G-864 Cesium Magnetometer...92131/EEC of 28 April 1992 and 93/68-EEC, Article 5 of 22 July 1993. The Technical documentation required by Annex IV(3) of the Low Voltage Directive is

Operation Manual

G-864 Cesium Magnetometer p/n 770-00105-01 Rev. A1

COPYRIGHT © 2021

We,

Geometrics, Inc. Geometrics Europe 2190 Fortune Drive

San Jose, CA 95131 USA ph: (408) 954-0522 FAX: (408) 954-0902

declare under our sole responsibility that our marine magnetometers, models G-864 and 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 89/336/EEC of May 1989 as Amended by

92131/EEC of 28 April 1992 and 93/68-EEC, Article 5 of 22 July 1993.

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 20 Eden Way Leighton Buzzard Beds LU7 4TZ, U.K. ph: +44 01525 383438 FAX: +44 01525 382200

Mark Prouty, President San Jose, CA, USA

CE March 14, 2003

Sunnyvale, California, USA

EC DECLARATION OF CONFORMITY

03

Warning This is a Class A product. In a domestic environment this product may cause radio interference in which case the user may be required to take adequate measures.

Table of Contents

CHAPTER 1: INTRODUCTION ........................................................................... 4

What magnetometers do: ......................................................................................................................... 4

G-864 configuration: ................................................................................................................................ 5

G-864 components (mineral configuration): .......................................................................................... 5

G-864 components (gradiometer staff assembly): .................................................................................. 6

G-864 components (4 mag array): ........................................................................................................... 6

CHAPTER 2: MAGNETIC SENSOR .................................................................... 7

Sensor orientation ..................................................................................................................................... 8

CHAPTER 3: G-864 COMPONENTS AND ASSEMBLY ................................... 15

Backpack Assembly and Adjustments .................................................................................................. 15

G-862 Cesium Sensor ............................................................................................................................. 17

Cesium Sensor Adjustments .................................................................................................................. 22

Tallysman TW5341 GPS ........................................................................................................................ 23

Battery ..................................................................................................................................................... 25

G-864 Data Logger Box .......................................................................................................................... 26

Getac ZX70 Tablet .................................................................................................................................. 28

CHAPTER 4: SURVEY MANAGER ................................................................... 29

Marked Acquisition GPX ....................................................................................................................... 32

SURVEY SETUP GUIDE .................................................................................... 33

Free-hand GPS Acquisition ................................................................................................................... 34

GPS acquisition with Navigation File ................................................................................................... 34

Marked Survey ....................................................................................................................................... 34

Import collected data to MagMap ......................................................................................................... 34

CHAPTER 5: MAGNAV SOFTWARE ................................................................ 37

Installing MagNav .................................................................................................................................. 37

Installation using microSD card ............................................................................................................ 43

OPERATING MAGNAV ...................................................................................... 47

Preliminary .............................................................................................................................................. 48

GETTING READY TO ACQUIRE ....................................................................... 49

ACQUIRING DATA FOR A MARKED ACQUISITION ....................................... 50

ACQUIRING DATA FOR GPS SURVEY ............................................................ 55

CHAPTER 6: GPS PROGRAMMING ................................................................. 57

Overview .................................................................................................................................................. 57

Collecting GPS Data ............................................................................................................................... 57

Tallysman TW5310 Smart Antenna Setup ........................................................................................... 57

APPENDIX I: MAGNETIC THEORY .................................................................. 62

APPENDIX II: TROUBLESHOOTING ................................................................ 66

APPENDIX III: G-862 SENSOR COMMANDS ................................................... 68

CM-221 Output Format ......................................................................................................................... 68

6.2 ............................................................................................................................................................. 71

Commands ............................................................................................................................................... 71

APPENDIX IV: SURVEYING PRINCIPLES ...................................................... 75

Guidelines for Small Ground Magnetometer Surveys ........................................................................ 75

Number of People ................................................................................................................................... 75

Survey Efficiency .................................................................................................................................... 75

Layout of the Survey Track ................................................................................................................... 76

Diurnal Correction ................................................................................................................................. 76

Survey Accuracy ..................................................................................................................................... 77

Survey Credibility ................................................................................................................................... 77

Location of Small Objects within Associated Anomalies .................................................................... 79

APPENDIX V: CSAZ .......................................................................................... 80

Chapter 1: Introduction

“How sensitive is the instrument, and how will this instrument save me time and

money?” These are the primary concerns of any surveyor. The G-864 has been developed and

designed with these two concerns in mind.

For years, the total field, land magnetometer systems commercially available have remained

stagnant in design and functionality. Data consoles are bulky, old, and not easily expandable to

address new features that customers require. The G-864 integrates a ruggedized tablet with a

modern Android application interface with the highest standard of total field magnetometers

available today. The bridging of established sensor technology with a new age data logger offers

customers the relief of getting the best data quality with new features and the opportunity of new

features introduced well after buying the system. This may well be the last land magnetometer

system that you will need to buy!

What magnetometers do?

A magnetometer measures the Earth’s magnetic field, which occurs naturally and varies in the

presence of ferrous materials. Magnetometers are used in a variety of applications and can be

fitted to airborne, marine and land-based surveys.

Geometrics is a leader in magnetometer development and is known worldwide for our total field

magnetometers. Our magnetic sensors measure the total magnetic field, or total field, without

directional information. In other words, they take the scalar measurements of the magnetic field,

and produce a value that is the magnetic field intensity, regardless of the direction in which the

field propagates. More information about the sensor used in this system is provided in Chapter 3.

Magnetometers can be used to map and locate man-made objects and naturally occurring iron or

other ferrous metals. For example, the Earth’s crust contains iron in the form of the mineral

magnetite. Magnetometer surveys are frequently used to map concentrations of ferrous minerals

in the Earth’s crust. Magnetite is a mineral often associated with kimberlites (diamonds), native

gold, copper and other economic deposits.

Man-made ferrous objects, such as those associated with archaeology, civil engineering,

unexploded ordnance, etc., alter the Earth’s magnetic field in a way that is detectable with a

magnetometer. The strength of the altered field depends on many factors, including the size, iron

content, orientation and depth. More detailed information on magnetic theory and survey design

can be found in the Applications Manual for Portable Magnetometers and can be found on our

website: www.geoemetrics.com.

http://www.geoemetrics.com/

G-864 configuration:

The G-864 land magnetometer is configurable to address the survey needs of both near and deep

surface investigations. Deeper geological investigations require a sensor mounted onto a

backpack with the sensor elevated above the operators head to remove the sensor from the

magnetic effects of surface debris or other near surface artifacts. For geological surveys, the G-

864 can use a sensor attached to the sensor electronics with a 3 ft. (1m) sensor cable for

separation to effectively fit onto the backpack without excessive cables potentially at risk for

snagging on branches or other obstructions.

For near surface investigations the sensor is connected to the sensor electronics module by a 9 ft.

(2.7m) sensor cable and is carried on a staff or cart towed behind a motorized vehicle. The sensor

electronics module is well suited to act as a counterweight on the staff to make a balanced unit

for easy surveying. In many cases, near surface surveys, specifically in archaeology and UXO

surveys, having multiple sensors as a linear array allows the operator to cover more area in a

single survey line, as well as gain gradient information that might shed more light on the targets

located in the data. The G-864 can handle up to 4 cesium magnetometer sensors at a time. For

operations of more than 2 sensors, customers will need to design their own cart or purchase from

a third party.

G-864 components (mineral configuration):

Below is a listing of the items included in the G-864 land magnetometer (backpack mounted

sensor configuration).

Geometrics P/N Description Quantity

900-00390-01 G-864 BACKPACK ASSEMBLY 1

900-00308-01 G864, TABLET RUGGED. GETAC ZX70, ANDROID OS 1

900-00392-01 G-864, LITHIUM BATTERY POUCH OPTION 0.3

900-00393-01 G-864, LEAD ACID BATTERY POUCH OPTION 0.7

0025307-23 BATTERY POWER PACK-LI-PO TYPE 29.2 VOLTS 0.3

0025445-23 LITHIUM BATTERY CHARGER ASSEMBLY-POWERSTREAM 0.3

0025307-22 BATTERY PACK-LEAD ACID TYPE ('NOT RESTRICTED""""""""-SPECIAL PROVISION 0.7

820-00188-01 LEAD ACID BATTERY CHARGER KIT 0.7

0027921-62 G-862 CESIUM ELECTRONICS & SENSOR W/3 FOOT CABLE 1

900-00391-01 G-864, GPS OPTION 0.5

For quantities that are less than one, this indicates that there is an option. For instance, above

there are options for a Lead-Acid battery pack with chargers and pouches or a Lithium-Polymer

battery with the appropriate chargers and pouches. Customers can decide if they wish to use a

Lithium-Polymer battery that is longer lasting, but as shipping regulations are changing, may

prove to be an issue if Lithium batteries are more strictly regulated.

G-864 components (gradiometer staff assembly):

Below is a listing of the items included in the G-864 land gradiometer (staff mounted

gradiometer kit)









0025366-14 G-864 IMC CHARGER 24V 2A 0.7


900-00309-01 G864 SYSTEM GRADIOMETER STAFF OPTION 1

900-00391-01 G-864, GPS OPTION 0.5

G-864 components (4 mag array):









0025366-14 G-864 IMC CHARGER 24V 2A 0.7


900-00391-01 G-864, GPS OPTION 0.5

For the most current part numbers and options please contact a Geometrics salesperson at

[email protected].

mailto:[email protected]

Chapter 2: Magnetic Sensor

The G-864 land magnetometer instrument is based around the G-862 airborne magnetometer

sensor for its adaptability to different survey types. This sensor technology is used in all

Geometrics cesium magnetometers, apart from the newly designed MFAM sensor. The sensor

electronics is based on the high sample rate, high sensitivity electronics used in both our G-882

marine magnetometer (industry standard for marine surveying), and the G-823A (industry

standard for airborne surveys). For a more complete explanation of the G-862 sensor please

consult the G-862 manual found on the USB stick with magnetometer instrument and software

manuals included in each instrument shipment, or contact a salesperson at

[email protected].

