GMW
BARTINGTON
MAG-01H Fluxgate Declinometer/Inclinometer
Including Zeiss Theodolite Instruction Manual
Operation and Maintenance Manual
Distributed by:
GMW Associates
955 Industrial Road, San Carlos, CA 94070
Tel: (650) 802-8292 Fax: (650) 802-8298
Email: sales@gmw.com Web Site: http://www.gmw.com
Manufactured by:
Bartington Instruments Ltd.
10 Thorney Leys Business Park
Witney, Oxford OX8 7GE
England
Tel: 011 44 1993 706565 Fax: 011 44 1993 774813
Email: sales@bartington.com Web Site: http://www.bartington.com/
Issue 10
_________________________________________________________________________________
955 Industrial Road, San Carlos, CA 94070 Tel: (650) 802-8292 Fax: (650) 802-8298
Email: sales@gmw.com Web site: http://www.gmw.com
GMW
OM0138
OPERATION AND MAINTENANCE
MANUAL FOR Mag-01H FLUXGATE
DECLINOMETER/INCLINOMETER
INCLUDING ZEISS THEODOLITE
INSTRUCTION MANUAL
Bartington Instruments Ltd
10 Thorney Leys Business Park
Witney,
Oxon. OX28 4GG
ENGLAND
Tel: +44 1993 706565
Fax: +44 1993 774813
Specifications may be subject to slight alteration without prior notice. This system is not qualified
for use in explosive atmospheres or life support systems. Consult Bartington Instruments for advice.
The copyright of this document is the property of Bartington Instruments Ltd. The document is
supplied on the condition that it is to be treated commercially confidential and it may not therefore
be disclosed to any third party without the written authorisation of the Managing Directors of
Bartington Instruments.
OM0138 ISSUE 10 PAGE 1 OF 50
LIST OF CONTENTS
1.0
INTRODUCTION
1.1.
THE NULL METHOD OF MEASUREMENT
1.2.
RESOLUTION
2.0
THE MAGNETOMETER
2.1.
FRONT PANEL CONTROLS AND THEIR FUNCTIONS
2.2.
REAR PANEL CONTROLS AND THEIR FUNCTIONS
2.3.
THE MAGNETOMETER PROBE
2.4.
ELECTROMAGNETIC COMPATIBILITY
3.0
THE THEODOLITE
3.1.
NIGHT VIEWING
3.2.
STEEP SIGHTING PRISMS AND DIAGONAL EYEPIECES
4.0
TAKING MEASUREMENTS
4.1.
MAGNETIC HYGIENE
4.2.
THEODOLITE SET-UP
4.3.
ADJUSTMENT OF HORIZONTAL CIRCLE TO REFERENCE AZIMUTH
4.4.
MEASUREMENT OF FIELD DECLINATION
4.5.
MEASUREMENT OF FIELD INCLINATION
4.6.
PERFORMING OBSERVATIONS OF D AND I WITH A NON RESETTABLE
HORIZONTAL CIRCULAR THEODOLITE
4.7.
PERFORMING OBSERVATION OF DECLINATION
4.8.
PERFORMING OBSERVATION OF INCLINATION
5.0
REPAIR AND MAINTENANCE
5.1.
CHECKING THE SYSTEM
5.1.1. BATTERY CHECK
5.1.2. FUNCTIONAL CHECK
5.1.3. THEODOLITE OPTICAL CHECK
5.1.4. RECALIBRATION
5.2.
5.3.
5.4.
5.5.
5.6.
PROBE ALIGNMENT
OFFSET TRIMMING
PROBE CABLE REPAIRS
FITTING THE MAGNETOMETER PROBE ASSEMBLY
BATTERY REPLACEMENT
6.0
TECHNICAL SPECIFICATIONS
6.1.
Mag-01H ELECTRONICS UNIT
6.2.
THEODOLITE MOUNTED Mag A PROBE
6.3.
CONNECTING CABLE
6.4.
THEODOLITE
7.0
ZEISS THEODOLITE INSTRUCTION MANUAL
OM0138 ISSUE 10 PAGE 2 OF 50
LIST OF DIAGRAMS
FIGURE 1
THE INTERNATIONAL GENERAL REFERENCE FIELD
FIGURE 2
Mag-01H SIMPLIFIED SCHEMATIC
FIGURE 3
Mag-01H FRONT PANEL FUNCTIONS
FIGURE 4
Mag-01/Mag-01H REAR PANEL FUNCTIONS
FIGURE 5
PLAN VIEW OF OBSERVATION POSITIONS FOR D AND I
FIGURE 6
OBSERVATIONS OF DECLINATION IN THE HORIZONTAL CIRCLE
FIGURE 7
OBSERVATIONS OF INCLINATION IN THE VERTICAL CIRCLE
FIGURE 8
THEODOLITE MOUNTED PROBE TYPE A ASSEMBLY
FIGURE 9
MAGNETOMETER - THE INTERNAL VIEW OF BATTERY AND
ADJUSTMENT COMPONENTS
FIGURE 10
Mag-01H PROBE TYPE A - CABLE AND CONNECTORS
OM0138 ISSUE 10 PAGE 3 OF 50
1.0
INTRODUCTION
The system permits very precise angular measurements of the terrestrial magnetic field F. The
angular components measured are Declination D (variation) and Inclination I (dip). Declination is
the azimuth angle between the geographical meridian GM and the magnetic meridian MM.
Inclination is the vertical angle between F and the horizontal measured in
the direction of the magnetic meridian. The value of F, together with the components X
(MM horizontal), Y and Z (vertical) may also be measured to an accuracy of 0.25%
The Mag-01H theodolite Declinometer/Inclinometer system comprises a high sensitivity
magnetometer type MAG-01H together with a vector sensing fluxgate probe type 'A' which is
mounted on either a Zeiss 010B, 015B, or 020B steel free theodolite. The system is suitable for
permanent installation in observatories but the provision of a non-magnetic tripod and re-chargeable
batteries within the magnetometer permit mobile observatory use. The system is used in
observatories to obtain reference data which may be used in the construction of Reference Field
Charts - See Figure 1. The mobility of the system permits highly detailed mapping of D and I.
