Geometrics Memory-Mag G-857 User manual

Geometrics, Inc. G-857 Operation Manual
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G-857 Memory-Mag
Proton Precession
Magnetometer
P/N 18103-02 Rev. C
Operation Manual
GEOMETRICS, INC.
2190 Fortune Drive, San Jose, CA 95131
Phone: [phone]
Fax: [phone]
Email: [email protected]s.com
Web: www.geometrics.com
COPYRIGHT © 2015

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Table of Contents
INTRODUCTION............................................................................................................. 1
WHAT IS A TOTAL FIELD MAGNETOMETER? ..................................................................... 1
MAGNETOMETER APPLICATIONS...................................................................................... 1
TERMS USED IN THIS MANUAL.......................................................................................... 2
THE G-857....................................................................................................................... 2
MAGNETOMETER SET-UP.......................................................................................... 5
SENSOR FLUIDS................................................................................................................ 5
STANDARD SYSTEM ASSEMBLY....................................................................................... 6
GRADIOMETER ASSEMBLY............................................................................................. 11
BASE-STATION ASSEMBLY............................................................................................. 15
GPS ASSEMBLY AND SETUP .......................................................................................... 16
SENSOR ORIENTATION.................................................................................................... 17
CONSOLE SET-UP........................................................................................................ 19
CONSOLE CONTROLS AND DISPLAY............................................................................... 19
SYSTEM CHECKOUT........................................................................................................ 20
OPERATING PROCEDURES............................................................................................... 21
1 - Clearing a Key sequence..................................................................................... 21
2 - Setting the internal clock..................................................................................... 21
3 - Setting the Year.................................................................................................... 22
4 - Setting the Line Number Marker......................................................................... 22
5 - Setting GPS Recording Mode.............................................................................. 22
6 - Manual Tuning of the Magnetometer.................................................................. 23
7 - Automatic tuning.................................................................................................. 25
8 - Acquiring and storing a magnetic field reading.................................................. 26
9 - Recalling measurements from memory................................................................ 27
10 - Erasing magnetometer readings........................................................................ 28
11 - Automatic reading set-up................................................................................... 30
12 - Retrieving magnetic field readings.................................................................... 31
13 - Clock set from GPS Time................................................................................... 32
FIELD OPERATION..................................................................................................... 33
SENSOR POSITION AND MEASUREMENT REPEATABILITY................................................. 33
MAGNETIC ENVIRONMENT ............................................................................................. 34
MAGNETIC SURVEYING.................................................................................................. 34
GPS Error Messages................................................................................................. 34
Standard operation ................................................................................................... 35
Gradiometer operation ............................................................................................. 37
Base station operation .............................................................................................. 38
DATA RETRIEVAL ...................................................................................................... 39
COMPUTER CONNECTION AND DOWNLOAD .................................................................... 39
G-857 format download............................................................................................ 39