Performance

Geometrics G-862 magnetometer produces a Cesium Larmor frequency output at 3.498572 Hz

per nT. ‘nT’ refers to the magnetic field strength as measured in nanoTesla. 1 nT equals 1

gamma or 10-5 gauss. So, at the earth’s surface, in a nominal 50,000 nT field, the Larmor

frequency is about 175 kHz. The output of the G-862 sensor electronics is a continuous sine

wave at the Larmor frequency. The typical signal amplitude is from 1 to 2 volts peak-to-peak

with the sensor in its optimal orientation. This frequency of this signal is counted and reported

via RS-232 at a user set rate. The sensor has a maximum sample rate of 100Hz.

The G-862 is intended for use in airborne, land and base station applications, and operates over

the earth's magnetic field range of 20,000 to 100,000 nT. Absolute accuracy depends on the

sensor orientation, internal light shift and the accuracy of the external counter's time base. An

error due to orientation of the G-862 does not exceed ± 0.25 nT or 0.5 nT peak-to-peak (p-p)

throughout the active zones shown in Figure 3. Environmental conditions for proper operation

are -35 to +50°C (-31 to +122° F), humidity to 99 percent non-condensing, over an altitude range

of 0 to 30,000 feet.

Like all magnetometers, performance of the G-864 is primarily dependent upon the counting

circuitry employed and the quality of the installation procedures. Compensation and/or noise

reduction techniques must normally be used to minimize the magnetic effect of the platform and

its motion. Navigational and positional errors, radiated electromagnetic noise, and heading errors

from the vehicle’s induced and remnant magnetic fields are typically the major contributors to

noise in the survey results.


Sensor orientation

Magnetic fields are vector fields. At any point, they are defined by their magnitude and direction.

If the G-862 sensor is going to accurately measure the local magnetic field magnitude, it must be

properly oriented relative to the local magnetic field direction.

The sensor head must be oriented so that the local field impinges at an angle of from 30º to 60º to

the cylindrical axis of the sensor, for all platform attitudes. Alignments that produce a field/axis

angle less than 15º place the magnetic field within the sensor’s “polar dead zone". Similarly,

alignments that produce a field/axis angle greater than 75º place the magnetic field within the

sensor’s “equatorial dead zone". The sensor will not produce usable data when the angle between

the earth's field and the cylindrical axis falls within one of these two zones.

Unless the sensor is quite near very magnetic objects, the local magnetic field will be almost

entirely due to the earth’s magnetic field. Therefore, in latitudes where the inclination of the

earth's field vector is 45º, vertical orientation of the sensor’s axis will allow operation in all

practical survey orientations. In Equatorial regions, it may be necessary to orient the sensor

horizontally and at an angle to the survey direction. In Polar Regions, the sensor may be mounted

with its major axis tilted east or west to obtain the desired angle.

Magnetic Inclination

The maps in the two figures above may be used to determine the inclination and total intensity of

the Earth's magnetic field in the intended area of survey. This inclination information should be

used to adjust the sensor orientation for the best performance in the survey area. The intensity

information may be used as a check of the system operation.

In regards to sensor orientation, the Earth’s surface can be divided into three zones based upon

magnetic field inclination: mid-latitude, equatorial, and polar. Within each of these zones, a

particular sensor orientation will yield adequate signal strength over the entire zone. These

regions and the corresponding sensor orientations recommended for each region are shown in the

following figures.

Note that the orientation zones overlap one another by 10º of magnetic inclination. In these

regions of overlap, there are two different recommended sensor orientations. In this region, the

magnetic field is nearly horizontal and there will be some restrictions on the direction of survey.

Choosing one of the two recommended orientations will allow you to choose survey directions

most suitable for your survey area.

The diagram to the left shows the

recommended sensor orientation for

operation in mid latitudes. This zone is

shown as the shaded regions above and

includes those areas where the absolute

inclination of the Earth’s magnetic field

is greater or equal to 20º and less than or

equal to 75º. There are no restrictions on

the direction of travel when using this

sensor orientation.


recommended sensor orientation for operation

in polar latitudes. This zone is shown as the

shaded regions above and includes those areas

where the absolute inclination of the Earth’s

magnetic field is greater or equal to 65º. There

are no restrictions on the direction of travel

when using this sensor orientation.


recommended sensor orientation for

operation in equatorial latitudes. This zone is

shown as the shaded region above and

includes those areas where the absolute

inclination of the Earth’s magnetic field is

less than or equal to 25º.

There are restrictions on the direction of

travel when using this sensor orientation in

this region. The bottom diagram to the left

shows the directions where the sensor will

produce good signal strength. These t

directions are 60º wide and are centered on

45º, 135º, 225º, and 315º.

The top diagram to the left shows an

alternative sensor orientation for

operation in equatorial latitudes. This

zone is the same as that shown in Figure

8 except that the sensor is rotated about

its equator by 45º allowing N-S, E-W

survey lines. It includes those areas

where the absolute inclination of the

Earth’s magnetic field is less than or

equal to 25º.

As with the sensor orientation shown in

Figure 8, there are restrictions on the

direction of travel when using this

sensor orientation in this region. The

bottom diagram to the left shows the

directions where the sensor will produce

adequate signal strength. These

directions are 600 wide and are centered

on the cardinal magnetic field directions

00, 900, 1800, and 2700.

In addition to the diagrams provided here, the program CsAz may be used to calculate the

sensor’s output for a particular orientation for the magnetic field attitude in your survey area.

This is a DOS program and is provided on the Magnetometer Support USB supplied with your

magnetometer.

Environmental Considerations

Optically pumped magnetometers are more sensitive to magnetic field variation than are proton

and fluxgate types. To realize the full performance of the cesium-vapor technology, special

precautions must be taken during planning and execution of the installation.

Vibration

Intense vibration of system circuitry can induce micro-phonic noise and shorten the life of

system components. The intense vibrations are typically not seen in a walking survey, however if

in larger arrays the system is mounted on a cart behind an ATV it may be a concern. Some

attachment points may be prone to intense vibration and we recommend the use of good quality

shock mounts that are designed to isolate the G-862 components from as much of the intense

vibration as possible. Special care should be taken in securing or routing the cable so that it does

not encounter hard or sharp objects that could damage the cable. Those components used to

mount the G-862 sensor or any or any objects near this sensor should be non-magnetic in order

to minimize the system heading error.

Temperature

The G-864 is designed to operate over an ambient temperature range of -35 to +50°C. In an

enclosed region it may be necessary to provide adequate cooling by free flowing air. If the sensor

and electronics are in an unconfined region, convection cooling is generally adequate. The

cesium lamp only needs to dissipate 3 to 4 watts of heat and when operating in cold regions

providing some insulation or baffling will help reduce the sensor’s power consumption.

The G-862 requires a minimum warm up period of 15 minutes. In cold regions the warm up

period will be longer and, to avoid delay, we recommend that the sensor power be left on

overnight when ambient temperatures are expected to fall below -10°C.

Chapter 3: G-864 Components and Assembly

This chapter covers the assembly of the different configurations of the G-864 land

magnetometer. Please reference the section that applies to the system that you are operating for

appropriate assembly.

Backpack Assembly and Adjustments

The backpack in this instrument is the same that is used in our previous land magnetometer

systems as it provides a comfortable and relatively lightweight solution to carrying the

magnetometer in a stable, secure manner over harsh terrain. The backpack consists of a military-

grade, fabric Mystery Ranch pack, an aluminum electronics tray to mount the data logger box,

poles and battery.

The pack frame commercial hardware has been replaced with brass and aluminum parts,

removing all ferromagnetic components to keep the system magnetic self-signature to a

minimum, thus reducing heading error and other platform noise. Never replace hardware with

untested bolts, nuts or rings. Always test the hardware first by turning on the

magnetometer and moving the hardware under test near the sensor. Typical goals are to

have less than 0.5nT effect at 2 feet (0.6m) from the sensor.

The first time the pack frame is assembled and used, it will be necessary to adjust it for the

individual user. This may require a second person to observe and adjust the fit while the system

is worn by the survey crewmember. The pack frame is a professional grade frame with a sliding

Velcro secured vertical pack adjustment system.

The Mystery Ranch Pack Frame system is unique in that it has internal adjustments available to

fit different body sizes. The following instructions are based on using two people to make the

adjustments. Raise the pack frame and fit it onto the individual who will be doing the survey.

With the waistband secured (just the pack frame belt attached) note where the shoulder harness

pads come to rest on the individual’s shoulders.

The seam between the back part of the pack and the shoulder pads should be level with the

collarbone (just over the crest of the shoulder). If the straps are too high, the weight of the pack

will not be evenly distributed on the shoulders, and if it is too low then all the weight will be on

the shoulders. The correct installation will have most of the pack weight on the hips and perhaps

20% on the shoulders. In addition, if the straps are too low the straps will not adjust in the front.

To extend or compress the shoulder harness, peel back the flap at the top of the front of the pack

and locate the Velcro Release tool as shown in the figure below. Remove this tool and then

insert it between the shoulder harness and the back of the pack, breaking loose the Velcro. You

will then be able to move the shoulder harness section to correctly position the height of the

shoulder pads. When the correct height is achieved, remove the tool, press the pack together

securing the Velcro and then replace the Release tool in its pocket.

G-862 Cesium Sensor

The basic system components of the G-862 consist of the sensor module, a sensor driver

module, and an interconnect cable that is permanently attached to the sensor module and

detachable from the sensor driver module. These components are identified in the figure below.

The weights, dimensions, and connector’s specifications for these components and ancillary

system components are also listed below for reference.

Description Weight Dimensions

Cesium sensor package

P/N 27516-45, -46, -47

1lb. 8oz. 6-3/4” long x 2-3/4” diameter cylindrical

housing with 9 or 3 foot cable

G-862 Sensor driver module

P/N 27519-30

2 lbs. 15-1/4” long x 2-3/4” diameter cylindrical

housing

Pin Diagram of G-862 Sensor driver module

Below is a pin diagram of the sensor electronics module used in this instrument, as

well as the cable diagram used to connect the magnetometer to the data logger box.

