Geokon 4500MLP User 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.
Copyright © 2003-2017 by Geokon, Inc.
(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
2.1 SATURATING THE FILTER STONE..........................................................................................................................3
2.2 SWAGELOK TUBE FITTING INSTRUCTIONS............................................................................................................3
2.2.1 Installation....................................................................................................................................................3
2.2.2 Reassembly Instructions...............................................................................................................................4
2.3 ESTABLISHING AN INITIAL ZERO READING...........................................................................................................5
3. INSTALLATION ....................................................................................................................................................7
3.1 GROUTING REQUIREMENTS...................................................................................................................................7
3.2 BOREHOLE INSTALLATION ...................................................................................................................................8
3.2.1 The Drop Weight Method.............................................................................................................................8
3.2.2 Pneumatic Cutter Method.............................................................................................................................9
3.2.3 Pull-Pin Method .........................................................................................................................................12
3.3 SPLICING AND JUNCTION BOXES ........................................................................................................................12
3.4 LIGHTNING PROTECTION ....................................................................................................................................14
4. TAKING READINGS...........................................................................................................................................15
4.1 GK-404 READOUT BOX......................................................................................................................................15
4.1.1 Operating the GK-404................................................................................................................................15
4.2GK-405 READOUT BOX......................................................................................................................................16
4.2.1 Connecting Sensors ....................................................................................................................................16
4.2.2 Operating the GK-405................................................................................................................................16
4.3 GK-403 READOUT BOX (OBSOLETE MODEL).....................................................................................................17
4.3.1 Connecting Sensors ....................................................................................................................................17
4.3.2 Operating the GK-403................................................................................................................................17
4.4 MEASURING TEMPERATURES .............................................................................................................................18
4.5CHECKING THE CALIBRATION ............................................................................................................................18
5. DATA REDUCTION ............................................................................................................................................20
5.1 PRESSURE CALCULATION ...................................................................................................................................20
5.2 TEMPERATURE CORRECTION..............................................................................................................................21
5.3 BAROMETRIC CORRECTION (REQUIRED ONLY ON UNVENTED TRANSDUCERS)....................................................22
5.4 VENTED PIEZOMETERS .......................................................................................................................................23
5.5 ENVIRONMENTAL FACTORS................................................................................................................................23
6. TROUBLESHOOTING........................................................................................................................................24
APPENDIX A. SPECIFICATIONS.........................................................................................................................26
A.1STANDARD PIEZOMETER WIRING ......................................................................................................................26
APPENDIX B. THERMISTOR TEMPERATURE DERIVATION.....................................................................27
APPENDIX C. HIGH TEMPERATURE THERMISTOR LINEARIZATION..................................................28
APPENDIX D. IMPROVING THE ACCURACY OF THE CALCULATED PRESSURE...............................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 FOR 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
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.

2
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
Figure 2 - Close up of 4500MLP

3
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.

4
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.
Figure 7 - Marks for Reassembly
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.

5
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.

6
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.)

7
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.
50 PSI Grout for Medium
to Hard Soils
4 PSI Grout for Soft Soils
Amount
Ratio by
Weight
Amount
Ratio by
Weight
Water
30 gallons
2.5
75 gallons
6.6
Portland
Cement
94 lb. (one sack) 1 94 lb. (one sack) 1
Bentonite 25 lb. (as required) 0.3 39 lb. (as required) 0.4
NOTES:
The 28 day compressive strength of this mix
is about 50 psi, similar to very stiff to hard
clay. The modulus is about 10,000 psi
The 28-day strength of this
mix is about four psi,
similar to very soft clay.
Table 1 - Cement/Bentonite/Water ratios
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.

8
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 Method

9
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.
Figure 11 - 4500MLP Pre-release
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.)

10
When the desired elevation is reached, the cutting tool is activated by connecting the
pneumatic tube from the piezometer to a bottle of CO2. (CO2can 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

11
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.

12
3.2.3 Pull-Pin Method
In this method, the piezometer assembly is held in its closed position by means of a pull-
pin. 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.

13
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 multi-
conductor 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

14
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