Other applications include checking of compasses and monitoring of the field for compass
correction purposes. Detailed knowledge of local variation in D and I may be of assistance in
interpreting total field magnetometer survey data.
The ultimate resolution achieved with this system is limited by three factors:
1.
2.
3.
4.
Prevailing magnetic conditions - measurements during magnetic storms can be extremely
difficult to perform.
The optical resolution of the theodolite. The 010B theodolite has a resolution of 1 second of
arc. The 015B theodolite has a 6-second scale but can, by careful observation, resolve 2.5
seconds of arc. The 020B theodolite has a 20 second scale but can resolve 10 seconds of
arc.
Plinth stability - the tripod is less stable with time and temperature than a brick pillar.
The noise level, and therefore resolution, of the magnetometer. Two sensitivity settings are
provided; x1 which produces a resolution of 1 nT and x10 which produces a resolution of 0.1
nT. The x10 sensitivity setting would normally only be used under ideal conditions.
The system is usually operated with the assigned magnetometer and theodolite combination specified
in the test documentation. Should a replacement magnetometer be used then offset errors no greater
than 5 nT will be encountered and the accuracy of the system will not be compromised provided that
the four-measurement method described in this manual is used.
Note:
a) Please note that as from 1st October, 1995 all type 015B theodolites are fitted with the
repetition clamp.
b) From the 1st November 2002 all type 015B theodolites will be supplied without the
horizontal circle setting facility.
c) From 1st January 2004 all theodolites are supplied without the horizontal circle setting
facility. See section 4.6 and no diagonal eyepieces are supplied
OM0138 ISSUE 10 PAGE 4 OF 50
1.1.
The Null Method of Measurement
Measurements are obtained by operating the theodolite-mounted probe in the null mode. In this
mode observations are performed with the fluxgate probe orientated perpendicular to the direction of
the terrestrial magnetic field F. At an angle of 90o to the field the cosine response of the
magnetometer probe produces the greatest sensitivity to small changes in the field direction. High
instrument stability, together with specific measurement procedures which nullify electronic and
mechanical errors, produces angular measurements of absolute accuracy.
The ultimate accuracy will depend on the choice of theodolite and the prevailing magnetic
conditions. The high flexibility probe connecting cable does not interfere with the measurement
procedure and will operate down to very low temperatures.
The use of low magnetic signature components within the Mag-01H instrument enable
this unit to be used close to the probe head. Errors will not be significant with the probe
and magnetometer as close as 0.5 metres, although the magnetometer is, in practice,
usually placed on the ground.
Variation in Declination dD (or dI) around a fixed null point can be continuously monitored via the
analog output. For small angular changes the relationship between magnetometer output and angle
will be linear.
1.2.
Resolution
The theoretical resolution R to small changes in field direction is proportional to the sensitivity of
the magnetometer and the strength of the perpendicular magnetic field. When measuring Inclination
the magnetic axis of the probe is parallel to the vertical plane of investigation and therefore the full
field strength F is available and the resolution becomes RdI = F sine dI.
When measuring Declination the magnetic axis of the probe is parallel to the horizontal plane of
investigation and therefore only the horizontal field component H = F cos I is available and the
resolution becomes RdD = H sine dD.
Therefore at any magnetometer sensitivity, resolution of Inclination I is dependent on the magnitude
of F alone, whereas resolution of Declination D is dependent on H and I and will generally vary with
latitude.
e.g. where F = 47,000 nT, I = 67o
On x1 sensitivity (1 nT):
RdI = circa 5 seconds RdD = circa 10 seconds
On x10 sensitivity (0.1 nT):
RdI = circa 0.5 seconds RdD = circa 1.0 seconds
Note: These are theoretical values and actual values will be determined by prevailing conditions.
From the IGRF chart in Figure 1 it can be seen that resolution in Declination is a minimum at the
poles and a maximum at the equator.
OM0138 ISSUE 10 PAGE 5 OF 50
2.0
THE MAGNETOMETER
See Figure 2
The Mag-01H instrument comprises an impact-resistant enclosure which contains the electronic
circuitry, a rechargeable battery and liquid crystal display. The instrument operates in the following
way:
An excitation waveform is transmitted to the probe which returns a measurement signal . This is
converted into a current by the signal processing electronics. The current is fed back to a winding
within the probe to null the magnetic field experienced by the probe. In this way very linear and
drift-free measurements are obtained. An analog voltage is generated by the signal processing
circuitry. This is digitised and displayed on a liquid crystal display. It is also available as an analog
output.
A precision reference voltage is available to produce a bipolar offset which can be selected in 10 µT
steps to back off the field experienced by the probe. In this way the measuring range can be
extended without loss of resolution.
The output from the rechargeable battery is converted into a dual voltage supply to power the
circuitry. The battery is charged via the charging circuitry which is polarity protected. The external
battery charger can be either a mains adaptor, producing 9 V to 18 V dc, or a vehicle dashboard
connector. The battery voltage is continuously monitored and an alarm will sound if the voltage falls
below 5 V. An LED illuminates whilst the battery is being re-charged. A new battery provides
around 10 hours use after re-charge but this will reduce as the battery ages.
THE BATTERY SHOULD NEVER BE ALLOWED TO BECOME COMPLETELY
DISCHARGED.
The liquid crystal display is an auto ranging 4½-digit display which displays measurements
in the range 0 to ±20 µT with 1nT resolution and 0 to ±200 µT with 10 nT resolution. Use of the x10
control will increase this resolution. The display will indicate a positive value when the front of the
probe is pointing towards North.
Following switch-on the battery voltage is displayed for a few seconds.
2.1.
Front panel Controls and Their Functions
See Figure 3
Power Switch
:
to switch the instrument on.