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Legacy format download........................................................................................... 45
MANUAL TRANSCRIPTION.............................................................................................. 46
AUTOMATIC TRANSCRIPTION IN REAL TIME.................................................................. 47
MAINTENANCE............................................................................................................ 49
INSTRUMENT STORAGE .................................................................................................. 49
VOLTAGE INDICATOR..................................................................................................... 49
BATTERIES..................................................................................................................... 49
GEL-CELL BATTERIES..................................................................................................... 50
LITHIUM BATTERY ......................................................................................................... 50
APPENDIX...................................................................................................................... 53
MAGNETIC FIELD INCLINATION (DEGREES) .................................................................... 53
MAGNETIC FIELD INTENSITY VARIATION (NT) ............................................................... 53
TROUBLESHOOTING ....................................................................................................... 54
RS-232 INTERFACE ........................................................................................................ 56
FRONT PANEL CONNECTOR PIN ASSIGNMENT ................................................................. 57
LEGACY MODE ON OUTPUT FORMAT............................................................................ 58
LEGACY MODE OFF OUTPUT FORMAT........................................................................... 59
AUTO CYCLE OUTPUT FORMAT ..................................................................................... 61
EXTERNAL POWER......................................................................................................... 61
EXTERNAL MAGNETOMETER CONTROL .......................................................................... 62
INTERNAL PROGRAMMING SWITCHES............................................................................. 63
Polarize and count time –Switches 1 through 4....................................................... 64
INTERNAL RESET SWITCH .............................................................................................. 67
SPECIFICATIONS............................................................................................................. 68
WARRANTY AND SERVICE.............................................................................................. 69
FIRMWARE REVISIONS.................................................................................................... 71
Table of Figures
Figure 1. G-857 proton-precession magnetometer. ........................................................... 6
Figure 2. Sensor staff sections. .......................................................................................... 7
Figure 3. Sensor preparation.............................................................................................. 8
Figure 4. Staff / sensor assembly....................................................................................... 8
Figure 5. Console battery compartment............................................................................. 9
Figure 6. G-857 Shoulder harness. .................................................................................. 10
Figure 7. Assembled magnetometer ................................................................................ 10
Figure 8. Location of 'Read' key on magnetometer console............................................ 11
Figure 9. Gradiometer components.................................................................................. 12
Figure 10. Removing standard sensor cable from top sensor.......................................... 12
Figure 11. Top sensor with gradiometer cable attached .................................................. 13
Figure 12. Bottom sensor with gradiometer cable attached............................................. 13
Figure 13. Connection of threaded staff adaptors............................................................ 13
Figure 14. Completed gradiometer staff.......................................................................... 14

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Figure 15. Attach the gradiometer switch box................................................................. 14
Figure 16. Base-station setup up using tripod kit and G-857 staff section...................... 15
Figure 17. Garmin Oregon GPS Option ........................................................................... 16
Figure 18. Alternate orientations for G-857 sensor mount.............................................. 18
Figure 19. Magnetic Inclination of the Earth’s field........................................................ 18
Figure 20. G-857 console display and keypad................................................................. 19
Figure 21. Magnetic Field Intensity Variation, (nT)........................................................ 24
Figure 22. Typical survey layout...................................................................................... 37
Figure 23. Location of console’s internal programming switch...................................... 63
Figure 24. Internal reset switch........................................................................................ 67
List of Tables
Table 1. An example of the console memory stack......................................................... 27
Table 2 GPS Error Messages.......................................................................................... 35
Table 3. RS-232 cable connector pin assignment............................................................ 56
Table 4. Summary of programmable switch settings....................................................... 64

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Geometrics, Inc. G-857 Operation Manual
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Introduction
This manual provides operating instructions for Geometrics G-857 portable proton-
precession magnetometer. It includes step-by-step instructions on magnetometer set-up,
survey usage, measurement data retrieval, and maintenance.
What is a total field magnetometer?
A total field magnetometer is an instrument that measures the scalar intensity of the local
magnetic field. The G-857 relies upon the proton-precession measurement technique.
This technique makes use of an induction coil to create a strong magnetic field around a
hydrogen-rich fluid such as Kerosene. This causes the hydrogen protons to align or
polarize their spin axis with the newly applied magnetic field. When the current
producing the polarizing field is interrupted, the protons begin to align themselves with
the Earth's magnetic field; but in doing so will momentarily precess about the Earth’s
field at a specific frequency that is proportional to the ambient magnetic field intensity.
This precession generates a small magnetic field that induces an alternating voltage in the
induction coil that was previously used to generate the polarization field. The
relationship between the precession frequency of the induced voltage and the strength of
Earth's magnetic field is called the proton gyromagnetic ratio and is equal to 0.042576
Hertz per nanoTesla (Hz/nT).
Magnetometer applications
Most rocks contain some magnetite, hematite or other magnetic material and will produce
disturbances in the local magnetic field. Because of this, most soils and many man-made
objects that contain iron or nickel have magnetic properties detectable by a sensitive
magnetometer because they create local or regional anomalies in the Earth’s main field.
Anomalies are revealed by systematic measurement of the variation in magnetic field
strength with position.
Interpretation of magnetometer readings allows the surveyor to make inferences about
what exists beneath the Earth’s surface. Based on experience with the survey area, the
surveyor might interpret the measurements to indicate to location of a pipeline, fired
pottery or bricks, a piece of ordnance, a particular mineral or geologic structure. The
interpretation of magnetic survey results is sometimes a difficult task, made even more
complex by constant changes in the Earth's overall magnetic field, the size and distance
of objects from the magnetometer, the amount of magnetic material the object contains,
as well as the magnetic susceptibility of the object and the host material. On the other
hand, in many applications, simple interpretations of anomalous magnetic fields will lead
to a straightforward understanding of the source of the anomaly.
The proton precession magnetometer is one of the principal instruments for magnetic
surveys because it combines high accuracy and ease of use. The Applications Manual for
Portable Magnetometers, supplied with this instrument and available for download from

