Geometrics G-882 Operation Manual

G−882 CESIUM MARINE

MAGNETOMETER

25919-OM REV. E

Operation Manual

COPYRIGHT © 2005

GEOMETRICS, INC.

2190 Fortune Drive, San Jose, California 95131 USA

Phone: [phone]

Fax: [phone]

email: [e-mail]

CE

March 14, 2003

Sunnyvale, California, USA

EC DECLARATION OF CONFORMITY

03

We, Geometrics, Inc.
Geometrics Europe
2190 Fortune Drive

San Jose, CA 95131 USA
ph: [phone]
FAX: [phone]

declare under our sole responsibility that our marine magnetometers, models G-880, G-881 and G−882 to which this declaration relates are in conformity
with the following standards:

EN 55022: 1995, EN50082-2 : 1995, ENV 50140: 1994, ENV 50141 : 1994, EN 61000-4-2: 1995, EN 61000-4-4: 1995
per the provisions of the Electromagnetic Compatibility Directive

93/68-EEC, Article 5

The Technical documentation required by Annex IV(3) of the Low Voltage Directive is maintained by Christopher Leech of Geometrics Europe
(address below).

The authorized representative located within the Community is:

Geometrics Europe
Christopher Leech
Manor Farm Cottage
Galley Lane
Great Brickhill
Bucks.MK17 9AB, U.K.
ph: [phone]
FAX: [phone]

of 22 July 1993.

89/336/EEC

of May 1989 as Amended by

92131/EEC

of 28 April 1992 and

Mark Prouty, President
San Jose, CA, USA

G-882 with Weight Collar

Depth Option & Altimeter

G-882 MARINE MAGNETOMETER

 CESIUM VAPOR HIGH PERFORMANCE – Highest detection range and probability of detecting all sized

ferrous targets

 NEW STREAMLINED DESIGN FOR TOW SAFETY – Low probability of fouling in fishing lines or rocks
 NEW QUICK CONVER SION FROM NOSE TOW TO CG TOW – Simply remove an aluminum locking

pin, move tow point and reinsert. Now with built in easy carry handle!

 NEW INTERNAL HIGH PERFORMANCE CM-221 COUNTER MODULE – UP TO 40 HZ – Provides

Flash Memory for storage of default parameters set by user

 NEW ECHOSOUNDER / ALTIMETER OPTION
 DEPTH RATING – 4,000 psi (2,700M)!
 HIGHEST SENSITIVITY IN THE INDUSTRY – 0.004 nT/√Hz RMS with the internal CM-221 Mini-Counter

 EASY PORTABILITY & HANDLING – no winch required, single man operation, only 44 lbs with 200 ft

cable (without weights)

 COMBINE TWO SYSTEMS FOR INCREASED COVERAGE – Internal CM-221 Mini-Counter provides

multi-sensor sync and data concatenation allowing side by side coverage which maximizes detection of
small targets and reduces noise

Very high resolution Cesium Vapor performance is now
available in a low cost, small size system for
professional surveys in shallow or deep water. High
sensitivity and sample rates are maintained for all
applications. The well proven Cesium sensor is
combined with a unique and new CM-221 Larmor
counter and ruggedly packaged for small or large boat
operation. Use your computer and standard printer
with our MagLogLite™ software to log, display and print
GPS position and magnetic field data. The G–882 is the
lowest priced, high performance, full range marine
magnetometer system ever offered.

The G-882 offers flexibility for operation from small boat,
shallow water surveys as well as deep tow applications
(4,000 psi rating, telemetry over steel coax available to 10
km). The G-882 also directly interfaces to all major Side
Scan manufacturers for tandem tow configurations. Being
small and lightweight (44 lbs net, without weights) it is
easily deployed and operated by one person. But add
several streamlined weight collars and the system can
quickly weigh more than 100 lbs. for deep tow
applications. Power may be supplied from a 24 to 30
VDC battery power or the included 110/220 VAC power
supply. The tow cable employs high strength Kevlar strain
member with a standard length of 200 ft. (61 m).

The maximum useable cable length with the standard
power supply is 300 m; 800 m with a Mini-Xantrex voltage

sense power supply; and up to 6000 m with telemetry over
coax. A rugged fiber-wound fiberglass housing is designed for
operation is all parts of the world allowing sensor rotation for
work in equatorial regions. The shipboard end of the tow cable
is attached to an included junction box or optional on-board
cable for quick and simple hookup to power and output of data
into any Windows 98, ME, NT, 2000 or XP computer equipped
with RS-232 serial ports.

1. Ship 1000 tons

0.5 to 1 nT at 800 ft (244 m)

2. Anchor 20 tons

0.8 to 1.25 nT at 400 ft (120 m)

3. Automobile

1 to 2 nT at 100 ft (30 m)

4. Light Aircraft

0.5 to 2 nT at 40 ft (12 m)

5. Pipeline (12 inch)

1 to 2 nT at 200 ft (60 m)

6. Pipeline (6 inch)

1 to 2 nT at 100 ft (30 m )

7. 100 KG of iron

1 to 2 nT at 50 ft (15 m)

8. 100 lbs of iron

0.5 to 1 nT at 30 ft (9 m)

9. 10 lbs of iron

0.5 to 1 nT at 20 ft (6 m)

10. 1 lb of iron

0.5 to 1 nT at 10 ft (3 m)

11. Screwdriver 5 inch

0.5 to 2 nT at 12 ft (4 m)

12. 1000 lb bomb

1 to 5 nT at 100 ft (30 m)

13. 500 lb bomb

0.5 to 5 nT at 50 ft (16 m)

14. Grenade

0.5 to 2 nT at 10 ft (3 m )

15. 20 mm shell

0.5 to 2 nT at 5 ft (1.8 m)

OPERATING PRINCIPLE:

Self-oscillating split-beam Cesium Vapor (non-radioactive)

OPERATING RANGE:

20,000 to 100,000 nT

OPERATING ZONES:

The earth’s field vector should be at an angle greater than 10° from the sensor’s equator and greater than 6 away
from the sensor’s long axis. Automatic hemisphere switching.

CM-221 COUNTER
SENSITIVITY:

<0.004 nT/ Hz rms. Up to 20 samples per second

HEADING ERROR:

1 nT (over entire 360° spin )

ABSOLUTE ACCURACY:

<2 nT throughout range

OUTPUT:

RS-232 at 1,200 to 19,200 Baud

MECHANICAL:

Sensor Fish:

Body 2.75 in. (7 cm) dia., 4.5 ft (1.37 m) long with fin assembly (11 in. cross width), 40 lbs. (18 kg) Includes Sensor
and Electronics and 1 main weight. Additional collar weights are 14lbs (6.4kg) each, total of 5 capable

Tow Cable:

Kevlar Reinforced multiconductor tow cable. Breaking strength 3,600 lbs, 0.48 in OD, 200 ft maximum. Weighs 17
lbs (7.7 kg) with terminations.

OPERATING TEMPERATURE:

-30°F to +122°F (-35°C to +50°C)

STORAGE TEMPERATURE:

-48°F to +158°F (-45°C to +70°C)

ALTITUDE:

Up to 30,000 ft (9,000 m)

WATER TIGHT:

O-Ring sealed for up to 4,000 psi (9000 ft or 2750 m) depth operation

POWER:

24 to 32 VDC, 0.75 amp at turn-on and 0.5 amp thereafter

ACCESSORIES:

Standard:

Operation manual, shipping storage container and ship kit with tools and hardware

Optional:

Telemetry to 6Km coax, gradiometer (longitudinal or transverse TVG), aluminum reusable shipping case

MagLog Lite™
Software:

Logs, displays and prints Mag and GPS data at full sample rate. Automatic anomaly detection and single sheet
Windows printer support

The G-882 system is particularly well suited for the

detection and mapping of all sizes of ferrous objects.
This includes anchors, chains, cables, pipelines, ballast
stone and other scattered shipwreck debris, munitions of
all sizes (UXO), aircraft, engines and any other object
with magnetic expression. Objects as small as a 5 inch
screwdriver are readily detected provided that the sensor
is close to the seafloor and within practical detection
range. (Refer to table at right).

The design of this high sensitivity G-882 marine unit is
directed toward the largest number of user needs. It is
intended to meet all marine requirements such as
shallow survey, deep tow through long cables,
integration with Side Scan Sonar systems and
monitoring of fish depth and altitude.

MODEL G-882 CESIUM MARINE MAGNETOMETER SYSTEM SPECIFICATIONS

Typical Detection Range For Common Objects

SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE 11/13

GEOMETRICS INC. 2190 Fortune Drive, San Jose, California
95131, USA Tel: [phone] – Fax: [phone] – Email:

[e-mail] Web: www.Geometrics.com

GEOMATRIX UK 20 Eden Way, Pages Industrial Park, Leighton Buzzard LU7
4TZ, UK Tel: [phone] – Fax: [phone] – Email:

[e-mail] [e-mail] - Web: www.Geomatrix.co.uk

Table of Contents

1.0 Introduction ............................................................................................. 1

1.1 How it Works .................................................................................................................... 2

2.0 Quick Start Hardware Guide .................................................................. 2

2.1 Nose Tow Configuration ................................ ............................................... 4

2.2 Converting Nose Tow to CG Tow ................................................................ . 8

2.3 Adjusting Handle And Orientation Weight ................................................... 9

2.4 Attaching the Tow Cable to the Vessel ...................................................... 10

2.5 Powering Up the System ............................................................................. 11

3.0 Quick Start Software Guide ................................................................. 12

3.1 What Does MagLog Do? .............................................................................. 14

3.2 The Survey Wizard ....................................................................................... 15

4.0 General Overview ................................................................................. 25

4.1 Operation and FAQ ...................................................................................... 25

4.2 Performance ................................................................................................ 28

4.3 Sensor Orientation Guide .......................................................................... 29

4.3.2 Main Field Inclination and Total Intensity Maps ...................................................... 33

4.4 CM-221 Counter Data Format and Command Structure ............................. 36

4.4.1 Output Format ............................................................................................................. 36

4.4.2 General Command instructions ................................................................................. 39

4.4.3 G−882 Quick Command list ........................................................................................ 39

4.4.4 G−882 Detailed Commands ........................................................................................ 40

4.4.5 Update Default Parameters ......................................................................................... 44

4.4.6 Command Set Descriptions ........................................................................................ 46

4.4.7 Power-up Initialization ................................................................................................ 54

4.5 Accessory Software .................................................................................... 55

4.5.1 Cesium Sensor Active Zones – CSAZ ...................................................................... 55

A newly designed CSAZ Windows™ program is available on our Magnetometer CD and
from our FTP site at ftp://geom.geometrics.com/pub/mag/Software/ (look for csaz­setup.exe). Please read the manual that is included with the program for complete
instructions on how to use the CSAZ program for worldwide inclination and sensor

orientation solutions. ............................................................................................................... 55

4.5.2 CM201 .......................................................................................................................... 55

4.5.4 Depth Cal .................................................................................................................... 63

4.5.5 Depth Calibration Using MagLog-Lite or MagLog ............................................. 67

4.6 Assembly, Installation and Use .................................................................. 72

4.6.1 Assembly of the Sensor Fish .................................................................................... 72

4.6.2 Installation of the G−882 Magnetometer .................................................................. 72

4.6.3 Deployment of the G−882 Magnetometer ................................................................. 73

5.0 Service Information and Trouble Shooting Guide .............................. 80

5.1 Connector Information ................................................................................ 80

5.2 O-ring Maintenance ..................................................................................... 82

5.3 Depth Sensor Ratings ................................................................................. 83

5.4 Tow Cable Strength Data ............................................................................ 83

5.5 Trouble Shooting Guide .............................................................................. 84

5.6 The Diagnostic Survey – How to use it ...................................................... 88

Final MagLog screen will look as above to provide diagnostics for system

troubleshooting. ................................................................................................... 95

5.7 Voltage Calibration for Magnetometers using CM-221 Counters ............. 95

Appendix A – Optically Pumped Magnetometer Theory ........................... 103

Appendix B – System Connection Wiring Diagrams ................................. 106

Appendix C: G-882 With Larmor Output ................................................... 109

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1.0 Introduction

The G−882 Marine Magnetometer has been designed and manufactured to make it
easy to use and to get great marine magnetometer data. The purpose of this
manual is to give new users start up information and experienced users reference
information.

We begin with an introductory overview on to how the system works and then
provide a Quick Start Hardware Guide to show you how to connect the
magnetometer fish and tow cable system. The G−882 offers field convertible nose
tow or CG (center of gravity tow) configurations and we explain how to convert one
to the other. In general the nose tow is used in shallower applications, the CG tow
for deeper tow requirements.

We continue with a description of the Kellems grip cable attachment system and how
it is used to safely attach your tow system to a secure point on your vessel or towing
winch. The Quick Start Hardware Guide concludes with a section on connecting the
tow cable (or on-board deck cable) to the power-data-junction box, power supply and
PC computer for data logging

Most G−882 magnetometers are supplied with our MagLog or MagLogLite software
which runs on a Windows™ PC. A Quick Start Software Guide walks you through
the basic setup using the MagLog Survey Wizard to configure logging of the
magnetometer, GPS and printer. We suggest that the user refer to the MagLog /
MagLogLite manual for more in-depth setup and operational information after using
the Quick Start Guide.

Your data may be processed in our accessory software MagMap2000 and MagPick
programs, also supplied with the magnetometer. Please review those manuals for
processing steps and map making. The manuals are part of the software installation
and can be found under the Help tab.

After the Quick Start Guides we offer the main part of the manual where we discuss
deployment scenarios, tow depths, sensor orientation requirements, digital data
transmission formats, troubleshooting and service information.

We have produced this manual to provide you with a basic understanding of the
procedures required to obtain the best survey data obtainable and give you some
tips on how to care for your magnetometer system. It is not meant to be exhaustive
for every case as there are many different situations and applications in which the
magnetometers can be used. As always, we are here to support you and help you
get the most out of your system, so we encourage you to call or email us with
questions.

Contact information:
Technical [e-mail]
[e-mail]

Tel: [phone] Fax: [phone]

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 1

1.1 How it Works

The G−882 magnetometer employs an optically pumped Cesium-vapor atomic
resonance system that functions as the frequency control element in an oscillator

circuit. The frequency of the magnetometer’s electrical oscillator is known as the

Larmor frequency. In Appendix A we give a more complete description of the
internal working of the sensor, but here it suffices to say that this oscillation
varies with the external ambient magnetic field. We measure those variations and
send them to a computer for display and recording.

Where there are materials that have iron in them (like cables, pipelines, different
types of rock, small artifacts like nails or big items like a steel ship) the earth’s
field distorts about the object and the cesium magnetometer sees this distortion

as an increase or decrease in earth’s field intensity. In the northern hemisphere,

we will typically see an “anomaly” over a ferrous object which presents dipole

structure with a magnetic high to the south of the object and a magnetic low to
the north. This phenomenon is fully described in our Applications Manual for
Portable Magnetometers (AMPM) which is available on the Magnetometer CD
that comes with the system. It is also available on our website
(www.geometrics.com).

The very high sensitivity of the cesium magnetometer allows it to detect small
targets at quite large distances. For localized objects, the magnetometer can
sense anomalies of 1 ton (1000 kgs) of iron or steel at 100 feet (30m) or more,
250 lbs (100kgs) at 50 ft (15m) and 30 lbs (15kgs) at 25 feet (10m) or more
depending on the background magnetic noise level of the earth.

Survey design is crucial to generating a data set that gives you the answers you
want. In general the height of the magnetometer above the sea floor must be
controlled to enable detection of the survey objective. Survey line spacing
should be approximately equal to twice the detection distance to the search
object for 100% coverage. The AMPM manual will give additional information on
survey design for different applications such geological survey and object
location. In addition, we are available to consult with you via phone or email to
help you design your survey for maximum productivity.

