Diver-operated buried pipe and chain locator

WAVY
PCE L_

Tech Va te
N-1858

May 1993
NI = By H. Thomson

Sponsored By Naval Facilities

Technical Note Engineering Command

TA
Sa
NZ

Nis58

DIVER-OPERATED
BURIED PIPE AND CHAIN
LOCATOR

ABSTRACT A prototype system has been developed for use by

the Navy Underwater Construction Teams (UCTs) in locating submerged
ferrous objects (such as pipelines and mooring chain). The system con-
sists of a commercially available magnetometer modified to meet the UCT
mission requirements. The magnetometer, a fluxgate sensor built for
terrestrial use, is manufactured by Forster Instruments, Incorporated. The
sensor was modified to be used underwater by divers, or dipped (slow
towed) from a small inflatable boat. This report documents the develop-
ment of this prototype tool, called the Diver-Operated Buried Pipe and
Chain Locator.

en

en

CIVIL ENGINEERING LABORATORY PORT HUENEME CALIFORNIA 93043-4328

Distribution limited to U.S. Government agencies and their contractors; Research and Development, May 1993.
Other requests for this document must be referred to the Naval Civil Engineering Laboratory,
Port Hueneme, California.

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SUOLOVA NOISUAANOOD OIMLAW

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1. AGENCY USE ONLY (Leave blank) 2, REPORT DATE 3. REPORT TYPE AND DATES COVERED

May 1993 Final: FY83 through FY92

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

DIVER-OPERATED BURIED PIPE AND CHAIN
LOCATOR

PR - Y1606-SL-01-001-A600
6 AUTHOR(S) WU - DN387346

H. Thomson

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESSE(S) 8. PERFORMING ORGANIZATION
REPORT NUMBER

Naval Civil Engineering Laboratory
560 Laboratory Drive TN - 1858
Port Hueneme, CA 93043-4328
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESSE(S) 10, SPONSORING/MONITORING
AGENCY REPORT NUMBER
Naval Facilities Engineering Command
Alexandria, VA 22332

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE
Distribution limited to U.S. Government agencies and their

contractors; Research & Development, May 1993. Other requests

for this document shall be referred to NCEL.

13. ABSTRACT (Maximum 200 words)

A prototype system has been developed for use by the Navy Underwater Construction Teams (UCTs) in locating
submerged ferrous objects (such as pipelines and mooring chain). The system consists of a commercially available
magnetometer modified to meet the UCT mission requirements. The magnetometer, a fluxgate sensor built for
terrestrial use, is manufactured by Forster Instruments, Incorporated. The sensor was modified to be used underwater
by divers, or dipped (slow towed) from a small inflatable boat. This report documents the development of this
prototype tool, called the Diver-Operated Buried Pipe and Chain Locator.

wom

14. SUBJECT TERMS 15. NUMBER OF PAGES

Magnetometer, fluxgate, pulse induced 60

16. PRICE CODE

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. UMITATION OF ABSTRACT
OF REPORT OF THIS PAGE OF ABSTRACT

Unclassified Unclassified Unclassified UL

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)
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CONTENTS

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BACKGROUND? F20ssor ais OF Wit THAN ACHES ET RORE TLE COPS CONEY,
ADVANCED DEVELOPMENT MODEL (ADM) SYSTEM ..............
Equipment Descriptionie gamete Livre. vrcuicks suctans Fmt clio Maka ter lan seeetolee
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Conclusions and Recommendations from the ADM Tests ............
ENGINEERING DEVELOPMENT MODEL (EDM) SYSTEM ............
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CONCLUSIONS Wr REF ON AECE, OR SURE NCEE MSE TTI OEE: TOES
RECOMMENDATIONS ill cca tnasvehe suai av euet outers een anie ten at coments kel one aleey eels
REDE RIENCES. haly ARE BME CORUTC EEOC, WO SUP OOR UND DMRS): CST
APPENDIXES

A - Component Description - Metal Detecting System
Mission and Required Operational Characteristics .............

B - Comparison of Physical Characteristics ....................
C - Detection Thresholds for Pulse-Induced Systems ..............

D - Detection Thresholds for Forster Ferex ...............2.+e8.

D-1

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INTRODUCTION

Under the sponsorship of the Naval Facilities Engineering Command (NAVFAC), the
Naval Civil Engineering Laboratory (NCEL) has developed a metal detecting system. This
system was developed for use by the Underwater Construction Teams (UCTS) to locate buried
or submerged metallic pipe, chain, anchors, and miscellaneous ferrous objects. The tool is a
marinized Forster Ferex magnetometer (Model 4.021) and is designed for use in either a dipping
mode (from an inflatable boat) or a self-contained diver-operated mode.

Attributes of the system include the following:

3

Zs

Visual and audio output.

Adjustable sensitivity.

Adjustable standoff device between the magnetic sensor and the operator.
Rechargeable battery-powered system (each set lasts up to 6 hours).

Minimal maintenance at the UCT level (the unit is sealed and will not be broken

down for repairs or overhaul except by the Depot maintenance activity Ocean
Construction Equipment Inventory (OCEI) or manufacturer).

This report documents the development of the Diver-Operated Buried Pipe and Chain
Locator (BP&CL), and provides documentation to support the production milestone decision.

BACKGROUND

An efficient, safe, and reliable metal detecting system for UCT use is required to provide
underwater detection and tracking of the following items:

Ile

De

oe

4.

Chain (1-1/2 inches or larger) buried up to 6 feet.
Pipelines buried up to 2-1/2 feet.
Anchors (6,000 pounds) buried up to 10 feet.

Armored cable (SD List 5) buried up to 3 feet.

In the past, several types of diver-operated systems have been investigated and developed
for use by Naval Underwater Demolition Team (UDT) and Explosive Ordnance Disposal (EOD)
divers. These include the MK-14 magnetometer, a cesium vapor magnetometer, and the MK-10
gradiometer. However, these developments were tailored to the special requirements of ordnance

l

work (i.e., low magnetic signatures and detection of nonferrous materials). In addition, these
systems typically require specialized training and diving equipment that is not readily available
to the UCTs.

To provide a suitable system for UCT use, an investigation of specific UCT requirements
and an evaluation of both military and commercially available systems were performed.
Appendix A lists the Test and Evaluation Master Plan (TEMP) thresholds for the BP&CL.

To identify candidate metal detecting systems and technologies suitable for UCT use, a
literature survey of metal detecting systems was performed by NCEL. This survey, documented
in Reference 1, encompassed both active and passive military and commercially available systems
and identified several promising candidate systems that appeared to be suitable for UCT use.
These systems were:

@ Navy MK-10
@ Garrett XL500

@ Fisher Pulse 10

Fisher Pulse 8
@ White’s PI-1000
@ Forster Ferex 4.021

Figure 1 shows the family of metal detecting systems.

The MK-10 is a portable diver-held fluxgate magnetometer designed as an ordnance
locator. It has been in service since the early 1960s. However, the Navy EOD community has
experienced extreme difficulties in keeping sufficient units operating (Ref 2) and is in the process
of phasing this system out.

