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CS-3
Operation Manual
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SCINTREX CS-3 Operation Manual

CS-3
Scintrex Cesium Vapor Magnetometer Sensor
OPERATION MANUAL
SCINTREX
CS-3 Manual - part # 762701 Revision 4.0
Rev Description of change ECO Date of issue App
1.0 Initial Release Feb 21, 2002 G.H.
2.0 Additional information Nov 30, 2005 G.M.
3.0 Additional information Oct 30, 2006 G.M.
4.0 Additional information 4405 Jan 18, 2007 R.L.
CS-3
Scintrex Cesium Vapor Magnetometer Sensor
Operation Manual
SCINTREX LIMITED
HEAD OFFICE
SCINTREX Limited
222 Snidercroft Road
Unit #1
Concord, Ontario
Canada, L4K 2K1
tel: +1 905 669 2280
fax: +1 905 669 6403
e-mail: scintrex@scintrexltd.com
World-wide web: http://www.scintrexltd.com
Copyright © SCINTREX Limited 2005. All rights reserved.
No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form, or by any means, electronic, mechanical, photo-copying, recording, or otherwise, without prior consent from SCINTREX Limited.
Document Part No. 762701, Revision 3.0
Printed and bound in Canada
CS-3 Manual - part # 762701 Revision 4.0
Foreword
Getting Started
About this manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Page Numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Type Styles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Chapter Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Understanding Instrument Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Sensor Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Sensor Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Old version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
2nd Draft
New version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
Operating the CS-3 in the Field
Setting Up the CS-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Mounting the CS-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
2
Powering Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Obtaining the Larmor Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Setting the Operating Hemisphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
Operating in the Presence of Spurious Magnetic Fields . . . . . . . . . . . . . . . . . . . . . . 2-9
2nd
Orienting Your CS-3
Understanding the Active Zone of the CS-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Using a Strapped Down CS-3 for Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Calculating the Tumble Angle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Recommended Survey Orientations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18
Comparison with the Locked Oscillator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
Table of Contents
Maintaining Your CS-3 and Trouble-shooting
Trouble-shooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
Reference Information
CS-3 Technical Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Instrument Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
CS-3 Standard Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
Warranty and Repair. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
v
Shipping Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
Appendix A: Theory of Operation
System Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
Appendix B: CS-3 Block Diagram
vi
CS-3 Manual - part # 762701 Revision 4.0

Foreword

The CS-3 is an optically pumped cesium vapor magnetometer sensor used for scalar measurement of the Earth's magnetic field. As shown below, the CS-3 sensor consists of a sensor head with cable and sensor electronics.
Foreword
Figure 1: CS-3 Magnetometer Sensor
The system excels in a variety of applications (ex. airborne, satellite, marine and ground magnetometry or gradiometry, base station magnetometry and ferrous ordnance location) due to its:
• high sensitivity
• high cycling rates
• excellent gradient tolerance
• continuous output
• automatic hemisphere switching
vii
• fast response
• low susceptibility to the electromagnetic interference
Magnetic field measurements performed by the CS-3 is based on quantum mechanics principles, and the phenomena of optical pumping and self-oscillation. When properly oriented in relation to the ambient magnetic field, cesium vapor in the sensor oscillates continuously by itself without any assistance. The frequency of oscillation (defined as the Larmor frequency) is proportional to the ambient magnetic field.
The sensor outputs a signal at the Larmor frequency which is normally processed by an external magnetometer processor linked to the system. The magnetometer processor converts the Larmor frequency into digital magnetic field readings and presents them for display and recording. Modern magnetic processors have a resolution of 0.001 nT and read 10 times each second or faster.
In summary, the CS-3 offers distinct and substantial benefits in measurement of magnetic fields due to the principles of both optical pumping and self-oscillation. These advantages are described in the next two sections.
Advantages of Optical Pumping
These benefits are shared by all well designed optically pumped magnetometers regardless of which atoms (cesium, rubidium, potassium or helium) are being pumped, and regardless which of two principles of operation is utilized (self oscillation, or locked oscillation).

High Sensitivity

Due to the narrow resonant linewidth and good signal to noise ratio the sensitivity of optically pumped magnetometers is in the range of few pT (1pT=0.001nT) in the measuring bandwidth of 1Hz. In contrast to the proton precession magnetometers, the sensitivity does not deteriorate as the measured ambient field decreases.