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our website, includes general information on the use of magnetometers. It should be
studied as a companion to this manual which deals specifically with the G-857 Memory
Mag™.
Terms used in this manual
The magnetic field intensity at the surface of the Earth has an average value of about
50,000 nano-Tesla (nT). Historically, one nT is sometimes referred to as a gamma or “”.
Throughout this manual we will always express field intensity in nT.
The terms “sampling”, “cycling”, and “reading” all refer to the magnetometer’s
measurement of the field intensity. Note that these terms do not necessarily refer to both
measurement and internal storage of the measurement value.
The G-857
Depending on its particular configuration, the G-857 can be a portable, man-carried
magnetometer, a gradiometer measuring the field with two sensors, or a "base station"
magnetometer. The G-857 can record optional Garmin GPS in all configurations. As a
hand-carried instrument, it features simple, push button operation and a built-in digital
memory that stores 65,000 single sensor measurements or 32,500 gradiometer readings.
This relieves the user of the need to physically write down the data in the field, eliminates
transcription errors and most importantly, allows the use of computers to automatically
record and process the data from the magnetic survey. Software Programs are available
from Geometrics to help the user process and interpret survey data. These programs
include MagMap2000 and MagPick and are available for download from our website:
www.geometrics.com.
The G-857 can also record data automatically at regular intervals, so it can be left
unattended to monitor diurnal changes in the earth's magnetic field. These readings (up to
65,000) are collected at a base station and used to correct simultaneous field
measurements for high accuracy surveys. Measurement data from the G-857 may also be
fed directly into an external computer. The time-of-day generated by the magnetometer’s
internal clock is recorded with each reading taken in either mode.
All operations are controlled from keys imbedded in a weatherproof membrane that
comprises the magnetometer console’s front panel. The key sequences for the various
magnetometer operations have been carefully designed to provide simple yet flexible
operation.
A single connector is used for the sensor signal input and data output. The output format
is in the universal RS-232 protocol that is accepted by most modern computers. Interface
software for downloading, profiling and gridding/contouring of data is provided by
Geometrics MagMap2000 software. A serial to USB converter is supplied for use with
computers that are not equipped with a serial port.

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Physically, the G-857 is compact and lightweight. It is weatherproof and operates over a
wide temperature range. It is powered either by an internal rechargeable lead acid gel
cell battery or an external 12 Volt battery.
Unlike other proton-precession magnetometers, the G-857 has an internal programming
switch which allows modification of the magnetometer’s cycle times to ensure that it will
work properly anywhere in the world.
Above all, the G-857 is a high-precision magnetometer, the result of many years of
experience in the manufacture of similar instruments. The operation of the instrument is
controlled by a microprocessor and the control program may be changed at any time for
product improvement or other considerations. In that event, you may find variations
between this manual and the operation of your actual instrument. Such variations will
have no adverse effect and should be recognizable as you familiarize yourself with
operation.

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