The Garrett, Fisher, and White’s units are commercially available pulse-induced systems.
With the exception of the Fisher Pulse 10, these systems were developed primarily for the
treasure or sport diver. The Pulse 10 is a boat-towed system.

The Forster Ferex 4.021 is a magnetometer designed for terrestrial use. UCT-ONE has
used this system with some limited success to locate a 12,000-pound anchor at the Naval
Weapons Station, Earle, New Jersey. It was reported (Ref 3) that one of three buried anchors
was located using this system. However, only the probe can be submerged. The power and
control modules are not submersible.

To determine the suitability of these systems for UCT use, tests and evaluations of these
systems were performed at NCEL. The results of this evaluation are provided in the next section
of this report, Advanced Development Model (ADM) System. Based on the results of the ADM
testing, the Forster Ferex magnetometer was modified to provide enhanced performance for UCT
use. This development is documented in the Engineering Development Model (EDM) System
section of this report.

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ADVANCED DEVELOPMENT MODEL (ADM) SYSTEM

To evaluate the most promising candidates identified in the state-of-the-art survey (Ref
1), the following units were purchased for test and evaluation:

li. Garrett XL500

De Fisher Pulse 10

35 Fisher Pulse 8

4, White’s PI-1000

ah Forster Ferex 4.021

The Navy MK-10 system was not available for evaluation. A request to the Navy EOD
community for loan of an MK-10 indicated that there were relatively few of these units
operating.

The following is a description of the systems purchased for evaluation.

Equipment Description

Pulse-Induced Systems (Garrett XL500, Fisher Pulse 8, and White’s PI-1000). Pulse-
induced systems operate by intermittently pulsing an electric current into a coil, creating a high-
energy magnetic field. When a transmitted pulse encounters a metallic object, eddy currents
begin to flow in the metal, which in turn generates a second magnetic field. This field is sensed
by the coil, amplified, and then either displayed by a meter or heard in an earphone.

Figure 2 shows the Garrett XL500. It is supplied with either a 10-inch or a 13-inch coil.
The electronics package is detachable so that it can be worn on a belt. Control features include
the following:

Ie Detection Depth Setting - A three-position rotary switch for maximum, normal,
or minimum output.

2: Audio volume.
3: Trash Eliminator - A rotary switch for adjusting the discrimination level.

The Garrett has both audio and visual output. Headphones are provided for the audio output.
A meter located on the electronics package provides visual indication of the signal strength.
Figure 3 shows the Fisher Pulse 8. It comes with a 10-inch-diameter coil. Detection is
indicated to the diver by both a meter and tone (via an earphone). The electronics package can
be removed from its holder for servicing or replacement. Control features include the following:

Ihe Detection Depth Setting - A three-position rotary switch for selecting high,
medium, or low output.

A

U/W Earphone

Handle
Extensions

Caseholder

Figure 2
Garrett XL500.

Figure 3
Fisher Pulse 8.

Manufacturer:
Garrett Metal
Detectors, Tx.

Model:
XL500

Class:
Metal Detector

Sizes:
8 inch coil standard
13 inch coil optional

Power Supply:
Rechargeable
Batteries

Description:

Totally Submersible,
Diver Held

Manufacturer:

J. W. Fisher Manu-
facturing Co, Ma.

Model:
Pulse 8
Class:

Size:

Charger Power Supply:

Rechargeable Bat-

terles

Description:

Totally Submersible,

Diver held

Metal Detector

10 inch dia. coil

De Zero Adjustment - A rotary switch for adjusting the discrimination level.
3F Battery check.

Figure 4 shows the White’s PI-1000. It comes with a 10-inch-diameter coil. Detection
is indicated to the diver by an audible clicking and by light-emitting diode (LED) display. It can
be powered by six "AA" alkaline or rechargeable batteries. Controls feature a rotary switch for
on/off operation, battery check, and tuning/zeroing.

Magnetometer (Forster Ferex 4.021). A fluxgate magnetometer is made up of a coil
of wire wound around a highly permeable core. The core is driven in and out of saturation by
a low-frequency electrical signal. This saturation, which is affected by changes in the total
ambient magnetic field, is sensed by a separate winding and amplified to provide a signal to the
operator.

Manufacturer:
_ White's Or.

Model:
PI 1000 -

Class:
Pulse Induced

Sizes:
10 inches dia. coil

Power Supply:
Batteries

Description:
Totally Submersible,
Diver Held

Figure 4
White’s PI-1000:

The Forster Ferex 4.021 consists of two fluxgate magnetometers mounted in the opposite
ends of a probing bar. This unit is available in both land and underwater versions. The
underwater version, shown in Figure 5, is designed for use in bore-hole applications. The
system consists of a 24-inch-long submersible probe, extension cable, power supply, and a
control/signal strength indicator unit. The power and control units are not waterproof. Control
features include the following:

1. Sensitivity Dial - The sensitivity of the unit is adjustable between 3 gammas and
10,000 gammas.

2 Operating Mode Switch - The operating mode switch provides selection of one of
the following:

a. Normal searching.
b. Normal searching with some small ferrous metals damped out.
(Bs Special searching for searching next to large ferrous metal objects such as
pipes.
d. Compass to find north, south, east, and west.
de Sensitivity Test Switch - A momentary contact switch for checking proper
operation.

4, Battery Check - Located at the first position of the sensitivity dial.

Do Volume Control - Two momentary contact switches (up and down) for adjusting
the audio output of the probe.

Laboratory Tests

The objective of the laboratory tests was to provide initial performance data on the
candidate metal detecting systems. Three sets of laboratory tests were performed: (1) comparison
of physical characteristics, (2) sphere of detection tests, and (3) electronic characteristics analysis.
The results of these tests are summarized below.

Comparison of Physical Characteristics. The physical characteristics of each unit were
examined for general construction, human factors engineering, and maintenance. Table 1 lists
test results of the items measured or evaluated. Appendix B contains a discussion of qualitative
results.

Manufacturer:
Institute Dr. Forster,
West Germany

Side view
—————— =775 ————_} L* "Bee Sag
Hal - ; : 3
<p I 3 ties —— ts B
a =e See aiG— Model:
Plan view Sa | Ferex 4.021
Ballast Probe Sealing plug Rope Powersupply Control unit
Class:
Magnetometer
Size:
, 24" long probe
Carring bag W Two spanners — | &P
SW 41 Extension :
| cable, 30m Power Supply: _
@ Self contained
= rechargeable
batteries
Description:

Submersible Probe
Hand-Held/Boat-Towed

(a)

—

—=—_

The pulling rope is taped to the
extension cable approx. every 30 cm

(b) Using the Ferex from a boat.

Figure 5
Forster Ferex 4.021.

Table 1. Comparison of Physical Characteristics

Poot
Fai Fai
Poor
Good

"Includes only the sensing probe, electronics module, and power supply.
>Includes only the probe with 2 pounds ballast weight.