Circuit description of the external signal/power interface cable Connector type SP02A-14 -19P

Pin # Function Description

A 30V power Magnetometer power; 24 – 32VDC

B GND Power ground

C TxD From logging computer, connects to RxD of G-862

D Rxd To logging computer, connects to TxD of G-862

E COMMON RS-232 Ground

F RESET Contact closure to GND

Figure 1: G-862 system components

G EVENT External Trigger Input

H CHANNEL 1 + Analog channel #1 – differential input, 5v full scale, 2K input

impedance. J CHANNEL 1 -

K CHANNEL 2 + Analog channel #2 – differential input, 5v full scale, 2K input

impedance L CHANNEL 2 -

M CHANNEL 3 + Analog channel #3 – differential input, 5v full scale, 2K input

impedance N CHANNEL 3 -

P CHANNEL 4 + Analog channel #4 – single ended 2.048v full scale, >10K input

impedance R CHANNEL 4 -

S CHANNEL 5 + Analog channel #4 – single ended 2.048v full scale, >10K input

impedance T CHANNEL 5 -

U Ext GND External Input Ground use for EVENT and RESET lines

V Boost Enable Wire to Pin A to enable Boost Power Supply.

Note: 1) All analog channels have 12 bit resolution 1%; 2) Differential channels 1, 2 and 3 may be

able accept other full-scale voltages if original order called for custom input specification - consult the

factory if you suspect that your system has non-standard input ranges; 3) If the single ended channels 4

or 5 are used, the signal source must be operated from a power source that is isolated from power

ground.

Mounting the Sensor and Sensor Electronics onto the Backpack

To mount the cesium magnetometer onto the backpack loosen the two black clamps on

the sensor electronics so that they are loosely fitted onto the sensor electronics. On the side that

you want to mount the sensor, loosen the knob securing the vertical aluminum pole mount until

you can lift the aluminum pole. Fit the pole through the two black electronics clamps and reinsert

the aluminum pole into the holder at the bottom of the pack frame and retighten the black knob

until everything is firmly in place. At the top of the pole, mount the pole assembly with the

sensor clamp and secure it in place with the black knob. Insert the sensor in the sensor clamp and

tighten the knobs until the sensor is securely in place. Avoid overtightening as the sensor clamp

can crack if too much pressure is applied. Finally, attach the sensor electronics bottle to the data

logger box by the sensor cable with appropriate keyed connector. Do not force the connector

together, line up the keys and then use the outer ring to secure the connection.

Staff Assembly with Single Sensor

The sensor and staff pieces for the instrument are located inside of the canvas bag in the smaller

case shown below

The sensor electronics acts as the counterweight when performing a single sensor survey.

To assemble staff attach the sensor electronics bottle to one of the bare staff sections,

unscrewing the black screw bolt on the sensor clamp enough to fit the aluminum pole through

and then tighten back down. Next, attach the staff section with the foam grip to the bare staff

section again by threading the black screw bolt into the groove of the next section and tightening

the bolt. Then attach the section with the four plastic cable holders using the same method as

before. These plastic cable holders secure the sensor cables so that they do not swing around

while collecting data, and reduces the chance that they get caught on brush or objects during a

survey. The next section to attach contains the strap, which will be threaded through the clamp

on the backpack assembly. Attach the end of the strap to the clip on a small aluminum insert that

attaches to the staff section holding the sensor electronics. The final section of the staff is the

short aluminum staff section with the white plastic sensor clamp on it. Adjust the orientation of

the sensor to the requirements of your GPS location.

Slide the staff strap through the strap clamp on the backpack to secure the staff while surveying.

Adjust the positioning of the staff so the counterweight properly balances out the weight of the

sensors in the front of the staff. When a good balance has been achieved, tighten the strap clamp

to secure the staff in one place during survey.

Gradiometer Assembly

To assemble to gradiometer staff attach the heavy counterweight to one of the bare staff

sections, sliding the black screw bolt into the groove of the aluminum staff section. Tighten the

screw bolt down to secure the counterweight. Next, attach the staff section with the foam grip to

the bare staff section again by threading the black screw bolt into the groove of the next section

and tightening the bolt. Then attach the section with the four plastic cable holders using the same

method as before. These plastic cable holders secure the sensor cables so that they do not swing

around while collecting data, and reduces the chance that they get caught on brush or objects

during a survey. The next section to attach contains the strap which will be threaded through the

clamp on the backpack assembly. Attach the end of the strap to the clip on the counterweight.

The final section of the staff is the “T” section which allows the sensors to be orientated in a

gradient mode. Attach the “T” section in the same fashion as before and then attach the sensors

to the “T” section. A completed assembly of the staff can be seen below.

Fitting the strap through strap clamp

Slide the staff strap through the strap clamp on the backpack to secure the staff while surveying.

Adjust the positioning of the staff so the counterweight properly balances out the weight of the

sensors in the front of the staff. When a good balance has been achieved, tighten the strap clamp

to secure the staff in one place during survey.

Lastly, take the magnetometer data cable and connect the magnetometer to the connector

labeled “MAG” on the grey data logger box. Again, align the keys and use the outer ring to

secure the connection. Avoid pushing the connector in as this can damage the pins and require

the system to be returned for repair. Extra cable can be tied down using the cable tie-wraps to

avoid loose cabling that can be snagged on branches or other obstructions.

Complete assembly of staff with sensors

Fitting the strap through strap clamp

Cable Diagram for Single Sensor Electronics to Data Logger Box

Below is a wiring diagram of the gradiometer cable:

When everything is connected, press the “POWER” button on the side of the data logger

box. This button should appear Green when powered on and inset into the box to avoid

accidental button presses during operation, which would cut the power.

Cesium Sensor Adjustments

Next, we will adjust the cesium sensor position. Note that the sensor may be mounted

vertically, at 45º to the vertical or horizontally. Basically, once you select the proper orientation

for your area it will always mount in that manner if you are surveying in a particular location on

the world. We suggest that you install and use CSAZ, a companion program on the

Magnetometer Software USB that shows you how you should mount your sensor for any

location on the globe. Suffice it to say that in the far northern and southern latitudes, the sensor

will be mounted at 45º; for the mid latitude zones including as far south as Northern S. America

you will mount the sensor vertically. In a narrow band about the earth’s magnetic equator (note

not zero latitude necessarily) you will mount the sensor at 45º or horizontally with the top of the

sensor tilted either North or South as you walk the survey line. See CSAZ for more information

There are two knobs on the sensor clamp. The knob closest to the sensor tightens the sensor

clamp to keep the sensor in place during survey. The knob furthest from the sensor allows you to

reorient the sensor. Loosen this knob to allow the sensor clamp to rotate up to 45 degrees or

horizontal as needed. If you need to orient the sensor at an angle to your survey direction fully

remove this knob and rotate the sensor clamp 90 degrees until the holes line up and then reinsert

the knob and tighten.

Figure 2: Left, knob to tighten sensor clamp around sensor. Right, knob to reorient sensor to match required

orientation for survey area

Tallysman TW5341 GPS

The G-864 systems comes complete with a non-magnetic GPS, the Tallysman TW5341.

This specific antenna was chosen for its non-magnetic properties which allows the GPS to be

mounted within 1 ft. of the G-864 sensor and not interfere with the magnetic measurements. This

is particularly important in a backpack mounted schemes. A magnetic GPS would require a

larger offset between GPS and magnetometer, which would mean mounting the GPS on a larger

pole from the backpack, which leaves the system susceptible to damage to low-hanging branches

or obstructions.

GPS Settings

The Tallysman GPS is set up at 19200 baud rate and outputs the GPRMC and

GPGGA NMEA data strings. The purpose of these two data strings is to gain the UTC

time and date information for properly time tagging the data. If one of the messages is

missing a warning message will appear. If you are using your own GPS, please ensure

that they are properly set up and that the pin wiring is correct. The pin diagram is

shown below:

Mounting the GPS on the backpack

Remove the GPS from the bag and line the slit with the black knob to mount the GPS

onto the backpack. Turn the knob until it becomes snug to ensure that the GPS is securely fixed

to the pole. You can wrap excess cable around the pole or bunched at the bottom of the backpack

to protect the cable from getting caught on branches or other objects during a survey. The GPS

cable should be fed through the opening on the bottom of the backpack to the corresponding

connector on the grey data logger box. Every connector has a keyed face which needs to be

properly aligned for connecting.

When connecting, simply rotate the cable until the keys lined up and then use the

outer ring to secure the connection. If you push the connectors together you could

potentially damage the pins, which will require the unit to be returned to Geometrics for

repair.

Battery

The G-864 offers two battery options, a Lead Acid battery that has historically been used

in the G-858AP and G-859AP land magnetometer systems, as well as a Lithium Polymer battery

that was designed to offer a lightweight, longer lasting battery solution to customers. The

Lithium Polymer battery consists of two packs of cells, each at 88W-hr rating which is below the

current standards for shipping on planes with the correct documentation. Many airlines also

allow at least two Li-Po batteries of this size in your carry-on luggage for transport. Check with

your airline and/or courier regulations before packing these batteries. Geometrics is not

responsible for any issues with Lithium battery transport after it has been shipped from the

factory.

The Lead Acid battery packs were fully charged before leaving the factory, but

depending on storage time, they may need to be recharged. Lithium Polymer batteries must be

discharged to 30% before they can ship so these batteries will need to be charged when received.

The system may come with the one of the battery packs pre-installed in the pack frame bag. In

this case you will check the voltage of the battery pack using the G-864 console battery meter

(you must turn on the G-864 to see the meter reading by pressing the Power button). Recharge

time is approximately 6 to 8 hours per battery. The battery may be recharged in the pack frame

battery box using the standard charger cable.

Inspect the connectors in the battery compartment and on the battery and note that they

are 3 Pin Bendix type connectors, which are keyed so that they can mate in only one orientation.

Line up the keyed sections and firmly push the connector together, then rotate the locking sleeve

to secure the connector.

Lift the battery pack and slide it into the battery bag. When the battery is seated in the

bag, close the battery bag with the Velcro bag cover.

Batteries will power the G-864 and integrated GPS for between 5 and 7 hours depending

on operating temperature. Cold temperatures will decrease battery capacity and increase

magnetometer current requirements. Note that in very cold areas, the cesium sensor should be

enclosed in an insulating jacket to keep heat loss to a minimum and extend battery life.

NOTE To best maintain battery life, you should periodically charge the batteries (about every 4

months) if the unit is not in use.

