G:Products03 - BartingtonMag-01 and Mag · PDF fileMAG-01H Fluxgate Declinometer/Inclinometer Including Zeiss Theodolite Instruction Manual Operation and Maintenance Manual Distributed

GMW

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GMW

955 Industrial Road, San Carlos, CA 94070 Tel: (650) 802-8292 Fax: (650) 802-8298 Email: [email protected] Web site: http://www.gmw.com

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: [email protected] 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: [email protected] Web Site: http://www.bartington.com/ Issue 10

OM0138 ISSUE 10 PAGE 1 OF 50

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.


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. PROBE ALIGNMENT 5.3. OFFSET TRIMMING 5.4. PROBE CABLE REPAIRS 5.5. FITTING THE MAGNETOMETER PROBE ASSEMBLY 5.6. 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


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


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. Prevailing magnetic conditions - measurements during magnetic storms can be extremely

difficult to perform. 2. 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.

3. Plinth stability - the tripod is less stable with time and temperature than a brick pillar. 4. 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


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.


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.


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.


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


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.


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.


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.


(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:


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


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.


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).


(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


(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.


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 Environmental Operating temperature range : -20 oC to +50 oC Relative humidity : 90% 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


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 Rear panel sockets 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 : -3 dB at 10 Hz x10 sensitivity : -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.


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 6.3 Connecting Cable 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 6.4 Theodolite Theodolite : Zeiss 010B, 015B or 020B steel free theodolite, with carrying case Tripod : Short wooden - non-magnetic Cable connections, comparison between the two different types of cable:

PIN FUNCTION MOGAMI 2893 BLACK CANFORD AUDIO 4.7 GREY 1 SCREEN SCREEN SCREEN 2 Ex CLEAR WHITE 3 Ex BLACK GREEN 4 N.C. N.C. N.C. 5 +Fb RED RED 6 -Fb BLUE BLUE


Figure 1 – INTERNATIONAL GENERAL REFERENCE FIELD DR0609 (1)


Figure 2 – Mag-01H SYSTEM SCHEMATIC DR0223 (4)

Figure 3 – Mag-01H FRONT PANEL FUNCTIONS DR0222 (4)

PROBE

EXCITATION WINDING

FEEDBACK WINDING

SUMMING AMPLIFIER &PRECISION VOLTAGE TO CURRENT CONVERTOR

6V 1.1AhSEALED BATTERY

0v

DEMODULATOR

CHARGE INDICATOR

CONSTANT VOLTAGEBATTERY CHARGER

12V d.c.INLET

+19.999

A-D CONVERTOR &4 1/2 DIGIT LCD

ANALOGOUTPUT

OUTPUTFILTER

-3dB @ 10Hz

-

0v

+

X10ATTENUATOR

RANGECONTROLSWITCH

SWITCHEDOFFSET CONTROL0-90 T IN 10 T STEPS

2

2FEEDBACKCURRENT

S

Fo

IC

4060

50

X1

INPUTFILTER

SIGNALIN

o2F

REGULATEDPOWERSUPPLY

-7V

0V

POWERON / OFF

+6V

90

DUALPRECISION

REFERENCE

+7V

PROBEEXCITATIONOSCILLATOR

m+-m

+ON

-

OFF

10

30

0

20

ON

8070

m

m T

Mag-01H

Select X10 to achieve 0.1nTsensitivitiy

Does not modify offset

POWER SWITCH

ILLUMINATED WHEN INTERNAL BATTERIES ON CHARGE

WATERPROOF CONNECTION TO PROBE

Precision OffsetSelect a magnitude and polarity which almost cancelsthe investigated field strength F, and brings themeasurement into the desired range of the displaye.g.F = 90.00 T set offset to -80Display will show +10.00

AUTO RANGING

Decimal point shifts to:LEFT when display value decreases below 10.00RIGHT when display value increases above 19.999Battery voltage automatically displayed at switch on - 5V minimum

4 1/2 DIGIT LCD DISPLAY

Displays directly inMicrotesla @ X1 sensitivityOn X10 sensitivitiy dividereading by 10

e.g. displayed value 0.001 = 1nTtrue measurement = 0.1nT

Bartington

MICROTESLA SENSITIVITY40

30

20

10

0

OFFSET

+ -

60

50

80

70

90

10

1

CHARGE

PROBE

ON

POWER

Single AxisFluxgate Magnetometer

DIVIDE BY TEN ON X10 SENSITIVITY


Figure 4 – Mag-01 & H REAR PANEL FUNCTIONS DR0237 (4)

