PROTON MAGNETOMETER Operating Instructions
Contents
1. 20215 1 CSE Crmeters By taking the maximum sensing distance for a given target and producing a simple scale diagram the optimum search lane width can be derived The procedure 1s as follows 25 MC5 Proton Magnetometer User Manual 111 poeta PEPPEN 4 1 Adopt a suitable scale say 2mm is equal to 1 metre 2 Draw a horizontal line representing the surface 3 Draw a vertical line downward from the horizontal line and perpendicular to it that is scaled to represent the mean depth of the target 4 From the base of the vertical line depth draw a line to scale relating to the maximum sensing distance to intersect with the surface horizontal line such that it creates the hypotenuse of a right angle triangle 5 The distance established between the point of intersection at the surface and the top of the vertical depth line represents the maximum horizontal sensing distance to the target The above calculations have assumed that the tow fish 1s deployed either at or near the surface however It will be readily observed that as the depth increases for a given target size the corresponding horizontal component of the sensing distance reduces accordingly In situations where the depth of water exceeds the maximum sensing distance and it becomes necessary to plan deployment of the tow fish to some depth it 1 to this level that the horizontal line corresponds and which in essence becomes our artificial2. al eee calce dien ined ipt as ee mm mmm rs a ae z OAE DCLEN SA ee oo fa aa a SIRE Pes 8 8 T mm aren zz HER Eon E 3 4 1 a a x RE DE m ZU UU mmm 1253 7 E 0 Enim t2 d 5 T nup ee TEE 1 2 EHE nm Fil sr a ad 2 Ometres 1 metres DISTANCE Alarm setting 50nT 1 kilometres 14 MC5 Proton Magnetometer User Manual FONELEE d 4 3 SENSITIVITY GRAPH Having established the resolution and detection criteria for the magnetometer the potential detection distance can be assessed for any given size of ferrous object within a reasonable predictability This 15 compiled as a graph of field strength deviation against distance This graph 15 very important to the magnetometer operator and can provide information base necessary for the
3. Maldives Ww o Seychilies Amirantes Is giles Comore 35 MC5 Proton Magnetometer User Manual APPENDIX 11D Magnetic Contour Map Japan amp Bering Sea 36 MC5 Proton Magnetometer User Manual d PEPPEN d APPENDIX Magnetic Contour Map Pacific Ocean Marquises Santa Cru 27 Hebrides Ls Vu n 4 5 48 56 Caledonia 37 MC5 Proton Magnetometer User Manual APPENDIX Magnetic Contour Map South America Xe t 479 2 C ET i MT gt la S Felix 5 Santiago Archo de Ld luan Fernandez E L Georgia ET AL N Is Diego agi PEPPEN 4 E 2 0 un D dud D D ON 2 z Uu APPENDIX South China Seas Magnetic Contour Map sp 39 MC5 Proton Magnetometer User Manual APPENDIX Magnetic Contour Southern USA amp Carib Martinique m Uu 40 Magnetic Contour Map USA amp
4. Canada E 2 0 un D dud D D ON 2 z Uu APPENDIX 11 41 MC5 Proton Magnetometer User Manual APPENDIX Magnetic Contour W Europe Med F roes Shetland Is Orkney Is Wien Vienna Madeira 0 Alexandria P gt Islas Canarias 42 MC5 Proton Magnetometer User Manual shetan ct Bergen en ey la NORTH 3 113 SEd 4 PE E EL 8 Berlin Amsterdam Warszawa Contour lines above relate to values of total magnetic field x 1000 eg 44 44000 The world has a wide variation in it s ambient magnetic field strength total intensity for our purposes this strength 1s expressed in gammas g or nano Teslas 11 The above mapped area shows the typical coverage of a single tuning module IPA 3 fitted to the MCSES amp MCSET units and relates to a magnetic field strength of between 42 000 to 50 000 nT Area coverage is associated with both the AREA TUNE switch and Zone settings pre set by internal dil switch S7 The AREA TUNE switch has 16 positions designated A to which in turn relate to the most Northerly and Southerly areas respectively Coverage of AREA TUNE 15 always greater than coverage of a single Magnetic Zone setting Zone coverage for the European area 1s as follows MAGNETIC FIELD S
5. A polarise time of 0 5 1 2 or 3 seconds can be selected by the front panel control Increasing the polarise time gives a greater signal strength from the sensor therefore a greater deflection of the signal strength meter The greater signal level enables the magnetometer to make a more accurate measurement giving the system more inherent stability Short polarise times allow faster updates and can be used when looking for relatively small objects With short polarise times the boat travels a shorter distance between successive measurements it therefore has more chances to be close to the object when a measurement is made 5 3 RANGE CONTROL The range control can be set to X2 X10 X100 grad or grad2 The range is the most sensitive with scale deflection on the field strength meter corresponding to 50 or 50 nT X2 decreases the sensitivity be a factor 2 X10 decreases the sensitivity further to give a full scale deflection of 500 or 500 nT and X100 reduces it by another factor of ten NOTE The range control will only affect the displayed meter reading it will not affect the data output to a PC where this additional facility 1s being utilised Select the X1 range initially as this is the most sensitive and is more generally used range whilst searching Once a magnetic field anomaly is detected it may be necessary to select a lower sensitivity range in order to measure the peak of the anomaly Should a change in magnetic field s
6. N C 7 BLUE 11V 8 N C N C 9 N C N C GOOO 30 MC5 Proton Magnetometer User Manual 9 0 CHANGING THE OPERATING ZONE aic 2 ed 7 e ar x E 58 7 I R33 Mag Zone 57 Switch A special board is fitted to nT 1000 Setting Produce the correct operating conditions for magnetic field strengths below 27 000nT 27 30 PT When other magnetic zones are 29 32 required switch on 31 34 sos Tad special board has to be changed 33 37 so that both positions 1 amp 2are 46 41 on For 27 000nT the switch 40 45 should be as shown i e 1 off 44 51 and 2 on 50 57 57 66 The above settings should be applied to positions 5 6 7 amp 8 of 57 the MCS Zone selection pre set switch NB Leave the factory settings on positions 1 to 4 For operating in the areas of the world with the listed magnetic intensity see relevant appendices The appropriate IPA 3 tuning module for the nominal magnetic intensity in the operating area should also be fitted The pre set gain adjustment control on the IPA 3 can be adjusted to increase or decrease the signal meter strength if necessary ideal signal meter reading 18 85 deflection when optimum Area Tune selection is made The location of the IPA 3 tuning module is in the upper left comer of the above image and beneath a metal shielding
7. can tolerate a natural variable magnetic background depends on the proximity and intensity of the geological features in comparison to the size of the anomaly anticipated Where the geological feature 18 at some depth or distance from our magnetic sensor a localised anomaly can still be picked out quite readily from the more gradual change due to the background anomaly 11115 Field Strength 100nT plot vith regional gradient dewviation alarm threshold d 23 et level datum Fig 10 5 0 GETTING STARTED The 5 consists of two units the sensor probe or towfish which 1 towed behind the boat with it s associated cable and the control box this being installed on the towing craft An independent 12 or 24 volt 2 x 12v series car or motorcycle battery 18 required to power the magnetometer this power source 15 connected to the control box via the power lead provided Prior to the MC5 being used to search a particular area the unit must be first be set up for maximum signal response from the towfish The MC5 18 generally provided with a suitable internal module to allow the system to be optimally tuned for the localised field strength of a given area The earth s magnetic field varies with geological location therefore the magnetometer will require tuning for your area Normally once carried out re tuning is not necessary within a 20 30 mile operating radius
8. cover Removal of the three securing screws allows access for removal and replacement of the IPA 3 tuning module 3l MC5 Proton Magnetometer User Manual APPENDIX I WORLD IPA 3 MODULE ZONES There are six standard versions of IPA 3 Module which enable optimum operation of your in all magnetic intensities of the world Below 15 a list of options available that indicate the operating range MODULE T A STEPS 5nf 6nSf 6nsf 10nf 151 151 52 000nT 43 000nT 37 800 nT 32 700 nT 27 500 nT 23 500 nT TO 64 000nT 52 200 nT 43 500 nT 38 700 nT 33 000 nT 27 000 nT N B For more specific requirements please contact your nearest service agent or the support department at Aquascan International Ltd 32 MC5 Proton Magnetometer User Manual 111 Magnetic Contour Map Africa Amirantes Is Helena 33 r1 lt Australia amp New Zealand APPENDIX Magnetic Contour E 2 0 un D dud D D ON 2 z Uu 34 MC5 Proton Magnetometer User Manual APPENDIX 11C Magnetic Contour Map Red Sea Gulf amp Indean Ocean Lakshadweep
9. earth s surface The relevance to the operator of this diagram is covered in the section that refers to initially setting the correct operating ZONE The contours are shown in Gauss 100 000 nT 1Gauss E 2 0 un D D D ON 2 z Uu gt ok 8 1 MEM cee LINES OF EQUAL INCLINATION Wi TUIS SWR IP 0 SUIT 01 LINES OF CONSTANT FIELD STRENGTH x1000 nanotesla 10 MC5 Proton Magnetometer User Manual 111 4 2 MAGNETIC ANOMALIES CAUSED BY FERROUS OBJECTS In order to understand how a magnetometer can locate a shipwreck or other ferrous object it 15 necessary to consider what happens to the earth s magnetic field around such an item Consider the diagram shown in Fig 3 this shows how the lines of magnetic flux are distributed for a simple bar magnet The spacing of these lines represents the strength and linearity of the magnetic field at any point it also shows the field 18 strongest at the poles When ferrous object 15 placed in the magnetic field the lines of flux are distorted and generally become concentrated through the object It is the ability of a material to concentrate the field that is termed its permeability Ferrous material can have a permeability factor in the order of thousands with a proportional impact on the surrounding earth s field G