Detection Threshold. The objective of this test was to obtain baseline detection threshold
data on each unit in air. Figure 6 shows the test setup for the pulse-induced systems. As a
standard, twin 72 SCUBA tanks were used as the detection target by moving them toward the
detector from various angles. Upon initial detection of the tanks, the angle and distance of
detection were noted. Figure 7 shows the test setup for the Forster Ferex magnetometer. Since
proper operation requires that the probe be oriented with its major axis perpendicular to the
earth’s surface, these tests were conducted by lowering the probe toward the tanks until a half-
scale reading was obtained.

Appendix C contains detection thresholds of the pulse-induced systems plotted for coil
angles of 0 degrees, 45 degrees, and 90 degrees at the various power settings of each unit.
Appendix D shows detection thresholds of the Forster Ferex plotted for sensitivities of 100 and
300 gammas. The results of these tests showed the following maximum ranges for each of the
units in air:

i Forster Ferex - 7.0 feet (sensitivity switch set at 100 gammas)
De Fisher Pulse 8 - 5.7 feet

3 Garrett XL500 (with 13-inch coil) - 5.1 feet

4, Garrett XL500 (with 7-inch coil) - 2.7 feet

os White’s PI-1000 - 3.3 feet

ANGLE
DETECTION

METAL
DETECTOR

GROUND

Figure 6
Setup for testing the range of pulse-induced systems.

From the results of these tests, it is clear (in air at least) that larger detection distances can be
expected with the Forster Ferex unit.

Electronic Characteristics Analysis. The electronic characteristics of the pulse-induced
systems were analyzed in order to obtain a baseline comparison of common features. Several
of the characteristics examined include pulse width, response time, energy per pulse, and battery
life. Figure 8 shows a general block diagram for pulse-induced metal detecting systems. Table
2 summarizes the test results. In comparing these results with the results of the detection
threshold tests, the units with the larger signal output have the greater detection range. They also
have the shortest battery life. Also, the response time of the different units should be noted.
In comparison to the other units, the Fisher Pulse 8 has a very long response time. The long
response time is undesirable since the unit can easily miss a target unless the coil is moved very
slowly.

Ocean Tests

In January and February 1986, ocean tests of the four candidate metal detection systems
were conducted offshore of the West Jetty at the Naval Construction Battalion Center, Port
Hueneme, California. These tests were conducted to determine the detection capability of each
unit for buried chain (1-1/2 inch) and buried armored cable (3-1/2-inch diameter). No tests were
planned at this time for detection of an anchor (6,000 pounds) buried to 10 feet and armored
pipeline (5-inch diameter) buried to 2-1/2 feet.

10

u Ferex we
Measured i Control Instrumentation | ~
Distance and. Power Supply

“ddd

Figure 7
Setup for testing the range of the Forster Ferex.

TIMING TRANSMIT
CIRCUIT DRIVER

SAMPLE/
HOLD

BATTERY/
POWER RECEIVER/
SUPPLY AMPLIFIER

EARPHONES

Figure 8
Pulse-induction metal detector block diagram.

Table 2. Electronic Characteristics Analysis

Garrett XL500 White’s PI-1000 _ Sas Pulse 8
Output Pulse Width

Output Pulse 9.5 milliseconds 300 milliseconds 11.5 milliseconds
Repetition Rate

Energy Per Pulse 4.6 millijoules 25 millijoules 13.8 millijoules

BOWE USURRIY. 9.6 volts DC 9.0 volts DC 8.2 volts DC
Voltage
Power Supply 110 to 125 ee 310 to 325
approximately 100 approximately 500 approximately 200
Receiver | Receiver Sensitivity _| | unable to measure _| to measure

12 to 15 hours on
six nonrechargeable
"AA" batteries

9 hours on fully
charged batteries

4 hours on fully
charged batteries

Battery Life

12

In preparation for these tests, an underwater search range consisting of 1-1/2-inch chain,
3-1/2-inch armored cable, and twin 90 steel tanks was prepared in about 35 feet of water. These
targets were buried in sand approximately 30 feet apart from each other with floats attached for
identification. The targets were buried by fluidizing the soil around the target with a jetting
nozzle. Burial depths were estimated by measuring between the surface of the sand and
reference marks on the float line.

The test procedure consisted of swimming the range with the metal detecting device and
searching each target location. At sites where a target was located, the maximum detection
distance was estimated by raising the sensor above the target until its detection threshold was
reached. The detection depth was estimated by adding the distance between the sensor and the
seafloor to the burial depth of the target (estimated from the tape marks on the float line).

In addition to these tests, the Forster Ferex was used in the dipping mode to assess this
operating scenario. During these tests, the Ferex was used from an inflatable boat with the probe
submerged to within about 10 feet of the bottom. The distance off the seafloor was estimated
by periodically lowering the probe until slack appeared in the cable.

Results of the detection tests are shown in Table 3. Detection thresholds from the TEMP
are also listed for comparison. These tests show the following:

ile The detection ranges of commercially available pulse-induced systems cannot meet
the detection thresholds of the TEMP. In addition, several serious deficiencies were noted for
each system. These are as follows:

a. Garrett XL500 - Although this unit out-performed the other pulse-induced
systems, it did not have the ruggedness required for UCT operations. During these tests the arm
rest bracket broke off. In addition, the meter display was small and difficult to view. The
headphones were awkward to wear and had a tendency to slip off the head. The sound was also
muffled significantly when the headphones were worn over a diving hood.

b. Fisher Pulse 8 - This unit was difficult to zero (adjust to background
interference) because of the 2-second response time of the electronics. Proper adjustment of the
zero is important for optimum performance. If the zero is overadjusted, then the unit becomes
too sensitive and is susceptible to the detection of small, insignficant items. If the zero is
underadjusted, then the sensitivity of the unit is decreased, thereby decreasing the detection
distance. Once properly adjusted, the slow response time requires that the unit be moved very
slowly to avoid missing a target. In addition to the zeroing problem, the unit was awkward to
handle because the front end "planes" from side to side. This is because the front-end housing
of the sensing coil is shaped in a solid disk and therefore presents resistance to forward motion.
This motion further compounds the problem related to the slow response time of the electronics.

Cc. White’s PI-1000 - This unit could not be zeroed during these tests.
Subsequent inspection of this unit indicated that the detent mechanism on the main switch was
either broken or worn at the position for tuning/zeroing the unit. No further tests were
conducted with this unit since it generally lacks the integrity and ruggedness required for UCT
use.

13

Table 3. Metal Detecting Systems Testing Summary

Tank (Twin

72) Armored pice Armored

Laboratory Cable (3- Pipeline
Tests 1/2-Inch (6000
Diam)

Pounds) Roc

Dn The Forster Ferex unit has the greatest detection range among the systems tested.
As shown in Table 3, the Ferex unit met the TEMP threshold for detection of armored cable and
was within | foot of meeting the TEMP threshold for detection of chain. These tests were con-
ducted with the unit set at a sensitivity of 300 gamma. While the unit does have a greater
sensitivity (and presumably a greater detection distance), it was difficult to use at a higher
sensitivity for the following reasons:

a. The diver’s gear became a significant magnetic target. To reduce this
effect will require either nonmagnetic equipment for the diver or a standoff device (about 5 to
7 feet) between the probe and the diver.

b. Periodic adjustment (zeroing) is required and the diver does not have direct
access to the control instrumentation with the present configuration of the unit. Since the control
instrumentation is not waterproof, all tuning adjustments (such as selecting the operating mode
(mode 1, 2, or 3) and the sensitivity, as well as periodic compensation for background noise)
must be done at the surface by a remote operator rather than at the dive site by the diver. This
operating scenario can easily result in confusion (particularily at the higher sensitivity levels)
unless the diver and top-side operator know exactly what the other person is doing.