Sensitivity Switch
:
increases the sensitivity of the magnetometer by a factor of 10
to increase the measurement resolution from 1 nT to 0.1 nT.
Charge
:
LED indicates that the unit is being charged.
Probe
:
the probe cable is connected to the magnetometer unit via a
Fischer 6-way socket.
Offset
:
the rotary switch and toggle switch are used to supply an offset
signal to the probe from 0 to ±90 µT in 10 µT steps. The
display value (and analog output value) becomes the algebraic
sum of the measured field strength and the value of the offset.
OM0138 ISSUE 10 PAGE 6 OF 50
Display
:
the auto-ranging LCD displays directly in µT units on x1 sensitivity
and µT x10 on the x10 sensitivity setting. The decimal point shifts to
the left when display value decreases below 10.00 and to the right
when display value increases above 19.999.
The display will over-range if a value above 199.99 occurs and
will appear blank except for the sign and first digit: 1----
2.2.
Rear Panel Controls and Their Functions
See Figure 4
Analog output
:
provides an analog output for logging continuously varying
fields. On x1 sensitivity full scale range 0 to ±500 µT
(100 µT/V) with a resolution of 1 nT and 0 to ±50 µT
(10 µT/V) with a resolution of 0.1 nT on the x10 sensitivity
setting.
Charger input
:
The unit is charged from either the power supply or a vehicle
dashboard via a connecting cable; alternative 12 V dc sources
can be used. The input is polarity protected against accidental
incorrect connection.
2.3.
The Magnetometer Probe
See Figure 8
The probe consists of a precision fluxgate magnetic field sensor mounted within a tube. A joystick
arrangement for trimming the alignment of the sensor relative to the tube is provided. The probe is
mounted on a pillar on the theodolite telescope and is retained with two screws. The probe is
enclosed in a rugged housing which fully protects it against mechanical damage or potential
misalignment. The enclosure is retained with a metal band clamped around the theodolite telescope.
Gasket sealing is provided to prevent the ingress of moisture.
The instrument is supplied with the probe aligned parallel to the optical axis of the theodolite to
within 10 seconds of arc.
A high flexibility cable connects the probe to the electronics unit.
2.4.
Electromagnetic compatibility
The Mag-01H instrument contains no high frequency electronics likely to cause emissions which
could affect other apparatus. The design, including the use of a rechargeable battery, charged from a
mains adaptor and decoupling of internal power supplies is intended to produce minimal emissions.
Other equipment operating in the area is therefore unlikely to be affected.
The unit is also unlikely to be affected by interference from other equipment in the normal operating
environment. However the sensors, being designed to measure the magnetic field, are susceptible to
electromagnetic interference and operation close to a high frequency sources of radiation should be
avoided. Interference is indicated by instability in the reading when the probe is maintained in a
fixed position.
OM0138 ISSUE 10 PAGE 7 OF 50
3.0
THE THEODOLITE
The Mag-01H and Mag A probe can be supplied with either a Zeiss 010B (1 second accuracy), 015B
(2.5 second accuracy) or 020B (3 second accuracy) steel-free theodolite (as specified). The accuracy
stated is for the mean square of a single Circular Left CL and Circular Right CR measurement. In
practice a single CL or CR observation of the target or reference only is required. The theodolite is
classed as steel-free and undergoes a rigorous magnetic hygiene inspection at Bartington
Instruments prior to fitting the fluxgate probe. Any contamination is totally removed to guarantee
complete magnetic cleanliness. Optical and magnetic calibration are also carried out prior to
despatch.
The theodolite is not suited to operation under very wet conditions. Rough handling should be
avoided as the bearing journals in this type of theodolite are manufactured from phosphor bronze
which are not as strong as those manufactured in steel.
Sufficient information is given in this manual to carry out routine checks and calibration. However,
a full calibration service is offered by Bartington Instruments, together with optional certification at
an observatory.
3.1.
Night Viewing
The scale illumination lamp unit normally supplied is unsuitable due to its magnetic signature. The
alternative recommended and supplied by Bartington is a chemiluminescent light stick. This
should be 47mm length x circa 6 mm diameter. To illuminate, bend the light stick and place
between the theodolite mirror and window. Night adjusted vision responds to this level of
illumination but, below freezing point, illumination may become inadequate.
3.2.
Steep Sighting Prisms
When performing steep angled telescopic observations or attempting to perform null mode
magnetic measurements for shallow angles of I, a pair of steep sighting prisms will be required. To
read the scales when I is between 25o and 35o steep sighting prisms will be required.
If any ancillary equipment, including eyepieces, is to be used in conjunction with the theodolite
simultaneously to taking magnetic observations, then it must be scrupulously tested for magnetic
cleanliness - See 4.1.
4.0
TAKING MEASUREMENTS
See Figures 5, 6 and 7
This section describes the procedures for measurement of Declination and Inclination in the null
mode. Four readings are obtained for calculation of D and four readings are obtained for calculation
of I. Each set of four readings comprises two pairs of readings. One pair is used to eliminate
electronic offset errors and the other pair is used to eliminate mechanical alignment errors (probe
collimation). Numbers in brackets refer to the Zeiss operation manual component identification list.
When making observations reference should be made to Figure 5, which describes the conventions
for identifying the directions of observation when performing null mode measurements. Figures 6
and 7 give further details of the null mode of measurements.
Declination is calculated from the mean of the four observations ED, WD, EU, WU. The reference
observation for Declination is the geographical meridian (GM) and the horizontal circle should be
set to zero, where facilitated, (either circle left or circle right) at that reference. Where the geodetic
OM0138 ISSUE 10 PAGE 8 OF 50
reference is other than GM the horizontal circle should be set to zero on the calculated GM.
Declination must be discovered before Inclination can be measured.