10. necessary for upgrade or service at a future date 2 0 SYSTEM INSTALLATION 2 0 SYSTEM INSTALLATION 2 1 MOUNTING 2 1 MOUNTING The 5 display unit 1s supplied with a conventional gimbals mount bracket allowing the unit to be mounted on horizontal vertical or sloping surfaces The degree of weatherproofing and the watertight nature of the connections make the unit suitable for mounting in exposed positions It is recommended that where possible the unit should be mounted behind some form of spray shield particularly when mounted on the console of RIBs and other similar type of high performance open boats Mounting the MC5 display should take account of the central role the instrument takes during magnetometer survey operations this demands concentration and ease of access to the controls Apart from the normal compass considerations mounting the unit close proximity to other general marine instruments should not cause any mutual interference MC5 Proton Magnetometer User Manual Wiggs The recommended minimum mounting proximity to a conventional compa for minimal effect If a central mounting position is not available then angle the unit as much as possible to present a view square to the operator 2 2 CONNECTIONS The 5 5 amp PET systems are fitted with four waterproof connectors these are complete with protective caps The protective caps should be utilised both during operation to cover unused connectors and
11. of the initial tuning position It can be useful if the operator is unfamiliar with the setting up procedure to try setting up the magnetometer on land before attempting to search at sea The following section describes the setting up procedure 5 TUNING PROCEDURE The magnetometer can only be used to search for ferrous materials or compounds and for this purpose it 15 extremely sensitive and has considerable range This high sensitivity to field variations means that the magnetometer may only be used remote from known earth field disturbers such as power lines or buildings Before attempting to set up the magnetometer ensure that it is positioned at least 50 metres 160ft from the 16 MC5 Proton Magnetometer User Manual c E 1 INTERNATIONAL nearest power line or building additionally ensure that any vehicles are at least 10 metres 30ft away Assuming the initial setting up is carried out on land the TOWFISH should be positioned at least 3 metres 10 ft from the electronics unit and battery The towfish should be set up horizontally at least 1 25 metres 4 ft off the ground using some form of totally non magnetic support NOT EVEN CONTAINING SMALL NAILS SCREWS OR EVEN STAPLES Elevation of the sensor is very important unless carrying out the land tuning on totally magnetically clean ground such as the sand of a beach Note Additionally if the magnetometer is provided with the Solenoid type towfish rather than t
12. planning required to guarantee a successful search operation If we analyse the graph whilst taking account of the above criterion we can establish the following useful factors 1 The maximum detection distance for any given ferrous mass by determining the intersection of the horizontal distance line to the 5nT point of the tonnage line 2 The relationship between increased tonnage and distance is roughly based on a 2 times increase in detection distance for a 10 times increase in ferrous tonnage 3 The change in deviation nT as distance from a given object changes this 15 seen a factor of 8 change in nT for a change of 2 times in distance The implications of the above have a significant impact on pre survey planning and in particular lane width to be adopted for searching and accordingly the degree of control required for the survey boat The importance of probe height during survey for relatively small targets can also be determined from the graph particularly where it 15 used in conjunction with depth of water information Further information on these aspects 1s covered in the section of this manual concerned with Survey Techniques and Magnetometer Applications 4 4 MAGNETOMETER SENSITIVITY The 5 sensitivity in terms of detection distance 1s based on its capability to resolve changes down to a resolution of 1 nanoTesla nT A magnetometer resolution of 1 nanoTesla is considered to be the optimum for mobile marine s
13. surface for the basis of calculations 7 0 SEARCH PATTERNS 7 1 PARALLEL LANE SEARCHING The most common and practical survey method 1 by means of the parallel lane search in N S E W runs where a predetermined lane length and calculated spacing 15 implemented Lane integrity 18 maintained by relating the required spacing to decimal parts of units of Lat amp Lon As a for instance if a 200 Metre spacing 15 required and the survey 15 along an East West line the choice of 0 1 of a minute of latitude gives slightly less than the 200 Metres required Increasing or decreasing the distance 18 just a question of proportionately changing the decimal part of a minute related to 1 000 minute 2 metres For control of Longitude spacing during N S runs the same principal applies but the actual metres to minutes of Lon have to be derived from a table or chart for the particular Latitude of operations E g at a Latitude of 50 degrees an increment of 0 1 minutes of Longitude gives about 120 metres The parallel lane search 1 particularly appropriate where a large area has to be searched on a speculative basis or where the position of a wreck 1 very approximate PA it 1s also a more precise way of covering a pre planned area of seabed as a square or rectangular shape 26 MC5 Proton Magnetometer User Manual Where the positi of a wreck or object is known with a high degree of certainty the simple circular search method can
14. the sensor coil is connected to a tuned amplifier The amplifier contains a filter to reyect noise and unwanted external signals induced in the coil The amplified signal is then fed to a microcomputer DETECTION STATE ma EM 2 FIELD STRENGTH B 4 Fig 2 OSCILLATOR AUDIBLE ALARM PROTON SPIN ALIGNED WITH 5 FIELD EARTH 5 MAGHETIC FIELD The use of a microcomputer makes it possible to programme in sophisticated features that would be uneconomical in previous designs To measure the frequency of the precession signal the microcomputer compares the signal with its own crystal oscillator This technique enables the MC5 to make very accurate measurements these can be stored as data in the microcomputer s memory to be compared with previous measurements The microcomputer 1s programmed to automatically actuate an alarm if the change in magnetic field strength is greater than the value selected this 1s controlled using the front panel switch This audible alarm facility avoids the need to continually concentrate on the magnetometer when searching as the microcomputer 1 analysing every measurement to check for any field change Each measurement is automatically converted into an analogue current to drive the large front panel Deviation meter and in some later or MC5 Proton Magnetometer User Manual depth information from an echo sounder 4 0 THE EARTH S MAGNETIC FIELD A reasonable understanding of the earth s ma
15. uk Technical Support support aquascan co uk Web Address www aquascan co uk HB 5 PES amp PET iss 6 Mar08 49
16. MC5 Proton Magnetometer User Manual AQUASCAN INTERNATIONAL LTD AQUASCAN HOUSE HILL STREET NEWPORT SOUTH WALES UK NP20 11 7 Aquascan International Limited Tel 44 0 1633 841117 Fax 44 0 1633 254829 UNDERSEA DETECTION EQUIPMENT unfo aquascan co uk Website www aquascan co uk MCs PROTON MAGNETOMETER TYPES PES PET Operating Instructions This manual is copyright 2008 Aquascan Int Ltd all rights reserved This document must not be replicated in whole or part without the prior express permission of Aquascan International Ltd Issue 6 March 2008 MC5 Proton Magnetometer User Manual 111 184144 INTRODUCTION 1 0 SYSTEM CODING 1 1 PACKING LIST CHECK 2 0 SYSTEM INSTALLATION 2 1 MOUNTING 22 CONNECTIONS 2 3 POWER SUPPLIES 2 4 TOWFISH INSTALLATION 3 0 PRINCIPLES OF OPERATION 3 1 PROTON PRECESSION 4 0 THE EARTH S MAGNETIC FIELD 4 MAGNETIC FIELD STRENGTH amp INCLINATION 4 2 MAGNETIC ANOMALIES CAUSED BY FERROUS OBJECTS 4 3 SENSITIVITY GRAPH 4 4 MAGNETIC SENSITIVITY 4 5 MAGNETIC CONTOUR amp ANOMALY MAPS 5 0 GETTING STARTED 5 TUNING PROCEDURE 2 2 POLARISE CONTROL 5 3 RANGE CONTROL 5 4 ALARM CONTROL 6 0 PLANNING amp CONDUCTING A SEARCH 6 1 HORIZONTAL DETECTION DISTANCE 6 2 SELECTING THE OPTIMUM SETTINGS 6 3 DEPLOYING THE TOWFISH 6 4 SEARCH METHODS amp SURVEY CONSIDERATIONS 6 5 CALCULATIONS 7 0 SEARCH METHODS 7 1 PARALLEL LANE SEARCHES 7 2 CIRCULAR
17. SEARCHES 7 3 DRIFT SEARCHES 8 0 NMEA amp PC INTERFACING 9 0 CHANGING THE OPERATING ZONE APPENDIXES IL IPA 3 TUNING MODULE OPTIONS MAGNETIC ZONE MAPS MC5 SPECIFICATION IV MC5 TROUBLESHOOTING amp INSTALLATION OPTIMISATION GUIDE IV MANUFACTURER CONTACT DETAILS 5 Proton Magnetometer User Manual INTRODUCTION Marine magnetometers have been used in professional applications with great success for many years However the high cost of these units have restricted their use for general wreck location Recent advances in electronic technology have however enabled such lower cost magnetometers to be produced without sacrificing any of the features of these professional models In fact the use of microcomputers has enabled costly features on previous designs to be implemented as standard For wreck location the magnetometers great advantage over an echo sounder 18 its ability to detect a wreck at a distance and then enable the search vessel to home onto it It can also detect wrecks buried in sand etc or lying on rocky ground both of which are very difficult with an echo sounder The AQUASCAN MCS is a proton magnetometer which is used to measure the earth s magnetic field strength and can detect variations in this field caused by the presence of ferrous objects The earth s field 1s normally uniform but will be disturbed by local concentrations of magnetic material such as a steel wreck These variations can extend u