G-864 Data Logger Box

The G-864 data logger box is attached to the aluminum electronics tray on the Mystery Ranch

Backpack. All components of the data logger box have been confirmed to be non-magnetic and it

is inadvisable to replace components locally without first checking the magnetic characteristics

of the parts first.

USB Port

The data logger box includes a USB port on the top of the box for data storage and is the primary

backup to the data logged onto the Tablet. If for any reason the data connection is lost, or the

data is corrupted or accidentally erased on the tablet, the USB stick will have a backup record for

data processing. The USB provided is 32GB, which can store up to 2 years of continuous data

before needing to be replaced.

The USB port is also the location where firmware updates take place. When a new firmware is

available from Geometrics, simply take out the USB stick, and load the new firmware onto it and

then place it back into the USB port on the data logger box. When the system is powered on, the

firmware will automatically be updated and the new system will be ready to go.

Status Lights

This section reviews the status lights and functions of each component of the grey data logger

box.

Battery

When the Blue LED light is on it signifies that the battery is connected and has

sufficient voltage to power the system.

PPS

White LED light that signifies if the system is receiving and is locked to the 1PPS

signal sent from the internal adafruit GPS unit. This LED will be off if no PPS is

detected. The PPS message is essential for surveying accurately for timing purposes

and a survey should not begin without first having the PPS message active.

GPS

Orange LED light that signifies that the logger box is receiving correct GPS messages.

The system requires both the GPGGA and GPRMC messages. The GPGGA is used

for counting the number of satellites for fix level warnings, as well as the time

information. The RMC message is used for the date to be included in the final

exported data. The LED will blink at the rate of the GPS message.

Status

A Green LED that signifies that the magnetometer data is being seen. The LED will

blink at the rate of the magnetometer sample rate.

USB Port

A Red LED light signifies that there is a USB inserted into the connector. A slow

flash signifies that data is being written to the storage unit.

Heat Sink

Located beneath the LED lights is a large heat sink to allow for heat generated from

the internal electronics to dissipate and avoid overheating inside the box. The heat sink

has been designed to effectively remove extra heat when four magnetometers are

being used at once at the extreme temperatures tolerable for the magnetometer (50C).

It is important to keep this heat sink clean and intact. If you see general wear and tear

on the heat sink please contact Geometrics to evaluate if it needs to be replaced.

Connectors

Located underneath the data logger box are connectors marked to represent the

appropriate device to be connected to it. Each connector has a different pin collection

to make it easier to properly connect each cable. Note that the connectors are all keyed

and you should never force the connectors together manually. Simply align the keys

on the cable to the connector and use the locking ring to force the connection.

Power Button

The power button is located on the bottom, left side of the data logger box. After each

device is connected press in the Power button to turn on the system. The button should

turn green to show that power is applied. The button will also be set into the box when

Power is applied to avoid accidental presses on the button while surveying.

Reset Button

The reset button is used in the event that the G-864 processor has hung or is not

responding. The reset will not turn off the magnetometer so you can avoid waiting for

the magnetometer to warm back up and start running again.

Getac ZX70 Tablet

The G-864 comes with the Getac ZX70 Android tablet as the main data logging, and user

interface device. This model is a ruggedized tablet that comes with no speaker to significantly

reduce the magnetic characteristics of the tablet for a clean survey. The tablet comes with a 3-

year warranty, standard and additional years of warranty are available for purchase. Warranty

claims must be made through Getac and their worldwide network of service stations:

https://eu.getac.com/support/servicewarranty.html.

Users can use their own Android tablet, however Geometrics is not able to provide support on

issues that arise from utilizing tablets that are not shipped with the system from the factory. The

data logging software has been tested with the latest version of Android at the time of shipping,

and will be maintained to the latest standard at each subsequent release to avoid issues in the

future.

https://eu.getac.com/support/servicewarranty.html

Chapter 4: Survey Manager

Surveys can be hectic and programming a data logger console in the field can easily cause data

collection issues that may not be easily fixable in software in the lab. Geometrics has developed

a program called Survey Manager that is used in the G-864 as well as our airborne MagArrow

system that allows the lead geophysicist to set up the survey prior to heading out to the field to

limit any confusion or mistakes by the field technician when they are ready to start surveying.

The Survey Manager program is included on the USB stick with the other software and manuals

that accompanies the instrument in the shipping case. To install this program simply insert the

USB stick with the software, open a browser and double click on the surveymgrsetup.exe file.

The first screen will ask if you want to allow the program to make changes to the computer,

press Yes. Press “Next” two times and then click “Install” to install the program. Once installed,

the program icon will appear on your desktop:

Open the software by double-clicking on the icon and the following page will appear:

Please be aware that this program will routinely be updated to include new features to address

customer’s requests and concerns. If your current version does not match the writing of this

manual, please contact MagSales@geometrics for the latest version of the manual.

Magnetometer Type

There are two options for the magnetometer. The MFAM, which is used in the MagArrow, and

the 864. In future versions of the G-864, we intend to incorporate the MFAM sensors to improve

the systems flexibility and battery life.

Survey ID

This is a random ID that is special to the survey file that you are currently working on. This is

not an editable field.

Survey Name

This is a user-determined identifier of the project database file that the survey files (acquisitions)

are intended to be saved under.

Number of Magnetometers

A drop-down menu with options for 1-4 magnetometers. Currently this is the maximum number

of G-862 sensors that can be powered and operated using the G-864 system. With the adaptation

of the MFAM sensor, this will increase to more than 10 sensors for large, multi-dimensional

arrays.

GPS Type

When the G-864 if selected for the magnetometer type the GPS type is automatically selected as

Tallysman. Any GPS should work provided that it is 1Hz data rate and includes the GPGGA and

GPRMC data strings.

Samples Per Second

The G-864 has the capability of operating at multiple different sample rates. It is important to

keep in mind the local mains frequency when selecting the sample rate. Sample rates at integer

factors of the mains frequency will alias the noise from the electrical grid to zero. For

frequencies of 60 Hz, you can select 1, 2, 5, 10, 20 Hz, whereas for 50 Hz you should select from

1, 2, 5, 10, 25 Hz.

Swath Radius

The swath radius is also useful in the Coverage view in the MagNav Android software to show if

the data in the survey adequately covers the survey area with a certain data density. Blue dots

with the defined swath radius appear at each GPS location to show where the survey has walked

and if adjacent lines were surveyed, close enough to meet a customer’s requirement for a certain

data density.

Line Spacing

Defines the distance in meters between adjacent lines. Consult the Applications Manual for

Portable Magnetometers for information about determining the appropriate line spacing for your

application.

Off Track Warning

Maximum allowable distance off the preset survey line before the MagNav application creates a

warning message to direct the operator back online.

Sensor Geometry

This sets the offsets from the GPS for the correct positioning of each sensor. The number of

offsets allowed are based on the number of magnetometers being recorded. For Offset Left,

positive is to the left of the GPS, right is negative. For Offset Forward, if the sensor is in front of

the GPS then it is a positive number, if it is behind the GPS it is negative. For offset below it is

the vertical difference between the sensor and GPS.

Acquisitions

Acquisitions, in Survey Manager, are considered grids or survey units. A survey is a collection of

acquisitions that maintain a similar set of survey parameters.

Selecting “New” brings up the following Menu Screen

The acquisition can have any name that the operator desires. Navigation chooses if the survey

should be a GPS survey or Marked Survey.

GPS Survey

Use GPS to navigate. When data is exported from Survey Manager, a location for each

magnetometer reading will be interpolated from GPS data.

Marked Survey

When using cones, tapes or other physical landmarks for defining the survey. When data is

exported from Survey Manager, a location for each magnetometer reading is interpolated from

waypoint locations in the acquisition’s GPX plot file.

Route File

If you have survey lines created already you can import them here. The route files must be

in GPX format. There are many GPX creating websites and programs which will work, or

you can use the function found under the Tools heading.

Marked Acquisition GPX

This function is a quick way to create GPX files for either Marked or GPS surveys. Go to Tools,

and select Marked Acquisition GPX. The following screen will appear:

Route Type

Lat/Long: Signifies that you will be working in GPS coordinates. This is used for GPS surveys.

X/Y: Signifies that you will be working in Cartesian coordinates. This is used for Marked

Surveys.

Route Name

Gives a name for the route file to be created.

Latitude/Longitude

Provides the origin of the survey line. If you are working in Lat/Long use decimal degrees. If

you are working in Cartesian coordinates the unit of measure is in meters.

Direction of first line

This is a compass direction of the survey line. 0 degrees will correspond to a North survey, 90

degrees is East, 180 degrees is South, and 270 degrees is West.

Line offset direction

This determines if the subsequent survey lines are positioned to the left or to the right of the first

survey line.

Length of Line

Provides the length of each survey line to be created.

Number of Lines

Creates the number of lines to the left/right of the initial survey line. This number does not

include the initial line. If you want 10 lines you would select 9 as the number of lines.

Line Spacing

Distance in meters between adjacent lines.

Mark Spacing

Distance between marks along a survey line. If you are using a GPS survey this is irrelevant as

the GPS will produce a mark every second.

Traversal Type

Choice of surveying bidirectional (in a zig zag pattern) or omnidirectional where after each line

is completed the operator needs to return to the baseline and survey in only one direction.

When you have completed the fields press Save and a .GPX file will be created. This GPX file

can be loaded into the route file under when creating a new acquisition.

Survey Setup Guide

This will serve as a general guide for the order of operation for setting up your survey depending

on how you expect to survey.

Free-hand GPS Acquisition

This is for when you will want to plot the data using GPS coordinates but to not have an exact

plan for surveying a site.

1. Click New Acqusition, Name the file and select Navigation: GPS. Click OK.

2. Select the acquisition file in the drop down menu next to Acquisition.

3. Fill in the fields on the left side of the program.

4. File…/Save… and name the database file (.DBT)

GPS acquisition with Navigation File

This function is for when you have a predefined survey route created. This can be created using a

website GPX generator or using the in-built program under Tools.

