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Geometrics, Inc. G-822/G-823 Magnetometer Manual

APPENDIX A4. CESIUM-VAPOR SENSOR THEORY

Note: The following section is provided for information purposes only. Understanding
this theoretical discussion is not required for proper operation of the magnetometer.

For purposes of this discussion, the ambient magnetic field or earth's magnetic field is
called H

. A separate magnetic field generated by an AC signal applied to a coil inside

the sensor is called H1. This coil is shown cross-section along with the other sensor
components in Figure A11.

Figure A11. G-822A cesium-vapor

Lamp

Lens

Filter

Polarizer

Photocell
Lens

H1 Coil

Absorption
Cell

Summary of Contents for G-822A

Page 1: ...and G 823A B CESIUM MAGNETOMETER 27597 OM REV B5 GEOMETRICS INC 2190 Fortune Drive San Jose CA 95131 USA Phone 408 954 0522 Fax 408 954 0902 EMAIL sales mail geometrics com Operation Manual COPYRIGHT...

Page 2: ...ii...

Page 3: ...e 12 5 0 OPERATION 12 6 0 TROUBLE SHOOTING 13 7 0 G 823A MAGNETOMETER 14 7 1 CM 201 Output Format 16 7 2 Commands 18 7 3 Detailed command descriptions 22 Cycle Time Set 22 A D channel select enable 22...

Page 4: ...Full Scale Set 40 Label 41 Set trace color 41 APPENDIX A1 MODEL G 822A SPECIFICATIONS 43 APPENDIX A2 MODEL G 823A SPECIFICATIONS 44 APPENDIX A3 SENSOR INSTALLATIONS 45 APPENDIX A4 CESIUM VAPOR SENSOR...

Page 5: ...L DECOUPLER CIRCUIT 12 FIGURE 12 SCHEMATIC OF CM 201 MAGNETOMETER AND COMPUTER CONNECTIONS 16 FIGURE 13 SCHEMATIC DIAGRAM OF DAISY CHAINED CM 201 COUNTER MODULES 18 FIGURE 14 G 823B INSTALLED AS BASE...

Page 6: ...Geometrics Inc G 822 G 823 Magnetometer Manual vi...

Page 7: ...t Because the G 822A is identical to the G 823A in all other respects the installation instructions are provided referencing the G 822A only However they apply to the G 823A as well A description of t...

Page 8: ...ct cable that is permanently attached to the sensor module and detachable from the sensor driver module These components are identified in Figure 2 The weights dimensions and connector s specification...

Page 9: ...armor frequency is about 175 kHz The output of the G 822A is a continuous sine wave at the Larmor frequency The typical signal amplitude is from 1 to 2 volts peak to peak with the sensor in its optima...

Page 10: ...4 0 INSTALLATION The particular installation requirements for each system component must be met in order to obtain the best performance from the system It is important to remember that the sensor driv...

Page 11: ...ld within the sensor s polar dead zone Similarly alignments that produce a field axis angle greater than 75 place the magnetic field within the sensor s equatorial dead zone The sensor will not produc...

Page 12: ...ientation the Earth s surface can be divided into three zones based upon magnetic field inclination a mid latitude equatorial and polar Within each of these zones there is a particular sensor orientat...

Page 13: ...horizontal and there will be some restrictions on the direction of flight Choosing one of the two recommended orientations will allow you to choose flight directions most suitable for your survey area...

Page 14: ...bsolute inclination of the Earth s magnetic field is less than or equal to 25 There are restrictions on the direction of flight when using this sensor orientation in this region The bottom diagram to...

Page 15: ...t includes those areas where the absolute inclination of the Earth s magnetic field is less than or equal to 25 As with the sensor orientation shown in Figure 8 there are restrictions on the direction...

Page 16: ...cceptable mount for the G 822A sensor will provide a stable nonmagnetic attachment to the vehicle provide vibration dampening and allow the sensor s orientation to be adjusted with minimal effort One...

Page 17: ...in two areas external electromagnetic noise and errors introduced from platform motion Electrostatic and electromagnetic signals from aircraft systems including other sensor instrumentation can signi...

Page 18: ...end that the sensor power be left on overnight when ambient temperatures are expected to fall below 10 C 5 0 OPERATION The G 822A produces an analog output signal on the BNC connector of its sensor dr...

Page 19: ...r cable or connector worn or damaged Locate and eliminate source of noise or relocate sensor Refer to Sensor Orientation section of this manual or use MagPick IGRF and CsAz software to model magnetic...