18. SSDDBT depth fully opto isolated RS232 output port Mc5spec 0602 doc 44 MC5 Proton Magnetometer User Manual APPENDIX IV TROUBLESHOOTING GUIDE Symptom Signal Level Constantly Low Check the following 1 Check that the supply battery has a sufficient charge gt place battery on charge and then re test or replace battery 2 Check the condition of the Phono Connector from the Towfish and on the rear of the 5 Display gt If one or both of the connectors is badly corroded then they should be replaced N B This work should be carried out by an authorised Aquascan service agent or a suitably qualifed person Please contact your nearest Service Agent or the Aquascan support department before any work 16 carried out 3 Check the resistance across the Towfish Phono Connector gt Connect good quality multi meter across the core inner pin and screen on the Phono plug and check the resistance You see a reading of around 9 15 NB It is good policy to firstly check the multi meter s reading with the leads shorted together this provides a measure of what residual reading to take into account Symptom Signal Level Constantly High Check the following Check to see if excessive noise 15 affecting the signal Attach a ferrous metal object on top of the towfish tow as normal and check to see if the signal level drops to a very low level If the signal level remains high then background noi
19. TRENGTH SETTING 57 SWITCH 5 PCB nT x 1000 POSITIONS 5 6 7 8 40 to 45 Southern France Spain Med amp Upper Red Sea VUAY 44 to 51 Default setting for UK etc ARVY NOTE A picture of the PCB showing the position of S7 is to be found towards the rear of the MCS handbook see section 9 0 CHANGING THE OPERATING ZONE 43 MC5 Proton Magnetometer User Manual 111 poeta APPENDIX 5 SPECIFICATION DIMENSIONS CABLE Diameter 8 0mm Arctic grade PVC Length options from 25M 250M INSTRUMENT CASE Housing 280x153x65mm Overall length between gimbals 330mm Bracket Stainless Steel 305x100x25mm SOLENOID PROBE Plastic pressure housing with moulded nose amp tailfin array Standard 460mm L x 90mm W x 150mm High power 700mm L x 90mm W x 150mm TOROID PROBE Cast Epoxy sealed housing 300mm L x 180 W Polarisation time 0 5 1 2 3 seconds Power 12 1 5 24v 0 2 5amps Alarm settings OFF 10 20 50 nT Ranges LIN 0 5000nT GRAD 0 100nT AREA TUNE RANGE World 25000 to 65000 nT W European 40000 to 65000 nT SENSITIVITY RESOLUTION InT in range 25000nT to 60000nT 2nT in range gt 60000nT GRADIOMETER RANGE Indicates the difference between successive readings MEASUREMENT DISPLAY ImA moving coil meter INPUT OUTPUT Print PC interface port 1200 4800 Baud 5v logic NMEA 0183 1 p interface port Lat Lon GGA GLL RMC 1 NMEA 0183 input interface port for
20. al supply voltage can be supplied by a PP3 Battery using the Battery Clip fitted on the PC interface lead this should only be connected during the period of recording data as the battery will continue to supply power even with the MC5 switched off The data output of the MCSPES PET is designed to simulate the AX2000 data string such that the AOLOGEDIT software can be utilised When using this software with the 5 the AX2000 option should be selected for the Log function Do not select the 29 MC5 Proton Magnetometer User Manual INTERNATIONAL Taco E option as this was for earlier version of 5 data For further information refer to the software users guide supplied with the AQLOGEDIT CD 5 Display Isolator La m Battery C v WU v Clip l 6 Way Plug PIN DATALEAD T SHAPED PP3 CLIP 1 YELLOW BLACK 2 RED N C 3 BROWN N C 4 N C RED 5 ORANGE N C 6 BLUE N C TN D type Connector 9 Way Skt configuration may vary PIN DATALEAD 1 2 BROWN DATA TX 3 RED DATA RX 4 ORANGE 5 YELLOW GND 6 N C
21. ally deflect across the scale as the boat moves position The function of the microcomputer in the grad mode 1 described in section 4 This assumes that the probe is towed a constant distance above the seabed and the seabed 15 relatively flat If for instance there are rock formations which rise above the surrounding seabed or the boat slows and the probe sinks closer to the seabed then the effect of the magnetic rock will be greater and will causes deflection on the field strength meter It 15 important to be aware of this type of effect as 1t can result in false optimism that a wreck has been located The sensitivity on the grad range is the same as the X1 range and the alarm trigger values are the same It may also be necessary in some magnetic areas to de sensitise the alarm setting to avoid the alarm being triggered by the response from magnetic rock 6 3 DEPLOYING THE TOWFISH The cable 16 fitted with a moveable sheath which can be pushed along the cable to any required position this sheath grips the cable tight when under tension and will allow the cable to be held when the loop end is secured if more cable needs to be paid out then this can be achieved by gripping the tail end of the sheath and easing it towards the transom to effectively take the tension off the weave at the same time hold the inboard section of cable to control the release of more cable Onc the required amount of cable 15 deployed the weave of the sheath should be
22. areas with magnetic rock the performance of a magnetometer 15 reduced as a greater change in the magnetic field 1s required before a positive detection 15 assumed Even though the detection range 15 less in these areas it is still large enough to make the use of a magnetometer a considerable advantage over just an echo sounder 18 MC5 Proton Magnetometer User Manual 111 poeta 5 4 ALARM CONTROL The alarm control can be set to either OFF 10 20 or 50nT This feature enables a search to be made without the need to continually watch the Deviation meter Each time the microcomputer makes a measurement it compares the change in field strength with the alarm setting and sounds the alarm if it 15 greater the lower sensitivity ranges not all the alarm settings are possible Table 1 shows the alarm value used by the computer for various settings TABLE 1 RANGE ALARM SETTING 10 20 50 10 20 50 2 20 20 50 10 20 20 50 100 1 10 20 50 Grad2 20 40 50 Even if the alarm control is set to off microcomputer will make the audible alarm bleep if a measurement 15 made which 15 greater than can be displayed on the meter This bleep is a prompt to indicate when the range control should be adjusted 6 0 CONDUCTING A SEARCH During search operations the probe is towed behind the boat at sufficient distance to avoid detecting any magnetic properties of the boat itself The probe should normally
23. arm setting of 1011 and the range control set to the maximum sensitivity X1 will give the optimum performance for the initial search Once the wreck is detected it will be necessary to reduce the sensitivity of the magnetometer in order to home onto the exact location of the wreck Switching to X10 reduces the sensitivity by a factor of ten For large wrecks or ones close to the surface the X100 range may be necessary to determine the exact point when the probe is over the wreck This ability to reduce the sensitivity 1s just one of the advantages the MC5 has over magnetometers which use the audio beat principal For wrecks in very shallow water 1 less than 10 metres when the probe actually passes over the wreck no signal will be obtained from the magnetometer This is not the magnetometer malfunctioning but 1 due to a very large magnetic gradient around the probe This phenomena can be used to advantage with shallow water wrecks as it 15 a positive indication that ferrous metal 1 very close to the probe The MCS s built in microcomputer requires less than half a second to measure earth s magnetic field strength so that very short polarise times can be used short polarise time of 0 5 second is used when searching for small objects such as iron cannon anchors etc This is because with small objects the magnetic anomaly 15 much more localised so with a short polarise time the magnetometer probe travels a shorter distance between measuremen
24. be towed as speeds of 1 to 5 knots 1f however it 1s desirable to search at faster speeds a cord with low a stretch specification can be attached to the brass towing loop to avoid undue strain on the cable Where possible lay out all of the available cable over the stern as any cable left lying on the deck may get damaged or may cause noise to be induced Take great care to avoid damaging the cable sheath as any water intrusion will result in a malfunction of the magnetometer 19 MC5 Proton Magnetometer User Manual RECOMMENDED LENGTHS OF CABLE SIZE OF BOAT MINIMUM CABLE LENGTH Up to 7 5 metres Wood GRP Aluminium 25 metres Up to 16 metres Wood GRP Aluminium 40 metres Up to 20 metres Wood GRP Aluminium 50 metres Up to 15 metres Steel 60 metres Up to 20 metres Steel 80 metres Up to 30 metres Steel 120 metres When commencing a survey a check can be made to determine if the probe 15 outside the detection range of the ferrous content of the boat Choose an area to carry out the search where there are no known wrecks or ferrous objects Steer the boat on a straight course with the magnetometer switched on there should be only a little variation of the field strength reading If 1096 of the deployed cable 18 carefully recovered the magnetometer should indicate little or no change in the displaye
