Geometrics Memory-Mag G-856AX User manual

G-856AX Memory-Mag
Proton Precession
Magnetometer
P/N 18101-02 Rev. E
Operation Manual
GEOMETRICS, INC.
2190 Fortune Drive, San Jose, CA 95131
Phone: [phone]
Fax: [phone]
Email: [email protected]metrics.com
Web: www.geometrics.com
COPYRIGHT © 2007
.

Geometrics, Inc.G-856AX Operation Manual iii
Table of Contents
INTRODUCTION.........................................................................................................1
WHAT IS A TOTAL FIELD MAGNETOMETER? ...................................................................1
MAGNETOMETER APPLICATIONS ...................................................................................1
TERMS USED IN THIS MANUAL .......................................................................................2
THE G-856AX .............................................................................................................2
MAGNETOMETER SET-UP.......................................................................................5
SENSOR FLUIDS ............................................................................................................5
STANDARD SYSTEM ASSEMBLY ....................................................................................6
GRADIOMETER ASSEMBLY.......................................................................................... 10
BASE-STATION ASSEMBLY..........................................................................................13
SENSOR ORIENTATION ................................................................................................14
CONSOLE SET-UP ....................................................................................................16
CONSOLE CONTROLS AND DISPLAY .............................................................................16
SYSTEM CHECKOUT ....................................................................................................17
OPERATING PROCEDURES ...........................................................................................17
1 - Clearing a Key sequence ..................................................................................17
2 - Setting the internal clock ..................................................................................17
3 - Setting the Line Number Marker....................................................................... 18
4 – Manual Tuning of the Magnetometer ...............................................................19
5 - Automatic tuning ..............................................................................................21
6 - Acquiring and storing a magnetic field reading ................................................22
7 - Recalling measurements from memory..............................................................22
8 - Erasing magnetometer readings .......................................................................24
9 - Automatic reading set-up..................................................................................25
10 - Retrieving magnetic field readings..................................................................26
FIELD OPERATION..................................................................................................29
SENSOR POSITION AND MEASUREMENT REPEATABILITY ...............................................29
MAGNETIC ENVIRONMENT ..........................................................................................30
MAGNETIC SURVEYING...............................................................................................30
Standard operation................................................................................................30
Gradiometer operation ..........................................................................................32
DATA RETRIEVAL................................................................................................... 33
COMPUTER CONNECTION AND DOWNLOAD ..................................................................33
MANUAL TRANSCRIPTION .......................................................................................... 34
MAINTENANCE ........................................................................................................35
INSTRUMENT STORAGE ...............................................................................................35
VOLTAGE INDICATOR .................................................................................................35
BATTERIES .................................................................................................................35
D-CELLS BATTERIES ...................................................................................................36
GEL-CELL BATTERIES .................................................................................................37