© Use of an earphone as the sole means to provide detection signals to the

diver is inadequate. Although the diver earphone provides a good general indication of target
strength, it does not adequately provide specific location information. This is because the tone

14

level does not change significantly when the unit is moving over a target (unless the probe is
moved very slowly over the exact magnetic center). By comparison, the meter located on the
control instrumentation swings from one extreme to the other (i.e., positive to negative) when
the sensor is moved over a target. This provides clear indication of the target location.

Results of the dipping test indicated that the Ferex used in this mode of operation
provides a system for general location of targets. This feature is clearly beneficial since it can
minimize diver time in the water. For use in this mode, the Ferex must be used at high sensi-
tivity levels since it is towed with the probe approximately 10 feet off the bottom. This requires
that a maximum distance be maintained between the probe and the boat since the boat can be a
significant magnetic target at high sensitivity levels. It was also noted that there is a tendency
for excess cable in the boat to become tangled and knotted. Snarling and entanglement of cable
in a small boat is a nuisance and a safety hazard, and can also result in damage to the electrical
conductors in the cable.

As shown in Table 3, the TEMP thresholds for detection of an anchor (6,000 pounds)
buried to 10 feet and armored pipeline (5-inch diameter) buried to 2-1/2 feet were not tested with
these systems. Based on the results of the laboratory and ocean tests, it appeared unlikely that
the pulse-induced systems in their current off-the-shelf form would meet these requirements.
However, the Forster Ferex appeared to have the capability for detecting these items. Table 4
shows the magnetic signature of SD cable (list 5), armored pipe (5-inch diameter), and a 6,000-
pound anchor at 5 feet, 4-1/2 feet, and 12 feet, respectively (Ref 1). Based on this information
and the results of the ocean tests, it appeared highly likely that the Forster Ferex could meet
these TEMP thresholds.

Table 4. Magnetic Signatures of SD Cable, 5-Inch Pipe, and 6,000-Pound Anchors

Burial Depth (ft) | Sensor Distance (ft) pee tae

SD List 5
S-Inch Pipe 2-12
6,000-Pound Anchor 3,055

Conclusions and Recommendations from the ADM Tests

1 Commercially available pulse-induced systems cannot satisfy the performance
requirements of the TEMP. Increasing the detection thresholds may be possible by modifying
these systems to incorporate a more powerful system with a larger sensing coil.

ae The Forster Ferex magnetometer had the greatest detection distance among the

units tested. Modification of this unit holds the most promise for providing a metal detecting
system suitable for UCT use.

15

Based on these results, the following recommendations were made for the Engineering
Development Model system:

le The Forster Ferex magnetometer should be modified for use in both dipping mode
(from an inflatable) and self-contained diver-operated mode. This system should also be
designed for quick and easy conversion between these two operating modes.

2 The dipping mode should incorporate a spring wound reel for paying-out and
handling the cable between the probe and the electronics module.

3) The self-contained diver-operated mode should incorporate ready access to all
control adjustments and a standoff mechanism between the sensors and the diver. No electronic
modifications are anticipated.

ENGINEERING DEVELOPMENT MODEL (EDM) SYSTEM

From May through August 1987, laboratory and ocean tests of the engineering
development model BP&CL were conducted to verify reliability and performance thresholds (as
specified in the Test and Evaluation Master Plan, TEMP) and identify any safety or human
factors deficiencies.

System Description

The EDM system consisted of a commercially available Forster Ferex (Model 4.021)
system modified for use by the UCTs. Modifications to the magnetometer consisted of new
waterproof housings and accessories for use in two different operational modes: (1) as a dipping
mode from an inflatable boat, and (2) as a self-contained, hand-held diver tool. Figure 9
illustrates the two operational modes.

The stock Forster Ferex 4.021 magnetometer is designed to sense anomalies in the earth’s
magnetic field resulting from the presence of a ferrous object. To sense the anomaly, the
magnetometer uses two fluxgate sensors located a fixed distance from each other inside a
cylindrical probe. The output from the fluxgate sensors are processed and converted to provide
the operator with both audible and visual signals. As the magnetic field disturbance increases,
the intensity of the signal output increases. The visual output is a meter with an indicator needle
that shows increasing signal strength by moving off-center to the nght or left depending on the
polarity of the section that the probe is approaching. As the probe is passed over the object, the
needle swings across the meter to indicate signal strength in the opposite polarity. The earphone
indicates increasing signal strength by increasing the frequency of the audio output.

Standard control features of the Forster Ferex 4.021 magnetometer include the following:

It Mode Selector Switch - Any one of four different search functions can be selected
with this switch. Mode 1 is for normal searching of all ferrous metals. Mode 2 is also for
normal searching but eliminates disturbances from small ferrous objects. Mode 3 is used when
searching next to a large ferrous object (such as a pipeline). Mode 4 allows the tool to be used
as a magnetic compass.

16

Figure 9
Two operational modes for the buried pipe and chain locator.

3 Compensation Switch - The compensation switch is used to "zero" the instrument
in operating modes | and 2. This feature compensates for magnetic noise at a search site by
resetting the output to read zero.

3s Test Switch - The test switch is used to check for proper operation of the system.

4, Sensitivity Selector Switch - The sensitivity switch is used to select one of eight
sensitivity levels between 0.3 to 1,000 gammas.

Do Volume Switch - The volume control switch regulates the output level of the
audible signal.

Modifications to the existing system consisted of reconfiguring the tool for use in both
the dipped mode (from an inflatable boat) and a diver-held mode. The modifications included
new, waterproof housings for the control electronics and batteries, a telescoping standoff device
(to maintain distance between the diver’s gear and the sensing probe), and a cable reel for using
the probe in the dipped mode. Figure 10 shows the EDM BP&CL.

Reliability Tests

Reliability is expressed as the probability that the BP&CL will perform its functions
without failure within performance characteristics for a-4-hour mission. The threshold reliability
specified for this tool by the TEMP is 90 percent.

The mean time between failure (MTBF) is an estimate of the true system reliability based
on the mission time and threshold reliability. To assure that the test duration will verify the
system reliability, a confidence level multiplier is applied to the MTBF estimate. Table 5
summarizes the required test durations for confidence levels of 60, 80, and 90 percent. The
number of failures recorded within the test period determines the confidence level achieved at
90 percent reliability. Based on this information, a 98-hour test period with no failures is
required to demonstrate a 90 percent reliability with 90 percent confidence for a MTBF of 42
hours.

Table 5. Reliability Test Time Required

MTBF (hours) Confidence Test Time (hours)
re

42.4 60 130
42.4 A as 180
42.4 97 160 220

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19

Table 6 shows the results of the reliability tests. No failures in over 107 hours of
operation were observed, demonstrating a reliability greater than 90 percent with 90 percent
confidence for a MTBF of 42 hours. The test was interrupted only once a day for replacement
of batteries.