2.0 Quick Start Hardware Guide

The information in this and the following section is provided to help you get the
magnetometer set up and running quickly and ensure that it is working properly.
It can be used prior to any survey as a system check-out.

The cesium-vapor sensor is located inside the magnetometer pressure vessel

and is situated at back of the tow fish in the cylindrical body that forms a ‘T” with

the long axis of the vessel. (see figure #1). The sensor is internally connected to
the sensor-driver electronics and Larmor frequency counter circuit module

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 2

Fig 2 Accessory Kit:
includes
A) O-Rings, silicone
grease, non-magnetic
brass screws, anti­seize compound in a
plastic bag with
trimmer string (to lock
nose to body)

B) Allen wrench set
C) Cable tote ties
D) Junction box
E) RS-232 cable
F) MagLog Manual w/

software disk
G) AC/DC power
supply

H) AC power cord
I) DC power cord

(with battery clips)
J) Franzus
international AC
adapter plug kit.

located in the front end of the pressure vessel. External electrical connection to
the sensor-driver module is made at the front bulkhead through a wet-mateable 8
pin connector.

It is important that the magnetometer fish be kept clean and free from magnetic
contamination (iron or steel particles, rust). Never replace any hardware that has
not been checked first for magnetic effect. We encourage you to use the tools
supplied with the magnetometer to minimize magnetic contamination of the fish
parts.

Begin by removing the sensor, tow cable, on-board deck cable (if purchased),
white junction box, power supply and software CD from the shipping crate. Have
your computer on hand for later software installation and system test.

Figure 1 G−882 Tow Fish with nose mounted echo-sounder altimeter housing

Figure 2 Accessory Kit

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 3

Figure 3 Tow Cable Assembly, 200 foot (60m)

Set the magnetometer on a clean dry surface and unroll a 15 ft (5m) section of
the tow cable and bring it to the nose of the fish.

2.1 Nose Tow Configuration

The G−882 may be towed in either nose tow or CG (center of gravity) tow
configurations. Nose tow is used in shallow water deployment (or attachment to
a Side Scan Sonar). CG configuration is more commonly used when going
deeper in the water column. We will discuss depth estimates later in section

4.6.3
In order to attach the tow cable to the front of the magnetometer the nose plug

must be removed from the front of the nose piece. Begin by removing the top
cover split-rings and linchpins and remove the top cover (Figure 4A to 4C below).

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 4

Fig 4

Fig 4 A

Fig 4 B

Fig 4 C

Clamping

Screws

Split

Ring

Note the red locking strings and nose clamping screws at the rear of the nose
piece in Fig 4C. Should you need to rotate the sensor tube (discussed under
sensor orientation) you will loosen these screws and rotate the nose piece and
weight relative to the sensor axis at the rear. Never remove the red locking

strings unless you need to replace the nose piece.

Next remove the nose plug cotter pin, black clevis pin and nose plug from the
nose assembly as shown in Fig 5 A to C. Store these parts in a safe place as you
will need them when you convert to CG tow configuration.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 5

Fig 5

Fig 5 A

cotter pin

Fig 5 B

clevis pin

Fig 5 C

nose plug

Fig 5 D

pigtail

Locking

Clevis

Remove

Remove

Extract

Remove

Sleeves on

Next carefully pull the pigtail cable assembly from inside the nose through the
nose hole (Fig 5 D) and remove the dummy plug. You do this by unscrewing the
locking sleeves and pulling the dummy plug straight out. Do the same on the
pigtail attached to the tow cable clevis termination.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 6

Figure 6

Figure 8

Locate the silicone
grease that comes with
the ship kit (in one of the
plastic bags, Fig 6, 7) and
apply a very small
amount of grease to
lightly cover the male pins
and female receptacles.
Note that too much
grease can interfere with
proper mating and that
grease need only be
applied when connectors
appear dry. Line up the
two connectors and push
firmly together until they seat (Fig 8). Do not bend the cables from side to side as
you do this. Firm pressure is required. Screw the locking sleeves together to
complete the electrical connection. Tighten finger tight and then give another
1/8th turn. Do not use pliers to tighten the locking sleeves.

Figure 7

Now push the connected cables back
through the nose hole and pull them up through the top cover port. Insert the tow
cable clevis into the nose hole and secure with black clevis pin and cotter pin.

Make sure you bend over the cotter pin after installation! You will require a

pair of pliers to make a good bend. Complete the nose tow assembly by gently
pushing the connected cables into the nose cavity and reassembling the top
cover.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 7

Fig 9

Fig 11

Pictures as shown include the optional altitude echo-sounder, your completed
assembly may look different if this option is not included.

2.2 Converting Nose Tow to CG Tow

Converting from nose tow to CG tow is quick and easy. Remove the top cover
and as shown previously (Fig 9), pull out the cable assembly and unscrew the
connected cable assembly locking sleeves. Separate the cables by manually
pulling them apart, straight out. Using a pair of pliers, straighten out the cotter
pin holding in the black nose clevis pin, remove the cotter pin and clevis pin and

then remove the tow cable
assembly from the nose
assembly by pulling straight out.
Replace the nose plug, black
clevis pin and cotter pin that were
removed in the first assembly
process.

Fig 10

Next attach the tow cable clevis assembly
to the tow point hole in the handle assembly using the stainless steel CG tow pin
as shown and secure with a supplied cotter pin (Fig 10 and 11). Make sure you

bend over the cotter pin with a pair of pliers when assembly is completed.

Note that the pigtail cable assembly (shown with protective spiral wrap above)
must exit the tow cable clevis termination as shown toward the front of the fish.

Next, inspect the mail and female connectors to ensure that there is sufficient
silicone grease and mate the connectors, screwing together the locking sleeves
to complete the connection (Fig 12 A). Then gently push the connector pair and

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 8

Figure 12
Final Nose Tow
Configuration

Fig 12 A

Fig 12 B

Fig 12 C

cables into the nose cavity (Fig 12 B). Feed the pigtail under the top cover and
secure the top cover with linchpins and split rings. See Figure 12 C for
completed assembly.

2.3 Adjusting Handle And Orientation Weight

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 9

Loosen these screws to
also rotate the nose. Do

not remove the red
locking strings.

Fig 13 A

Under some circumstances (surveying at the far north or south latitudes) it may
be necessary to rotate the sensor housing by 45º or 90º (see section 4.3 on
sensor orientation). To do this, loosen the three bolts holding the handle to the
orientation weight collar and the clamping screws on the nose piece (Fig 13 B)
and rotate the weight, handle and nose assembly by 45º or 90º. Before
retightening bolts, apply some anti-seize compound that is supplied with the
system as shown in Fig 13A.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 10

Fig 14

<-- Vessel

--> Towfish

Use a strong line to attach

2.4 Attaching the Tow Cable to the Vessel

this loop to the vessel.

Each tow cable comes equipped with a Kellems grip for attaching the tow cable
to a strong tow point on the tow vessel. Slide the Kellems grip to the position on
the tow cable that will allow you to deploy the magnetometer to the desired
distance. Attach the Kellems to the tow cable by wrapping vinyl adhesive
(electrical) tape around the free end (end without the loop). The tape should be
started on the cable and lap onto the Kellems. The wrapping should be applied in
several layers as show in Figure 14. DO NOT tape along the whole length of the
Kellems; this will prevent it from working properly.

Tie the loop end of the Kellems to your vessels tow point with a strong rope prior
to casting the magnetometer overboard. The line and or hardware used for
towing should be rated to meet or exceed the 4000 lb breaking strength of the
tow cable. In addition, the tie-off point should have a similar static load rating.
Additional discussion of appropriate tie points will be found in section 4.6.2.

2.5 Powering Up the System

Connect the tow cable to the DC/Data Junction Box (via onboard deck cable if
purchased) and fix the tow cable to the tow vessel. Determine whether you will
use AC power or DC power. The AC supply will accept 120/240 VAC and there
is an adapter plug kit supplied for various international plug styles.

If you elect to supply DC power via two 12 volt batteries in series, note that a
minimum of 24VDC must be presented to the Magnetometer. Therefore 26 to
28VDC may be required at the junction box depending on cable length. Typically
fully charged batteries present about 13 volts each, and so this should function
well. Discharged batteries may not have enough voltage to start the
magnetometer although keeping it running once warmed up requires less
voltage. The DC Power Cable is provided to connect to battery power

With all of the components of a system connected, apply power by first turning
the AC supply on. There is a switch next to the mains power entry connection. If
DC power is used, hook up the batteries and DC cable. Connect to the junction
box.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 11

Figure 15

To the tow
cable

To the Logging
Computer

To DC power

Ground to hull,
if required

Power On/Off Switch.

Locking switch, pull
bat to change position.

Next, turn the Junction box DC power switch on using the locking toggle switch
on the junction box. The power indicator will light up green if the DC input polarity
is correct. If the DC input is derived from a battery set, there is the possibility of
accidental reverse connection of the power. If this should happen, the power
indicator will light up red, but no damage will occur. In this case, turn off the
junction box switch and recheck the DC power connections.

When power is applied, after a short warm up period (1 to 2 minutes), the
magnetometer will begin producing data. The default transmission protocol from
the CM-221 counter in the G−882 Magnetometer will be RS-232 at a 9600 Baud
rate. After about 2 to 5 minutes, the output from the magnetometer will be
stabilized and can be observed using “View201” (a DOS program supplied by
Geometrics) or HyperTerminal supplied with Windows or MagLog software. See
the section under Troubleshooting (section 5.5) on how to set up HyperTerminal.

Under some circumstances you may get better data if you connect the ground
lug on the DC/Data Junction Box to the ship’s hull using a ground cable. (Typical
noise levels at sea will be under 0.2nT peak-to-peak and may be less than 0.1nT
depending on sea state, ocean waves can generate magnetic signals). This
connection may be required if the AC Mains power is grounded to the steel hull.
See troubleshooting section for more information.

Connect the Logging Computer to the DC/Data Junction Box using the RS-232
Serial Data cable provided. See Figure below.

3.0 Quick Start Software Guide

This section of the manual refers specifically to the installation and setup of
MagLogLite or MagLog, Geometrics data logging and display programs. We use
the terms MagLogLite and MagLog interchangeably to refer to the logging
programs made by Geometrics; differences in performance between MagLog
and MagLogLite are not important for our discussion here. If you are using
another logging program such as Coastal Oceanographics Hypack™ please read

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 12

the first section below for tips on getting a good signal from the magnetometer on
board ship before setting up the software.

A cesium magnetometer will operate inside a room or lab or on the back deck of
a ship as long as two criteria are met. First, the sensor must be oriented as it
would be if it were being towed. In other words, for most survey areas the sensor
tube cylinder (at right angles to the main sensor tube body) should be positioned
vertically so that the long axis of the “T” is pointed up (see CSAZ program).
Second, the sensor must not be within a few feet of large steel objects such as
winches or steel decks. If the towing vessel is steel, place the sensor assembly
on top of a large cardboard box or plastic drum to get it 3 to 4 feet above the
steel deck. On very large steel ships you may need to move the sensor to the
wharf area or deploy it a short distance aft to get sufficient distance from the steel
structure.

MagLog and other logging programs require positioning information to operate
properly. We strongly recommend that you have your GPS turned on and
transmitting data during the software initialization process. MagLog uses the
standard $GPGGA string that all current GPS receivers transmit. Most modern
computers no longer support direct serial communication ports, but all do support
USB (universal serial buss) ports. We suggest that you purchase (from us or
directly) a Keyspan™ 1 or 4 port Serial to USB converter unit and have it
installed on your computer. This will provide one or more serial ports for use with
the magnetometer system. For the G−882 system you will need two serial ports,
one for the GPS and one for the magnetometer.

At this time we also recommend that you install the MagLog printer port software
key (also referred to as a “dongle”) that will give you access to the MagLogLite
data logging features. MagLog and MagLogLite will install from the CD but will
run in demo mode unless and until a printer port key dongle is installed on the
PC printer port. In case of trouble, Customer Service at Geometrics can give you
a temporary software key code to type into the computer and get you running.

Install MagLogLite from the supplied CD. Insert the CD into the CD player and
follow the menu selections to install MagLog / MagLogLite. The dongle will
determine which version of the program initializes. Note that for most surveys,
MagLogLite provides all the features you will need. MagLog is used primarily in
airborne surveys and with USBL tracking systems.

With the sensor properly positioned turn on the power switch on the white
junction box. A green light will indicate proper power connections, a red light
indicates reversed polarity on the DC voltage input. Turn on the computer and
click on the MagLog icon on your desktop. Ensure that the GPS is running and
the G−882 junction box shows a green power light.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 13

3.1 What Does MagLog Do?

MagLog is a sophisticated data logging and display tool that has a large number
of customizable features. These features include but are not limited to the
following:

 automatic calculation of fish position in real time (interpolation)
 automatic anomaly detection and Lat/Long position flagging
 plotting of GPS ship track, fish position and data on the map
 user setup of survey grid area with survey lines to show which survey lines

have been completed on the GPS track screen

 Automatic start stop of logging when sensor is in survey area
 multiple “slots” with multiple “pens” so that many different kinds of data

can be displayed simultaneously. Arithmetical operations like Depth +
Altitude to show water column; gradient calculations

 printing to dot matrix or to inkjet or laser printers which can be set up to

print only when there are detected anomalies

 survey playback at high speed to search for anomalies

There are many more features but the purpose of this section is to show how to
set up MagLog and quickly begin logging data. For this purpose we use the
Survey Wizard which you will find listed under File on the MagLog menu bar.
Click on File and then on Survey Wizard (see Figure 16 below). After the
introduction screen is displayed, click “Next”.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 14

Figure 16

3.2 The Survey Wizard

The Survey Wizard will take you step by step through the initialization process to
set up the GPS, magnetometer, real time layback calculation (interpolator),
printer and depth and altitude sensors (if included).

The next screen asks us to define a new survey name. In this case we have
used “test.survey” as our survey name. Note that the program creates several
files based on this root name, including files for the GPS, for the magnetometer,
a file for the line number, another for the Interpolator, which is the file with the
actual relocated fish positions. Type in a name and click next (Figure 17).

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 15

Figure 17

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 16

The next screen shows the GPS communication setup parameters. You should
have the GPS connected and sending data at this time.

Figure 18

Set the Port to the proper number and baud rate value (if you do not know this
information the program will scan for it) and then press the “Autoset

communication parameters” button. When the program detects the GPS it will

report back as below:

Figure 19

The next screen offers a facility to import Arc Info shape file maps. This is a
feature covered in the MagLog Manual and for later discussion. Press next.

Figure 20 shows the magnetometer setup screen. As before, if you know the
name of the communications port the mag is using and the baud rate (default
9600 baud) set it now. Otherwise the program will search for the connection.
Select the type of magnetometer you have where 88x stands for all marine

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 17

magnetometer systems. Essentially we are selecting one mag, or one mag with
depth sensor or one mag with depth sensor and altitude echo-sounder (or two

mags for gradiometer array). The cycle time is set in tenth’s of a second, e.g. 0.1

means 10 samples per second, which is the system default. Click on “Autoset
communications parameters” to interrogate and set up the magnetometer

communications.

Figure 20

You will get a screen as shown in Figure 21 while the magnetometer is being
detected. You will be notified when the magnetometer is communicating and
setting the analog channels (used for depth and altitude). Note that the 1st
analog channel is always reserved for magnetometer signal strength. Therefore,
if you have 1 and 2 shown in this screen, 1 is signal strength and 2 is depth
transducer.

At the bottom of the screen is a button named Store Configuration. When this
button is pressed, the default settings (power-up default parameters) are loaded
from MagLog into the magnetometer CPU Flash memory. This means that you
can change how the magnetometer initializes so that it will wake up with the

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 18

proper number of channels turned on and the selected cycle rate, etc. If you
make changes to the magnetometer operation and wish to store them
permanently in the Flash Memory, use this button. You can change the stored
parameters at any time.