Continuous Signal

The operation of the optically pumped magnetometers is not cyclic. Highly sensitive readings could be obtained at the high repetition rate.
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CS-3 Manual - part # 762701 Revision 4.0

High Gradient Tolerance

Absorption cells of the optically pumped magnetometers in which the detection of the ambient field is taking place are normally much smaller than the sensors of proton precession (including Overhauser) magnetometers. Consequently, the field gradients over the sensor volume are much smaller and the proper operation of the magnetometer is much less affected, e.g. the volume of the CS-3 absorption cell is only 0.006 liters.

Low Radiated Electromagnetic Interference

Sensors of the optically pumped magnetometers radiate low disturbing EM fields. The H is well confined and of the high frequency - around 165 MHz for the CS-3.
2nd Draft
field is the order of 10 nT. The RF field for the lamp excitation
1

Insensitivity to Motion Induced Doppler Effects

Irregular motion of the platform carrying the sensor modulates (adds to) the precession frequency and introduces noise into the measurements of the
2
magnetic field.
2nd
Proton precession (including Overhauser) magnetometers are affected to a much greater degree by motion noise due to much lower gyromagnetic constant, e.g. in the ambient magnetic field of 50,000nT the Larmor frequency of the CS-3 is 175,000Hz, which is 82 times larger than 2100Hz, the precession frequency of the proton magnetometer.
Foreword
Advantages of Self Oscillation
Use of the self-oscillating principle of operation results in the following additional benefits not available from optically pumped magnetometers using locked oscillator principle of operation:

Fast Start-up

If the sensor head is properly oriented inside its active operating zone, the CS-3 will start oscillating shortly after it is turned on. The warm-up time is determined by the time required for the electronically controlled heaters to bring the absorption cell and the cesium lamp to the proper operating temperature.
ix
The warm-up is over in few minutes after a cold start. However, if the operating temperature is already established, it takes only few milliseconds for the magnetometer to start oscillating after a turn on or after an orientation change from a dead zone into the active zone.
In contrast, a locked oscillator magnetometer invariably contains a voltage controlled oscillator (VCO), whose frequency in normal operation is forced (locked) by the control electronics to follow the resonant Larmor frequency.
However, at every start-up, cold or warm, before the locking is acquired, the VCO frequency has to be swept relatively slowly until it comes close enough to the Larmor frequency. Then the locking takes place and the magnetometer becomes operational.
Note that the Larmor frequency is known beforehand only coarsely and consequently this search process takes several seconds. The same search procedure takes place if the lock is lost because of a fast field change or a disturbing AC magnetic field.

Fast Response and Tracking

The response of a self-oscillating magnetometer to the magnetic field changes is extremely fast. It has been experimentally determined that the Larmor frequency precisely changed in response to the step changes of several thousand nT within a Larmor period. Equally, the magnetometer followed sinusoidal field changes of the amplitude of hundreds nT at the rate of several kHz without appreciable lag in response.
In contrast, the rate of ambient field change, which a locked oscillator magnetometer could follow without losing lock, is much smaller. In addition, spurious fields, either AC (50-400Hz) or pulsed, in the range of several hundred nT cause the magnetometer to lose lock.

Low Susceptibility to Electromagnetic Fields

The susceptibility to spurious EM fields depends very much on the principle of operation. Most widely encountered spurious fields originate from the power lines and the airborne geophysical EM systems, and are in the frequency range of 50Hz to several thousand Hz. In general, the susceptibility increases greatly as the frequency of the interfering field approaches the operating (Larmor, proton precession) frequency.
Proton precession magnetometers (including Overhauser) have low susceptibility for two reasons:
• they use induction coils to detected proton precession
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CS-3 Manual - part # 762701 Revision 4.0
• the interfering EM field are normally at the frequencies close to the proton
precession frequency.
Neither of above liabilities apply for optically pumped magnetometers because:
• signal detection is optical
• the interfering frequencies are normally far from the Larmor frequency.
In addition, the susceptibility of the self-oscillating magnetometer is low, because its feedback loop is very simple and fast, allowing it to respond with little lag to the fast changing fields.
In contrast, the locked oscillator response is much slower because its control loop frequency bandwidth is limited to few hundred Hz. Furthermore, the
2nd Draft
feedback control is achieved by monitoring a modulating signal, which frequency is in the range of one hundred Hz, and which detection could be readily upset by the interfering EM fields.
For either of above reasons, the locked oscillator may lose lock and become temporary non-functional for few seconds in presence of a spurious EM field.
2

