed as the piezometers are installed. This is because when using the drop weight method the top piezometers are released first.)

For shallow inclinations and upward directed holes, (and for other situations where the drop weight method is not desired or possible,) the pneumatic cutter method or the pull-pin method can be used. See Sections 3.2.2 and 3.2.3.

3.2.1 The Drop Weight Method

4500MLP sensors are designed to be installed around flush coupled, one inch, Schd 80 PVC grout pipe; however, other grouting arrangements may be used.

Preparing the grout pipe:

1) Connect the sections of grout pipe together and lay them out along the ground.

2) Mark the desired locations of the piezometers on the grout pipe at the calculated

depths.

3) Drill a single 7/32 or 1/4 inch drill hole diametrically through the pipe in each marked

location.

Attaching the piezometers:

Each piezometer assembly is held to the grout pipe by means of a single 50 lb. nylon zip tie (supplied), which passes through the two holes on opposite sides of the pipe. The zip tie also holds the piezometer assembly in its closed position.

Pass the zip tie through the grout pipe, through the spaces between the leaf springs, around the two platens, and then back to itself. Keep the cables from lower piezometers inside the zip tie and leaf springs. The zip tie should pass just below the center leaf spring so that the bottom of the platen assemblies will be held tight to the grout pipe.

Pull the zip tie tight around the grout pipe (Figure 10).

Figure 10 - 4500MLP zip Tied for Drop Weight Me thod

As the grout pipe is assembled and pushed into the borehole, the piezometer assemblies are added, and the electrical cables are fed into the borehole. When the grout tube has reached its final position and the assembly is complete, a special weight (provided with the equipment,) is tied to a length of aircraft cable and allowed to fall freely down the inside of the grout pipe. As the weight hits each of the zip ties stretching across the pipe, the zip tie is snapped, allowing the leaf springs to expand and force the filter stones against the walls of the borehole.

3.2.2 Pneumatic Cutter Method 4500MLP sensors are designed to be installed around flush coupled, one inch, Schd 80

PVC grout pipe; however, other grouting arrangements may be used.

The assembly is held in its closed position during installation by two nylon zip ties (supplied). Making sure the grout pipe is between the platens, and the cables from the lower piezometers are kept inside the zip tie and leaf springs, attach the body of the piezometer to the grout pipe by passing the zip ties through the eyebolts in the platens and through the holes in the cutting tool. Orient the tool in such a way that it will be above the assembly when pushed into the borehole. See Figure 11.

If the grout pipe is going to be removed from the borehole the grout pipe is assembled and pushed into the borehole first, then each piezometer assembly is pushed around the grout pipe (and any lower piezometer cables) to the desired elevation. Piezometers should be installed sequentially, from the base of the borehole to the mouth.

If the grout pipe is to be left in place, the piezometers can be taped to the grout pipe. (Make sure not to put the tape around the outside of the filter stone and spring mechanism.)

Figure 11 - 4500MLP P re-release

When the desired elevation is reached, the cutting tool is activated by connecting the pneumatic tube from the piezometer to a bottle of CO2. (CO2 can be obtained locally from any welding supply outlet.) The CO2 bottle should have a pressure regulator that is set to a pressure of at least 2.5 MPa (350 psi), with the shutoff valve closed (Figure 12).

Figure 12 - Pneumatic Cutter Equipment

The shut off valve is then opened suddenly, allowing the pressure to reach the cutting tool. The cutting tool cuts the zip ties, releasing the spring-loaded platens against the borehole walls (Figure 13).

Figure 13 - 4500MLP Post-release

If installed in drill casing:

The sensor is lowered to the proposed elevation and the casing is pulled just above this elevation before the assembly is released. The cutting tool is then removed from the drill hole and the next assembly is prepared for installation.

When lowering the subsequent piezometers down the hole, feed the cables from the lower piezometers through the middle of the assembled piezometer rather than around the outside. (This will prevent the cables from interfering with the filter contacting with the borehole wall).

When all the assemblies are installed, the hole can be grouted from the bottom up using bentonite cement grout.

3.2.3 Pull-Pin Method

In this method, the piezometer assembly is held in its closed position by means of a pullpin. After the filter stone and the platen are squeezed together, the pull-pin passes through two sets of three eyebolts each, which are mounted on the filter stone and the platen.