Geometrics, Inc.G-856AX Operation Manualiv
LITHIUM BATTERY......................................................................................................37
SENSOR FLUID............................................................................................................38
APPENDIX..................................................................................................................41
MAGNETIC FIELD INCLINATION (DEGREES) ..................................................................41
MAGNETIC FIELD INTENSITY VARIATION (NT) .............................................................41
TROUBLESHOOTING....................................................................................................42
RS-232 INTERFACE.....................................................................................................43
FRONT PANEL CONNECTOR PIN ASSIGNMENT ...............................................................44
OUTPUT FORMAT........................................................................................................44
EXTERNAL POWER ..................................................................................................... 45
EXTERNAL MAGNETOMETER CONTROL ........................................................................45
INTERNAL PROGRAMMING SWITCHES ..........................................................................46
Polarize and count time – Switches 1 through 4..................................................... 47
INTERNAL RESET SWITCH ...........................................................................................49
SPECIFICATIONS .........................................................................................................50
WARRANTY AND SERVICE...........................................................................................52
DECLARATION OF CONFORMITY..................................................................................54
Table of Figures
Figure 1. G-856 proton-precession magnetometer...........................................................6
Figure 2. Sensor staff sections. .......................................................................................7
Figure 3. Sensor preparation. ..........................................................................................7
Figure 4. Staff / sensor assembly. ...................................................................................8
Figure 5. Console battery compartment. .........................................................................8
Figure 7. G-856 shoulder harness. ..................................................................................9
Figure 8. Assembled magnetometer................................................................................9
Figure 9. Location of 'Read' key on magnetometer console...........................................10
Figure 10. Gradiometer components. ............................................................................10
Figure 11 Removing standard sensor cable from top sensor...........................................11
Figure 12. Top sensor with gradiometer cable attached................................................. 11
Figure 13. Bottom sensor with gradiometer cable attached. ..........................................11
Figure 14. Connection of threaded staff adaptors. .........................................................12
Figure 15. Completed gradiometer staff........................................................................12
Figure 16. Attach the gradiometer switch box............................................................... 13
Figure 17. Base-station setup up using tripod kit and G-856AX staff section. ............... 14
Figure 18. Alternate orientation for G-856AX sensor mount......................................... 15
Figure 19. Magnetic Inclination of the Earth’s field...................................................... 15
Figure 20. G-856AX console display and keypad. ........................................................ 16
Figure 21. Magnetic Field Intensity Variation, (nT)......................................................20
Figure 22, Typical survey layout. .................................................................................. 31
Figure 23. Location of console’s internal programming switch. ....................................46
Figure 24. Internal reset switch.....................................................................................50

Geometrics, Inc.G-856AX Operation Manual v
List of Tables
Table 1. An example of the console memory stack. ......................................................23
Table 2. Battery endurance comparison. .......................................................................36
Table 3. RS-232 cable connector pin assignment. .........................................................43
Table 4. Summary of programmable switch settings. .................................................... 47

Geometrics, Inc.G-856AX Operation Manualvi

Geometrics, Inc.G-856AX Operation Manual 1
Introduction
This manual provides operating instructions for Geometrics G-856AX portable proton-
precession magnetometer. It includes step-by-step instructions on magnetometer set-up,
survey usage, measurement data retrieval, and maintenance.
What is a total field magnetometer?
A total magnetometer is an instrument that measures the scalar intensity of the local
magnetic field. The G-856AX relies upon the proton-precession measurement technique.
This technique makes use of an induction coil to create a strong magnetic field around a
hydrogen-rich fluid such as Kerosene. This causes the hydrogen protons to align or
polarize their spin axis with the newly applied magnetic field. When the current
producing the polarizing field is interrupted, the protons begin to align themselves with
Earth's magnetic field but in doing so will momentairly precess abou the earth’s field at a
specific frequency that is proportional to the ambient magnetic field intensity. This
precession generates a small magnetic field that induces an alternating voltage in the
induction coil that was previously used to generate the polarization field. The
relationship between the precession frequency of the induced voltage and the strength of
Earth's magnetic field is called the proton gyromagnetic ratio and is equal to 0.042576
hertz per nanotesla (Hz/nT).
Magnetometer applications
Most rocks contain some magnetite, hematite or other magnetic material and will produce
disturbances in the local magnetic field. Because of this, most soils and many man made
objects that contain iron or nickel have magnetic properties detectable by a sensitive
magnetometer because they create local or regional anomalies in the Earth’s main field.
Anomalies are revealed by systematic measurement of the variation in magnetic field
strength with position.
Interpretation of magnetometer readings allows the surveyor to make inferences about
what exists beneath the Earth’s surface. Based on experience with the survey area, the
surveyor might interpret the measurements to indicate to location of a pipeline, fired
pottery or bricks, a piece of ordnance, a particular mineral, or geologic structure. The
interpretation of magnetic survey results is sometimes a difficult task, made even more
complex by constant changes in the earth's overall magnetic field, the size and distance of
objects from the magnetometer, the amount of magnetic material the object contains, as
well as the magnetic susceptibility of the object and the host material. On the other hand,
in many applications, simple interpretations of anomalous magnetic fields will lead to a
straight forward understanding of the source of the anomaly.
The proton precession magnetometer is one of the principal instruments for magnetic
surveys because it combines high accuracy and ease of use. The Applications Manual for
Portable Magnetometers, supplied with this instrument and available for download from