25. be the more appropriate method The anticipated position is marked with a large bright coloured marker buoy this datum is then used to commence PAPALLEL LANE SEARCH expanding spiral search as shown in the diagram at some point in the search a response will occur which will indicate the general direction of the target Once the general direction is established the search becomes a number of short parallel runs across the anticipated area until the maximum peak reading 15 obtained in the case of a structure standing proud of the seabed the final confirmation 1s obtained on a graphical echo sounder goes off scale 7 2 CIRCULAR SEARCHES The circular search pattern is particularly suited when a graphical plotting navigator can be used conjunction with the AX2000 magnetometer second buoy dropped at point In both the above search methods the procedure once the initial alarm threshold has been exceeded is the same If the boat position is observed whilst monitoring the display for the peak in the initial response a line of position running through the anomaly and at right angles to the course of survey lane width 15 equal to the estimated change fange E response goes off scale 245300 horizontal detection distance can generally be established CIRCULAR SEARCH PATTERN Having established a line of Lat O 9 95 or Lon that runs through the anomaly it is just a question of establishing t
26. closed by stretching the weave over the cable with a smoothing action towards the tail end efectively stretching the sheath The following points should be considered when deploying the tow fish probe 1 The ferrous mass of the operating vessel The vessel itself must be considered as a mobile magnetic anomaly and as such has a detectable field distribution pattern that surrounds it this pattern will not be symmetrical and will vary as vessel rotates within the earth s field A positive means of evaluating safe distance for probe 15 to initialise the magnetometer whilst the boat 1s maintaining a steady course Once a stable reading has been established the probe 1 gradually drawn towards the towing vessel this should be done a couple of metres at a time allowing the magnetometer to update each time At some point a detection will be indicated on the magnetometer by a ve or ve change in the steady reading This exercise should be repeated with the vessel operated on different bearings with the result noted for each direction Once the minimum distance is established this should be taken as the minimal deployable length of cable and should be marked accordingly With this distance established and the cable deployed the boat should be able to complete a long circular course without any significant change in the steady state reading of the magnetometer 22 MC5 Proton Magnetometer User Manual 14111115 2 T
27. d deviation If the probe 1s detecting the boat this will be seen as deflection on the field strength meter as the boat turns If this 1 greater than 10 or 15 nT a longer cable 18 necessary For small boats with outboard motors keep the tow cable away from the motor as this may induce ignition interference in the cable If you have not used a magnetometer before try detecting some known wrecks of different sizes to get a feeling for the type of response produced A simple rule of thumb for estimating the detection range 18 to assume that a response will be noted at a distance of between two to five times the longest dimension of the object Examples Two to three ton 4 metre anchor typically 8 to 20 metres detection distance One Hundred ton 30m steel wreck typically 60 to 150 metres detection distance Five thousand ton 100m steel wreck typically 200 to 500 metres detection distance With further regard to detection distance you will find the distance at which you detect a wreck of a given size will vary according to how lies on the seabed and which direction you approach it Sensing distance 1s not uniform in all directions Finally when towing the magnetometer sensor towards a target don t forget your towfish 1 always further away than the boat by the trailing distance this will foreshorten the apparent sensing distance If you consider a wreck as a permanent magnet with North amp South poles laying in the earth
28. d to avoid snagging The essential factor with this method 1 to ensure that the tow fish 1s below the detection range of the search boat smaller boats are obviously more suited where this 1s carried out in fairly shallow water This method can also be used as a follow up to a search that has located an anomaly in a low visibility area by conventional towed searching but needs to be pinpointed very accurately for follow up diving activities The particular advantage being the ability to drop a shot line in very close proximity to the tow fish in response to magnetic indications The recommended procedure 1s as follows 1 With the tow fish and cable deployed such that the sensor 1s suspended horizontal and clear of the seabed or any anticipated hazards 2 A marker buoy is placed at the start of the first run as a reference point 3 The run 18 terminated after set distance either by use of a positional navigator transits or timing the run in conjunction with current speed 4 A marker is dropped to indicate the termination of the first run this enables subsequent runs to be terminated after the same distance 5 The tow fish 1 temporarily retrieved whilst the boat 1s returned to the start line 6 The second and subsequent runs are started at a set spacing from the first marker based on the calculated lane spacing required 7 The accuracy of the lanes can be confirmed by noting that the spacing at the terminating marker co
29. e of vessel deployed for the search The larger the survey vessel the less the manoeuvrability which is fine for the survey of a large area where each lane 18 of substantial length but 1s not necessarily an asset for the search exercise in small confined areas Another disadvantage of large vessels 15 the fact that a long cable length has to be deployed giving an appreciable difference between boat position and actual tow fish position 8 The total size of area required to be surveyed Assuming that sufficient is known about the target in terms of tonnage and dimensions a plan of action can be determined to cover the search area in such a way that a The survey 15 fully data logged to allow an accurate assessment both during and subsequent to the search b The survey 1 carried out to a standard guaranteeing that should the target not be located within the prescribed area then the ground covered can confidently be eliminated from any future search activity 6 5 SURVEY CALCULATIONS By reference to the sensing distance graph it 1s possible to determine 1 The maximum distance at which a given target can be detected from the surface 2 The degree of magnetic change that can be anticipated when size tonnage and nature are known 3 The approximate lane width to be adopted SE 1O6 000nT 1 FELD STRENGTH manocteslias
30. earch and survey applications This 1nT value in terms of the total field measurement made gives typical resolution in the order of 1 part 50000 for measurements carried out in northern Europe Resolution quoted as a fraction or a ratio will obviously relate to the total intensity for the part of the world where the magnetometer 15 employed An accepted level of change that 1s the smallest change attributable as a positive indication of an anomaly 18 5nT Fundamentally important to maximise sensitivity is to achieve a stable base line from which to analyse changes if the base line changes outside detection range of any anomalies can be maintained within 2 to 3nT this relates to a well optimised magnetometer installation 4 5 MAGNETIC CONTOUR amp ANOMALY MAPS The above analysis has been concerned with the effects and detect ability of man made ferrous objects there are however many anomalies due to the natural occurrence of 15 MC5 Proton Magnetometer User Manual geological features that exhibit magnetic properties in many parts of world these can have a serious impact on the interpretation of results from a magnetometer The general magnetic geological nature of many parts of the world can be obtained by reference to magnetic anomaly maps these maps can be obtained through an Institute of Geological Science or similar body that 15 generally concerned with the compilation of geological data The degree to which we
31. enerally the ferrous object will additionally possess its own permanent magnetisation this will further distort the flux density around the object ferrous object Fig 3 The distortion caused to the earth s field by a steel wreck 1s shown in Fig 6a This distortion 1s usually referred to as a magnetic anomaly The associated graph Fig 60 shows the variation in field strength measured by the proton magnetometer as the probe 1 towed past a wreck The detection distance used for the graph 1 the distance obtained by drawing a straight line between the magnetometer sensor coil and the wreck The magnitude of the field disturbance 15 very small at the maximum detection range while large variations exist close to the wreck It 1s this large increase the anomaly amplitude as the wreck is approached that enables the wreck to be homed onto once an initial detection is made The peak value of the magnetic anomaly depends on the mass of metal and the depth of water 11 MC5 Proton Magnetometer User Manual Fig 6a arths magnetic 11844 inclined at 70 Fig 6b PLOT OF MAGNETIC FIELD STRENGTH AGAINST DISTANCE FROM THE WRECK reference level The above plot 1 a representation of the change in field strength as a survey progresses across the centre of an anomaly Levels below the reference level are related to areas where the field strength has been reduced by the presence of the anomaly The rate of change of field st