Two items requiring minor modification were identified during these tests: the sensitivity
switch and the low battery indicator system. The sensitivity switch is a "break before make"
type that sometimes tums the output volume off when changing sensitivity levels. Since this
does not affect completion of the mission (the operator simply readjusts the volume), this item
was not categorized as a failure. However, a more suitable switch will be used on the
preproduction models.

The low battery indicator system monitors the battery voltage and provides early warning
to the operator when the battery is getting low. During the initial part of these tests, the indicator
system was only providing about 2 to 3 minutes warning before the system would quit working.

Table 6. Reliability Summary

: Test Hours ae
Completed
Volume level sometimes affected by changing sensitivity levels.
2 20.6 Battery voltage low. Low battery indicator not yet lit. Battery
test functioning and shows a low battery condition.
New batteries installed.
Battery voltage low. Low battery indicator not yet lit.
5 64.5 New batteries installed. Battery life was 43.9 hours. Note: No
audio output was generated during this period of battery use.
meee | 105.1 Battery voltage low.
7 107.5 New batteries installed. Battery life was 43.0 hours. Note: No
. audio output was generated during this period of battery use.
Pe 107.5 Reliability testing completed.

This problem was corrected during the testing by changing a resistor value in the low battery
circuit. About 30 minutes of operation is available after the low battery indicator light comes
on.

Operational Effectiveness
To determine the operational effectiveness of the BP&CL, both laboratory and ocean tests

were conducted. The objective of the laboratory tests was to establish detection thresholds for
the BP&CL. The effects of sand on the detection distance of buried objects were also

20

investigated. The ocean tests were performed to verify performance under operational conditions
and to identify any safety or human factor deficiencies.

Laboratory Tests. The objective of the laboratory tests was to verify the detection
thresholds specified in the TEMP. Table 7 lists the TEMP detection thresholds for SD List 5
cable, armored Simplex Pipe, 1.5-inch chain, and a 6,000-pound anchor.

Table 7. Vertical Detection Distances

TEMP Hee Ge ty an (ft)
Detection ensitivity Level (gamma)

Threshold Sah an ea Dae ioae

Pipe (5-inch)

Simplex with

Armor

inch)

CHO Set OO | Oe) SO a SHG

Pounds)

gro] [Leos [| fe

In theory, the sand or water covering a buried ferromagnetic object should not greatly
affect the detection distance (provided this covering has a relatively undetectable magnetic
signature of its own). To verify this, the detection thresholds for an SD List 5 cable section
(about 7 feet long) and 3/4-inch chain were measured while they were buried in sand and lying
on the beach surface.

The results of this test confirmed that the individual detection distances of the SD List 5
cable and the 3/4-inch chain were the same whether the objects were buried or lying on the sand.
The detection threshold for both the buried and unburied cable was 36 inches with the tool set
for a sensitivity of 100 gammas. The detection threshold for both the buried and unburied chain
was 20 inches with the tool set for a sensitivity of 100 gammas.

Based on the above results, the detection thresholds for the buried objects listed in the
TEMP were determined in the laboratory by measuring the vertical distance between the probe
and the object with the object lying on a bed of sand. These tests were performed by lowering
the probe directly over the target for each sensitivity level until a half-scale deflection of the
meter was observed. The vertical distance between the probe and the target was then recorded
for each sensitivity setting.

21

The results of these tests and TEMP threshold values are shown in Table 7. These results
show that the BP&CL met or exceeded all of the detection distance thresholds specified in the
TEMP.

During these tests, it was observed that a slight swinging of the probe produced detection
ranges that were greater than those possible with the probe hanging still over the target. With
the probe hanging still over the target, increasing signal strength is indicated by an increase in
the deflection of the indicator needle. As the probe is moved over the object, the indicator
needle swings from one polarity to the other. The motion of the indicator needle swinging from
one polarity to the other provides a better indication of the presence of the object than a slowly
increasing needle deflection.

In performing these tests, the accuracy of locating the position of the target was also
evaluated. The TEMP specifies an accuracy of 1 foot or the depth of burial, whichever is
greater. Because the indicator needle swings from one polarity to the other as the midpoint of
the object is crossed, the accuracy of locating the target is very good. Based on these tests, the
accuracy of locating the target is estimated to be within the TEMP specifications.

Ocean Tests. The objectives of the ocean tests were to verify the operational
performance of the system and to identify any safety or human factor deficiencies. These tests
were conducted offshore Port Hueneme, California, with dive support provided by the NCEL
dive locker.

To verify the operational performance of the system, both the dipping mode and diver-
held mode of operation were tested from an inflatable boat. Prior to beginning the test, a 7-foot
length of SD List 5 cable and a 6-foot length of 3/4-inch chain were positioned on the ocean
floor in approximately 35 feet of water. The chain was stretched out in a line to produce a line
source target (as opposed to a point source for a pile of chain). The relative positions of the tar-
gets were recorded using visual sightings.

To verify the operational performance of the system in the dipping mode, the system was
assembled for operation in the inflatable boat (at the test site) and suspended in the water column
while the boat performed a slow speed grid pattern search. The probe was positioned about 3
feet off the seafloor during this search by periodically lowering it to get slack and then reeling
in 3 feet of cable. To aid in towing the probe, a 2-pound brass weight was attached to the end
of the probe.

While executing this search pattern, both the cable and the chain were located with a
sensitivity setting of 10 gammas. In both cases, the meter polarity was observed to change as
the probe passed over the target.

To verify the location of the target, the system was converted on site (in the inflatable)
to the diver operation mode and used by the divers to pinpoint and provide positive identification
of the target. To locate objects on the seafloor, the divers were given about 1/2 hour of
instruction prior to the operation. Locating objects in the diver operation mode requires the diver
to conduct an iterative procedure of rotating 360 degrees (with the probe extended outward),
observing the direction of the largest magnetic signature, and following the direction of the
largest magnetic signature until he finds the object or travels 20 to 30 feet. Using this technique,
both divers were readily able to find both targets in water with visibility of about 5 feet. In one
case, the diver reported that he walked right by the target without seeing it but observed that he
passed it by the change in the meter polarity.

After completing the above tests, the operators were asked to complete a human factors
evaluation form on the system. In general, the tool qualities were judged to be suitable for use

22

by the UCTs. One of the divers felt the probe end of the telescoping rod was slightly heavy and
could use a small amount of buoyancy (less than 2 pounds). This addition would make the tool
almost neutrally buoyant in the water and easier to handle and operate.

Two of the divers commented on the need for diver training in the operation of the tool.
Neither felt the amount of training required would be excessive, perhaps an hour or so of
instruction in its use, restrictions, operating procedure, and search techniques. In addition, many
of the operators commented that the audio output turned off at least once when they switched
sensitivity settings.

Controls were judged easy to operate and located properly for a hand-held tool. In the
2- to 3-foot visibility, the display could be seen and the individual LEDs were distinguishable.
One diver commented that the green color of the display LEDs might be more difficult to see
under certain limited visibility conditions than a red display.