Geometrics, Inc.G-856AX Operation Manual2
our website includes general information on the use of magnetometers. It should be
studied as a companion to this manual which deals specifically with the G-856AX
Memory Mag™.
Terms used in this manual
The magnetic field intensity at the surface of the Earth has an average value of about
50,000 nano-Tesla (nT). Historically, one nT is sometimes referred to as a gamma or “”.
Throughout this manual we will always express field intensity in nT.
The terms “sampling”, “cycling”, and “reading” all refer to the magnetometer’s
measurement of the field intensity. Note that these terms do not necessarily refer to both
measurement and internal storage of the measurement value.
The G-856AX
Depending on its particular configuration, the G-856AX can be a portable, man-carried
magnetometer, a gradiometer measuring the field with two sensors, or a "base station"
magnetometer. As a hand-carried instrument, it features simple, push button operation
and a built-in digital memory that stores over 5000 single sensor measurements or 2500
gradiometer readings. This relieves the user of the need to physically write down the data
in the field, eliminates transcription errors and most importantly, allows the use of
computers to automatically record and process the data from the magnetic survey.
Software Programs are available from Geometrics to help the user process and interpret
survey data. These programs include MagMap2000 and MagPick and are available for
download from our website: www.geometrics.com.
The G-856AX can also record data automatically at regular intervals, so it can be left
unattended to monitor diurnal changes in the earth's magnetic field. These readings (up to
12,500) are collected at a base station and used to correct simultaneous field
measurements for high accuracy surveys. Measurement data from the G-856AX may also
be fed directly into an external computer. The time-of-day generated by the
magnetometer’s internal clock is recorded with each reading taken in either mode.
All operations are controlled from keys imbedded in a weatherproof membrane that
comprises the magnetometer console’s front panel. The key sequences for the various
magnetometer operations have been carefully designed to provide simple yet flexible
operation.
A single connector is used for the sensor signal input and data output. The output format
is in the universal RS-232 protocol that is accepted by most modern computers. Interface
software for downloading, profiling and gridding/contouring of data is provided by
Geometrics MagMap2000 software. A serial to USB converter is available for use with
computers that are not equipped with a serial port.
Physically, the G-856AX is compact and lightweight. It is weather proof and operates

Geometrics, Inc.G-856AX Operation Manual 3
over a wide temperature range. Depending on the model version, it is powered either by
nine (9) D-cell batteries or, more commonly, by an internal rechargeable lead acid gel
cell battery.
Unlike other proton-precession magnetometers, the G-856AX has an internal
programming switch allows modification of the magnetometer’s cycle times to ensure
that it will work properly anywhere in the world.
Above all, the G-856AX is a high-precision magnetometer, the result of many years
experience in the manufacture of similar instruments. The operation of the instrument is
controlled by a microprocessor and the control program may be changed at any time for
product improvement or other considerations. In that event, you may find variations
between this manual and the operation of your actual instrument operation. Such
variations will have no adverse effect and should be recognizable as you familiarize
yourself with operation.