Inclination is calculated from the mean of the four observations SU, ND, SD, NU. The reference
observation for Inclination is the horizontal which is automatically derived from the pendulum
compensated vertical reference within the theodolite. Observations are made on the vertical circle,
the plane of which is parallel to the magnetic meridian.
The azimuth reference for Declination may be a surveyed point. Alternatively the geographical
meridian GM can be discovered using a North seeking gyroscope which can be mounted using a
suitable adaptor on the theodolite "handle" (1) in place of the target carrier (86). The gyroscope,
which contains an electric motor, should be detached from the theodolite and moved several metres
distance from the theodolite before taking magnetic observations.
4.1.
Magnetic Hygiene
Before attempting magnetic observations ensure adequate personal magnetic hygiene, for example,
garments should be free from steel fasteners or buckles. Hygiene can be checked when commencing
observations by moving hands, head and torso close to the magnetometer probe and observing any
change in reading. Readings should not vary by more than 0.2 nT. In practice only the hand used for
circle slow motion adjustment will be close to the magnetometer sensor at critical times during
measurement. Ultimate accuracy will depend on ambient magnetic noise. The diurnal variation of
the terrestrial field becomes most active at dawn and dusk.
4.2.
Theodolite Set Up
(See section 4.1 - 4.3 of Zeiss manual)
When moving to a new site allow 1 minute/1 oK of temperature difference for mechanical
settling.
(a)
Position the tripod over the ground point with its head level and mount the theodolite.
Level the instrument using the circular level and footscrews.
(b)
Focus the optical plummet (20) on the graticule by turning the eyepiece and focus on the
ground point by pulling or pushing the eyepiece tube. Line up the graticule and target point
by adjusting the tripod legs and/or instrument footscrews as necessary.
(c)
Re-level the instrument with the footscrews and complete fine centering by moving the
instrument on the tripod head. If necessary repeat levelling and centering procedure until
instrument is level, directly over the ground point.
4.3.
Adjustment of Horizontal Circle to Reference Azimuth
In this procedure the horizontal circle is set to the described azimuth such that it will be zeroed to the
GM. The types 010B and 015B are normally fitted with a coarse-fine circle drive while the type
020B is fitted with a repetition clamp for setting the horizontal circle. Instructions are given for
setting the horizontal circle with each of the mechanisms.
OM0138 ISSUE 10 PAGE 9 OF 50
A. Setting the horizontal circle of Theodolites with repetition clamp
(See Zeiss manual section 4.8.1)
(a)
Release the horizontal clamping lever (31) and with the stop lever (11) depressed, turn the
upper part of the theodolite until an approximation of the desired reading becomes visible in
the reading microscope.
(b)
Depress the clamping lever (31) into the clamping position.
(c)
Look into the circle reading microscope (7) and illuminate the reading scales by adjusting the
illumination mirror (16). Use the horizontal slow motion screw (30) to set the desired
reading precisely.
(d)
Depress the clamping lever (12) of the repetition clamp. This connects the circle to the upper
part of the theodolite.
(e)
Focus the cross lines by turning the telescope eyepiece (8) - (Zeiss sec. 4.5 & 4.6). Release
the clamping lever(31) of the horizontal setting clamp, focus on the reference point using the
focusing ring (9).
(f)
Precisely align the cross lines with the reference point.
(g)
Carefully open the repetition clamp by depressing the stop lever. For the type 015B make
sure that the degree mark is centred in the pair of lines on the graticule at the completion of
the setting.
(h)
Check the sighting and reading and re-adjust if necessary.
B.
Setting the horizontal circle of Theodolites with coarse-fine circle drive
(See Zeiss manual section 4.8.2)
(a)
Release the horizontal and vertical clamping levers (31,33) and aim the telescope at the field
reference point with the aid of the optical site on the bottom of the telescope.
(b)
Tighten the clamping levers. Focus the cross lines by turning the telescope eyepiece (8) and
focus on the reference point using the focusing ring (9) - (Zeiss sec.4.5 & 4.6).
(c)
Precisely align the cross lines with the reference point using the horizontal slow motion knob
(30).
(d)
Look into the circular reading microscope (7) and illuminate the reading scales by adjusting
the illumination mirror (16). Set the individual minutes and seconds to the
azimuth using
micrometer knob (36).
(e)
Release the guard lever (38) for the coarse and fine circle setting knobs (39, 40). Set the
degrees and tens of minutes to the described azimuth using these knobs. For the type 015B
make sure that the degree mark is centred in the pair of lines on the graticule at the
completion of the setting. Secure the guard lever. The theodolite is now aimed at the
reference target and the horizontal circle is set to the described azimuth.
OM0138 ISSUE 10 PAGE 10 OF 50
4.4
Measurement of Field Declination
See Figures 5, 6 and 7
(a)
Connect the magnetometer probe cable to the magnetometer and switch on the instrument.
Prior to commencing measurements decide which sensitivity setting can be used. Attempt a
trial null measurement on x10 sensitivity (0.1 nT resolution). If noise exceeds 0.5 nT p-p
then x1 sensitivity setting should be used. This is recommended for most observations.
IMPORTANT - A small (a few nT) offset error will be present when switching between the
x1 and x10 sensitivity settings. This in no way affects observation accuracy provided that
the sensitivity setting is not changed during any set of four measurements per observation.
(b)
Release the vertical circle clamping lever (33) and rotate the telescope so that it is in the
horizontal position with the magnetometer probe in the Down position below the telescope.
Set the telescope to the precise horizontal position (270o 00') by locking the clamping lever
and using the vertical circle slow motion knob fine adjustment (29).
(c)
Release the horizontal circle clamping lever (31) and rotate the instrument to obtain a
positive peak magnetometer output which will correspond to approximate alignment to
magnetic meridian. Note this direction. Transit the horizontal circle to adopt the ED
position. When the magnetometer reading is as close to zero as one can practically
achieve, clamp the horizontal circle using the clamping lever and adjust the final null
position using the horizontal circle slow motion knob (30). Record the reading ED.