If the grout pipe is going to be removed from the borehole:

The piezometer assembly must be pushed around the grout pipe, down to the desired elevation. This is accomplished using a second pipe, which can be another length of the grout tube. While holding the piezometer in position by the second pipe, the pull-pin cable should be pulled gently until all the slack is taken out. With a sudden and strong jerk, pull on the pull-pin cable. This will release the platens without changing the position of the piezometer relative to the borehole. (A bit of practice pulling the pins before the

actual installation will give some "feeling" and confidence as to how the system works.)

Piezometers should be installed sequentially, from the base of the borehole to the mouth.

If the grout pipe is going to be left in the borehole:

The piezometer assemblies should be attached to the grout pipe in a manner that does not restrict the movement of the platens. The grout pipe is assembled, length by length, while the piezometer assemblies, (each with its own pull-pin,) are attached to it by taping the electrical cable to the grout pipe near the piezometer. The grout pipe and piezometer assemblies can then be pushed down the hole as a unit. When the final position is reached the pull-pins are pulled, activating the platens.

If installed in drill casing:

The sensor is lowered to the proposed elevation. The casing is pulled just above this elevation before the assembly is released. The tool is then removed from the drill hole and the next assembly prepared for installation. When lowering (or pushing) the subsequent piezometers down the hole, feed the cables from the lower piezometers through the middle of the assembled piezometer rather than around the outside. This will prevent the cables from coming between the filter and the borehole wall.

When all the assemblies are installed, the hole can be grouted from the bottom up using a bentonite cement grout. The grout pipe can either be removed from the hole or left in place.

3.3 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 multi-conductor cable. (See Figure 14.) This multiconductor cable would then be run to the readout station. For these installations, it is recommended that the piezometer be supplied with enough cable to reach the installation depth plus extra cable to pass through drilling equipment (rods, casing, etc.).

The cable used for making splices should be a high quality twisted pair type with 100% shielding 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 that 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 available. Contact Geokon for specific application information.

Figure 14 - Typical Multi-Piezometer Installation

3.4 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 15.)

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 15.) 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.

Figure 15 - Recommended Lab-3 Lightning Protection Scheme

4. TAKING READINGS

4.1 GK-404 Readout Box

The Model GK-404 Vibrating Wire Readout is a portable, low-power, handheld unit that is capable of running for more than 20 hours continuously on two AA batteries. It is designed for the readout of all Geokon vibrating wire gages and transducers, and is capable of displaying the reading in either digits, frequency (Hz), period (µs), or microstrain (µε). The GK-404 also displays the temperature of the transducer (embedded thermistor) with a resolution of 0.1 °C.

4.1.1 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

16). Insert the Lemo connector into the GK-404 until it locks into place.

Figure 16 - 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 GK-404 Manual.)

The GK-404 will continue to take measurements and display readings until the unit is

turned off, either manually, or if enabled, by the Auto-Off timer.

For more information, consult the GK-404 manual.

4.2 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.

4.2.1 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).

4.2.2 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 on the handheld PC by tapping on “Start”, then “Programs”, then the GK-405 VWRA icon. After a few seconds, the blue light on the Remote Module should stop flashing and remain lit, indicating that the remote module has successfully paired with the handheld PC. The Live Readings Window will be displayed on the handheld PC. Figure 17 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 6 for troubleshooting suggestions. For further information consult the GK-405 Instruction Manual.

Figure 17 - Live Readings – Raw Readings

4.3 GK-403 Readout Box (Obsolete Model)

The GK-403 can store gage readings as well as 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.

4.3.1 Connecting Sensors

Connecting Sensors with 10-pin Bulkhead Connectors Attached:

Connecting Sensors with Bare Leads:

4.3.2 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 5.1.) The last digit may change one or two digits while reading.

4) The thermistor reading will be displayed above the gage reading in degrees

centigrade.

5) Press the "Store" button to record the value displayed.

If the no reading displays or the reading is unstable, see Section 6 for troubleshooting suggestions.

The unit will automatically turn off after approximately two minutes to conserve power.

4.4 Measuring Temperatures

All vibrating wire piezometers are equipped with a thermistor that 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 14.7 ohms per one thousand feet. Multiply this factor by two to account for both directions.)

2) Look up the temperature for the measured resistance in Appendix B, Table 7. For high

temperature models use Appendix C, Table 8.

4.5 Checking the Calibration

The following procedure can be used to verify the calibration factor as supplied on the calibration sheet:

1) Saturate the filter stone and fill the space between it and the diaphragm with water (see

Section 2.1).