Figure 21

The next screen enables the user to enter the calibration coefficients for either
the depth sensor, altitude echo-sounder or both. These coefficients are found on
the tailfin of the magnetometer and in the accompanying documentation.

For the depth sensor calibration, enter the scale and bias information for the type
of water in which you will be surveying (different scales and biases are supplied
for saltwater and fresh water surveys). If you have an echo sounder altimeter
installed, enter the scale and bias information for that accessory as well. When
you have completed entering the data, click next to continue. (see Figure 22)

If you do not have the calibration coefficients for your system, you may use the
manual calibration facility included in MagLog. This feature is accessed from the
configuration menu for the particular device and will be covered later in this
manual under section 2.5.5.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 19

Figure 22

The next screen presented will set up the Interpolator feature. The interpolator
does the following:

1. Uses the GPS antenna latitude and longitude information and converts it to
UTM coordinates in meters.

2. Based on user input in this section (offset of antenna from tow point, length
of cable deployed), the program computes the position of the fish in UTM
coordinates. MagLog employs a proprietary “dragging algorithm” which
analyzes the track of the boat and makes a best estimate of the position of
the fish based on the physics. The computed UTM fish position is then
recalculated in Lat/Long and that information stored in the Interpolator file
(*.int).

3. This process occurs at 10 or 20 times per second (Hz) so that the position of
the fish is computed and stored with every reading. Because the GPS
information typically comes at 1 or 2 Hz, the position of the fish is
interpolated in between GPS fixes. This is why the feature is called the
Interpolator.

4. Addition of a heading Compass or Gyro greatly improves the computation of
the fish position. This is because when the ship is pointed in a direction
different from the direction of travel (due to side currents) the currents also
affect the position of the cable and fish system. MagLog will log common

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 20

Figure 23

Gyro and Fluxgate Compasses for automatic correction of side currents.
Contact Geometrics for more information and a case study.

To use the Interpolator feature, click the button that says “Yes, I want real time
layback calculation”.

The Survey Wizard
provides set up of the
Interpolator to
calculate the positions
of one or two sensors

(more “fish” may be

added later) in real
time. If a gradiometer
array is being
deployed, the sensors
may be configured in
either a longitudinal
(one behind the other)
or transverse (side by
side) manner. You
have the option of
putting in information
to describe either
configuration. For
typical one sensor
surveys, use the
longitudinal configuration
button.

For a single sensor installation you will be defining the geometry by entering
information regarding distances defined by A, B and D in the left of Figure 23
above.

Enter data as shown in the Figure 24 below to define the position of the GPS
antenna relative to the tow point on the back of the ship, and the amount of cable
deployed. MagLog will then interpolate and calculate the fish position in Lat/Long
in real time for the purposes of drawing the fish position on the GPS screen

during actual survey (make sure you click the box that says “Draw 1-st fish real

time”). In addition, this information is used to flag anomalies that exceed your
preset anomaly detector criteria set up in the “Configure Input Devices” described

later. A table of these anomalies may be exported for direct import into programs
like Geosoft, MagPick and Surfer to show the location of the targets. This is of
course much better information than simply the location of the boat at the time
the fish passed over the anomaly. Now the user can steer the boat using the
GPS, back to the calculated location of the fish when the anomaly was detected.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 21

Figure 24

Figure 25

Put a “0” in the “Second Mag offset” if there is only one tow fish deployed
and two are shown (Figure 24). Recent versions of MagLog will have only
the number of fish displayed that are logged, however your program may
show two fish. Make sure you have the latest version from our web site or
contact us for a CD.

The next screen in the
Survey Wizard shows the
user how the Interpolator file
will be generated. Note that
all relevant data is stored
including magnetic field,
signal strength, sensor depth
and altitude if available, GPS
position, fish 1 and fish 2
position, etc. This file may
be brought directly into

MagMap2000 using the “all
files” input description in

order to plot the actual fish
positions for further analysis
(Note: bringing in MagLog
*.survey files [pertains to
MagLogLite as well] give
ship position plots, not
sensor position plots. Only
bringing in Interpolator files
will show the actual
calculated fish position on
the GPS track plots in
MagMap2000.

You may save this header
file for future reference

using the “Save this

information to file” button.
Next the Survey Wizard will

help us define the look and
feel of the logging display
(Figure 26). We are
presented with certain

default “slot” line colors and

plot definitions. We
recommend that you use
the Horizontal (Landscape)

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 22

Figure 26

display mode and that you accept the basic wizard color definitions at this stage
of set up. You can always change these items later during program operation.

Slots are defined as subsets of “Windows”. Windows may have one or more
slots and in each slot there may be one or more pens. Pens may represent such
things as depth in meters or magnetic field with 200nT full scale and a second
pen in the same slot with 20nT full scale. Configuration of these parameters are
covered in more detail in the MagLog manual.

The next screen shows the Slot Display parameter controls (Figure 27) which set
the full scale value, grid settings and chart speeds of the graphics presentations.
We recommend that you just accept these parameters as defaults for now.
Again, these can be easily changed once the program is running.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 23

Figure 27

Figure 28

The Survey Wizard now asks us to set up either a dot matrix printer or
laser/inkjet Windows printer for making hardcopy of the data on site. Note that if
you do not intend
to make printouts
in-field plots of
the data, you do
not need to set
up this feature.
Of the two types
(dot matrix and
Windows™
laser/inkjet
printers), we
recommend the
user of the
Windows™
printers (see next
screen, Figure

29). The reason

is that while dot
matrix printers

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 24

Figure 29

use continuous roll paper and can plot the entire survey in one profile, the
Windows™ printers may be configured to print on anomaly only. Thus when an
anomaly exceeds the preset values it will be printed with positions and other data
as selected on the center of an 81/2 x 11 inch sheet.

Note that when you

configure the “Windows”

printer, you must have the
printer connected to the
computer or network and
turned on.

This completes the Survey
Wizard dialog boxes and
this Quick Start Software
section. Clicking on the
final screen of the Survey
Wizard will start the survey.
Note that the program
starts in display mode only,
and that in order to log data
you must use CTRL-S to
start logging the data (or
File – Start Logging).

The following sections deal with deploying the sensor in different latitudes and
technical data regarding data formats. The final sections include a trouble
shooting guide and contact information.

4.0 General Overview

The G−882 Marine Magnetometer consists of two modules: sensor and sensor
driver electronics module mounted in a fiberglass pressure vessel. The G−882
sensor driver module contains a CM-221 frequency counter which is used to
count and digitize the Larmor frequency. The counter then transmits the data in
digital RS-232 format up the tow cable.
.
A basic description of the physics employed in the G−882 Marine Magnetometer,
and optically pumped resonance magnetometers in general, is included in
Appendix A under Cesium Vapor Magnetometer Theory.

4.1 Operation and FAQ

The G−882 Marine Magnetometer is usually purchased with Geometrics logging
software package MagLog-Lite or MagLog. Please refer to the Manual
associated with this software for complete instructions regarding installation and
setup. If MagLog-Lite or MagLog are not purchased, other serial port

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 25

logging software or terminal software may be used to communicate with the
G−882. Refer to the front of this manual for the Quick-start G−882 Harware
and Software Operating Instructions to help with the initial setup and running
of the magnetometer.

We receive many common questions about how to operate the G−882
magnetometer and we offer a few of them here for your review:

A. What is a good boat speed? Is there a maximum or minimum?

Most surveys are conducted at between 4 and 6 knots. The speed of the
vessel will control the depth of the sensor fish because the drag of the cable
dominates. Therefore higher speeds mean a more shallow tow. The tow
cable is rated for 700 lbs continuous working load. Short tow cables (less
than 500 ft) can be towed at up to 10 knots.

B. I want to tow 200 ft deep, what are my options?

In general, we suggest that you use our online depth calculator offered on our
website at http://www.geometrics.com/TowDepth.htm . Users can substitute
G−881 for the G−882 in the program. (See Figure 30 below).

A quick calculation will show you that getting your sensor to 100 feet depth
(30m) is not too difficult but to get beyond that depth, it will require
significantly more cable, slowing down the survey and adding weight collars
to the fish. Each weight collar is 14lbs. To get to 100 ft (30m) depth will
require 500 ft of Kevlar cable, towing at 3 knots with 1 extra 14lb collar
weight. Moving to 4 knots will raise the fish to a depth of 75 feet (25m)!

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 26

Figure 30

To get very deep we offer steel armored coaxial cable with a telemetry
system and high voltage power supply. This system can operate over 6 to 10
Km of steel coax cable.

C. How tight a turn can I make?

Tight turns remove the forward tension on the tow cable and therefore allow
the sensor to sink. The tighter the turn, the longer the cable and fish will be
without forward motion. Long cables will also lengthen the sink time. We
recommend keeping the sensor under forward motion by performing an eye­bolt type maneuver or using a racetrack pattern (line 1, line 6, line 2, line 7,
etc) to keep forward progress.

D. Isn’t Cesium radioactive?

There are certain isotopes of cesium that are radioactive, but we do not use
radioactive isotopes in cesium magnetometers. We use extremely small
amounts (micrograms) of the pure elemental metal which is non-radioactive
and essentially non-reactive in those amounts.

E. How far can the magnetometer “see”?

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 27

Total field magnetometers like the optically pumped cesium magnetometer
are passive devices, they do not send out waves or pulses. They measure
distortions in the earth’s normally homogenous magnetic field and can sense
distortions due to ferrous objects at great distances.

The basic rule of thumb is that one ton (1000 Kg) of steel or iron will give us a
1nT anomaly at 100 ft or 30m. Since the amount of distortion falls off as the
cube with distance (compare a metal detector which falls off as the inverse 6th
power!) and is linear with mass, every time we cut the distance in half, we can
see 1/8th the mass. Therefore, we can sense 250 lbs (100kg) at 50 feet
(15m), or 30lbs (15kg) at 25 feet (8m), or 4lbs (2kg) at 12 feet (4m).
However this is not the whole story. The factors given above are for induced
magnetic fields only. Many targets also have remanent or permanent
magnetic effects (meaning they have become magnetized either in production
or by the earth’s field) and can therefore have larger anomalies by a factor of
3 or 5 or more. Also many hollow objects like barrels or other tubular
structures appear as though they are solid due to self-shielding from the
earth’s field, and thus have much larger anomalies than their mass would
predict alone. Pipes fall off as the inverse square and are thus detectable at
even greater distances. Please see our Applications Manual for Portable
Magnetometers for more information. Our website contains additional FAQ
questions.

4.2 Performance

Geometrics G−882 magnetometer produces a Cesium Larmor frequency output
at 3.49872 Hz per nT (in this text, nT refers to nanotesla or gamma or 10-5
gauss). Thus, in a nominal 50,000 nT field this frequency is about 175 kHz. The
output of the system is a continuous sine wave at the Larmor frequency. The
typical signal amplitude is approximately 2 volts peak-to-peak at optimal
orientation of the sensor.

This frequency is counted with the internal counter at 10 readings per second but
the cycle rate can be set to one reading every 3 seconds to 20 times per
second.. The G−882 is intended for use in marine applications, and operates
over the earth's magnetic field range of 20,000 to 100,000 nT.

Absolute accuracy (relative to National Bureau of Standards facility at
Fredricksburg, VA) depends on sensor orientation, internal light shift and the
accuracy of the external counter's time base. Typically cesium magnetometers
offer absolute accuracies to within ±2nT of this standard. Since the offset if any
is constant (no drift over the lifetime of the product) this is of no consequence in
survey activities. Orientation error of the G−882 does not exceed 1 nT p-p (peak­to-peak) throughout the entire 360º polar and equatorial spins of the sensor.

Like all magnetometers, performance of the G−882 in a mobile installation is
primarily dependent upon the stability of the tow fish and the proximity to large
steel objects (e.g., the tow vessel). Navigational or positional errors, radiated

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 28

electromagnetic noise and heading error from the ship's induced and remnant
magnetic fields are typically the major contributors to "noise" in the marine
environment.

The G−882 Sensor Package consists of a sensor head and sensor electronics
package joined by a cable. The electronics package contains an integral
Geometrics CM-221 counter which converts the Larmor signal into a
magnetometer reading in nano-Teslas. Digital data is transmitted via RS-232 to
a data logging system. An eight pin underwater connector on the sensor
electronics package receives power on two pins. Three pins are used to provide
an RS-232 connection upon which the G−882 transmits magnetometer data
readings in digital format. The other pin(s) is reserved for future and special
uses.

Environmental conditions for proper operation are -35 to +50°C (-31 to +122° F).
The G−882 will operate to a depth of 4,000 psi (9000 ft.).

4.3 Sensor Orientation Guide

The G−882 is designed so that the sensor optical axis is perpendicular to
direction of the tow. The sensor may be oriented at any angle from vertical to
horizontal by rotating the main fish tube or “T” section.

The sensor head should be oriented so that the earth's field vector arrives at an
angle of from 15 to 75 to the optical axis of the sensor. The earth’s field vector

is vertical at the poles, between 50º and 60º in the mid latitudes and horizontal at
the magnetic equator. (See CSAZ program on Magnetometer CD). Adjusting the
sensor for the polar and mid-latitude regions is simple, by orienting the sensor
either at 45º (rotating the main tube 1/8th turn for polar regions) or 0º (no rotation
required at mid-latitudes) respectively. The vast majority of surveys will be
conducted using these two orientations.

The equatorial region is a special case. There is a band of approximately 500
miles wide in which the magnetometer can survey only in certain directions with a
given sensor orientation. For instance, if the survey will be conducted in an east­west direction at the magnetic equator, simply rotating the sensor to the 45º
position (same as for the polar region) will produce excellent data

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 29

Figure 31

Figure 32

Loosen these two
cap screws to

rotate the nose.

5/32" HEX L-

60

Dead Zone
30º Cone

Active Zone
60º zone

Changing sensor orientation is simple. This adjustment will allow the sensor‘s
optical axis roll angle to be set to any angle (typically only 0º, 45º or 90º
required.)

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 30

The Geometrics
program "CSAZ"
available on your
CD or our website
will give the user
the optimal sensor
angles for the area
of interest. See the
CSAZ manual
(under help in the
program) for further
explanation of the
use of CSAZ

Figure 33

7/16" Wrench

3/16" HEX L-

Loosen these
three screws
to rotate the
keel weight.

This roll angle is set by
the position of the keel
weight on the tow fish
body in relation to the
“T” containing the
sensor. To change this
angle, loosen the three
clamping screws at the
top of the clamp and
rotate the keel weight to
the desired position and
then tighten the
clamping screws (Figure

33)

NOTE: In current
design, the carrying
handle attaches directly
to the keel weight so
that loosening the
carrying handle will also
loosen the keel weight allowing rotation of the weight and handle at one time.

If a echo-sounder Altimeter is employed, then you will need to rotate the nose of
the fish also to keep the altimeter pointed towards the sea floor. Simply remove
the nose top cover and loosen the clamping screws (Figure 32) and rotate the
nose to line up the altimeter with the orientation weight. Retighten the nose
clamp screws and you are done. (Note: Do not remove the red trimmer string
that attaches the nose to the fish body unless you are replacing the nosepiece).

4.3.1 Sensor Positioning in Relation to the Dip Angle of the

Survey Area

Optimal positioning the G−882 cesium sensor is necessary to insure that the best
performance will be obtained for any given survey area. To accomplish this, we
recommend that the sensor be oriented such that the Earth’s magnetic field lines
(H field) are centered in its active zone. We also want the orientation to provide
nearly equal performance in all four towing directions (forward and reverse of two
orthogonal towing directions for tie lines) to facilitate a methodical survey plan.
To get information about sensor orientation we suggest you use the program
CSAZ available from our website and on the Magnetometer CD for complete
worldwide survey recommendations.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 31

Figure 34

The G-882 Magnetometer is shown with the keel weight positioned such that the

cesium sensor will tow in a position that is vertical to the surface of the earth.