Geometrics, Inc.G-856AX Operation Manual 5
Magnetometer Set-up
The standard G-856AX system is used as a mobile instrument for measurement of the
magnetic field intensity sequentially at discrete locations. With the appropriate
accessories the standard system can be configured for measurement of the differential
magnetic field (gradient) over the survey area or the magnetometer can be set up to
record the temporal changes in the magnetic field intensity at a fixed point to acquire
base station measurements.
Sensor fluids
The sensor contains coils of insulated wire and for optimum operation these coils must be
submerged in a hydrogen-rich fluid. The following section provides information about
this fluid and the correct procedure for filling the sensor with fluid.
It is important that you DO NOT operate the sensor for an extended period without
fluid as this can damage the sensor. The sensor should be filled so that the fluid level is
about 1cm below the fill port. There is a fill port tube inside the sensor that provides for
an air gap when the sensor is filled. Correct fluid level can be checked approximately by
shaking the sensor and judging the fluid level by the degree of sloshing. A more accurate
level check requires removal of the sensor’s fill plug and visual inspection of the
contents. If the sensor is empty or needs filling proceed as follows:
A. Place the sensor on a flat, level surface.
B. Remove the blue cap plug on the sensor. Observe that the fill-port is a threaded
tube extending into the sensor vessel. This design provides a 1cm air gap that
allows for thermal expansion of the sensor fluid.
C. Fill with acceptable sensor fluid to within 1 cm. from the top. Acceptable fluids
for proton-precession magnetometers include:
Shell SOL-71 (Shell Oil Co. product).
Charcoal Lighter Fluid (Kingsford, Wizard, etc.)
n-Decane (chemical supply houses, oil refineries)
ISOPAR-1 (Exxon Oil Co. product)
Odorless Mineral Spirits (also known as Naptha)
Kerosene
D. Pour only clear fluid into the sensor. If fluid is dirty use a paper coffee filter or
fine screen to eliminate particles.
E. Slowly pour fluid into sensor until it is full. The sensor is full when the fluid just reaches
the bottom of the fill-port as described above.
F. Place Teflontape around the fill plug then screw it into the fill-port and tighten. Note:
the fill plug and fill-port have tapered threads designed to form a tight seal. Tighten the
plug just enough to prevent leakage - over tightening may crack or damage the sensor
housing.
G. Sensor is now ready for use.

Geometrics, Inc.G-856AX Operation Manual6
The different sensor fluids listed above will provide slightly different signal amplitudes
but their use will ensure that the magnetometer measures the magnetic field strength
correctly and that the sensor will not be damaged interaction with the fluid. Geometrics
does not recommend the use of gasoline (petrol) as a sensor fluid. Experience as shown
that local formulation of gasoline may include additives that can damage the sensor. Do
not put any solvent containing acetone or toluene into the sensor: these will dissolve the
sensor body.
Standard System Assembly
As shown in Figure 1 the standard G-856AX comes packed in a durable plastic carrying
case, with compartments for its accessories. It contains:
G-856AX console
Sensor
Sensor signal cable
Aluminum staff (four (4) mating sections)
Console chest harness
Two (2) rechargeable lead acid battery packs and charger (or D-cell alkaline
batteries, nine (9) required)
G-856 Operator's Manual (on CD)
Application Manual for Portable Magnetometers (on CD)
MagMap2000 Software and Manual (on CD)
RS232 Data Output Cable
If the magnetometer is new it was shipped without sensor fluid. Before the
magnetometer will operate correctly the sensor must be filled with the appropriate
fluid. See the preceding section for a list of appropriate sensor fluids.
Figure 1. G-856 proton-precession magnetometer.
Assembly of the magnetometer is quite simple. Proceed as follows referring to Figure 2
through Figure 8.

Geometrics, Inc.G-856AX Operation Manual 7
1) Assemble the staff by inserting each section into the next twisting them until they
are locked. As shown in Figure 2a, there are four staff sections. The section with
the rubber tip is the bottom section and the section with the treaded end is the top
section. Figure 2 b shows the cam-lock end of the staff section. This end is
inserted into the open end of the matching section. Twisting the jointed sections
by ¼ turn will lock them together.
a b
Figure 2. Sensor staff sections.
2) Verify that the sensor contains fluid. You may shake the sensor to determine if
contains fluid. A sloshing sound indicates proper filling. Some air space above
the fluid needed for thermal expansion - see instructions on sensor fluids in this
section for details. Figure 3 shows the location of the sensor fluid fill port and the
mounting points of the sensor cable. Any tools used for adding fluid, tightening
fasteners or the port plug should either be non-magnetic or have a clean, rust free
hard-chromed finish.
Fill port
Electrical
connection
Strain
relief
a
Use pliers or
nut driver to
tighten
fasteners
b
Figure 3. Sensor preparation.
Note: Geometrics recommends using non-magnetic tools for this task and it is
important to use the original brass nuts and washers supplied with the instrument as
substitutes could be contaminated with ferrous material.
3) Mount the sensor on the threaded staff section. As shown in Figure 4a and b,
there are two ways the sensor can be mounted, either vertically, on its end or