1. Click New Acqusition, Name the file and select Navigation: GPS.

2. Click Select file to import the predefined survey route file. Click OK




Marked Survey

1. Go to Tools and open the Marked Acqusition GPS

2. Complete the appropriate fields and save the file.

3. Click New Acquisition. Name the file and select Navigation: Marked.

4. Click Select file to import the predefined survey route file. Click OK




Import collected data to MagMap

After finishing the survey and the data has been moved to the computer with Survey Manager and

MagMap installed it is time to load the data into MagMap for data processing. First, the data stored

in the tablet is as a .dbt file which is not initially read into MagMap. First open Survey manager

and select File…/ Open and select the file to be read in.

When the file is read into Survey Manager the settings for the file are updated. Select the

acquisition you wish to export and then click Export Data to save the file as a .CSV file.

Open MagMap and click Open and choose the correct file extension (SURFER *.dat, Interpolator

*.INT, *.txt, Comma-separated *.csv, IAGA 2002).

Choose the file that you collected and the following Data file Definition screen will appear:

You will need to manually change the fields to make sure that they are correct. If you have multiple

sensors make sure that you have added each data channel.

If you have a base station remember to have that file open as well when you’re ready to export the

data to MagPick or a third party program to ensure that the data is diurnally corrected. For more

information about data processing in MagMap or MagPick please consult the manuals for those

programs or contact [email protected].


Chapter 5: MagNav Software

The MagNav software is initially designed to meet the basic needs of the operator for collecting

magnetic data quickly and efficiently. The MagNav software will continually be updated and

improved based on user feedback and requests for additional features and benefits to make the

surveying process easier and to gain the most amount of information while in the field. If the

version of MagNav that you are running differs than the images shown in this manual, please

contact [email protected] for an updated version of the manual.

Installing MagNav

MagNav is installed on the non-magnetic Getac tablet that is designed to be the main data logger

and console. If the software is uninstalled or needs to be updated the following steps can be

taken.

Manual installation

When you are installing the APK (refer to the last 3 character in the MagNav file name) yourself

this process is called side-loading. Alternative way to install the MagNav APK is go to the

Google Play store search for the MagNav APK and then click on it to install it onto the Getac

tablet this is call automatic installation. This document is intended for manual installation only.

For security reason all Android devices come with side-loading disable by default including the

Getac tablet. In order to install any APK via side-loading the device must be allowed to accept

APK from unknown sources. Please follow the steps outline here to enable it.

1. Obtain the MagNav APK

You can obtain the MagNav APK from various sources such as via an attachment in

email, from download off an FTP or Web site, from USB stick or microSD card that

someone handed to you. The easiest way to install the APK is to copy the APK onto the

USB stick then plug it into the USB port at the bottom of the Getac tablet.

2. Prepare the Getac for side-loading installation

Check security and enable Unknown sources by tapping on the Settings Gear icon

then


Tap on Security lock icon then

Scroll down to find the label name Unknown Sources

Tap on Unknown sources then tap on OK to dismiss the warning message that popup

1.5 The switch icon should turn green to indicate that side loading is now enabled

3. Install the MagNav APK onto the Getac tablet

Plug in the USB stick that contain the APK into the USB port and then tap on the file

manager icon (it looks like a person and folder) to open it

Tap on external storage on left side of the screen then tap on the folder icon with

number (The Getac file manager display external source such USB or microSD

card as number instead of recognizable name so remember which one is the USB or

SD card

Tap on the number folder to open it. Now you can navigate to the APK file and install it by Tap

on its icon

Tap on the APK icon to start the installation process, and then tap on install on popup screen to

actually install it

When the installation is completed you can tap on open to run the APK

Here is the screen of MagNav APK that is running

Installation using microSD card

The GetacZX70 tablet comes with both USB port and microSD card slot. This instruction is for

the installation via microSD card. With the microSD card, you have a choice to either set it as a

semi- permanent internal storage or mobile storage.

The microSD card slop is on the left side of the device under a plastic cover, you will need a

small Philip screwdriver to open it. The microSD card slop it the one on the top slot the bottom

slot is for SIM card.

Once you copy the APK into the microSD card from your computer you can slide the microSD

card into its slot with the front facing up and a little push.

An icon represent the SD card is shown when the Getac recognize the SD card

Tap on the file manager icon to open it

Tap on External storages to navigate to the SD card

Getac file manager show the SD card as a folder with number as name tap on it to open

To navigate to the folder that may contain the APK tap on the folder to open it

Tap on the APK icon to open it

Tap on install to start install the APK

After the installation is completed, you can open the APK by tap on Open or dismiss the dialog

window by tap on Done

Tap on allow to give permission to MagNav it needs these permission to operate

Operating MagNav

MagNav is an Android app running on the Getac tablet that is part of the G864 system. You will

use MagNav to control the acquisition system and to collect data.

Preliminary

Before you can acquire data with MagNav, you have some easy first steps:

1. Create a survey in Geometrics Survey Manager. Your G864 is loaded with some basic

surveys, but most of the time you will want to create your own survey and acquisition

definitions. Refer to the Survey Manager manual or chapters for instructions for creating

surveys. Load the survey file onto a USB drive, and insert the USB drive into the USB

port on the Getac tablet.

2. Import your new surveys into MagNav.

a. Turn on the Getac tablet, and start the MagNav app, by clicking on the MagNav

icon. To import a survey, you do not need to have the acquisition backpack. You

will see the MagNav home screen:

b.

c. Select the “Import Survey” item from the list.

d. Press “Choose a DBT file”, then use the file manager interface to navigate to the

USB drive, where you will pick the survey you just added to the USB drive. It

will normally be a file with the DBT file name extension.

e. After importing, your survey will be in the list:

Getting ready to Acquire

When you are ready to acquire data, you have a couple of steps before starting MagNav. If you

already have MagNav running before doing these steps, you must exit MagNav before doing

these steps:

1. Turn on the acquisition backpack’s power. The GPS and status LEDs should begin

flashing after a few seconds. If they don’t, let the system warm up for a few seconds,

then press the Reset button; the LEDs should start flashing.

2. On your Getac tablet, connect to the acquisition box’s Wifi network. Your box is given a

unique network name in the factory.

3. Now, start MagNav. You should see the main screen again; this time, in addition to

seeing the list of surveys, you should see an active data trace: magnetometer data flowing

to the tablet from the acquisition box:

4.

5. Select the survey that you imported earlier, or select one of the default surveys shipped

with your system. You should see a list of acquisitions:

6.

Acquiring data for a Marked Acquisition 1. Select a marked acquisition from the list. This is one of the acquisitions that you created

in Survey Manager that uses physical landmarks (cones, etc.) for navigation, and does not

depend on GPS.

2. When you enter the acquisition, you should see the data page, which shows active data.

If the page does not show active data, return to the acquisition list and re-select the

acquisition. Note that the title of the page says “Not Acquiring”:

3. Swipe the page to the left or pick the Navigation tab on the screen. You will see the

Navigation view, with a variety of lines and marks:

a. A marked acquisition is a route consisting of one or more lines. Each line has a

start (marked with a green square) and an end (marked with a red square). Along

each of the lines may be some marks, with arrows indicating the direction of

travel. These items are specified in the GPX file that you chose when you created

the acquisition in Survey Manager. Starts, ends, and intermediate marks often

correspond to cones, tapes, or other physical aids or objects.

b. You can drag and stretch and shrink the plot using standard Android gestures.

Note that the scale adjusts so that you can judge distances in the plot.

4. Collect a line of data, following these steps:

a. Verify that you are standing at the start of the line that you want to acquire, and

that you are ready to begin walking along the line.

b. Press and hold your finger on the point at which you are starting to survey. A

small menu will appear:

c.

d. Select “Start next segment here”.

e. Your starting point is circled, and a new “Start line” button is on the screen.

f. When you are ready to start moving, press the “Start line” button and commence

walking along the line. Note that the circle advances to the next mark: it always

shows the next destination – the location that will be recorded when you press the

mark button:

g. When you get to the next mark, if you are comfortable that you have traversed the

segment correctly, press the button (which now says “MARK”. Note that the

destination circle moves to the next mark, and the first segment is drawn

differently, to show that you have collected data on that segment:

h. Continue in this fashion until you get to the end of the line. On the last mark the

button will say “End line”. When you have reached the end and pressed the

button, MagNav will stop acquiring data. The first line will be drawn to show

that you can collected data all along the line.

5. Collect the remaining lines.

Follow the same steps as for the first line, until you have collected data for the entire

route.

6. Correcting mistakes:

You have two primary methods to deal with errors or interruptions:

a. Interrupt data collection. Let’s say that you successfully collected data on the first

segment of the second line of your acquisition. You have started traversing the

second segment, and MagNav is waiting for you to press “Mark”, after which the

next mark will be circled, and you will walk the next segment. But something

interrupts you, and you won’t be able to finish this segment correctly:

i. Swipe from the left edge of the window, to open the “drawer”. Select

“stop” from the menu. Acquisition will stop, and any data that was

collected after finishing the first segment will be ignored.

ii. After dealing with the interruption, recommence acquisition where you

left off, or if the interruption was a physical barrier or impediment such as

a wall or creek, recommence acquisition at the next mark.

b. Delete data. Perhaps you realize that the data you’ve collected on some segments

is invalid.

i. Press and hold the mark at which you want to start deleting data. This

time, rather than starting another segment, select “Delete data…”. The

point will be circled to indicate the starting point of deletion. Note that

you can cancel deletion by pressing the cancel button:

ii. Next, press and hold the mark at which you want to end deletion. Press

“Delete data….”. Your display will now show that a section of data has

been deleted.

iii. Re-collect data on that section, if needed.

Acquiring data for GPS Survey

1. Select a marked acquisition from the list. This is one of the acquisitions that you created

in Survey Manager that uses predefined survey lines.

2. When you enter the acquisition, you should see the data page, which shows active data.

If the page does not show active data, return to the acquisition list and re-select the

acquisition. Note that the title of the page says “Not Acquiring”:

3. Swipe the page to the left or pick the Navigation tab on the screen. You will see the

Navigation view, with the survey lines imported as well as your physical location with

respect to the survey lines:

4. Using the cursor that designates the operator’s current location, walk over to the first line

that you wish to survey.

5. When you are at the start of the survey line, or the first part of the line that is accessible

in the event of an obstruction, swipe from the far left part of the screen (start your finger

on the black edge and swipe to the right) to open the drawer.