(d)
Release the horizontal circle clamp and transit the telescope 180o to obtain a null
read-out in the opposite direction WD. Record the reading WD.
(e)
Rotate the telescope 180o so that it is again in the horizontal position but with the
magnetometer probe in the Up position. The vertical circle should now read 90o
(f)
Null the magnetometer read-out using the horizontal circle slow motion knob. Record the
reading of the horizontal circle EU.
(g)
Repeat (d). Record the reading WU.
(h)
The declination angle can be calculated as follows:____
DEC = DEC
____
WHERE DEC = [(ED + WD + EU + WU)/4]-180
4.5
Measurement of Field Inclination
(a)
Release the vertical circle clamp and rotate the telescope so that the magnetometer
probe is in the Up position.
(b)
Release the horizontal circle clamping lever and transit the telescope to the
approximate calculated Declination +180o while viewing the read-out through the
microscope. Lock the horizontal circle-clamping lever. Use the horizontal circle slow
motion knob to bring the degrees and minutes into coincidence with the calculated
Declination 180o. The instrument is now aimed along the magnetic meridian of the
field and in the SU position.
OM0138 ISSUE 10 PAGE 11 OF 50
(c)
Without inverting the telescope rotate it so that the magnetometer reading peaks. Note the
approximate angle of the nearest degree. Rotate the telescope 90o to the SU position. Fine
adjustment to the null reading is made by locking the vertical circle clamping lever and
adjusting the final position using the vertical circle slow motion knob. Record the reading
SU.
(d)
Release the vertical circle clamping lever and rotate the telescope 180o (through the
peak direction) to the other null position as per (c). Record the reading ND.
(e)
Transit the telescope 180o so that it is exactly aligned parallel to the magnetic meridian in the
direction of D.
(f)
Repeat procedures in (c) and (d) to obtain two more null readings SD and NU.
(g)
The Inclination angle can be calculated as follows:INC = INC - 180 IF INC >90 OR
_____ ____
INC = INC IF INC <90
___
WHERE INC = [(180 - SU)+(360-ND)+(SD-180)+NU]/4
4.6 Performing Observations of D & I with a Non-Resettable Horizontal Circle Theodolite
The resettable circle is not required for accurate measurement of D and I and has been eliminated.
The likelihood of incorrect circle settings is reduced and the best observation method is adopted
A digital calculator will be required which can convert degrees, minutes and seconds to decimal
values and vice-versa. Strict magnetic hygiene should be observed by the operator.
The zeiss Operation Manual should be studied. The observation conventions are described
pictorially in figures 5, 6 and 7.
Two optical and four magnetic measurements are performed for each observation and the results
averaged to eliminate system optical and magnetic errors. Worked examples are given at the end of
this section. The examples are for explanation only and do not show the usual system errors.
4.7 Performing Observation of Declination
For this observation a reference target with a known Azimuth (TA) is required. This is the angle
subtended between the target and the geographical meridian (GM) at the point of observation. The
target azimuth can be surveyed using GPS observations, solar or astral transit using appropriate
tables and chronometer or a north-seeking gyroscope.
The setting of the horizontal circle will be arbitrary therefore the target datum (TD) reading must be
recorded first.
1. Observe the target and record both the circle left (CL) and circle right (CR) horizontal circle
readings. Calculate the target datum (TD) as follows:
OM0138 ISSUE 10 PAGE 12 OF 50
TD = (CL + CR)/2
To avoid ambiguities place the centre of the theodolite in the tribrach such that the 0/360º horizontal
circle transition is clear of the CL or CR observation.
2. Set the vertical circle to 90º or 270º as appropriate. Perform the four null mode magnetometer
observations and calculate the magnetic meridian mean value (MM).
Where MM = (ED + WD + EU + WU)/4
3. Calculate the Declination (D)
Where D = MM + (TA) - TD ±90º
Select the value expected for D and reject the larger value.
Note
§
D will be positive if to the east and negative if to the west of GM
§
Observe correct use of brackets and signs
Example 1 (ideal observations)
If;
TA = -30º
CL = 260º
CR = 80º
EU, WD = 14º
WU, ED = 194º
TD = (CL + CR)/2
= (260º + 80º) /2
= 170º
MM = (ED+ WD + EU + WU)/4
= (194º + 14º + 14º + 194º)/4
= 104º
D = MM + (-30°) - TD ± 90°
= 104º - 30º - 170º + 90º = - 6º - Select
= 104º - 30º- 170º - 90º = - 186º - Reject
OM0138 ISSUE 10 PAGE 13 OF 50
4.8 Performing Observation of Inclination
For this measurement the reference is the pendulum compensated vertical scale.
1. Set the telescope NU to the mean value (MM) or (MM + 180º) corresponding to the north
observation of D
2. Obtain the (NU) and (SD) null magnetic measurements
3. Set the telescope to MM or (MM + 180º) and obtain the SU and ND null magnetic
measurements.
4. Calculate the Inclination, I
Where I = [ (180º - SU) + (360º - ND) + (SD - 180º) + NU ] /4
Example (ideal observations):
If; SU = 120º, ND = 300º, SD = 240º, NU = 60º
Then, I = ( 60º + 60º + 60º +60º) / 4
= 60º
5.0 REPAIR AND MAINTENANCE
This section describes procedures for testing a theodolite and magnetometer system and carrying out
field adjustments to maintain full accuracy. Procedures for mounting the probe on the theodolite are
included. Maintenance procedures are restricted to probe cable test and repair and replacement of
the Mag-01H battery.
5.1
Checking the System
5.1.1. Battery Check
Connect the battery charger to a live supply and observe that the charge indicator illuminates.
After 10 to 20 minutes switch on the magnetometer and observe that the battery voltage has risen to
between 6.5V and 7V.
Disconnect the battery charger and switch off and on again. Observe that the battery voltage is not
less than 6V
5.1.2. Functional Check
Set the sensitivity switch to x1. Vary the orientation of the probe with respect to the direction of the
earth's magnetic field and observe that the display responds by changes in sign and magnitude.