Superior Worldwide Orienting Capabilities

2nd
The analysis presented in Chapter 3, “Orienting Your CS-3” proves that, contrary to the widely accepted belief, a well designed self-oscillating magnetometer is as easy to orient as the locked oscillator. Even more important, it offers wider safety margins to the boundaries of operating zone, than the locked oscillator.
Foreword
xi
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CS-3 Manual - part # 762701 Revision 4.0
1

Getting Started

About this manual

Page Numbering

The numbering scheme used consists of two parts: the chapter number and page number. For example,
For your convenience, each chapter has a thumb-tab on the right-hand side allowing you to quickly locate a chapter of interest. The thumb-tabs are arranged in descending order, with Chapter 1 always starting at the top.
3-1 would refer to chapter 3, page 1.
Startup
1-1
Getting Started

Type Styles

The following typeface conventions will be used throughout the manual.
Convention Use
Bold Italic Indicates an action to be taken
Italic Denotes a new term being introduced
ALL CAPS Denotes the name of a screen, key or mode (function)
1-
2
CS-3 Manual - part # 762701 Revision 4.0

Chapter Layout

This manual is divided into six chapters and four appendices with the information flow detailed in the following table.
Chapter Description
1. Getting Started Gives an overview of the manual and describes the
2. Operations Tells how to set up your CS-3 for a survey, including how
3.Orientation Gives a detailed theoretical and practical review of the
4. Maintenance Gives a brief overview of how to maintain and
5.Reference Contains the technical specifications, instrument parts
A.Theory of
Operation
About this manual
instrument’s components.
to mount and operate the system.
considerations for orienting the instrument to obtain best results.
trouble-shoot your system.
list and warranty information.
Explains the scientific and instrumentation theory for the CS-3 instrument.
Startup
1-3
CS-3 Manual - part #762701 Revision 4.0
Getting Started

Symbols

The following symbols will be used to highlight specific sections of text throughout the manual.
Symbol Meaning
Warning:
Denotes an important point concerning safety
Important:
Indicates a important topic, particular attention should be paid to this section
Note:
Denotes a point of interest, or information you should read
Tip:
Denotes an interesting hint for smoother operation
Question:
Indicates a relevant question concerning an important topic
1-
4
CS-3 Manual - part # 762701 Revision 4.0

Understanding Instrument Basics

Understanding Instrument Basics
The CS-3 Magnetometer Sensor consists of a sensor head and sensor electronics that are interconnected by a cable. This section provides schematics and descriptions for each of these components and their subsystems.

Sensor Head

The sensor head houses electro-optical detection system. All the parts of the sensor head, including the outside plastic housing, are made of carefully screened nonmagnetic materials. The following figure shows a schematic of the sensor head.
Startup
3
Figure 2 - Schematic of the sensor head
CS-3 Manual - part #762701 Revision 4.0
1-5
Getting Started
The actual measurement of the ambient magnetic field takes place inside the absorption cell which has diameter 22mm, and the length 25mm. The position of the cell's centre is marked by a narrow groove, machined on the outside of the plastic cylindrical housing. The adjacent wider grove is provided to facilitate secure grip for the mounting clamps.
The interconnecting cable exits at the right angle on the top end of the sensor head. For properly orienting the sensor head as described in “Orienting Your CS-3”, it is important to know the direction of the optical axis. In Figure 1 on page relation to the outside mechanical features of the sensor head.
The sensor head housing provides an air/water tight enclosure for the sensor components, and it should not be opened. In addition, critical optical components inside the sensor head are carefully aligned in order to minimize the orientation errors, and opening the sensor head by unqualified people may upset the alignment.
Important:
To minimize the static magnetic interference from the electronic components which are slightly magnetic, the sensor head should be kept away from the electronics assembly by the full cable length.
Chapter 3,
vii, the direction of the optical axis is depicted in
1-
6
CS-3 Manual - part # 762701 Revision 4.0