None of the divers felt the need to increase the length of the standoff because of
interference from ferromagnetic items of their scuba gear. One diver commented that he was
able to swim with the tool as he operated it.

High/Low Temperature Testing. To verify the operation and performance of the
BP&CL at extreme operating and storage temperatures, both high and low temperature tests were
performed. Table 8 shows the TEMP thresholds for temperature. Temperature thresholds as
listed in the manufacturer’s literature on the commercial Ferex are also listed for comparison.
Since the modifications to the commercial unit were limited to the housing and the LED operator
display, the manufacturer’s temperature values apply only to the sensing probe and the processing
electronics.

Table 8. TEMP and Manufacturer Thresholds for Temperature

TEMP Thresholds
Operational Water Temperature 28 to 85 °F -22 to 130 °F

Nonoperational (storage) ‘ ;

To verify the cold operating and cold storage temperature thresholds in the TEMP (28°F
and -20°F, respectively), the BP&CL was tested in the NCEL Polar Laboratory Facility. These
tests were performed in air and in a tank filled with fresh water. The temperature in the fresh
water tank was regulated by adjustment of the air temperature in the cold chamber. A
thermocouple with digital readout was used to monitor the temperature of the water. Air
temperature was monitored using the temperature gages provided in the cold chamber.

To begin the cold tests, the air temperature in the cold chamber was lowered to about
-17°F. The BP&CL was then placed in the chamber (going from a temperature of about 63°F
to -17°F) over night while the cold air cooled the water in the tank. In the morning, new
batteries were placed in the BP&CL and the tool was turned on and used (in air) to find rebar
placed in the cold chamber. The BP&CL was then placed in the tank while the water

23

temperature was being lowered. After about 4 hours, the BP&CL was pulled from the tank and
operated in air to find the rebars. The water temperature was about 34°F with ice beginning to
form at the surface. No operational problems were encountered during these tests.

To verify the high temperature operating and storage thresholds in the TEMP (85°F and
140°F, respectively), tests of the BP&CL were performed with the tool submerged in a tub of
warm water after sitting outside (in direct sunlight) while packaged inside its storage container.
To monitor the temperature inside the container, both a thermometer and a thermocouple (with
digital readout) were placed inside the contain. With the ambient air temperature (in the shade)
at approximately 82°F, the temperature inside the box eventually reached 125°F. The BP&CL
was then taken from its storage container and placed in a tub of warm water (approximately
90°F) for about 20 minutes. The BP&CL was then turned on inside the tub of water and then
pulled out and used in air to locate rebar laid on the ground. No operational problems were
encountered during these tests.

USER TESTS

To verify the suitability of the tool for UCT use, user tests of the modified Forster Ferex
system were performed offshore Anacapa Island by the NCEL dive locker. Although these tests
were originally scheduled with UCT-TWO (and NCTC Delta Company as a backup), fleet
scheduling conflicts required using the NCEL dive locker to avoid further schedule delays and
additional project costs. Reference 4 authorized NCEL to conduct the user tests with in-house
personnel previously stationed with either UCT-ONE or UCT-TWO. These tests were performed
in March 1988.

The test consisted of divers using the BP&CL (in the diver-held mode) to find a 10-foot
section of 1.5-inch chain placed on the seafloor. The chain was placed about 100 feet away from
the dive station (LCM-8 boat) in about 45 feet of water. The sea conditions were considered
good, with 10 feet of visibility, no current, and a water temperature of 65 degrees.

Prior to beginning the dive, the operators received a 15-minute instruction on how to use
the BP&CL (both divers were unfamiliar with its use). Upon reaching the bottom, the divers
determined which course to take by using the audio and visual output of the BP&CL while
making a 360-degree turn. This procedure was repeated after traveling a short distance (about
30 to 40 feet) until the chain was found. The total time on the bottom actually searching for the
chain was about 5 minutes.

Comments from the divers indicated that the BP&CL meets the operational effectiveness
and operational suitability thresholds stated in the TEMP. One problem mentioned was the loss
of the audio output signal while adjusting the frequency control. This problem will be solved
by substituting the switch with a "make before break" type.

CONCLUSIONS

The EDM test results show that the BP&CL has met or exceeded the TEMP thresholds.
Table 9 shows TEMP thresholds and summarizes test results.

The reliability thresholds were met with a confidence factor of 90 percent. There were
only two minor incidents observed during this portion of the test and neither would prevent the
unit from performing its mission. The test battery life of 43 hours was judged to be in excess

24

of actual operating battery life since the unit was not generating any audio output during the
tests. It is estimated that actual battery life will consist of at least 25 hours of operation.

The detection thresholds were met for all items listed in the TEMP. This includes a
detection range of: (1) 2-1/2 feet for 5-inch-diameter Simplex pipeline (with a layer of armor),
(2) 3 feet for SD list 5 armored cable, (3) 6 feet for 1-1/2-inch chain, and (4) 10 feet for a
6,000-pound anchor.

The weight and balance of the tool in the diver-operated mode was judged acceptable by
the divers. However, making the probe end of the standoff device neutrally buoyant would add
to the tool’s effectiveness. In the dipping mode of operation it was noted that the unit can be
used effectively from an inflatable boat. The speed of the boat must be kept slow enough to
permit the probe to remain perpendicular to the seabed.

RECOMMENDATIONS
Based on the results of the development effort, it is recommended that:

1. The Buried Pipe and Chain Locator be approved for limited production of three systems.

2. The performance of the three systems should be monitored by NCEL during a UCT operation
to insure a smooth transition into fleet use.

3. The User Data Package prepared during the EDM effort should be updated with as-built
drawings after fabrication of the three production systems.

4. The Buried Pipe and Chain Locator should be included in the NCTC school as part of the
training curriculum.
REFERENCES

1. Naval Civil Engineering Laboratory. Memorandum to files on the survey of diver-operated
metal detecting systems, by Eastport International, Inc. Port Hueneme, CA, Jul 1985.

2. Naval Explosive Ordnance Disposal Technology Center ltr Ser FL/165 of 19 Sep 1985.
Subj: Use of MK-10 magnetometer.

3. M. Oliver, CEC (DV). Personal communication, Naval Civil Engineering Laboratory,
Ocean Operations Division, Port Hueneme, CA, Jan 1986.