6. In the drawer is the button “Start”. Press this button and begin walking. The cursor

should have a direction based on the compass of the Getac Tablet. If the orientation is not

matching your walking path consider recalibrating the Tablet’s compass device. This

should be done when the system is not collecting data.

7. After the system has started acquiring there is currently a warning message that says that

the screen will be pinned. This is to avoid accidentally exiting from the software during

acquisition which could result in data corruption or loss. This will become automatic in

future releases, so at this time press “Got it” to make the screen go away.

8. Use the operator’s position, represented by the cursor, to guide your way down the survey

line. Past positions are represented by blue dots to show how well you have stayed on the

survey line.

9. When you reach the end of the line, you can either continue to collect data as you walk

towards the start of the next line, or open the drawer by swiping from the far left of the

screen and selecting “Stop”.

10. Work your way through each survey line until you have completed the survey in its

entirety. When you have finished make sure that you have selected “Stop” from the

drawer, and then you can press the “Back” button (the triangle at the bottom of the

screen) to return to the Main Menu screen, or press the “Home” (the circle at the bottom

of the screen) to return to the startup screen for the Getac Tablet, or press the square

button to list the running apps and swipe to the right to kill the app entirely.

When you have completed either a Marked Survey, or GPS survey, make sure you copy the

.DBT file that is saved in the internal memory (go to File Manager, Documents, and then G-864)

and then save it to the USB drive. The .DBT file is opened in Survey Manager (as is explained at

the end of the previous chapter) and is then exported as a .CSV file to be opened in MagMap or a

third party software package.

Chapter 6: GPS Programming

Overview

The G-864 is designed to simultaneously acquire GPS positions while it is acquiring

magnetic data. The supplied GPS is preset at the Geometrics factory to send only the $GPGGA

and $GPRMC position and time strings in order to maximize memory utilization. The

magnetometer interface for logging the GPS position data is also preset, and so the only

requirements are that the user start the survey in either or Marked or GPS mode and the GPS

information will be automatically logged. The console is set up so that the GPS is not logged

when in Pause or at the End-of-Line. Again, this is to maximize memory space.

Collecting GPS Data

Most G-864 magnetometers are equipped with a Tallysman TW5341 mounted on a

backpack frame. These GPS units are cabled to the G-864 logging console and pack frame

battery box. All necessary wiring connections are in the power cable supplied with the battery

box. The supplied GPS is pre-configured by Geometrics to provide the $GPRMC and $GPGGA

NMEA sentences only.

There is no need to program the supplied GPS unless the GPS memory has become corrupted

and it has lost its programming. If that were to occur it could start sending improper GPS serial

data. If so, we recommend the following procedures:

Tallysman TW5310 Smart Antenna Setup

Required Equipment:

1. Windows XP - 8 PC with RS-232 Serial port or USB to Serial port converter

2. Visual GPS software (installed onto Windows PC from Tallysman CD)

3. Tallysman TW5X10Configurator.exe software (installed onto Windows PC from

Tallysman CD)

4. P/N 25358-20 upload/adapter cable (supplied with every system)

Procedure:

1. Turn off the battery box GPS power switch.

2. Using P/N 25358-20 upload cable connect the GPS between the magnetometer power

cable wired into the pack frame (disconnect the power cable from the G-864 console) and

a serial port on the computer.

3. Turn on the battery box GPS power switch.

3. Start the Visual GPS program to confirm the GPS baud rate (19200 baud), Comport

number, and properly formatted data strings.

4. Start the GPS Configuration program TW5X10Configurator.exe to double-check GPS

connection settings.

The Tallysman GPS uses a special Windows configuration program called

“TW5X10Configurator.exe” to setup the GPS. In order to use this program the Windows

computer has to interface directly to the GPS via a serial port. In the normal operating mode the

GPS data gets combined with magnetometer data and sent to the logger. To allow the

configuration mode to work we must first make sure the GPS baud rate and comport settings

match the PC monitor’s settings.

Once you have the GPS connected to both the power cable and serial port, open the Visual GPS

program. We will use this program to confirm the baud rate of the GPS and the monitor port, to

confirm the correct Comport in use, and to verify that there are visible data strings coming in the

proper format.

Below is an example screenshot of the Visual GPS application program. The bottom left

window is the Command Monitor window and it displays data streams coming in from the GPS.

With the Visual GPS program open, make sure the Command Monitor window is also open. If

the window is not open already, click the square “Command Monitor” icon located underneath

the drop down menu items. In this window you should see GPS data strings as they come in.

The data strings should begin with $GP and values within the data strings should be separated by

commas.

If no visible GPS data strings are coming in, check the connection between the GPS, Windows

PC, and batteries. If there is still no visible data, try selecting a different Comport number. (The

USB to Serial converters supplied with the system have several different serial ports to choose

from).

Figure 25 Visual GPS Application Program

If you can see GPS data but the data is unrecognizable and/or the data string does not start with

$GP, that means the baud rate of the GPS is not the same as the PC monitor and needs to be

changed to match. The next paragraph will explain how to change the GPS baud rate and

Comport number so that you see GPS data strings popping up in the Command Monitor window.

Click the “Connect to GPS” drop down menu and select “Connect using serial port.” A small

window will pop up on the screen. Enter the correct baud rate for the GPS (19200) and Comport

number that’s in use. Click “OK.” If you can now see data strings in the Command Monitor

window, and they are in the proper format, that means that communication with the GPS is

successful and the GPS is ready to be configured. It is recommended to make note of this Baud

Rate and Comport number because we will need them in the following step. You can now close

the Visual GPS program and open up the configuration program TW5X10Configurator.exe.

Once the TW5X10 Configurator program has been opened, this is the startup screen you will see:

The first thing we want to do is make sure that the PC monitor Comport number and baud rate

matches that of the GPS. To do this, click on the “Program” drop down menu, and then “COM

Port”:

Figure 26 Tallysman Configurator Program

As shown below a menu box will appear asking which Com Port on your computer you will be

using, and what the baud rate is. In this case it is COM Port 1 and 19200 baud. Click the “OK”

button when finished entering the data.

Tallysman Configurator Program Dropdown Menu (top left)

Now we want to confirm that the Configuration program is communicating properly with the

GPS. Do this by selecting the “Program” drop down menu and click on “Read” (shown in

Figure above). Click “Start.” The configuration contents of the GPS will be read in and you will

notice that some of the checked boxes and configurations have changed. You will see a small

window with a green checkmark once parameters have been read. Click “OK.”

The final step is to update the settings so that they become permanent. First change the baud rate

to 19200 (upper right pull down menu) and make sure the selected NMEA message is GGA and

RMC only. Next, go back to the “Program” drop down menu and click “Write.” Click “Start.”

You will see a small window with a green check mark once the settings have been written. Click

“OK” on this small window. You can now exit the Tallysman Configurator and begin using

your Tallysman GPS.

Please note that in order to save the changes to the GPS settings, the GPS needs to be power

cycled (disconnect the GPS from power and reconnect it again).

Figure 28 COM Port Settings Window

Appendix I: Magnetic Theory

Note: The following section is provided for information purposes only. Understanding this

theoretical discussion is not required for proper operation of the magnetometer.

For purposes of this discussion, the ambient magnetic field or earth's magnetic field is called H0.

A separate magnetic field generated by an AC signal applied to a coil inside the sensor is called

H1. This coil is shown cross-section along with the other sensor components in Figure A11.

To initiate operation of the sensor, the lamp oscillator's RF power increases until the lamp strikes

(plasma ignites and fluoresces). The lamp oscillator then reduces its power to produce the

regulated amount of light. The heater warms the absorption cell until a Cesium vapor is formed.

A lens bends the light from the lamp to parallel rays. The lamp produces many spectral lines but

only one line in the infrared region is employed. All of the other light is blocked by a high grade

optical filter.

The infrared line of interest is then passed through a split-circular polarizer. On one side of the

polarizer the transmitted light has an electrostatic vector that advances with a right-handed

rotation. For conceptual purposes, it can be said that all of the photons in this light have the

same right-hand spin direction. The light transmitted through the other side of the split-circular

Figure A11. G-862RBS cesium-vapor

Lamp

Lens

Filter

Polarizer

Photocell

Lens

H1 Coil

Absorption Cell

polarizer produces light in which the vector advances with a left-handed rotation, therefore

having the opposite spin. Both circular polarized light beams pass through the absorption cell.

Because there is a buffer gas in the cell, the single cell can be considered as two separate cells,

each having the opposite sense polarized light passed through it. Both light beams exit the cell

and pass to a second lens. This lens focuses the light onto an infrared photo detector.

Because Cesium is an alkali metal, the outer most electron shell (orbit) has only one electron. It

is the presence of this single electron that makes the Cesium atom well-suited for optical

pumping and therefore magnetometry.

The Cesium atom has a net magnetic dipole moment. This net dipole moment, termed F, is the

sum of the nuclear dipole moment, called I, and the electron's angular momentum, called J.

In a Cesium atom:

I = 7/2

J = 1/2

and thus F can have two values depending on whether the electron's angular momentum adds to

or subtracts from the nuclear dipole moment. Therefore, F can have the value of 3 or 4. These

values are called the hyperfine energy levels of the ground state of Cesium.

Normally the net dipole moments are randomly distributed about the direction (vector sum of the

3 axial components) of the ambient magnetic field (H0). Any misalignment between the net

atomic dipole moment and the ambient field vector causes the Cesium atom to be at a higher

energy level than if the vectors were aligned. These small differences are called Zeeman

splitting of the base energy level.

The laws of quantum electrodynamics limit the inhabitable atomic magnetic dipole orientations

and therefore the atomic excitation energy to several discrete levels: 9 levels for the F=4 state

and 7 levels for the F=3 state. It is this variation in electron energy level state that is measured

to compute the ambient magnetic field strength.

When a photon of the infrared light strikes a Cesium atom in the absorption cell, it may be

captured and drive the atom from its present energy level to a higher energy level. To be

absorbed the photon must not only have the exact energy of the Cesium band gap (therefore the

narrow IR line) but must also have the correct spin orientation for that atom.