Keel weight

Cesium sensor

Altimeter

Collar weight

Grab handle/CG tow point

Nose assembly

You can use the INCLINATION map (see figure 35) to estimate the proper
orientation angle anywhere in the world as described below A TOTAL
INTENSITY map is also provided to enable determination of the expected range
of readings for the survey area (see figure 36).

Since the G−882 has “automatic hemisphere switching”, reversing direction is
automatically handled and identical sensor positions are required for operation in
the Northern or Southern hemispheres. Thus there are three regions in either
hemisphere that are of interest with regards to positioning the G−882 cesium
sensor. These regions have dip angles or magnetic field inclination angles of 0 -

22.5, 22.5 - 67.5 and 67.5 - 90 in either hemisphere.

Assembling the G−882 as pictured below (vertical sensor) provides the best
operation in the 22.5 - 67.5 region. Note that in this picture the orientation

weight and CG tow point are attached to the tow fish such that the cesium sensor
will be maintained in a position vertical to the Earth’s surface while under either
nose tow or CG tow.

If an altimeter is present, the nose assembly must also be adjusted so that the
altimeter is also directed towards the seabed. See previous section on
adjustment procedures.

For the 67.5-90 inclination angle regions, roll the sensor to an angle of 45 with
respect to the Earth’s surface.

For the 0-22.5 inclination angle regions, roll the sensor 90°until it is horizontal
with respect to the Earth’s surface. CSAZ has more information on fine tuning
this orientation in equatorial regions.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 32

Roll angles other than 0, 45, and 90 tend to produce signal to noise ratio
patterns that are asymmetrical. This could cause unequal instrument
performance in the reverse and orthogonal directions of a typical survey.
See CSAZ program.

4.3.2 Main Field Inclination and Total Intensity Maps

The maps on the following two pages may be used to determine the inclination
and total intensity of the Earth's magnetic field in the survey area. The inclination
information may be used to properly adjust the sensor position for the best
performance in the intended area of survey. The intensity information may be
used as a check of the system operation, i.e., that the readings appear to be in
the range that is expected for the survey area. This information is also included
in the CSAZ program.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 33

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 34

Figure 35

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 35

Figure 36

36

CM-221
COUNTER

PC
MAGLOG

Trig/Event Mark
Not implemented
In the G-881

4.4 CM-221 Counter Data Format and Command Structure

The CM-221 counter module is a counting device that converts the cesium
Larmor signal (70 kHz to 350 kHz) into magnetic field strength in nano-Teslas
(20,000 nT to 100,000 nT). In addition there are 5 external 12 bit A/D channels
and 1 internal A/D channel that can be digitized and appended to the output data.
A Julian clock string can be enabled and added to the output data stream as well.
Finally there is an External Event pin that can be used for external trigger or event
marking.

The output data format is programmable. For example each of the A/D channels
can be added/removed from the output data stream by sending the appropriate
commands. There are several other commands that are discussed in detail later
in this document.

4.4.1 Output Format
Figure 13 shows the standard single counter configuration. Commands from the

PC are sent out the RS232 transmit pin (TxD) to the counter. Mag and other data
return on the receive pin (RxD).

Figure 37

Geometrics Inc. G-882 Cesium Marine Magnetometer Page

37

Upon power on the counter module defaults to its last saved setup as defined by
the user using the UPDATE function described later.

Baud rate: 9600 baud, 8 data bits, no parity, 1 stop bit
Cycle rate: 10 Hertz
Analog channels: Channel 0 (Larmor signal level) enabled, depth and altitude

Channels, when applicable, enabled, and channels 3-8 disabled.
Julian Clock: Disabled
Output Format: ASCII
The default output data stream contains all printable ASCII characters with each

sample terminated with a carriage return/ line feed sequence. The following
example illustrates this format where there are no depth or altitude analog
channels enabled:

char # description

------- ---------------------------------­ 1 An ASCII '$' (marks first character of data stream)

2 an ASCII '1' or a blank (depending on whether Mag reading is above or
below _99999.999 nT).

3-7 5 digits of Mag data
8 an ASCII decimal point ['.']
9-11 3 more digits of Mag data
12 an ASCII comma [',']
13-16 4 digits of A/D channel 0 (9999 full scale, 0 to +5 volts in). This channel

is internal
and contains the signal level of the magnetometer.

17 an ASCII carriage return
18 an ASCII line feed

Geometrics Inc. G-882 Cesium Marine Magnetometer Page

38

If the data were captured to a file and then copied to a line printer the printout
would look something like this:

$ 49895.131,1249
$ 49895.376,1287
$ 49995.517,1245
$ 49995.293,1272
$ 49995.835,1229
$ 49995.071,1281
$ 49995.159,1298
$ 49995.508,1214
$ 49995.216,1245
$ 49995.347,1297

Counter modules can be daisy chained to form multiple sensor arrays as shown
in Figure 14. Note that the output data from counter 0 goes into the input port of
counter 1, and so on. This allows each counter module to append its output data
onto the end of the data stream coming from the previous counter(s). As each
counter receives data characters from previous counters they get echoed to the
next. An exception to this is the carriage return/ line feed sequence. The carriage
return is replaced by a comma and the line feed is ignored. Thus one long
concatenated string from all counters is output from/through the last counter, and
is terminated by a carriage return/ line feed sequence by the last counter only.

Note that only the first counter outputs a preamble character (the default
character is '$').

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Figure 38

MULTI-COUNTER MODULE CONFIGURATION

4.4.2 General Command instructions

Commands are sent into the input port of the first counter. Note that commands
are the only characters that enter the first counter. A command string is stored in
an incoming buffer until terminated by a carriage return. The command will then
be executed at the end of the current sample, immediately after the last 'data' byte
has been sent out the output port. Then the command will be echoed to the next
counter (or back to the logging computer if it is the last/only counter in the chain).

Subsequent counter modules in multiple counter arrays differentiate between
output data and commands by assuming that all characters between the data
preamble character ('$' is the default) and the next line feed are Data bytes from
the previous counter(s). Commands only arrive at subsequent counters after the
data transmission is complete. Each command is identified by the first character,
followed by some number of operand characters and a carriage return.

Only one command can be sent at a time. After each command wait for the
command echo before sending another.

All commands are terminated with a carriage return. A line feed may be sent as
well, but it will be ignored by each counter module. However, at the end of every
output data string there will be a carriage return and a line feed sent. This method
insures that the final counter will have a carriage return/line feed sequence so that
if the file is printed it will look correct on paper. By using the carriage return as the
command terminator and stripping input line feeds insures that dumb terminals
(and dumb terminal emulation software) can be used to control the counter
output. (Dumb terminals do not normally transmit line feeds when <Enter> is
pressed).

4.4.3 G−882 Quick Command list

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This is a list of commonly used commands for the G−882 magnetometer. For a
full list of commands and command options refer to the commands section of the
manual (below).

Set Cycle time
C0100 <enter> sets the magnetometer to sample at 1 second intervals.
C0010 <enter> sets the magnetometer to sample at 0.1 second intervals.

Set A/D channels on/off for a single magnetometer (see full list for control of more
than one magnetometer) '0' = turn off channel; '1' = turn on channel.
The G−882 has a total of 8 analog channels (0-7) plus magnetic field reading.

A11 turns on channel 1
A12 turns on channel 2
A13 turns on channel 3 (up to 8 analog channels)

A01 turns off channel 1
A02 turns off channel 2
A03 turns off channel 3 (up to 8 analog channels)

In a typical system they are designated as follows:
Magnetic field (always on)

Chan. 0 signal
Chan. 1 depth
Chan. 2 altimeter
Chan. 3 Brightness indicator
Chan. 4 RF effort indicator
Chan. 5 28 volts at magnetometer
Chan. 6 humidity inside magnetometer
Chan. 7 heater

Note: The depth, altimeter, and 28 volts need to have calibration coefficients
applied to convert to feet, meters, or volts.

4.4.4 G−882 Detailed Commands

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Here are the current list of commands and the format of each:

Command Format: Description:

----------------- ----------- ---------------------------------­Set Cycle time Byte 1: 'C' Set time in 0.01 sec increments

2: x MS digit of number ('0'-'9')
3: x 3S digit of number
4: x 2S digit of number
5: x LS digit of number
x: x 5 MS optional char ('0' or '5')
6/7: CR carriage return

[Note: the 5 MS char is optional. It was added
to allow setting the cycle time to more precision
after the initial software release]

Set A/D ch's Byte 1: 'A' Enable/disable A/D channels
2: x '0' = turn off channel; '1' = turn on
3: x select channel #('0'-'7')('0'-'7' for CM-

221)
4: x MS digit of counter # ('0' or '1')
5: x LS digit of counter # ('0' - '9')
6: CR carriage return

[Note: characters 4 and 5 can be omitted. If this is done the
command will default to counter 0.]

Change Baud Rate Byte 1: 'B' Baud rate change command
2: x MS char (1,0,0,0,0,0,0)
3: x S char (9,9,4,2,1,0,0)
4: x 3S char (2,6,8,4,2,6,3)
5: x 2S char (0,0,0,0,0,0,0)
6: x LS char (0,0,0,0,0,0,0)
7: CR carriage return

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Command Format: Description:

----------------- ----------- ---------------------------------­Output Format Byte 1: 'O' select output format

2: x format select:
'A'= ASCII (default)
'E'= excess 3
'P'= packed BCD
'S'= Sandia G822A fmt
x: x '0' = Sandia single Mag
'1' = Sandia dual Mag
3: CR carriage return

[Note: the '0' and '1' 3rd characters are valid only when selecting the
Sandia format]

Julian Clock Format: Byte 1: 'O' select output format
2: J format select:
3: x Day field: '1'= on ; '0' = off
4: x Hour field: '1'= on ; '0' = off
5: x Min field: '1'= on ; '0' = off
6: x Sec field: '1'= on ; '0' = off
7: x 10mS field: '1'= on ; '0' = off
8: x MSB of counter # ('0' or '1')
9: x LSB of counter # ('0' thru '9')
10: CR carriage return

[Note: characters 8 and 9 can be omitted. If this is done the
command
will default to counter 0.]

Julian Time Enable: Byte 1: 'J' Enable/Disable Julian time output
2: x '0' = turn off; '1' = turn on
3: x MS digit of which counter ('0','1')
4: x LS digit of counter # ('0' - '9')
5: CR carriage return

[Note: characters 3 and 4 can be omitted. If
this is done the command will affect all
counters in the chain.]

Set Julian Day: Byte 1: 'D' Set the Julian day number
2: x MS digit of number ('0'-'3')
3: x 2S digit of number ('0'-'9')
4: x LS digit of number ('0'-'9')
5: CR carriage return

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Command Format: Description:

----------------- ----------- ----------------------------------

Set Hour: Byte 1: 'H' Set the hour
2: x MS digit of number ('0'-'2')
3: x LS digit of number ('0'-'9')
4: CR carriage return

Set Minute: Byte 1: 'M' Set the minute
2: x MS digit of number ('0'-'5')
3: x LS digit of number ('0'-'9')
4: CR carriage return

Set Second: Byte 1: 'S' Set the second
2: x MS digit of number ('0'-'5')
3: x LS digit of number ('0'-'9')
4: CR carriage return

Find counters: Byte 1: 'F' Find and assign counter numbers
2: '0' assign first counter as # 0 (MSB)
3: '0' LSB
4: CR carriage return

Set Preamble Byte 1: 'P' Set the preamble char ('$')
2: x The desired character
3: CR carriage return

Jump to debug Byte 1: 'X' first char of 'XBUG' string
2: 'B' 2'cnd char
3: 'U' 3'rd char
4: 'G' 4'rth char
5: CR carriage return

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Command Format: Description:

----------------- ----------- ---------------------------------­Error echo Byte 1: 'E' Syntax err - echo 'ERR' + counter #
2: 'R' 2'cnd char
3: 'R' 3'rd char
4: x MS digit of counter number ('0'-'1')
5: x LS digit of counter number ('0'-'9)
6: ':' colon delimits error message cmd

[Note: xxx: bad command string is echoed in the
following characters, followed by a ...
x: CR carriage return]

Reset Byte 1: 'R' Reset the microprocessor
2: 'E' 2'cnd char
3: 'S' 3'rd char
4: 'E' 4'th char
5: 'T' 5'th char
6: CR carriage return

Interrogate Setup: Byte 1: 'I' Interrogate command
2: x item select:
'A'= Analog output fields selected
'J'= Julian Clock fields selected
'V'= software version number.
3: x MS digit of counter number ('0'-'1')
4: x LS digit of counter number ('0'-'9)
5: CR carriage return

[Note: Characters 3 and 4 are optional. If they are omitted the
command
will return the output from counter 0.

4.4.5 Update Default Parameters

Your magnetometer has been supplied with a default parameter update function.
This means that you may change the operational parameters (baud rate, cycle
time, number of analog channels turned on) and then save that configuration in
the processor non-volatile memory so that the next time the magnetometer is
started, these parameters are loaded. Once the configuration is set by the user,
and the user determines he or she would like to save this configuration,
the UPDATE command is sent by the MagLogLite or MagLog program via the
CM201CFG.EXE program. The CM201CFG is placed on the computer desktop
when the MagLogLite or MagLog program is installed and is available to check or
change the magnetometer configuration and store the values in non-volatile
memory. Clicking on the STORE CONFIGURATION (lower left button) sends
the proper commands to the magnetometer counter board(s).

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Figure 39

Alternately the user may store the configuration manually using a terminal
emulator such as Hyperterminal by entering the following commands:

Update Byte 1: 'U' Update operation parameters
2: 'P' 2nd character
3: 'D' 3rd character
4: 'A' 4th character
5: 'T' 5th character
6: 'E' 6th character
7: CR carriage return
[Note: If it is desired to permanently save any changes to the operation
parameters that may have been made, sending an UPDATE command before
powering down will save them. The next time the system is powered-on the new,
saved parameters will be used.]

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The addressed counter will insert characters into the command string just
before the carriage return before echoing to subsequent counters. See
detailed command description for format and definition of these added
characters.

4.4.6 Command Set Descriptions
Cycle Time Set:

Cycle time is set by transmitting the number of 0.01 second increments needed to
make the desired output rate. The default rate is 10 hertz (C0010). To set the
output rate to 1.2 seconds the command string would be "C0120".

After the initial software release another character was added to allow the cycle
time to be set to 5 ms resolution. To maintain compatibility with older versions
this character is optional. For an example on using this extra precision, the
command "C00125" would set the cycle time to 8 hertz (125 ms).

A/D channel select/enable:

Three pieces of info are needed to select and turn on/off an A/D channel: The
counter #, the channel number, and a flag indicating whether to enable or disable
that channel. The enable/disable flag is sent first (after the 'A' command
identifier). A '0' character will turn off the channel, a '1' turns it on. The next
character specifies the channel number (0-5 for CM-201 or 0-7 for CM-221),
followed by 2 characters indicating the counter number (00-19). If the counter
number is not sent then it defaults to counter 0.

Baud Rate Change:

The baud rate can be commanded to change by giving a 'B' command character
followed by 5 more number characters specifying the desired baud rate. Valid
baud rate commands are: 'B19200', 'B09600', 'B04800', 'B02400', 'B01200',
'B00600', and 'B00300'. This command will not execute until the entire command
has finished echoing out to the next counter/logging device. This allows the
command to propagate through all counters and be implemented before output
data arrives at a different rate.

Output Format Select:

The default (ASCII) output format is described in detail at the beginning of this
document. This is the easiest format to view and import into various processing
utilities. It is also very inefficient in terms of disk storage space and time required
to transmit each cycle. There are three other output formats that can be used as
well:

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Packed BCD:

Packed BCD format throws away all commas, decimals, spaces, and the
magnetometer most significant byte ('1' if more than 100,000 nT, or a blank is less
than 100,000nT). The Preamble character is left alone. In addition all numeral
characters (ASCII codes 30 hex through 39 hex) have the upper nibble (always a

3) discarded and two lower nibbles combined to form one byte. Finally, the
carriage return, line feed sequence is replaced with a single terminating
character '*' (2A hex).