Page 20: ...stment Authorized Repair Facility only a Potentiometer on GSN board adjusted for 2 0 Volts Peak to Peak at 50 000 nT after 20 minute warm up 7 Heater check and adjustment Authorized Repair Facility on...

Page 21: ...g computer The signal power cable also carries analog signal but the junction box does not break these channels out to its DB9 connector If the user wishes to observe or record analog signal they may...

Page 22: ...oltages if original order called for custom input specification consult the factory if you suspect that your system has non standard input ranges 3 If the single ended channels 4 or 5 are used the sig...

Page 23: ...CII marks first character of data stream 2 an ASCII 1 or a blank depending on whether Mag reading is above or below 99999 999nT 3 7 5 digits of Mag data 8 an ASCII decimal point 9 11 3 more digits of...

Page 24: ...terminated by a carriage return line feed sequence by the last counter only Note that only the first counter outputs a preamble character the default character is 7 2 Commands Commands are sent into t...

Page 25: ...it will look correct on paper By using the carriage return as the command terminator and stripping input line feeds insures that dumb terminals and dumb terminal emulation software can be used to cont...

Page 26: ...r logging software program and is now obsolete Excess3 is used for high speed multi sensor array data transmissions Julian Clock Format Byte 1 O select output format 2 J format select 3 x Day field 1...

Page 27: ...n Set Second Byte 1 S Set the second 2 x MS digit of number 0 5 3 x LS digit of number 0 9 4 CR carriage return Find counters Byte 1 F Find and assign counter numbers 2 0 assign first counter as 0 MSB...

Page 28: ...r 0 The addressed counter will insert characters into the command string justbefore the carriage return before echoing to subsequent counters See detailed command description for format and definition...

Page 29: ...of this document This is the easiest format to view and import into various processing utilities It is also very inefficient in terms of disk storage space and time required to transmit each cycle Th...

Page 30: ...e is that each byte has 33 hex added to it after converting to Packed BCD The reason for adding 33 hex to each packed BCD number is to avoid some difficult pitfalls with Packed BCD Packed BCD is a ver...

Page 31: ...at is to allow customer with existing G 823A Sandia logging software to be able to use the CM 201 without upgrading to new logging software Note that Geometrics no longer supports the Sandia logging s...

Page 32: ...00 03 00 06 2A 24 99 99 82 93 34 72 00 05 00 06 2A 24 00 07 88 35 33 29 00 04 00 05 2A 24 00 03 20 71 33 81 00 06 00 06 2A 24 99 97 91 59 34 98 00 03 00 07 2A 24 86 77 85 08 35 14 00 04 00 07 2A 24 78...

Page 33: ...the last A D channel and before the CR LF DxxxHxxMxxSxx_xx The x s would be ASCII characters 0 9 as required The time registers are not incremented until enabled with the J1xx command so they can be...

Page 34: ...m showing which character corresponds which each display field command OJ0111103 __Counter number LSB __Counter number MSB __10 ms field __Seconds field __Minutes field __Hours field __Days field In t...

Page 35: ...tion of data field position within each sample being sent out In addition the software revision number can be interrogated The first character I designates the interrogate command the second letter de...

Page 36: ...ine feed Software Version Number The command IV02 will command counter 2 to send its two character software version number Counter 2 would change the command string to IV02 xx where xx is the version...

Page 37: ...201 counter apply In this application the D A converters installed in the CM 201 can be used to convert such other parameter e g barometric altitude and include these values in the data stream Recordi...

Page 38: ...Install disk in either your a or b floppy drive switching to that drive typing install at the DOS prompt and pressing return Install will ask a number of questions to which you should respond to conf...

Page 39: ...ounter is connected cm201 bat This batch file is created by Cm201set bat It invokes cm201go exe to send any command lines necessary to correctly configure the CM 201 counter s for the users applicatio...

Page 40: ...needed to be able to use some software batmenu exe drawbox exe gotoxy exe yymmdd exe foreach exe getkey com These programs are utility programs that allow the batch files to interact with the user 9 2...

Page 41: ...ee circle represents survey directions in which the earth s magnetic field vector would be in the sensor s active zone and provide good data The longer the white line the better the response of the Ma...

Page 42: ...isk if desired The program defaults to using Com port 1 although Com port 2 can be used be adding COM2 to the command line after View201 Upon startup the program listens to the output data stream from...

Page 43: ...ognizes the ASCII output format This is the default output format but there is nothing preventing a change format command from being sent to the counter module If the output format is changed the View...