Geometrics, Inc.G-856AX Operation Manual8
horizontally on its side. For now, mount it vertically as shown in Figure 4 a.
a b
Figure 4. Staff / sensor assembly.
4) Remove the console cover by flipping the plastic tabs on its sides outward and
sliding the cover completely off as shown in Figure 5 \a and b. Depending on the
G-856AX version either a) Install fresh D-cell alkaline batteries or b) connect the
internal rechargeable gel-cell battery. Gel-cell batteries are held in place with
Velcro straps as shown in Figure 5c. Reinstall the cover before proceeding.
Clasps securing
console case
a
Slide consol cover off
to access batteries
b
Velcro straps
securing
batteries
c
Figure 5. Console battery compartment.
5) The magnetometer is shipped with the signal cable attached to the sensor. If this
cable is not connected to the sensor connect it as shown in Figure 3b. The sensor
cable terminals are secured to the studs with brass washers and brass nuts. Do not
substitute other hardware for these parts unless then completely non-ferrous.
Tighten the terminal nuts finger-tight and then tighten an additional 1/8th turn
(between 18 in-lb and 24 in-lb). Connect the signal cable to the magnetometer.
6) Put the console harness on as shown in Figure 6a. Hold the console to your chest

Geometrics, Inc.G-856AX Operation Manual 9
and clip the shoulder strap to the D-ring on the console holster as shown in Figure
6b. Do the same with the waist strap and then repeat this procedure on the other
side of the holster. Adjust the harness so that the console is centered on your
torso as shown in Figure 6c.
a b c
Figure 6. G-856 Shoulder harness.
7) Raise the sensor staff assembly to a vertical position and hold it steady for 3-4
seconds before taking a reading. Figure 7a shows the completed assemble ready
for measurement. Figure 7b shows an alternate method for carrying the staff with
the sensor with its central axis vertical. This method uses the saddle mount as the
attachment point for the staff and will require a non-magnetic counter weight
(available from the factory).
a b
Figure 7. Assembled magnetometer.
8) Verify that the console is powered and properly connected to the sensor by
momentarily depressing the READ key. The position of this key is shown in
Figure 8. The displays will light, turn off, then light again for 5 seconds. If the

Geometrics, Inc.G-856AX Operation Manual10
displays did not light, check battery power or the Troubleshooting section in this
manual.
READ KEY
Figure 8. Location of 'Read' key on magnetometer console.
Gradiometer Assembly
G-856AX gradiometer operation requires an optional set of accessories. These items are
shown in Figure 9 and include:
Gradiometer sensor
Lower staff adapter
Upper staff adapter
Gradiometer sensor cable
Gradiometer Switch
Velcro attachment pack
Figure 9. Gradiometer components.
Proceed with gradiometer assembly as follows:
1) Start by removing the standard (single sensor) cable from the top sensor. This
will require removal of the sensor clamp and brass stud nuts as shown in
Figure 10a and b.
Comment [jj1]:

Geometrics, Inc.G-856AX Operation Manual 11
a b
Figure 10 Removing standard sensor cable from top sensor.
Note: Geometrics recommends using non-magnetic tools for this task and it is
important to use the original brass nuts and washers supplied with the instrument as
substitutes could be contaminated with ferrous material.
2) Attach one of the thinner gradiometer sensor cables to the top sensor as shown
in Figure 11 using the stud nuts washers and clamp that secured the standard
cable.
Figure 11. Top sensor with gradiometer cable attached.
3) As shown in Figure 12, attach the other gradiometer sensor cable to the
bottom sensor in the same manner used on the top sensor.
Figure 12. Bottom sensor with gradiometer cable attached.