2) Lower the piezometer to the bottom of a water-filled borehole using the cable to measure the

actual depth.

3) Allow 15 to 20 minutes for the piezometer to come to thermal equilibrium.

4) Using a readout box record the reading at that level (see Section 4 for readout instructions).

5) Raise the piezometer a known amount and record the reading.

6) Calculate the calibration factor using the change in pressure and the reading.

7) Compare to the calibration sheet value. The two values should agree within ±0.5%.

When doing this test please be aware that the actual water level inside the borehole might change due to displacement of water by the different lengths of submerged cable. This is especially critical where the cable length is long and the borehole diameter small. Allowing sufficient time for the water level to equilibrate may solve this problem, or keep the borehole filled to the top.

Figure 18 - Sample Calibration She e t

5. DATA REDUCTION

5.1 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 =

󰇡

Period

x 10-3 or Digits=

󰇢







Equation 1 - Digits Calculation

For example, a piezometer reading 8000 digits corresponds to a period of 354 µs 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

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 18, 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 that 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 →

psi

.036127

.43275

.0014223

1.4223

.49116

.019337

14.696

.014503

14.5039

.14503

145.03

"H2O

27.730 1 12

.039372

39.372

13.596

.53525

406.78

.40147

401.47

4.0147

4016.1

'H2O

2.3108

.08333

.003281

3.281

1.133

.044604

33.8983

.033456

33.4558

.3346

334.6

mm H20

704.32

25.399

304.788

1000

345.32

13.595

10332

10.197

10197

101.97

101970

m H20

.70432

.025399

.304788

.001

.34532

.013595

10.332

.010197

10.197

.10197

101.97

"HG

2.036

.073552

.882624

.0028959

2.8959

.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

.000986

.98692

.009869

9.869

mbar

68.947

2.4908

29.8896

.098068

98.068

33.863

1.3332

1013.2

1000

10000

bar

.068947

.002490

.029889

.0000981

.098068

.033863

.001333

1.0132

.001 1 .01

kPa

6.8947

.24908

2.98896

.0098068

9.8068

3.3863

.13332

101.320

100

1000

MPa

.006895

.000249

.002988

.0000098

.009807

.003386

.000133

.101320

.0001

.001

↓

psi

"H2O

'H2O

mm H20

m H20

"HG

mm HG

atm

mbar

bar

kPa

MPa

Table 2 - Engineering Units Multiplication Factors

(Note: Due to changes in specific gravity with temperature, the factors for mercury and water in the above table are approxi m ati ons.)

5.2 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

4.4 for instructions regarding obtaining the piezometer temperature.

The temperature correction equation is as follows:

Temperatur e Correction =

(Current Temperature - Initial Temperature) × Therm a l Factor

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.

PT = (T1-T0) x K

Equation 3 - Temperature Correction

5.3 Barometric Correction (required only on unvented transducers)

Since the standard piezometer is hermetically sealed and unvented, 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 ≈1 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. A separate pressure transducer (piezometer), kept out of the water, may be used for this purpose.

The barometric correction equation is as follows:

Barometric Correction =

(Current Barometer - Initial Barometer) × Convers ion Factor

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.

Equation 5 shows the pressure calculation with temperature and barometric correction applied.

corrected

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 that is not required. In these cases, Geokon recommends 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 correction is to use piezometers that are vented to the atmosphere. See Section 5.4.

= (R1 – R0)G + (T1-T0) K - (S1-S0) F

Equation 5 - Corrected Pressure Calculation

5.4 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 (integral 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 can find its way into the inside of the transducer and ruin it.

In order to keep the desiccant fresh during storage and transportation, the outer end of the desiccant chamber is closed by means of a seal screw when 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.

5.5 Environmental Factors

Since the purpose of the piezometer installation is to monitor site conditions, factors that 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.

6. TROUBLESHOOTING

Maintenance and troubleshooting of vibrating wire piezometers is confined to periodic checks of cable connections and maintenance of terminals. The transducers themselves are sealed and are not user serviceable. Gages should not be opened in the field.

Should difficulties arise, consult the following list of problems and possible solutions. For additional troubleshooting and support, contact Geokon.

Symptom: Thermistor resistance is too high

 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 3.3.

Symptom: Thermistor resistance is too low

 A short is likely. Check all connections, terminals, and plugs. If a short is located in the

cable, splice according to instructions in Section 3.3.

 Water may have penetrated the interior of the piezometer. There is no remedial action.