32. es a means of testing the complete installation for interference 2 4 TOWFISH INSTALLATION Although the magnetometer sensor is a towed unit Towfish or Probe the inboard section of cable has to be routed to the control unit The main considerations routing this cable are as follows 1 Avoid the cable passing close to the outboard inboard engine 2 Avoid the cable passing close to the main battery supply and charging cables 3 Where it 15 necessary to cross other cables do this at 90 degrees if possible 4 Any runs parallel to other cables should be kept as short as possible and with maximum spacing even spacing of a few centimetres can make an appreciable difference to the induced interference level 3 0 PRINCIPLES OF OPERATION The principle of operation of a proton magnetometer is unlike that of any conventional metal detector that generally relies on creating it s own localised field of influence Conventional metal detectors producing their own dynamic field can detect localised disturbances in the field caused by metal objects This time varying dynamic field only extends about 2 metres from the search coil so consequently the maximum detection range even for larger metal objects 15 still only 2 metres Conversely the proton magnetometer uses the existing static earth s magnetic field as a medium for determining the presence of MC5 Proton Magnetometer User Manual UL ferrous metal by measuring changes occu
33. et of results NB When towing long cable lengths in busy waterways caution 15 necessary to avoid interfering with legitimate boat movements of other vessels and to minimise the danger of damage or at worst total loss of the cable and probe S The possibility of other detectable material within the search area or adjoining area much information as possible about the search area should be obtained relating to wrecks debris pipes and cables Other more obvious structural features such as Jetties piers and breakwaters etc also have to be taken account of both in the survey activity and during the post processing of the data obtained Even where the survey has to operate within the detectable distance of such structures it still be possible to observe secondary localised magnetic anomalies by the difference in rate of change of magnetic field 6 The nature of the local geology which could influence the magnetometer readings Aeromagnetic anomaly maps can be of great assistance in establishing the general level of change that can be expected as the search progresses Taking account of the direction of magnetic contours can also be influential in deciding the general direction of the search lanes Following the general direction of the contour lines can 24 MC5 Proton Magnetometer User Manual 4 11115 give a very base line and hence maximum ability to note changes due to man made anomalies 7 The size and typ
34. for protecting the instrument and cable end connections when unmated The interconnect system allows ease of disconnection and hence removal from the boat as required Connectors cater for the following needs a Coaxial connection to the tow fish cable or indirectly via an extension lead b 12v 24v supply c Data output facility for PC d NMEA 0183 GPS amp Echo sounder data MCS interconnect PROBE The Towfish sensor is connected via the tri axial double shielded coax cable this cable connects the sensor to the MC5 the PROBE connector NOTE It is essential to maintain this connection a clean dry condition 12 24v POWER The power supply lead 15 fitted with an inline fuse NB The control unit also has an internal 3 15A protection fuse The 5 will provide a higher quality performance using 24v however it will in many cases provide a very adequate performance with a 12v supply PRINTER PC RS232 This provides the connection point for the RS232 data lead In addition to data amp data ground the interface lead provides external power from the PC serial port to energise the internal opto isolator In some cases where a laptop 18 used the port may not energise the opto isolator circuit in this case a PP3 style 9v battery can be used with the connector provided Note The 9v battery will continue to supply power even when the MCS is switched off NAVIGATOR INTERFACE 0183 data is fed to the connec
35. gnetic field 1s fundamental to a successful operation of a proton magnetometer particularly when used for detection purposes The earth s field has a number of parameters the most important of which 1 the total intensity and this 1s the parameter measured and analysed by the magnetometer Under short term static conditions the total intensity value 15 maintained to a stability which allows the magnetometer to measure to a resolution of better than 1 nT gamma 4 1 MAGNETIC FIELD STRENGTH amp INCLINATION The earth s magnetic field 1s similar to that of a bar magnet with the maximum strength at the magnetic poles Fig 4 However it is not an ideal bar magnet but has variations in field strength due to certain geological effects Fig 5 15 a magnetic map showing lines of constant field strength throughout the world The change in magnetic field strength measured by a proton magnetometer is expressed in nanoTesla nT or gamma InT 1gamma As an example around the UK the earth s magnetic field strength varies from approximately 47000nT in the south to 50000nT north of SCOTLAND The lines of magnetic flux are not horizontal to the ground but inclined at 70 degrees Although the earth s field varies by 3000nT over the UK it can be considered uniform over the localised area of search EARTH S MAGNETIC FIELD QOD Fig 4 The upper part of Figure 5 below shows the distribution of magnetic field strength over the major part of the
36. he Omni directional Toroid version then position it so that it is aligned in approximately an east west direction to maximise the response If the initial tuning is being done at sea then it should be carried out with the TOWFISH cable fully extended if carried out in very shallow water it is advisable to use float such as tubular boat fender as a support for the sensor Control Unit Settings Set the POLARISE control to 3 sec the range to X1 and the alarm to 10nT Set the AREA TUNE control to the centre of its tune range 1 6 position J Connect the power cable to the battery red to positive the 15 now ready to be switched on After switch on observe that the small signal meter needle deflects across the scale every 3 seconds Adjust the AREA TUNE control one step at the time to find the setting that maximises this deflection Note this optimum setting for subsequent usage the magnetometer 1s now set up for your area If you now switch off then on again the magnetometer will now set itself up with the benefit of maximum signal level NOTE If the initial set up 1s carried out on land then the procedure should be repeated at sea as this may vary by one or two steps due to distortion of the natural field value by buildings or underground features When the magnetometer 18 switched on there 1s a short delay period before an initial bleep 18 heard then two measurements are made to determine the reference value of the magnetic f
37. he peak reading when running at right angles to the initial course Once a peak reading has been established in the other direction and the Lat Lon numbers for the anomaly have reasonably accurately been established some account needs to be taken for the layback of the tow fish For instance with 60m 200ft of cable deployed and the boat on a N S course the navigator readings need to be corrected by a factor of 0 030 minutes decimal Whilst on an E W course the correction factor will be related to the actual latitude this however at a Latitude of 50 degrees would relate to a correction factor of 0 050 minutes decimal NB There is no substitute for practising the art of magnetometer survey on a known target or range of targets before venturing on to the more serious activity of locating a totally new wreck The response although predicable from a familiar wreck does give a feeling of elation at mastering the black art of magnetometers 21 MC5 Proton Magnetometer User Manual CAUTION in all surveys with the magnetometer it is important to ensure that the initialisation of the magnetometer is away from the centre of operation such that the magnetometer gets a true initial sample of the earth s magnetic field 7 3 DRIFT SEARCHING A particularly effective method of maintaining close proximity to the seabed 18 by drift searching this entails suspending the tow fish directly beneath the boat at a suitable height above the sea river be
38. he potential hazards of snagging the tow fish The anticipated minimum depth of water including any potential hazards that could allow tow fish to snag has to be taken account of The tow fish has a natural tendency to sink particularly at low speeds and related to the amount of cable deployed To eliminate the possibility of snagging particularly in depths of water less 10m 308 a tail float on a light line of a suitable length will act as a drogue and should the boat become stationary will support the weight of the tow fish The ideal float 1s a slim line fender with the ease of attachment through the eyelets and it s reasonable ability to be towed through the water 3 The nature and mass of the object to be detected The relative depth of the tow fish in the water has to be considered in relation to the size of the object to be detected Fig gives the maximum distance at which various tonnage s can detected this has to be related to the depth of water in which the search has to be carried out Where the target 1s estimated to give a sensing distance which 15 large in relation to the depth of water the depth at which the probe 18 deployed 18 relatively unimportant however where the detection distance 1 close to or greater than the depth of water the probe needs to be deployed as deep as possible NB From the earlier stated laws relating to magnetic signatures of ferrous objects the general rule is anomaly response