OM0138 ISSUE 10 PAGE 14 OF 50
Orientate the probe so that the display indicates some low value, e.g., approximately 5nT (+0.005).
Momentarily select x10 sensitivity. The LCD should respond by displaying +0.050. Alternatively
select ±30µT using the offset control and observe that the display responds by ±30 µT.
5.1.3. Theodolite Optical Check
Follow the procedures given in Section 5 of the Zeiss manual to discover and eliminate optical
errors.
5.1.4. Recalibration
Offset errors should not exceed ±5 nT per annum absolute worst case. Mechanical misalignment
resulting from wear and tear cannot be predicted, but recalibration on a yearly basis is
recommended. The entire system needs to be returned to the manufacturer for this to be carried out.
5.2
Probe Alignment
See Figure 8
The theodolite is set up in a site of known absence of magnetic gradients, less than 1 nT per metre.
In this procedure the telescope is erected vertically and rotated about the horizontal axis to discover
and eliminate any errors due to differences between the magnetic and optical axis. Errors are
removed using the joystick.
Accuracy of this setting will depend on the magnitude of the horizontal geomagnetic field H at the
geographical latitude. This will be strongly dependent upon the Inclination angle I and will yield a
resolution equivalent to that of dD. This procedure is unaffected by any residual offset errors.
For this procedure it is necessary to offset the vertical component Z of the geomagnetic field to
obtain measurements with a resolution of 1 nT.
METHOD
(a)
To gain access to the joystick remove the protective cover which is retained by four M3
countersunk bronze screws. The probe collimation joystick adjuster is clamped by two
screws which act against a clamping plate at the base of the joystick. These screws should be
slackened one half turn each to free the joystick. Some practice will be required to obtain
the correct degree of slackness to permit adjustment.
(b)
Carefully level the theodolite. Switch on the magnetometer and adjust to obtain high
resolution. Set the vertical circle to precisely 180o using the vertical scale and note the
reading on the Mag-01H.
(c)
Release horizontal circle and rotate the theodolite.
(d)
Record the position and magnetometer value for the maximum and minimum
magnetometer readings. Calculate the mean of the two magnetometer readings
(R1 + R2)/2.
(e)
Set the direction of the theodolite to produce a maximum value and move the joystick in a
North-South direction along the magnetic meridian to obtain the mean value in (d).
OM0138 ISSUE 10 PAGE 15 OF 50
(f)
Repeat steps (a) to (e), whilst progressively tightening the clamping screws, until the
difference between two readings and each pair of readings is 1 nT.
(g)
Replace probe protective cover and four retaining screws.
5.3.
Offset Trimming
See Figures 5 and 9
The electronics in the magnetometer unit must be exposed to facilitate this adjustment.
(a)
Set up the theodolite as if to perform Inclination measurements. Select the x10 range and set
theodolite to position SU to achieve a null in I. Record this angular value. Rotate vertical
circle to a position ND to achieve null and record the second value. In the presence of an
offset error these values will not be 180o apart. Adjust the vertical circle to a value which is
the mean of SU and ND, (SU + ND + 180)/2, and adjust the x10 offset potentiometer to
produce a displayed magnetometer value of 00000.
(b)
Select x1 sensitivity and adjust x1 offset potentiometer to produce a value of 0000.
5.4.
Probe Cable Repairs
See Figures 8 and 10
Should the cable fail due to fatigue or damage the display will always read as if over-ranged. If the
cable is suspected check the electrical resistance using a suitable meter and with reference to the
values in Figure 10. The cable can be replaced in the following way:
(a)
Remove probe cover screws
(b)
De-solder the four wires from the tag strip
(c)
Unscrew the cable gland
(d)
Reconnect in the reverse order
5.5.
Fitting the Magnetometer Probe Assembly
See Figure 8
The MAG Probe A comprises three parts:
(i)
The fluxgate magnetometer mounted on a pillar which occupies the position of the
previously removed rough sighting telescope (Rough Sighting Telescope No. 4 in the
Zeiss manual).
(ii)
A protective enclosure which is retained in position around the magnetometer probe by a
retaining band. Clamping screws and nuts are supplied with this enclosure.
(iii)
A cable assembly consisting of a high flexibility audio grade cable terminated at one
end with a screw-in cable head for connection to the magnetometer probe and at the
other end with a WW Fischer 6-pole waterproof connector.
If the cable is not already fitted to the cover follow the instructions for fitting in 6.4.
Fitting the Protective Cover
OM0138 ISSUE 10 PAGE 16 OF 50
(a)
Fit the cable assembly to the protective cover if not already fitted.
(b)
Insert the bronze retaining band in to the narrow slots on the underside of the enclosure.
(c)
Place the enclosure over the theodolite so that it fits snugly.
(d)
Place the two nylon nuts beneath the bent over eyes of the bronze retaining band and
insert the two retaining screws, whilst holding the nuts with a pair of pointed pliers.
Tighten the band around the telescope until the enclosure is firmly in place.
Do not overtighten screws.
Fitting the Magnetometer Probe
(a)
Remove the Rough Sighting Telescope and if possible save the screws as they are useful for
replacement parts.
(b)
Place the probe pillar carefully into the counterbored position and almost tighten the
two probe mounting screws.
(c)
Swing the direction of the probe to be precisely parallel with the optical axis of the
theodolite as indicated by the ridge which runs along the top of the telescope.
(d)
Fully tighten the probe retaining screws.
(e)
Connect the cable wire tails in the correct positions.
The probe is now ready to be aligned.
NOTE: Bartington Instruments cannot accept responsibility for the absolute vertical alignment of a
sensor, relative to a theodolite telescope, when fitted by the customer after delivery. Some filing of
the base of the pillar may be required due to unknown imperfections in the theodolite datum.
5.6.