It is very difficult to show what these files would look like if displayed on a
computer screen since each type of computer would display these binary
characters differently. Many of these binary characters would be interpreted as
screen commands which might ring the bell or clear the screen. Therefore it is
necessary to convert ASCII printouts to hexadecimal numbers to show the
Packed BCD format.

An ASCII counter output of:
'$ 54369.127,1234,5678,0000'(plus carriage return line feed)
converted to hexadecimal numbers would be:
24 20 35 34 33 36 39 2E 31 32 37 2C 31 32 33 34

2C 35 36 37 38 2C 30 30 30 30 0D 0A

[ '$'= 24, ‘ '= 20, '.'= 2E, ','= 2C, CR/LF = 0D 0A,

'0'-'9'= 3x (where x = number 0-9)]
Note: ‘ ‘ signifies a blank

Using the above definition the same data in packed BCD
output format would be:

24 54 36 91 27 12 34 56 78 00 00 2A
\ \ \ \ \ \___Terminating character ('*')
\ \ \ \ \__analog channel #3 ('0000')
\ \ \ \__analog channel #2 ('5678')
\ \ \__analog channel #1 ('1234')
\ \__Mag reading ('54369.127')
\__Preamble Character ('$')

Note how easy it is to see the numbers if viewing a hex dump of the data.
Remember though that it must be translated to printable characters before
copying the raw data to printers or a CRT screen.

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Commands that are echoed through the counter chain are received and sent as
unmodified ASCII strings. Thus all commands will appear in the binary data set
after the next '*' data terminating character and will be terminated itself by a
carriage return line feed sequence. Binary transmission then resumes with the
next sample.

Excess 3 format:

Excess three format is very similar to packed BCD. In fact the only difference is
that each byte has 33 hex added to it after converting to Packed BCD. The
reason for adding 33 hex to each packed BCD number is to avoid some difficult
pitfalls with Packed BCD:

Packed BCD is a very common format but has many potential problems that can
arise. ASCII digits are combined to form bytes with hexadecimal values in the
control character range (less than 20 hex) which must be handled very carefully
by the logging program. Examples of these characters include the Ctrl-S and
Ctrl-Q software handshake controls (11 hex and 13 hex), the bell character (Ctrl­G, 07 hex), and the ASCII null (Ctrl-shift-@, 00H). Most terminal emulation
programs can be configured to handle these characters as data instead of
commands, but this is not the way the typical default configuration is set up.

Packed BCD eliminates this by shifting all numbers up by 33 hex. This moves all
possible output values out of the control character range. It also makes them
printable to a screen or printer without bells, beeps, screen clears, form feeds,
etc. However they will still look like gibberish without translation.

Sandia/G822A format:

This is a printable ASCII format that mimics the output from a one or two channel
G822A magnetometer. Its output is limited to one counter module, with the Mag
and signal level values as the only data being sent out. The Mag reading is
preceded with an 'A' followed by 10 characters of ASCII Mag data. The G822A
format sometimes has a second Mag reading following the first which is preceded
with an ASCII 'B'. If selected the CM-221 counter places the signal level in the
first 4 significant characters of the second Mag data slot. The sample is
terminated by a carriage return line feed sequence.

The purpose of this format is to allow customer with existing G822A Sandia
logging software to be able to use the CM-221 without upgrading to new logging
software.

The single channel Sandia format is selected with the command string "OS" or
"OS0". The dual channel output is selected by the command string "OS1".

Example outputs:

This is the ASCII output example from earlier, but with 3 A/D channels:

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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
$ 49895.131,1249,0004,0005
$ 49895.376,1287,0003,0007
$ 49995.517,1245,0003,0006
$ 49995.293,1272,0005,0006
$ 49995.835,1229,0004,0005
$ 49995.071,1281, 0006,0006
$ 49995.159,1298, 0003,0007
$ 49995.508,1214,0004,0007
$ 49995.216,1245,0004,0004
$ 49995.347,1297,0003,0005

Similar data displayed in hexadecimal:

- - - - - - - - - - - - - - - - - - - -
24 20 39 39 37 37 38 2E 31 33 31 2C 33 37 34 39

2C 30 30 30 34 2C 30 30 30 35 0D 0A 24 20 39 39
38 39 30 2E 33 37 36 2C 33 36 38 37 2C 30 30 30
33 2C 30 30 30 37 0D 0A 24 20 39 39 39 35 35 2E
35 31 37 2C 33 35 34 35 2C 30 30 30 33 2C 30 30
30 36 0D 0A 24 20 39 39 39 39 38 2E 32 39 33 2C
33 34 37 32 2C 30 30 30 35 2C 30 30 30 36 0D 0A
24 31 30 30 30 37 38 2E 38 33 35 2C 33 33 32 39
2C 30 30 30 34 2C 30 30 30 35 0D 0A 24 31 30 30
30 33 32 2E 30 37 31 2C 33 33 38 31 2C 30 30 30
36 2C 30 30 30 36 0D 0A 24 20 39 39 39 37 39 2E
31 35 39 2C 33 34 39 38 2C 30 30 30 33 2C 30 30
30 37 0D 0A 24 20 38 36 37 37 38 2E 35 30 38 2C
33 35 31 34 2C 30 30 30 34 2C 30 30 30 37 0D 0A
24 20 37 38 37 37 38 2E 32 31 36 2C 33 36 34 35
2C 30 30 30 34 2C 30 30 30 34 0D 0A 24 20 36 39
39 37 38 2E 33 34 37 2C 33 37 39 37 2C 30 30 30
33 2C 30 30 30 35 0D 0A

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Similar data in Packed BCD format:

- - - - - - - - - - - - - - - - - ­ 24 99 77 81 31 37 49 00 04 00 05 2A 24 99 89 03

76 36 87 00 03 00 07 2A 24 99 95 55 17 35 45 00
03 00 06 2A 24 99 99 82 93 34 72 00 05 00 06 2A
24 00 07 88 35 33 29 00 04 00 05 2A 24 00 03 20
71 33 81 00 06 00 06 2A 24 99 97 91 59 34 98 00
03 00 07 2A 24 86 77 85 08 35 14 00 04 00 07 2A
24 78 77 82 16 36 45 00 04 00 04 2A 24 69 97 83
47 37 97 00 03 00 05 2A

Similar data in Excess 3 format:

- - - - - - - - - - - - - - - - ­ 57 CC AA B4 64 6A 7C 33 37 33 38 5D 57 CC BC 36

A9 69 BA 33 36 33 3A 5D 57 CC C8 88 4A 68 78 33
36 33 39 5D 57 CC CC B5 C6 67 A5 33 38 33 39 5A
57 33 3A BB 68 66 5C 33 37 33 38 5D 57 33 36 53
A4 66 B4 33 39 33 39 5D 57 CC CA C4 8C 67 CB 33
36 33 3A 5D 57 B9 AA B8 3B 68 47 33 37 33 3A 5A
57 AB AA B5 49 69 78 33 37 33 37 5D 57 9C CA B6
7A 6A CA 33 36 33 38 5D

Similar data displayed in dual channel Sandia/G822A ASCII format:

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
A9977813100B3749000000

A9989037600B3687000000
A9995551700B3545000000
A9999829300B3472000000
A0007883500B3329000000 (Note how the most significant '1'
A0003207100B3381000000 is truncated for readings greater
A9997915900B3498000000 than 100,000 nT).
A8677850800B3514000000
A7877821600B3645000000
A6997834700B3797000000

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The same data in single channel Sandia format (ASCII):

A9977813100
A9989037600
A9995551700
A9999829300
A0007883500
A0003207100
A9997915900
A8677850800
A7877821600
A6997834700

Julian Time Set:

The Set Time commands (D,H,M,S) will initialize the time in all counter modules.
If a particular counter has all Julian clock fields enabled the output string will have
the following inserted after the last A/D channel and before the CR/LF:

,DxxxHxxMxxSxx_xx
The x's would be ASCII characters (0-9) as required. The time registers are not

incremented until enabled with the 'J1xx' command, so they can be set up then
synchronized by sending the enable command at the correct time.

In Packed BCD and excess format the letters D,H,M,S, and _ are stripped and
the data encoded as per the Mag data above. The Day info is put into 2 bytes
with the most significant nibble of the most significant byte set to zero.

Julian Time Enable:

This command starts/stops the Julian clock. To start the clock on counter 0 the
command would be "J100". "1" turns on the clock, while the "00" selects counter

0. To turn off the clock update on counter 2 the command would be "J002".
If the counter number information is omitted the command will affect all counter in

the chain. Thus the command "J0" will turn off the update for every counter.
Note that the "Jxxx" command only affect whether the clock increments with time.

It has no effect on whether or which clock fields are output. The "OJxxxxxyy"
commands selects which field are output.

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Julian Output format:

There are five clock output fields that can be turned on or off. These are the
Julian Day, Hour, Minutes, Seconds, and Fractional seconds (to .01 seconds).
These are selected with the "OJxxxxxyy" command. Each of the five x's
corresponds to an output field, and can either be a '0' or a '1'. '1' turns the field
on, '0' turns the field off. The yy characters is the counter number. Following is a
diagram showing which character corresponds which each display field:

command: "OJ0111103"
\ \ \ \ \ \ \__Counter number LSB
\ \ \ \ \ \__Counter number MSB
\ \ \ \ \__10 ms field
\ \ \ \__Seconds field
\ \ \__Minutes field
\ \__Hours field
\__Days field

In this example counter three would have all clock fields output except the Julian
Day.

The counter number characters are optional. If not present the command would
affect only counter 0 in the chain.

Find Counters:

This command is used to figure out how many counters there are in the daisy
chain. An 'F00' is sent to the first counter which assigns it as counter 0. Before
the command is echoed to the next counter the command is modified to 'F01'.
The next counter modifies it to 'F02', and so on until the logging PC gets the
command echo of 'Fxx' where xx is the number of counters in the chain.

Continuous data output can be inhibited by sending the command 'F01' to the first
counter. In this mode there is no first counter (#00) which normally starts data
transmission. Data output can be resumed by sending a new 'F00' command.

Set Preamble character:

By default the first character of each data stream is a '$'. If another character is
desired the 'Px' command is used to change it to the character sent following the
'P'. All characters are allowed except control characters, digits (0-9), spaces,
commas, decimal points, and the termination char ('*').

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Echo Error command:

This is not really a command but a message. If a command string is incorrectly
sent or garbled the counter receiving it will change it to 'ERRxx' before echoing it
to the next counter. 'xx' specifies the counter number where the syntax error first
occurred. This error message is interpreted as a command by subsequent
counters which echoes the string unchanged.

Interrogate Setup command:

This command allows the operator or logging software to identify which analog
channels and Julian clock fields are being output via the serial port. This
information is used to verify output fields with their hardware channels, and to
allow automated calculation of data field position within each sample being sent
out. In addition the software revision number can be interrogated.

The first character 'I' designates the interrogate command, the second letter
designates which item to interrogate. 'A' specifies interrogating the analog
channels, 'J' specifies the Julian clock, and 'V' specifies the software revision
number.

The next two characters specify the counter number '00' through '19'. If the
counter number is omitted, counter 0 will respond.

The addressed counter will insert a response into the command string before
sending echoing it out the serial port to the display terminal or subsequent
counter modules. Subsequent counter modules will ignore these extra response
characters and pass them unmodified down the chain. The response format for
each of the three interrogate items are detailed in the examples below:

Analog channels:
The command "IA01" will command counter number one to output

characters indicating which of the six analog channels have been selected
for output. Counter 1 will modify the command string to "IA01:abcdef"
where the letters a-f are either an ASCII '0' (channel off) or '1' (channel on)
corresponding to channels 0-5 respectively. If analog channel 0,3, and 4
were selected on counter 1 the echoed command string would be

"AI01:100110" followed with a carriage return line feed.
Julian Clock:
The command "IJ" will command counter 0 to output which Julian clock

fields have been selected for output (note that the two digit counter number

was not specified, so counter 0 responds by default). Counter 0 will modify

the command string to "IJ:abcde" where the letters a-e would be replaced

with an ASCII '0' (field off) or '1' (field on). The five output fields are:

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a: Julian day
b: Hour
c: Minute
d: Second
e: Fractional Seconds (to 10 milliseconds)

If counter 0 had all clock fields selected for output except the Julian Day it

would modify the command string to "IJ:01111" followed with a carriage

return line feed.
Software Version Number:
The command "IV02" will command counter 2 to send its two character

software version number. Counter 2 would change the command string to

"IV02:xx" where xx is the version number of the software. If Counter 2 was

software version "A4" then the echoed command string would be

"IV02:A4" followed by a carriage return line feed.

Reset command:

If the command 'RESET' is sent to the counter a power up reset will occur
initializing all parameters to default. The reset sequence will not start until the
reset command has finished echoing out the RS232 port to the next
counter/logging device. This allows each device down the chain to reset in
sequence.

Update command:
If the command 'UPDATE' is sent to the counter, any parameters that were

changed, will be saved and be the default parameters the next time the system is
powered on. This command must be sent before powering down of the changes
will be lost.

Jump to debug:

If the command string 'XBUG' is received the counter will do a one way jump to
factory debug mode where a rudimentary operating system allows probing of
registers, ports and memory for debugging purposes. It will only function properly
with a single counter module (no daisy chained counters).

4.4.7 Power-up Initialization
By default all counters will wake up thinking that they are counter #0 and begin to

output data at the default 10 hertz rate or as set by default parameters in flash
memory. This data will appear as a synchronization command to subsequent

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counters and will cause a brief adjustment period until each counter determines
where it stands in the daisy chain. Thus there will be a short period of garbled
transmissions to the logging PC upon power-up or reset.

4.5 Accessory Software

4.5.1 Cesium Sensor Active Zones – CSAZ

A newly designed CSAZ Windows™ program is available on our Magnetometer
CD and from our FTP site at ftp://geom.geometrics.com/pub/mag/Software/
(look for csaz-setup.exe). Please read the manual that is included with the
program for complete instructions on how to use the CSAZ program for
worldwide inclination and sensor orientation solutions.

4.5.2 CM201

Note: Cm201 and View201 are DOS software and compatible with CM-221
counters. They are installed from the Magnetometer CD under Utilities. Some
modern computers may not run these DOS programs correctly.

Cm201 is a program that facilitates sending a command start-up file to the

G−882 counter(s) and initiating system operation. The program is executed by

typing “cm201” at the DOS prompt and pressing return. Cm201 expects a

counter command file that must be called Cm201go.cnf. This file is a list of
counter commands, each followed by a carriage return that may be required to
configure the counter to your application.

This software and all its necessary files may be installed on your system by
placing the Install disk in either your a: or b: floppy drive, switching to that drive,
typing “install” at the DOS prompt and pressing return. Install will ask a number
of questions to which you should respond to configure the CM-221 counter to
your system and create the Cm201go.cnf file.

If, after installing Cm201, if further commands are required (such as CLOCK) to
configure CM-221 operation to your application, they may be added to the
Cm201go.cnf file by editing this file with any suitable text editor.

The following describes Cm201 and the files that will be installed on your C:
drive:

Install.bat

This is a batch file used to copy the contents of the Utility Software onto your
hard disk. A directory called "GeoUtil" is created on the "C" drive and then all
of the files are copied into that directory. After the files are copied, this batch
file then runs Cm201set.bat

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Cm201Set.bat

This batch asks the user questions and based on the answers to these
questions creates a batch file called "Cm201.bat". The questions include such
things as, to which COM port the CM-221 counter is connected.

Cm201.bat

This batch file is created by Cm201set.bat. It invokes Cm201go.exe to send
any command lines necessary to correctly configure the CM-221 counter(s) for
the users application.