39. ield Once the reference measurement has been completed it calibrates the magnetometer to the measured field strength and sets the large meter to centre scale The field strength measured at calibration 1 stored in the microcomputer memory and all subsequent measurements are compared with this value to determine the magnitude of any field disturbances After each subsequent measurement the audible alarm will provide a short reassurance bleep if a valid measurement is made This bleep indicates that the magnetometer 18 working correctly If the magnetometer fails to bleep when the alarm control is on then something is wrong i e low battery voltage or electrical interference etc Once the system 15 taking regular measurements a ferrous object gradually brought near to the probe will cause the alarm to sound immediately the change in magnetic field strength exceeds the alarm setting Based on the above you should now have a working understanding of the setting up procedure It is not necessary to repeat the setting up procedure each subsequent time you switch on provided you operate within 20 miles of your original setting up point and maintain your chosen AREA TUNE selection Just switch on and the magnetometer will automatically calibrate itself The following two sections describe how to use POLARISE and RANGE controls to optimise the survey 17 MC5 Proton Magnetometer User Manual FONELEE d 5 2 POLARISE CONTROL
40. incides with that at the start 28 MC5 Proton Magnetometer User Manual 111 8 0 NMEA INTERFACE The 5 5 amp MCSPET control units are fitted with an NMEA combiner to allow positional data amp depth of seabed SDDBT to be merged with the magnetometer measurement MGD NB If a combined GPS Sounder is used then NMEA output should be supplied to both the GPS amp Sounder leads in parallel NOTE It is important to have the GPS connected and full operational at the time of starting up the MCS to ensure the internal combiner can verify the presence of a GPS signal it will otherwise revert to a magnetometer data only this will only be recognised by the AQLOGEDIT software if the OTHER option is selected for the data source 5 Data System L SGPG A MC5 DISPLAY Echo ombiner iu Combiner Sounder SDDET NMEA Interface connections PC INTERFACE 1 GPS ReLurn pin 4 GPS 2 Depth Return pin 3 Depth Data The 5 5 amp 5 control units are fitted with an Opto Isolator which protects the MC5 from unwanted noise or spikes from the PC The Opto Isolator is powered via the PC lead using the voltage present on pins 4 or 7 of the 9 way connection On some occasions the computer is unable to provide the required power such as when using a USB to Serial adaptor In this situation an extern
41. ine The addition of a Sea Earth can sometimes be the final step to minimise any residual induced noise in the magnetometer system however the improvement should be verified by checking the signal to noise ratio of the system both with and without the Sea Earth attached See the later section on checking signal to noise ratio 46 MC5 Proton Magnetometer User Manual NOISE VIA INTERFACES Another point of entry for noise to get into the magnetometer system 15 via the PC amp NMEA interface connections The NMEA input has an internal opto isolator providing full ground isolation this eliminates ground noise except in very rare cases The PC laptop connection is a likely route for noise to get into the magnetometer particularly when the PC is powered via a DC to AC inverter Prior to 2003 models an external opto isolator 1s provided with some models and 15 optional extra with others models supplied 2003 onwards have the opto isolator fitted internally Noise elimination Test methods The following is a method of confirming the amount of noise being produced in the magnetometer MCS With a piece of steel such as a spanner taped centrally on the body of the towfish the signal is suppressed Trail the tow fish at a suitable distance behind the boat in an open sea area and observe the reading on the signal small meter The observed readings should only be about 5 to 10 deflection Rotate the Area Tune switch and see that a low mete
42. is gives the worst signal level and increases vulnerability to noise 6 Any unused towfish cable should be stowed in a figure 8 on deck to avoid noise induction 7 Any inboard cable should be kept away from outboard inboard alternators amp Ignition systems 8 Ensure that no additional metal 1tems such as stainless steel shackles have been introduced on auxiliary towing lines at the towfish end of the cable 47 MC5 Proton Magnetometer User Manual FONELEE d Possible Cable Damage If all the above recommendations have been followed and still a high level of noise persists on the magnetometer it 15 possible that damage to the insulation of the cable is the cause Any leakage between the inner cores of the magnetometer cable and the seawater will induce noise into the signal path In models with a secondary cable for depth of sensor monitoring the problem could exist in this cable or the main cable try testing the magnetometer with the secondary cable disconnected at the rear of the magnetometer if the problem disappears the insulation of the depth cable 18 likely to be damaged Tests can be carried out to check the integrity of the cable insulation using a multi meter the procedure 18 as follows 1 Attach a small piece of metal to one of the leads of a multi meter to act as submersible conductor e g brass stainless steel or copper 2 Either prepare to submerge the cable directly into the sea or otherwise fil
43. l a plastic bin or tub with sea water or fresh water with sufficient salt to make it very conductive The plastic container should be large enough to submerge the whole cable and tow fish 3 Place the lead with the conductive metal contact into the salt water and connect the other lead to the centre contact of the tow fish connector 4 Setthe multi meter to the highest M ohm resistance range available Slowly immerse the tow fish and cable into the salt water monitoring the multi meter reading continuously Any sudden reduction in the reading which should normally be completely open circuit or be at least be in the tens of M ohms will indicate a weakness in the insulation it will also localize the problem 6 The same test can be carried out with the depth cable where this 1s also included if possible make contact with all three contacts in the depth connector or test with each in turn 7 weakness is detected cable this will need remedial action a short term solution may be to use insulation tape locally however once salt water has entered the cable it should ideally be replaced as the cable will continue to deteriate TESTING AN 2000 MAGNETOMETER ON LAND Where the performance of the magnetometer needs to be tested prior to going to sea or to check the noise and tuning performance an effective test can be carried out on land The high sensitivity to field variations means that the magnetometer may
44. only be used remote from known earth field disturbers such as power lines or buildings Before attempting to set up the magnetometer on land ensure that it 15 positioned at least 50 metres 160ft from the nearest power line or building additionally ensure that any vehicles are at least 10 metres 30ft away Assuming the initial setting up 15 carried out on land the TOW FISH should be positioned at least 3 metres 10 ft from the electronics unit and battery The tow fish should be set up horizontally at least 1 25 metres 4 ft off the ground using some form of totally non magnetic support NOT EVEN CONTAINING SMALL NAILS SCREWS OR EVEN STAPLES Elevation of the sensor 1s very important unless carrying out the land tuning on totally magnetically clean ground Note although beach sand 15 generally magnetically clean this 1s not always guaranteed to be the case 1f 1n doubt elevate the tow fish as described above 48 MC5 Proton Magnetometer User Manual APPENDIX V Manufacturer Contact Information If you should need to contact Aquascan International Limited for advice on your purchase to order further equipment or to arrange a repair please use the following contact information Mailing Address Aquascan International Limited Aquascan House Hill Street Newport South Wales NP20 ILZ United Kingdom Tel 44 1633 841117 Fax 44 1633 254829 E mail Sales Enquiries sales aquascan co uk General Inquiries info aquascan co
45. p to several hundred metres from a wreck site with the maximum occurring over the wreck itself It is however difficult to give accurate performance figures for the detection of various objects as much depends on the size attitude and permeability of the object disturbing the field A major feature of the MC5 is simple operation This simplicity of operation has been achieved by linking manual controls to the internal microcomputer The microcomputer has also allowed an upgrade path for the MCS to provide a link to an external computer for display and storage of data Expanded I O facilities allow data logging of GPS positional data and water depth from a compatible echo sounder with an NMEA data output Depth contours bathymetric data can add valuable information to the magnetic survey data analysis PC support software options are available to allow both real time graphical viewing and or later use of a PC this can provide a very powerful aid for survey downloading and post processing and evaluating the accumulated data Real time display and direct data MC5 Proton Magnetometer User Manual logging of measurements on a PC can greatly enhance a survey The application of the PC for the processing of magnetometer data can virtually bring order to chaos an apparent meaningless set of magnetic deviations can be processed and represented as a series of contours giving a clear picture for interpretation The current high resolution colour sc