4. H. Herrman. Telephone conversation, NAVFAC and H. Thomson and S. Black, NCEL,
Mar 1988.

25

Table 9. TEMP Thresholds and Test Results

Characteristics TEMP Threshold EES ® Test Results
Specification

1. Operational Effectiveness

Self-contained,
rechargeable, or
replacable

6 to 12 volt (6 mono-
cells each 1.5V)

Power Supply 6 replacable alkaline D

cells

Operational life cycle 6 hours

Detection Distance

6 feet 6.1 feet

Buried chain, 1.5 in. or larger

2.5 feet

Buried pipeline (S-in.-diam Simplex 4.0 feet

w/armor

Anchors (6,000 Ib) 10 feet

10 feet

Armored cable (SD List 5) 3 feet

6 feet

Location on seafloor will <1 foot
be 1 foot or the depth of
burial, whichever is

greater

Accuracy of Detection Location on
Seafloor

Weight (system)

In air 35 pounds 21 pounds (excluding

20.8 pounds
= case)

In water 3 pounds +/- | pound N/A 3 pounds

On the beach to 190 feet
of water

Demonstrated 0 to 55
feet

Operational Range 0 to 300 feet (probe)

Handling

Diver-held mode Carried by one free
swimming diver (requires
only one hand to carry
underwater, but may
require two hands to

operate)

One hand to carry,
two hands to operate

Boat-towed mode The sensing probe can be
towed at slow speed from

an inflatable boat

Demonstrated towing
from inflatable boat

28 to 85°F 5 to 149°F Demonstrated 34 to

90°F

Operational Water Temperature

Demonstrated -20 to
125°F

Nonoperating Temperature -58 to 176°F (with

lithium batteries)

Operating Turbidity N/A Demonstrated 3- to 10-

foot visibility

Clear water to zero
visibility

26

Table 9. Continued

Characteristics TEMP Threshold A Enea Test Results
Specification

2. Operational Suitability
Life

Mean Cycles Between Failure >20 based on MTBF of
42 hours

Reliability of a Single Unit >90% at 90%
confidence level

Preventative Maintenance Times

Daily (excluding recharging power <1 hour (limited to
source) wash-off and O-ring

lubrication)

End of Project 1.5 hours <1 hour (limited to
wash-off, O-ring
lubrication, and systems
check)

<3 hours (recalibration
at Depot level)

1 hour <1 hour (limited to O-
ring replacement)

Skill Level 75% of all divers can 4 out of 4 divers can
operate with | hour of operate with | hour of
instruction on beach instruction on the beach

27

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Appendix A
COMPONENT DESCRIPTION - METAL DETECTING SYSTEM
MISSION AND REQUIRED OPERATIONAL CHARACTERISTICS
MISSION: To locate and track underwater metal pipelines, armored cable, and chain.
Characteristic Threshold
A. Operational Effectiveness

@ Power Supply Self-contained, rechargeable
or replaceable

- Operational life cycle 6 hours

@ Detection Distance

- Buried chain (1-1/2 inches 6 feet
or larger)
- Buried pipeline (5-inch 2-1/2 feet

diameter Simplex with
layer of armor)

- Anchors (6,000 Ib) 10 feet

- Armored cable (SD List 5) Sifeet
®@ Accuracy of Detection <1 foot or depth of burial
@ Weight

- In air <35 Ib

- In water 3) oe Mt Me)
®@ Operational Range On the beach to 190 feet

of water

Characteristic Threshold

@ Handling

- Diver-held mode Carried by one free swimming
diver (requires only one
hand to carry underwater,
but may require two hands to
operate)

- Boat-towed mode* The sensing probe can be
towed from an inflatable
boat

@ Operational Water Temperature 28 to 85°F
@ Operational Turbidity Clear water to zero visi-
bility
B. Operational Suitability
@ Life (sensor system or >7 years
component which will likely
contact seafloor regularly
during operation shall be
abrasion resistant (on sand or
gravel) or inexpensive and
easy to operate)
@ Mean Cycles Between Failure >20
®@ Reliability of Single Unit >90%
@ Redundant Supply or Two or More
Units is Acceptable
@ Reliability of Two Units >99%
@ Preventative Maintenance Times
- Daily (excluding recharging 1.0 hour

power source)

Characteristic
- End of project
- Annual
@ MTTR/On-Site Maintainability
(limited to replacing O-rings
and power pack - all other
repairs at depot level)

@ Production Cost (assume order
of 5, FY85 dollars)

@ Skill level

*Revised content.

Threshold
1.5 hour
3.0 hours

1.0 hour

$20,000/unit

75% of all divers can
operate with 1 hour of
instruction on the beach

» Vantin 0 MONEE
Mia besos Lo erg
soe 0.1

fi \O00 OSE
Heatownnd) “ingde”

fey aot the Yo aET
to wow | Rew stew
Seaidiaiiibneihibiaiiaal

@ Dennen Tiartidiey

B, Capevaticoaad, Sciiatylliny

® Lith (sensor svokim ir
component welrich will likely
contact pratoor rexgularty:
during operation «ial. an
sherman. fasistant (oe. sail ‘or
Braves) of inenpensive oe
Rey 1h Operate

® Meng Cycits Between Failure

Reltabitity of Single ( fot

* —oeys ub Supe ply iar Two or More
Jit la Agesptabie

*

Ratiability of Teo Unit |
* Proventalive Mainienante Termin "1

Dally (excludi ig there
prone wutgn) Hime

:

Appendix B

COMPARISON OF PHYSICAL CHARACTERISTICS

VISUAL OUTPUT
Garrett XL500

POOR. The indication meter is located on the top of the electronics housing, which is
either worn around the waist or attached to the top of the sensing wand. Target strength is
indicated by an analog meter with scale readings between low and high. In either position, the
meter is poorly positioned for viewing. With the housing attached to the sensing wand, the
operator must lean forward over the wand and electronics housing to view the meter. With the
housing attached to the belt, the operator must twist and bend over at the waist to view the
meter. In addition, the meter is not back-lit for viewing in dark or low visibility areas.

White’s PI-1000

POOR. There are two light-emitting diodes that are located inside the electronics
housing. One diode provides a battery check indicator. The other diode indicates the presence
of metallic objects by blinking (the higher the frequency of blinking, the greater the target
strength). Although these diodes are positioned well for viewing, this form of indication is
somewhat ambiguous since the output is qualitative in nature.

Fisher Pulse 8

FAIR. The target indication meter is located on the sensing wand and is an integral part
of the handle. The meter is adequately sized and positioned well for viewing. However, the
meter is not back-lit for viewing in dark or low visibility areas.

Forster Ferex

GOOD. Signal strength, battery status, and check indicator for proper operation are all
displayed on an analog meter. Although the meter is not submersible, it provides a good
indication of target strength and location. This is because the sensitivity of the unit can be
adjusted to obtain quantitative readings and the meter swings from one extreme to the other (i.e.,
positive to negative) when moving over a target.

B-1

AUDIO OUTPUT
Garrett XL500

FAIR. The audible output from this unit is an oscillating tone that increases in volume
as an object is detected. This method of detection is adequate and allows for a reasonable
reaction time. However, the headphones are cumbersome and the sound may become muffled
if the headphones are worn over a hood.

White’s PI-1000

FAIR. This unit has a clicking indicator that changes clicking speed as an object is
detected. Discernment of the change in clicking rate is fair. However, the headset has only one
transducer and is not well balanced. Because of this, the headset is very difficult to keep from
sliding off the user’s head. The sound may also become muffled if the headset is worn over a
hood.

Fisher Pulse 8

GOOD. This unit comes with a diver earphone that may be used inside a diver’s hood.
The earphone indicates the presence of a target by a change in its output tone (higher frequencies
indicate increased target strength).

Forster Ferex

FAIR. This unit has a clicking indicator that changes clicking speed as an object is
detected. Discernment of the change in clicking rate is rated as fair.