Symptom: Piezometer reading unstable

 Make sure the shield drain wire is connected to the blue clip on the flying leads. (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 electrical noise such as motors, generators, antennas, or

electrical cables. Move the piezometer cable away from these sources 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. If the resistance is very low, the gage conductors may be shorted.

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; Table 4 is provided for the customer to fill in the actual resistance found. Cable resistance is approximately 14.7Ω per

1000' of 22 AWG wire. Multiply this factor by two to account for both directions. 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 3.3.

 Check the readout with another gage to ensure it is functioning properly.  The Piezometer may have been overranged or shocked. Inspect the diaphragm and housing

for damage.

≅180Ω

3000Ω

25°C

3000Ω

25°C

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

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

infinite

Green

Shield

Table 4 - Resistance Work Sheet

Model

4500S

4500AL1

4500B

4500C

45802

Available

0-50

0-15000

0-5

0-50

0-1

Resolution

0.025% FS

0.05% FS

0.01% FS

Linearity

0.5% FS3

Accuracy

0.1% FS4

0.1% FS

Overrange

1.5 x Rated Pressure

Thermal

Coefficient

<0.025% FS/

°C

<0.05% FS/

°C

<0.025% FS/

°C

<0.05% FS/

°C

<0.025% FS/

°C

.75"

19.05 mm

25.40 mm

.687"

17.45 mm

.437"

11.10 mm

1.5"

38.10 mm

5.25"

133.35 mm

5.25"

133.35 mm

5.25"

133.35 mm

6.5"

165.10 mm

6.5"

165.10 mm

Frequency

Range Hz

Vibrating Wire Gage +

Red

Vibrating Wire Gage -

Black

Thermistor

White

Thermistor

Green

Cable Shield

Shield

F-K

Not Used

APPENDIX A. SPECIFICATIONS

Ranges

(psi)

Length

0-100 0-150 0-250 0-500

0-750 0-1000 0-1500 0-3000 0-5000

0-10000

0-10 0-25

0-100 0-250

0-5

Accuracy of Geokon test apparatus: 0.1% Contact Geokon for specific application information. Notes:

1 2 3 4

A.1 Standard Piezometer Wiring

1400-3500 1400-3500 1400-3500 1400-3500 1400-3500

Table 5 - Vibrating Wire Piezometer Specifications

Accuracy of test apparatus: 0.05% Other ranges available upon request.

0.1% FS linearity available upon request. Derived using second order polynomial.