Sensor Electronics

CS-3 ELECTRONIC HOUSING
The sensor electronics are housed in a cylindrical container as shown in the following schematic.
Understanding Instrument Basics
Startup
Figure 3 - Schematic of the electronics housing
The electronics consist of three major subsystems:
• Larmor amplifier
• Lamp and absorption cell heaters
• RF lamp exciter
The RF exciter generates few watts of RF power at the frequency of about 165MHz. In order to keep the radiated electromagnetic interference low, the exciter is located inside a metallic enclosure. In addition, all the sensor electronic systems are enclosed inside a cylindrical, metal box.

Electronic Housing

Internally, the sensor electronic housing is connected to the negative line of the input supply voltage. If the negative side of the power supply, which provides the power for the CS-3, is grounded to the frame of the vehicle, and if the electronic box of the CS-3 makes an electrical contact to the same frame, then the return current could flow partially through the frame instead of being confined to the return line inside the supply cable.
1-7
CS-3 Manual - part #762701 Revision 4.0
Getting Started
The stray magnetic field created by this current could corrupt the measurement of the ambient field. To prevent that happening, the outside of the electronics box is covered with a thin, plastic insulating sleeve.
The sensor head connector is mounted on one side panel of the electronic box. On the opposite side, following components are mounted on the control panel, see Figure 4.

Hemisphere Control Switch

The hemisphere control switch is a four-position rotary switch as shown below. Please note that depending upon the version of your Cs-3, you will have either version.
Important:
Please, make sure that this plastic sleeve is not damaged to such an extent that the metal part of the CS-3 electronics housing is making contact to a metal part of the airplane or vehicle frame.
OLD VERSION
Figure 4 - Schematic of the hemisphere control switch
1-
8
CS-3 Manual - part # 762701 Revision 4.0
NEW VERSION

Old version

The swich settings perform the following functions:
N - Manually sets the CS-3 to operate in northern operating hemisphere.
S - Manually sets the CS-3 to operate in southern operating hemisphere.
L - Local setting allows the operation of the CS-3 to be controlled by the
TTL voltage level at the pin D of the four pin connector (pin A is ground): open circuited or high level voltage for operation in southern hemisphere, low level voltage or short connected to pin A for operation in northern operating hemisphere.
R - (JP3 - OFF, JP2 - ON). Remote setting allows the operation of the CS-3 to be controlled remotely by superimposing on the supply voltage an 80Hz sine signal. In the absence of the signal, the CS-3 is set to operate in the northern hemisphere.
R - (JP3 - ON, JP2 - OFF). Automatic hemisphere switch.
Understanding Instrument Basics
Startup
Note:
JP2 and JP3 refer to jumpers on the Larmor board.

New version

The swich settings perform the following functions:
N - Manually sets the CS-3 to operate in northern operating hemisphere.
S - Manually sets the CS-3 to operate in southern operating hemisphere.
R - Remote setting allows the operation of the CS-3 to be controlled by the
TTL voltage level at the pin D of the four pin connector (pin A is ground): open circuited or high level voltage for operation in southern hemisphere, low level voltage or short connected to pin A for operation in northern operating hemisphere.
A - Automatic hemisphere switch.

I/O Connector

Four pins of the I/O connector carry following signals:
1-9
CS-3 Manual - part #762701 Revision 4.0
Getting Started
A - ground level
B - positive input of the supply voltage +24 to 35 V; this input is connected in
parallel to the centre pin of the coaxial TNC power connector on the same panel
C - Larmor output signal, TTL compatible square voltage signal at Larmor frequency
D - TTL compatible input: high level or open for operation in the southern operating hemisphere, low level or connected to pin A for operation in the northern hemisphere. This input is effective only if the Hemisphere Control switch is in the Remote (R) position.
1-10
CS-3 Manual - part # 762701 Revision 4.0
2

Operating the CS-3 in the Field

By now you have familiarized yourself with your CS-3. This chapter reviews the basic steps required to carry out a survey. They include the following:
• setting up the CS-3
• mounting the CS-3
• powering up
• obtaining the Larmor frequency
• setting the operating hemisphere
• operating in the presence of spurious magnetic fields
Operations
2-1
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