Cm201go.exe

This program is intended to send any commands to correctly configure the CM­221 counter module(s). Normally the commands are taken from the file
Cm201go.cnf, but this can be overridden if needed.

The calling syntax for this program is:
Cm201go FileName.cnf /b:BBBBB /p:P /i:I /d:D
Where:

BBBBB Is the baud rate that the CM-221 starts at. Normally this is

9600.

P The port number /p:1 would mean use COM1. This

parameter is optional. If it not specified COM1 will be used.

I The interrupt number to use. This parameter is optional. If

it is not specified the normal interrupt for the COM port is
used.

D Any value other than zero will turn on the debugging

display. This parameter is optional. If it is omitted the
debugging display is disabled.

The contents of the Cm201go.cnf file are sent line by line to the CM-221
counter module(s). After each line is sent the CM201go program waits for the
confirmation that the command was received correctly. If the confirmation is
not received the line is repeated. For lines that change the CM-221's baud rate
the Cm201go program changes its baud rate as required. If the input line has
the special code "[CLOCK]" on it, the CM-221's clock will be set to match that of
the PC.

A typical Cm201go.cnf would be:

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[CLOCK]
c0010
oj11111

Commflip.exe
Given the port numbers of two COM ports this program will exchange their

addresses. On some note book computers this is needed to be able to use
some software.

batmenu.exe, drawbox.exe, gotoxy.exe, yymmdd.exe, foreach.exe,
getkey.com

These programs are utility programs that allow the batch files to interact with
the user.

4.5.3 View201 Lab Display Software

View201 is a program that enables programming and viewing the
magnetometer and analog data from one to three CM221 counter modules. It
was written primarily as a factory debug/test utility and is provided as a tool to
help installation and testing of the counter(s) in the field. The output can be
viewed in both raw text and in graphics mode. In addition the output data can
be logged to disk if desired. The program defaults to using Com port #1,
although Com port #2 can be used be adding " /COM2" to the command line
after "View201".

Upon startup the program listens to the output data stream from the counter(s)
and synchronizes to the output baud rate. The raw output data is then
displayed in a data text window. Along the top is a status bar showing the
condition of the serial port and the serial input buffer.

View201 defaults to using COM port #1. COM port #2 can be selected by
typing "View201 /COM2" and <ENTER> at the DOS prompt.

After the magnetometer has warmed up the first comma delimited field should
be showing a stable magnetometer reading. The default counter output format
includes the 4 character signal level in the next field (9999 full scale). Other
data may be present as well depending on output configuration. If more than
one magnetometer is daisy chained together there will be other magnetometer
data field embedded in the output stream.

Commands can be sent to the counter module(s) at anytime. There are many
commands that control the CM-221 which are detailed in the magnetometer
manual. As an example, the command "A0000" followed by a carriage return
turns off analog channel 0 (signal level) in counter 00: Each character is sent

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as it is typed and stored by the counter. When a carriage return is received by
the counter the command is executed and then echoed down the daisy chain of
counters until it is received back by the View201 program and displayed in the
data window. A correctly echoed command string is a confirmation that the
command was received and executed properly. Mis-typed or invalid commands
will be turned into an error message and echoed through to the View201
display window. (Type A1000<return> to turn the signal level channel back on).

The magnetometer data can be viewed in graphics mode by pressing the <F5>
function key. View201 defaults into displaying the magnetometer data from
counter #0 at 10 nT full scale. Data from the second and third magnetometer
can be displayed by pressing <F2> and <F3> respectively. If magnetometer 2
or 3 are not present the data fields are set to zero.

Data can be logged to disk at any time by pressing <F10>. A filename is
created based on date and time and logged to disk. A logging message is
displayed and a low frequency beeper plays to indicate that logging is taking
place. Pressing <F10> again stops the logging process.

Currently, View201 only recognizes the ASCII output format. This is the default
output format, but there is nothing preventing a change format command from
being sent to the counter module. If the output format is changed the View201
program will cease to function correctly.

A list of function keys and their use can be viewed at anytime by typing a
question mark (?).

Following is a description of each View201 function key. These are all
functions that control the operation of the View201 program and should not be
confused with commands that affect the counter module:

4.5.3.1 Function Keys

<F1> = Toggle graphics display of Mag1 on/off. Default setting is on.
This
key has effect in graphics mode only.

<F2> = Toggle graphics display of Mag2 on/off. Default setting is off. If
turned on and no magnetometer#2 is present the magnetometer 2
data value is forced to zero. This key has effect in graphics mode
only.

<F3> = Toggle graphics display of Mag3 on/off. Default setting is off. If
turned on and no magnetometer#3 is present the Mag3 data
value
is forced to zero. This key has effect in graphics mode only.

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<Alt F1> = Toggle graphics display of Grad1 on/off. Gradient channel 1 is
the
difference between Mag1 and Mag2. This key has effect in
graphics mode only.

<Alt F2> = Same as <Alt F1> except it applies to Grad2 channel.
<Alt F3> = Same as <Alt F1> except it applies to Grad3 channel.
<Shft F1>= Change graphics display color for Mag1. Press this key several

times to cycle through the 16 colors available for displaying
mag1.
Note that the display indicator for Mag 1 in the lower left hand
corner of the graphics display changes as well, aiding in
identifying
which trace belongs to which variable. This key only has effect in
graphics mode.

<Shft F2>= Same as <Shft F1> except it applies to Mag2 channel.
<ShftF3> = Same as <Shft F1> except it applies to Mag3 channel.
<Ctl F1> = Change graphics display color for Grad1 trace. Press this key

several times to cycle through the16 colors available for
displaying
Grad1. Note that the display indicator for Grad1 in the lower right
hand corner of the graphics display changes as well, aiding in
identifying which trace belongs to which variable. This key only
has effect in graphics mode.

<Ctl F2> = Same as <Ctl F1> except it applies to Grad2 channel.
<Ctl F3> = Same as <Ctl F1> except it applies to Grad3 channel.
<F4> = Toggle between true and normalized gradient display. When

measuring gradients it often desirable to center the display trace
to
the center of the screen so that small variations do not cause
screen wrapping. Pressing F4 will calculate and add an offset
value to force the gradient display traces to the center. Pressing
F4 again will toggle back to absolute display mode. Note that the
Grad display indicators in the lower right hand corner of the
graphics display screen change from "Gradx" to " "GradZx"
indicating the current mode. Note that this normalizing only takes
place on gradient channels.

<Alt F4> = Toggle true and normalized w. offset grad display. When

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measuring gradients with all three gradient channels turned on it
is
often desirable to move the three gradient traces close to the
center of the display - but not place them right on top of each
other. This key works the same as F4 above but leaves the
traces
slightly offset from one another.

<F5> = Toggle between graphics and text display mode.
<F6> = Lower the magnetometer full scale coefficient in the graphics

display window. This key only affects the Mag channels (not
gradient).

<F7> = Raise the magnetometer full scale coefficient in the graphics
display window. This key only affects the Mag channels (not
gradient).

<Alt F6> = Lower the Grad full scale coefficient in the graphics display
window. This key only affects the Grad channels (not
magnetometer).

<Alt F7> = Raise the Grad full scale coefficient in the graphics display
window. This key only affects the Grad channels (not
magnetometer).

<F8> = Clear next graphics screen and jump to it.
<F9> = Clear Break, Frame, and Parity errors in the Com port status bar

(text display screen only).
<ALT F9>= Auto adjust to incoming baud rate and clear errors.
<F10> = Toggle logging to disk.
<Esc> = Exit to text mode (if in graphics display mode). Exit to DOS (if text

mode and not logging to disk).

4.5.3.2 Displaying Analog Channels

When in graphics display mode [F5] up to six analog channels may be enabled
by typing <CTRL A>. This will activate a series of questions to format the
analog data for display:

Display Channel Number [0-5]:

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Selects one of six display channels. Any channel can be selected. The default
number is the first unused display channel. If a channel currently in use is
selected all subsequent menu items will have their default values set to the
current values. This makes it easy to modify the format of a channel currently
being plotted by simply pressing <enter> until the parameter to modify is
reached.

Display channel ON/OFF [0/1]:
Type '0' to turn a channel off. No further menu parameters will follow and the

channel will stop plotting. Type '1' to turn the display channel on or just
<ENTER>, which defaults to on.

Counter Number [0-2]:
Selects which counter the analog data will come from. Up to three daisy

chained counters may be logged by this program. The default is always
counter 0 (the first [or only] counter).

Analog Channel Number [0-5]:
Selects which A/D channel of the above counter is to be displayed.

Note:

1) Do not confuse "analog channel number" with "display channel

number" above. They are not related in any way. Think of the

display channels as 6 separate input channels to a 6 channel

analog strip chart recorder. The counter channel numbers (along

with counter number information) specify a particular analog

information channel. With three counters there could be 18

separate information channels - anyone of which could be

configured to any display channel. In fact one analog channel

could be assigned to two display channels with differing full scale

coefficients - allowing a course and fine graphics display of the

same channel.

2) This program does not know which analog channels are

actually coming out of the counter. It is possible, for example, for

the counter to be commanded to output channels 0, 4, and 5 only.

This program sees only three analog channels in the counter's

data stream and will refer to them as channels 0,1, and 2.
Unipolar/Bipolar [U/B]:
As described in the magnetometer/counter manual there are 4 unipolar

(including the signal level) [0 to +4.096 volts], and 2 bipolar channels [ñ 2.048
volts]. This parameter is used to signify which type of analog channel this is.

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Clip/Wrap [C/W]:

This parameter specifies what to do when the analog data exceeds the full
scale setting (see next paragraph). Clip mode causes the data to be clipped at
full scale so that the channel traces the top of the display screen (or possibly
the bottom of screen in bipolar mode). Wrap allows the trace to over-scale and
wrap back around to the bottom or top of the screen.

Full Scale Set:
Set the full scale value of the display using the "+" and "-" keys. Note that a

value of 10000 nT FS display as "0000" full scale. All other values display
correctly in the allocated 4 digits.

Label:

This allows a 10 character label to be associated with the analog channel.
These labels make it easy to identify what each trace is at a glance by looking
at the label (which is printed at the top of the screen) and correlating the
label's color to the matching display trace color. To erase the default label of
"channel n" use the backspace key, then enter a new one.

Set trace color:

Use the "+" and '-' keys to cycle through all the possible trace colors using the
label name entered above as a guide.

After the above data have been entered, the display channel will be plotting. At
the top of the screen all of the activated display channels are documented in
the same color as their associated trace color as in the following example:

Pitch
A131000C

The display channel in this case was labeled "Pitch". Underneath it is a
shorthand display of all the setup parameters:

"A" : signifies this is an analog channel.
"1" : the counter number [0-2]
"3" : the counter channel number [0-5]
"" : Bipolar mode, would have been set to "-" for unipolar
"1000" : Full scale value. If "0000" is displayed it mean "10000" full scale.
"C" : Clipped display, would be a "W" for wrap mode.

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At the right edge of the screen are two normalized scales for the analog data.
One scale is for unipolar analog channels [0-100%],and the other is for bipolar
channels [ 50%].

4.5.4 Depth Cal

This program is intended for use only if you purchased logging software other
than MagLog-Lite or MagLog from Geometrics that might allow calibration
of the depth sensor by determining a bias and scale factor. For additional
automatic depth calibration, see Depth Calibration using MagLog-Lite or

MagLog™ in section 4.5.5 of this manual.
The Depthcal.exe program provides BIAS and SCALE values for entry into

logging software to calibrate the depth sensor. This program was installed in
C:\GEOUTIL on your hard drive when you installed the Utility software.

DepthCal is an independent program (you may need to exit the logging
software to use it) that will lead you through an experiment with your G−882 to
derive the BIAS and SCALE values. To execute, at the DOS prompt in
C:\GEOUTIL, type DEPTHCAL and press the Enter key. The questions that
you answer will guide you through a simple experiment and then calculate the
BIAS and SCALE values.

Bias and Scale Factors Explanation and Calculation:
The depth transducer provides full scale readings of '9999' regardless of

whatever there range may be.
The DepthCal program supplied on the Magnetometer CD under Utilities may

be used to calculate the bias and scale factors for the depth transducer as
explained below.

The DepthCal program assumes that the logging software has initial settings of
zero bias with a scale factor of 1.000. What this means is that the logging
software should output zero meters when the serial data stream has "0000" in
the appropriate analog channel and 128 meters when it has '0128', 5000
meters when '5000' and 9999 meters when '9999' (full scale).

The depth channel does not put out exactly zero volts at zero depth. Nor does
a change of one digit '0001' equal one meter. And it varies from unit to unit due
to differing sensor full scale values that may have been installed per the
customer's system requirements. To correct for this, logging software may
allow the user to input a bias (offset) value and a scale factor to transform the
incoming device data such that the display readings that correspond to the
device's actual reading. DepthCal can be used to avoid having to do the math
required to obtain the bias and scale factors as shown in the example below.

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NOTE: The depth transducer uses a strain gauge mechanism to measure the

depth. Strain gauges as a rule are also greatly affected by temperature
changes. The depth sensor used in the G−882 has been specially designed to
compensate for temperature variations using calibration curves stored in a
lookup table which is custom set for each device. None the less it is not
perfect. For the best possible depth accuracy the depth bias and scale factors
should be set at sea water operating temperatures. A magnetometer on the
deck can get very warm from the sun and internal dissipation in contrast to the
much cooler ocean even though both are technically at zero depth. The depth
sensor is also mounted to a thermally massive aluminum pressure vessel which
takes a while to stabilize at the local ambient temperature. Keeping these
points in mind please observe the following:

Submerge the magnetometer before performing any of these
procedures and wait 15 minutes for the magnetometer to warm
up and allow the sensors to normalize to the water
temperature.

Let’s do an example with a typical depth sensor.

1. First in the logging software, set the bias and scale factors to their
starting points.

2. Adjust Units to meters (if not in meters already).

3. While logging data, tie off the magnetometer at the surface (zero depth)
and write down the value that is reported for depth. You need not be
logging to disk. Let’s say it reads 112 meters.

4. Lower the sensor down to a known depth (lets say 9 meters). Now, write
down the values. You can watch the raw data coming in from the
magnetometer. At this point, a one digit LSB change results in a 1 meter
change in the depth value reported. Let’s say the depth reads 917.0
meters.

5. Now run the Depth Cal program and enter the values written down
above for the surface and at some known depth. DepthCal will return
Bias and Scale Factors.

6. (In this example we get a Bias = -1.2522 and a Scale = 0.0112). Write
these values down for use when setting up your logging software.
Restart your logging software and enter the bias and scale factors which
were generated by the DepthCal program. Depth should now be
working correctly. See example below:

Depth calibration calculator Version 1.2

Note:

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All depth values are assumed to be in
meters.

With the sensor at the surface:
What number is displayed for the depth? 112

With the sensor at a known depth:
What depth did you place the sensor at ? 9
What number is displayed for this depth ?
917

Enter a BIAS value of : -1.2522
Enter a SCALE value of : 0.0112

NOTE: Some older versions of the DepthCal program instruct you to measure

the “Zero Depth” value on the deck of the boat. Instead tie off the G−882 over
the side at the surface but still submerged to do this measurement. See the
discussion about temperature affects of the depth sensor in the paragraphs
above.

Here is what the DepthCal numbers mean:

We entered a depth change of 9 meters and got a change of 805 meters (917
at depth minus the 112 at surface). To get your logging software to correctly
display a change in depth for a given depth change we have to multiply the
incoming data by (9/906) which equals 0.0112. This is the scale factor
calculated by DepthCal above.

We read 112 meters out of your logging software when the magnetometer was
at the surface. Its not really 112 meters though. Using the scale factor
correction above we get an actual error of 1.2522 meters (0.0112 * 112). Thus
to make it read correctly, we have to add a bias of –1.2522 meters which is
the bias value calculated by
DepthCal.