Figure 5 – PLAN VIEW OF OBSERVATION POSITIONS FOR D & I DR0611 (2)

ED

V = 270

WD

V = 270

EU

V = 90

WU

V = 90

CR

CL

SU ND SD NU

N

W E

S

MEASUREMENT OF INCLINATION

MEASUREMENT OF DECLINATION

m

Va OUTPUT ++ 5V FS

z=1k

W

ANALOGUE OUTPUT +5V maximum = +500 T Offsets and range change apply ( For high field probe D +4.5V = +4.5mT)

2.1mm d.c. inletCharge from mains adaptor orvehicle dashboard cable

Voltage may be between 9-18V

Serial No.

FULL CHARGE 6 HOURS

POLARITY PROTECTED

12V DC


Figure 6 – OBSERVATIONS OF DECLINATION IN THE HORIZONTAL CIRCLE DR0612 (2)

Figure 7 – OBSERVATIONS OF INCLINATION IN THE VERTICAL CIRCLE DR0613 (2)

0360

3600

N(0)

(+Z)

S

NADIR

F

ANGLE OF INCLINATION I (DIP)IS THE VERTICAL ANGLE OF THETERRESTRIAL FIELD F RELATIVETO THE HORIZONTAL PLANE.THE PLANE OF THE VERTICAL CIRCLEIS SET PARALLEL TO THE MAGNETICMERIDIAN MM

THE HORIZONTAL DATUM (O) IS DETERMINEDBY THE PENDULUM COMPENSATEDVERTICAL REFERENCE (+Z)

AXIS

NULL

HORIZONTAL DATUM

VE

RTI

CA

LR

EFE

RE

NC

E

ISU SD

NUND

AXIS

NULL

-D

360 0

W (-90)(-Y)

(+90)(+Y) E

S

NMM

FGM(+X)

EU,WD

WU,ED

ANGLE OF DECLINATION D (VARIATION)IS THE AZIMUTH ANGLE BETWEEN THEGEOGRAPHICAL MERIDIAN GM AND THEMAGNETIC MERIDIAN MM

F IS THE DIRECTION OF THETERRESTRIAL FIELD

+TA

REFERENCETARGET DATUM

TD


Figure 8 – THEODOLITE MOUNTED PROBE TYPE ‘A’ ASSEMBLY DR0614 (1)

MOGAMI CABLE CANFORD CABLE

REDBLUE

GREENWHITE

CABLE TO PROBE WIRINGSHOWING ALTERNATIVE CABLES

REDBLUE

BLACKCLEAR

FRONT VIEWOF THEODOLITE

PLAN VIEW OFTHEODOLITE WITHPROBE EXPOSED

5M CABLE TOMAGNETOMETER

SCREW-INCABLE HEAD

PROBE COLLIMATIONJOYSTICK ADJUSTER

LOCKING SCREWS

PROBEMOUNTING

SCREWS

FLUXGATEPROBE

TYPE 'A'

PROTECTIVEENCLOSURE

ENCLOSURERETAINING

SCREWS

ENCLOSURERETAININGBAND


Figure 9 – Mag-01H INTERNAL VIEW DR0615(1)

Figure 10 – Mag-PROBE TYPE ‘A’ CABLE & CONNECTIONS DR0616(2)

-

RV3

PC 13 TP2

+

RV5

M1 DPM

RV4TP1

BR

OW

N

TP4

GR

EY

IC7

J1

TP3

8-WAYRIBBONCABLE

LK1

BATTERY 6V 1.2AhLEAD ACID GEL TYPE

VR3 X1 O/S

VR2 X10 O/SDPM SCALING

VR1PRECISIONREF.ADJUST

5200mm

ITEM 1WIRING SIDE VIEW

BLACKEx

CLEAREx

23

4

N.C.

SCREEN1

RED +Fb6

5

4

CABLE PREPARATIONSCALE 5=1

2.5

ITEM 1WIRING SIDE VIEW

GREENEx

WHITEEx

23

4

N.C.

BLUE-Fb

SCREEN1

RED +Fb6

5

MOGAMI CABLE

CANFORD AUDIO CABLE

























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G:Products03 - BartingtonMag-01 and Mag · PDF fileMAG-01H Fluxgate Declinometer/Inclinometer Including Zeiss Theodolite Instruction Manual Operation and Maintenance Manual Distributed