GENERAL HANDLING
Garrett XL500

FAIR. The handle design and weight distribution is good for supporting this unit.
However, the wand length is adjusted by adding either one or two extension rods that are
connected together by nuts and bolts. This type of fastening arrangement is not well suited for
quick adjustment to wand lengths, particularly in a small boat or by divers in the water. The
parts of the fasteners are also likely to become lost.

White’s PI-1000

GOOD. The handle design and weight distribution is good for use in handling this unit.
In addition, the length of the wand is easily adjusted by means of a telescoping mechanism on
the wand. The rod uses compressive pins that lock into holes on the outer tube. Since no tools
are required for adjustment, varying the length can be done easily on land, boat, or in the water.

Fisher Pulse 8

POOR. The handle design and weight distribution is poor due to inadequate balancing
(the front end is heavy) and lack of a forearm rest. As a result, short duration, limited handling
of this unit is likely to fatigue the arm. The mechanism for adjusting the wand length is also
rated as poor. Adjusting the wand length is done by unscrewing threaded pieces of PVC pipe
and removing or adding sections. The extra sections would have to be taken with the diver for
adjustment to be made underwater.

Forster Ferex

NOT APPLICABLE. This system was not designed as a diver tool.

RUGGEDNESS
Garrett XL500

FAIR. The ruggedness of this unit is rated as only fair. Although the electronic housing
appears very rugged, the arm rest and sensing coil attachments appear weak and prone to
damage. All plastic portions of the wand should be replaced with aluminum tubing.

White’s PI-1000

FAIR. The wand and the attachment points for the handle, arm rest, and coil appear to
be fairly rugged. However, the overall rating is only fair because the electronics housing appears
prone to damage. The housing is a thin-walled plastic enclosure that is positioned on the top of
the wand grip. In this position, the housing extends outside the body of the unit and is
susceptible to impact or snagging.

Fisher Pulse 8

POOR. This unit is poorly constructed. The wand, fabricated from PVC pipe, is weak
and inadequately designed for supporting the components of the system. The attachment points
for the coil, handle, and electronics housing are welded PVC and also appear fragile. The
electronics housing appears to be the only ruggedly constructed component of this system.

Forster Ferex
GOOD. The components of this system appear very rugged and well constructed.

However, only the probe is submersible. The electronics housing and power supply would
require redesign to make these components waterproof.

MAINTENANCE
Garrett XL500

GOOD. Maintenance is rated as good since this is limited to recharging the batteries
(required after 9 hours of operation), periodic lubrication of O-rings, inspecting for signs of wear
or damage, and rinsing the unit with fresh water after use. The batteries are charged by plugging
a 12-volt transformer (supplied with the unit) into the earphone connector. All O-rings on the
connectors and the electronic housing cover are accessible and easily replaced.

White’s PI-1000

GOOD. Maintenance on this item is rated as good since it is limited to replacing the
batteries every 12 hours, lubricating O-rings on the cover to the electronics housing, inspecting
the unit for wear or damage, and rinsing the unit with fresh water after use. Although the
batteries are nonrechargeable (six "AA" batteries) they should be readily available in most
locations.

Fisher Pulse 8

FAIR. Maintenance on this unit is minimal (limited to charging the batteries, inspecting
the unit for wear or damage, and rinsing the unit with fresh water after use) but is rated as only
fair since the batteries require recharging after 4 hours of operation.

Forster Ferex

GOOD. Maintenance on this unit is limited to replacing the batteries, inspecting the unit
for wear or damage, and rinsing the probe with fresh water after use.
REPAIR

Repair of all four systems is rated as fair. Repair of these units in the field is limited to
replacement of O-rings. All other repairs such as replacement of faulty electrical components
or repair of mechanical items (i.e., broken handles, stripped threads, or damaged electrical
housing) must be conducted at the Depot level.
MATERIALS OF CONSTRUCTION
Garrett XL500

SENSING WAND: aluminum tube and plastic

COIL COATING: plastic

ELECTRONIC HOUSING: plastic
OUTPUT TRANSDUCER: plastic earphones

B-4

White’s PI-1000

SENSING WAND:
COIL COATING:

ELECTRONIC HOUSING:
OUTPUT TRANSDUCER:

Fisher Pulse 8

SENSING WAND:
COIL COATING:

ELECTRONIC HOUSING:
OUTPUT TRANSDUCER:

Forster Ferex

SENSING PROBE:

ELECTRONIC HOUSING:
POWER SUPPLY HOUSING:

aluminum
plastic

plastic

plastic coated

PVC pipe

plastic and potting compound
plastic

plastic coated

aluminum
aluminum
aluminum

clear with yellow stickers

orange with clear cover

COLOR
Garrett XL500
WAND: white and silver
COIL: white
ELECTRONIC HOUSING:
White’s PI-1000
WAND: black
COIL: black
ELECTRONIC HOUSING:
Fisher Pulse 8
WAND: gray
COIL: black

ELECTRONIC HOUSING:

Forster Ferex

PROBE:

ELECTRONIC HOUSING:
POWER SUPPLY HOUSING:

yellow with clear cover

gray
gray
gray

B-5

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ions a ERS sein PES Re Cover ire: Pre ae bait

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CAig.. *aioranmn ov, phy enn is Balpn.aga IEA

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ee ae, A Rea te dastigs, wus ere? ABV RT ‘wad, foes. water alter. dem.
adnate: ae cn aN sAnaiteca ae Lene) ey shoud pa. haga’

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ee py a:

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Pieter Ptr’: . | eeeneenies

a, Aeleaibeatatenanits aa ie aS ee iia HO: veene os
ido: cath foe rome ver dace, Gd rinsing the cab, wiih) fiegh water after“aue) Wut
likey ties the, bea sovton fe’ wi renhangine weft 4 hours of sail 2 ne

om T eens

VD, NenaeeHgbel by aay is oath vite
a renny OW Samoan, ad = RANE OR

ShPAse

Rayalr uf all (our yystenns is tated as (Wir, Regasr ary hy
rephicementat Outings, Another aayetsl aired RETR alt
oe Weir of cnharical lems (1.4) broken. aren spo trea, ha
heater). Wee: le comeiyictany eM the Depot siti

VAT aa ») yes
LAT CHtALS OF OO aie ro a rng

Garvert ALA HATO AERTS

SENTING WAITS shat tube and pe

CONE COATING: pilastie.

bc TRE BO Po pbaatie. hia.
MSTREY PRs ANH ry lassi: ree

Appendix C

DETECTION THRESHOLDS FOR PULSE-INDUCED SYSTEMS

NS as
St.
a

be
o>

60°
\\ fo)
6' = as ; 90

Ss
“a oa

[ERE

Ws)
SEY

high settings, O° coil angle.

COILANGLE: 45°

VES

Ror

TG RATT
NZ,

Appendix D

DETECTION THRESHOLDS FOR FORSTER FEREX

| Deaton arene (i ihe
| a panes

Probe Position Relative to Tartet at Half Scale Reading

Height Above Target (Feet)

100 Gammas

7 ———=

5 300 Gammas

Horizontal Distance From Target (Feet)

D-3

er tbean efeok

(Yost) dupe) onpdd tipieh |

‘ee oul feck

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