Battery Replacement
See Figure 9
If the battery fails it can be replaced as follows:(a) Remove the top of the case.
(b) Disconnect the push-on battery tags.
(c) Remove the battery from the back panel clamp.
(d) Install a new battery with the positive terminal to the left.
(e) Re-connect the push-on battery tags, ensuring correct polarity.
(f) Refit the top of the case.
OM0138 ISSUE 10 PAGE 17 OF 50
6.0 TECHNICAL SPECIFICATIONS
6.1. Mag-01H Electronics Unit
Mechanical
Dimensions
:
15.5 cm x 17 cm x 6.8 mm
Materials
:
high impact ABS
Weight
:
1.5 kg
Operating
temperature range
:
-20 oC to +50 oC
Relative humidity
:
90%
Environmental
Environmental sealing to IP65
Performance
Measuring range
:
0.1nT - 0.2mT
Bandwidth - x1 sensitivity
:
dc to -3 dB at 10 Hz, 20 µT p-p
-12 dB per octave roll off
Calibration accuracy
:
0.25%
Maximum resolution
:
0.1nT
Zero field offset
:
±1 nT at room temperature
reducing to ±5 nT after circa 1 years' use
Offset drift
:
0.01 nT/ oC
Calibration temperature
coefficient
:
<10ppm/ oC
Liquid crystal display
:
4½ digit autoranging
x1 sensitivity
:
displays 0-±20 µT with 1 nT resolution and
20-±200 µT with 10 nT resolution
x10 sensitivity
:
displays 0-±2 µT with 0.1 nT resolution and
2- ±20 µT with 1nT resolution
OM0138 ISSUE 10 PAGE 18 OF 50
Front panel controls/sockets
On/off switch
:
switches on the internal battery supply
Probe input
:
via 6 pole waterproof Fischer connector
Charge indicator
:
LED illuminated when external supply is connected
Offset control
:
allows a preselected field strength between ±90 µT
in ±10 µT steps to be subtracted from the field
experienced by the probe to increase the measuring
range without affecting the resolution
Sensitivity control
:
increases the sensitivity of the magnetometer by a factor
of 10
Battery charger inlet
:
2.1 mm socket dc 0.5 A max.
polarity protected 9-18 V continuous or intermittent
use
Analog output
:
5 volts full scale via 2 x 4 mm rear panel insulated
sockets
Scaling
x1 sensitivity
:
100 µT/V, ±500 µT max., 1 nT resolution
x10 sensitivity
:
10 µT/V, ±50 µT max., 0.1 nT resolution.
Offset can be used to increase range.
Output Impedance
:
1 kohm
Bandwidth
x1 sensitivity
x10 sensitivity
:
:
-3 dB at 10 Hz
-3 dB at 1 Hz
-12 dB per octave
Battery charger input
:
polarity protected 12 V dc 0.5 A max. via a 2.1 mm
rear panel socket. Full charge in 5 to 6 hours max.
May be left on indefinitely.
Rear panel sockets
OM0138 ISSUE 10 PAGE 19 OF 50
6.2
Theodolite Mounted Mag A Probe
Operating temperature range :
-20 oC to 80 oC
Calibration accuracy
:
0.1%
Fluxgate probe
:
Temperature coefficient 10ppm/ oC, length 55 mm with precision feedback
solenoid, rigidly mounted on theodolite telescope,
10 minutes of arc adjustment provided.
Protective cover
:
aluminium housing clamped to theodolite mechanically
isolated from probe mounting.
Dimensions
:
10.0 cm x 2.5 cm x 5.8 cm
Weight
:
250 g
Materials
:
Diecast aluminium
Cable type
:
4-core overall screened high flexibility audio grade with
6 pole Fischer connector
Length
:
5 m standard (other by request)
Core-screen capacitance
:
160 pF/m
Resistance
:
92 ohms/km
Connector
:
Fischer 6-way waterproof
Theodolite
:
Zeiss 010B, 015B or 020B steel free theodolite, with
carrying case
Tripod
:
Short wooden - non-magnetic
6.3
6.4
Connecting Cable
Theodolite
Cable connections, comparison between the two different types of cable:
PIN
1
2
3
4
5
6
FUNCTION
SCREEN
Ex
Ex
N.C.
+Fb
-Fb
MOGAMI 2893 BLACK
SCREEN
CLEAR
BLACK
N.C.
RED
BLUE
CANFORD AUDIO 4.7 GREY
SCREEN
WHITE
GREEN
N.C.
RED
BLUE
OM0138 ISSUE 10 PAGE 20 OF 50
Figure 1 – INTERNATIONAL GENERAL REFERENCE FIELD DR0609 (1)
OM0138 ISSUE 10 PAGE 21 OF 50
A-D CONVERTOR &
4 1/2 DIGIT LCD
RANGE
CONTROL
SWITCH
SUMMING AMPLIFIER &
PRECISION VOLTAGE TO
CURRENT CONVERTOR
PROBE
FEEDBACK WINDING
2
+19.999
ATTENUATOR
X10
IC
FEEDBACK
CURRENT
+
X1
S
2
-
ANALOG
OUTPUT
0v
EXCITATION WINDING
Fo
SWITCHED
OFFSET CONTROL
0-90m T IN
+
- 10mT STEPS
PROBE
EXCITATION
OSCILLATOR
SIGNAL
IN
2Fo
50
60
70
80
90
40
30
20
10
0
+
ON
OUTPUT
FILTER
-3dB @ 10Hz
ON
OFF
DUAL
PRECISION
REFERENCE
DEMODULATOR
12V d.c.