There is a high probability that the atom will immediately decay back to the initial energy level

but its original orientation to the ambient field is lost and it assumes a random orientation. An

atom that returns to the base level aligned such that it can absorb another photon, will be driven

back to the higher state. Alternately, if the atom returns to the base level with an orientation that

does not allow it to absorb an incoming photon, then it will remain at that level and in that

orientation. Atoms will be repeatedly driven to the higher state until they happen to fall into the

orientation that cannot absorb a photon. Consequently, the circularly polarized light will

depopulate either the aligned or inverse aligned energy states depending on the orientation (spin)

of light polarization. Remember that one side of the cell is right-hand polarized and the other

left-hand polarized to minimize sensor rotational light shifts and subsequent heading errors.

Once most of the Cesium atoms have absorbed photons and are in a state that does not allow

them to absorb another photon, the light absorption of the cell is greatly reduced, i.e., more light

hits the photo detector. If an oscillating electromagnetic field of the correct radio frequency is

introduced into the cell, the atoms will be driven back (depopulating the energy level) into an

orientation that will allow them to absorb photons again. This frequency is called the Larmor

frequency and is exactly proportional to the energy difference caused by the Zeeman splitting

mentioned previously. This energy splitting is in turn directly proportional to the ambient

magnetic field strength. The relationship between frequency and energy is given by:

E = f

Where:

E is the Zeeman energy difference

f is the frequency of the Larmor

is Planck's constant

In Cesium this Larmor frequency is exactly 3.49872 times the ambient field measured in nano-

Teslas (gammas). In the G-862RBS this radio frequency field is generated by a coil, called the

H1 coil that is wound around the tube holding the optical components. When the R.F. field is

present the total light passing through the cell is reduced because atoms are in an energy state in

which they can again absorb the infrared light.

There is a small variation in the atomic light absorption at the frequency of the applied H1

depopulation signal. This variation in light intensity appears on the photo-detector as a small AC

signal (micro-volts). If this AC signal is amplified and shifted to the correct phase, it can be fed

back to the H1 coil to produce a self-sustaining oscillation. In practice, simply connecting the

90° phase shifted and amplified signal to the H1 coil will cause the oscillation to spontaneously

start. Reversing the direction of the earth field vector (H0) through the sensor requires the drive

to the H1 coil to be inverted to obtain oscillation.

Appendix II: Troubleshooting

Operation of the G-862 is relatively simple and when trouble arises it is usually easy to recognize and correct. Table

2 is a troubleshooting guide provided to help in quickly locating the probable cause of the most common system

problems.

Symptom Probable Causes Corrective Actions

Long warm-up time. Low voltage.

Low ambient temperature.

Low heater setting.

Defective internal sensor or

electronic components.

Increase voltage (minimum 24 VDC at the

electronics) or repair the Coax cable.

Insulate sensor housing.

Adjust heater to 34.5 K-ohms: contact

factory for details.

Return sensor and electronics to Geometrics

for repair.

Noisy magnetic field

readings.

Local field is noisy.

Sensor not oriented correctly.

Heater setting incorrect.

Signal amplitude too low with

correct orientation.

Sensor cable or connector

worn or damaged.

Locate and eliminate source of noise or

relocate sensor.

Refer to Sensor Orientation section of this

manual, or use MagPick IGRF and CsAz

software to model magnetic field and sensor

behavior, and correct orientation if

necessary.

Adjust heater to 34.5 K-ohms: contact

factory for details.

Adjust signal amplitude or return sensor and

electronics to Geometrics for repair.

Replace sensor cable and connector

assembly.

Sensor cable kinked or

cut.

Handling or mechanical

problem.

Change handling or mechanical mount.

Then replace sensor cable and connector.

Excessive current

consumption.

Damaged multi conductor

cable.

Defective sensor or

electronics.

Replace multi conductor cable.

Return sensor and electronics to Geometrics

for repair.

Preventing a problem is almost always less costly than correcting the problem. We recommend checking the follow

items as part of any new installation or whenever an existing installation is altered. It is also recommended that these

items are checked periodically as part of a scheduled platform or system safety check.

1. Power check

a. Minimum 24 Volts DC at electronics bottle. 28VDC recommended

b. Maximum 35 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

a. Dirt or corrosion

b. Bent pins

c. Back-shell tight

3. Cable jacket check

a. Kinks

b. Abrasions

c. Cuts

4. Sensor orientation

a. Use 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 CsAz model estimate

b. Sample to sample noise less than 0.1 nT @ 10 Hz when not moving

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

a. Potentiometer on sensor-driver board adjusted for 2.0 Volts Peak to Peak at 50,000 nT after 20

minute warm up

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

Appendix III: G-862 sensor commands

Circuit description of the external signal/power interface cable Connector type SP02A-14 -19P

Pin # Function Description

A 30V power Magnetometer power; 24 – 32VDC

B GND Power ground

C TxD From logging computer, connects to RxD of G-862

D Rxd To logging computer, connects to TxD of G-862

E COMMON RS-232 Ground

F RESET Contact closure to GND

G EVENT External Trigger Input

H CHANNEL 1 + Analog channel #1 – differential input, 5v full scale, 2K input

impedance. J CHANNEL 1 -

K CHANNEL 2 + Analog channel #2 – differential input, 5v full scale, 2K input

impedance L CHANNEL 2 -

M CHANNEL 3 + Analog channel #3 – differential input, 5v full scale, 2K input

impedance N CHANNEL 3 -

P CHANNEL 4 + Analog channel #4 – single ended 2.048v full scale, >10K input

impedance R CHANNEL 4 -

S CHANNEL 5 + Analog channel #4 – single ended 2.048v full scale, >10K input

impedance T CHANNEL 5 -

U Ext GND External Input Ground use for EVENT and RESET lines

V Boost Enable Wire to Pin A to enable Boost Power Supply.

Note: 1) All analog channels have 12 bit resolution 1%; 2) Differential channels 1, 2 and 3 may be

able accept other full-scale voltages if original order called for custom input specification - consult the

factory if you suspect that your system has non-standard input ranges; 3) If the single ended channels 4

or 5 are used, the signal source must be operated from a power source that is isolated from power

ground.

CM-221 Output Format The output data format of the G-862 is programmable. For example each of the A/D channels can be added or removed

from the output data stream by sending the appropriate commands to the CM-221. There are several other commands

that are discussed in detail below. Figure 12 shows the standard single counter configuration. Commands from the PC are sent out the computer RS-

232 transmit pin (TxD) to the counter. Magnetometer and other data are read on the computer receive pin (RxD).

Upon power on the counter module defaults to the following setup:

Baud rate: 19200 baud, 8 data bits, no parity, 1 stop bit

Cycle rate: 10 Hz

Analog channels: Channel 0 (Larmor signal level) enabled, channels 1-5 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. Table 5 illustrates an example of this format.

Figure 3: Schematic of CM-221, magnetometer, and computer connections

Character # 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 99999.999nT).

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

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

$ 99778.131,3749

$ 99890.376,3687

$ 99955.517,3545

$ 99998.293,3472

$100078.835,3329

$100032.071,3381

$ 99979.159,3498

$ 86778.508,3514

$ 78778.216,3645

$ 69978.347,3797 Counter modules can be daisy chained to form multiple sensor arrays as shown in Figure 13. 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. Here, 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 '$').

Table 1: Example of CM-221 default output data stream.

6.2

Commands 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, you must 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).

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

Figure 4: Schematic diagram of daisy-chained CM-221 counter modules.

[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'-'5')

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)


Output Format Byte 1: 'O' select output format

2: x format select:

'A'= ASCII (default)

'E'= excess 3

'P'= packed BCD

'S'= Sandia G-822A fmt

x: x '0' = Sandia single Mag

'1' = Sandia dual Mag


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

format was developed for an earlier logging software program and is now obsolete. Excess3 is

used for high speed multi-sensor array data transmissions.]

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')


[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')


[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


3: x 2S digit of number ('0'-'9')

4: x LS digit of number ('0'-'9')


Set Hour: Byte 1: 'H' Set the hour


3: x LS digit of number ('0'-'9') 4: CR carriage return

Set Minute: Byte 1: 'M' Set the minute




Set Second: Byte 1: 'S' Set the second




Find counters: Byte 1: 'F' Find and assign counter numbers

2: '0' assign first counter as # 0 (MSB)

3: '0' LSB


Set Preamble Byte 1: 'P' Set the preamble char ('$')

2: x The desired character


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


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


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)


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

the output from counter 0. 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.]

Enable Trigger Byte 1: 'T' Trigger Command

2: 1 Cycle and output on Trigger Input


Disable Trigger Byte 1: 'T' Set the preamble char ('$')

2: 0 Cycle and output on internal timing


[Note: External triggers are input to the CM-221 counter via the External Event

Pin of the counter board (JP1 pin 4) which is also wired to pin G of the 19 pin

Bendix connector on the G-862 electronics module. The external event input is

compatible with both TTL and RS232 signal levels. A logic low is defined as

any input level in the range of +0.8 volts to -25 volts. Logic high is defined as

any input level in the range of +2.0 volts to +25 volts. A trigger occurs on an

input transition from low to high. The external trigger input has no internal pull

up and floats near ground. The input impedance is 3000 ohms or higher. The

external trigger input is edge triggered. Therefore the external trigger signal must

have sharp edges. If a mechanical switch is used as a trigger input it must be

properly debounced to prevent multiple triggers. The trigger pulse must be

greater than 2 microseconds in width. When not in external trigger mode any

external triggers received are ignored.]

Update Counter Byte 1: 'U' store current settings in microprocessor

2: 'P' 2'nd char

3: 'D' 3'rd char

4: 'A' 4'th char

5: 'T' 5'th char

6: 'E' 6'th char


Appendix IV: Surveying Principles

This section outlines the principles of performing a magnetic survey for anomaly

location. It covers setting up, performing the survey and location of items of interest within the

anomalous zones. Regional or geologic surveys for mineral exploration require a different set of

procedures and are not covered in this overview. However, many of the guiding principles are

identical and review of this section will be helpful.

Guidelines for Small Ground Magnetometer Surveys

The general comments below cover only the site layout and preparations for a survey.

The survey objectives, determination of parameters for the instrument data collection and the

actual data processing and map preparation are covered elsewhere.