Page 44: ...s Ctl F1 except it applies to Grad2 channel Ctl F3 Same as Ctl F1 except it applies to Grad3 channel F4 Toggle between true and normalized gradient display When measuring gradients it is often desirab...

Page 45: ...if in graphics display mode Exit to DOS if text mode and not logging to disk Displaying Analog Channels When in graphics display mode F5 up to six analog channels may be enabled by typing CTRL A This...

Page 46: ...of the same channel The program does not know which analog channels are actually coming out of the counter It is possible for example for the counter to be commanded to output channels 0 4 and 5 only...

Page 47: ...ing the label name entered above as a guide After the above data have been entered the display channel will be plotting At the top of the screen all of the activated display channels are documented in...

Page 48: ...Geometrics Inc G 822 G 823 Magnetometer Manual 42...

Page 49: ...75 60 32 mm dia 6 25 158 75 mm long 12 oz 339 g without cable 24 oz 680 g with cable SENSOR ELECTRONICS 2 5 63 5 mm dia 11 279 4 mm long 24 oz 680g CABLES Sensor to electronics 109 2 77 m standard Cab...

Page 50: ...2 mm dia 6 25 158 75 mm long 12 oz 339g without cable 24 oz 680 g with cable SENSOR ELECTRONICS 2 5 63 5 mm dia 11 279 4 mm long 29oz 822g CABLES Sensor to sensor driver counter 109 2 77 m standard Ca...

Page 51: ...Geometrics Inc G 822 G 823 Magnetometer Manual 45 APPENDIX A3 SENSOR INSTALLATIONS Figure A1 G 822A sensor and G 822A Bird components Figure A2 Airborne Stinger showing sensor mount...

Page 52: ...ics Inc G 822 G 823 Magnetometer Manual 46 Figure A3 Aircraft fitted with stinger assembly Figure A4 Aircraft fitted with horizontal transverse and longitudinal gradiometer using faired wingtips and s...

Page 53: ...Geometrics Inc G 822 G 823 Magnetometer Manual 47 Figure A5 G 822A Boom installation on Ultra lite autogyro Figure A6 Single sensor boom installation on Helicopter...

Page 54: ...Geometrics Inc G 822 G 823 Magnetometer Manual 48 Figure A7 Multi sensor 7 MTADS Helicopter installation for UXO survey Figure A8 Rack mount for airborne geophysical survey system...

Page 55: ...Geometrics Inc G 822 G 823 Magnetometer Manual 49 Figure A9 MTADS multi sensor array for UXO survey applications Figure A10 Multi sensor array on cart for archaeological surveying...

Page 56: ...proper operation of the magnetometer For purposes of this discussion the ambient magnetic field or earth s magnetic field is called H0 A separate magnetic field generated by an AC signal applied to a...

Page 57: ...cell and pass to a second lens This lens focuses the light onto an infrared photo detector Because Cesium is an alkali metal the outer most electron shell orbit has only one electron It is the presenc...

Page 58: ...toms have absorbed photons and are in a state that does not allow them to absorb another photon the light absorption of the cell is greatly reduced i e more light hits the photo detector If an oscilla...

Page 59: ...e shifted and amplified signal to the H1 coil will cause the oscillation to spontaneously start Reversing the direction of the earth field vector H0 through the sensor requires the drive to the H1 coi...

Page 60: ...TING AND INTERFACE HARDWARE G 822 SENSOR ELECTRONICS 27502 xx OPERATION AND TECHNICAL MANUAL 27597 OM SIG PWR CABLE ASSY 27565 xx SENSOR DRIVER ELECTRONICS 27512 xx SENSOR PACKAGE ASSEMBLY 27516 xx SE...

Page 61: ...LE ASSY 27565 xx SENSOR DRIVER ELECTRONICS 27512 xx SENSOR PACKAGE ASSEMBLY 27516 xx SENSOR DRIVER ASSEMBLY 27521 xx SENSOR CABLE ASSEMBLY 27553 01 GSN ASSEMBLY 27587 01 SENSOR PHYSICS PACKAGE 320438...

Page 62: ...ONICS 27512 xx SENSOR PACKAGE ASSEMBLY 27516 xx SENSOR DRIVER ASSEMBLY 27521 xx SENSOR CABLE ASSEMBLY 27553 01 GSN ASSEMBLY 27587 01 SENSOR PHYSICS PACKAGE 320438 220 CARRYING CASE 27615 01 MINI COUNT...

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