INLET
CONSTANT VOLTAGE
BATTERY CHARGER
+7V
INPUT
FILTER
REGULATED
POWER
SUPPLY
CHARGE INDICATOR
+6V
POWER
ON / OFF
6V 1.1Ah
SEALED BATTERY
0V
-7V
0v
Figure 2 – Mag-01H SYSTEM SCHEMATIC DR0223 (4)
Select X10 to achieve 0.1nT
sensitivitiy
Does not modify offset
Mag-01H
40
MICROTESLA
50
30
60
4 1/2 DIGIT LCD DISPLAY
Displays directly in
Microtesla @ X1 sensitivity
On X10 sensitivitiy divide
reading by 10
e.g.
displayed value 0.001 = 1nT
true measurement = 0.1nT
SENSITIVITY POWER
1
POWER SWITCH
10
mT
DIVIDE BY TEN ON X10 SENSITIVITY
Single Axis
Fluxgate Magnetometer
Bartington
20
70
10
80
0
90
+
-
ON
CHARGE
ILLUMINATED
WHEN INTERNAL
BATTERIES ON CHARGE
PROBE
WATERPROOF
CONNECTION
TO PROBE
OFFSET
AUTO RANGING
Decimal point shifts to:
LEFT when display value decreases below 10.00
RIGHT when display value increases above 19.999
Battery voltage automatically displayed at switch on - 5V minimum
Precision Offset
Select a magnitude and polarity which almost cancels
the investigated field strength F, and brings the
measurement into the desired range of the display
e.g.
F = 90.00mT set offset to -80
Display will show +10.00
Figure 3 – Mag-01H FRONT PANEL FUNCTIONS DR0222 (4)
OM0138 ISSUE 10 PAGE 22 OF 50
ANALOGUE OUTPUT
+5V maximum = +500 m
T
Offsets and range change
apply
( For high field probe D
+4.5V = +4.5mT)
Serial No.
Va OUTPUT +
+ 5V FS
12V DC
POLARITY
PROTECTED
z=1kW
FULL CHARGE 6 HOURS
2.1mm d.c. inlet
Charge from mains adaptor or
vehicle dashboard cable
Voltage may be between 9-18V
Figure 4 – Mag-01 & H REAR PANEL FUNCTIONS DR0237 (4)
CR
ED
WD
EU
WU
V = 270
V = 270
V = 90
V = 90
CL
MEASUREMENT OF DECLINATION
SU
ND
SD
NU
N
W
E
S
MEASUREMENT OF INCLINATION
Figure 5 – PLAN VIEW OF OBSERVATION POSITIONS FOR D & I
DR0611 (2)
OM0138 ISSUE 10 PAGE 23 OF 50
MM
F
ANGLE OF DECLINATION D (VARIATION)
IS THE AZIMUTH ANGLE BETWEEN THE
GEOGRAPHICAL MERIDIAN GM AND THE
MAGNETIC MERIDIAN MM
N
GM
(+X)
REFERENCE
TARGET DATUM
TD
+TA
360 0
-D
F IS THE DIRECTION OF THE
TERRESTRIAL FIELD
AXIS
W
(-90)
(-Y)
WU,ED
EU,WD
(+90)
(+Y) E
NULL
S
Figure 6 – OBSERVATIONS OF DECLINATION IN THE HORIZONTAL CIRCLE DR0612 (2)
ANGLE OF INCLINATION I (DIP)
IS THE VERTICAL ANGLE OF THE
TERRESTRIAL FIELD F RELATIVE
TO THE HORIZONTAL PLANE.
THE PLANE OF THE VERTICAL CIRCLE
IS SET PARALLEL TO THE MAGNETIC
MERIDIAN MM
REFERENCE
0 360
360 0
THE HORIZONTAL DATUM (O) IS DETERMINED
BY THE PENDULUM COMPENSATED
VERTICAL REFERENCE (+Z)
S
HORIZONTAL
SU
SD
IS
AX
(0) N
DATUM
VERTICAL
LL
NU
ND
NU
I
F
(+Z)
NADIR
Figure 7 – OBSERVATIONS OF INCLINATION IN THE VERTICAL CIRCLE
DR0613 (2)
OM0138 ISSUE 10 PAGE 24 OF 50
5M CABLE TO
MAGNETOMETER
PROBE COLLIMATION
JOYSTICK ADJUSTER
SCREW-IN
CABLE HEAD
LOCKING SCREWS
PROBE
MOUNTING
SCREWS
CLEAR
BLACK
BLUE
RED
FLUXGATE
PROBE
TYPE 'A'
MOGAMI CABLE
WHITE
GREEN
BLUE
RED
CANFORD CABLE
CABLE TO PROBE WIRING
SHOWING ALTERNATIVE CABLES
PROTECTIVE
ENCLOSURE
PLAN VIEW OF
THEODOLITE WITH
PROBE EXPOSED
ENCLOSURE
RETAINING
SCREWS
ENCLOSURE
RETAINING
BAND
FRONT VIEW
OF THEODOLITE
Figure 8 – THEODOLITE MOUNTED PROBE TYPE ‘A’ ASSEMBLY DR0614 (1)
OM0138 ISSUE 10 PAGE 25 OF 50
BATTERY 6V 1.2Ah
LEAD ACID GEL TYPE
+
RV3
PC 13
TP2
IC7
8-WAY
RIBBON
CABLE
GREY
BROWN
J1
LK1
TP3
TP1
RV4
RV5
TP4
M1 DPM
VR1
PRECISION
REF.ADJUST
VR3 X1 O/S
DPM SCALING
VR2 X10 O/S
Figure 9 – Mag-01H INTERNAL VIEW DR0615(1)
5200mm
BLUE
-Fb
MOGAMI CABLE
SCREEN
1
SCREEN
1
5
2
4
WHITE
Ex
N.C.
BLACK
Ex
ITEM 1
WIRING SIDE VIEW
2
.5
3
4
RED
+Fb
6
5
2
CLEAR
Ex
CABLE PREPARATION
SCALE 5=1
RED
+Fb
6
4
3
N.C.
GREEN
Ex
CANFORD AUDIO CABLE
ITEM 1
WIRING SIDE VIEW
Figure 10 – Mag-PROBE TYPE ‘A’ CABLE & CONNECTIONS DR0616(2)
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