Miscellaneous:

Note that once these values are entered, if your logging software remembers
them, you will not have to enter them again. Of course, if a different instrument
is connected at some later time, new values will be required corresponding to
the new instrument.

Slope – Intercept Method

Here is a method for calculating the Scale Factor and Bias for depth calibration.
At the first depth, let the depth in meters be d1, and the raw reading r1.

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A B 1 True Depth

Raw Reading

2 1 30 3 5

34 4 30

46 5 6

=INTERCEPT(A2:A4,B2:B4)

7 =SLOPE(A2:A4,B2:B4)

At the second depth, let the depth in meters be d2, and the raw reading r2.
The formula for the Scale Factor is:

(d1d2)  (r1r2)
The formula for the Bias is:

(d2r1d1r2)  (r1r2)
You may also use Excel to calculate these values using linear regression. The

advantage here is that you can use more that 2 depths and get a best fit for all
the readings.

Put the actual depths in the first column. Put the raw readings in another
column:

Use the INTERCEPT function to calculate the Bias. Use the SLOPE function to
calculate the Scale Factor. Examples are shown in the table above. For this
example, the Slope (Scale Factor) is 1.875, and the Intercept (Bias) is –56.75.

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4.5.5 Depth Calibration Using MagLog-Lite or MagLog
MagLog logging software from Geometrics provides capability to perform

calibration of the depth sensor. It is preformed very much like the methods
described above. Refer to the excerpt from the MagLog-Lite/ MagLog
NTmanual below.

Depth/Analog channel calibration

In order to get an accurate depth sensor reading, the pressure transducer
sensor must be calibrated. This means that the depth sensor reading needs to
be compared with a known depth to account for the variations occurring due to
air pressure variations and to manufacturing variances. Bias and linearity
adjustment can be made in the program to empirically calibrate for depth. (You
can read more about this method at the end of the section).

The depth reading from the magnetometer is an integer between 0 and 9999.
This represents the full-scale range of the depth transducer. There may also
be a certain offset that must be adjusted.

MagLog™ offers a few ways of calibrating the depth.

Note: These methods also work for calibrating other analog channels

Calibration Procedure:

The basic procedure for calibrating the depth sensor is as follows:

1) Place magnetometer in the water for at least 15 minutes at a known

depth, say 3 meters. This will give the temperature of the sensor
time to stabilize.

2) Write down the depth and reading that MagLog™ gives you.

3) Place magnetometer in the water at a DIFFERENT depth.

4) Write down the depth and reading that MagLog™ gives you.

5) Use either automatic calibration feature or manual calibration to apply

results.

Note: If you use automatic depth/analog channel calibration, you can do this
while in the calibration screen.

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Figure 40

Automatic Depth/Analog Channel Calibration:

1) From your configuration screen, you should select the magnetometer. This

should bring up the “Settings” screen that you originally used to input the

number of sensors and analog channels. (You can get to this screen by
going into your main list of devices, and then double clicking on the
magnetometer description). You should see a screen similar to the one
below:

2) In the section

labeled “Analog
channel calibration
setup” select the

sensor and
channel number
that you want to
calibrate, e.g., to
calibrate the depth
of the first sensor
in the earlier
example, select

Sensor #: 1
Channel #: Depth

3) Select “Auto
calibration. You

should then see

the following dialog box:

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Figure 41

Note: At this time depth data is

coming from the fish that is
being analyzed by the
program to compute the
bias and scale factor. You
must place the fish on at
least two depths to get an
accurate calculation. During
Altimeter Calibration
discussed later, you must be
over a hard bottom and the
fish must be held
horizontally level.

You can add measured points to
this menu and have it automatically
calculate your scale factor and
bias. The depth sensor needs to
be in the water for at least 15
minutes before you take your first
measurement. This allows the
temperature of the electronics to
stabilize.

To add a new point, place fish at
known depth. Press Reset av. To discard current average and wait for a few
minutes to acquire a new one. Number after text Current average: should
stabilize. Then enter the depth that the device is at under
“Value” and press “Add to the list”. This will take the average
measurement MagLog™ currently sees for the depth, and it
will add it to a list of calibration points.

It is important to remember to reset the average if you move the sensor. You
can do this by pressing “Reset Av.”.

You can also specify an acceptable range of points to be used by pressing

“Acceptable Range”. This will bring up a dialog box that will allow you to set a

minimum and maximum allowed value. This is particularly important when you
calibrate your altimeter because occasionally you might get a spiked reading
(missed echo) that you don’t want included in the calculation of your average.

After you have at least two points, MagLog™ will then try to calculate a scale
factor and bias. You need to make sure that you have at least two different
depth points (e.g. it is advised to have one point near the surface, and the
second point as close to the bottom as possible). Otherwise, the calibrations

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Figure 42

will not be accurate. It is advised to add more than two points to get improved
accuracy.

You should also select “Channel Represents Depth” from the dialog box in
MagLog™. This option is important if you have an ORE Track Point II or other
Sonar USBL tracking device and will be using the depth sensor to improve the
tracking calculations.

If you are satisfied with the calibration, select “OK”.

4) You will then be given the opportunity to save your calibrations into a file.
The file will keep track of the scale and bias calculated, and the readings
used to make the calculation. It is advised to keep this for your records.

Manual Calibration

Manual calibration gives you the opportunity to enter the scale and bias directly
without having MagLog™ calculate it for you.

You can find the scale and bias by hand, or use third party software.
To use the MagLog™ manual calibration feature, select “Manual Calibration”

from your device settings menu. (Make sure that you have the correct sensor
and channel selected as discussed in the section on “Auto Calibration”.)

You will see a dialog box:

Enter your scale and bias values, and check “Channel represents depth” if this
is a depth calibration. Then press “OK”.

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You will be given the opportunity to save these into a file.

Effects of Depth Calibration

After you have calibrated your depth sensor, you should see immediate
changes in your data. The graphs and displays will use the new calibrated
values.

However, the device file will have the uncalibrated values (.880).
If you need to store calibrated values, you should use the Interpolator device

that will write calculated depths and altitudes in the interpolator file.

Why Should We Calibrate?

This is a brief discussion on how MagLog™ calculates scale and bias values
and why this is needed.

The depth sensor is a pressure transducer. This means that for a given
pressure, it will output a number proportional to the pressure measured.
However, the number is meaningless until we solve for a few factors.
Assume that the depth reading is related to the pressure reading by the
following:

Depth = APressure + b
In this case, the two parameters A and b are the scale and bias values that we

need to find.
We can solve for these two value if we have at least two sets of measurements.

If we measure the following:
Depth MagLog Reading (pressure)

Y1 X1
Y2 X2

I can then get two independent equations:
Y1 = AX1 + b Y2 = AX2 + b
Solving for A and b, I get:
A = (Y1  Y2)  (X1  X2) b = (Y2X1  Y1X2)  (X1  X2)

From here, we can now use these new values to calculate the correct depth,

given only the pressure.

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MagLog™ can then use these equations to automatically adjust all pressure

readings to accurately reflect the depth measured.

4.6 Assembly, Installation and Use

4.6.1 Assembly of the Sensor Fish

As can be seen in Figures 54, the G−882 is assembled and ready for
deployment, as shipped. The G−882 may be deployed in a nose towed
configuration or a center of gravity (CG) towed configuration. Greater tow
depths may be obtained using the CG towed configuration. The following will
describe how to configure the G−882 for the desired to method. See section

2.6.2 in the Quick Hardware Guide for instructions on how to configure each of

these tow methods.

DO NOT substitute any other hardware (steel, stainless steel, or

anything that you may think is brass) here or anywhere else on the G−882
Magnetometer Fish. Spare hardware is supplied in the Ship Kit. All of the
supplied hardware is magnetically tested to insure that it is clean
(exhibits no magnetic signature). Failure to follow this caution could
introduce heading errors into the data that is acquired making it useless
or very difficult to interpret.

4.6.2 Installation of the G−882 Magnetometer

There are several appropriate tie points that can be used to firmly attach the
magnetometer tow cable to the vessel. Remember that the tow cable is rated
at 4,000 lb breaking strength (about 700 lbs working load) and while tension
during towing at 5 to 7 knots will be a fraction of that with the standard cable
length of 200 feet, catching the sensor fish in a net or rock will transfer that
force to the attachment point.

a. Attach the Kellems grip to a winch if you are using a substantial amount of
tow cable. We recommend a winch if the length of the tow cable exceeds 120
m (400 ft). An on-board deck cable available from Geometrics is used to
traverse the distance from the winch installation point to the logging equipment
installation site.

b. The tie point may be on the aft deck. Again an onboard cable is required to
traverse the distance from the aft deck to the logging equipment installation
place.

c. The tie point may be close to where the logging equipment is located. A
short adapter cable is provided to connect the tow cable to the DC/Data
Junction Box. An RS-232 cable will then run from the junction box to the

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logging computer. A 6 foot cable is supplied but an RS-232 extension cable of
up to 40 or 50 feet could be used.

While reading this section, refer to the System Connection Diagram in
Appendix B.

The Junction Box functions as the connection point for power and signals
required for a functioning G−882 magnetometer system. The Data Logging
computer, Junction Box and the power source should be installed in a protected
environment. These items are susceptible to water damage and most likely will
cease to function if they become wet, particularly with salt water from a sea
wave. Their installation could be in the cabin of the boat or the equipment room
if there is one. In a very small boat, provide some protection by elevating this
equipment from the deck and covering it with a tarp or provide a waterproof
enclosure.

4.6.3 Deployment of the G−882 Magnetometer

Turn the power on the DC/Data Junction Box and the Logging Computer. After
five minutes warm up for the magnetometer and boot up of the Logging
Computer, start the logging software as described in the Quick Start Software
Guide or the MagLog manual. If you have not previously used the Survey
Wizard to set up a survey, do so now. If you have previously created a survey,

use the “Start New Survey” from the File menu and then select “Same

Hardware as Last Survey” to set the configuration.

If the magnetometer is positioned horizontally on the deck away from any steel
objects, you may begin to see readings that represent the intensity of the
earth’s field in the survey area. If you are on a steel hulled vessel, you may not
see quiet data until you launch the magnetometer fish and it is about 30m
(100ft) behind the vessel. With the system running you can proceed to perform
the calibration of the depth sensor as described in Section 4.5.4 of this manual.

If the logging software is operating at power-on time, the following outlines what
might be observed as the magnetometer is powered-on and warms up to
operating temperature. If the numbers observed are somewhat outside the

ranges given below, the magnetometer is still in most situations,
operating properly. Extreme temperature conditions may cause some of

these values to go significantly outside these ranges during normal operation.

1. Just after power-on and before the counter begins normal operation

some erroneous data may be observed for a brief period of time.

2. When the counter begins normal operation the following may be

observed as the magnetometer begins to warm up:

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A. The magnetometer reading will be erratic as the sensor begins to

warm up.

B. Analog channel 0, the signal level, will be around 0010 and will

increase during warm-up.

C. Analog channel 1, the depth sensor, will exhibit a value near 0100

(unscaled) with the G−882 in air, out of the water. If no depth
sensor is installed in the G−882, the value could vary between
0000 and 0050.

D. Analog channel 2, the altimeter, will exhibit a value near 9900

(unscaled) with the G−882 in air, out of the water. If no altimeter
is installed in the G−882, the value could vary between 0000 and

0050.

If the additional diagnostic analog channels are enabled, the
following may be observed:

E. Analog channel 3, the brightness, will exhibit numbers beginning

about 3400, jump to 4300 after a minute or two and then slowly
rise towards a number around 5600 as the magnetometer warms
up.

F. Analog channel 4, the RF, will exhibit numbers beginning low,

fairly quickly ramping up to some high numbers and as the
magnetometer warms up slowly settling down to a number around

2100.

G. Analog channel 5, the heater, will exhibit numbers beginning low,

very quickly ramping up to some numbers as high as 3400 (this
final value will be determined in part by the ambient temperature)
and then settling down to a number around 1600.

H. Analog channel 6, if not used, could vary between 0000 and

0050. As shipped, jumpered to an internal voltage, 28V, analog
channel 6 could immediately exhibit numbers between 5005 and

7890. If used for an external input (this capability not currently
implemented in the G−882), the values will depend upon the
characteristics of the user device attached.

I. Analog channel 7, if not used, could vary between 0000 and

0050. As shipped, jumpered to an internal voltage, 21V, analog
channel 7 could immediately exhibit numbers between 4600 and

5300. If used for an external input (this capability not currently
implemented in the G−882), the values will depend upon the
characteristics of the user device attached.

3. When the magnetometer is warmed up the following may be observed:

A. If the magnetometer is properly oriented to the ambient field and

not near any large metal objects, a reading indicating the
magnitude of the ambient field will be observed.

B. Analog channel 0, the signal level, depending on the field

magnitude and sensor orientation, a normal signal could vary
between 0900 and 1200.

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C. Analog channel 1, the depth sensor, will exhibit a value near 0100

(unscaled) with the G−882 in air out of the water. If no depth
sensor is installed in the G−882, the value could vary between
0000 and 0050. If the G−882 is in the water the value should vary
with and be indicative of depth.

D. Analog channel 2, the altimeter, will exhibit a value near 9900

(unscaled) with the G−882 in air, out of the water. If no altimeter
is installed in the G−882, the value could vary between 0000 and

0050.

If the additional diagnostic analog channels are enabled the following
may be observed:

E. Analog channel 3, the brightness, will exhibit a value around

5600, but may vary between 5350 and 5850.

F. Analog channel 4, the RF, will exhibit a value around 2100, but

vary between 2000 and 2400.

G. Analog channel 5, the heater, will exhibit value around 1740, but

vary between 1700 and 1900 depending upon ambient
temperature.

H. Analog channel 6, if not used, could vary between 0000 and

0050. As shipped, jumpered to an internal voltage, 28V, analog
channel 6 could exhibit a value around 6500, but vary between
5005 and 7090. If used for an external input (this capability not
currently implemented in the G−882), the values will depend upon
the characteristics of the user device attached.

I. Analog channel 7, if not used, could vary between 0000 and

0050. As shipped, jumpered to an internal voltage, 21V, analog
channel 7 could exhibit a value around 5100, but vary between
4600 and 5300. If used for an external input (this capability not
currently implemented in the G−882), the values will depend upon
the characteristics of the user device attached.

In either configuration above, nose or CG tow, the magnetometer can be lifted
over the side by one person. However, the deployment will be much easier and
smoother with two or more people handling the operation. Due to much lower
levels of drag force, the nose towed magnetometer may be handled by one
strong person. Cowhide work gloves provide the best protection and grip for
handling the wet tow cable.

There are two methods to handle the cable on deck if a winch is not used:

1. Neatly fake (figure eight) the cable down on the deck beginning with

the onboard end. As this is done remove any twists in the tow cable.
The cable may be deployed from the figure eight without knots and
kinks. One person should be assigned to tend the cable on and off of
the figure eight. This method is better for cable up to 120m (400ft).

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2. Neatly lay the cable out in long loops bow to stern on the deck
beginning with the onboard end. As this is done remove any twists in
the tow cable. The cable may be deployed from the loops on the deck
without knots and kinks. One person should be assigned to walk the
loops back on the deck during retrieval. This method works well with
cables up to 60m (200 ft).

Tow cables longer than 90m to 120m (300ft to 400ft) should probably be
handled with a winch.

Manual deployment, is best handled with two people, especially when
additional depressive weights are being used, a third person should manage
the tow cable. The vessel should be making 1 to 1 ½ knots during deployment.
It may be necessary to increase the vessel speed as more cable is deployed to
prevent the magnetometer from striking the bottom. The more quickly the
desired cable length can be deployed and the desired tow speed attained
reduces the chances of the magnetometer going too deep striking the bottom or
becoming hung. The recommended cable management mentioned above will
aid in quick deployment. Another method is to stop playing out tow cable a few
times during deployment while under tow. This will allow the tow fish to rise
towards the surface. If a CG towed fish with a depressor wing is being
deployed, it pulls with significant force. It may require two or three people to
hold it during the play-out stops.