In order to accomplish a successful ground survey magnetometer data acquisition, survey

path over the ground and processing of the data into map form must be handled in a precise and

accurate manner. Each element is completely interdependent upon the others and if one is

compromised in quality or accuracy then all are compromised. During a survey, possibilities for

error are numerous and great care and concentration are required to avoid mistakes, some of

which may be so serious as to require starting the survey over. The focus should be on

completing the survey completely error-free.

Typically, the most difficult surveys are those involving detection of small magnetic

targets and the presentation of an accurate 1 or 2 nT contour map. In these cases, the survey

must include: a close line spacing (1-2 m) with precise tracking in both the X- and Y- directions;

diurnal correction (0.5 nT or better); correction of heading errors from instrument and/or

operator; maintaining the sensor a constant distance above the ground; and absolutely no

mistakes in procedure and data processing.

Number of People

Under certain conditions, the survey can be laid out and run by one individual; but this is

rare and risky. It is far better to have a minimum of two people closely involved and ideally,

three or even four people. Not only must the layout and marking of the survey lines be

considered but also an individual must be designated to maintain a separate survey log, set up the

base station, and operate the portable magnetometer. Note also that the operator doing all of the

walking may require relief, for oftentimes the terrain and distance conspire to make his job very

grueling.

Survey Efficiency

Speed and cost-efficiency in completing the survey is of course the ideal objective. This

does not, however, require the use of innovative short cuts, new gadgetry or excessive

manpower, but rather the avoidance of mistakes and errors. To prevent wandering off line even

once in the course of a survey, with the entire attendant time spent sorting out and making the

corrections, easily justifies a slower but more positive method. Efficiency will only be achieved

by avoiding confusion, the immediate correction of errors, and by the use of fail-safe procedures.

All of the methods suggested below are simple low tech, and relatively slow, but proven

effective. They can easily be improved on but at the risk of greater time, poorer survey quality

or greater cost. So in the beginning, keep it as simple as possible.

Layout of the Survey Track

Having determined the optimum line spacing, layout the survey area in a square or

rectangular format with the lines running N to S if possible. Use a Theodolite if available;

otherwise use a measurement tape (non-stretch) of the required length. Designate one side of the

area to be the “baseline” and layout and mark on this line each survey profile. Note that any

stakes driven into the ground must be non-magnetic. (Wooden stakes driven into the ground will

work well but may not be visible at distance.) If the site will be reoccupied in the future, it may

be desirable to drive a one-meter iron rod (re-bar) into the ground at each corner of the survey

area as a permanent marker. Since the profile line markers may not be visible at a distance, a

method must be found that will allow the Magnetometer operator to locate and follow the line: a

light cord or rope stretched on the ground between the beginning and end of each line; a long

PVC pipe or other colored marker to be held at the end of each line and then sequentially moved;

use of spray paint to mark a series of dashes along the path of each line, etc.

If the terrain is rough or bushy, ground markers along each line will be essential.

Otherwise, if the terrain is flat and each end of the line is readily visible, a marker at each end

and in the center may suffice. (The operator should have at least two markers to line up on when

starting a line.) Whatever method is chosen, it must be completely non-magnetic, positive, easily

moved in a coordinated way, and must give the operator a precise direction.

Note that coordination between the people moving the markers is sometimes difficult and

frequently a source of error. In addition, if the survey lines are closely spaced, e.g., one- or two-

meter separation, the Magnetometer operator may have trouble distinguishing between which

marker to head for. The most certain and positive method in all cases is to mark the path by

stretching a light string or rope the entire length of the pathway; or, to paint or otherwise mark

the ground at short intervals.

If the area to be surveyed is larger than say 100 x 100 meters or difficult to walk through,

then the area should be broken up into convenient sub-sections which overlap by at least one

profile line. If some sections of line are not passable, then provisions should be made for the

operator to detour around them but only after establishing a procedure to stop/start (pause) and

annotate the data. (This must be foolproof, simple and fully coordinated with the data

processing.) Note that the Magnetometer operator must be aware of what line he is on at all

times and the line number must agree with the line number recorded in the data. This is once

again a frequent source of error and should be double-checked by another person.

In no case should a survey be started until all lines have been laid out and marked, and all

aspects of the survey carefully re-checked. A few hours more or less at this stage means very

little. What is crucial is to prevent major errors (or even minor ones) that may cost extra days of

time and effort.

Diurnal Correction

There are many types of surveys that do not require correction for time varying field

errors (diurnal). Generally they involve large magnetic targets such as pipelines and tanks, or

coarse line spacing, or where the survey may be accomplished in a very short period of time. In

these cases, once it is determined that a severe magnetic storm is not in progress, the survey can

proceed without the normal base station correction and with good reliable results.

Note that the high measurement rate of the G-864 allows a rapid walking speed along the

profile line. Thus, even large target anomalies are covered within tens of seconds, reducing the

potential Diurnal effects.

Surveys that involve very close line spacing, small or subtle targets or where the

maximum accuracy is desired require diurnal correction from a base station installed close to the

survey area. Ideally, equal sensitivity and measurement rates to the field instrument should be

employed in the base station. In general practice, whatever instrument is available is used. In

most cases this works well even during periods of relative high field activity.

It should be remembered that "diurnal error" will have the same effects in the mapping

process as "location error", and that without correction, low amplitude/high frequency anomalies

could appear in the measured data that would seem to be targets but in fact would not be real. In

addition, if the survey has been broken up into blocks that are acquired on different days, the

blocks will not fit smoothly together unless a diurnal correction is made and their DC level

shifted.

There are also other types of local magnetic field disturbances that can seriously affect

the map accuracy and quality. These include ground currents and other local AC or DC fields

from power lines or urban electric trains or trolleys. Of these, electric trains or trolleys are the

more serious as their effects may be large in amplitude and extend for many miles. Usually it is

more effective to complete the survey at night when these noise fields are greatly diminished.

Survey Accuracy

Commercial survey specifications may allow an “off line” error of up to ±20% (or more)

of the line separation. For a magnetic object having an anomaly extending over several lines,

this amount of location error does not prevent the object’s detection but does distort the

anomaly’s shape, its peak-to-peak amplitude and its true location. Large changes in speed along

the profile line will have a similar effect but can be prevented by the use of intermediate

waypoints. (The worst case condition would be “off line” by +20% in one direction and "off

line” by -20% in the opposite direction with each line having a 10% change in speed.) Location

errors of this magnitude will not seriously change the overall correctness of the final map,

considering that this type of survey is primarily for detection/location. This is not the case;

however, if the location errors substantially exceed ±20%, e.g., off by one or more line

separations. This amount of error may cause targets of interest to go undetected, or target

anomalies to be shifted in location, resulting in, at worst, an erroneous map or at best an

untrustworthy one. Careful layout and accurate tracking along the line will avoid these

problems.

Survey Credibility

How does a client or survey manager know that a survey has been conducted properly

and that the results are correct and believable? He examines the finished contour map for gross

errors in data fit, location of target signatures, and overall map quality.

1) Selected anomalies that have been detected are re-acquired to see if they are in the proper

location.

2) The raw data are examined to ensure that line numbers are correct, data corrections have

been properly executed, etc.

3) Selected tests are made on the finished data, e.g., a plot of “stacked profiles” to determine

that start/stop points are correct, speed changes are not excessive, there are no data gaps, etc.

Location of Small Objects within Associated Anomalies

When data has been acquired over an area and processed into map form, it is often

necessary to reacquire the location of each anomaly and dig to expose the ferrous object. The

relocation of the anomaly is relatively simple since the coordinates can be taken directly from the

map produced. However, the exact location of the object within the anomaly is often times

difficult to identify and the convoluted magnetic field can be very confusing.

The anomaly may be sharp and steep (high frequency) indicating a small object close to

the surface. It may be just one peak or it may be multiple peaks depending upon the object’s

shape, its orientation within the earth’s field, and whether the anomaly is largely due to

permanent or induced effect. It may appear as a dipole or monopole, and its shape on the map

may be further distorted by the distance between profiles, especially if this is large with respect

to the object size. Each of these factors will also affect the anomaly signature when the object is

much larger in ferrous mass and/or is buried much deeper with the resultant areal coverage of the

anomaly much larger (low frequency).

As one sweeps the G-864 sensor over these peaks, it is difficult to conceptually grasp

their significance, especially when using the audio output as a reference. To reduce confusion

and to provide the basis for a systematic approach, it is very helpful to produce a 3-D map

showing each of the peaks and valleys with the perspective of depth. Generally, a high and low

pair (monopole) will stand out from the rest of the peaks and if these peaks are relocated using

the G-864, the object will be midway between them.

When undertaking this exercise in the field, the audio tone should be turned down or even

disregarded with the visual display of the earth’s field on the front panel becoming the primary

focus. By slowly moving the sensor over the anomalous area, the exact high and low peak can

be located and a spot on the ground marked for each. A dipole, in the earth’s field inclinations of

greater than 60° will have its low North of the high peak, and in horizontal fields (inclination of

0°), the low will be in the center with a high at the North and the South ends. The point midway

between high and low will contain the highest gradient and will be directly over the object or

very close to it. In those cases where there is only one strong peak, the object will be directly

beneath the peak.

For very large anomalies the distance between high and low peaks may be two to ten

meters or even greater. To reduce the amount of digging, it is suggested that a short profile be

run completely over the anomaly, passing directly over each peak previously located and marked

on the ground. Viewing this profile on the G-864 display will allow the estimation of the point

of inflection of the curve between the peaks indicating the point of maximum Gradient (which

should be directly over the object), and the depth of burial by means of the half width rule.

(Refer to Chapter V of Applications Manual for Portable Magnetometers.)

Appendix V: CSAZ Cesium Sensor Azimuth Program

CSAZ is a program written by Geometrics for users of Cesium magnetometers. The

purpose of the program is to determine the proper orientation of the Cesium sensor at various

Earth field dip angles (field inclination). AZ stands for azimuth or inclination.

The program is located on the MagMap2000 install disk included with the G-864. Once

MagMap2000 is installed, CSAZ will also be installed.

A newly designed CSAZII program is available from our FTP site at

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

Please read the manual that is included with the program for complete instructions on how to use

the CSAZII program for sensor orientation solutions at various locations on the globe. Note that

you should use the “generic” CSAZ mode for G-864 solutions.

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