Pin Function Wire Color

Table 6 - Standard Piezometer Wiring

Ohms

Temp

Ohms

Temp

Ohms

Temp

Ohms

Temp

Ohms

Temp

201.1K

-50

16.60K

-10

2417

+30

525.4

+70

153.2

+110

187.3K

-49

15.72K

-9

2317

507.8

149.0

111

174.5K

-48

14.90K

-8

2221

490.9

145.0

112

162.7K

-47

14.12K

-7

2130

474.7

141.1

113

151.7K

-46

13.39K

-6

2042

459.0

137.2

114

141.6K

-45

12.70K

-5

1959

444.0

133.6

115

132.2K

-44

12.05K

-4

1880

429.5

130.0

116

123.5K

-43

11.44K

-3

1805

415.6

126.5

117

115.4K

-42

10.86K

-2

1733

402.2

123.2

118

107.9K

-41

10.31K

-1

1664

389.3

119.9

119

101.0K

-40

9796 0 1598

376.9

116.8

120

94.48K

-39

9310

1535

364.9

113.8

121

88.46K

-38

8851 2 1475

353.4

110.8

122

82.87K

-37

8417 3 1418

342.2

107.9

123

77.66K

-36

8006 4 1363

331.5

105.2

124

72.81K

-35

7618 5 1310

321.2

102.5

125

68.30K

-34

7252 6 1260

311.3

99.9

126

64.09K

-33

6905 7 1212

301.7

97.3

127

60.17K

-32

6576 8 1167

292.4

94.9

128

56.51K

-31

6265 9 1123

283.5

92.5

129

53.10K

-30

5971

1081

274.9

90.2

130

49.91K

-29

5692

1040

266.6

87.9

131

46.94K

-28

5427

1002

258.6

85.7

132

44.16K

-27

5177

965.0

250.9

83.6

133

41.56K

-26

4939

929.6

243.4

81.6

134

39.13K

-25

4714

895.8

236.2

79.6

135

36.86K

-24

4500

863.3

229.3

77.6

136

34.73K

-23

4297

832.2

222.6

75.8

137

32.74K

-22

4105

802.3

216.1

73.9

138

30.87K

-21

3922

773.7

209.8

72.2

139

29.13K

-20

3748

746.3

203.8

100

70.4

140

27.49K

-19

3583

719.9

197.9

101

68.8

141

25.95K

-18

3426

694.7

192.2

102

67.1

142

24.51K

-17

3277

670.4

186.8

103

65.5

143

23.16K

-16

3135

647.1

181.5

104

64.0

144

21.89K

-15

3000

624.7

176.4

105

62.5

145

20.70K

-14

2872

603.3

171.4

106

61.1

146

19.58K

-13

2750

582.6

166.7

107

59.6

147

18.52K

-12

2633

562.8

162.0

108

58.3

148

17.53K

-11

2523

543.7

157.6

109

56.8

149

Table 7 - Thermistor Resistance versus Temperature

55.6

150

APPENDIX B. THERMISTOR TEMPERATURE DERIVATION

Thermistor Type: YSI 44005, Dale #1C3001-B3, Alpha #13A3001-B3 Resistance to Temperature Equation:

A+B(LnR)+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.

-273.2

Temp

(ohms)

LnR

LnR3

Calculated

Temp

Diff

Error

Temp

(ohms)

LnR

LnR3

Calculated

Temp

Diff

Error

-30

113898

11.643

1578.342

-30.17

0.17

0.06

120

407.62

6.010

217.118

120.00

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

-20

65805

11.094

1365.581

-20.12

0.12

0.04

130

320.21

5.769

191.998

130.00

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

-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

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

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

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

12423

9.427

837.843

14.98

0.02

0.01

165

148.83

5.003

125.210

165.08

-0.08

-0.03

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

8200

9.012

731.893

25.00

0.00

175

122.1

4.805

110.927

175.08

-0.08

-0.03

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

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

4592

8.432

599.519

40.02

-0.02

-0.01

190

92.086

4.523

92.512

190.09

-0.09

-0.03

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

3202.92

8.072

525.913

50.01

-0.01

200

77.088

4.345

82.026

200.05

-0.05

-0.02

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

2276.32

7.730

461.946

60.02

-0.02

-0.01

210

64.985

4.174

72.729

210.00

0.00

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

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

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

1211.14

7.099

357.808

80.00

0.00

230

47.142

3.853

57.207

229.82

0.18

0.06

1044.68

6.951

335.915

85.00

0.00

235

43.673

3.777

53.870

234.77

0.23

0.08

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

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

250

35.055

3.557

45.001

249.54

0.46

0.16

105

598.44

6.394

261.447

105.00

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

260

30.496

3.418

39.917

259.34

0.66

0.23

115

461.91

6.135

230.952

115.00

0.00

APPENDIX C. HIGH TEMPERATURE THERMISTOR LINEARIZATION

High Temperature Thermistor Linearization using Stein-Hart Log Equation

Thermistor Type: Thermometrics BR55KA822J Resistance to Temperature Equation:

A+B(LnR)+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.

-273.2

Table 8- Thermistor Resistance versus Temperature for High Temperature Models

APPENDIX D. IMPROVING THE ACCUR ACY OF THE CALCULATED PRESSURE

Most vibrating wire pressure transducers are sufficiently linear (±0.2 % FS) 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:

Pressure = AR2 + BR + C

Equation 8 - Second Or de r Polynomial Expression

Where;

R is the reading (digits channel B) A, B, and C are coefficients

Figure 18 shows a typical calibration sheet of a transducer that has fairly normal nonlinearity. The figure under the “Linearity (%FS)” column is

1-R0

F.S.

)

-P x 100%

Calculated Pressure-True Pressure

G(R

x 100%=

Full Scale Pre ssure

Equation 9 - Linearity Calculation

Note: The linearity is calculated using the regression zero for R0 shown on the sheet.

For example when P= 420 kPa, G (R1 – R0) = - 0.1795(6749-9082), gives a calculated pressure of 418.8 kPa. The error is 1.2 kPa equal to 122 mm of water.

Whereas the polynomial expression gives a calculated pressure of A (6749)2 + B (6749) + 1595.7 = 420.02 kPa and the actual error is only 0.02 kPa or two millimeters 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 2.3. 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)2 + B(9074) from which C = 1595.7

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.

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