46. process By reference to the graph showing the tonnage distance relationship the maximum detection range can be established 2 The depth of water to be searched The general and maximum depth of water to be encountered is the second factor in order of importance to establish a lane with for the search Increasing water depth has the effect of reducing the distance to each side of the target that detection can be anticipated 3 The local conditions at the time of search Whilst the general search pattern should establish it s lines along lines of Latitude EW Longitude N S it is sometimes necessary to move away from the ideal to take account of strong tidal flow and wave action The effect of tide can in some circumstances be used to advantage for both control of direction and improved depth of tow fish against speed over ground The tow fish can be more easily deployed at depth whilst travelling with the tidal flow where the speed over ground can far exceed the speed in water 4 The presence of other craft busy waterways the affects of other vessels both moored or mobile can have a serious impact continuity of survey where this cannot be avoided the positions of moored vessels should be noted for subsequently relating to logged results The area masked by the vessel can then subsequently searched to complete the survey The unexpected passing of a vessel within sensing distance of the tow fish can also corrupt a s
47. r deflection is observed over the whole range If the displayed readings are higher than 10 then try re routing the towfish cable to minimise any induction from ignition generator or echo sounder transducer cables In addition try the Sea Earth to see if an improvement lower reading is obtained if so make this a permanent part of the installation Having achieved the desired low noise result then the metallic object can be removed from the towfish the standard tuning procedure can now be carried out to determine the optimum setting for the Area Tune Switch Tuning should be carried out in an E W or W E direction where possible and give a deflection of between 60 to 95 Once established this area tune selection will be appropriate within a 50 mile radius AX2000 The above procedure is also valid for the AX2000 the only difference is that the tuning procedure is controlled by the menu and the results monitored on the graphical display General recommendations for optimum performance 1 Use a fully isolated dedicated 24V battery system 2 Use a sea earth between the ve ground of the magnetometer battery and the seawater this is a stranded wire link attached to a stainless steel or bronze plate into the sea 3 Avoid any mobile phones or VHF antenna close to the AX2000 receiver this can cause spurious responses during each start of transmission 5 Avoid traveling towards the equator Due south in the Northern hemisphere as th
48. reens VGA SVGA used on PCs allow a further dimension to the display of processed data Progressive changes in the measured values of the magnetic field can be attributed a range of colours from the spectrum available alternatively successive surveys can be overlaid on the same screen with a clear separation AQUASCAN MCSHETHE 1 0 SYSTEM CODING A simplified coding system has been adopted to cover a range of options available with the MCS series the letters and numbers following determine the status type of sensor and length of cable supplied Some examples are listed below MCSES 40 System for European operation with Solenoid sensor and 40m cable MCSET 40 System for equatorial operation with Toroid sensor plus 40m cable MCSRES 40 System for European operation with Solenoid sensor plus 40m cable and RS232 output of magnetic deviation MCSPES 60 System for European operation with Solenoid sensor plus 60m cable and full NMEA RS232 interface facilities amp supplied with Windows software 1 1 PACKING LIST CHECK A loose sheet packing list will be found at the front of this manual representing a comprehensive inventory of individual items that have been included this sheet should be used as a checklist Any queries resulting from this initial check should be raised with your local representative or directly with AQUASCAN NB we suggest you keep the packing material as a precaution for returning the instrument should this be
49. rength for an isolated magnetic anomaly is based on an inverse cube law hence the rapid build up to a peak which in reality has a broader peak than the diagram illustrates Another way of expressing the law relating to change 15 that 2 times distance gives 8 times deviation change The other major influence on detect ability of an object 1 the presence of it s own permanent magnetic field this will itself produce a surrounding distortion in the earth s field Like the variations permeability the strength of permanent magnetic field displayed will also be variable for different ferrous material The above described influences plus other general factors contribute to the overall size of the magnetic anomaly and hence detection distance these are listed below a Mass b Permeability c Permanent magnetism d Orientation within the earth s field e Scattering 12 MC5 Proton Magnetometer User Manual Fig 7 shows the relationship between distance and the theoretical maximum anomaly amplitude that would be measured by the magnetometer this 1 shown for various sizes of ferrous objects These maximum anomalies are estimated values and are only valid to within an order of magnitude however they do give some idea of what to expect for different objects Whereas a steel wreck can cause measurable magnetic anomalies extending to several hundred metres around the wreck site smaller objects such as cannons anchors and pipelines etc ca
50. rring in surrounding area this can yield detection distances of several hundred metres A proton magnetometer for wreck location measures the strength of the earth s magnetic field to a resolution of about 1 part in 50 000 for this level of resolution it has to be extremely sensitive The earth s field 18 a static field and because most non ferrous metals do not have any significant effect a static magnetic field then they cannot be detected by a proton magnetometer A good rule of thumb to determine if a material will be detected by a magnetometer is to consider if it will be attracted to a conventional bar magnet The proton precession magnetometer 15 so named because it utilises the precession of spinning protons in a sample of hydrocarbon fluid to measure the strength of the magnetic field within the fluid sample In practice the magnetometer sensor consists of a chamber of hydrocarbon fluid 1 e Kerosene around which is wound an inductor sensor coil 3 1 PROTON PRECESSION The MC5 proton magnetometer utilises the well established principle related to deriving an AC signal from the PROTON PRECESSION activity that can be induced in a hydrocarbon sample contained within the core of an electromagnet In the case of the MC5 the electromagnet sensing element is formed by a multi turn inductor in the form of a solenoid or Toroid inductor The inductor 15 initially formed as an air cored coil but subsequently has the core filled with or imme
51. rsed in a hydrocarbon fluid To measure the earth s field the fluid must first be polarised for a time period in the order of a second or more The polarising state entails connecting the sensor coil to a battery this produces a strong magnetic field through the fluid The protons behave as small spinning magnets and temporarily align themselves with this strong field as shown in Fig 1 When the battery 18 disconnected the magnetic field collapses and the spin of the protons causes them to precess about the direction of the earth s magnetic field The precessing protons generate a small signal of approximately a few microvolts in the coil the frequency of this signal 18 directly proportional to the strength of the earth s magnetic field The precise relationship between the frequency of the signal and the magnetic field is known as the gyromagnetic ratio MC5 Proton Magnetometer User Manual TONAL 111 184144 POLARISE STATE FOLARISING j FIELD BATTERY EARTHS MAGNETIC FIELD PROTON SPIN ALIGNED WITH POLARISING FIELD After the battery is disconnected the amplitude of the precession signal slowly decays over a second or so as the signal from the individual protons gradually loose phase coherence The magnetometer must resolve the frequency of this signal within a second of switch off This is the Detection state measurement phase Fig 2 during this period
52. s increase by a factor of eight for a change in proximity of a factor of two 4 The requirement to add ballast weight to the tow fish DEPTH Of THE PROBE DEPENDANT ON i LENGTH OF Tow SPEED SIZE OF WEIGHT In cases where the object to be detected 18 at a depth that would not allow positive detection with the tow fish at the surface requires that the tow fish be deployed at a height above bottom that would guarantee a response within the search parameters employed The use of a lead ballast weight close to the tow fish 15 a simple but effective method of achieving increased tow fish depth for a given speed NB Care should be exercised in the way the lead weight 15 attached to the tow cable the weight should never be attached directly to the cable but via an auxiliary line which should be taped to the tow cable at a maximum of 2 metre 6ft intervals The final section of cord attaching the lead weight should be the weakest link in the chain to safeguard the system in the case of an accidental foul of the ballast weight 5 2 a A L INTERNATIONAL 23 MC5 Proton Magnetometer User Manual d 6 4 SEARCH METHODS amp CONSIDERATIONS A number of search patterns and methods exist for the magnetometer survey to be carried out The following factors influence the methods adopted 1 The size and nature of the target This 1s without doubt the most fundamental single aspect of the decision making