Geometrics, Inc.G-856AX Operation Manual12
4) Next, connect the threaded staff adaptors parts to the top of one staff section
and the bottom of another staff section as shown in Figure 13 a. The bottom
sensor is configured with opposing mounting points and the adaptors should
be screwed into one set of these mounting points as shown in Figure 13 b.
a b
Figure 13. Connection of threaded staff adaptors.
5) The separation between gradiometer sensors is determined by the lengths and
number of the staff sections linking the sensors. The minimum separation will
always include one of the threaded adaptors and the top (threaded) staff
section as shown in Figure 14 a. Typical sensor separation will be two staff
sections (4ft.). Note that Figure 14a shows only one staff section separating
the sensors. Normally, two staff sections will support the bottom sensor so
that the top sensor is at 8 ft and the lower sensor at 4 ft. An alternative
configuration is shown in Figure 14b where three staff sections support the
lower sensor. With any gradiometer configuration it is best to hold the staff at
arms length when measuring the gradient. This will prevent the lower sensor
from coming too close to the console and better isolate it from the magnetic
effects of the system circuitry and batteries.
a b
Figure 14. Completed gradiometer staff.
6) The sensor cables may now be connected to the Remote Start Switch box, and
the Remote Start Switch may be connected to the G-856AX front panel
connector. As shown in Figure 15, attach the Velcro strip to the top of the G-
856AX black front panel bezel. Mount the Remote Start box to this mating
Velcro strip.

Geometrics, Inc.G-856AX Operation Manual 13
a b
Figure 15. Attach the gradiometer switch box.
Base-station Assembly
The effects of the diurnal variation of the Earth’s magnetic field can be removed from
survey measurements if measurements were made during the survey with a base-station
magnetometer. This magnetometer operates in a fixed location while the survey
magnetometer is used to acquire magnetic field measurements over the survey area.
In order to provide a useful base-station reference, the base-station magnetometer sensor
should be positioned at least 1 m above the ground surface and well away from moving
magnetic objects or structures that will generate a strong magnetic gradient. The sensor
should also be mounted on a stable structure in order to minimize wind-induced motion
of the sensor. Geometrics provides a base-station kit that can be used with the G-856AX
staff sections to construct a stable base-station tripod.
The tripod kit includes a tripod base and two (2) leg tips. The tripod assembly is shown
in Figure 16 with sensor attached. Here, the bottom staff section and the two middle staff
sections have been inserted into the three inclined holes on the underside of the tripod
base. Leg tips have also be slipped on the ends of the two middle staff sections. Attach
the sensor to the top staff section before inserting this piece into the tripod base. The top
staff section is inserted into to central hole on the top of the tripod base so that it slides
past the internal O-ring and rests on the bottom of the hole. The O-ring will prevent the
sensor from rotating under the influence of the wind.

Geometrics, Inc.G-856AX Operation Manual14
Figure 16. Base-station setup up using tripod kit and G-856AX staff section.
Sensor orientation
The G-856AX sensor may be mounted on the sensor staff in either of two orientations: 1)
vertically, so that the cylindrical axis of the sensor is parallel to the sensor staff or 2)
horizontally so that the sensor axis is perpendicular to the sensor staff. This is
accomplished by screwing the sensor staff into either of the threaded receptacles in the
standard sensor body. These receptacles are shown in Figure 17 a. End mounting is
shown Figure 17 b and saddle mounting in Figure 17 c. These alternative modes of
mounting the sensor allow the G-856AX to be configured for use anywhere in the world.
Horizontal and vertical mounting is also accommodated on the gradiometer sensor.
When making a measurement, the correct sensor orientation will be determined by the
Earth’s magnetic field inclination in the survey area. In regions were the magnetic
inclination is greater than +/-40° the sensor should be end-mounted if the measurement
is made with the sensor staff held vertically. That is, the sensor should be mounted so
that its cylindrical axis is vertical. Note that in this configuration the sensor has a North
arrow on its top surface. This arrow should be directed toward magnetic north when
taking a measurement. Aligning the sensor this way will place the axis of the sensor’s
internal coils perpendicular to the Earth's field and produce optimum signal.
When surveying in regions when the Earth’s field is inclined at less than +/-40° the
sensor should be mounted with its cylindrical axis horizontal as shown in Figure 18c.