It is best if the tow cable is tied to the vessel before the vessel begins to acquire
the desired tow speed. The magnetometer with the depressor wing produces
strong pull forces under tow speed of 4 to 6 knots.

Determine the approximate length of tow cable to be deployed to achieve the
required survey depth. We recommend that the Kellems grip provided on the
tow cable be used to secure the tow cable to the towing vessel. Slide the
Kellems grip to set the length of tow cable desired to be deployed plus some
additional cable to account for the distance from the ship to the cable water
entry point. Secure the Kellems to the tow cable as shown in Figure 43. DO
NOT tape along the whole length of the Kellems; this will prevent it from
working properly. Attach the Kellems to the towing vessel using a strong line
tied to the loop of the Kellems grip.

A Kellems grip is like a child’s toy finger trap. The stronger the forces that pull
on it, the tighter it grips the cable. If the Kellems grip needs to be moved to
adjust the amount of tow cable deployed, remove the tape anchoring it to the
tow cable and compress each end to the Kellems towards the other along tow
cable. This will expand the Kellems and allow it to slide easily along the cable
to its new position. Release the ends of the Kellems, re-anchor the end
towards the towfish as shown Figure 43 and then smooth it back down along
the cable towards the vessel.

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Figure 43. Kellems grip installed on the tow cable.

Vessel

Towfish

Use a strong line to attach
this loop to the vessel.

Retrieval is best performed with the vessel at full stop (propeller not turning) or
maintaining just enough headway to keep the cable from going under the
vessel. The intent is to prevent the tow cable from becoming entangled in the
propellers. Nothing destroys surveys and propeller shafts quicker than
entangling the tow cable in the propellers.

Retrieve the cable as quickly as possible to help prevent the magnetometer
from striking the bottom. Again, neat tow cable management as described
above will greatly facilitate survey execution.

It is recommended that some form of quick communications be provided
between the vessel captain and the magnetometer handlers. This will greatly
ease handling and make the operation safer. Radios work well.

The tow cable length is generally determined by a number of factors. The most
important factor is the desired depth of tow that must be achieved for the
survey. The longer the cable, the greater the depth that can be achieved. The
depth of tow may also be improved by the type of towing method selected for
the magnetometer tow fish.

For shallow surveys on short tow cables (30 to 60 meters), the Nose Tow
method works the best. One man can manage deployment and retrieval with a
second man to manage the tow cable. The depth of tow graph below for a

nose towed G−882 is derived from actual tests. However, it DOES NOT
provide exact numbers. It is just intended to provide an indication of the tow
depths that might be expected. The actual depth of tow can be affected by
water current speed and turbulence. Also, turns to change course greatly slow
the speed of tow increasing the tow depth. If you know you are towing in an
area that may have potential snags upon which the tow fish may hang, retrieval
of tow cable in the turns may be required to manage the tow fish depth
guarding against snagging. This graph is provided as a suggestion of what tow
depths might be expected using a nose towed G−882 magnetometer.

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0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5 6

Depth (ft)

Speed (knots)

G-881 Nose Tow Depth vs Speed on a 175 ft Cable Length

G-882 Nose Tow Depth vs Speed on a 175ft Cable Length

Figure 44

Towing a magnetometer fish from its center of gravity provides a method to
allow the fish to be towed deeper, hence closer to the bottom for a better
detection range. Generally, a CG towed G−882 will tow two to three times
deeper than when nose towed. Adding a depressor wing to the CG tow point
may double the depth again. Geometrics offer both options for the G−882.
The following provide information regarding tow depths that may be expected
and instructions for assembling.

The following graphs provide an approximate indication for tow depths that may
be expected versus the cable length deployed versus the speed of tow. These

graphs are derived from actual tests. However, they DO NOT provide exact
numbers. The actual depth of tow can be affected by water current speed and
turbulence. Also, turns greatly slow the speed of tow increasing the tow depth.
If you know you are towing in an area that may have potential snags upon
which the tow fish may hang, retrieval of tow cable in the turns may be required
to manage the tow fish depth guarding against snagging.

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79

Figure 45

0

5

10

15

20

25

30

35

40

45

0 50 100 150 200 250 300 350 400

Depth (ft)

Cable Length in water(ft)

G-881 CG Tow Cable Length vs Depth

3
knots
4
knots
5
knots

G-882 CG Tow Cable Length vs Depth

Figure 1. CG TOW

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80

Figure 46

Figure 47

1

2

3

4

5

6

7

8

Figure 48

Figure 49

1 2 3

4 5 6

7

8

5.0 Service Information and Trouble Shooting Guide

It is possible to open the G−882 in the field, but is not recommended. There
are no easily assessable parts that can be field serviced. It is recommended
that if service is required, the G−882 be returned to the factory for service.

5.1 Connector Information

The following Figures provide views of the connectors used on the G−882 tow
cable.

Figures 59 and 60 show the male water tight connector on the nose bulkhead
of the G−882 magnetometer. Figure 60 also shows the pin numbers for this
connector. The Geometrics part number for this connector is 21-236-400.

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Figure 50

Figure 51

1

2

3

4 5 6 7 8

Figure 52

Figure 53

A

B

C

D

E

Figures 48 and 49 show the female water tight connector on the wet end of the
tow cable. This connector mates with the connector of Figures 50 and 51.
Figure 49 also shows the pin numbers for this connector. The Geometrics part
number for this connector is 21-236-410.

Figures 50 and 51 show the male water tight connector on the dry end of the
tow cable. This connector mates either to the adapter cable shown below or to
a winch if one is used. Figure 51 also shows the pin numbers for this
connector. The Geometrics part number for this connector is 21-236-411.

If the tow cable purchased with your system is terminated as shown in above in
Figure 50, an adapter cable as shown in Figure 52 is provided to allow
connection the DC/Data Junction Box. The connector on the left in Figure 52 is
a Bendix connector. It mates with the connector labeled ONBOARD on the
DC/Data Junction Box. Figure 53 shows the pin numbers for the Bendix
connector.

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Figure 54

A

B

C

D

E

The connector that should be connected to the tow cable is the same as the
wet end of the tow cable shown in Figures 48 and 49. This end should be
mated with the dry end of the tow cable. Prepare these connectors for
installation by insuring that the connectors on the tow cable and the adapter
cable are clean and free of dirt. Using a finger, wipe a small amount of silicon
grease across the face of the connector of the adapter cable. If this is done
properly, there will be a “half moon” of grease visible in each of the pin sockets
of this connector. The correct silicon grease is provided in a small circular,
snap-lid container in the ship kit. Unless it is cleaned, once greased this
connector may never require grease again.

The connector shown in Figure 54 is the DC power connector on the AC/DC
power supply. The connector in Figure 54 is a Bendix connector. It mates with
the connector labeled 22-32 VDC on the DC/Data Junction Box. Figure 54
shows the pin numbers for the Bendix connector.

5.2 O-ring Maintenance

The O-rings do not require maintenance. Unless the a bulkhead is removed
from the magnetometer fish, the O-rings do not require maintenance.
Geometrics does not recommend the customer open the magnetometer fish
under any circumstances. There are no customer maintainable parts within.

Should the customer inadvertently remove a bulkhead or do so under
instructions from Geometrics, the following procedure should be observed to
re-install the bulkhead.

Remove the two O-rings from their grooves on the bulkhead. Using a clean
towel, clean any contaminants that may be observed on the barrel of the
bulkhead or in the O-ring grooves. Inspect the inside of the magnetometer fish
from where the bulkhead was removed. Clean any contaminants that may be
observed.

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83

Take the two replacement O-rings provided in the ship kit and apply some
silicon grease provided in a small circular, snap-lid container in the ship kit.
Take a little grease between your thumb and index finger. Gently pull the
circumference of the O-ring between your greased fingers to thoroughly apply a
complete layer of grease to the O-ring. Gently stretch the O-ring over the
small end of the bulkhead and slide it into one of the O-ring grooves. Repeat
this process with the second O-ring and place it in the other O-ring groove of
the bulkhead. Take a little more grease on your index finger and wipe it on the
circumference of the O-rings on the bulkhead.

Install the bulkhead into the magnetometer fish. Push the bulkhead straight in
to insure proper installation.

5.3 Depth Sensor Ratings

There are four choices for a Depth Sensor that may be installed in a G−882.
They are: none
100psi
250psi
500psi

These depth(pressure) sensor(s) will operate to 200% (for a 100psi sensor this
would be 200psi) over pressure without damage or the calibration change.
Exceeding 200% may cause a permanent change in the calibration as the
sensor is permanently deformed. Sensor failure to produce data may occur if
200% over pressure is exceeded.

These depth sensors are safe from bursting up to 400% over pressure with out
bursting. The pressure sensor will be useless after this over pressure but it
should not burst protecting the magnetometer from flooding. The pressure
sensor will not burst at exactly 400% over pressure and may survive higher
pressure without bursting. However, if pressure is approaching 400%, every

effort should be immediately undertaken to prevent the G−882 from going
deeper to prevent bursting of the depth sensor.

5.4 Tow Cable Strength Data

Recent design changes have made a stronger tow cable available. Data for
both the "original" and the "new" cable are provided for those who may have
the original cable with a magnetometer previously purchased from Geometrics.

Original Tow Cable

Color: black
Marking: GEOMETRICS, INC., P/N 60-453-095
Breaking Strength: 4000 lbs.

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Maximum Working Load: 800 lbs.
Minimum Bend radius: 4.5 in.

New Tow Cable
Color: Green

Marking: GEOMETRICS, INC., P/N 60-453-101
Breaking Strength: 4000 lbs.
Maximum Working Load: 800 lbs.
Minimum Bend Radius: 9 in.

The working loads exerted on the tow cable by the G−882 vary depending on
the type of towing method used. The lowest amount of force exerted is the
G−882 nose tow configuration. Next is the CG towed configuration. Care
should be taken to minimize the working load exerted on the tow cable.
Exceeding the maximum working load, will, over time, cause the tow cable to
fail electrically. The conductors may become work hardened and break.
Following are some suggestions to minimize the work load:

1. Keep the tow speed to a maximum of six knots.

2. Slow the vessel down to 1-2 knots to retrieve tow cable.

3. Slow the tow speed in high seas to reduce the effect of heave on the tow
cable, or cease the survey.

Should the tow fish become snagged, the much higher breaking strength may
help insure that the tow fish is successfully retrieved. However, this will exert
loads on the cable well in excess of the working load. Before the cable is used
again it should be carefully inspected and tested. It may still be usable, but its
life will have been shortened. How much, depends upon how close to the
breaking strength the force induced by the snag was.

5.5 Trouble Shooting Guide

Always record Serial Number, Signal Level, Sensor Orientation, and
Latitude/Longitude before contacting Geometrics.

1. Power check (Use MagLog Diagnostic Survey or multiply channel 7 by

0.004805 then subtract 2.048 to scale to Volts DC)

a. Minimum 24 Volts DC at electronics bottle
b. Maximum 33 Volts DC at electronics bottle
c. Starting current 1 Ampere at 28 Volts
d. Running current 0.3 to 0.6 Ampere at 28 Volts depending upon ambient

temperature

2. Connector checks

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85

a. Dirt or corrosion
b. Bent pins
c. Backshell tight

3. Cable jacket check

a. Kinks
b. Abrasions
c. Cuts

4. Sensor orientation

a. Use MagPick IGRF and CSAZ to model sensor behavior
b. Adjust sensor orientation and observe dead zones
c. Return sensor to correct orientation for the survey area

5. Field readings

a. Reasonably close to MagPick IGRF model estimate
b. Sample to sample noise less than 0.1 nT when not moving.

6. Field Larmor amplitude check – Signal should be at least 800 when correctly

oriented. Maximum signal should be less than 2000.

7. Larmor amplitude check and adjustment (Authorized Repair Facility only)

a. Pot on GSN to adjust for 1.5 to 2.0 Volts Peak to Peak at 50,000 nT after

20 minute warm up.

8. Heater check and adjustment (Authorized Repair Facility only)

a. 34.5 K ohms after warm up

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Symptom

Probable Causes

Corrective Actions

Long warm-up time

Low voltage

Faulty sensor cable
connection

Heater setting too cool

Excessive cold

Defective internal sensor or
electronics components

Increase voltage (minimum 24
VDC at the electronics) or
repair the Coax cable

Connect the fish directly to
the deck cable or cable
adapter

Disconnect sensor from
electronics and carefully
clean the pins and
sockets*

Adjust heater to 34.5 Kohms*

Normal – allow extra time for
sensor to warm up in
extremely cold environments

Return fish to Geometrics for
repair

Noisy magnetic field readings

Sensor not oriented correctly

Magnetically “Noisy”

location

Signal amplitude too low

Sensor cable or connector
worn or damaged

Use MagPick IGRF and CsAz
software to model magnetic
field and sensor behavior, then
determine a correct orientation

Move to a magnetically clean
area

See next section on low signal
causes

Replace sensor cable and
connector assembly. Check
connector on electronics
module for wear and replace if
required*

Low Signal Level

Sensor not oriented correctly

Use Magpick IGRF and
CSAZ software to model
magnetic field and sensor

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Symptom

Probable Causes

Corrective Actions

High magnetic gradient

Low power supply voltage

Heater setting incorrect (too
hot or too cold)

Insufficient warm up time

Signal adjustment is set
wrong

behavior, then determine
correct orientation.

Check gradient by moving
sensor back and forth
East/West, North/South, and
Up/Down while noting
changes in the magnetic field.
Signal level diminishes
rapidly when the magnetic
field is changing by more than
200 nT per foot. Move the
sensor to a less magnetically
cluttered area if the gradient is
more than 200 nT per foot.

Increase power supply voltage
(minimum of 24 VDC at the
electronics).

Adjust heater such that the
temperature sensing
thermistor stabilzes at 34.5K
ohms*

Allow 20 minutes for the
magnetometer to warm up and
stabilize (longer in extreme
cold).

Adjust signal level*

Sensor connector damaged or
worn

Handling, mechanical
problem, accident, or normal
wear.

Correct handling or
mechanical problem. Then
replace sensor cable and
connector*

Excessive current
consumption.

Defective sensor or
electronics

Return fish to Geometrics for
repair.

*Authorized repair shop only

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 87

Figure 55

5.6 The Diagnostic Survey – How to use it

Geometrics is now distributing a Diagnostic Survey
as part of the MagLog software that can be
downloaded from the Geometrics ftp site:

ftp://geom.geometrics.com/pub/mag/Software

Choose the file, MagLog_latest.exe to download and
install MagLog with the Diagnostic Survey. The
Diagnostic Survey will be installed in the same
directory as MagLog, usually:

C:\Program Files\Geometrics

You can now Start a new survey and use the
Diagnostic Survey as a template.

Normal values for the various slots are:

mag – A trace indicating magnetic field variations
signal – Between 600 and 1500 after 15 minutes of

operation with the sensor properly oriented
depth – Between 100 and 9900
alt – Between 100 and 9900
Bright – Between 5332 and 5893 after 15 minutes of

operation
RF – Less than 2500 after 15 minutes of operation
Heat – Approximately 1600 at room temperature. Maximum is about 3400 and

minimum is about 0800
+28V – Between 24.0 and 33.0
+21Va – Between 20.0and 23.5
Start by choosing Start New Survey from the File menu.
Next choose a location for your survey.

You can choose to make a new folder by clicking on the icon with an asterisk, then
naming the folder as shown below.

Geometrics Inc. G-882 Cesium Marine Magnetometer Page 88

Figure 56

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Press the Enter Key after naming the new folder until the Save As dialog box
shows no files or folders.

Figure 57

Figure 58

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Figure 59

Figure 60

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