53. s magnetic field then depending on which section of the wreck you approach will determine whether you observe or a ve deviation The distortion caused to earth s magnetic field 15 a complex mix of induction and combining of two static 3 dimensional fields 20 MC5 Proton Magnetometer User Manual FOLE d 6 1 HORIZONTAL DETECTION DISTANCE The single most important factor affecting the detectability of an object 1s the distance between the magnetometer probe and the object With knowledge of the mass of ferrous material on the wreck site and the depth of water an approximate horizontal detection range can be determined Using Fig 7 the maximum distance between the probe and the object that will just trigger the alarm can be found For search purposes it 1s necessary to determine the horizontal component of this distance as this indicates how close the search vessel must pass by the wreck in order to detect it The horizontal detection range can either be determined mathematically or for those who have forgotten their school maths Pythagorus by a scale drawing This estimated horizontal detection distance 15 good choice for the width of each search lane as it allows for a certain amount of error in the initial estimate 6 2 SELECTING THE OPTIMUM CONTROL SETTINGS For a steel wreck a polarise time of at least 2 seconds is best as this gives a more accurate measurement and therefore a greater detection range An al
54. se may be causing the problem 2 Check the integrity of the cable insulation gt Feed the entire length of the cable into the sea and measure the resistance between the the outer of the connecter contacts and a metal contact placed into the sea If you measure less than a few Mohm the cable insulation may have been damaged The cable should be laid out on land and checked for physical damage If none of the above checks help cure or identify your problem then please contact your nearest service agent or the support department at Aquascan International Ltd 45 MC5 Proton Magnetometer User Manual FONELEE d Minimising noise and interference AX2000 amp MCS installation INTRODUCTION Magnetometers can be successfully installed in almost any type of vessel with minimal intimidation from other electrical equipment however a number of rules have to be obeyed and precautions taken Due to the high sensitivity of a proton magnetometer enabling it to respond to signal levels of a few microvolts there will always be a risk of interference from other electrical equipment and instrumentation This document is intended to define the rules and detail the precautions to enable a successful installation amp optimised performance to be achieved POWER SUPPLIES The power supply for the magnetometer is the most common source of interference where this 15 not a totally independent supply devoted only to the magnetometer A n
55. tor via the NMEA lead supplied the connections are identified with printed labels Internally the NMEA inputs are opto isolated 12724U SERIAL NO PRINTER NAUIGATOR POWER CHART RECORDERINTERF ACE MC5 Proton Magnetometer User Manual 2 5 POWER SUPPLIES The 12 24v power supply is one of the most fundamental aspects to get right for optimum system performance The combination extremely high sensitivity together with the very low operating frequency make the magnetometer instrument very vulnerable to interference via the power supply cables The ideal power source for the AX2000 magnetometer is a totally isolated amp independent battery isolation eliminates both noise from a ships charging generator the major source of interference and the superimposed noise from other instrumentation 24v Battery supply The ideal 24v power source is a pair of 12v 60AH or larger lead acid batteries in good condition this will allow an operational period in excess of 24 hours before it becomes essential to recharge NB Even vessel installations where a dual battery system is available allowing one battery system to be isolated from the charging system both ve and ve leads have to be fully isolated from the boat system to ensure interference free operation of the magnetometer To evaluate the feasibility of using a boats un isolated main battery system a test facility is outlined in the SETTING UP PROCEDURE section this giv
56. trength exceed the range displayed on the meter the audible alarm will bleep to indicate this 1s so When searching in areas containing exposed or underlying magnetic rock the associated magnetic variations will cause the meter to either gradually deflect across the scale as the boat moves position or in cases with very localised geological anomalies it will deflect more randomly the X2 X10 and X100 ranges the operator can re position the meter to centre scale by switching the magnetometer off momentarily This will cause the microcomputer to re calibrate the magnetometer to the boats new position However if either of the grad positions is selected on the range control the microcomputer attempts to cancel the effect of the gradual change in the magnetic field strength while still responding to localised changes caused by ferrous objects It does this by only comparing the differences between any two successive readings On making a measurement the microcomputer compares the field strength with the previous reading and displays the difference It also saves the current reading as the new reference for comparison with the next reading In this way only significant changes in the field strength are registered the gradual change caused by the magnetic rock has little effect However when searching for a steel wreck then the enormous change in the magnetic field caused by such a wreck will leave little doubt that a wreck has been detected In
57. ts and is therefore much more likely to be making a measurement when near the object Selecting the X1 range and an alarm setting of 10nT ensures maximum sensitivity when searching for small objects If the probe can be made to pass relatively close to the object then there will be a much greater chance of detection One technique 1s to sink the probe by adding a weight to the cable just in front of the probe Fig 9 The depth the probe will run at is dependent on the size of weight the length of cable and the speed of the boat It is best to use long thin weights which will offer the minimum resistance to the water and must be made of a non magnetic material such as lead If the probe cannot be made to run deep enough using weights a drift search should be used The probe 15 suspended directly below the boat to the required depth and the boat drifts the current As the same influences both the boat and probe current the 21 MC5 Proton Magnetometer User Manual PLNM d probe remains directly below boat The probe should be suspended so that it 15 horizontal during the search In areas containing magnetic rock the choice of the X1 range may be inappropriate Fig 10 shows the effect of a regional magnetic gradient caused by such rock In the UK this type of rock is mainly found in north Wales and the west of Scotland It s effect on the magnetometer when switched to range is to cause the field strength meter to gradu
58. umber of factors can combine to produce a high level of noise in the audio frequency range in which the magnetometer operates these include A Harmonics amp voltage spikes from the charging system B Harmonics from power inverters one of the worst offenders C Voltage spikes from pulsed instruments such as sonar amp radar D Bilge pumps and other motors The answer 1 to provide the magnetometer with it s own battery supply of either 12v or 24v as appropriate 12v 18 normally adequate if the magnetometer 18 supplied with a reasonably short towfish cable up to 60m 200ft however in all cases a better signal to noise ratio 1s achieved with a 24v supply 24v powering will provide a more aggressive polarisation of the protons in the towfish sensor with a corresponding higher returned signal level The battery system should consist of a single 12v or series connected pair 24v well maintained condition with clean terminals for good low resistance connections The size of the batteries 15 not the most important factor however the minimum recommended size 15 15A H this should be capable of supplying the magnetometer for an 8 hour survey period before requiring a full recharge MAGNETOMETER SEA EARTH A magnetometer Sea Earth is a direct connection between the low side ve of the isolated battery system and a metallic contact with the sea this can be a Bronze or stainless steel strip attached to the hull below the waterl
59. use somewhat more localised measurable anomalies The static earth s magnetic field 18 substantially unaffected by sand sediment and other mobile seabed materials therefore the detection distances indicated above also apply equally to wrecks buried below the seabed The 5 will equally detect objects that are buried or proud of the seabed it s only the distance away from the sense coil that matters 13 5 Proton Magnetometer User Manual 10 000 nT 1 000 1 31 1 4 FIELD STRENGTH nanotesla Aquascan International Limited Fig 7 1 EI 01 dI uui AERE TE mEnE NG iii 77 AL riii nius set CHRONIC 1 EE AY 211 HH SE A FA Ez MANEN UE Ee m cn ees See 21 5 a Ae SS H 5 1 E E z i i Fi E aE M M Ld ee n es nr merus ame
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